95 = 6.2), which is indistinguishable from the paleoequator.
Site 1215 (26°1.77´N, 147°55.99´W) is located north of the Molokai Fracture Zone in 5396-m water depth. It is situated on typical abyssal-hill topography in an area of thin but continuous sediment cover. Based on magnetic lineations, basement age at this site should be in the youngest part of Anomaly An26r, or ~58 Ma. This site was the northernmost of the transect drilled on crust of this age during Leg 199. Double APC/XCB coring at Site 1215 recovered a sedimentary section from red clays at the seafloor to hydrothermal sediments immediately above basalt. The 70-m-thick sediment section consists of pelagic red clay (Unit I; ~0-26 mbsf) overlying 42 m of clayey calcareous ooze with chert (Unit-II; ~26-68 mbsf) and a thin basal unit of hydrothermal sediment (Unit III; ~68-70 mbsf) over basalt. The upper and lower units of the section are unzoned biostratigraphically, but calcareous fauna and flora and magnetostratigraphy indicate that Unit II is complete (to the zone/chron level) from the lower Eocene through upper Paleocene section (NP8 through NP12; C25n-C23n, or ~56.2-52 Ma). Porosity values increase steadily with depth from ~73% near the seafloor to ~91% at the base of the red clay unit (25.8 mbsf) and then decrease steadily to values near 58% at the base of the Unit II carbonates (67.2 mbsf). The one sample analyzed from the lithologic Unit III hydrothermal sediments has a porosity of ~82%. Interstitial pore water profiles from Site 1215 primarily reflect the dissolution of biogenic silica, alteration of underlying basalt, and extremely low levels of labile organic matter available for oxidation.
A light to dark color change occurs in the upper portion of lithologic Unit I (red clay) and has been observed in cores of pelagic clay throughout the north central Pacific Ocean. LAS, elemental solid phase chemistry, and both discrete and GRA bulk density data from Site 1215 indicate a downcore transition from illite to smectite between ~5 and 10 mbsf consistent with a change in the source of wind-blown dust from Asia (illite rich) to America (smectite rich) during late Miocene time.
The interval between ~30 and ~50 mcd at Site 1215 shows a clear succession of cycles in color reflectance and physical properties data on a decimeter scale that appears modulated in amplitude as well as in thickness. This amplitude modulation, when combined with biostratigraphic time control, is consistent with a climatic forcing related to climatic precession (~19,000- to 23,000-yr period). In the CaCO3-bearing sediments, both nannofossil assemblages and planktonic foraminifers are strongly affected by dissolution, but the former provide well-constrained biostratigraphic control. The benthic foraminifers present are characterized by hyaline calcareous tests, are better preserved than the planktonic foraminifers, and are promising for shore-based paleoecological and paleooceanographic studies.
An interval of dark-brown (10YR 2/2) nannofossil clay at ~54.7 mbsf in Hole 1215A (interval 199-1215A-8H-3, 128-148 cm) is interpreted to represent the first P/E boundary section to be recovered from the central tropical Pacific Ocean. Calcareous nannofossil biostratigraphy indicates that the boundary occurs in NP9, and the P/E benthic extinction event is observed between ~54.5 and ~55.5 mbsf.
Site 1216 (21°27.16´N, 139°28.79´W) is located on abyssal hills just south of the Molokai Fracture Zone at a water depth of 5163 m. The crustal age, based on magnetic lineations, is ~57 Ma (magnetic Anomaly An25r). The site was chosen for drilling because it is near the thickest section of lower Eocene sediments along the 56-Ma transect. Based on previous coring and drilling ~1° to the south in latitude, we expected to find a moderately thin red clay section overlying middle Eocene radiolarian oozes and lower Eocene carbonates. Instead, we drilled a 50-m section of red clay overlying thin cherts in sediment and abandoned the site before reaching basement. We recovered only chert in the chert sediment section. Microfossils are absent until ~40 mbsf where small numbers of middle Eocene radiolarians appear. The cherts are early middle Eocene-early Eocene in age. We abandoned the site after drilling to 62 mbsf because of the likelihood of large amounts of chert in the section with little sediment recovery and because we could use the saved time to ensure more complete programs at the remaining sites.
The red clay unit is similar to the red clay section of Site 1215 but expanded (40 m vs. 25 m thick). The upper part of the Site 1216 red clays are illite rich (based upon LAS analyses) grading to smectite rich at the base. The transition begins at ~10 mbsf. Fe-Mn oxyhydroxides are also abundant in the lower part of the red clays, reaching a maximum ~29 mbsf as shown by bulk-sediment analyses and by grain density. A transition from relatively high to low natural gamma ray (NGR) activity occurred at ~25 mbsf. A similar transition in NGR activity was observed at Site 1215.
The sediments at Site 1216 are surprisingly barren of microfossils. Upper middle Eocene radiolarian oozes are absent at the site, and lower middle Eocene radiolarians are not abundant. Calcareous microfossils are absent in the drilled section. Only agglutinated benthic foraminifers were found, but none are age diagnostic. The uppermost radiolarians (from RP13 zone; ~44 Ma) occur at ~40 mbsf. The base of the drilled section (62.2 mbsf) is in radiolarian Zones RP9 and RP10, which straddle the middle/early Eocene boundary (~49 Ma). The first cherts encountered downhole occurred at ~50 mbsf. These upper cherts, thus, appear in an interval of slow sedimentation rate, at most 4-5 m/m.y., presumably at the top of more rapidly deposited lower Eocene sediments with larger amounts of biogenic components. We estimated from the seismic reflection profile that ~60 m of sediments remained to be drilled in the cherty section until basement was reached.
It was possible to identify magnetic polarity chrons in the red clay section but none in sections with microfossils because of coring disturbance. Based on the microfossil dates, the oldest chron detected is probably C20n. Magnetic intensity of the red clays is strong, and drilling-induced magnetic overprints are mostly removable by standard procedures.
The red clay section at Site 1216 has several similarities to the red clay section cored at Site 1215, although it is 60% thicker. Both red clay units have a transition from illite to smectite with depth. Both show a significant decrease in NGR activity downcore. The lower parts of each red clay unit are enriched in Fe-Mn oxyhydroxides. When MST records are compared, smaller events appear to correlate between these two sites. Provided that some age control can be developed, it may prove possible to develop a much more detailed red clay stratigraphy for the North Pacific than is now available.
