Site 1127 is located in a water depth of 479.3 m on the eastern Eyre Terrace. The Pleistocene-Miocene (see "Biostratigraphy") succession was deposited in a prograding upper slope depositional setting. The succession is a continuation of the transect described by James et al. (1994) and part of the prograding wedge described by James and von der Borch (1991). The sequence stratigraphic framework is described in "Seismic Stratigraphy" and in Feary and James (1998, reprinted as Chap. 2).
Holes 1127A and 1127B intersect a 510.7-m-thick succession dominated by very fine to fine-grained, heavily bioturbated, unlithified to partially lithified, greenish gray wackestone to packstone. Three units are defined on the basis of sediment type and the presence of coarser grained beds (Figs. F3, F4).
The top part of the succession is unlithified. Partial lithification starts at 119 mbsf, and thin lithified beds occur between 170 and 200 mbsf. The beginning of lithification corresponds to a change in amplitude of seismic reflectors, from low-amplitude in the unconsolidated upper strata to high-amplitude reflectors in the partially lithified lower strata. Core recovery was good, but deformation caused by gas expansion (including extrusion of sediment from the liner on the rig floor) was common throughout the core, making it difficult to recognize fine-scale features and to identify the exact position of some depositional boundaries.
Unit I consists of calcareous ooze with varying amounts of nannofossils and planktonic foraminifers. It is divided into two packages: an upper nannofossil ooze and a lower foraminiferal ooze. The packages have wackestone and packstone texture, respectively, and are bioturbated and massive. The contact between packages is bioturbated and gradational, and it is associated with a downward darkening from light olive gray to pale olive.
The matrix of the unlithified nannofossil ooze package is dominated by calcareous nannofossils, mainly coccoliths, with accessory tunicate spicules, bioclasts, and sponge spicules. Components in the >63-µm fraction include abundant large planktonic foraminifers and sponge spicules, abundant bioclasts, pteropods, and rare ostracodes. Macrofossils are rare and consist of centimeter-sized pteropods. The deposits are bioturbated throughout, shown by a lighter to darker gray mottling. Burrows include Thalassinoides traces. Faint planar lamination is present in Section 182-1127A-1H-1, 70 cm.
The planktonic foraminiferal ooze package has a very fine to fine-grained sand size, and the color varies between pale olive gray, light gray, and olive. Color contacts are gradational. Sediments in this package are bioturbated throughout, as shown by diffuse color mottling. Calcareous nannofossils and planktonic foraminifers are common, and there are traces of quartz. Components in the >63-µm fraction are abundant planktonic foraminifers, pteropod fragments, and sponge spicules, and rare benthic foraminifers and ostracodes. Macrofossils are scarce and include gastropods, bivalves, pteropods, and bryozoans. Macrofossil abundance increases downward toward the base of the package, where there are also glauconite traces.
Unit II is the thickest unit at Site 1127 (458.7 m), consisting of alternating bioclastic wackestone- and packstone-dominated sediment interbedded with thin grainstone beds. The contact between Units I and II is a textural and compositional boundary. Across the boundary, from Unit II to Unit I, the grain size and relative abundance of bioclasts decreases and the abundance of carbonate mud increases. The lower boundary of Unit II corresponds to a major hiatus (see "Biostratigraphy"), and the unit contact is marked by the base of a slump.
Unit II is organized into three subunits (IIA through IIC). Subunit IIA consists of nannofossil and minor foraminiferal wackestone that grades upward into bioclastic wackestone, packstone, and grainstone. Nannofossils are common throughout. Subunit IIB is characterized by alternating bioclast-rich wackestone, packstone, and grainstone. Subunit IIC has a base characterized by synsedimentary deformation, interpreted as slumps, with abundant bioclasts including bryozoans.
