MARINE ICE-SHEET DECOUPLING AS A MECHANISM FOR RAPID, EPISODIC SEA-LEVEL CHANGE - THE RECORD OF SUCH EVENTS AND THEIR INFLUENCE ON SEDIMENTATION

Unlike terrestrial ice sheets, marine ice sheets display more sensitivity to sea level than to climate, and they are capable of rapid mass wasting. This mass wasting involves ice shelf decoupling from the sea floor and rapid collapse, followed by "drawdown" of the ice sheet. Glaciologists argue that the marine ice-sheet decoupling mechanism could cause sea-level rises of a few meters within several hundred years. Information regarding late Wisconsinan-Holocene glacial history suggests that ice-sheet deterioration did not occur at a steady rate. Studies of the Antarctic continental shelf indicate ice sheets grounded over large portions of the shelf during the late Wisconsinan glacial maximum, and that their retreat from the continental shelf was rapid. A study of the Trinity/Sabine incised valley of the Texas continental shelf yields a continuous record of Holocene sedimentation and sea-level change. Paired upper-bay and tidal-inlet estuarine systems reflect periods when relative sea level was either at a still-stand or slowly rising. The flooding surfaces of back-stepping parasequences reflect periods of rapid sea-level rise. Large sand bodies on the adjacent shelf, used to derive previous sea-level curves for the region, may represent former shoreline deposits, but they also show extensive reworking. Therefore, the curves generated from studies of these sand bodies are inaccurate. Marine ice sheets have existed in Antarctica since at least the late Eocene, so this mechanism for rapid sea-level rise has been active throughout much of Cenozoic time, as well as during older glacial episodes.