AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
A Comparison of the Geometries of Two Plio-Pleistocene Shelf Margin Delta Sequences, Vermilion South Addition and Northeast Garden Banks, Gulf of Mexico
(1) University of Houston, Houston, TX.
Shelf margin delta systems are the result of the progradation of sediment to the shelf edge during a period of low relative sea level, a depositional system that has few modern proxies. The present-day Gulf of Mexico contains numerous Plio-Pleistocene shelf margin deltas, many of which have been deformed extensively by the underlying Louann Salt. Two of these vertically stacked delta sequences, located in the South Vermilion Addition and northeastern Garden Banks, have been described using 3D seismic data and well logs. They are found in a salt mini-basin about 160 km off the Louisiana coast in the Gulf of Mexico.
The lower deltaic sequence contains a wave-influenced delta with burgeoning muddy-silty clinoforms, scoured by a mass transport complex. This delta contains a sprawling network of tributive shelf and slope channels that feed past the edge of the dataset into deeper waters. The shelf-slope break of this facies was eroded by a sandier slump-type mass transport complex containing normal faulting at its head and thrust faults at the toe. Over this, a thin sandy, late-lowstand river-dominated delta prograded, lobate in shape and connected to a clearly-imaged single trunk channel that siphoned sediment over the shelf-slope break. This delta system is onlapped by a transgressive belt of heterolithics in the distal margin of the delta (Trangressive Systems Tract). This system is capped by a maximum flooding surface.
The smooth-fronted upper deltaic sequence comprises a second lowstand and contains clearly imaged muddy-silty clinoforms that show some reworking of sediment in the more proximal areas of the delta. Both of these delta sequences contain complex systems of tributive shelf and slope channel systems that extend from the delta front and into the deeper upper slope and basin. Within the clinoforms extending the length and breadth of the mini-basin is an intricate network of shelf and slope channels that flush sediment directly from the most proximal end of the basin straight to the continental slope, and presumably, to the abyssal plain as a deepwater fan. Understanding the sequence stratigraphy and 3D seismic architecture of shelf margin deltas and their corresponding channel systems will further our understanding of the means by which reservoir-quality sediments are deposited on the continental shelf and transported to deepwater systems.