Morphology and stratal geometry of the Antarctic continental shelf : insights from models

This paper is not subject to U.S. copyright. The definitive version was published in Geology and Seismic Stratigraphy of the Antarctic Margin, edited by Peter F. Barker and Alan K. Cooper, 1-24. Washington, DC: American Geophysical Union, 1995. ISBN: 0875908845

Supported by NSF grant OPP-20462and the U.S. Geological Survey Marine and CoastalProgram.

Reconstruction of past ice-sheet fluctuations from the stratigraphy of glaciatedcontinental shelves requires understanding of the relationships among the stratal geometry,glacial and marine sedimentary processes, and ice dynamics. We investigate the formation ofthe morphology and the broad stratal geometry of topsets on the Antarctic continental shelfwith numerical models. Our models assume that the stratal geometry and morphology areprincipally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the seaward edge of the grounded ice. The location of the grounding line varieswith time almost randomly across the shelf. With these simple assumptions, the models cansuccessfully mimic salient features of the morphology and the stratal geometry. The modelssuggest that the current shelf has gradually evolved to its present geometry by many glacialadvances and retreats of the grounding line to different locations across the shelf. Thelocations of the grounding line do not appear to be linearly correlated with either fluctuationsin the δ180 record (which presumably represents changes in the global ice volume) or with theglobal sea-level curve, suggesting that either a more complex relationship exists or localeffects dominate. The models suggest that erosion of preglacial sediments is confined to theinner shelf, and erosion decreases and deposition increases toward the shelf edge. Some of thedeposited glacial sediments must be derived from continental erosion. The sediments probablyundergo extensive transport and reworking obliterating much of the evidence for their originaldepositional environment. The flexural rigidity and the tectonic subsidence of the underlyinglithosphere modify the bathyrnetry of the shelf, but probably have little effect on the stratalgeometry. Our models provide several guidelines for the interpretation of unconformities, thenature of preserved topset deposits, and the significance of progradation versus aggradation ofshelf sediments.