Site 1101 is located on the proximal part of sediment Drift 4 on the Antarctic Peninsula continental rise. The drift has an asymmetric profile in directions parallel and perpendicular to the margin, similar to Drift 7, which was drilled at Sites 1095 and 1096 (see "Background and Scientific Objectives"). Site 1101 lies on the gentler side of the drift, ~5.5 km northwest of the drift crest (Fig. F36). Previous seismic stratigraphic interpretations of this sedimentary body can be found in Rebesco et al. (1996, 1997).

Only one MCS profile, collected by the Osservatorio Geofisico Sperimentale of Trieste (Line IT92AW-114; Fig. F36; "Appendix" and Fig. AF1, both in the "Leg 178 Summary" chapter), crosses Site 1101. Regional cover does exist, however, and was made available during Leg 178 (Fig. F1; "Seismic Stratigraphy"  in the "Explanatory Notes" chapter). This data set has been used to establish the seismic stratigraphy described below. Individual laboratory (Hamilton Frame) measurements of P-wave velocity on cores recovered at Site 1101 (Fig. F31) have been used to estimate velocities and thus to assign depths to reflectors (Fig. F37).

Drilling at Site 1101 reached a depth of 217.7 mbsf. We identify three seismic units (Fig. F36; Table T19).

Seismic Unit I (0-79 mbsf) consists of parallel and subparallel high-amplitude and continuous reflectors that alternate with lower amplitude disrupted reflectors (Fig. F38). The sub-bottom 3.5-kHz profile, obtained by the JOIDES Resolution on approach to the site, penetrated approximately the upper 50 m of seismic Unit I (see Fig. F3). This profile shows higher and lower amplitude reflector packages in a cyclic pattern. The base of Unit I at Site 1101 is marked by a high-amplitude reflector that, southwestward, has lateral variations in amplitude and continuity. Although the overall external geometry of seismic Unit I at Site 1101 is of a sheet drape, it is 25-30 m thicker at the crest of the drift than at Site 1101 (Fig. F36).

Seismic Unit II (79-141 mbsf) is characterized by low-amplitude reflectors and is acoustically semitransparent (Fig. F38). Toward the crest of the drift, 0.4 km southwest of Site 1101, this unit is marked by parallel and subparallel continuous and disrupted reflectors with lateral variation in amplitude (Fig. F36). The base of Unit II at Site 1101 corresponds to a low-amplitude disrupted reflector that grades southwestward to a high-amplitude reflector that can be traced to the crest of the drift. Seismic Unit II is characterized by a sheet drape external geometry (Fig. F36).

Seismic Unit III (143-216 mbsf) extends to the base of the hole and is bounded there by a high-amplitude reflector. Internally, seismic Unit III is semitransparent with only one low-amplitude discontinuous reflector apparent in the MCS profile (Fig. F38). The thickness of seismic Unit III increases from 76 m at Site 1101 to ~200 m at the crest of the drift. The external regional geometry of Unit III is that of a wedge. Internally, the wedge is semitransparent with some higher amplitude reflectors that thin or pinch out or downlap the base of the unit in a seaward direction before reaching the location of Site 1101 (Fig. F36).

Drilling of Site 1101 placed some constraints on the nature and age of the seismic units defined above (Fig. F38). Several general observations can be made from the seismic profile across the drift site.

The overall sheet drape geometry of seismic Units I and II compares well with lithostratigraphic Units I (0-53.3 mbsf) and II (53.3-142.7 mbsf) (see "Lithostratigraphy"). Lithostratigraphic Unit I is a well-defined alternation of massive biogenic-rich and laminated terrigenous sediments. The cyclic pattern can be recognized in the sub-bottom 3.5-kHz profile (Fig. F3). Lithostratigraphic Unit II is a repetitive succession of laminated and foraminifer-bearing massive facies. Sediments from lithostratigraphic Units I and II are dominantly hemipelagic, deposited under a regime of low-density turbidity current flow and weak bottom currents (see "Lithostratigraphy").

The transition from seismic Unit II to Unit III corresponds to a marked change in lithologic character. Lithostratigraphic Unit III (142-216 mbsf) contains a 50-m-thick, massive clayey silt with low biogenic content and beds of diamict (see "Lithostratigraphy"). This unit has been interpreted to have formed by meltwater plumes and sediment gravity flows or turbidity currents during times of ice-sheet expansion (see "Lithostratigraphy"). The greater regional thickness of Unit III away from the site, compared to seismic Units I and II, suggests greater sedimentation rates during its deposition. The change in external geometry from a well-developed wedge in seismic Unit III to sheet drape in seismic Units I and II may represent a shift from a higher to a lower energy sedimentation environment.

The ages assigned to the seismic units recognized at Site 1101 (Fig. F38) are based on preliminary paleomagnetic data from drilled cores (see "Paleomagnetism"). Seismic Unit I is Holocene to late Pleistocene in age (0-1.1 Ma), seismic Unit II is late Pleistocene to late Pliocene (1.1-2.16 Ma), and seismic Unit III is late Pliocene (2.16-3.1 Ma).