Seismic-stratigraphic analysis of shelf-margin delta/slope fan and basin floor fan on high-latitude and middle-latitude margins (Ross Sea, Weddell Sea and Alabama/West Florida shelf): Paleoclimatic and eustatic implications
Bart, Philip John
Anderson, John B.
Doctor of Philosophy
This dissertation consists of three chapters describing seismic stratigraphic studies in three very different continental margin settings. The first chapter discusses the northwestern Ross Sea, the second discusses the southeastern Weddell Sea and the third discusses the Alabama/west Florida margin. The purpose was to investigate stratigraphic relationships between deposition during glacial periods (i.e., eustatic lowstands) and interglacial periods (i.e., eustatic highstands) on high-latitude and low-latitude margins. The high-latitude Antarctic margin is of particular interest because it is over-deepened and surrounds a continent that is free of melt-water. Because of these factors, the shelf/shelf-edge were not subaerially exposed and fluvially incised during eustatic lowstands. Seismic-stratigraphic analysis of the southeastern Weddell and northwestern Ross Sea margins shows that sediments were sequestered in pre-existing glacial troughs or upper-slope fans, at the mouth of glacial troughs. Locations of trough fans and trough mouth fans were strongly controlled by the location of ice streams. This point-source component of stratal architecture contrasts with the implicit line-source assumption that dominates recent thinking of Antarctic stratal development. Point-sourced trough mouth fans are relatively stable features, but as evidenced in Weddell Sea, they have experienced intermittent large-volume collapse. Upper-slope collapse is predicted to have been related to a dramatic change in over-burden, initiated early in an interglacial period following a long-duration glacial period. Interglacial shedding contrasts with models of low/middle-latitude sedimentation, which suggest that the basin is sediment starved during the interglacial. Seismic stratigraphic analysis of the Alabama/west Florida low-subsidence, middle-latitude continental margin indicates that upper-slope shelf-margin deltas have remained intact throughout the glacial cycle, in spite of widespread subaerial exposure. It is concluded that Pleistocene (?) relative-sea-level fall was insufficiently rapid to initiate major bypass of the upper slope. Therefore, other factors (antecedent topography, salt tectonics and growth faulting) are deemed to be more important initiators of upper-slope canyon formation on the middle-latitude margin.