Ice-sheet evolution in James Ross Basin, Weddell Sea margin of the Antarctic Peninsula: The seismic stratigraphic record

Abstract

The stratigraphic architecture of the James Ross Basin, NW Weddell Sea continental shelf, shows three major phases of deposition: preglacial, ice-sheet growth, and ice-sheet dominated. The preglacial phase shows stratigraphic sequences that are similar to low-latitude margins. During the ice-sheet growth phase, there is evidence for initial ice-sheet grounding in the southern part of the basin, which migrated in steps northward. Sediment supply was also high during the ice-sheet growth phase. During the ice sheet–dominated phase, both north and south parts of the basin inherited all the classic features indicative of glacial strata: large glacial troughs hundreds of meters deep and tens of kilometers wide, truncation of sequences overlain by chaotic seismic facies and topped with coherent laminated reflections, and an oversteepened continental slope. The James Ross Basin strata are divided into five units (S5–S1). Each unit is characterized based upon seismic facies and stratigraphic architecture, and the age of each unit is inferred from a seismic stratigraphic age model. End-member strata (S5 and S1) were drilled and dated during SHALDRIL and help to constrain this age model. In total, 34 grounding events of the Antarctic Peninsula Ice Sheet (APIS) are recorded on the continental shelf. This is similar to the 31 grounding events imaged on the Pacific side of the peninsula. Ice grounding on the continental shelf is shown to have occurred as early as late middle Miocene to early late Miocene in the southern part of the basin. The ice sheet advanced northward to encompass the northern peninsula by late Miocene time. The seven oldest glacial unconformities are believed to predate all previously identified unconformities on the peninsula continental shelf. An expanded section of late Pliocene–Pleistocene deposits shows a minimum of 10 grounding events; this record more closely matches the deep-sea oxygen isotope record than previous seismic studies of Antarctic margins have shown.