Sites 1095 and 1096 are located on a hemipelagic sediment drift on the continental rise off the northwestern Pacific margin of the Antarctic Peninsula (Fig. F1). These two sites are complementary and together cover the last 10 m.y., which spans most of Antarctic Peninsula glacial history. The expanded upper part of the sedimentary section within the drift was obtained at Site 1096, close to the crest of the drift, and the lower part of the drift section was obtained at Site 1095, where the overlying sediments are thinner than at the drift crest.
The 570-m-thick sedimentary section extends from the Holocene to the early late Miocene. This section is composed of alternations of predominantly fine-grained terrigenous and hemipelagic deposits and is divided into three depositional units (Shipboard Scientific Party, 1999b). The uppermost 50 m consists of laminated and massive, often extensively bioturbated, diatom-bearing silty clays. Lithostratigraphic Unit II extends from 50 to 435 meters below seafloor (mbsf) and consists mainly of green laminated silts and muds of Pliocene and late Miocene age. Mean sedimentation rates vary from ~2 to 11 cm/k.y., based on the magnetostratigraphic record (Shipboard Scientific Party, 1999b). The sediment cores exhibit meter-scale cycles between structureless, intensely bioturbated mud sections and sections of abundant thin silt laminae (distal turbidites). These alternations are interpreted as glacial cycles that controlled sediment supply (Shipboard Scientific Party, 1999b). Longer-period variations in construction of the continental shelf may be reflected in coarsening- and fining-upward trends. Sediments below 435 mbsf consist of nonbioturbated parallel-laminated siltstone-claystones. This facies (thin-bedded turbidites) does not show the second-order cyclic pattern observed in overlying sediments, which may be significant for understanding glacial history. Sedimentation rates are higher, reaching 12 cm/k.y.
The 607-m-thick sedimentary section extends in age from the Holocene to the early Pliocene (~4.7 Ma). Sediments are predominantly fine grained and terrigenous and are divided into three depositional units (Shipboard Scientific Party, 1999c). Unit I (0-33 mbsf) consists of laminated and massive, often intensely bioturbated, diatom-bearing silty clays of Pleistocene age. Unit II is an upper Pliocene to Pleistocene partly turbiditic succession some 140 m thick (33-173 mbsf) with a generally low calcareous biogenic component. Sedimentation rates average 9 cm/k.y. Sediments below 173 mbsf (Unit III), Pliocene in age, exhibit alternations of very thinly laminated and generally nonbioturbated clays and intensely bioturbated homogenous silty clays with a higher biogenic component. Overall, Unit III has a sedimentation rate of 18 cm/k.y.
In Units II and III, the alternation of laminated sediments (interpreted as turbidite facies) and bioturbated hemipelagic facies records cyclic fluctuations in sediment supply and transport processes. Some of these fluctuations may be related to glacial-interglacial cycles along the Antarctic Peninsula margin, but longer-period cycles appear to exist.