Subunit IIA consists of unlithified bioclastic packstone with minor wackestone and unlithified nannofossil wackestone with subordinate foraminiferal grainstone. The contacts between different lithologies are gradual and bioturbated. Unlithified packstone is uniformly burrowed and massive, and the overall grain size is very fine. The color is light gray to light olive gray, with gradual color transitions. The proportion of mud varies, with packstones containing less mud generally found near the top of the succession where components are coarser (fine sand size with rare grains of medium sand size). Gastropod, serpulid, other shell fragments, and benthic foraminifers constitute the dominant macrofauna. The fraction coarser than 63 µm contains dominant bioclasts and abundant benthic foraminifers. Planktonic foraminifers are common to abundant, and sponge spicules, pteropods, pollen, ostracodes, and echinoid spines are present. The mud matrix (<63 µm) consists of abundant to dominant bioclasts and nannofossils, common to present sponge and tunicate spicules and planktonic foraminifers, and rare quartz grains.
Unlithified to partially lithified bioclastic wackestone is a minor lithology that occurs near the base of the subunit. Lithification is more common in wackestone near the base of the unit. Colors are gray to light olive gray, with gradational contacts. The sediment is burrowed throughout. Burrowing is enhanced in areas of color transition by the color contrast between burrow fill and substrate and, in some cases, by packstone infilling of the burrows. Macrofauna is rare, with the exception of shell fragments accumulated in burrows. The fraction coarser than 63 µm contains dominant bioclasts, abundant to common small foraminifers and sponge spicules, and traces of tunicate spicules and organic fragments. The matrix is dominated by nannofossils, bioclasts, and sponge and tunicate spicules, together with benthic and planktonic foraminifers.
Nannofossil ooze is light olive gray, bioturbated throughout, and has a wackestone texture. Some of the burrows are filled by coarse sand-sized shell fragments. The fraction coarser than 63 µm contains dominant bioclasts and common planktonic foraminifers and sponge spicules. The matrix consists of dominant nannofossils, common bioclasts, sponge spicules, and planktonic foraminifers, as well as traces of clay.
Foraminiferal ooze is light gray in color, composed of fine to medium sand-sized grains, and has a grainstone texture. The coarser than 63-µm fraction contains abundant planktonic foraminifers and bioclasts and abundant benthic foraminifers. Echinoid spines are present. The matrix consists of abundant bioclasts, common nannofossils, sponge spicules, and planktonic foraminifers and traces of quartz, tunicate spicules, and clay. The nannofossil and foraminiferal oozes occur in the middle of the subunit between the lower wackestone and upper packstone packages.
The abundance of nannofossils in Subunit IIB is lower than in Subunit IIA and Unit I (see "Site 1127 Smear Slides" in PDF format). Bioclasts are dominant in both the matrix and >63-µm fraction. The contact between Subunits IIA and IIB (Section 13H-4, 76 cm) corresponds to a textural boundary separating muddy sediments above from grainy sediments below. The uppermost part of Subunit IIB (Sections 13H-4, 72 cm, through 14H, 64 cm) consists of 1- to 8-cm-thick alternating layers of coarse-grained grainstone and fine- to very fine grained packstone. The compositional difference between grainstone and packstone layers is the presence of more sponge spicules and foraminifers (both planktonic and benthic) in the matrix of the packstone and the presence of echinoid spines and ostracodes in the >63-µm fraction of the grainstone. The grainstone is mainly light gray, and the packstone is light olive gray. Both lithologies are bioturbated throughout.
Most of Subunit IIB is unlithified to partially lithified bioclastic packstone and wackestone. The packstone is light olive gray in color, but light gray intervals are present. The wackestone has a light gray and occasionally pale olive color. Both textures alternate, although packstone is dominant at the base and top of the subunit, and wackestone in the middle of the subunit. Macrofauna, although rare, include benthic foraminifers, shell fragments, and gastropods. Packstone and wackestone have a similar composition in the >63-µm fraction, dominated by bioclasts, abundant benthic and planktonic foraminifers, sponge spicules, ostracodes, and echinoderm spines, as well as traces of glauconite. In addition, packstone beds contain blackened grains, bryozoan fragments, opaque minerals, and pteropod fragments. Packstone and wackestone matrix is similar, with abundant bioclasts and nannofossils, common sponge and tunicate spicules, and traces of echinoderm spines. Planktonic foraminifers are abundant in wackestone and rare in packstone.
