According to Sawyer, Whitmarsh, Klaus, et al. (1994), the lithostratigraphic succession could be subdivided into four lithostratigraphic units on the basis of changes in lithology and the degree of lithification.
The regional stratigraphic correlation between lithologic Units I and II is shown in Figure 4 (Sawyer, Whitmarsh, Klaus, et al., 1994). At Sites 897 through to 900, the lithostratigraphy consists of an upper turbidite-pelagic sequence (Unit I and Subunit II A) and a lower contourite-turbidite-pelagic sequence (Subunit II B) with a decreased carbonate content. The two sequences contrast sharply in terms of evidence of reworking by contour currents (which are present only in the lower sequence) and in the abundance of siliceous allochems (virtually absent in the upper sequence) (Sawyer, Whitmarsh, Klaus, et al., 1994).
The two lithostratigraphic sequences recovered at Site 901, consisting of a thin film of Lower Cretaceous clay followed by lower Tithonian black clay, silt, and sandstone (Shipboard Scientific Party, 1994e), could not be correlated with the other sites.
Unit I is characterized by terrigenous turbidites, the product of turbidity current deposition on an abyssal plain, and pelagic sediments. Pleistocene to Pliocene terrigenous turbidite sequences (Unit I) comprise 292 m at Site 897 and 163 m at Site 898. Their lithologies are described in detail by Milkert et al. (this volume). Only 22 m of Unit I terrigenous turbidites and pelagic sediments were recovered at Hole 899A because the hole was washed down to 82 m. Unit I at Site 900, although containing both turbiditic and pelagic facies, shows little siliciclastic sand in comparison to its counterparts at Sites 897, 898, and 899. At Site 900, the unit is divided into three Subunits. Subunits IA and IC contain turbiditic and pelagic sediments, and are separated by the pelagic nannofossil clays and oozes that comprise Subunit IB (Shipboard Scientific Party, 1994d).
Major lithologies in Unit II comprise calcareous claystones, claystones, silty claystones, siltstones, and sandstones. They reflect deposition on an abyssal plain setting and reworking by contour currents. The lower Pliocene to middle Eocene Unit II at Site 897 consists of 328 m of muddy turbidites and calcareous contourites. Here, Unit II was subdivided into three Subunits on the basis of color and the proportion of claystone vs. coarser-grained lithologies (Sawyer, Whitmarsh, Klaus, et al., 1994).
At Site 898, lithologic Unit II comprises 177 m of middle Miocene to upper Oligocene sediments and is divided into two Subunits. Subunit IIA shows homogeneous clay lithologies, whereas Subunit IIB, with its upward-darkening alternations of carbonate-rich and relatively carbonate-poor sediments containing biogenic siliceous material, contrasts with the clearly turbidite-related lithologic association of Unit I. This unit seems to be a combination of possible turbidites and contourites such as the ones described by Stow and Piper (1984). At Site 899, the sedimentary sequences of this unit consist of 211 m of lower Pliocene to upper Eocene calcareous claystones, claystones, silty claystones, siltstones, and sandstones. Subunit IIA (early Pliocene to middle Miocene) consists of intensely bioturbated brown claystone with scattered turbidites. Subunit IIB is dominated by greenish gray upward-darkening sequences with basal fine sandstone beds. The tops often show "lag deposits" or large foraminiferal tests. All these features point to reworking by contour currents, as described by Stow and Piper (1984); a few mud turbidites are intercalated (Sawyer, Whitmarsh, Klaus, et al., 1994).
At Site 900, Unit II is dominated by claystone, claystone with silt/silty claystone, nannofossil claystone, and nannofossil chalk. Foraminifer-rich sandstones and calcarenites occur as a distinctive minor lithology in Subunit IIA and form as much as 20% to 30% in some cores in Subunit IIB, where they are often cemented by calcite. Both contain upward-darkening sequences and are interpreted as deposits of turbidity flows and contour currents.
Unit III is mainly siliciclastic in composition and occurs at Sites 897 and 899. It reaches a total thickness of 30 m at Site 897 and around 10 m at Site 899. The unit was divided into two Subunits. Subunit III A at both sites is composed entirely of brown terrigenous clays that are of latest Maastrichtian-early Eocene age (Kuhnt and Collins, this volume). Subunit IIIA is interpreted as the product of slow accumulation of clay in an oxygenated environment. The clay and fine silt are most likely continental material supplied by low-density turbidity flows or by the nepeholoid layer of contour currents. At Site 897, Subunit IIIB is characterized by upward-fining sequences of carbonate pebbles and gravel conglomerates, coarse sandstones, sandstones, and silty claystones of Aptian age (de Kaenel and Bergen, this volume). Lithologies in Subunit IIIB at Site 899 show great variability, and include variegated sandstone, white highly altered volcanic ash, laminated brown claystone, lighter colored silty claystone with black concretions, and poorly cemented, multicolored, polymictic, clayey conglomerate. Highly altered basaltic clasts are present in the graveland sand-sized fractions. The highly variegated conglomerates (Subunit IIIB) are of Campanian/late Maastrichtian (Gervais, this volume) to middle/late Eocene age (Kuhnt and Collins, this volume). This Subunit is interpreted as a mixture of fine-grained pelagic deposits and high-density turbidity currents or fluidized sand-silt-clay debris flows that developed on relatively gentle slopes.
The late Aptian to late Hauterivian age Unit IV (de Kaenel and Bergen, this volume) comprised a maximum of 38 m (Hole 897D) of serpentinized peridotite between intervals of siliciclastic and carbonate lithologies (Fig. 5) and directly overlies acoustic basement.
At Site 899 Unit IV comprised 188.2 m of an unusual sequence of rocks with three different lithologies: (1) three serpentinite breccias that range in thickness from nearly 100 (upper breccia) to less than 10 m (middle and lower breccia), described in further detail by Shipboard Scientific Party, 1994c, Comas et al. (this volume), and Gibson et al. (this volume); (2) an association of claystones, calcareous claystones, soft, altered, and deformed serpentine masses, and minor siltstone that is intercalated between the breccia intervals and sections of serpentinized ultramafic rocks; and (3) discrete sections of unbrecciated serpentinite, serpentinized peridotite, gabbro and basalt fragments. The basalt fragments are of variable composition and some occur within the claystones and the soft, altered, and deformed serpentine masses. The breccia units are poorly sorted and are composed of ultramafic clasts of a restricted compositional range.
At Site 897, no unit clearly analogous to the serpentinite breccia at Site 899 is well developed. Nevertheless, certain broad similarities can be identified between lithologic associations in Unit IV. Serpentinized peridotite, ranging from 15 cm to 1.5 m thick, is sandwiched between dark-green claystone and a variety of other lithologies, including various breccias at Site 897 (Shipboard Scientific Party, 1994a). Sedimentary intervals yield ages that young upwards and range from late Hauterivian to early Aptian. Deposition at this site occurred at the foot of a fault escarpment that exposed serpentinized peridotite basement during the Early Cretaceous.