The first core recovered from Hole 1155A was a wash barrel that sampled the interval from the seafloor to 177.3 mbsf. Although all the sediment recovered is clay, we have subdivided the recovered material into four informal zones based on variations in color and composition (Fig. F22). These zones imply no stratigraphy, except that, based on the lack of evidence of severe drilling disturbance throughout most of the section, the sediment types have not been displaced vertically relative to each other.
Zone A (0.0-0.57 m in Section 187-1155A-1W-1) is a siliceous pelagic clay. The upper 50 cm of this interval is very soupy and contains abundant, coarse, sand-sized clay pellets. The lower 7 cm of this interval is significantly less disturbed by drilling and has a slightly lighter color. At 57 cm there is a sharp contact with Zone B. The contact is marked by a break in the core, suggesting an interval of no recovery rather than a stratigraphic contact. Zone B is a homogeneous dark grayish brown siliceous clay, which extends to 70 cm in Section 187-1155A-1W-2. The bottom of Zone B is marked by a planar but diffuse (>1 mm) contact with medium light brown calcareous clay. The calcareous clay marks the top of Zone C (0.70-0.90 cm in Section 187-1155A-1W-2). Zone C was defined because, below a 5-cm-thick calcareous interval, another 10-cm-thick siliceous clay, devoid of calcite, is present. This is distinctive in that, in all the sediments we have recovered so far, the division between siliceous clay and calcareous clay is a compositionally well-defined break. Zone D (Section 187-1155A-1W-2, 90 cm, to the bottom of the core) is all calcareous clay but exhibits distinct to subtle color changes. Within this interval are several 3- to 25-cm-thick layers of medium dark brown clay intercalated with intervals of light brown clay. Most of these intervals have planar but diffuse (>1-2 mm) contacts, although in Section 187-1155A-1W-4, a 1-cm-thick dark layer is dipping about 20° across the core face and also has an 0.5-cm offset apparent in the cut face of the core. At 23.5 cm in Section 187-1155A-1W-4 is a disseminated, very fine grained black silt marking the top of a 0.5-cm-thick very light yellow-brown layer. This layer has diffuse upper and lower contacts (>1 mm) with the light brown calcareous clay above and below.
A smear slide from Zone A contains abundant honeycomb-textured fragments of radiolarians, as well as colorless translucent spines. Rare cigar-shaped microfossils with visible septa are also present. All clay pellets from Zone A completely disaggregate in water, suggesting that they formed during drilling. Zone B and the siliceous sediment from Zone C contain 1%-2% subrounded brown volcanic glass fragments (3 to 4 µm across) and much more rare colorless crystal shards and siliceous microfossil fragments. The calcareous clay of Zones C and D contains abundant microfossils and <1% brown volcanic glass and crystal shards. Abundant calcareous microfossils predominate in the thin light yellow-brown interval in Section 4, to the exclusion of most other components in other sediment intervals from this core. In a smear slide, the thin disseminated black silt at the top of this layer appears to consist of 25- to 50-µm-sized fragments of dark volcanic glass. A 2-cm fragment of altered volcanic glass was embedded in the sediment at the bottom of the core.
Hole 1155B recovered 28 cm of dark brown homogeneous siliceous clay, similar in appearance to the material in Zone B of Hole 1155A. No calcareous clay was recovered from this hole.