OCEAN DRILLING PROGRAM LEG 182 PRELIMINARY REPORT GREAT AUSTRALIAN BIGHT: CENOZOIC COOL-WATER CARBONATES Dr. David Feary Co-Chief Scientist Australian Geological Survey Organisation G.P.O. Box 378 Canberra, ACT 2601 Australia Dr. Albert C. Hine Co-Chief Scientist Department of Marine Science University of South Florida, St. Petersburg 140 7th Avenue South St. Petersburg, FL 33701 USA Dr. Mitchell J. Malone Staff Scientist Ocean Drilling Program Texas A&M University Research Park 1000 Discovery Drive College Station, TX 77845-9547 USA Dr. Jack Baldauf Deputy Director of Science Operations ODP/TAMU Dr. Mitchell J. Malone Leg Project Manager Science Services ODP/TAMU January 1999 This informal report was prepared from the shipboard files by the scientists who participated in the cruise. The report was assembled under time constraints and is not considered to be a formal publication which incorporates final works or conclusions of the participating scientists. The material contained herein is privileged proprietary information and cannot be used for publication or quotation. Preliminary Report No. 82 First Printing 1999 Distribution D I S C L A I M E R This publication was prepared by the Ocean Drilling Program, Texas A&M University, as an account of work performed under the international Ocean Drilling Program, which is managed by Joint Oceanographic Institutions, Inc., under contract with the National Science Foundation. Funding for the program is provided by the following agencies: Australia/Canada/Chinese Taipei/Korea Consortium for the Ocean Drilling Deutsche Forschungsgemeinschaft (Germany) Institut Franáais de Recherche pour l'Exploitation de la Mer (France) Ocean Research Institute of the University of Tokyo (Japan) National Science Foundation (United States) Natural Environment Research Council (United Kingdom) European Science Foundation Consortium for the Ocean Drilling Program (Belgium, Denmark, Finland, Iceland, Italy, The Netherlands, Norway, Spain, Sweden, and Switzerland) Marine High-Technology Bureau of the State Science and Technology Commission of the People's Republic of China Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the participating agencies, Joint Oceanographic Institutions, Inc., Texas A&M University, or Texas A&M Research Foundation. The following scientists were aboard JOIDES Resolution for Leg 182 of the Ocean Drilling Program: David A. Feary Co-Chief Scientist Australian Geological Survey Organisation G.P.O. Box 378 Canberra, ACT 2601 Australia Internet: dfeary@agso.gov.au Work: 61-2-6249-9798 Fax: 61-2-6249-9980 Albert C. Hine Co-Chief Scientist Department of Marine Science University of South Florida, St. Petersburg 140 7th Avenue South St. Petersburg, FL 33701 U.S.A. Internet: hine@seas.marine.usf.edu Work: 813-553-1161 Fax: 813-553-1189 Mitchell J. Malone Staff Scientist Ocean Drilling Program Texas A&M University Research Park 1000 Discovery Drive College Station, TX 77845 U.S.A. Internet: mitchell-malone@odp.tamu.edu Work: 409-845-5218 Fax: 409-845-0876 Miriam Andres Sedimentologist Geologisches Institut Eidgenîssische Technische Hochschule -Zentrum Sonneggstrasse 5 ZÅrich 8092 Switzerland Internet: miriam@erdw.ethz.ch Work: 41-1-632-4818 Fax: 41-1-632-1080 Christian Betzler Sedimentologist Geologische-Palaontologisches Institut Johann Wolfgang Geothe-Universitat Frankfurt am Main Senskenberganlage 32-34 Postfach 11-19-32 Frankfurt-am-Main 60054 Federal Republic of Germany Internet: betzler@em.uni-frankfurt.d400.de Work: 49-69-798-23107 Fax: 49-69-798-22958 Gregg R. Brooks Sedimentologist Department of Marine Science Eckerd College 4200 54th Avenue South St. Petersburg, FL 33711 U.S.A. Internet: brooksgr@eckerd.edu Work: 813-864-8992 Fax: 813-864-7964 Charlotte A. Brunner Paleontologist (planktonic foraminifers) Center for Marine Science University of Southern Mississippi Building 1103, Room 102 Stennis Space Center, MS 39529 U.S.A. Internet: cbrunner@sunfish.st.usm.edu Work: 228-688-3402 Fax: 228-688-1121 Michael Fuller Paleomagnetist Hawaii Institute of Geophysics and Planetology-SOEST University of Hawaii 2525 Correa Road Honolulu, HI 96822 U.S.A. Internet: mfuller@soest.hawaii.edu Work: 808-956-4038, Fax: 808-956-3188 Roberto S. Molina Garza Paleomagnetist Department of Earth and Planetary Sciences University of New Mexico Northrop Hall Albuquerque, NM 87131-1116 U.S.A. Internet: molina@unm.edu Work: 505-277-5261 Fax: 505-277-8843 Ann E. Holbourn Paleontologist (benthic foraminifers) Department of Paleontology Natural History Museum Cromwell Road London SW7 5BD United Kingdom Internet: a.holbourn@nhm.ac.uk Work: 44-171-938-9046 Fax: 44-171-938-9277 Mads Huuse LDEO Logging Trainee Department of Earth Sciences Aarhus Universitet Finlandsgade 8 Aarhus N 8200 Denmark Internet: mhuuse@geoserver1.aau.dk Work: 45-8942-4343 Fax: 45-8610-1003 Alexandra R. Isern JOIDES Logging Scientist/Physical Properties Specialist Division of Geology and Geophysics University of Sydney Building F05 Sydney, NSW 2006 Australia Internet: aisern@mail.usyd.edu.au Work: 61-2-9351-3998 Fax: 61-2-9351-0184 Noel P. James Sedimentologist Department of Geological Sciences Queen's University at Kingston Kingston, ON K7L 3N6 Canada Internet: james@geol.queensu.ca Work: 613-545-2597 Fax: 613-545-6592 Bryan C. Ladner Paleontologist (nannofossils) Department of Geology Florida State University 108 Carraway Building Tallahassee, FL 32306-4100 U.S.A. Internet: ladner@quartz.gly.fsu.edu Work: 850-644-5860 Fax: 850-644-4214 Qianyu Li Paleontologist (planktonic foraminifers) Department of Geology and Geophysics University of Adelaide Adelaide, South Australia 5005 Australia Internet: qli@geology.adelaide.edu.au Work: 61-8-8303-5826 Fax: 61-8-8303-4347 Hideaki Machiyama Sedimentologist Deep Sea Research Department Oceanic Crust Dynamics Research Japan Marine Science and Technology Center 2-15 Natsushimacho Yokosuka, Kanagawa 237 Japan Internet: bucci@jamstec.go.jp Work: 81-468-67-3395 Fax: 81-468-67-3409 David J. Mallinson Physical Properties Specialist/Stratigraphic Correlator Department of Marine Science University of South Florida, St. Petersburg 140 Seventh Avenue South St. Petersburg, FL 33701 U.S.A. Internet: davem@seas.marine.usf.edu Work: 813-553-3927 Fax: 813-553-1189 Hiroki Matsuda Sedimentologist Department of Earth Sciences Kumamoto University 2-39-1 Kurokami Kumamoto, Kumamoto 860 Japan Internet: hmat@sci.kumamoto-u.ac.jp Work: 81-96-342-3424 Fax: 81-96-342-3411 Richard M. Mitterer Organic Geochemist Programs in Geosciences University of Texas at Dallas P.O. Box 830688 Richardson, TX 75083-0688 U.S.A. Internet: mitterer@utdallas.edu Work: 972-883-2462 Fax: 972-883-2537 CÇcile Robin Physical Properties Specialist Laboratoire de GÇologie de Bassins Sedimentaires Universite Pierre et Marie Curie 4 Place Jussieu Paris Cedex 05 75252 France Internet: robin@ccr.jussieu.fr Work: 33-1-4427-2760 Fax: 33-1-4427-4965 Joellen L. Russell Physical Properties Specialist Scripps Institution of Oceanography University of California, San Diego Marine Physical Laboratory 9500 Gilman Drive La Jolla, CA 92093-0208 U.S.A. Internet: jlrussel@ucsd.edu Work: 619-534-2582 Fax: 619-456-9079 Samir Shafik Paleontologist (nannofossils) Marine Geoscience and Petroleum Geology Program Australian Geological Survey Organisation GPO Box 378 Canberra, ACT 2601 Australia Internet: sshafik@agso.gov.au Work: 61-6-249-9436 Fax: 61-6-249-9981 J. A. (Toni) Simo Sedimentologist Department of Geology and Geophysics University of Wisconsin-Madison 1215 West Dayton Street Madison, WI 53706 U.S.A. Internet: simo@geology.wisc.edu Work: 608-262-5987 Fax: 608-262-0693 Peter L. Smart Physical Properties Specialist Department of Geography University of Bristol University Road Bristol BS8 1SS United Kingdom Internet: smartpl@gma.bris.ac.uk Work: 44-1179-288305 Fax: 44-1179-287878 Guy H. Spence LDEO Logging Scientist Department of Geology University of Leicester Borehole Research Leicester LE1 7RH United Kingdom Internet: ghs2@leicester.ac.uk Work: Fax: 44-116-252-3918 Finn C. Surlyk Sedimentologist Geologisk Institut Kobenhavns Universitet Oster Voldgade 10 Kobenhavn K 1350 Denmark Internet: finns@geo.geol.ku.dk Work: 45-3532-2453 Fax: 45-3314-8322 Peter K. Swart Inorganic Geochemist Rosenstiel School of Marine and Atmospheric Science University of Miami 4600 Rickenbacker Causeway Miami, FL 33149 U.S.A. Internet: pswart@rsmas.miami.edu Work: 305-361-4103 Fax: 305-361-4632 Ulrich G. Wortmann Inorganic Geochemist Department of Geology Eidgenossische Technische Hochschule - Zentrum Sonneggstrasse 5 Zurich 8092 Switzerland Internet: uliw@bonk.ethz.ch Work: 41-632-3694 Fax: 41-632-1080 SCIENTIFIC REPORT ABSTRACT Sediments recovered in the Great Australian Bight during Leg 182 record carbonate deposition in a middle- and high-latitude setting against the background of an evolving Southern Ocean and northward drift of the Australian continent. Approximately 3.5 km of sediments was recovered from nine sites, in water depths ranging from 202 to 3875 m. Most drilling took place on the shelf edge and upper slope, in 202-784 m water depth, through a mainly carbonate succession. Two distinct groups of strata, Eocene-middle Miocene and Pleistocene in age, form the upper Cenozoic component of the continental margin, separated by a thin, upper middle Miocene-Pliocene interval characterized by slumps, sediment gravity- flow deposits, or unconformities. Such erosion, corrosion, and/or mass wasting and redeposition processes reflect periods of margin instability, seismicity, or lowered sea level. The older succession consists of Eocene shallow-water terrigenous sands and carbonates that deepen upward into Oligocene and early-middle Miocene pelagic ooze and chalk. The carbonate component was poorly recovered because of irregular selective silicification, with available cored material indicating a sequence dominated by nannofossil chalk with abundant sponge spicules and characterized by stained hardgrounds and numerous omission surfaces. The high-quality downhole logs collected through all poorly recovered intervals will enable more detailed postcruise lithological analysis for this part of the succession. In contrast, the middle Eocene-early Oligocene succession was well recovered on the continental rise at Site 1128 in 3875 m water depth, and it contains an excellent expanded (>350 m) siliceous biogenic record of proto Circum-Antarctic Current evolution. The younger Pleistocene package is a spectacular, extraordinarily thick (> 500 m), seaward-dipping wedge of carbonate sediment on the shelf-edge/uppermost slope that prograded seaward onto the Eyre Terrace and downlaps onto older sediments. Rates of accumulation exceed 40 cm/k.y., equivalent to many shallow-water tropical carbonates and twice the rate of Bahamian slope sedimentation. These green and gray carbonate strata are surprisingly uniform in composition, made up of fine carbonate sand and silt composed of skeletal fragments, mainly delicate bryozoans, ostracodes, benthic and planktonic foraminifer tests, tunicate sclerites, nannofossils, and siliceous sponge spicules. The facies transition upslope into shallower water is marked by the presence of numerous spectacular bryozoan-rich buildups. These mounds, in water depths of ~200-350 m, are characterized by numerous and diverse bryozoans, with intervening bioclastic sand and mud. These are among the first modern analogs of similar mounds that were an important component of carbonate depositional regimes in earlier Phanerozoic time. One of the surprising discoveries of Leg 182 was the presence of a brine, varying in salinity between 80 and 105, within and underlying seven drill sites. The Cl- distribution at three sites (1127, 1129, and 1131) suggests that the top of the brine has an essentially uniform depth below sea level and, therefore, crosscuts sequence boundaries. Although the origin of the brine has not yet been established, pore fluids in the Pleistocene portion of the sediments from the shallow water sites possess a Na+/Cl- ratio greater than that of seawater, suggesting that fluids in these sediments were involved in the dissolution of NaCl. It is likely that further postcruise study of the nature and distribution of this brine will shed light on lowstand shelf evaporative processes and the nature of fluid flow within cool-water carbonate margin sediments. Because of high sedimentation rates and their location at the edge of a broad continental shelf, the shallow water sites initially contained a high concentration of organic material. The brine underlying and within the Pleistocene succession contains up to three times normal sulfate concentrations and, with sufficient organic material, was therefore able to produce significant amounts of hydrogen sulfide. In addition, the relatively low iron concentration in these carbonate sediments means that the H2S was not sequestered as iron sulfides. Consequently, H2S concentrations were able to reach high levels, >150,000 ppm at one site. The oxidation of organic material also had an important influence on carbonate recrystallization, which is occurring at higher rates than previously thought possible for cool-water carbonates. INTRODUCTION Carbonate sediments and sedimentary rocks contain a particularly sensitive record of paleoceanographic and biostratigraphic evolution. The focus of the Ocean Drilling Program (ODP) carbonate drilling on continental margins has largely been in warm- water environments. There is a complete sedimentary realm whose nature and history have not yet been investigated- that of continental margin cool-water carbonates. These biogenic sediments, formed where seawater temperatures rarely rise above 20¯C, commonly mantle continental margins in middle and high latitudes. They are untapped storehouses of information regarding the evolution of global climates, eustacy, and marine biology. The southern Australian continental margin is the ideal location to study cool-water carbonate facies and evolution. The shelf has been the site of cool-water carbonate sedimentation since Eocene time, resulting in an almost 1-km-thick succession. It is now the largest area on the globe composed of such sediments. In addition, slight tectonic tilting during the late Miocene has led to subaerial exposure of Eocene-middle Miocene strata in extensive, shallow basins. These sediments form a more compressed and less continuous section than the section offshore, yet they have allowed the development of actualistic models for the formation and development of cool-water carbonates. These models can be tested and greatly expanded by drilling. A critically important benefit of drilling in the Great Australian Bight is that, because the shelf is latitudinally parallel to the southern margin of the Australian plate, the sediments contain a record of the development of the Southern Ocean. In particular, the region offers the potential to collect high-resolution stable isotopic and biostratigraphic profiles to clarify several important stages in the evolution of the Southern Ocean. Drilling in the Great Australian Bight provided essential and original information on the contrast between the sedimentologic, paleontologic, paleoceanographic, and climatic records from warm- and cool-water realms. It will also allow the development of well-constrained and greatly needed models that can be used in the interpretation of older Mesozoic and Paleozoic continental margin carbonate systems. Background Tectonic Setting The southern margin of the Australian continent is a divergent, passive continental margin that formed during the protracted period of extension and rifting that led to the separation of Australia and Antarctica in the Cretaceous and that evolved during the subsequent northward drift of the Australian continent. The initial extension phase before breakup in the mid-Cretaceous (96 Ma), together with the subsequent period of slow spreading until the middle Eocene (49 Ma), resulted in deep continental margin basins filled with as much as 12 km of mainly terrigenous clastic sediments (Willcox et al., 1988; Davies et al., 1989). These basins broadly correspond to the sites of modern upper slope terraces (e.g., the Eyre Terrace at 400-1600 m depth in the western Great Australian Bight; Fig. 1). The onset of faster spreading in the middle Eocene also corresponded with the establishment of fully marine conditions and the initiation of carbonate sedimentation in the widening "gulf" between Australia and Antarctica. Carbonate sedimentation continued throughout the remainder of the Cenozoic as the gulf evolved first into a broad, open seaway and then into the modern Southern Ocean. Cenozoic sedimentation resulted in an extensive, relatively thin (up to 800 m; Feary and James, 1998) Eucla Basin succession deposited in a predominantly platform-sag to platform-edge tectonic regime (Stagg et al., 1990). Throughout the Cenozoic, the western Great Australian Bight portion of Australia's southern continental margin has been particularly stable, with geohistory analysis of the Jerboa-1 exploration well indicating minimal Tertiary subsidence (Hegarty et al., 1988). Slight regional tilting (<1¯?) during the middle Miocene resulted in uplift and exposure of the Nullarbor Plain and restriction of Neogene sedimentation to the modern outer shelf and upper slope. Cenozoic Stratigraphy of the Eucla Basin The Eucla Basin extends inland as far as 350 km from the present coastline and seaward some 200 km to the modern shelf edge and upper slope. Inland, the Eucla Basin succession thins and feathers out against Precambrian basement; it then gradually thickens southward to its thickest point beneath the modern shelf edge (Fig. 2). The Eucla Basin succession is entirely carbonate, apart from the basal siliciclastic sequence both offshore (Sequence 7) and onshore (Hampton Sandstone), and a thin, transgressive, paleovalley-filling and strandline succession of terrigenous clastics on the inland margins of the basin. The succession is basically divisible into two mega-sequences: a Mesozoic (Late Jurassic?