Central Louisiana Deep Water: Structural Provinces and Depositional Patterns

Rowan, Mark G.¹; Hutton, Bob ²; Sandberg, Andy ²; Anderson, Dave ²; Mozer, Ed ^2
1 Rowan Consulting, Inc., Boulder, CO.
² Samson Offshore Co., Houston, TX.

Green Canyon and NW Atwater Valley, in the central Louisiana deepwater, are divided into three structural provinces: a distal foldbelt, a narrow zone of turtle structures, and a more proximal region of expulsion rollovers. The foldbelt formed in response to gravity spreading of the margin and has a complex western boundary that trends NNW through central Green Canyon. Lesser amounts of shortening exist to the SW in Walker Ridge because slope failure occurred above more proximal canopies.

The turtle province has vertical feeders that are sometimes squeezed, whereas the rollover province has welded, basinward-leaning feeders and associated counterregional faults. We infer that the boundary between the two marks the paleo-toe-of-slope, with inclined diapirs forming on the slope and vertical diapirs forming on the abyssal plain. Although both provinces are in the translational domain of the failing margin, local extension, contraction, and strike-slip deformation occurred as primary minibasins jostled about with respect to one another during basinward translation.

Wilcox and Miocene strata are mostly at or above regional in the foldbelt province. This was an area of partially confined deposition, with topographic highs defined by diapirs and associated linear folds, depending on the timing of shortening. In the turtle province, strata are mostly at or slightly below regional. This area was characterized by unconfined deposition, with thickness patterns controlled by local diapiric highs and the timing of turtle formation. In both cases, extensive canopies were not emplaced until late in the Miocene.

In the rollover province, strata are mostly at or significantly below regional, and depositional patterns were markedly different and relatively confined. Canopies were being emplaced locally throughout the Miocene, with fairways in between the salt tongues, and basinward-shifting depocenters were bounded by inflated salt and arcuate systems of counterregional feeders and faults. Ponded turbidite facies were deposited in these slope minibasins, which are not in trap configurations. The primary targets are structural highs just basinward of the bounding feeders/faults, where fan lobes may have formed as turbidite flows diverged at the entry points into the next minibasins.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009