Near-surface Sediment Structures at Cold Seeps and their Physical Control on Seepage: A Geophysical and Geological Study in the Southern Gulf of Mexico and at the frontal Makran Accretionary Prism/Pakistan

Abstract

Mainly high resolution multichannel seismic and bathymetry data were used to study near-surface seismostratigraphy, structure and seismic fluid-indicators in two seepage provinces: Campeche Knolls, southern Gulf of Mexico and the frontal Makran/Pakistan. Campeche Knolls is a salt tectonic province. The study specifies the deformation sequence since the Late Tertiary, with initial active salt diapirism, followed by salt evacuation. This sequence prescribes the subsurface structural styles in the area. These structures in turn cause (1) accumulation of heavy petroleum in very shallow depth, and precipitation of asphalts on the seafloor; (2) different aerial distribution of seep sites atop different knolls. The frontal Makran lies along an accretionary margin, directly behind the deformation front, with accreted sediments since ~ 3 Ma BP. My study outlines a scenario for initiation of a thrust/fold motif at the deformation front. This motif is then modified by further faulting and sedimentation. Hydrocarbons are accumulated in those shallow folds, and in turn trigger seepage above: a more passive-margin like fluid seepage style is revealed.