-Cenomanian; Stagg et al., 1990) siliciclastic-dominated syn- to early postrift section, and a Cenozoic (Paleocene-Holocene) predominantly carbonate-dominated section. These two sections are separated by a major, basinwide unconformity. The subject of the bulk of this drilling leg is the upper succession, which makes up an overall sigmoid-shaped series of sequences reaching a maximum thickness beneath the present-day outer shelf (Fig. 2). The stratigraphy of the lower, Mesozoic succession can be derived from the sequence intersected in the Jerboa-1 exploration well (Fig. 1); however, little information on the upper, Cenozoic section was obtained from this hole. The extensive erosional unconformity at the top of the synrift section forms an easily recognizable and mappable surface. Seven unconformity-bounded seismic sequences have been recognized overlying this unconformity (Fig. 2) (Feary and James, 1998). One of the most striking elements of this seismic stratigraphic analysis is the identification of numerous mound-shaped structures interpreted as biogenic mounds (Feary and James, 1995), that are present throughout the Cenozoic succession. These structures are likely to preserve a detailed record of cool-water faunal community relationships and potentially to provide an analog for cool-water mounds recognized in the rock record, but for which no modern analogs have previously been identified. The ages assigned to this succession precruise were extremely tentative and are based on (1) correlation of Sequence 6B with the onshore Eucla Group (Fig. 2); (2) the similarity in depositional style between the Sequence 7 progradational wedge and Paleocene?-early Eocene progradational sequences elsewhere along Australia's southern margin; and (3) the division of the remainder of the sequences into a reasonable time-stratigraphic framework. On this basis, the offshore sequences can be placed in the following stratigraphic framework (based on Feary and James, 1998): Sequence 7: Paleocene-middle Eocene progradational siliciclastic wedge deposited in a depositional sag, representing initial transgressive sedimentation; Sequence 6A: middle-late Eocene to early-middle Miocene deep-water carbonates forming a multilobed sediment apron; Sequence 6B: cool-water ramp carbonates with biogenic mounds (middle-late Eocene to Oligocene), overlain by an upper, warm-water, flat-topped platform rimmed by the early?-middle Miocene "Little Barrier Reef" (Feary and James, 1995); Sequence 5: small late-middle Miocene lowstand sediment wedge with restricted distribution, lying at the foot of the steepest part of the progradational carbonate shelf escarpment zone; Sequence 4: extensive late Miocene aggradational deep-water carbonate ramp sequence; Sequence 3: latest Miocene and early Pliocene highstand aggradational deep- water carbonate ramp sequence; Sequence 2: thick succession of highstand, Pliocene-Pleistocene, cool-water carbonates with spectacular clinoform ramp geometry that forms most of the modern outer shelf and contains large deep-water biogenic mounds; and Sequence 1: thin Quaternary deep-water drape. Existing Data Present knowledge of the western Great Australian Bight margin is based on extensive, high-quality seismic reflection data, together with a single oil exploration drill hole, which provide little information about the Cenozoic succession. The original Leg 182 drilling proposals (James and Feary, 1993; Feary et al., 1994) were based on detailed seismic stratigraphic interpretation (Feary and James, 1998) of a grid of 2350 km of high-quality, regional 2-D seismic reflection lines. These lines were collected and processed by the Japan National Oil Corporation (JNOC) in 1990 and 1991, over an area of 155,000 km2 on the continental shelf and upper slope of the western Great Australian Bight. An additional 1380 km of moderate-quality, regional 2-D seismic lines, collected by Esso Australia in 1979 and reprocessed by JNOC, were also used to fill gaps in the JNOC dataset. The 1996 seismic-site survey cruise (Feary, 1995) collected high-resolution, 80-channel generator-injector (GI) gun seismic data as 0.5- nmi-spaced grids centered on each site, together with tie-lines between sites. These data permitted minor refinements of some site locations to avoid potential safety concerns. Jerboa-1 was drilled by Esso/Hematite in 1980 as a wildcat oil exploration well in a water depth of 761 m, above a prominent tilted basement fault block located in the southern half-graben of the Eyre Sub-basin (Bein and Taylor, 1981). Jerboa-1 penetrated 1738 m of a Cenozoic and Cretaceous sedimentary section before bottoming in Precambrian metabasalt basement and did not encounter any significant hydrocarbon shows. The top 232 m was washed down and cased so that only 145 m of Tertiary section was actually drilled and logged. No cores were cut in this interval, so lithologic and biostratigraphic inferences are based on cuttings and downhole logs. Thermal modeling and vitrinite data (Stagg et al., 1990) indicate that the entire sedimentary section at Jerboa-1 is thermally immature (Rv = < 0.65%). SCIENTIFIC OBJECTIVES Leg 182 drilling in the Great Australian Bight was designed around six fundamental scientific topics to be addressed: The paleoceanographic history of a carbonate-dominated, mid-latitude continental margin and adjacent basin during evolution of the Southern Ocean. Because the Southern Ocean is one of the major controlling influences on global circulation and climate, it is imperative that the oceanic history of this region be refined as much as possible. However, the paleoceanographic development of this area is not nearly as well known at present as that of the high-latitude North Atlantic (Kennett and Barron, 1992). Although there are numerous paleoceanographic problems that can be answered by the Leg 182 drilling transect, four stand out as critical: The relationship between circulation patterns in the deep ocean and on the shelf during times of warm vs. cold ocean conditions. The stratigraphic record in the Southern Ocean is punctuated with numerous breaks in sedimentation that are attributed to erosive periods related to increased circulation during initiation of the Circum-Antarctic Current (Miller et al., 1987; Kennett and Barker, 1990). Although such hiatuses are thought to develop on deep margins during times of lower sea level and to correlate with unconformities on the continental shelf, there are apparently continuous onshore sequences of Oligocene shelf carbonates that were deposited concurrently with erosion or nondeposition of the entire Oligocene succession on the adjacent ocean floor. The precise timing and nature of the opening of the Tasman Gateway. Subsidence of the Tasman Rise, which permitted initiation of the cold Circum-Antarctic circulation and thermal isolation of Antarctica, is one of the most important developments in Cenozoic paleoceanography (Kennett, 1982). The history of this event is poorly constrained because so much of the oceanic record is missing as a result of seafloor erosion. The Leg 182 shelf- to-basin transect is sufficiently proximal to the Tasman Rise that it should contain an excellent record of the paleoceanographic development of this seaway. The evolution and effect of the Leeuwin Current. The first evidence for the existence of the Leeuwin Current occurred in middle Eocene time, when currents from the Indian Ocean were deflected into the elongate proto-Great Australian Bight embayment. In support of this, the record of warm-water intervals is more common in the west than it is in the east, implying that the source of the water is from the west. Studies of Quaternary cores from the Great Australian Bight suggest a complex interplay between the Leeuwin Current and the West Wind Drift. This interplay appears to have had dramatic effects on primary productivity, as the Leeuwin Current is a source of warm oligotrophic waters, whereas the West Wind Drift causes upwelling of cooler eutrophic waters. The relationship between primary productivity and cool-water carbonate development. The Leg 182 shelf-to-basin transect should contain an important record of paleoproductivity linked to upwelling. Such periods should be recorded in the biota by low species diversity, high numbers of individuals, increased sedimentation rates, and distinctive changes in stable-isotopic and trace-element compositions. The formulation of models for carbonate sedimentation on continental margins bathed predominantly by cool oceanic waters. The deposition and accumulation of platform (neritic) carbonate sediments under cool-water (~<20¯C) conditions is poorly understood compared to warm-water carbonates, primarily because the database is so small (Nelson, 1988; James and Kendall, 1992). Yet because of their dominantly skeletal composition, nutrient- dependent biology, and low diagenetic potential, cool-water carbonates record the history of oceanic change in ways that are profoundly different from tropical carbonates. In hydrodynamic terms, cool-water carbonate shelves are hybrids, possessing some of the characteristics of both terrigenous clastic shelves and warm-water carbonate shelves. Sediments are produced on the shelf, in contrast to terrigenous clastic shelves where sediment is transported onto the shelf from the hinterland. Without the elevated rim that typifies warm-water carbonate shelves, however, the sediments are subject to the full sweep of oceanic waves and swells, because they are on terrigenous clastic shelves. Cenozoic exposures of inner-shelf facies in Australia suggest that storm- and wave-dominated processes tend to control deposition. By contrast, many contemporaneous deposits in New Zealand are clearly tide dominated. Are the models of wave-dominated shelf deposition developed onshore applicable throughout the Cenozoic? All seismic profiles across the southern margin of Australia indicate that a large proportion of the youngest part of the succession is made up of prograding clinoforms (James and von der Borch, 1991; Feary and James, 1998). Such clinoforms seem to be a signature of cool-water platforms and ramps and are postulated to be a product of accumulation dynamics (Boreen and James, 1993). There is little information regarding the composition of these deposits. Specifically, are they produced by in-place, enhanced bioproduction along the shelf edge, or are they made up of finer grained material produced on the shelf and swept offshore to accumulate below the wavebase? Determination of the Southern Ocean basin sea-level record, and the effect of sea-level fluctuations on stratigraphic packaging and early diagenesis of cool- water carbonates. The Eucla margin is rich in biogenic carbonate sediments that respond in a sensitive way to variations in sea level and contain vital geochemical information needed for linking sea-level changes to paleoceanography. This information can be utilized to address two major questions of global and temporal significance. What is the detailed sea-level history of the Southern Ocean basin, and can it be linked to paleoceanographic variations? The southern Australian neritic shelf record, derived largely from onshore successions in which the marine record is preserved only in highstand systems tracts, appears to be at odds with the global model (Haq et al., 1987) during several critical periods. Is this because the sediments were deposited in cool water? Through the use of a combination of physical stratigraphy and proxy paleoenvironmental parameters in a much more expanded section than exists onshore, the well- preserved Eocene-Oligocene and early to middle Miocene successions will allow a thorough testing of this part of the sea-level curve and resolution of specific eustatic events. The late Miocene-Pliocene sequence is unknown onshore except for the early Pliocene highstand, so this will be the first clear record of this component of the sea-level record in the region. How do cool-water carbonate platforms respond to changes in sea level? Carbonate platforms, with their chemically metastable sediments born largely in place, are particularly responsive to changes in seawater temperature and chemistry and variations in sea state and sea level. To date, most information on carbonate platforms comes from rimmed, warm- water platforms (Kendall and Schlager, 1981; Sarg, 1988). There is almost no information on the manner in which cool-water carbonate platforms respond to changes in these critical parameters at a variety of different time scales. Specifically, we require information to describe how different segments of the shelf react during different parts of the sea-level cycle and to determine whether cold- and warm-water carbonate platforms have basically different depositional geometries as a result of the different ways the carbonate factory responds to sea-level changes. The circulation patterns of shallow subsurface fluids in an area of low hydraulic gradient and minimal recharge. The Eucla margin is one of the few modern shelves where the onshore recharge zone is an areally vast, flat-lying karst (the Nullarbor Plain). The high primary depositional permeability of winnowed grainstones of the Eucla Shelf and the lack of early cementation suggest that significant ground-water circulation may occur, at least at shallow depths. The drive for such a circulation may come from temperature contrasts between cool ocean waters and ground waters warmed by geothermal heat flux (and possibly volcanics) within the shelf, concentrating waters on the shelf margin (Simms, 1984). Alternatively, despite inland aridity, recharge occurring over the vast continental hinterland may drive brackish to saline waters southward to discharge through the flooded shelf. Such a circulation has been recognized by James (1992) and is associated with cave development on the Nullarbor Plain (James et al., 1989). In contrast to the long-lived nature of the above systems, differences in sea-surface elevation, on and off the shelf, associated with regional wave buildup (Feary, 1995), current flow (Rockford, 1986), and atmospheric pressure system changes may cause pumping of marine waters into and out of the platform (Marshall, 1986). Early seafloor and