--> --> Influence of Local Topography on Gravity-Driven and Current-Controlled Sedimentary Processes

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Influence of Local Topography on Gravity-Driven and Current-Controlled Sedimentary Processes

Abstract

Gravity-induced sedimentation in deepwater settings has been investigated for decades. However, the magnitude of influence exerted by current-controlled processes in deep water is only beginning to be realized. Researchers have shown that the hydrodynamic behavior of deep waters (below 1000m) in the Gulf of Mexico (GOM) is dominated by topographic Rossby waves. These waves run along the slope, trapped by topographic barriers such as the Sigsbee Escarpment. They result in increased current velocities that can reach up to 90cm/s at water depths of 2000m and are believed responsible for a variety of erosional and depositional features associated with the escarpment. A survey of current-deposited deepwater sediments was undertaken to better understand the locations, sedimentology and morphology of sediment wave fields, as well as inform on the nature of topography in and around known modern and ancient wave fields. In addition, detailed analyses using high resolution subbottom profiler records of shallow sedimentary sequences (last ∼25,000 years) were performed in different provinces of the ultra-deep central GOM. Our goal was to examine the manner in which deep seafloor topography influences both gravity-induced and current-controlled sediment movement in basins. Of the over 60 instances documented worldwide of current-driven sediment waves, 20% are considered sandy. Observations by the authors suggest that the shape and nature of topography influences both gravity- and circulation-driven currents which in turn, drive the apparent associations of fill architecture and topography. Although mass transport deposits are higher in number, there is no denying their close association with sediment wave fields, which are frequently found, here and worldwide underlying mass transport deposits. The worldwide drivers of ocean current behavior are poorly defined, but erosion is seen frequently in association with regional seafloor barriers, such as the Sigsbee Escarpment, and is attributed, not always to global drivers, but here, to more localized increases in flow confinement and subsequent enhanced velocities and strengths. A truer understanding of the power of deep-ocean currents to move and mold sediments, and induce mass failures will lead to a much more complete process and reservoir model of these complex environments. This paper will review a variety of settings where gravity- and current-induced sedimentation has interacted with topography.