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Sedimentological Nature of the Bryant Canyon Area, Northwest Gulf of Mexico
Forty-eight jumbo piston cores, up to 20 meters long, have been recovered in an attempt to reconstruct the paleosedimentological events that were acting in the Bryant Canyon area. Detailed descriptions and X-radiographs were made from seven cores located on the slope, the flanks, and the thalweg of the canyon. Eight sedimentological units were identified from the cores that strongly correlated with detailed bulk density profiles. Seven of the sedimentological units are related to sea level fluctuations, whereas the remaining one reveals the influence of slope instabilities caused by salt diapir activity. The lower three units are not clearly related to the recorded eustatic cycles, of the late Pleistocene up to Holocene, and there is confusion, whether they represent isotopic stages 3, 4, 5 and 6 or only 3 and 4. The lower unit is characterized by well-developed turbidites, indicating a stage of a low sea-level stand. This unit is covered by normal hemipelagic sediments (foraminifera ooze), indicating a climatic transition to an interglacial stage. The overlying unit is composed mainly by hemipelagic sediments of a pinkish to yellowish gray shade, interbedded by a few irregularly spaced depositions by nepheloid layers and/or very low density gravity flows. Due to its complex nature, it is not clear, whether this unit represents the upper half of middle Wisconsinan or early and middle Wisconsinan deposits. In contrast, the upper three units are strongly correlated to the isotopic stages 1 and 2 (late Wisconsinan up to present). The late Wisconsinan glacial stage is characterized by alternating deposits of hemipelagic sediments, deposits from nepheloid layers, and /or by very diluted sediment flows. The lack of turbidites, in this unit, indicates that the deformation of Bryant Canyon had started sometime before late Wisconsinan. Finally, highly laminated zones, containing rhythmites more than 6 meters thick, were observed in the upper (late Wisconsinan) and lower glacial units. The origin of the rhythmites is unknown but they may be the result of deposition by nepheloid layers, and/or by tails of turbidity currents, uniform deposition of sediments entrained in river plumes, detached turbidity currents, or aeolian processes.
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