shallow burial diagenesis and dolomitization of calcite- dominated sediments. Cool-water carbonates exhibit a radically different pattern of diagenesis from that of tropical aragonitic carbonates. Slow sedimentation permits seafloor lithification by intermediate Mg-calcite cements, but these appear to be volumetrically limited and localized to omission surfaces and hardgrounds, which are ubiquitous in the inner platform. Indeed, both shallow-marine and meteoric cements appear to be very sparse, with magnesium being lost from high-Mg calcite to low-Mg calcite during grain recrystallization. Sparse calcium-rich dolomites may be present (Reeckmann, 1988; Bone et al., 1992), and at some locations replacement can be pervasive (James et al., 1993), although the fine subtidal evaporation-related dolomites typical of tropical platforms are absent. It is not known whether dolomitization is episodic, as recognized in other present-day platforms (Vahrenkamp, et al. 1991; McKenzie et al., 1993), or occurred over extended time periods. The Eucla margin carbonates will provide an opportunity to determine the present- day associations among ground-water circulation, fluid geochemistry, and diagenetic products, and by inference from the temporal and spatial distribution of ancient diagenetic components, those that occurred under different conditions in the past. This has the potential to provide fundamental insights into the diagenesis of cool-water, open-shelf carbonates, which are direct analogs for the comparable carbonate platforms that were ubiquitous during Paleozoic and other times. The pace and style of evolution of mid-latitude oceanic and neritic biotas. The Leg 182 drilling transect offers the opportunity for pioneering analysis of the Cenozoic evolution of cool-water calcareous biota, with direct applicability to studies of ancient carbonate platforms presently lacking modern analogs. Linked information from the neritic and oceanic high- to mid-latitude carbonate realm should produce an unmatched record of paleobiological information. Specifically, the patterns and modes of speciation and diversification of coeval shallow- and deep-water benthic organisms as well as contemporaneous planktonic biota should be revealed. By comparing these results with those from Antarctica and the northeast Australian shelf, the geography of such processes and their relationship to physiochemical factors should be discernible. SYNTHESIS AND RESULTS Lithostratigraphy Sediments recovered during Leg 182 record carbonate deposition in a mid- and high-latitude setting against the background of an evolving Southern Ocean and northward drift of the Australian continent. Sediment in 3875 m of water at the toe of slope (Site 1128) chronicles the change from early Paleogene time, when a humid onshore climate flushed large amounts of terrigenous clastic sediment into the deep sea, to Neogene time, when increasing continental aridity promoted mostly marine carbonate deposition. Green Eocene siliciclastic sands and silts that accumulated largely below the carbonate compensation depth (CCD) in a poorly oxygenated, bathyal setting become finer grained upward, with much of the deep-water late Eocene represented by clay deposition (Fig. 3). Initiation of the contemporary Southern Ocean circulation system, and thus the modern global ocean, is signaled by a gradual change to lower Oligocene brown clay and carbonate, as this part of the seafloor became ventilated and the CCD deepened. The deep-water Neogene record is one of pink pelagic carbonate ooze punctuated by white planktonic foraminiferal turbidites. Early-middle Miocene time is represented by a major hiatus and sediment gravity-flow deposits. Most drilling took place on the upper slope and outermost shelf, in 202-784 m of water, through a mainly carbonate succession (Figs. 3, 4). Two distinct groups of strata, Eocene-middle Miocene and late Miocene-Quaternary in age, form the upper part of the continental margin. The older succession is stratigraphically equivalent to and roughly coeval with most of the Eucla Group, exposed onshore in the Eucla Basin beneath the Nullarbor Plain. Sediments are a package of Eocene shallow-water terrigenous sands and carbonates that deepens upward into Oligocene and early- middle Miocene pelagic ooze and chalk (Fig. 3). Although recovery was generally poor through the Oligocene and Miocene interval because of silicification (Site 1134 is an exception for the Miocene), recovered carbonates are characterized by stained hardgrounds and numerous omission surfaces. The younger, wholly Neogene succession is a large, seaward-dipping wedge of carbonate sediment that downlaps onto the older sediments and has been prograding seaward onto the Eyre Terrace since late Miocene time. The contact between the two successions is represented, particularly the late Miocene and especially the Pliocene, by slumps, sediment gravity- flow deposits, or unconformities. Such erosion, corrosion, and/or mass-wasting and redeposition processes reflect periods of margin instability, seismicity, or lowered sea level. The most astonishing discovery of Leg 182 was that the huge wedge of slope sediment prograding onto the Eyre Terrace is nearly entirely Pleistocene in age (Figs. 3, 4). This deposit, formed by carbonate produced on the outer shelf and upper slope and swept seaward, is more than 500 m thick in the center (Fig. 4), where rates of accumulation exceed 40 cm/k.y., equivalent to many shallow-water tropical carbonates and twice the rate of Bahamian slope sedimentation. The green and gray material is surprisingly uniform in composition, made up of fine carbonate sand and silt that was reworked in place by generations of burrowing organisms, leading to multitiered trace fossil assemblages. Particles are all skeletal fragments, mainly delicate bryozoans, ostracodes, benthic and planktonic foraminifer tests, tunicate sclerites, nannofossils, and siliceous sponge spicules. The deposit grades from mud and sand at the top downward to partially lithified sediment in the middle, and finally to hard limestone at the base. Sediment below 400 mbsf is usually neomorphosed with numerous fossil molds, or partially altered to sucrosic dolomite. The facies transition upslope into shallower water is marked by the presence of numerous bryozoan-rich buildups (Figs. 3, 4). These mounds, in water depths of ~200-350 m, are dominantly muddy and characterized by the prolific growth of numerous and diverse bryozoans. The mounds in particular have seafloor relief of as much as 20 m and extend laterally many hundreds of meters. These are among the first modern analogs to similar mounds that were an important part of the carbonate depositional systems in earlier, Phanerozoic time. Biostratigraphy Age of Sediments and Hiatuses The Cenozoic sequence penetrated at Leg 182 sites mainly represents the Pleistocene, Miocene, Oligocene, and Eocene. Biostratigraphic data indicate that these Cenozoic successions are mostly hiatus bound (Fig. 5). The Pliocene and the later part of the middle Miocene successions are either missing or highly condensed. Other intervals of the Miocene and Oligocene are also missing, though unmatched between sites along the eastern and western transects. A greatly expanded Pleistocene section was recovered at shallow-water sites from the eastern transect (Sites 1129, 1131, and 1127). The longest at Site 1129 exceeds 540 mbsf, with an average accumulation rate of more than 300 m/m.y. (Fig. 6). In contrast, the Pleistocene sections from the western transect only extend down to ~250 mbsf at Sites 1130, and ~230 mbsf at Site 1132. The biostratigraphic units, however, are similar between eastern and western transect sites. The Pleistocene section is underlain by a thin upper Miocene interval, which in turn disconformably overlies a unit of mainly early-middle Miocene age. The absence of many Pliocene to later middle Miocene biozones from Sites 1127, 1129, and 1130 signifies a hiatus of at least 7 m.y. between the Pleistocene-Pliocene and the middle Miocene. This major unconformity was detected at all other sites as two shorter hiatuses of ~3 m.y. each at the middle/late Miocene and late Miocene/Pliocene-Pleistocene boundaries. They are more clearly recorded as disconformities capping the upper Miocene section at Sites 1126, 1134, and 1133 in intermediate water depths, and at shallow-water Sites 1130 and 1132 along the western transect (Fig. 5). Thus, it is reasonable to speculate that the unconformity at the Pleistocene-Pliocene/middle Miocene boundary, as observed at eastern sites, probably resulted from at least two major events that subsequently almost completely erased the sedimentation record of the later middle Miocene-Pliocene. The late Miocene succession is better represented in the west, especially at Site 1130 and at deep-water sites. The middle Miocene, mainly the early part, is present at all sites except Sites 1128 and 1130. It also represents the oldest sediment penetrated at most sites along the eastern transect, although a thin lower Miocene unit was encountered at the base of Hole 1131A (~590 610 mbsf). An expanded middle Miocene section at Site 1132 was accompanied by sedimentation rates ranging 14 54 m/m.y. (Fig. 6). A similar rate of 50 m/m.y. was recorded for the middle Miocene at Site 1133. The absence of middle-early Miocene biofacies from Sites 1130 and 1128 is interesting because these two sites respectively represent the intermediate and deepest water sites along the western transect. At Site 1130 (495 mbsf), the upper Miocene section was disconformably underlain by sediments of mainly early-middle Oligocene age, indicating a depositional gap of ~15 m.y. At Site 1128 (3890 mbsf), the entire middle Miocene-upper Oligocene interval corresponds to a ~15-m-thick debrite with mixed calcareous nannofossil and planktonic foraminifer assemblages of early to late Miocene age, suggesting unconformities totaling ~13 m.y. in duration. Sites 1126 and 1134, the two intermediate-water sites from the west, exhibit remarkable similarities in assemblage compositions, ages of recovered sediments, and position and number of hiatuses. These are the only sites yielding definite early Miocene calcareous nannofossils and planktonic and benthic foraminifers. Sediments of Oligocene age and older were recovered only from the west. At Sites 1130 and 1132, the Oligocene section disconformably overlies Eocene sediments, and a hiatus of at least 2 m.y. is indicated by biostratigraphic data. However, the zonal succession of nannofossils and planktonic foraminifers is largely continuous across the Oligocene/Eocene boundary, suggesting a conformable succession at Sites 1126, 1128, and 1134. Mainly early Oligocene assemblages are present at Sites 1132, 1130, and 1128 in the west, and an expanded lower Oligocene section was indicated by nannofossils at Site 1128. Biostratigraphic resolution below 70 mbsf at Site 1128 was largely achieved by calcareous nannofossils because planktonic foraminifers were rare or barren in sediments dominated by siliceous oozes and packstones. Holes 1126D and 1134A are the only holes containing rich calcareous microfossils of Eocene age. Poor preservation, however, impaired proper recognition of species and biozones in some intervals. Although present at all western sites, the middle Eocene is represented by poorly preserved, impoverished assemblages in various poorly recovered lithologies. It consists of a siltstone (~150 m thick) at Site 1128 with sporadic nannofossils, a calcareous packstone (~30 m thick) at Site 1126 with moderately preserved nannofossils and planktonic and benthic foraminifers, and a dark, iron-stained sand (30 m thick) at Site 1134 with rare and poorly preserved microfossil assemblages. A calcareous sandstone at Site 1130 and a bioclastic limestone at Site 1132 both contain shallow-water associations of planktonic and benthic foraminifers. No calcareous nannofossils or foraminifers were discovered in dark green sandstone at the base of Hole 1126D, which may correspond to Cretaceous synrift sediments along the southern Australian margin. Paleobathymetry and Paleoceanography The succession of microfossil assemblages from Leg 182 provide an unmatched record of sea-level and circulation changes in the Great Australian Bight from the Eocene to Holocene. Expanded Pleistocene successions at Sites 1127, 1129, 1130, 1131, and 1132 contain upper bathyal benthic foraminifer assemblages with a redeposited neritic component. Apparent fluctuations in the relative proportions of neritic taxa and upper bathyal taxa indicate that downslope transport periodically varied in intensity during the Pleistocene. These changes, together with the periodic intrusion of warm-water species into temperate planktonic foraminifer assemblages, indicate responses to changing climate and oceanic circulation. Calcareous nannofossil assemblages dominated by Braarudosphaera bigelowii indicate that a major ecological crisis affected the planktonic ecosystem at base of the Pleistocene. At the three shallow-water sites (Site 1129, 1131, and 1132), diversified, extremely well-preserved benthic foraminiferal assemblages, including unusually large specimens (>1 mm), are found together with abundant and well-preserved bryozoan fragments (Fig. 5). These assemblages were probably part of a highly dynamic ecosystem that became established at the seafloor during the later Pleistocene, coincident with bryozoan buildups in paleodepths of 200-300 m. A shallowing-upward trend from middle bathyal paleodepths in the middle and late Miocene to upper bathyal paleodepths in the Pleistocene is recorded at Sites 1129, 1130, and 1132 (Fig. 5). Middle bathyal faunas at these sites reflect middle and late Miocene transgressive pulses that are also expressed onshore southern Australia by thin transgressive tracts. Middle bathyal assemblages from upper Eocene-upper Miocene successions show major changes in composition at intermediate water Sites 1126 and 1134. The most severe changes in the early Miocene probably relate to global changes in deep- and intermediate-water circulation affecting the distribution of bathyal benthic foraminifers worldwide. The composition of abyssal assemblages at Site 1128 indicates deposition above the CCD during the Pleistocene, close to lysocline in the late Oligocene-middle Eocene, and below the CCD in early-middle Eocene in the deep basin (Fig. 5). Assemblage boundaries appear to be coeval in the Eocene, Oligocene, and lower Miocene of intermediate- and deep-water Sites 1126, 1128, and 1134, suggesting that benthic foraminifer distribution was controlled by major environmental changes during these periods. Discrepancies between assemblage boundaries of deep-, intermediate-, and shallow-water sites in the middle Miocene-Pleistocene sequence relate to stratigraphic or lithological differences, and reflect distinct depositional and paleoceanographic regimes in the region. Paleomagnetics Previous carbonate legs have proved very unsatisfactory for paleomagnetists because the magnetic intensity of the sediments has been so low that remanence measurements were essentially unreliable. However, with the change to direct-current superconducting quantum interface devices (DC SQUIDs) in the new instrument, it was possible to measure the magnetization at most sites during Leg 182. Nevertheless, the natural remanent magnetization (NRM) of sediments from Sites 1126 and 1134 was so weak that after a coring overprint was removed the magnetization was at the noise level of the instrument for much of the hole. Coring Experiments During Leg 182, an experimental nonmagnetic cutting shoe was used in advanced hydraulic piston core (APC) coring. The shoe and other components of the bottom- hole assembly were used to continue investigations of anomalous magnetization observed in these cores. Comparisons were made between cores taken with standard core-barrel assemblies, with standard core-barrel assemblies and the nonmagnetic shoe, and with nonmagnetic core barrels and shoe. On some occasions, it was clear that the nonmagnetic shoe and assembly greatly improved the paleomagnetic