Three major sedimentary units were recognized at Site 1133 and subdivided on the basis of major sediment type, texture, composition, color change, and presence of firmgrounds (Fig. F3). The upper sedimentary package consists of Pleistocene (see "Biostratigraphy") pelagic calcareous ooze, and the middle sedimentary package is upper Miocene-lower Pliocene pelagic calcareous ooze. A lower, poorly recovered interval consists of lower-middle Miocene (see "Biostratigraphy") neritic carbonate sediment. These deposits are unlithified to lithified bioclastic wackestone, packstone, grainstone, and chert/porcellanite (silicified limestone) (Fig. F3).
Recovery was more than 85% within the upper 35 mbsf of the cored interval, but then dropped abruptly because of the presence of unlithified to partially lithified bioclastic packstone interbedded with hard chert/porcellanite layers.
Unit I consists of gray to light gray and white, moderately to strongly bioturbated calcareous ooze with varying amounts of calcareous nannofossils and planktonic foraminifers. Unit I is divided into two subunits based on color changes, textural differences, different patterns of sediment alternation, and the presence of firmgrounds in Cores 182-1133A-1H, 182-1133B-2H, and 182-1133C-2H.
Subunit IA consists of light gray to gray, pale yellow, and white very fine grained calcareous ooze, characterized by a textural alternation between mudstone and wackestone, mostly as a result of variations in the proportion of planktonic foraminifers. The most conspicuous aspect of this subunit is the rapid variation in color. The lowermost bed in Subunit IA is a nannofossil ooze.
The matrix is dominated by calcareous nannofossils, common bioclasts, planktonic foraminifers, sponge spicules, and tunicate spicules (see "Site 1133 Smear Slides"). Components of the sand-sized fraction (>63 µm) are dominant planktonic foraminifers and abundant to common bioclasts. Echinoid spines, ostracodes, and broken sponge spicules are also present. The abundance of benthic foraminifers varies from trace to common. Pteropod shields, gastropod shells, and large miliolid foraminifer tests are scattered throughout Subunit IA.
The sediment is moderately to strongly bioturbated throughout. Bioturbation is manifest as lighter to darker gray to pale olive color mottling. Burrows are filled by nannofossil foraminiferal ooze with a mudstone texture, or planktonic foraminiferal ooze with a wackestone texture. Burrows within the latter, with a diameter of as much as 3 cm, are interpreted as Thallasinoides ichnofossils. The lower boundary of Subunit IA lies at the base of a light gray nannofossil ooze containing planktonic foraminifers.
The upper boundary of Subunit IB is marked by a firmground as well as a change in lithology and color. Nannofossil ooze directly below the boundary contains well-defined burrows that are usually stiffer than the surrounding sediment, with a particularly large and deep Thallasinoides burrow in interval 182-1133A-1H-4, 85-145 cm. The lower boundary of Subunit IB is placed at the scoured base of a thin planktonic foraminiferal ooze turbidite (Fig. F4), above which is an interval of minor synsedimentary deformation interpreted as a slump. These boundaries are recognized in both Hole 1133B and Hole 1133C. The basal planktonic foraminiferal ooze has a grainstone texture and contains glauconite, bioclasts, and sponge spicules.
The main part of Subunit IB consists of silt to very fine grained nannofossil ooze and nannofossil planktonic foraminiferal ooze, with color alternations ranging from light olive gray to very light gray and white. This color change is rapid and dramatic, with contacts between colors generally burrowed. Sediment texture ranges from mudstone to wackestone. The matrix is dominated by nannofossils and abundant to common bioclasts (see "Site 1133 Smear Slides"). Planktonic and benthic foraminifers and tunicate spicules are also present, as well as traces of dolomite. Most grains in the >63-µm fraction are very fine to fine-grained, abundant to dominant planktonic foraminifers, with lesser benthic foraminifers and rare glauconite grains and blackened particles. Large benthic foraminifers are scattered throughout.
The sediment is moderately to strongly bioturbated, and burrows are commonly filled with packstone to grainstone of very fine to medium sand size composed of mainly planktonic foraminifers. Some burrows, 4-5 cm across and with diffuse outlines, are probably Thallasinoides.
The lower part of Subunit IB is slump folded (Fig. F5). Disharmonic and isoclinal folds are present, usually outlined by thin bands of white nannofossil ooze with a mudstone texture. All burrowing is considered to be preslumping.