One of the major surprises found from drilling Site 1216 is the remarkable lack of late or middle Eocene radiolarian oozes. These are biogenic sediments that have no modern analog but are prominent sedimentary features from piston cores and drill sites only 1° to the south. DSDP Site 40 recovered 140 m of upper-middle Eocene radiolarian ooze beneath ~10 m of red clay. DSDP Site 41 with a thinner sediment column (34 m of sediment above basalt) contains 16 m of radiolarian ooze below 18 m of red clay. Piston core EW9709-3PC, taken on the site survey for the potential Leg 199 drill site PAT-13 (19°46´N, 138°55´W) also cored 5 m of middle Eocene radiolarian ooze beneath 10 m of red clay. On the basis of this apparent sharp zonation in tropical biotic communities, a major oceanographic boundary must have existed between the paleoposition of Site 1216 and Sites 40 and 41.
Site 1217 (16°52.01´N, 138°06.00´W) is situated ~1° north of the Clarion Fracture Zone on abyssal hill topography at a water depth of 5342 m. The site was chosen for drilling because it is thought to have been located just outside of the equatorial region at 56 Ma (~5°N, 106°W, based upon a fixed hotspot model; Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles). At 40 Ma, the site was located at ~8°N, 111°W. Thus, Site 1217 should help define the paleoceanography of the northern tropical Pacific and, in particular, help to locate the ancient North Equatorial Countercurrent (NECC) region. Based on site survey seismic data and piston coring together with results from the nearest drill site (DSDP Site 162, situated on 48-Ma crust ~300 km south and west), we expected the sedimentary sequence at Site 1217 to comprise a relatively thick (25-35 m thick) section of red clays, overlying a radiolarian ooze. We also expected a basal carbonate section with possible chert near basement (estimated total depth of ~125-150 mbsf) deposited when the site was near the ridge crest in the late Paleocene and early Eocene.
The sedimentary section overlying basalt at Site 1217 is ~138 m thick and records a lower Eocene nannofossil chalk overlain by a poorly recovered lower-middle Eocene chert-clay sequence. Middle Eocene-Holocene deposition is represented by radiolarian ooze followed by red clays at the surface. The recovered sediments from all three holes at Site 1217 were affected by coring disturbance, downhole debris, and flow-in associated with chert fragments blocking the core liner. One stratigraphic interval in the APC-cored section was highly disturbed or not recovered in all three holes (~37-49 mbsf), which prevented the recovery of a complete continuous sedimentary section. Nevertheless, it was possible to generate a spliced, but discontinuous, record in the upper 90 m of the section.
The uppermost red clays at Site 1217 (Unit I) are ~39 m thick. The clays show an uphole mineralogical transition from smectite rich to illite rich at~7 mbsf, which indicates a change in wind-blown dust provenance from American to Asian sources associated with the movement northward of the Pacific plate. The red clay unit also contains a thin (~2.5 m thick; ~30 mbsf) subunit of nannofossil ooze interbedded with nannofossil clay. Below the red clays are a radiolarian ooze with clay grading to clayey radiolarian ooze (Unit II; ~39-90 mbsf). The radiolarian ooze is of middle Eocene age (~38-43 Ma) and contains a rich and well-preserved middle Eocene radiolarian fauna. Below 90 mbsf, we encountered a unit of chert and interbedded clay (90-128 mbsf) before recovering a thin, ~1.13-m-thick, section of early Eocene chalk (Unit III; 128-129 mbsf). The chalk is partially to extensively dolomitized (washed core catcher samples yield abundant near-perfectly euhedral rhombs ~100 mm in size) but contains nannofossils and planktonic and benthic foraminifers. Basement basalt was encountered at 138 mbsf.
Wet bulk density values at Site 1217 are high between the seafloor and 22 mbsf (mean values = 1.37 g/cm3) and decrease sharply to a minimum of 1.18 g/cm3 at 25.58 mbsf—a value that is very similar to the density of the radiolarian oozes at the site. In contrast, the wet bulk densities of the Oligocene nannofossil ooze subunit and lower Paleocene nannofossil chalk are distinctly higher (~1.28 and 1.79 g/cm3, respectively).
The magnetic intensity of the sediments is relatively strong, and drilling-induced magnetization was mostly removed with mild alternating-field (AF) demagnetization. Site 1217 sediments provided a good record of geomagnetic reversals that could be interpreted as chrons. Characteristic remanent magnetization (ChRM) inclinations are usually shallow, as expected in these latitudes. A record from Chron C20 to Chron C12 was established from the middle Eocene to the early Oligocene, but the reversal stratigraphy in the upper 15 m (late Oligocene-Holocene) could not be established because of the low sedimentation rate of the upper sediments and the lack of either core orientation or an independent age model.
High levels of sulfate and concomitant low levels of ammonium in interstitial pore waters at Site 1217 indicate a relatively oxic system consistent with very low levels of labile organic matter, the presence of metalliferous oxides, and the strong and stable magnetic signature in the host sediments. Relatively high pore water silica concentrations are consistent with dissolution of biogenic silica in the sediments. The solid-phase chemical content reflects the microfossil content and the low level of reductive diagenesis. The whole section at Site 1217 shows relatively high levels of Mn and Fe in the solid phase. Within the upper red clays, solid phase Si levels generally increase southward in the Site 1215, 1216, and 1217 transect, presumably indicating higher export of biogenic debris to the ocean floor closer to the paleoequator.
The average LSRs in the red clays (shallower than 23 mbsf) are very low (~0.8 m/m.y.). Sedimentation rates in the underlying fossiliferous and cherty lower sections are substantially higher but are, nevertheless, modest (~5 m/m.y.).
Assuming that a distinct normal polarity chron seen in paleomagnetic data at 23.27 mbsf in Hole 1217A represents Chron C12n, the succeeding downhole normal polarity interval is interpreted to represent Chron C13n, which lies at the base of the Oligocene. This interpretation is consistent with the underlying spacing and length of several normal and reversed intervals and places the thin subunit of nannofossil-rich carbonate ooze (all from nannofossil Zone NP22) in the lowermost Oligocene. This brief interval of carbonate sediment preservation may represent the dramatic deepening of the CCD recorded elsewhere in the deep-sea tropical Pacific Ocean (e.g., DSDP Sites 42, 70, 161, and 162) associated with the Eocene-Oligocene transition, but this possibility can only be validated by shore-based studies.
At Site 1217, we collected the first near-continuously drilled sequence of Eocene radiolarian oozes by deep-sea drilling. In the presence of a well-defined magnetostratigraphy, this section will help to define and calibrate radiolarian stratigraphic zonation. Radiolarian oozes have no modern analog but are prominent sedimentary features of the middle Eocene low-latitude Pacific Ocean, having been recovered from piston cores and drill sites up to 4° to the north (e.g., DSDP Sites 40 and 41) and 10° to the south (e.g., DSDP Sites 70 and 162). In contrast, middle Eocene radiolarian oozes are absent at Site 1216. Thus, Sites 1216 and 1217, along with DSDP Sites 40 and 41, appear to define the northern extent of this type of biogenic sedimentation.