record. On other occasions, the shoe alone improved the record compared with the core- barrel standard assemblies. However, there were also sites where neither the nonmagnetic shoe nor the whole nonmagnetic core-barrel assembly had any obvious effect. This is consistent with the intermittent nature of the anomalous magnetization experienced during past legs. Work postcruise will focus on trying to isolate other sediment properties such as grain size, porosity, or shear strength, which may affect the coring contamination. Rock Magnetism A common feature of the rock magnetism of the upper sections of Leg 182 holes was the extremely high ratio of anhysteretic remanent magnetization to isothermal remanent magnetization (ARM/IRM). This is a measure of the degree to which single- domain particles dominate among the magnetic phases present in the samples. This ratio generally decreased downhole and was accompanied by a decrease in intensity of magnetization and coercivity. This decrease in intensity of magnetization is generally interpreted as dissolution of the finest grained magnetic phases in the sediment. IRM acquisition suggests that magnetite and magnetic sulfides are the principal remanence carriers. The observation of a downhole decrease in ARM/IRM and intensity is consistent with diagenesis models of organic matter oxidation and sulfate reduction as the principal processes that regulate the preservation of ferromagnetic phases. Magnetostratigraphy Long-core and discrete sample measurements yielded a record of inclination from which a Pliocene-Pleistocene magnetostratigraphy was interpreted. Overall, deeper water records are of good to fair quality, yielding accurate estimates of the expected inclination for the present latitude. In contrast, lower intensities in the shallow-water sites result in shallow inclinations with large scatter. The Brunhes/Matuyama boundary was identified in five high-sedimentation-rate sites (Fig. 7; Table 1). The Jaramillo Subchron (C1r1n) and the top of the Olduvai Chron (C2n) were also found at three sites. The interpretation of magnetic polarity in Figure 7 implies that sedimentation rates in the early Pleistocene were considerably lower than during the Brunhes Chron. In addition, variations of the intensity of the remanence after partial demagnetization were found to oscillate on time scales comparable with those of the geocentric axial dipole. Although the intensities have not been normalized to account for variations in concentration, these sediments may provide a valuable relative paleointensity record that can be used for high-precision correlation between sites. For Sites 1126 and 1134, magnetostratigraphic data were obtained for parts of the Miocene. Site 1128 also contains a long record of the polarity sequence of the early Oligocene. Geochemistry The drilling of nine sites off the Eucla margin provided a unique insight into the fluid dynamics along a continental margin dominated by cool-water carbonates. With respect to this objective, the most significant discovery was the presence of a brine, varying in salinity between 80 and 105, that was present in and underlying seven of the nine sites (the exceptions being Site 1128, drilled in a water depth of 3884 m, and Site 1133). At Site 1133 (located in 1043 m of water) fluids were encountered with a salinity of 40, but recovery problems precluded the measurement of the salinities in deeper samples. The brine was present at relatively shallow depths at the deeper sites (1134 and 1126), whereas the maximum salinities were not encountered until depths Ú400 mbsf at the shallower sites (1127, 1129, 1130, 1131, and 1132). The impact of the brine is more readily visible along the eastern transect (Sites 1129, 1131, and 1127; see also Fig. 4). Similar processes appear to occur at Sites 1130 and 1132, although they are reduced in nature. At Sites 1129, 1131, and 1127, a gradual increase in salinity was encountered, reaching a maximum value of ~100 at Site 1127 (farthest away from the margin) and 92 at Site 1129 (closest to the platform). A contour map of the distribution of Cl- at the three sites is shown in Figure 8. Pore fluids in the Pleistocene portion of the sediments from these sites also possess a Na+/Cl- ratio exceeding that of seawater, suggesting that the fluids in the sediments were involved in the dissolution of NaCl. Although the origin of the fluids has not yet been established, a probable explanation is that they formed during the Pleistocene when the Eucla shelf was exposed numerous times during sea-level lowstands. We suggest that large hypsersaline lagoons developed during these episodes of low sea level. Because of the greater hydrostatic head, fluids with high salinity were forced into underlying strata and out onto the adjacent continental slope. During sea-level highstands high salinity fluids then diffused upward as additional sediment was deposited, and the profiles of the individual ions were modified by diagenetic reactions in the sediments. This sequence may have occurred a number of times as sea level fluctuated during the Pleistocene. This hypothesis is supported by an examination of the Cl- distribution between the three sites (Fig. 8) which suggests that the top of the brine has a common depth below sea level and, therefore, crosscuts sequence boundaries. All three sites exhibited high concentrations of hydrogen sulfide (H2S) and methane, combined with high values of alkalinity. The high concentrations of H2S are derived from the oxidation of organic material by sulfate-reducing bacteria. The relatively low concentrations of iron in carbonates, in contrast to those found in locations adjacent to continental margins with a large amount of siliciclastic input, means that the H2S is not sequestered as iron sulfides. Consequently, concentrations of H2S are able to reach high levels (>150,000 ppm at Site 1129). As a result of the high rate of sedimentation (>200 m/m.y.) and the position of the sites close to the continental shelf, these sites contained an initial high concentration of organic material. Under normal conditions, the organic material would be oxidized first by oxygen and then by sulfate-utilizing bacteria, thereby creating alkalinity and hydrogen sulfide. Although this process also takes place in the Eucla margin, the high-salinity brines underlying and within the Pleistocene succession provide as much as three times the normal sulfate concentrations; therefore, with sufficient organic material, significantly higher amounts of hydrogen sulfide can be formed. As the sediments are buried, the concentration of sulfate is depleted in the sediment and a gradient is established between the sediments, the overlying seawater, and the underlying brine. Because of the high sulfate concentration of the brine, the flux of sulfate diffusing into the zone of organic material remineralization is significantly greater than in a normal marine sediment, thus resulting in greater than normal sulfate reduction and higher alkalinity. In addition to H2S, high concentrations of methane and the presence of other higher molecular-weight hydrocarbons were discovered in the sediments at Sites 1129, 1131, and 1127. At Site 1127, gas pockets in the core were found to contain as much as 73% methane and 365 ppm ethane. We suggest that these gases, including the higher molecular-weight hydrocarbons, are bacterial in origin, being generated in situ. Higher molecular-weight alkanes are generally only believed to form through thermogenic processes (Fig. 9). However, the concentration of ethane, propane, and butane did not increase with depth, but instead reached a maximum associated with the maximum in methane, suggesting that these gases also originated in this portion of the sediment and were not thermogenic in origin. The oxidation of organic material also has an important influence on the process of carbonate recrystallization. The sediments at all the sites cored during Leg 182 initially contained a mixture of aragonite, high-Mg calcite (HMC), and low-Mg calcite (LMC). Of these minerals, aragonite and HMC are metastable and gradually will alter to the more stable forms of LMC and dolomite. This process is evident at all the sites drilled and is greatly accelerated by the processes of sulfate reduction and the consequent formation of H2S. During the oxidation of organic material, two important chemical reactions take place that alter the carbonate chemistry in the pore waters: (1) sulfate reduction creates two moles of alkalinity for every mole of sulfate that is consumed and (2) one mole of H2S is produced (2CH2O + SO42- = H2S + 2HCO3- ). The H2S dissociates in the pore water causing the pH to be reduced and the speciation of carbonate in the pore waters to move from being dominated by HCO3- to H2CO3. This sequence of events produces pore fluids that are undersaturated with respect to the metastable carbonate minerals. The most thermodynamically soluble form of calcium carbonate, HMC dissolves first, followed by aragonite, and LMC. This trend is followed at all of the sites. The high-alkalinity environment creates a thermodynamic regime favorable for the formation of dolomite. Dolomitization consumes Mg2+ from the pore waters, setting up a strong diffusive gradient into the reaction zone from the overlying seawater and the underlying brine. The formation of dolomite is well illustrated at Sites 1127, 1131, 1129 (Fig. 10), which shows concentrations of ~5% at Sites 1127 and 20% at Sites 1129 and 1131. Although the high-salinity pore fluids were also present at other sites (Sites 1130, 1132, 1126, and 1134), these sites showed lower concentrations of H2S and methane and consequently lower amounts of carbonate diagenesis. The controlling factor at these sites is the supply of organic material combined with the rate of sedimentation. Petrophysical and Downhole Measurement Data Downhole logging data were collected at eight of nine sites drilled during Leg 182. To complement these data, an extensive program of sediment physical properties measurements was undertaken. Both datasets will provide detailed information for intersite correlation, characterization of lithostratigraphic boundaries, and core-log correlation. The presence of chert, particularly in the post-Pleistocene sequences sedimentary section, resulted in low recovery. Downhole logging data will provide the information necessary to fill in recovery gaps, refine the placement of lithostratigraphic boundaries, and enable interpretation of sedimentary facies, composition, and structure within missing intervals. Checkshot surveys conducted at five sites will facilitate correlation of the drilled strata to the regional grid of high-resolution seismic data to formulate and refine models of temperate-water carbonate sedimentation and view the influence of eustatic sea-level variations on this sedimentation. The downhole logging and physical properties measurement program undertaken during Leg 182 provided an unparalleled opportunity to investigate early and postdepositional diagenesis in a nontropical carbonate depositional system. Preliminary diagenetic characterization of temperate-water carbonate sediments recovered during Leg 182 show distinct geochemical, mineralogic, and textural variations, despite the preconceived notion that cool-water carbonates have low diagenetic potentials because of their dominantly low-magnesium calcite mineralogy. Postcruise analysis of Formation MicroScanner (FMS) and conventional logs will provide a more detailed analysis of mineralogical and textural changes occurring during diagenetic alteration. An important finding of Leg 182 was the discovery of distinct, possibly Milankovitch, cyclicity recorded in gamma-ray and density data from the thick Pleistocene sediment wedge drilled at numerous sites (Fig. 11). The high sedimentation rates of this deposit, in excess of 40 cm/k.y., will enable frequency analysis of the logging and physical properties datasets to assist in the refinement of the biostratigraphic ages within this time interval. FMS data collected at six of the logged holes will allow for detailed investigation of depositional facies and sedimentary structure in the sediment cycles, particularly in the intervals where recovery was poor. Correlation of the cyclicity present in the temperate-water carbonate wedge to other Pleistocene carbonate and noncarbonate marginal systems will provide important information on differences in eustatically influenced sedimentation patterns occurring on continental margins from the seafloor to the bottom of the drilled interval. PRINCIPAL RESULTS Site 1126 Site 1126 is located on the eastern Eyre Terrace upper slope in 783.8 m of water. This site was designed to intersect Cenozoic seismic Sequences 2, 3, 4, and lobes 1 and 3 of Sequence 6A, and to intersect as much of the upper part of the Cretaceous section as time permitted. The target depth at this site was a high-amplitude reflector of probable Cenomanian age, estimated before drilling (on the basis of stacking velocities) to be at 525 mbsf. Because this was also the first ODP site in this basin, it provided the opportunity to establish a basic stratigraphy for the Cenozoic sequences that could then be refined at later sites. Five lithostratigraphic units were delineated at Site 1126. Unit I (0-60.2 mbsf) is a calcareous ooze with a gradational alternation between two major sediment types: (1) white gray nannofossil-rich matrix-supported ooze and (2) light gray grain-supported ooze rich in planktonic foraminifers. Unit II (60.2-116.8 mbsf) is characterized by several intervals of slumped calcareous ooze. Sediment composition in these bodies is the same as in the undisturbed sediments. The first downhole occurrence of silicified layers (porcellanite) subdivides Unit II into an upper Subunit IIA and a lower Subunit IIB. As in Unit I, intervals that are not affected by slumping display a light/dark alternation. In the lower part of Unit II, these cycles are increasingly asymmetric, with the dark portions becoming dominant. Unit III (116.8-165.5 mbsf) consists of calcareous ooze with interbeds of silicified layers in the upper part of the unit. The lower part of the unit is porcellanite free and displays the same type of cyclicity as sediments in the overlying units. Unit IV (165.5-396.6 mbsf) coincides with an interval of low core recovery and thus cannot be described in detail. It consists of an alternation of calcareous ooze to chalk intervals and silicified pelagic limestones with some planktonic foraminifers and bioclasts. Unit V (396.6-455.9 mbsf) consists of black to green sandstones, silty sandstones, clayey siltstones, and minor granule conglomerates. Nannofossil and planktonic foraminifer biostratigraphies show that Quaternary through middle Eocene sequences were recovered. Sandstones of probable Cenomanian age (Unit V) recovered at the base of the drilled interval are barren of marine microfossils. Sedimentation rates were relatively high in the Quaternary (31 m/m.y.) and lower Pliocene (24 m/m.y.) and slow in the remainder of the Neogene and Paleogene sections, where rates alternate between 7-8 m/m.y. and 11-15 m/m.y. with faster rates in the upper Miocene, lower Miocene, and upper Oligocene. Two intervals of slow sedimentation are present at the Miocene/Pliocene and early/middle Miocene boundaries. Benthic foraminiferal assemblages show a change in benthic environments from lower bathyal to middle bathyal in the upper part of the middle Eocene nannofossil zone, NP16. Slumps between ~55 and 110 mbsf are marked by a mixture of late Miocene and early Pliocene planktonic taxa found within a latest early Pliocene assemblage. The slump is also flagged by a mixture of a displaced upper bathyal assemblage of benthic foraminifers found within an in situ middle bathyal assemblage. The results of paleomagnetic long-core measurements of cores from Hole 1126B and 1126C were disappointing. The NRM was dominated by a vertically downward coring contamination that was largely removed by 20 mT demagnetization, whereupon the signal was almost uniformly reduced to the noise level of the instrument. In