Abstract

Seismic facies in Gulf of Mexico intraslope basins reflect the interplay of a variety of deep-water depositional processes and the evolution of accommodation space on the slope. This interplay of processes results in a transition from an early, sand-prone ponded basin-fill succession (ponded facies assemblage) to a later shale-prone, slope-bypass succession (bypass facies assemblage). Convergent-baselapping facies in combination with localized chaotic and draping facies dominate the ponded facies assemblage. Stratigraphic relationships among these three units illustrate how fill-and-spill depositional processes occur within ponded-basin accommodation space. Convergent-thinning facies with widespread chaotic and draping facies dominate the bypass facies assemblage. These units represent filling of different types of slope accommodation space. The transition from ponded to bypass facies assemblages can be sharp or gradational over hundreds of meters. Transitions occurred across the central Gulf of Mexico during the late Pliocene between 2.0 and 1.8 Ma, and in the early Pleistocene between 1.2 and 1.0 Ma. Nearly synchronous transitions throughout basins in the upper to middle slope suggest that increased sediment supply, resulting from a second-order sea level fall, and capture of large drainage areas by the Mississippi River during the Pleistocene are the primary controls on development of this large-scale stratigraphic architecture.

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