Subunit IIC is divided into an upper package consisting of alternating partially lithified packstone and wackestone with a capping grainstone, and a lower package characterized by slumped beds. The upper unit boundary corresponds to a textural change between fine-grained fossiliferous packstone and grainstone below and the very fine grained wackestone of Subunit IIB. The lower boundary corresponds to an unconformity separating Units II and III. The mineralogy of Subunit IIC is dominated by low-Mg calcite (LMC) (see "Inorganic Geochemistry").
The lower part of Subunit IIC (Sections 47X-1 through 50X-4, 20 cm) consists of partially lithified bioclastic wackestone and packstone with abundant macrofauna (benthic foraminifers including miliolids, shell fragments, bryozoans, and gastropods), blackened grains, rotated blocks of mudstone, deformed beds, and a chaotic mixture of fine-grained packstone, coarse-grained grainstone, and mudstone. This package is interpreted to be slumped.
The upper part of Subunit IIC (Sections 42X-3, 125 cm, through 47X-1) consists of alternating packstone and wackestone, with wackestone more abundant in the lower part of the package and packstone with thin grainstone in the upper part. Contacts between the two textural types are gradational and bioturbated. The packstone is light olive gray, light gray, to gray in color, burrowed throughout, and of fine- to very fine grained sand size. Coarse components are serpulids and benthic foraminifers. The >63-µm fraction contains abundant bioclasts, common planktonic and benthic foraminifers, and sponge spicules. There are traces of bryozoans, echinoderm spines, and pollen. Thin, medium-grained, normally graded grainstone layers are intercalated with the packstone beds. A firmground overlain by rip-up clasts occurs at Section 44X-CC, 11 cm.
The wackestone is light gray and burrowed, although thin dark gray laminae are preserved occasionally. Coarse components are shell fragments and benthic foraminifers. The matrix consists of abundant nannofossils and bioclasts, sponge spicules, benthic foraminifers, and planktonic foraminifers.
Unit III has an upper boundary marked by a sharp color contact between light gray nannofossil chalk below and light greenish gray bioclastic packstone above. The surface coincides with the contact between sediments of Miocene and Pliocene?-Pleistocene age, with a possible hiatus in the record of as much as 3 m.y. (see "Biostratigraphy"). This unit extends down to 510.7 mbsf, the base of the drilled interval. Unit III is divided into an upper nannofossil chalk package and a lower bioclastic packstone package characterized by the presence of glauconite and minor grainstone beds with intraclasts.
The 1.3-m-thick nannofossil chalk package contains bioclasts and grades downward into partially lithified packstone. The sediment has a wackestone to mudstone texture, is light gray in color, and is bioturbated by Planolites and Chondrites throughout. The major components of the matrix are nannofossils. Sponge spicules and planktonic and benthic foraminifers are common. The >63-µm fraction is dominated by bioclasts, abundant planktonic foraminifers, and sponge spicules.
The bioclastic packstone package is partially lithified and poorly sorted. The main characteristics of the package are the presence of rotated intraclasts near the top of the section (Section 50X-7, 30 cm) and blackened bioclastic grains and glauconite throughout the interval. Glauconite is abundant (>50%), forming bioclastic glauconitic packstone to grainstone beds (Sections 51X-CC through 52X-1, 130 cm, and intervals 52X-2, 95-140 cm, and 52X-3, 30-105 cm). The fine to medium sand-sized glauconite is dark green to black. One of the glauconite-rich layers (Sections 51X-CC through 52X-1, 130 cm) is partially silicified. The bioclastic packstone is burrowed throughout, and the >63-µm fraction (see "Site 1127 Thin Sections" in PDF format) contains bioclasts, disseminated glauconite, planktonic and benthic foraminifers, and sponge spicules. The matrix consists of bioclasts and very few nannofossils. Macrofossils are rare and are represented by a few small mollusks.