addition, there were anomalous peaks in intensity near the tops of most cores and of several sections. These were so large that we interpret them as contamination. Only a single core gave a sequence of reversals that could be interpreted magnetostratigraphically. A comparison between whole-core and archive-half core measurements showed that the two measurements are not significantly different from each other, thereby settling a long-debated question. The nannofossil chalks gave stronger signals, but poor recovery precluded determination of a useful magnetostratigraphy. In the sandstone recovered toward the base of Hole 1126D (Unit V), normal magnetizations were observed. Their high inclination, giving a paleolatitude of ~50¯S, is in accordance with northerly motion of the Australian plate as it moved away from the Antarctic-Australia spreading center. Rock magnetic properties of representative samples from the various sedimentary units differ in a manner that is consistent with the NRM variation. In the nannofossil chalk and in some of the more strongly magnetized nannofossil oozes, the magnetic carrier appears to be single-domain magnetite consistent with a magnetotactic bacterial origin, whereas a different and harder phase dominates in the uppermost nannofossil ooze sediments. The upper 154.0 m of sediment at Site 1126 was double cored. Construction of the composite section from Holes 1126B and 1126C indicates that a complete record of the sedimentary section was not recovered. Correlation between cores was hindered by significant differential core distortion, particularly at the very top of each core where an expanded record was indicated. Correlations were further hindered by a decrease in core recovery below 100 mbsf, resulting from the presence of multiple thick chert layers. Below 60 mcd, large data gaps and the presence of numerous slumps made correlations difficult and highly tentative. The composite section indicates gaps in the record at ~26-27, 64-65, 73-74, 86-87, 109-112, 124-125, and 130-137 mcd. Only low concentrations of methane and ethane were detected at Site 1126. Methane ranges from 2.2 to 13.6 ppm. Ethane is present in five samples between 186.5 and 236 mbsf (1.1-2.7 ppm) but is not detected at greater depths. The carbonate content is uniformly high (80-91.2 wt%) in the upper 116 mbsf but becomes highly variable (30.6-93.2 wt%) from 116 to 254.2 mbsf. Because of poor core recovery, no samples are available in the interval from 254.2 to 348.6 mbsf. From 348.6 to 389.6 mbsf, the carbonate content returns to high levels within a narrow range (79.5-90.0 wt%), dropping again to very low values in sandstones (0.4-0.6 wt%) from 406.4 to 454.5 mbsf. Total organic carbon is low throughout the cored interval except for the bottommost sample of Hole 1126D, which has 1.33 wt% organic carbon. All other organic carbon values are less than 0.8 wt% and most are less than 0.2 wt% Site 1126 is characterized by a large increase in salinity that manifests itself as shallowly as 10 mbsf, reaching a maximum of 106 (about three times normal salinity) by a depth of ~100 mbsf. Most of the other geochemical parameters exhibit nonconservative behavior with respect to chloride, including calcium which shows a net excess, and magnesium, sulfate, and alkalinity, all of which show net losses. The pore waters have a sodium/chloride ratio close to that of seawater. We believe that the origin of these saline fluids may relate to fossil brines that penetrated the sediments during a previous sea-level lowstand. Physical properties data closely reflect the location of sequence boundaries and changes in lithology and mineralogy. These data were subdivided into five units on the basis of shifts in measured parameters. Physical properties (PP) Unit 1 is characterized by high natural gamma radiation (NGR) with a trend of increasing P- wave velocity and bulk-density measurements to the bottom of the unit. The base of PP Unit 1 roughly coincides with the late Pliocene/Pleistocene boundary. PP Unit 2 is characterized by relatively high natural gamma radiation that dramatically decreases toward the base of the unit. This decrease occurs because of the downhole disappearance of aragonite. P-wave velocity increases throughout PP Unit 2, as does thermal conductivity. The base of the unit coincides with the late Pliocene/early Miocene boundary. PP Unit 3 is characterized by low variability in P-wave velocity and NGR. The base of this unit was not recovered in the sediments, but can be defined at 185 mbsf using downhole logs. PP Unit 4 is characterized by alternations of high- velocity porcellanite and lower velocity oozes. This high contrast of sediment induration was probably the major cause of the low recovery in this unit. The top of PP Unit 5 coincides with a major hiatus at the base of the Tertiary. PP Unit 5 shows much greater NGR values and higher P-wave velocities reflecting the transition from PP Unit 4 ooze into PP Unit 5 sandstone. This indicates that PP Unit 5 sediments were affected by diagenesis. Thermal conductivity co-varies with water content, bulk density, and P- wave velocity. Hole 1126D was logged with three tool strings: the triple combination logging tool, Sonic/Geologic High Resolution Magnetic Tool (GHMT) combination, and the well seismic tool (WST). The FMS tool was not run with the Sonic as usual because of (1) excessive heave caused by dual swell directions that was not compensated for by the wireline heave compensator and (2) a large hole diameter as indicated by the caliper on the triple combo. The triple combo was deployed from 439 mbsf to well above the mudline. The Sonic/GHMT tool string was deployed from 430 mbsf to above the mudline. The WST was used for recording nine checkshot stations between 420 and 130 mbsf. Several zones of washed out hole affected readings made by excentric tools (e.g., neutron porosity and density), whereas readings measured by hole-centered tools (e.g., magnetic susceptibility, sonic, and resistivity logs) were little influenced by hole conditions. The magnetic susceptibility data were useful for subdividing the measured section into 10 provisional logging units, some of which correlate with the seismic stratigraphic units. In the interval below 160 mbsf where core recovery was poor, changes in several logs provide the detail and continuity necessary to further subdivide the section. The spectral gamma-ray log measured by the triple combo proved very useful for correlating the part of the section measured through pipe (upper 116 mbsf) with core measurements. In the lower siliciclastic part of the section, photoelectric effect (PEF) values indicate the presence of iron minerals. The checkshot survey showed that the actual time-depth conversion curve fell within the narrow envelope of time-depth curves derived from stacking velocities, so depth estimates for other sites based on stacking velocity curves can be viewed with more confidence. The preliminary biostratigraphic data permitted ages of the regional Cenozoic seismic sequences to be defined, showing that Sequence 2 corresponds to the Pleistocene, Sequence 3 is of Pliocene-late Miocene age, Sequence 4 is of latest Miocene age, and Sequence 6A is of Eocene-Oligocene age. Site 1127 Site 1127 was the first and most seaward site of a planned three-site transect through a spectacular set of late Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1127, located on the upper slope in 480.6 m of water, intersects an expanded record of the youngest clinoforms as well as the lowest, more condensed portion of the clinoform sequence. The principal objective of this transect was to collect detailed, high-resolution profiles through a late Neogene shelf-edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment to determine the response of this type of depositional system to Pliocene-Pleistocene sea-level fluctuations. At Site 1127, we recovered a 510.7-m-thick monotonous succession (Table 2) that is dominated by very fine- to fine-grained, heavily bioturbated, unlithified to partially lithified, greenish gray wackestones to packstones, made up of three units. Unit I (0-6.0 mbsf) consists of two subunits, an upper nannofossil ooze and a lower foraminiferal ooze. Unit II (6.0-464.5 mbsf) consists of alternating bioclastic wackestone- and packstone-dominated packages with thin grainstone beds, divisible into five subunits. These subunits are characterized by a lower portion composed of wackestones to packstones, grading up into wackestones, and dominated at the top by packstones with thin capping grainstones. Shallower water fauna are most abundant near the top of each subunit. The lowermost subunit (~420-464.5 mbsf) has a slumped base with abundant clasts, including bryozoan and large skeletal fragments within an ooze matrix. Unit III (464.5-510.7 mbsf) consists of an upper nannofossil ooze and a lower glauconite-rich bioclastic packstone, with minor capping grainstone beds with intraclasts. Calcareous nannofossils and planktonic foraminifers indicate an extraordinarily expanded Pleistocene sequence of more than 450 m, with a hiatus of over 3 m.y. between basal Pleistocene (Zone NN19) and underlying Miocene sediments. Based on preliminary biostratigraphic datums, average sedimentation rates were 240 m/m.y. in the Pleistocene, and 2-8 m/m.y. in the Miocene. The thin Miocene section contains a strongly mixed planktonic foraminiferal assemblage. A well-preserved benthic Pleistocene foraminiferal assemblage is recognized down to 414.5 m. Between 414.5 and 501.1 mbsf, two benthic assemblages were identified that contain mainly upper bathyal taxa but include large numbers of abraded and corroded tests, indicating extensive mixing or reworking. Calcareous nannofossil assemblages throughout most of Zone NN19 are dominated by small forms, suggesting some sorting. Similarly, Pleistocene benthic foraminiferal assemblages display a uniformity in test size and lack of medium to large tests that is consistent with grain-size sorting and downslope redeposition. The cool temperate Pleistocene fauna is accompanied by warm-water species at various intervals, probably reflecting a combination of global climatic fluctuations and regional paleoceanographic variations, especially in relation to flow of the Leeuwin Current. Paleomagnetic measurements revealed a long section of normal polarity to 343.4 mbsf, which we interpret as the Brunhes Chron. The mean inclination was -49.9¯, with a standard deviation of 22¯. It was only possible to locate a very approximate onset (380 mbsf) and end (395 mbsf) of the Jaramillo Subchron. We found intensity fluctuations within the Brunhes Chron in the NRM after 20 mT demagnetization that appear to correlate with standard records of geomagnetic field fluctuations back to 400,000 yr. The calculated sedimentation rate for the whole Brunhes Chron is 480 m/m.y., whereas the rate for the first 400,000 yr based upon the intensity estimation is 277 m/m.y. Rock magnetism analysis revealed that the dominant magnetic phase was chemically unstable, so that the saturation remanence decayed by as much as 60% within 48 hr. This behavior is typical of the ferromagnetic sulfide greigite, which inverts sluggishly to paramagnetic pyrite. The high ARM/IRM suggests a dominant single- domain grain size and a strong magnetotactic bacteria input. However, if this suggestion is correct, the magnetotactic bacteria synthesize greigite rather than magnetite. The most striking organic geochemical results at Site 1127 are the very high concentrations of methane and hydrogen sulfide present throughout the section. Gas pockets within the core were common from 47 to 312 mbsf, and these were sampled directly through the core liner with a gas-tight syringe (vacutainer). Methane concentrations in these gas pockets range from 165,000 to 730,000 ppm, with most values between 400,000 and 600,000 ppm. Hydrogen sulfide ranges from ~60,000 to 138,000 ppm. Methane is present at lower and highly variable concentrations in headspace samples, with the lowest values at the top and bottom of the drilled interval. Methane/ethane ratios in vacutainer samples decrease downhole from 2728 to 1309, with a decrease in the ratio to 174 in headspace samples. Carbonate content values predominantly range between 85 and 92 wt%, with a trend toward lower values with increasing depth. Organic carbon values are primarily in the range of 0.1-0.6 wt% down to ~250 mbsf, and then vary from 0.5 to 1.0 wt% to the bottom of the hole. Although similarly influenced by high-salinity pore fluids (up to 100 in Pliocene and older portions of the section), pore-water geochemistry at Site 1127 was fundamentally different than at Site 1126 because of an extended sulfate reduction zone. Because of the more inshore location, Site 1127 not only had a higher initial organic matter content compared to Site 1126, but more of the organic material was preserved as a result of higher sedimentation rates. Because of the high sulfate concentration in the deeper, higher salinity fluids, the sulfate reduction zone is enlarged and the consequent production of hydrogen sulfide is much higher than in normal organic-rich sediments. In addition, the relatively iron-poor nature of these sediments precludes the formation of iron sulfide phases that would normally sequester hydrogen sulfide. The greatest amount of carbonate recrystallization appears to occur at the lower interface between the sulfate-depleted zone (~180 mbsf) and the underlying sediments, where sulfate is actively diffusing upward from the higher salinity fluids below. This process produces pore fluids undersaturated with respect to metastable minerals, causing the precipitation of low-Mg calcite and dolomite. Striking variations in the amount of low-Mg calcite, high-Mg calcite, aragonite and dolomite also occur throughout the succession, with presumed sea-level lowstands characterized by increased high-Mg calcite and the presence of dolomite. Because of disruption of the sediments during degassing, laboratory physical properties measurements are of limited value for developing a downhole stratigraphy. However, the NGR measurements were only affected to a minor extent, and can be used to define three PP units: PP Unit 1, from 0 to 130 mbsf, is characterized by three high-amplitude cycles superimposed on a rising trend, and corresponds to seismic subsequence 2a. PP Unit 2 is from 130 mbsf to the Pliocene/Pleistocene boundary at 467 mbsf, which is marked by a sudden decrease in NGR values. This unit is characterized by low-amplitude, high-frequency cyclicity in NGR values and corresponds to seismic subsequences 2b and 2c. PP Unit 3 corresponds to the Pliocene sediments below the Sequence 2 boundary, which are also significantly denser than the Pleistocene sediments. Magnetic susceptibility was uniformly very low, and the data were shown to be nonreproducible at the core-section scale. Hole conditions were excellent for logging, with most caliper readings within 10 cm of bit size. Hole 1127B was logged with three tool strings: the triple combo and FMS/Sonic to the mudline, and the GHMT to 59 mbsf. The triple combo was run without the nuclear source in the hostile environment lithodensity sonde (HLDS) because of safety concerns, and consequently density logs are not available for this site. During and after logging, close examination showed that there was no obvious damage to either the logging cable or tools from the limited H2S exposure. Cycles and surfaces seen in the high-quality FMS data correlate well with conventional logs (gamma ray [GR], sonic, and resistivity) and indicate the presence of high-frequency cycles (10-20 m thick) in the lower part of the Pleistocene succession. Simultaneous peaks on GR, resistivity, sonic, and susceptibility logs may reflect changes in sediment lithification throughout the logged section. Because of the high quality and uniform response of the sonic log, the WST was not deployed at this site. We anticipate that a checkshot survey at one of the other sites in this transect will provide appropriate drift control on the integrated sonic log. Site 1128 Site 1128, the deep-water