The contact between Units I and II is an erosional surface at the top of a white nannofossil ooze with a mudstone texture that is overlain by light gray, grainy planktonic foraminiferal ooze in Cores 182-1133B-4H and 182-1133C-3H. This boundary is recognized in both Holes 1133B and 1133C. The fact that the sediments beneath this boundary are slightly more lithified suggests partial early marine cementation. The sediment texture is matrix supported (mudstone to wackestone). A minor firmground is recognized in Section 182-1133B-4H-2, 21 cm, but no lithologic change is present.
The major components of the matrix are calcareous nannofossils, together with planktonic and benthic foraminifers, tunicate spicules, and sponge spicules (see "Site 1133 Smear Slides"). Dolomite rhombs are present in trace amounts. Components of the >63-µm fraction are abundant planktonic foraminifers, common sponge spicules, and minor glauconite grains. Macrofossils are rare throughout Unit II.
The sediments of Unit II are moderately to strongly bioturbated. Burrows also occur as diffuse color mottling throughout this subunit, but distinct burrows are visible. The sediment infillings in these burrows are coarser grained than the surrounding sediments. Such infilling sediments have a packstone texture, and many of the burrows are rich in pyrite grains.
The boundary between Units II and III is a firmground at the top of an unlithified bioclastic wackestone that is overlain by white nannofossil ooze with a mudstone texture. This boundary is clearly recognized in Holes 1133B and 1133C.
Only the upper part of this unit was well recovered. The sediment is (1) gray to light gray, poorly sorted, unlithified bioclastic wackestone with very fine grained silt- to sand-sized particles; (2) gray, light gray to light olive-gray, uniform, unlithified to partially lithified bioclastic packstone with poorly to well-sorted silt- to sand-sized grains; and (3) gray to dark gray chert/porcellanite (silicified limestone with wackestone texture). Most sediments recovered were fragmented during drilling. Some porcellanite/chert fragments are draped by a thin layer of unlithified to partially lithified bioclastic packstone. We infer that the entire unit of packstone and chert consists of these sediments, with beds or lenses of preferentially silicified limestone (formerly nannofossil planktonic foraminiferal ooze/chalk), forming the bulk of the material recovered.
The matrix of unlithified bioclastic wackestone contains calcareous nannofossils, bioclasts, traces of benthic foraminifers, clay, dolomite, and some rock fragments (see "Site 1133 Smear Slides"). The coarse fraction (>63 µm) is dominated by bioclasts. Benthic and planktonic foraminifers are also present, as well as traces of echinoid spines and sponge spicules, all of which are overgrown by calcite cement. The coarse fraction (>63 µm) of unlithified to partially lithified bioclastic packstone contains dominant bioclasts, very small benthic foraminifers, sponge spicules, glauconite grains, and blackened grains.
Gray, fine-grained, laminated bioclastic grainstone and packstone/grainstone occurs in Cores 182-1133B-16X and 18X. Black particles and glauconite grains are present. Gray, fine-grained, silicified bioclastic packstone in interval 182-1133B-17X-CC, 0-16 cm, contains traces of planktonic foraminifers and glauconite grains. A thin section of Sample 182-1133B-17X-CC, 67-68 cm, contains 40% silt-sized dolomite rhombs (see "Site 1133 Thin Sections"). The silicified limestone (porcellanite/chert) has a very fine to fine-grained wackestone texture, with distinct light gray to white burrows filled by lithified to partially lithified bioclastic wackestone and nannofossil foraminiferal chalk with a packstone texture.
Recovery of Unit III was poor, and thus little information could be acquired regarding the sedimentary development of this part of the succession. Sediment composition indicates a mid-slope hemipelagic environment containing a mixture of pelagic particles and shelf-derived bioclasts. This interpretation is corroborated by the benthic foraminiferal assemblage, which indicates a middle to lower bathyal depositional setting for these deposits (see "Biostratigraphy").
A firmground forms the boundary between Units II and III, suggesting strongly reduced sedimentation rates. This level also coincides with a change to a more pelagic regime, as indicated by the calcareous ooze of Unit II. As a result, this firmground is interpreted as a flooding surface. Condensed sedimentation at the boundary between Units II and III is supported by the planktonic foraminiferal and calcareous nannofossil assemblage (see "Biostratigraphy").
An interruption of the pelagic sedimentation dominating during the Pleistocene is reflected by a slump in the basal part of Unit I. The redeposited sediments are calcareous ooze, indicating that middle Miocene deposits are not involved in the slump.
The remainder of Unit I consists of pelagic calcareous ooze. This middle and upper Pleistocene interval, however, is much reduced in thickness compared to other Leg 182 sites. Reduced sedimentation rates are also reflected by the firmground dividing Unit I. As Unit I corresponds to seismic Sequence 2, this firmground could represent the lateral equivalent of the intra-Pleistocene flooding surface found at other sites (e.g., Site 1130).