By coring to basement at Site 1217, we recovered sediments needed to address a number of Leg 199 objectives, including an improvement in our understanding of the following: (1) the location of the Paleocene/Eocene paleoequator, (2) the biotic composition and rate of accumulation of sediments in the tropical Eocene Pacific Ocean, and (3) the behavior of the silica budget and CCD during the early Eocene. Broadly speaking, the sequence drilled at Site 1217 conforms to the classical sedimentary succession predicted for a deep-sea drill site situated on relatively old oceanic crust in the Central Pacific (red clays overlying siliceous and, in turn, carbonate biogenic sediments). However, the lowermost sediments drilled (lower-middle Eocene chert and chalk) surprised us in two ways. First, these sediments show average LSRs are relatively slow (<5 m/m.y.), consistent with results from Site 1216. Second, the basal lower Eocene chalks that overlie basement are, like their Site 1215 counterparts, dolomitized—an intriguing discovery given their proximity to what is generally considered to be a kinetically more favorable geochemical sink for Mg (alteration minerals in the upper oceanic crust).
Site 1218 (8°53.38´N, 135°22.00´W) is the only Leg 199 drill site from the 40-Ma transect and is situated at a water depth of 4826 m. It was chosen for drilling in order to investigate paleoceanographic processes in the equatorial Paleogene Pacific Ocean during the inferred transition of Earth's climate from the early Paleogene greenhouse into the late Paleogene icehouse state. Site 1218 is situated on a basement swell ~3°N of the Clipperton Fracture Zone in the central tropical Pacific at a water depth of 4826 m. Pacific plate motion carried Site 1218 across the equator at ~40 Ma based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles). Based upon the same model, the site remained within 2° of the equator from the time crust was formed (42 Ma) until 27 Ma. The sediments recovered from Site 1218 should therefore record near-equatorial oceanographic conditions from the middle Eocene until the early Oligocene. The precise age of basement at the site was poorly constrained prior to Leg 199 because little magnetic anomaly data are available between the Clipperton and Clarion Fracture Zones (Cande et al., 1989).
At Site 1218, we recovered a complete sediment section to within 15 m of basaltic basement. A continuous spliced section (from 0 to 263 mbsf [~41-42 Ma; nannofossil biostratigraphic Subzone CP14a]) was developed using the three drilled holes. The sediments immediately overlying basalt are from near the CP14a/CP13 boundary (42 Ma), which indicates that basement at Site 1218 is slightly older than originally expected. A full suite of downhole logs were obtained to the base of the Hole 1218A, and the data are of excellent quality.
The sediment column at Site 1218 is made up of four sedimentary units. At the top of the sedimentary column is 52 m of yellowish brown radiolarian clay with occasional barren intervals and intervals with nannofossils. The age of this unit is Pleistocene-middle Miocene. Below this unit are nannofossil oozes and chalks of early Miocene-Oligocene age from 52 to 217 mbsf. The basal boundary is abrupt. The upper Eocene and upper middle Eocene sediments (217-250 mbsf) are composed of radiolarites and nannofossil chalk with occasional chert beds. In contrast to other sites, the cherty sections at Site 1218 were completely recovered by XCB coring, undoubtedly because they were interbedded with chalks rather than ooze. The base of the sediment column is middle Eocene chalk (250-274 mbsf). The lower 7 m of the chalk is dolomitized with up to 20% dolomite in the coarse fraction. Basalt was recovered at the base of the drilled section.
Planktonic foraminifers occur sporadically through the lower Miocene, Oligocene, and middle Eocene sediments at Site 1218 with generally less consistent presence than other calcitic groups such as benthic foraminifers and calcareous nannofossils. Most samples show at least some dissolution of planktonic foraminifers with preferential preservation of large, thick-walled specimens in many cases. Middle Oligocene sediments (Zones P21 and P20) were generally the best preserved and most species-rich sediments for planktonic foraminifers at Site 1218. Benthic foraminifers are present in core catchers throughout the cored interval except in the upper radiolarian clays and the upper Eocene interval. Calcareous nannofossils, in contrast, are present at varying concentrations and states of preservation from uppermost middle Miocene Zone NN8 (37 mbsf) to the base of the sediment section. Radiolarians were found in all recovered cores.
Pore water chemical profiles at Site 1218 are subtle. Sulfate concentrations are near seawater values throughout the section, indicating the lack of significant organic matter diagenesis, whereas trends in Ca and Mg reflect modest basement alteration. Bulk-sediment concentrations (measured every 1.5 m) outline the major lithologic units described above. Only Ca and Sr concentrations are high in the lower Oligocene-Miocene nannofossil oozes, and all other elements tend to be higher in the clays and radiolarite sediments. Biogenic enrichment of Ba can be detected through Ba/Ti ratios (Fig. F19). High Mg concentrations can be found in the basal dolomitized chalk.
Natural remanent magnetization (NRM) intensity of the sediments at Site 1218 is relatively strong, and magnetic overprint from drilling can be mostly removed by AF demagnetization. An excellent record of magnetic reversals was made for the entire APC-cored sediment section (0-210 mcd) to Chron C12r of the early Oligocene. In addition, magnetic inclinations were determined on discrete samples after more thorough demagnetization. Middle and early Miocene samples have an average inclination of 5.2° (+2.2°/8.4°), whereas the Oligocene samples have an average inclination of 3.8° (95 = 6.2), which is indistinguishable from the paleoequator.
Recovered sediments at Site 1218 have high-amplitude MST data sets, which gave us the ability to direct drilling (in real time) in Holes 1218B and 1218C in order to construct a complete composite sediment section to a depth of ~263 mbsf (~287 mcd). This section will help to define and calibrate Cenozoic biostratigraphic zonation, to develop an astronomically tuned Cenozoic timescale, and to generate high-resolution paleoceanographic and paleoclimatic records of the Paleogene-Neogene transition.
The short range of nannofossil species Sphenolithus delphix provides a reliable marker close to the O/M boundary between Subchrons C6Cn.3n and C6Cn.2n (Raffi, 1999), and on this basis, the O/M boundary in Site 1218 occurs at ~98 mbsf. The first occurrence of the planktonic foraminifer Paragloborotalia kugleri (the marker for the O/M boundary) and first occurrence of the radiolarian Cyrtocapsella tetrapera also occur at this depth.
Calcareous benthic foraminifer assemblages indicate lowermost bathyal and upper abyssal paleodepths at Site 1218. Examination of test walls under transmitted light indicates that most of the benthic foraminifers at this site have suffered little or no postburial diagenetic alternation. Average sedimentation rates across the Oligocene-Miocene transition (~1-2 cm/k.y.) are relatively high for a deep-ocean Pacific setting.