component of the Leg 182 shelf-to-basin transect, is located on the upper continental rise in 3874.6 m of water. The primary goals of this site were to (1) recover pelagic ooze from the upper continental rise to compile a paleoceanographic record of the Cenozoic opening of the Southern Ocean and development of the Circum-Antarctic Current, (2) determine the history of Cenozoic and Late Cretaceous CCD fluctuations and deep-water mass variations during the evolution of the Southern Ocean, and (3) determine depositional and diagenetic facies on the upper continental rise. The sedimentary succession intersected at Site 1128 was divided into four major lithostratigraphic units. Unit I (0-95.6 mbsf) is a pink to brown, bioturbated, calcareous nannofossil ooze punctuated by numerous thin glauconite and planktonic foraminiferal sand calciturbidites and conglomeratic sediment gravity-flow deposits. A chaotic zone of debrites and slumped sediment (54.4-70.0 mbsf) separates this succession into three subunits containing variable proportions of resedimented material. Unit II (95.6-281.9 mbsf) is a thick section of uniform, green, variably calcareous clay and claystone that is locally interrupted, particularly in the upper parts, by several centimeter-thick turbidites composed of planktonic foraminiferal and nannofossil ooze. The relatively few carbonate particles in the sediment are etched and corroded, suggesting accumulation near the carbonate lysocline. The lower parts of this unit contain numerous well-preserved trace fossils (Planolites, Chondrites, Zoophycos, Terebellina, and Thalassinoides), and numerous thin chert horizons. A thin unit of green, glauconitic sand-to-carbonate nannofossil ooze turbidites forms Unit III (281.9-284.0 mbsf) and marks a sharp change in sedimentation to the coarser, green, carbonate-free silts and clays of Unit IV (284.0-452.6 mbsf). Unit IV was subdivided into an upper Subunit IVA (284.0-358.4 mbsf) composed of bioturbated clayey siltstone with minor chert and glauconitic sand turbidites, and Subunit IVB (358.4-452.6 mbsf) made up of highly burrowed sandy siltstone that grades to green silty sandstone at the base. The well-preserved siliceous microfossils and almost total lack of calcareous microfossils indicates accumulation below the CCD. The burrowed green sediment points to accumulation in dysoxic bottom waters. Two major biostratigraphic successions were recovered at Site 1128, dated by calcareous nannofossils and planktonic foraminifers as late Miocene-Pleistocene (0-55 mbsf) and early Eocene-early Oligocene (72-427 mbsf). These intervals are separated by the debrite interval (55-72 mbsf) containing mixed upper Paleogene and Miocene nannofossils and planktonic foraminifers. Calcareous nannofossil data indicate four possible hiatuses within the Neogene succession, and a major unconformity spanning the Miocene/Oligocene boundary at ~72 mbsf. Both nannofossil and planktonic foraminifer data show that this unconformity spans a gap of at least 5 m.y., as the entire upper Oligocene is missing. Below 72 mbsf, nannofossils and planktonic foraminifers show increasing signs of dissolution and are absent at some levels, suggesting deposition near the lysocline and CCD. Sedimentation rates were 10-12 m/m.y. through the Neogene, 50-60 m/m.y. in most of the early Oligocene, and 4 m/m.y. in the late Eocene. Although characterized by poor core recovery and barren intervals, datum levels from the remainder of Eocene sediments suggest a sedimentation rate of 40-45 m/m.y. Five benthic foraminiferal assemblages are distinguished: (1) a diversified Pleistocene and Pliocene assemblage indicating abyssal paleodepths above the CCD; (2) a mixed assemblage of displaced faunas in the debrites; (3) an impoverished early Oligocene-early-late Eocene assemblage indicating lower bathyal to abyssal paleodepths close to the lysocline; (4) an impoverished early-late to late-middle Eocene calcareous assemblage indicating lower bathyal to abyssal paleodepths close to the lysocline; and (5) an impoverished late-middle to late-early Eocene agglutinated assemblage indicating deposition below the CCD. Long-core measurements established a magnetostratigraphy for the uppermost 40 mbsf, spanning the Brunhes Chron, Matuyama Chron, and part of the Gauss Chron. Below this, the interval characterized by debris flows disrupts the record and it is not possible to recognize a magnetostratigraphy until a depth of ~60 mbsf, where the record was correlated with the early Oligocene magnetic polarity time scale. A nonmagnetic APC coring assembly was used at this site, and produced significant improvement in the declination record in shallow APC cores. Excellent records were obtained both with and without the nonmagnetic assembly toward the bottom of the intervals cored by APC. Construction of a composite depth section from Holes 1128B and 1128C indicates that a complete Pleistocene through upper Miocene sedimentary record was recovered at Site 1128. A break in the record occurs at ~68 mcd, corresponding to a 15-m-thick debris flow separating upper Miocene from lower Oligocene sediments. The numerous turbidites in the section aided correlation. The primary lithologic parameters used to create the composite section were magnetic susceptibility, gamma-ray attenuation (GRA) wet bulk density, natural gamma emissions data acquired by the multisensor track on whole cores, and color reflectance data (400 nm) measured on split cores. Only low concentrations of methane were detected (maximum of 6.2 ppm), with most samples having less than 3 ppm. Calcium carbonate content has a bimodal pattern with generally high values (75-90 wt%) present in the upper 50 mbsf, followed by a decrease to a low of 2.1 wt% at 138 mbsf. Between 138 and 240 mbsf, carbonate content increases to a second mode with a maximum value of 68 wt%, and then decreases downhole with very low values (0-1 wt%) below 353 mbsf. Organic carbon concentrations are generally less than 0.16 wt% down to the base of Hole 1128B. Because organic carbon values are 0 wt% from 200 to 276 mbsf, and headspace methane concentrations in this depth range are barely above background, no samples in Hole 1128D were analyzed for organic carbon. Sulfur is present in only five samples in Hole 1128B, with values ranging from 0.05 to 0.21 wt%. Nitrogen is not detectable in any sample. Sulfur and nitrogen were not analyzed in samples from Hole 1128D. Site 1128 does not appear to be influenced by the high-salinity pore fluids observed at Sites 1126 and 1127. With the exception of the lower part of the cored interval, salinities are close to normal seawater values throughout. As a consequence of slow rates of deposition and low concentrations of organic material, pore fluids are not significantly depleted in sulfate in the upper sediments, and rates of carbonate recrystallization are relatively low. Two significant changes in pore-water chemistry occur at Site 1128, the first at 20-40 mbsf, and the second between 236.8 and 253.3 mbsf. The change in pore-water chemistry at the shallow depth is manifest as an abrupt decrease in silica concentration from values of ~570 to 350 mM, corresponding to a slump unit. Seismic imagery indicates that this unit outcrops at the seafloor, so it is possible that bottom water infiltrates the formation to cause this effect. The second major change in pore-water chemistry, accompanied by a decrease in salinity, is evident in most of the major and minor cations and occurs between the transition from lithostratigraphic Unit II to Unit IV. Concentrations of magnesium, potassium, sulfate, and sodium show a marked decrease, whereas lithium, alkalinity, and calcium increase. Although the change in salinity is accompanied by a decrease in chlorinity, the chloride decrease is not of the magnitude expected from the salinity decrease alone, indicating that a portion of the salinity decrease is a result of the removal of cations and anions through precipitation and adsorption. Downhole logs indicate the presence of numerous relatively impermeable layers in the interval between lithostratigraphic Units II and IV, which would effectively limit vertical diffusion between these two units and allow them to geochemically evolve relatively independently of each other. The sediments in lithostratigraphic Unit IV contain very low concentrations of carbonate minerals, and reactions leading to the enrichment and depletions in the pore-water constituents principally involve clay minerals. Sediment physical properties data at Site 1128 closely reflect lithologic variations observed in the recovered sediments and provide essential data for core-log correlation. Physical properties data were subdivided into five units on the basis of trends in the measured parameters. Unit 1 (0-70 mbsf) is characterized by high variability in all datasets, corresponding to the lithologic sequence of turbidites and debris flows interbedded with nannofossil ooze. The base of this unit is marked by abrupt shifts in all parameters measured. Unit 2 (70-139 mbsf) is characterized by low variability in all datasets, punctuated by a number of distinct data offsets (1-5 m thick) corresponding to sharply bounded intervals of redeposited nannofossil ooze. Unit 3 (139-231 mbsf) is an interval characterized by relatively low and nearly constant values for all parameters, corresponding to a sequence of monotonous clays. An increase in NGR, magnetic susceptibility (MS), GRA, discrete P-wave velocity, and a decrease in porosity is observed at the upper boundary of Unit 4 (231-363 mbsf), after which all parameters display increased variability reflecting alternations of indurated and nonindurated sediments. The upper boundary of Unit 5 (363-452 mbsf) is marked by a negative shift in GRA, MS, and NGR, corresponding to the transition into lithostratigraphic Subunit IVB. Other than porosity, which decreases through the unit, the other parameters measured show constant downhole trends for the rest of the recovered interval. Site 1128 was successfully logged with the triple combo and Sonic/FMS tools. Because of time constraints, the GHMT and WST tools were not run. Downhole logging data were divided into four units, with trends closely correlating with lithologic and sediment physical properties data. Unit 1 (0-242 mbsf) is characterized by uniform values, punctuated by sharp decreases in gamma-ray values and increases in density and resistivity apparently corresponding to intervals of redeposited nannofossil ooze. Unit 2 (242-295 mbsf) is characterized by high variability in all datasets measured, corresponding to an interval of high variability in sediment physical properties data and an interval of variable lithification in cores. The lower part of this unit corresponds to lithostratigraphic Unit III and consists of nannofossil ooze interbedded with variably indurated sandstone turbidites. These interbedded sediments are reflected in logging data as alternations of low gamma-ray, high- density, and resistive intervals corresponding to calcite-rich layers, and high gamma- ray, low-density, and conductive intervals corresponding to sandstones. Logging Unit 3 (295-362 mbsf) has low variability and nearly constant values on all logs except the gamma ray, which increases downcore. Increased concentrations of thorium and potassium correspond to an increased concentration of terrigenous sediment. Unit 4 (363-414 mbsf) has minimal variability in most parameters, with the exception of cyclic variations in gamma-ray values. Downhole measurements from Unit 5 indicate the presence of clays and quartz through the unit as shown by the recovered sediment. Site 1128 provided the first opportunity to sample and establish a seismic stratigraphy for this thick (containing over 10 km of sediment) and laterally extensive continental rise basin. Seismic imagery shows that the thin (72 m), relatively condensed Neogene section (largely corresponding to lithostratigraphic Unit I) was deposited in a small perched sub-basin lying within a thick Paleogene and Mesozoic succession and that the Neogene sequence is thin or absent over much of the basin. Exposed Mesozoic sediments on the middle and lower slope are the presumed source of lithified material commonly present within resedimented intervals. Although not intersected because of operational time constraints, a prominent angular unconformity ~150 m below total depth at Site 1128 almost certainly marks the base of the Cenozoic. Apart from hiatuses between the lower and middle Eocene and Oligocene and Miocene, Site 1128 results indicate that the upper part of this basin contains a thick, almost continuous biosiliceous record of Southern Ocean development through the Paleogene. Site 1129 Site 1129 was the third and proximal site of a planned three-site transect through a spectacular set of late Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1129, located just seaward of the shelf edge in 202.4 m of water, intersects the most expanded record of the oldest part of the clinoform sequence. The principal objective of this transect is to collect detailed, high-resolution profiles through a late Neogene shelf-edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment, to determine the response of this type of depositional system to Pliocene-Pleistocene sea-level fluctuations. The succession recovered at Site 1129 is 604.2 m thick (Table 2) and was subdivided into three lithostratigraphic units. Unit I (0-149.8 mbsf) consists mainly of unlithified bryozoan floatstone to rudstone and bioclastic packstone to grainstone, with abundant bryozoan fragments. The floatstone and rudstone are pale yellow to light gray and have a poorly sorted, very fine to medium sand-sized bioclastic packstone matrix. The floatstone and rudstone contain abundant granule- to pebble-sized bryozoan fragments exhibiting highly diverse growth forms. The bioclastic packstone to grainstone is pale yellow, light gray, and light olive gray, and consists of very fine to fine sand-sized bioclasts with some coarse sand- to granule-sized bryozoan fragments. The unit is subdivided into five subunits, each forming a package grading upward from bioclastic packstone at the base to bryozoan floatstone and rudstone at the top, with each subunit representing an individual mound-building episode. Unit II (149.8-556.7 mbsf) consists of thick, light gray, light olive gray, and gray bioturbated bioclastic packstone and minor grainstone and wackestone with four nannofossil chalk intervals. Lithification increases from unlithified at the top of Unit II, to partially lithified with well-lithified chalk intervals at the base. The upper part of Unit II is dominated by very fine to fine sand-sized, generally well-sorted, massive bioclastic packstone with subordinate grainstone and wackestone. The lower part is characterized by muddy bioclastic mudstone, wackestone, and packstone with abundant well-defined burrows. Unit II therefore exhibits an overall coarsening-upward trend. Unit III (556.7-604.2 mbsf), with very poor recovery, consists of dolomitized fine sand-sized bioclastic grainstone and chert fragments. It is likely that the chert fragments represent thin beds and lenses of preferentially silicified wackestone/ooze. The boundary between Units II and III is very sharp, and represents a major hiatus. Site 1129 contains two biostratigraphic units: (1) an expanded Quaternary section, more than 554 m thick, that is underlain by a thin and conformable Pliocene section, and (2) a middle-lower Miocene section. These units are separated at 556 mbsf by an unconformity representing ~12 m.y. The unconformity is marked by a bryozoan turbidite overlying indurated sediments and chert layers. Calcareous nannofossils are generally abundant and moderately well preserved in the upper part of the section, but below 371 mbsf the preservation is poor. Preservation and abundance of planktonic foraminifers degrade more rapidly downhole than the nannofossil assemblages. Below ~68 mbsf, most characteristic features of foraminifers are obscured by carbonate cement and recrystallization. Benthic foraminifers are generally abundant and well preserved in