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The Louann Salt and Its Relationship to Gulf Coast Salt Domes
Donald I. Andrews (1)
A review was made of the literature and other available data pertaining to the Louann or "Mother" salt of the Gulf Coastal basin. Numerous facts and theories relating to various aspects of the salt are presented, and the most widely accepted ideas are discussed in terms of recent developments.
The Louann salt is part of an evaporite sequence found in the Gulf Coastal basin of the United States. It is best studied at its updip bedded limits where the sequence unconformably overlies Paleozoics, and is in turn overlain, perhaps unconformably, by the Norphlet and Smackover formations of Upper Jurassic age. The age of the salt itself cannot be definitely proven. It is known to be older than Upper Jurassic, but believed to be no older than Upper Permian. The original average bedded salt thickness is estimated to be approximately 5,000 feet.
Chemical experiments indicate that there is an excess of Louann salt in relation to the amount of underlying Werner anhydrite. Therefore, it is believed that prepared brines of highly concentrated sodium chloride content may have been introduced into the Louann basin from an outside source--two possible sources being the Permian basin of West Texas and the Sabinas basin of northeast Mexico. The Louann-Werner depositional basin or basins could have had several different forms, but is believed to have been a single, vast, widespread basin. Conditions comparable to Branson's "Modified Bar Theory" probably existed during evaporite deposition, The present day Gulf of Mexico, a large gravity maximum, appears to be closely related to the original salt depositional basin.
A more or less continuous bed of Louann salt is believed to underlie the entire Gulf Coastal basin. The Louann is probably the source or "Mother" bed for all the salt found in the piercement domes of the four subbasins, which now exist within the Gulf Coast basin. Although the salt found in the downdip Texas-Louisiana Coastal basin domes, theoretically could be younger than Louann, a study of the available evidence points to this salt also being Louann. The absence of salt domes in the "barren" or "void" band, which runs west-east from east central Texas through central Louisiana and into southern Mississippi, may be due to shifting areas of sediment overburden, and/or the possibility that salt was thinly deposited in this area.
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