The E/O boundary at Site 1218 is characterized by a major lithologic change involving a two-step downcore shift from pale nannofossil chalk to dark radiolarite. This transition from carbonate-rich to carbonate-poor sediments is also evident as a two-step decrease in GRA bulk density and an increase in magnetic susceptibility values in MST data. Based upon biostratigraphic information, this transition occurs across or just above the Eocene-Oligocene transition.
The extinction of the calcareous nannofossil D. saipanensis is estimated to have occurred ~0.3 m.y prior to the E/O boundary event sensu stricto (extinction of the planktonic foraminifer genus Hantkenina), and the last representative of the Paleogene rosette-shaped discoasters, Discoaster barbadiensis, disappeared ~0.2 m.y. before D. saipanensis. D. barbadiensis and D. saipanensis are constrained to have disappeared over narrow (~20-30 cm) intervals in Site 1218 sediments shortly below the major change in lithology. These findings reveal that the entire two-step change in lithology occurred in Zone NP21 (CP16c), above the extinction of the last Eocene discoasters. Based on an LSR the estimated position of the E/O boundary is at 243.3 mcd, whereas the midpoint of the initial change in carbonate composition is at 242.0 mcd (Fig. F27). The midpoint of the second, final step in carbonate is at 240.0 mcd. The boundary condition change of the ocean-climate system that caused the first step of this drastic deepening of the CCD and accompanying change in sedimentation in the tropical Pacific Ocean occurred near the middle of Oi-1 (33.5-33.1 Ma) (Zachos et al., 2001a) on the common timescale used (Cande and Kent, 1995). The abrupt change in the lithologies across the Eocene-Oligocene transition is a reflection of the rapid deepening of the CCD (van Andel et al., 1975) in the Oligocene. Site 1218 demonstrates that the change in CCD occurred during the earliest Oligocene in two steps, as a rapid increase in CaCO3 over 10-20 k.y. followed by a pause of ~100-200 k.y. and then another rapid increase in CaCO3 over 10-20 k.y. The CCD was shallower than ~3600 mbsl in the latest Eocene radiolarite interval, based on the paleodepth of Site 1218.
From Site 1218, it is clear that radiolarian-rich sediments are characteristic of the late and late-middle Eocene Pacific Ocean even near the equator. Nannofossils occasionally are dominant sediment components, showing that the CCD deepened beyond the paleodepth of Site 1218 at times in the late and middle Eocene. The presence of radiolarians and occasional intervals of nannofossils and the relative absence of diatoms (except in specific intervals near the E/O boundary) is more typical of Neogene plankton assemblages found at the fringes of the equatorial high-productivity zone than in the near-equatorial position that Site 1218 probably occupied during the middle and late Eocene.
The basal nannofossil chalks of Site 1218 abruptly become radiolarites upcore at ~40 Ma (base of nannofossil Subzone CP14b; Core 199-1218C-21X). The transition from chalks to radiolarites occurs over only 1.5 m when the site was at a paleodepth of 3000-3100 m. The middle Eocene rise in CCD at 40 Ma is almost as abrupt as the drop in CCD at the E/O boundary.
Finally, the basal 7 m of nannofossil chalk at Site 1218 that overlies basement is, like its Site 1215 and 1217 counterparts, dolomitized—an intriguing discovery given its proximity to what is generally considered to be a kinetically more favorable geochemical sink for Mg (alteration minerals in the upper oceanic crust).
Site 1219 (7°48.01´N, 142°00.94´W) is the southernmost site drilled during Leg 199. It is situated on the 56-Ma transect ~3° north of the Clipperton Fracture Zone and is located at a water depth of 5063 m on abyssal hill topography. The age of basement at Site 1219 was poorly constrained prior to Leg 199 because little reliable magnetic anomaly data are available between the Clipperton and Clarion Fracture Zones (Cande et al., 1989). At the outset of Leg 199, based on one interpretation of the location of magnetic Anomaly An25r (~57 Ma) (Petronotis et al., 1994), previous drilling, and assumed spreading rates, we estimated the age of basement at Site 1219 to be ~55 Ma. Site 1219 is the only site drilled during Leg 199 that features all of the seismic horizons identified for a Paleogene equatorial seismic stratigraphy (Lyle et al., this volume).
Based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles), Site 1219 should have been within 2° south of the equator between 40 and 21 Ma and should have crossed the equator at 29 Ma. Thus, the sediments should record equatorial conditions from the late middle Eocene through the early Miocene. In addition, Site 1219 should provide an analog for Site 1218, except that it is on older, deeper crust.
Two holes were drilled at Site 1219. Hole 1219A was a remarkable operations success. We advanced to ~225 mbsf using ODP's APC technology and, thereby, achieved one of our high-priority objectives by recovering sediments suitable for whole-core magnetostratigraphy below the lower Oligocene (including the E/O boundary). Basement was reached at ~250 mbsf shortly after switching to XCB coring. A full suite of downhole logs was obtained to the base of Hole 1219A, and the data are of high quality. In addition to these downhole logs, MST data from the latest Eocene to the earliest Miocene interval in this hole bore a striking resemblance to those recovered from Site 1218, and it was possible to correlate between Sites 1218 and 1219 (which are separated by 7° of longitude and 1° latitude, or ~800 km) to a submeter scale.
In contrast to Hole 1219A, Hole 1219B was terminated when an APC core jammed in the bottom-hole assembly (BHA) at the depth of the E/O boundary (~155 mbsf). In light of these difficulties in Hole 1219B and the successes of both Hole 1219A and Site 1218, the shipboard party took a collective decision to abandon Site 1219 earlier than planned in order to target additional and more complete programs at forthcoming sites having early and middle Eocene objectives.
Holes 1219A and 1219B can be spliced to form a continuous section to 130 mcd (~30 Ma) with two apparent gaps at ~90 and ~100 mcd. Excellent correlations between Site 1218 and 1219 allow us to estimate the properties of the unrecovered intervals, whereas correlations between logging data and the cores can be used to estimate the size of core gaps deeper in the sedimentary section. Sedimentation rates over the Oligocene interval were ~16% slower than at Site 1218 based upon the site-to-site correlation.
