Seismic data from the Northern basin, Ross Sea, record extreme expansions of the East Antarctic Ice Sheet during the late Neogene

Approximately 3700 km of intermediate-resolution single-channel seismic data from the Northern basin were analyzed to investigate the late Neogene history of East Antarctic Ice Sheet (EAIS) grounding events on the shelf, and to evaluate how glacial unconformities on the shelf are manifested on the upper slope. The Northern basin was chosen as the site of this study because ice-sheet reconstructions show that the basin received sediment by ice emanating from East Antarctica. In addition, seismic correlations to DSDP Site 273 suggest that a relatively thick late Neogene section exists on the basin's outer shelf and upper slope. On the Northern basin shelf, glacial unconformities exhibiting broad, low-angle relief, topset truncation, and cross-cutting relationships reveal a dynamic history of expansions and contractions during which the EAIS was larger than present on at least eight occasions during the late Neogene. On the upper slope, the correlative conformities of the glacial unconformities are indistinct reflections within thick trough-mouth fan (TMF) depocenters at the mouths of Drygalsky and Joides basins. The glacial unconformities and correlative conformities define TMF sequences, and each TMF sequence contains several topset-truncated prograding-slope reflectors. We infer that the correlative conformities on the continental slope correspond to the interface between prograding glaciogenic deposits (glacial maximum) and diatomaceous glacial-marine sediments (glacial minimum). The seismic-stratigraphic analysis and regional mapping indicate that the upper slope does not contain a more complete late Neogene section than that which exists on the shelf. We infer that diatomaceous glacial-marine sediments on the slope may be relatively undisturbed. and hence may provide a means of dating the TMF sequences. It is hoped that these results will stimulate efforts to core the late Neogene section in the Northern basin TMFs to investigate how these EAIS expansions and contractions relate to other records of late Neogene climate and eustasy. (C) 2000 Elsevier Science B.V. All rights reserved.