Stratigraphic framework and origin of shallow geohazards on the upper slope, northeastern Gulf of Mexico

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Conference Proceeding

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Multidisciplinary analysis of a research borehole on the upper continental slope in Viosca Knoll block 774 suggests links between lowstand shelf-edge deltaic deposystems of the ancestral Mobile River and deep Gulf of Mexico fan deposition. Paleontology, C-dating, stable-isotopes, sedimentology, and seismic stratigraphy detail a significant break in depositional architecture 10-15 m below the seafloor. The apparent erosion or 'by-pass' surface is traceable down-slope as a distinctive higher-order seismic sequence boundary capping sand-rich lowstand clinoforms. Reflector signatures, seismic amplitudes, and reflector terminations immediately above the boundary define a gas-charged channel-levee system. Benthic foraminiferal faunas in the 19 ka BP clinoforms below the boundary record warmer than modern winter ocean temperatures and carbonate bank paleoenvironments. Biostratigraphic and isotopic correlations indicate that a widely reported Gulf of Mexico δ O glacial meltwater event (11-16 ka BP) is truncated at the boundary. Two modes of slope sedimentation are postulated for the northeastern Gulf: (1) accretionary progradation, with distal clinoform deposition, and (2) erosional by-pass, with development of leveed channels above truncated section. Channel-levee deposits and paleoecological reconstructions of lowstand sea temperatures and salinities offer evidence of a direct link between lowstand shelf-edge deltas and unconfined slope-fan deposits which, when gas or fluid-charged pose a significant geohazard. Our study confirms the utility of a sequence stratigraphic and regional paleoceanographic approach to the recognition of geohazards. 14 18

Publication Source (Journal or Book title)

Proceedings of the Annual Offshore Technology Conference

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