Rift Models and the Salt-Cored Marginal Wedge in the Northern Gulf of Mexico: Implications for Deep-Water Paleogene Wilcox Deposition and Basinwide Maturation
Pindell James, Lorcan Kennan, 2007. "Rift Models and the Salt-Cored Marginal Wedge in the Northern Gulf of Mexico: Implications for Deep-Water Paleogene Wilcox Deposition and Basinwide Maturation", The Paleogene of the Gulf of Mexico and Caribbean Basins: Processes, Events and Petroleum Systems, Lorcan Kennan, James Pindell, Norman C. Rosen
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Two primary issues continue to plague geological assessments of the Gulf of Mexico. The first is the common view of “mother salt,” with terms such as “basinward depositional limit” or “onlap limit” of salt being used in reference to the deep Gulf basin without apparent concern for whether or not this limit is depositional. Backstripping techniques clearly show that the crust in the deep Gulf is typical oceanic crust, accreted (crystallized) at about 2.7 km paleo-water-depth, such that this contact cannot be a depositional one if the salt was deposited in shallow water in a basin more or less full to sea level. We argue that the seaward salt limit, even where not reactivated in the Tertiary, is a structural contact formed by salt flow onto oceanic crust. The second is the portrayal of the abyssal plain continuing well north of today’s continental slope prior to the Miocene, and approaching the Sligo-Stuart City carbonate shelf edge (to beneath present-day onshore areas) in the Late Cretaceous. These portrayals appear to presume that the Louann Salt was conveniently “stored” beneath the northernmost abyssal plain (i.e., without bathymetric expression) until the Cenozoic. This paper sets out to revise these long-held concepts, and to replace them with alternatives that explain primary observations in the Gulf much better. We start by assessing the Jurassic rift configuration and its impact on subsequent basin development, which in our view was very different to traditional models. We propose that a “salt-cored marginal sediment wedge” existed between the Sligo-Stuart City carbonate shelf edge and the deep water Wilcox trend which provided a continuous (but perhaps stepped) continental slope, down which Wilcox clastic sediments were free to flow from source to sink without first having to cross hundreds of kilometers of flat abyssal plain to reach their final position. In addition, the analysis hints at a mechanism for the incision of deep canyons (e.g., Yoakum) along the northern and western Gulf shelf margins and leads us to propose a new maturation mechanism in the northern Gulf margin.