The sediment column at Site 1219 has a strong resemblance to that of Site 1218. Thirty meters of clay (lithologic Unit I) overlies Oligocene-lower Miocene nannofossil ooze (Unit II; 30-151 mbsf). Strong cyclic variations in nannofossil content are apparent in both the upper and lower parts of Unit II. An abrupt change in lithology from nannofossil ooze to radiolarian clay and clayey radiolarian ooze occurs at 151 mbsf in the E/O boundary interval. The lithologic change marks the upper boundary of lithologic Unit III, an upper and middle Eocene unit composed of radiolarian ooze and radiolarian clay, which becomes radiolarite, chert, and zeolitic clay at the base. A short section in Unit III in polarity Chron C18r (40.1-41.3 Ma) contains alternating diatom and nannofossil ooze. Below the cherty, clay-rich section at the base of Unit III are the chalks of lithologic Unit IV (234-243 mbsf; ~53-54.8 Ma). The oldest sediments above basalt are slightly younger than the P/E boundary.
NRM intensity of the sediments at Site 1219 is relatively strong, and magnetic overprint from drilling can be mostly removed by AF demagnetization. An excellent record of magnetic reversals was made for the entire APC-cored sediment section (0-223 mbsf), from Pleistocene Chron C1n to early middle Eocene Chron C20r (43.8-46.3 Ma). This remarkably clean magnetic reversal stratigraphy allows us to calibrate biostratigraphic events and to develop detailed sedimentation rate curves downhole through lower middle Eocene sediments. Inclination patterns in discrete samples show that at least the lower part of the sedimentary section was located in the Southern Hemisphere during deposition. The mean inclination depicts a time-averaged paleolatitude of 1.6°S for the site, but this result is preliminary and will require further testing. The paleolatitude inferred from the inclination is consistent with the expected latitudes as calculated from both paleomagnetic pole positions and those based upon a fixed hotspot model.
Nannofossils are present to abundant in the Oligocene-middle Miocene sediments (~151-10 mbsf) but absent from upper Eocene sediments. Nannofossils reappear briefly in polarity Chron C17r (~38.3 Ma) in the middle Eocene, disappear, and then reappear and are present between the middle of polarity Chron C18r to the base of C20n (~40.5-43.8 Ma) and are found in the chalk in the lower Eocene interval. Planktonic foraminifers are present in the lower Miocene to Oligocene sediments and in the lower Eocene chalks. Preservation quality and abundance are highest in the lower Miocene (Zones M4-M2) and the middle part of the Oligocene (Zones P20 and P21). Benthic foraminifers are consistently present and well preserved through the Miocene and Oligocene at Site 1219 but are scarce and very poorly preserved through much of the Eocene sections. Radiolarians were found in all cores except the deepest one (Core 199-1219A-27X), which recovered chalk over basalt basement.
The magnitude of the downhole calcium concentration increase and magnesium and potassium-concentration decrease in pore waters at Site 1219 is the greatest seen at all sites during Leg 199. This pattern is consistent with the extensive alteration (e.g., chlorite formation) of basement rocks observed here. Depth gradients of pore water alkalinity, pH, sulfate, and ammonium reflect the small amount of organic matter degradation occurring in these sediments, whereas the chlorinity profile may reflect the diffusion of the more saline Pacific bottom water of the last glacial maximum into the sediments. Bulk-sediment geochemical analyses from Site 1219 reflect the shifts in lithology back and forth between sediments dominated by silica and carbonate. Clay-rich units are high in Ti and Al, but they are also high in Fe and Mn, presumably reflecting the deposition of authigenic ferromanganese oxyhydroxides. Physical properties of the sediments also primarily reflect lithology. The carbonate sediments are higher in density, lower in porosity, and lower in magnetic susceptibility than the clay or radiolarian ooze lithologies. This is true even on a fine scale (see Fig. F29 and "Physical Properties" both in the "Site 1219" chapter). The radiolarian ooze has higher compressional wave velocity than the carbonates despite having higher average porosity.
The clean record of magnetic reversal history from Site 1219 (for the entire APC-cored sediment section; 0-223 mbsf), from the Pleistocene down to Chron C20r (43.8-46.3 Ma), is remarkable for a tropical site and, together with the superb cyclostratigraphic correlations to Site 1218 (see following paragraph) will provide invaluable time control for shore-based high-resolution paleoceanographic studies.
The MST data from Site 1219 bear a striking resemblance to those recovered from Site 1218 from the middle Eocene to the lowermost Miocene interval. The excellent match in these data sets between the two sites made it possible to align both records on a common (Site 1218 mcd) depth scale. The two records show such high quality correlation (down to the submeter scale) that successful a priori prediction of biostratigraphic zones and magnetic reversals was possible at Site 1219. The mapping from Site 1219 mcd to Site 1218 mcd results in relative sedimentation rates at Site 1218 that are ~16% higher than at Site 1219 over the Oligocene interval. The remarkable fidelity of the correlation between these two sites, separated by >1° of latitude and 7° of longitude (~800 km), suggests that drilling results from these two sites are representative of large-scale paleoceanographic forcing functions in the late Paleogene eastern equatorial Pacific Ocean. We anticipate that the continuously cored sediments from Site 1218 with supplementary control from correlative sediments in Site 1219 will provide a paleoceanographic reference section for the late Paleogene tropical Pacific Ocean.
Calcareous nannofossils suggest a placement of the O/M boundary ~55 mcd in polarity Subchron C6Cn.2r at Site 1219, where the range of Sphenolithus delphix was observed. On the Cande and Kent (1995) timescale, an age estimate of 24.28 S. delphix at Site 1219. With conversion to the orbitally tuned timescale of Shackleton et al. (2000) by subtracting 0.9 m.y. from the Cande and Kent (1995) timescale estimate, an age of 23.38 Ma is obtained for the base of S. delphix. This value is 0.14 m.y. older than the orbitally tuned estimate for this datum derived from the eastern South Atlantic (DSDP Site 522) and the western equatorial Atlantic (Sites 926, 928, and 929) (Shackleton et al., 2000). Yet, the calibration of the S. delphix event to the geomagnetic polarity record is remarkably consistent in Chron C6Cn.2, from the South Atlantic Ocean to the Mediterranean region (Raffi, 1999) and to the tropical Pacific Ocean (Site 1219).
The Eocene-Oligocene transition at Site 1219 is associated with an abrupt lithologic change from radiolarian clays below to nannofossil ooze above. This transition is similar to but sharper than that observed at Site 1218, presumably reflecting higher rates of carbonate dissolution at Site 1219 (the contemporaneous paleowater depth is ~400 m deeper at Site 1219 than Site 1218). Together with drilling results from Site 1217, this finding offers exciting prospects for shore-based investigation of the first Pacific Ocean depth and latitudinal transect across this important paleoceanographic boundary.
