AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Constraints on Sigsbee Salt Canopy Advancement and Its Implications for Neogene Deformation in the Northern Gulf of Mexico
(1) Geology, Washington and Lee University, Lexington, VA.
(2) INEXS, Houston, TX.
(3) ION Geophysical, Houston, TX.
The Sigsbee Salt Canopy represents the allochthonous contractional toe of the gravity-driven linked deformational system in the northern in the Gulf of Mexico. We present a regional synthesis of reimaged seismic reflection data and deepwater wells in the Keathley Canyon and western Walker Ridge protraction areas of the GOM. We conclude that while the canopy is an indirect measure of contraction from updip extension, the relationships observed provide constraints on the Neogene structural development of the central western GOM. The seismic data are newly imaged long-offset, long-record-length, regional seismic data that are processed utilizing Reverse Time Migration (RTM) throughout all stages of the imaging. These new data allow for better imaging of the subsalt reflector geometry and combined with paleontological data from deepwater wells enable us to construct a subcrop map of the frontal salt canopy. The frontal salt canopy has footwall cutoffs of lowermost Miocene age, located on average 70 km inboard from the Sigsbee Escarpment. These continental rise strata are generally continuous, mainly flat-lying strata up to Pleistocene age that subcrop under the canopy. From these cutoff positions we conclude an average salt-sheet advancement rate of about 3 mm/yr in the Keathley Canyon and western Walker Ridge areas from the beginning of the Miocene to the present. This represents a maximum advancement rate because unrecognized discrete sheets may have amalgamated. If that is the case, we estimate a lower limit for salt-sheet advancement would be about a third of this value. Paleontological data of the roof strata above the salt canopy in the central western GOM provide additional constraints on the Neogene contractional response to gravity loading. All reported wells from this part of the canopy, as well as southwestern Garden Banks, have condensed strata of pre-Oligocene age. Thus these roof rocks were part of previous salt highs that have been laterally transported a substantial distance in the Neogene along with the allochthonous salt advance. This coincides with a well-recognized lack of autochthonous contractional structures in the central western GOM. We suggest that these observations support the notion that Neogene contraction in the central western GOM has occurred mainly by squeezing of preexisting salt stocks, and/or deflation of previous salt sheets, and that no substantial autochthonous fold belt probably exists under the canopy.