Maureen White

2002-The Michael J. Keen Award

The MacEachern - Ponsford Memorial Award - 2003

Nova Scotia and its continental margin have endured numerous shelf crossing glaciations and eustatic sea level lowstands during the Cenozoic. As a result, the sedimentary sequence is not well preserved and therefore the geologic record is not well understood. In the deep water of the Scotian Slope, on the other hand, there is an opportunity to study the preserved sedimentary sequence. The objective of this study is to apply high resolution, two dimensional seismic surveying on the Scotian Slope to understand Cenozoic depositional environments and their associated sedimentation processes, in relation to glacial and non glacial epochs, and sea level change. The Mohican Channel area is an ideal site for this study because it contains a comprehensive record of the Plio Pleistocene sedimentary sequence. Within the study area, an experimental seismic system known as the digital deep towed hydrophone (DDH) was tested in an effort to improve seismic resolution and therefore interpretation. The DDH consists of a source towed at the sea surface and a receiver towed at depth. This unconventional geometry is predicted to result in greatly improved vertical and horizontal resolution compared with its conventional seismic equivalent. Trial seismic lines have proven to significantly increase near surface resolution; however, imaging at depth within the section is lost in comparison to conventional surface seismic reflection profiles. For the objectives in this study, conventional seismic profiles, with greater imaging depths, were the most useful. These profiles allowed definition of five seismic facies and regional correlation of six seismic horizons. These are broadly grouped into two stratigaphic units which correspond to pre glacial and glacial/interglacial periods. Prior to the onset of glacial influence, at approximately 0.45 Ma, major sedimentation processes included hemipelagic sedimentation, unconfined low density turbidity current deposition, and mass transport deposition, as interpreted from the seismic data. Throughout the mid Late Pleistocene glacial periods, deposition was dominated by turbidity currents derived from high volumes of glacial discharge. Interglacial stages were dominated by hemipelagic sedimentation. The Mohican Channel incises the entire Pleistocene section suggesting it is at least late Pleistocene in age. The channel is interpreted as a major glacial outwash conduit that was active during the last glacial maximum and possibly during each shelf crossing glaciation. Thickness of the Pliocene stratigraphy does not vary over the slope, indicating that pre glacial deposition was uniform over the study area. In comparison, mid late Pleistocene stratigraphy thins both downslope and westward towards Mohican Channel, indicating preferential deposition on the upper slope from a northwestern sediment source during glacial periods. Approximate sedimentation rates show that deposition during glacial influence was at least double that of non-glacial periods, indicating that glaciation plays an important role in the evolution of deep water sediments on the Scotian Slope.

Keywords:
Pages: 71
Supervisors: David Mosher (GSC-A) / Patrick J. C. Ryall / Grant Wach