The Eocene sediments at Site 1219 are dominated by radiolarian oozes from the period between ~45 Ma through the E/O boundary. Nevertheless, there are intervals of carbonate in the section, most notably at ~40.5 Ma but also at ~38.3 and ~43.5 Ma. These carbonate units can be detected by density, reflectivity, velocity, and LAS mineralogy as well as by chemical analyses and microscopic examination of the sediments. The 40.5-Ma event and 38-Ma event are also found at Site 1218, but the oldest of these events is older than the base of the sediment column at Site 1218.
The lower middle Eocene interval is represented by cherty sediments that were not recovered by drilling. This is one of five sites on the 56-Ma transect in which we encountered cherts in roughly the same interval. Immediately below the cherts at Site 1219 are zeolitic clays barren of microfossils, suggesting that the chertified interval was deposited slowly. The uppermost lower Eocene chalk in contact with the zeolitic clay has an age of ~53 Ma (nannofossil Subzone CP9b), whereas the lowermost radiolarian ooze above the cherty interval is dated as ~46 Ma. Thus, the average sedimentation rate over the 10-m-thick cherty interval could be as low as 1.4 m/m.y. The interval has been condensed by diagenesis, but an estimate of the bulk MAR using sediment density measured by downhole logging (~2 g/cm3) is about half that of the sediments immediately above it.
The lower Eocene chalks were poorly recovered but appear to be typical basal carbonate-rich sediments. There is little evidence of hydrothermal sediments in the chalks.
Site 1220 (10°10.601´N, 142°45.491´W) forms a southerly component of the 56-Ma transect to be drilled during Leg 199. It is situated halfway between the Clipperton and Clarion Fracture Zones at a water depth of 5218 m in typical abyssal hill topography. On the basis of regional magnetic anomalies, we anticipated basement age at Site 1220 to be equivalent to Anomaly An25n (~56 Ma; Cande et al., 1989), slightly older than at Site 1219.
Based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) Site 1220 should have been located ~3°S of the equator at 56 Ma and in an equatorial position at 40 Ma. Thus, Site 1220 should have been situated beneath the South Equatorial Current in the early Eocene. Site 1220 will act as a deeper analog to Site 1218. Both sites are thought to have been located in an equatorial position at ~40 Ma, but Site 1220 was ~400 m deeper at this time.
Three holes were drilled at Site 1220. Hole 1220A was terminated when an APC core jammed in the BHA at ~100 mbsf, but basement was reached in Holes 1220B and 1220C at ~200 mbsf. Cores from Site 1220 overlap and form a continuous sedimentary sequence down to ~144 mcd (base of Core 199-1220B-10H; Figs. F11 and F12 in the "Site 1215" chapter). The sedimentary sequence recovered at the site is divided into five major sedimentary units. The uppermost unit (~0-19 mbsf) consists of very dark grayish brown clay with zeolites and is underlain by a lower Miocene-Oligocene Unit II (~19-40 mbsf) of radiolarian and nannofossil oozes with varying clay content. The underlying Oligocene radiolarian and nannofossil oozes of Unit III (~40-70 mbsf) are notable by the presence of a significant (~15%-45%) diatom component toward the base. Unit IV (~70-185 mbsf) consists of upper Eocene radiolarian oozes with clay and middle-lower Eocene chert with clayey radiolarian ooze. These sediments are underlain by a lower Eocene-upper Paleocene unit (~185-200 mbsf) of partially dolomitized nannofossil ooze, radiolarian nannofossil ooze, radiolarian ooze, calcareous chalk, and black clay atop an aphanitic to fine-grained phaneritic basalt.
Paleomagnetic data from Site 1220 gave excellent results and a reliable record of geomagnetic reversals from the early to the middle Eocene to the early Miocene. The composite depth record from Holes 1220A, 1220B, and 1220C shows a remarkable match of the cores between the different holes. In fact, the virtual geomagnetic pole (VGP) latitude changes were used as a basis to help fit the cores to the mcd scale. Correlation of the magnetic stratigraphy at Site 1220 to the geomagnetic polarity timescale (GPTS) shows a record that spans from the top of Chron C21n to Subchron C6An.1n (~20.5-46.3 Ma).
Biostratigraphic results indicate that we recovered a nearly complete sequence of lower Miocene-lower Eocene radiolarian zones at Site 1220, interrupted only by a poorly recovered chert sequence from the uppermost lower Eocene and the lowermost middle Eocene. Calcareous fossils are generally poorly preserved or absent through much of the sequence. Calcareous nannofossils are sufficiently well preserved in the lowermost Miocene and Oligocene to provide a basic zonation. Planktonic foraminifers are almost entirely absent above the lower Eocene, but dissolution-resistant species allow the lower/upper Oligocene boundary to be approximated. Both planktonic foraminifers and calcareous nannofossils provide a detailed zonation of a condensed sequence of lower Eocene nannofossil oozes and chert in the basal 10 m of Site 1220. The extinction of Paleocene benthic foraminifers, the appearance of the nannofossil genus Rhomboaster, the extinction of the nannofossil genus Fasciculithus, and the presence of excursion fauna of planktonic foraminifers provide a detailed biostratigraphy of the P/E boundary in Unit V. The nannofossil events occur 0.8-1.4 m above the extinction of Paleocene benthic foraminifers. The excursion fauna of planktonic foraminifers is present in sediments below the level of the benthic foraminifer extinction (sediments immediately overlying basalt). Thus, none of these events are precisely synchronous with the benthic foraminifer extinction, the marker we used for the P/E boundary, at this site.
Interstitial pore water profiles from Site 1220 are very similar to the profiles of all other Leg 199 sites (except Site 1219) and primarily reflect minor organic matter degradation, the dissolution of biogenic silica, and minor alteration of underlying basalt. The bulk geochemistry of the sediments from Site 1220 reflect the shifts in lithology between sediments dominated by silica and carbonate.
Physical properties of the sediments also primarily reflect lithology. The carbonate sediments are higher in density, lower in porosity, and lower in magnetic susceptibility than the clay or radiolarian ooze lithologies. The radiolarian-rich sediments of Units II and IV are marked by high porosities, which average 88% and 85%, respectively. The radiolarian oozes maintain their porosity despite burial. The Eocene radiolarian oozes have the highest P-wave velocities of the unconsolidated sediment lithologies.
The clean record of magnetic reversal history from Site 1220 (for the entire APC-cored sediment section; 0-150 mbsf) spans the lower Miocene to lower-middle Eocene (Subchron C6An.1n to the top of Chron C21; 20.05-46.3 Ma). This record is remarkable for a tropical site and will provide invaluable time control for calibration of radiolarian biostratigraphy. Because there are cyclic variations in radiolarian content of the Site 1220 Eocene section presumably driven by orbital forcing of insolation, this record could be highly important for orbital tuning of the geomagnetic polarity timescale from the middle Eocene to the early Miocene.
