Abstract

High-resolution bathymetry is used to derive a new structural interpretation of a submerged inverted graben on the English Channel shelf (northwest Europe). The bathymetry provides a continuous plan-view image of the bedrock geology and resolves fine structural detail, particularly in areas of steeply dipping strata where traditional seismic imaging fails. The imagery, combined with shallow core, deep borehole, and two-dimensional seismic reflection data, shows a marked asymmetry in the bedrock outcrop and structural style, both across and along the axis of the basin. For example, the oldest synrift rocks crop out in a complex south-verging anticline along one margin, whereas more massively bedded younger rocks are folded into a simpler anticline at the other. Comparison of our observations with both recent analog modeling and a neighboring inverted basin highlights the importance of the mechanical properties of the basin stratigraphy in controlling the structural development. We conclude that the inversional asymmetry developed because of the distribution of strong competence contrasts within the synrift fill.

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