Abstract

Very high-resolution seismic facies, classified, mapped, and interpreted from 3.5 kHz echograms, reveal that turbidity-current, mass-transport, and bottom-current depositional processes have all contributed to the regional sediment distribution in the intraslope basin province of the northwest Gulf of Mexico. Piston cores from these deposits confirm the interpretations of the processes. Turbidity currents transport sands into the intraslope mini-basins via channels and canyons. A few turbidity-current pathways, such as Bryant Canyon, allow extensive volumes of terrigenous sediment to bypass through many mini-basins and be deposited beyond the Sigsbee Escarpment to form large submarine fans, such as Bryant Fan. Bryant Fan is a large mud-rich fan that extends hundreds of kilometers from the mouth of Bryant Canyon but has only one meandering channel on the modern seafloor that extends down the length of the fan. In contrast, the much smaller Rio Grande Submarine Fan is deposited on a plateau area of the continental slope. Prolonged 3.5 echo character and numerous small, unleveed channels suggest this is a sand-rich fan with a braided channel system. These two submarine fans appear to present unique architectural and growth patterns not previously described in the numerous fan descriptions of W.R. Normark or other workers. Thus, these two fans appear to represent two new types of fans, which may be related to the complex structures of the intraslope basin province. Mass-transport deposits (MTDs) are ubiquitous throughout the mini-basins. Extensive areas affected by MTDs also occur along the upper continental slope and at the base of the eastern portion of the Sigsbee Escarpment. Piston cores confirm that the majority of MTDs are debris flows, which are characterized by mud clasts of variable size, shape, and color. Most have a muddy matrix, but sandy debris flows also occur in a few mini-basins. Some cores show deformation, folds, and faults that indicate slump or slide deposits. The East Breaks Slide Complex is the largest MTD complex and extends downslope from the shelf edge for >100 km off central Texas. The western portion of the complex is slump and/or slide blocks and debris flows. In contrast, the proximal part of the eastern portion of the complex is characterized by a modern leveed turbidite channel system. However, extensive MTDs underlie the channel-levee deposits and occur at the seafloor on the distal part of the eastern portion of the complex. Three large regions of migrating sediment waves occur on the Sigsbee Abyssal Plain and eastern Bryant Fan and appear to have been formed by circulation of the Loop Current. Sediment waves also occur locally at the base of the Sigsbee Escarpment in conjunction with previously reported erosional furrows.

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