A combination of magnetostratigraphy and nannofossil biostratigraphy indicates that we recovered a further E/O boundary at Site 1220 (~70 mbsf). Shore-based work on this section, together with those recovered at Sites 1217, 1218, and 1219, will allow us to improve existing constraints on the links between global cooling, Antarctic ice sheet growth, and a deepening CCD across this important paleoceanographic boundary.
In Hole 1220B, just above basement basalt, we recovered a lithologically striking interval of calcareous chalk and clay (199-200 mbsf). Based on biostratigraphic data, this sequence represents the P/E boundary. Layers of calcareous chalk and clay display a large range in composition and color downcore. Alternating intervals of white and very pale-brown calcareous chalk occur between 198.9 and 199.4 mbsf and contain a minor amount (5%-10%) of poorly preserved nannofossils. White layers occur between 199.15 and 199.23 mbsf and contain 15%-30% planktonic foraminifers. The sediments below this interval consist of faintly banded, dark yellowish brown calcareous chalk but are barren of microfossils. Dolomite (up to 10%) and clay (10%-35%) also occur in this lithology. Below 199.50 mbsf is a 4-cm-thick layer of very dark-brown (7.5YR 2.5/3) calcareous chalk underlain by a black clay. Major components of both sediments are dolomite, iron manganese oxides, and clay. Volcanic glass occurs as a minor component. Dolomite content decreases over the interval from 199.52 to 199.54 mbsf, and no calcareous or siliceous fossils were observed in corresponding smear slides. Directly beneath the black clay is a 4.5-cm-thick interval of yellowish red calcareous chalk. Within this interval is a 1-cm-thick brownish yellow layer of calcareous chalk. Sediments in the yellowish red layers are weakly laminated and contain clay, dolomite, calcite, and a minor percentage of nannofossils. Iron manganese oxides and opaque minerals are minor components. The brownish yellow chalk layer contains clay, dolomite, iron manganese oxides, volcanic glass, and abundant small mottles. Nannofossils are rare in these layers.
The base of the sedimentary section contains a 9-cm-thick interval of brownish yellow clayey calcareous chalk (199.59-199.68 mbsf) with thin black laminations. Dolomite comprises up to 10% of these sediments. Zeolites and nannofossils also occur as minor components. Iron manganese oxides are rare. Laminations contain clay, iron manganese oxides, dolomite, zeolites, and small amounts of volcanic ash and are barren of calcareous fossils.
Site 1221 (Fig. F1 in the "Site 1221" chapter); 12°01.999´N, 143°41.572´W) forms an equatorial component of the 56-Ma transect drilled during Leg 199. It is situated about three quarters of the way between the Clipperton and Clarion Fracture Zones in typical abyssal hill topography at a water depth of 5175 m. On the basis of regional seafloor magnetic anomalies, we anticipated basement age at Site 1221 to be equivalent to Anomaly An25n (~56 Ma; Cande et al., 1989), about the same age as Site 1220. At the outset of drilling at Site 1221, our estimate for total sediment thickness was ~150 m (Fig. F2 in the "Site 1221" chapter).
Based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) Site 1221 should have been located ~1° south of the equator at 56 Ma, in an equatorial position at ~50 Ma and ~2° north at 40 Ma. Thus, Site 1221 should have been situated underneath the early Eocene equivalent of the South Equatorial Current.
Four holes were drilled at Site 1221. Hole 1221A was abandoned because of a stuck XCB barrel that resulted in a pipe trip to clear the BHA. Hole 1221B recored the Oligocene interval at the top of the sediment column, whereas Hole 1221C was cored to cover the major gaps in the upper sediment column and then cored continuously to basement. Hole 1221D was drilled to obtain a second copy of the lower Eocene and Paleocene sediments.
The heave of the vessel frequently exceeded 5 m while we were drilling at Site 1221. The ship heave compromised the quality and recovery of the core. The uppermost ~20 mbsf encountered severe flow-in problems, whereas in the remaining intervals, the often soupy nature of the sediment (radiolarian ooze) resulted in MST data that were not suitable for correlation purposes, with the exception of the P/E boundary interval. A continuous sediment column could not be correlated below 19.5 mcd.
The sediment column is a variation of lithologies seen at other Leg 199 sites. A very thin clay and radiolarian ooze lithologic unit overlies lower Oligocene nannofossil ooze, terminated by an abrupt transition to clay rapidly grading to radiolarian ooze. The abrupt transition is typical of the E/O boundary. At Site 1221, however, latest Eocene and earliest Oligocene time is represented by a hiatus of ~1 m.y. in extent. The middle and upper Eocene radiolarian ooze section is the thickest of any site of Leg 199. Deposition of the radiolarian ooze was highest in the period between 45 and 43 Ma, when sedimentation rates reached 18 m/m.y.
A chert-rich section covering the time interval from ~48 Ma (radiolarian Zone RP11) to 53.8 Ma (nannofossil Subzone CP9a) lies beneath the radiolarian ooze. Although only chert was recovered, coring times were relatively short, suggesting a significant amount of radiolarian ooze or clay is also present. Hole 1221C drilled somewhat faster than Hole 1221D, indicating some variability in the thickness and areal extent of the chert. In the recovered sediments below the chert unit, clay layers in Hole 1221C can be correlated to clay layers in Hole 1221D. Beneath the chert-rich interval are nannofossil chalks of early Eocene-Paleocene age that comprise the basal sedimentary unit. Within this basal chalk, we recovered two copies of the P/E boundary interval. The P/E boundary interval is recognizable by a multicolored clay-rich unit remarkably similar in structure to the P/E boundary interval at Site 1220, 206 km to the south. The lowermost chalks above basement were dated at 56.5-57 Ma with foraminifers and nannofossils.
Physical properties of the sediments follow lithology. The densest unit is the lower Eocene chalk (~1.6-1.8 g/cm3) followed by the upper clays and nannofossil ooze. The radiolarian ooze sediments have the lowest wet bulk densities (~1.14 g/cm3) and the highest porosities (~84%), as well as the highest velocities of the unconsolidated sediments (1530-1550 m/s).
Biostratigraphic analyses indicate that Site 1221 contains a continuous sequence of radiolarian-bearing sediments from the early Oligocene-early Eocene. The uppermost sequence contains considerable quantities of reworked middle Eocene radiolarians, whereas the interval from ~7 to 111 mbsf is almost exclusively brown radiolarian ooze with a sugary texture. No radiolarians were recovered in the chert-rich interval except in the core catcher of Core 199-1221C-10X at a depth of 141 mbsf. These radiolarians are from the late Paleocene to the early Eocene Zone RP7. No radiolarians are found in the basal chalk.
