Geologic Survey of the Ewing Bank, Northern Gulf of Mexico



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Located along the edge of the continental shelf in the northwestern Gulf of Mexico, the Ewing Bank is a significant geologic feature: yet, little information about the bank is generally available. This thesis represents a preliminary survey of the distribution and structure of the seafloor sediments that comprise the bank and the surrounding area. Two research vessels were utilized to accomplish the survey: the RV Gyre collected geologic cores and sub-bottom profiler lines courtesy of TDI-Brooks International and the RV Falkor collected multibeam echo sounder bathymetry courtesy of the Schmidt Ocean Institute. The bathymetry collected by the sub-bottom profiler and multibeam echo sounder data for this study is consistent with the coarser resolution data previously available. The pattern of seismic reflectors in the sub-bottom profiles indicated the orientation and type of faults as well as other structures. The geologic cores and sub-bottom profiler data helped to identify the different types and distributions of the sediments that made up this two terrace bank system. A core from the surface of the top terrace contained coarse carbonate sands while the seafloor surrounding this bank was comprised of firm clay sediment. The characteristics of surficial sediments on the second, deeper terrace were closer to those on the seafloor surrounding the bank than the top terrace of the Ewing Bank itself. This difference may reflect winnowing by the shelf edge currents interacting with the structure of the Ewing Bank together with the fact that the top terrace was subject to shallow water wave action and subaerial exposure during the lowstand of sea level associated with the last glactiation; while the surficial sediments of the second terrace were deposited since sea level rose after the end of the last glaciation. The features of the Ewing Bank compared well with those of the surrounding banks of the area. The results of this preliminary survey of the Ewing Bank contribute to the general understanding of the geologic features and biological habitat at the many banks in the north western Gulf of Mexico and the geologic processes that affect them.