the upper part of Hole 1129C. At a depth of ~140 mbsf, preservation and abundance deteriorate markedly. Three main assemblages are recognized at Site 1129: (1) a distinctive, well-preserved Pleistocene assemblage found in bryozoan-rich accumulations (down to ~140 mbsf); (2) a Pleistocene assemblage (140-565 mbsf), which includes a variable redeposited neritic component; and (3) a sparse Miocene assemblage. The two Pleistocene assemblages indicate upper bathyal paleodepths, whereas the Miocene assemblage indicates an upper to middle bathyal paleodepth. Long-core measurements of Hole 1129C sediments revealed an extensive interval of normal magnetization to a depth of ~340 mbsf. Sediments record reverse polarity magnetizations below that depth, with the boundary best defined by measurements on discrete samples. This reversal is interpreted as the Brunhes/Matuyama boundary. In Hole 1129D, a long interval of predominantly reverse-polarity magnetizations to a depth of ~540 mbsf is interpreted as the upper part of the Matuyama Chron (C1r). The Jaramillo Subchron (C1r1n) is recorded in both holes at depths of ~400-440 mbsf. Normal polarities are recorded again in Hole 1129D at depths of 540-550 mbsf, possibly representing the Olduvai Chron (C2n). This would indicate a variable sedimentation rate, with late Pleistocene sedimentation nearly triple the rate of the early Pleistocene. Rock magnetic characteristics, such as near saturation with inductions of 400 mT and median destructive fields of the IRM of 20-40 mT, suggest that magnetite and possibly magnetic sulfides are the principal remanence carriers. ARM/IRM indicate a high relative abundance of single-domain grains, possibly biogenic magnetite. High concentrations of methane and hydrogen sulfide through much of the section are a major feature at Site 1129. Methane and H2S concentrations at this site fall between the levels found at Sites 1127 and Site 1131. Calcium carbonate content is uniformly high, primarily in the range of 86-94 wt%. Organic carbon concentrations generally vary from 0.4 to 0.7 wt%. Site 1129, like many other sites drilled during Leg 182, is influenced by the presence of high-salinity pore fluids within and below the cored interval. Within the cored interval, the presence of pore waters with sodium/chloride ratios significantly higher than seawater indicates the influence of fluids that have been involved in the precipitation and dissolution of halite. Site 1129 was characterized by high rates of sulfate reduction of organic material and consequent production of alkalinity. The absence of significant iron concentrations resulted in a pH less than 6. Although high concentrations of hydrogen sulfide and high alkalinity values were measured at relatively shallow depths, significant sulfate reduction did not occur until below 100 mbsf. This suggests that hydrogen sulfide is diffusing from the underlying sediments into the overlying oxic sediments, where it is oxidized to sulfate. Rates of carbonate alteration, reflected in the strontium concentration (>2 mM), were the highest yet observed during Leg 182. Dolomite is ubiquitous below a depth of 70 mbsf and reached values as high as 24 wt%. Physical properties measurements at Site 1129 correlate well with lithologic changes observed in the sedimentary section and provide an important data set for core-log correlation. In general, Site 1129 is characterized by significant variations in NGR and GRA bulk density. In general, variations are less marked in P-wave velocity, porosity, and other physical properties data. A well-defined cyclicity is seen in the NGR record and can be correlated with the downhole gamma-ray logs and NGR records from Site 1127 and 1131. Physical properties data were divided into three major units. Unit 1 (0-40 mbsf) is characterized by a rapid increase in NGR, as observed at most other Leg 182 sites. The base of this unit coincides with the top of the three bryozoan mound sequences, which form the lower part of lithostratigraphic Unit I. P-wave velocity and bulk density also increase with depth toward the base of this unit. Unit 2 (40-258 mbsf) is characterized by a uniformly high NGR with some cyclic variations and by a slight increase in GRA bulk density and P-wave velocity. A significant offset to higher values of P-wave velocity and bulk density can be seen at 90 mbsf in Unit 2. Unit 3 (258-558 mbsf) is characterized by increasing P-wave velocity (1650-2450 m/s) and bulk density and decreasing porosity, which reflects the increasing induration of the succession. Below 558 mbsf, core recovery was too low for physical properties characterization of the deeper part of the sedimentary section. Hole 1129D was successfully logged with three logging-tool strings. The triple combo produced very good results, except for the interval between 360 and 460 mbsf, where the porosity log was affected by excessive borehole rugosity. The log patterns are very similar to the logs from Hole 1131A; the uranium gamma-ray log showed distinct cyclicity in the lower part of the Pleistocene sequence, with 18-20 individual cycles, each measuring 10-20 m in thickness. Chalk layers and firmgrounds in the Pleistocene succession, as indicated by the conventional logs, are clearly imaged by FMS data. The FMS data also provide a detailed picture of the thickness distribution of thinly bedded cherts (~20 cm) and carbonates (1-2 m) in the middle upper Miocene succession, where recovery was very poor. The high-resolution site survey seismic data at Site 1129 clearly images the bryozoan mound complex within lithostratigraphic Unit I and shows that this or similar mound complexes have existed at and immediately below the shelf edge throughout the Pleistocene. A combination of the results from Sites 1129 and 1131, now correlated with the recognition of a distinctive motif on seismic data, confirms that development of extensive bryozoan mound complexes has been one of the characteristic features of Pleistocene cool-water carbonate sedimentation across a large area of the western Great Australian Bight. Site 1130 Site 1130 was located to intersect and characterize Neogene cool-water carbonate shelf-edge sequences and the nearshore portion of a Paleocene?-middle Eocene progradational siliciclastic wedge (seismic Sequences 2, 4, and 6A). The principal objectives were to (1) recover a detailed record of siliciclastic progradation and aggradation to evaluate the complex interaction among Paleogene sea-level fluctuations, accommodation space, and subsidence, (2) determine the facies characteristics, sea-level response, and paleoceanographic history of a Neogene cool-water carbonate succession in a shelf-edge setting, and (3) evaluate diagenetic history and processes within the Neogene facies in a shelf-edge setting. The sediments recovered at Site 1130 were divided into four major lithostratigraphic units. Unit I (0-261.43 mbsf) is a light gray to pale olive, strongly bioturbated, unlithified to partially lithified bioclastic packstone. This succession is punctuated by unlithified bioclastic wackestone layers and occasional nannofossil foraminiferal ooze to chalk intervals. The upper part of this unit is characterized by a repetitive uphole textural change from matrix-supported to grain-supported sediment. Lighter intervals in the otherwise monotonous packstones are fine grained and foraminifer rich, whereas the generally coarser and darker intervals contain more bioclasts. The lower part of Unit I is typified by gradual color changes ranging from light gray to olive gray, with a few abrupt transitions. Soft sediment deformation structures interpreted as slumps are present at the base of Unit I. Unit II (261.43-328.86 mbsf) is dominated by strongly bioturbated, white to light gray nannofossil foraminiferal chalk with a wackestone to packstone texture. Disseminated black grains (pyrite, glauconite, and other unidentifiable grains) are scattered throughout the unit. Unit III (328.86-369.5 mbsf) consists of chert layers (silicified nannofossil planktonic foraminiferal ooze) interbedded with intervals of white nannofossil planktonic foraminiferal ooze. The light to dark gray, partially translucent chert fragments contain burrows filled with white, fine-grained, lithified planktonic foraminiferal packstone to grainstone. Unit IV (369.5-386.51 mbsf) is dominantly a calcareous sandstone, but with compositional and textural variability encompassing red bioclastic glauconitic wackestone, sandy bryozoan grainstone, pink, coarse- grained bivalve grainstone, and red, very coarse-grained calcareous sandstone. Calcareous nannofossils and planktonic foraminifers indicate that three biostratigraphic successions were recovered at Site 1130: (1) Pleistocene-upper Miocene (0-327 mbsf), (2) upper-middle Oligocene (327-~355 mbsf), and (3) a sandy limestone of unknown age from the bottom of Holes 1130A and 1130C. Preliminary results indicate that part of the Pliocene section is either missing or highly condensed and that the major disconformity between upper Miocene and Oligocene sediments represents a hiatus of at least 15 m.y. The sedimentation rate for the middle-upper Oligocene was 10-30 m/m.y., although this should be viewed with caution because of poor core recovery. The rate fluctuated between 15 and 30 m/m.y. during the Pliocene-Miocene, and reached as high as 240-260 m/m.y. during most of the Pleistocene. The three benthic foraminiferal assemblages recognized correspond respectively to the Oligocene, Pliocene-Miocene, and Pleistocene and indicate a shallowing-upward trend during these time periods. The Oligocene and Pliocene-Miocene assemblages are typically cosmopolitan, middle bathyal assemblages, whereas the Pleistocene contains a mixed assemblage representing upper bathyal paleodepths and containing many well-sorted specimens from shelf environments. Long-core measurements revealed a deep episode of normal magnetization and then a sharp reversal to normal polarity at 199.9 mbsf, interpreted as the Brunhes/Matuyama boundary. Intensities of magnetization varied from 0.01 to 1 mA/M, with an overall decreasing trend downhole. Within this general trend are fluctuations with dominant wavelengths of a few tens of meters. The ratio of ARM/IRM, a measure of the relative importance of single-domain to multidomain behavior, decreases downcore, suggesting that the role of biogenic magnetite diminishes. Coupled with the decrease in magnetization, this strongly suggests that fine-grained magnetite of biogenic origin is preferentially dissolved. An experimental nonmagnetic cutting shoe was used for alternate cores on Cores 182-1130A-3H to 7H, and an entire nonmagnetic core-barrel assembly was used on Cores 182-1130B-3H to 7H. Both the nonmagnetic shoe and core-barrel assembly produced reductions in radial component contamination, but the effects were not as dramatic as at Site 1128. Construction of the composite section from Holes 1130A and 1130B indicates that a continuous sedimentary record was not recovered at Site 1130. Low recovery in Core 182-1130A-3H and no recovery in Core 182-1130B-3H produced a gap at 22 24 mbsf. The record below this is apparently continuous to ~191 mcd (all Pleistocene), at which point core overlap becomes minimal to nonexistent, disrupting continuity of the spliced section. The primary lithologic parameters used for correlation at Site 1130 were natural gamma emissions and a ratio of the 700:400 nm color reflectance data. Only low concentrations of methane were detected, with most samples having less than 7 ppm (maximum = 11.3 ppm). Calcium carbonate content ranges from 80.9 to 93.2 wt% in lithostratigraphic Units I and II, with most samples varying between 85 and 90 wt%. No carbonate analyses were conducted in Units III and IV (328.9-386.51 mbsf) because of low core recovery. Site 1130 is influenced by high-salinity pore fluids, as was the case at Sites 1126 and 1127. The maximum rate of salinity increase, 5.7/m, is the highest observed during Leg 182. The steep gradient down to ~32 mbsf, and then the constant salinity concentration (83) below, suggest nonsteady-state conditions. In contrast to Site 1127, the sulfate reduction zone is incomplete and confined to the upper part of the profile, and the degree of sulfate reduction is ~40% less than at Site 1127. These differences are probably caused by a lower initial organic carbon content at Site 1130. As a consequence of the decreased sulfate reduction activity, interstitial waters are saturated with respect to strontium sulfate, limiting pore-water strontium concentrations. Sediment physical properties data closely reflect Oligocene-Holocene lithologic variations observed in recovered sediments and downhole logging data. Three physical properties units were recognized primarily on the basis of trends in NGR. The homogenous bioclastic packstones of Unit 1 (0-43 mbsf) are characterized by low variability in all measured parameters. The large increase in NGR from 5 to 35 cps at the base of Unit 1 does not correlate to any lithologic change, but is roughly coincident with an increase in P-wave velocity variability, suggesting that it results from diagenesis. Unit 2 (43-254 mbsf) is dominated by cyclic variations in NGR that appear to be related to Milankovitch cyclicity on a 100-k.y. frequency from 43 to 175 mbsf and on a higher 41-k.y. frequency for the remainder of the unit. This change in frequency occurs near the Brunhes/Matuyama boundary and is clearly seen in downhole logging data from this site. From 199 to 254 mbsf in Unit 2, increased variability in P-wave velocity corresponds to a series of firmgrounds observed in the recovered sedimentary section. The upper boundary of Unit 3 (254-335 mbsf) correlates well with a distinct change in lithology (lithostratigraphic Unit II) from packstone/wackestone to nannofossil oozes and chalks. NGR and P-wave velocity show low variability within Unit 3, whereas bulk density shows a general increasing trend. Three large-scale units were identified in downhole logging data from Hole 1130C, based on shifts in conventional and FMS logs, with boundaries at 258 and 329 mbsf. The interval above 260 mbsf is characterized by a near-constant background level of gamma radiation of 20 API, with individual spikes reaching 40-45 API. The boundary at 260 mbsf is defined at a sharp downhole decrease in the uranium gamma-ray log, and the boundary at 329 mbsf corresponds to the change from carbonate sediments above to siliciclastic deposits below. Integration of the various datasets with the regional seismic stratigraphic interpretation provides a sequential record consisting of an Eocene? progradational wedge deposited at shelf water depths, overlain, after an indefinite hiatus, by deep- water late Oligocene oozes that have since been irregularly silicified. The record then contains another hiatus of ~20 m.y., before deposition of Miocene-Pliocene oozes that pass up into a packstone unit, as a continuation of a shallowing-upward trend. A further short hiatus was then followed by rapid deposition of a thick sequence of Pleistocene wackestones and packstones at upper slope/shelf-edge depths. Site 1131 Site 1131 was the second and intermediate site of a planned three-site transect through a spectacular set of late Neogene clinoforms immediately seaward of the present-day shelf edge. Site 1131, located on the upper slope in 333.6 m of water, intersected the best record of the middle part of the clinoform sequence. The principal objective of this transect was to collect detailed, high-resolution profiles through a late Neogene shelf-edge (high energy) to upper slope (low energy) succession deposited within a cool-water carbonate environment and to determine the response of this type of depositional system to Pliocene-Pleistocene sea-level fluctuations. Three major lithostratigraphic units were identified at Site 1131. Unit I (0-25.0 mbsf) consists dominantly of bioclastic packstone, floatstone, and rudstone. The upper part of Unit I is composed of a massive, homogeneous, light gray to olive gray, unlithified, bioclastic packstone, which includes a significant bryozoan component. The lower part of Unit