The sediments of Site 1221 contain calcareous microfossils in only the uppermost and lowermost units. Calcareous microfossils are completely absent in the siliceous sediments between ~7 and ~111 mbsf, and biostratigraphic control through this interval was provided entirely by radiolarians. The carbonate content of sediments increased in the basal reaches of Holes 1221C and 1221D, and nannofossil and planktonic foraminiferal biostratigraphy allow basic zonation of a condensed sequence of lower Eocene nannofossil ooze and chert. Section 199-1221C-11X-3 contains an interval of dramatic and colorful banding, the base of which, as at Site 1220, corresponds to the extinction of Paleocene benthic foraminifers and, therefore, the P/E boundary. Preservation of calcareous microfossils improves below the P/E boundary, and planktonic foraminifers and nannofossils allow a detailed zonation of upper Paleocene nannofossil ooze and clay. Calcareous benthic foraminiferal assemblages occur only in the basal sediments below 140 mbsf. These assemblages are moderately well preserved, but the presence of small calcite microcrystals on the surfaces of the tests indicate some diagenetic alteration.
Interstitial pore water profiles from Site 1220 are very similar to the profiles of all other Leg 199 sites except Site 1219 and primarily reflect minor organic matter degradation, the dissolution of biogenic silica, and minor alteration of underlying basalt. The bulk geochemistry of the sediments from Site 1221 reflect the shifts in lithology between sediments dominated by silica and carbonate.
The P/E boundary was recovered twice (intervals 199-1221C-11X-3, 50-90 cm, and 199-1221D-4X-2, 70-125 cm). The two intervals are very similar, with the interval in Hole 1221D appearing slightly expanded relative to that in Hole 1221C and exhibiting more disturbance.
The benthic foraminiferal fauna were examined in small surface scrapes prior to more complete shore-based analysis. The first occurrence of Eocene benthic foraminifers is at 50 cm in Section 199-1221C-11X-3, whereas the last occurrence of Paleocene forms is at ~91 cm in the same section.
The Site 1221 P/E boundary interval appears remarkably similar to that recovered at Site 1220. Distinctive brown, pink, black, and dark-brown layering can be correlated between the two sites 206 km apart.
Site 1222 (13°48.98´N, 143°53.35´W) is situated ~2° of south of the Clarion Fracture Zone in typical abyssal hill topography at a water depth of 4989 m. On the basis of regional seafloor magnetic anomalies, we anticipated basement age at Site 1222 to be equivalent to Anomaly An25 (~56-57 Ma; Cande et al., 1989), slightly older than at Site 1219. At the onset of drilling at Site 1222, our estimate for total sediment thickness was ~115 m; based upon a fixed hotspot model (Gripp and Gordon, 1990, for the 0- to 5-Ma Pacific hotspot rotation pole; Engebretson et al., 1985, for older poles) Site 1222 should have been located ~1° north of the equator at 56 Ma and ~4°N at 40 Ma.
Two holes were drilled at Site 1222. Hole 1222A was drilled to basement, which was reached at ~98 mbsf. Hole 1222B recored the APC-suitable portion of the sediment column (to ~60 mbsf). The sediment column at Site 1222 contains a sequence of lithologies significantly different to that found at other Leg 199 sites. Site 1222 recovered a 97.8-m-thick section dominated by clay-rich lithologies and chert. Unit I consists of an ~55-m-thick yellowish brown to dark gray brown clay with zeolites grading to radiolarian clay. A thin interval of diatomaceous clay occurs near 17 mbsf (Sections 199-1222A-3H-2 to 3H-4). Within the diatom clay is an interval with unusual layers of laminated diatom ooze that contain a nearly pure diatom component of Pliocene age. Laminations are mainly white to olive. Diatom frustules in some laminae contain significant pyrite making them appear very dark gray to black. A sharp contact exists at the base of the diatom ooze interval and the underlying clay of Subunit IA. In Hole 1222A, this contact also contains a large (5-cm diameter) botryoidal manganese nodule. Unit II, ~3 m thick, consists of dark-brown to brown nannofossil clay grading downcore to yellowish brown nannofossil ooze. Very pale brown mottles are common. Nannofossil content (estimated from smear slides) gradually increases from 30% in the upper portion to 80% near the base of the unit. Unit III consists of an ~8-m-thick sequence dominated by clay with iron oxides and zeolites. Unit III is underlain by a thick (>30 m) poorly recovered sequence of massive chert that, in turn, overlies basement basalt.
Radiolarians provide the biostratigraphic framework for Site 1222. Planktonic foraminifers are completely dissolved in all samples investigated. Calcareous nannofossils of early Oligocene age occur in Unit II and early Eocene nannofossils were found in chalk attached to a piece of chert occur just above basement. This large chert nodule is rimmed with very pale brown nannofossil chalk that provides datums indicating an early Eocene age (NP10). The biostratigraphic distribution of radiolarians suggests massive reworking and mixed Pliocene assemblages in the uppermost two and a half cores, between ~0 and 21 mbsf. The following two cores, between ~21 mbsf and 40 mbsf, contain upper and lower Miocene radiolarian assemblages. Two cores between ~40 and 60 mbsf hold upper and lower Oligocene radiolarian assemblages. Nannofossils are present between ~55 mbsf and 60 mbsf, supporting the radiolarian biostratigraphy. This upper part of the section at Site 1222 appears to contain several breaks in sedimentation. A major hiatus occurs between the lowermost Oligocene and the middle Eocene, having a duration on the order of ~5-6 m.y.
It was possible to construct a continuous spliced record from Site 1222 down to 34.44 mbsf (37.88 mcd), below which it was possible to align most cores from the two drilled holes to each other, but without continuous overlap. Cores 199-1222A-7H and 199-1222B-7H, however, showed good overlap and allowed the splicing of an additional ~13 m from ~59 to 72 mcd.
The paleomagnetic data from lithologic Subunit IA, down to ~40 mbsf, are not interpretable, except for the very top of the Hole 1222A. A large group of ChRM directions show relatively high magnetic inclinations after demagnetization especially in the most clay-rich lithologic units. The cause of the steep inclinations is unclear and might be indicative of unrecognized deformation and physical grain rotation caused by drilling. A preliminary correlation of the magnetic stratigraphy to the GPTS shows that we were able to identify the bottom of polarity Chron C1n (Brunhes) at the very top of the section. Below 40 mcd, we note magnetic reversals but can only identify Chrons C6Cn to C11n with any confidence.
The pore water profiles from Site 1222 primarily reflect minor organic matter degradation and the dissolution of biogenic silica. Most of the dissolved chemical constituents show a lack of gradient with depth and values similar to or slightly higher than seawater.