The lower part of Unit III was poorly recovered; therefore, the stratigraphic development of this unit is unclear. However, the presence of grain-supported textures, blackened grains, intraclasts, and glauconite at the base suggests reworking and concentration of the coarser fraction. Benthic foraminifer data indicate faunal reworking (see "Biostratigraphy"), supporting the sedimentological observation. Upward, there is an increase in planktonic fauna, and the overall unit is interpreted to represent a deepening-upward succession. The interval is sharply overlain by slumped beds and grainy and bioclastic-rich deposits of the younger Unit II after a hiatus of ~3 m.y.
The middle Miocene and lower Pliocene carbonates are equivalent to the distal portion of seismic Sequence 3 and probably contain fauna reworked from Sequence 4 (sequences after Feary and James, 1998, reprinted as Chap. 2).
The slumped interval at the base of Subunit IIC is interpreted to represent erosion and mass wasting associated with formation of the unconformity separating Units II and III, and it probably represents the base of seismic Sequence 2 (James and von der Borch, 1991; Feary and James, 1998, reprinted as Chap. 2) (see "Seismic Stratigraphy"). Unit II formed as a prograding wedge associated with an increased influx of neritic sediment into an upper slope setting. Seismic data show a vertically stacked succession of offlapping sigmoidal reflections overlying a major discontinuity surface (see "Seismic Stratigraphy"). Site 1127 intersects the distal portion of the prograding wedge.
One of the most interesting aspects of Unit II is its grain size and bioclastic composition, suggesting allochthonous off-shelf transport. There is mud as well as fine to very fine sand-sized skeletal grains. The grains (e.g., mollusk fragments and benthic foraminifers) are abraded and derived from inner to middle neritic environments (see "Biostratigraphy"). Most of the grains were probably produced on the shelf and subsequently transported to the slope environment. Overall sediment accumulation rates for Unit II are high, ranging from 130 to 400 m/m.y. (see "Biostratigraphy" and "Paleomagnetism"). The estimated accumulation rates are similar to modern shallow-water tropical carbonates (James, 1997), indicating that thick, fine-grained, and mud-rich successions can be produced in cool-water carbonate environments in a relatively short time interval. This observation also points toward a very effective offshore transport mechanism such as "wave sweeping" and downwelling (James, 1997). Sedimentation on the slope was probably continuous throughout changes in Pleistocene sea level because of the broad ramp morphology and constant sediment production.
Unit II is characterized by cyclic variations in lithology, gamma-ray values (especially uranium) (see "Downhole Measurements"), magnetic susceptibility (MS) (see "Physical Properties"), and mineralogy (both aragonite and LMC) (see "Inorganic Geochemistry"). Based on textural and grain-size variability, Unit II is divided into five high-frequency depositional sequences (HFSs), 1 through 5, from oldest to the youngest (Fig. F4). Superimposed on the HFSs are meter-scale (higher frequency) cycles recorded by downhole measurements, MS, and mineralogy. Future detailed sedimentologic analysis will clarify the relationship between high-frequency cycles and lithologic and faunal changes. The HFS-1 sequence encompasses Subunit IIC and the lower part of Subunit IIB. The HFS-2 to HFS-4 sequences occur within Subunit IIB, and HFS-5 is equivalent to Subunit IIA. Each HFS is composed of a wackestone to packstone base, a middle part made up of wackestone, and a top dominated by packstone with thin capping grainstone. The grain size and abundance of shallow-water fauna increase near the top of each high-frequency unit sequence. The high-frequency sequences are interpreted to represent deepening followed by a shallowing-upward succession.
The thin youngest Unit I forms a drape over the older, more progradational Unit II. At the base of Unit I there is an increase in macrofossils and glauconite, and the abrupt contact with Unit II suggests that there is a condensed section or hiatus at the base of Unit I. The boundary is interpreted to represent a change in depositional style, from a progradational system with neritic-dominated fauna below to a drape system with pelagic-dominated fauna above.