AAPG ACE 2018

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Scaling Relationships Between Stratigraphy and Morphology of Submarine Channels

Abstract

Submarine channels are key elements of sediment routing systems and important hydrocarbon reservoir targets, but predicting the architecture and scale of channel deposits remains a challenge. From interpretations of seafloor bathymetry and previously published subsurface data, our work uses morphometrics and scaling relationships of levee-confined submarine channels to draw connections between channel-forming processes, active channel morphologies, and the dimensions of channel element deposits. Analysis of over 29,000 width and depth measurements from modern channels in five geographic regions shows that channels of widely varying dimensions (<100 m to >10 km wide) occupy roughly the same range of aspect ratios (10:1 to 100:1). This demonstrates a potentially universal, autogenic control on aspect ratio, which may be explained by feedback processes in levee growth and bank erosion. Channels in different geographic areas exhibit different ranges in width, suggesting that local, allogenic factors (e.g., gradient, sediment supply/caliber) control channel width, and that channel depth adjusts to maintain the preferred range of aspect ratios. We further interpret that thalweg and levee modifications may not be directly related, with the former driven by the basal, higher-concentration and higher-shear stress portion of a turbidity current and the latter by the dilute upper portion. This interpretation is supported by observations of an apparent lag in the adjustment of levee height to thalweg steepness in channels with local gradient changes, and by the imperfect relationship between thalweg and levee crest sinuosity. A disconnect between levee- and thalweg-modifying flow processes would potentially produce channel-thalweg deposits that are smaller than expected from bankfull dimensions of seafloor channels. Integrating high-resolution bathymetry with subsurface data from preserved channel element deposits can be used to address this potential disparity. The quantitative morphometric relationships documented here in conjunction with subsurface comparisons can aid in predicting reservoir dimensions and volumes in ancient submarine channel systems where data resolution precludes direct measurement.