I is a heterogeneous interval of unlithified bryozoan floatstone and rudstone punctuated by thin (decimeter scale) layers of wackestone, packstone, and grainstone. Unit II (25.0-531.7 mbsf) consists of a very thick (>500 m), homogeneous succession of light gray to olive gray, bioclastic packstone, grainstone, and wackestone. In general, lithification and diversity of the bioclastic component increase downhole, and large miliolid foraminifers appear in the lower part of Unit II. Unit III (531.7-607.4 mbsf) is separated from Unit II by an unconformity representing a major hiatus. Below the unconformity, recovery was incomplete in a succession consisting of dark gray, silicified nannofossil ooze beds or lenses within olive gray, partially to strongly lithified bioclastic grainstone containing blackened grains and glauconite. Two biostratigraphic successions were identified at Site 1131: (1) an expanded Quaternary interval more than 510 m thick, underlain by a thin and conformable Pliocene (?) interval, and (2) a middle and lower Miocene section lacking hiatuses within the resolution of available biostratigraphic data. These successions are divided by a disconformity at 532 mbsf that spans ~10 m.y. An environmental crisis produced an unusual nannofossil assemblage dominated by Braarudosphaera bigelowii near the base of NN19 at ~522 mbsf. A similar event was observed in the same stratigraphic interval at Site 1127. Carbonate microfossils, especially foraminifers, were strongly affected by overgrowths, cementation, and recrystallization below 60-100 mbsf. These effects are consistent with the pore-water geochemistry and the onset of lithification. One main Pleistocene upper bathyal assemblage of benthic foraminifers is recognized above 100 mbsf. This assemblage also contains a large proportion of small neritic tests (63-150 Êm), probably redeposited from the shelf. Poor preservation prevented detailed faunal analysis below 100 mbsf. Magnetic measurements of archive-half cores established a magnetostratigraphy to a depth of 320 mbsf, which includes the Brunhes and uppermost Matuyama Chrons. Below this, drilling disturbance disrupted the record and no further magnetostratigraphic data were obtained. Rock magnetic properties show minimum downhole variability and are consistent with single-domain biogenic magnetite, except for cores at intermediate depths (70-150 mbsf) that display the typical behavior of ultrafine-grained (superparamagnetic) greigite. Magnetic susceptibility is dominated by contributions from the diamagnetic carbonate matrix. Composite section construction from Holes 1131A and 1131B indicates that a continuous record was not recovered. Overlap between cores in adjacent holes was maintained to ~55 mcd, until poor recovery in Core 182-1131C-6H resulted in a short (few centimeters) data gap. Below 70 mbsf, low recovery from extended core barrel (XCB) cores resulted in reduced core overlap and prohibited splicing below 78 mcd. The primary parameters used for correlation were natural gamma-ray emissions, GRA bulk density, and color reflectance. Comparison of data between holes revealed a low degree of similarity, making correlations difficult. The most striking organic geochemical results from Site 1131 were the high concentrations of methane (C1) and hydrogen sulfide in the upper part of the section. In comparison to Site 1127, gas pockets were less abundant, and the concentration of C1 in both gas pockets and headspace samples at Site 1131 was lower. Hydrogen sulfide concentrations, however, were comparable at both sites. Atypically, C1/C2 values first increase and then decrease with increasing depth in Hole 1131A, essentially mirroring the methane profile as C2 varies little throughout the section. Calcium carbonate content is uniformly high (86-94 wt%). Organic carbon is less than 0.4 wt% down to 125 mbsf, with higher values (up to 1.0 wt%) at greater depths. Site 1131 exhibited similar inorganic geochemical features as Site 1127, with the exception of more extreme changes in pore-water geochemistry profiles because of increased oxidation of organic material. For example, alkalinity reached a maximum value of 137 mM, compared to 106 mM at Site 1127. In contrast to Site 1127, although there was significant depletion in the concentration of sulfate, measurable concentrations remained even in the zones of highest alkalinity, suggesting that organic material was the limiting factor in the production of hydrogen sulfide at Site 1131. Excess sulfate in the upper portion of the core suggests that the oxidation of hydrogen sulfide originated lower in the section. In the upper 300 m, there was depletion in the concentration of calcium and magnesium and enrichment in Sr, indicating the recrystallization of aragonite and HMC. This was confirmed by mineralogical analyses, which showed that HMC had disappeared by 50 mbsf. Aragonite gradually decreased with increasing depth, and vanished at the Pliocene/Pleistocene boundary. Ratios of sodium to chloride were in excess of the ratio in seawater throughout the Pleistocene section, indicating that the waters responsible for the high-salinity fluids had participated in the precipitation and dissolution of halite. Physical properties measurements at Site 1131 correlate well with lithologic changes observed in the sedimentary section and provide the basic data for core-log correlation to reconstruct poorly recovered intervals. Correlation of downhole gamma- ray logs with NGR data from the multisensor track (MST) indicates that moderate to poor recovery at Site 1131 may have aliased and concealed in cores the cyclic fluctuations that are clearly visible on downhole logs. Physical properties data indicate that the cored interval is divisible into two units. Unit 1 (0-31 mbsf) is mainly defined by a large increase in NGR toward the base of the unit, corresponding to the lower limit of the bryozoan floatstone/rudstone comprising lithostratigraphic Subunit IA. This NGR peak is also observed on downhole logs, with spectral gamma data indicating that it reflects uranium content and, accordingly, is either the result of increased organic matter content or carbonate diagenesis. P-wave velocity and bulk density also increase toward the base of this unit. Unit 2 (31-532 mbsf) is characterized by gradual increases in porosity, P-wave velocity, and bulk density, primarily reflecting increased compaction, but also showing data excursions corresponding to coarser and more lithified horizons. More indurated layers within the generally homogenous sediments of Unit 2 have increased velocities and bulk densities, and generally lower NGR. Below 532 mbsf, core recovery was too low for physical properties characterization of the deeper part of the sedimentary section. Three successful logging-tool strings were deployed in Hole 1131A. Downhole logging data indicate that the uppermost part of the cored section (0-28 mbsf) correlates with bryozoan-rich horizons described in core. As was noted with the physical properties data, a uranium peak at the base of this unit reflects increased organic content and/or carbonate diagenesis and may indicate a firmground. The remainder of the cored section to 575 mbsf contains porosity-density crossovers that coincide with low PEF values and high resistivity and sonic values. These crossovers are interpreted as probable chert layers. In contrast, low-porosity peaks associated with density, PEF, sonic, and resistivity peaks may represent possible firmgrounds. Integration of coring results with high-resolution site survey seismic data at Site 1131 confirms that the mounded features visible in the uppermost part of the seismic section are in fact bryozoan-dominated mounds. The spectacular clinoform geometry corresponding to the remainder of the cored interval consists of bioclastic packstone, grainstone, and wackestone, with variable lithification as the dominant factor controlling seismic data amplitude and impedance variability. The lithostratigraphic and biostratigraphic boundary toward the base of the section coincides with a major regional unconformity and sequence boundary. Site 1132 Site 1132 was located to intersect and characterize Neogene cool-water carbonate shelf-edge sequences and the nearshore portion of a Paleocene?-middle Eocene progradational siliciclastic wedge (seismic Sequences 2, 3, 4, and 6A). The principal objectives were to (1) recover a detailed record of siliciclastic progradation and aggradation to evaluate the complex interaction between Paleogene sea-level fluctuations, accommodation space, and subsidence; (2) determine the facies characteristics, sea-level response, and paleoceanographic history of a Neogene cool-water carbonate succession in a shelf-edge setting; and (3) evaluate the diagenetic history and processes within the Neogene facies in a shelf-edge setting. The recovered succession was subdivided into six lithostratigraphic units. Unit I (0-113.5 mbsf) consists of bryozoan floatstone and rudstone, alternating with bryozoan packstone and, in the lower part, also bioclastic wackestone with bryozoans. The abundant bryozoan fauna are highly diverse and include a great variety of growth forms. The sediments are unlithified and burrow mottled, and the color is dominantly light gray with thinner pale olive and white intervals. This unit represents a major bryozoan mound complex. Unit II (113.5-158.3 mbsf) consists of uniform bioclastic packstone with a great diversity of bryozoan growth forms. The color is light gray, with minor light olive gray and white intervals. The sediment is burrow mottled and mainly unlithified, but thin, partially lithified beds are present at 130-140 mbsf. Unit III (158.3-250.7 mbsf) consists of unlithified bioclastic packstone and minor wackestone and grainstone, with an interbedded thin package of foraminiferal ooze and chalk. The unit is strongly burrowed and mainly unlithified down to 168 mbsf and partially lithified below that level. The color is dominantly light olive gray with thinner olive, pale olive, and white intervals. Several prominent firmgrounds are the basis for subdivision into five subunits. Unit IV (255.8-437.33 mbsf) was poorly recovered; however, available data suggest that it consists of bioclastic packstone and grainstone with an interval of nannofossil foraminiferal chalk partially replaced by nodular, light to dark gray chert. Unit V (441.5-517.7 mbsf) is also characterized by poor recovery, but recovered material indicates that it consists of bioclastic packstone and grainstone and lacks chert. Glauconite is abundant, and the colors vary between very pale brown and pale yellow. Unit VI (517.7-555.95 mbsf) is topped by a prominent mineralized hardground and consists of lithified bioclastic packstone and wackestone. It differs from overlying units in its colors, prominent firmgrounds and hardgrounds, solution seams, and centimeter-sized bioclasts. The color is pale yellow at the top and passes downward into light gray, pale yellow, red yellow, to pale and dark red at the bottom. The lowest recovered bed contains pebbles of siliciclastic sandstone, rich in lithic fragments. Calcareous nannofossils and planktonic foraminifers indicate that drilling at Site 1132 recovered a thick Pleistocene-Eocene sequence (~550 m thick), overlying a relatively thin, barren section (~45 m). Calcareous nannofossils from the basal Pleistocene registered a nannofossil event, the "Braarudosphaera Event," which previously was recorded at Sites 1127, 1130, and 1131, indicating a dramatic short- lived change in surface-water conditions over a large geographic area. The thick Pleistocene section contains (~230 m) Zones NN21/NN20 and NN19, and the equally thick middle Miocene section (~300 m) contains Zones NN6 and NN5/NN4. These sections are separated by a thin interval (~20 m) with poor core recovery. Hiatuses are likely within this thin interval, where the recovered nannofossils and planktonic foraminifers suggest late Miocene age. Another similarly thin interval (~20 m) with poor core recovery, which is also likely to contain hiatuses, is recorded between the middle Miocene section and the underlying mainly lower Oligocene. An Eocene age is indicated for the section underlying the lower Oligocene, based on thin-section analysis of two samples at ~530 and ~547 mbsf, respectively. A sharp change in sedimentation rates corresponds to the condensed interval between Pleistocene and middle Miocene sections. The Pleistocene section registered an average sedimentation rate of 175 m/m.y., whereas the middle Miocene showed an average rate of 20 m/m.y. Another condensed section between the middle Miocene and Oligocene successions is indicated by the sparse biostratigraphic datums through this interval. Four main benthic foraminifer assemblages are identified. These indicate upper to middle bathyal paleodepth for the Pleistocene-Oligocene section. In the Pleistocene, a striking, well-preserved assemblage characterized by many large (>1 mm) agglutinated forms is found within bryozoan-rich accumulations. This assemblage probably reflects a diverse, highly dynamic ecosystem that became established at the seafloor at various times during the Pleistocene, corresponding to episodes of bryozoan mound growth. Changes in the composition of this assemblage may relate to sea-level or circulation fluctuations. The Brunhes/Matuyama boundary was found at ~180 mbsf, yielding a sedimentation rate of ~230 m/m.y. There were indications of the same intensity fluctuations observed at earlier sites; therefore, there is a possibility of high-resolution stratigraphy within the Brunhes Chron after further shore-based work. The top of the Jaramillo Subchron was found at 230 mbsf, which is consistent with this sedimentation rate. Magnetic anomalies were found associated with hardgrounds with mineralized crusts, and with lithified skeletal limestones. In some cases, this suggests that diagenesis occurred extremely early, within 100,000 yr of sedimentation. As at Sites 1126, 1128, and 1130, only low concentrations of methane were detected at Site 1132. Of the four sites, Site 1132 has the highest methane content, with a maximum value of 54 ppm. Unlike the other low-methane sites, hydrogen sulfide is present at Site 1132 in low concentrations. Calcium carbonate content is between 85 and 95 wt%, with values at the higher end of the range near the surface and declining gradually toward the lower end of the range with depth. Organic carbon values are primarily in the range of 0.3-0.6 wt%. Nitrogen concentrations are all less than 0.1 wt%, and sulfur is present, at low concentrations, in only a few samples in the upper 90 mbsf. Site 1132, similar to the previous sites except 1128, is influenced by the presence of high-salinity fluids. However, unlike the neighboring Site 1130, the rate of salinity increase with depth is uniform and shows no evidence of nonsteady-state conditions. Site 1132 possibly had an initially higher organic carbon content, producing slightly higher sulfate reduction rates and a more extended sulfate reduction zone. In turn, carbonate diagenesis is more active, causing carbonate precipitation in the upper part of the profile, whereas the lower part is characterized by carbonate dissolution. As with Site 1131, Site 1132 displays a sodium/chloride anomaly in the upper part of the profile. Site 1132 is characterized by a constant seawater composition of both conservative and nonconservative interstitial water constituents in the upper 30 mbsf, suggesting active flushing with seawater. With the completion of the slope transect from Site 1130 to 1132, we can draw initial conclusions about the horizontal distribution of brine in this area. It appears that salinity values at Sites 1130 and 1132 stabilize at about the same depth below the sea surface, suggesting a horizontal top of the main brine body ~520 meters below sea level (mbsl). High-quality NGR and gamma-ray attenuation porosity evaluator (GRAPE) bulk density data were obtained from the MST. Variations of NGR and GRAPE bulk density, supplemented by index properties measurements of porosity and thermal conductivity, form the basis fo