Seismic Geomorphology and Stratigraphy of Incised Valleys in the Late Miocene Mississippi River Delta, Louisiana

Incised valleys are significant geomorphic features created when rivers incise into substrate in response to base level fall. We use a 1400 km² 3D seismic volume located under Breton Sound, LA, integrated with a selection of well logs to characterize the geomorphology and fill of 8 valleys present within the upper 1.5 kilometers of the seismic volume. Interaction between growth faults and these valleys is also evaluated. Seismic attributes used to image the valleys in planview, include: a) instantaneous sweetness, an attribute calculated as reflection strength divided by frequency; and b) similarity, an edge detection attribute. Additionally, inversion for an impedance volume was performed in order to provide lithologic constraint in the absence of well logs.

Valley fills are 1 to 5 kilometers wide, 30 to 50 meters thick, and imaged for distances up to 30 kilometers across the survey. Valleys in planview display a characteristic ‘scooped’ shape, interpreted as the time-transgressive composite erosion associated with laterally migrating channels. Eleven wells penetrate valleys and show a predominantly sandy fill with incision into thick, laterally extensive muds. We suggest that these muds are of marine origin and represent transgessive deposits.

The data images approximately 30 growth faults, some of which may have interacted with channels and affected valley morphology. In contrast to the majority of smaller distributary channels found within the survey, valleys appear to be steered by growth faults. This observation suggests that faults are able to affect the course of valleys to a greater extent than small channels. We propose that this is because valleys are long lived features which do not avulse before feeling the effect of shorter time scale faulting events.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California