Architectural styles of glacially influenced marine deposits on tectonically active and passive margins

Abstract

Abstract The ancient glacial record is dominated by glacial marine sediments which have accumulated on continental shelves and slopes. Stratigraphic models showing the gross architecture of the principal glacial geological deposits are developed from onshore and offshore studies of Late Cenozoic deposits in the Gulf of Alaska and across the Scotian Shelf and Slope. These should be applicable to other areas, and should be of use in establishing the tectonic setting of glacially influenced marine deposits in the ancient record. The processes of deposition (including ice-rafting, suspension rainout, and turbidity currents) are the same on both tectonically active and passive margins, yet the large-scale depositional architecture of glacial marine deposits on both types of margin differs because sediment preservation is strongly influenced by the impact of tectonics on local relative sea-level changes. Ice sheets can destroy any glacial marine deposits on the continental shelf, provided they can advance across it. Eustatic sea-level falls during world-wide glaciations, so that ice sheets may advance across passive margin shelves, whereas rapid subsidence at active margins may restrict glacial advance into the offshore, thereby preserving shelf deposits. As a result, over a long sequence of glacial and interglacial events, slope deposits will be selectively preserved on passive margins, whereas both shelf and slope deposits will be preserved on active margins. Furthermore, as the shelf builds up and out in the active margin, the importance of shelf deposits may be expected to increase upsection.