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Quantitative Seismic Geomorphologic Analysis of Early Pliocene-Age Fans Outboard of the Sigsbee Escarpment, Mad Dog Area, Northern Gulf of Mexico

Morgan, Jessica L.1; Wood, Lesli 1
1 Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin, Austin, TX.

The Mad Dog study area lies along the western edge of the middle Miocene to Pliocene-age, Atwater deep water fold belt. The data set includes ~2200 km sq. of 3D seismic data, along with information from several wells. Logs show these deposits are characterized by several hundred feet thick, sharp-based, basal coarse-grained fining up cycles. Sandy basin floor fans, mass transport complexes and small leveed channels comprise the major components of the system. Quantitative seismic geomorphologic analysis of these E. Pliocene fans can provide significant data for purposes of de-risking similar subsalt systems, building reservoir models of similar subsalt and non-subsalt systems and assessing the history of sediment pathways in this active salt tectonic province.

Two cycles of deep water fan development occupy the undeformed strata at the front of the modern salt sheet. The older Fan 1 initiates with a 400-700 meters (m) wide channel, with a meander belt over 6000 m wide and individual meander lengths of ~ 7000 m long. Channel sinuosity is approximately 2.53. This system is underlain by a large mass transport deposit and overlain by a second phase of lower sinuosity channel development. Fan 2 shows channels ~ 1200 meters wide with a narrower meander belt (~2-2.5 km wide). Sinuosity in the upper fan system is ~ 1.06. Several secondary, escarpment-front drainages riddle the area. They shows bright high amplitude reflectivity in the channel core, and appears to be draining into the main leveed channel system, sourced by an area wholly contained within the interchannel areas of the escarpment front. This particular system is ~ 8 km from end to end with a straight trunk drainage and up to three orders of bifurcation to the northwest. Bifurcation angles range from 37 degrees up to a 90 degree trellis pattern that may be influences by faulting. The channels themselves are very consistent width, averaging 261 meters.

Levees in all three of these systems appear well developed. They are all oriented generally north-northwest to south-southeast and appear to have been sourced by large drainages that were uninhibited by salt wall inflation at the time of deposition, an indication of the through-going sediment pathways that existed at Pliocene time in the area.


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