David C. Shelley1, Timothy F. Lawton1
(1) New Mexico State University, Las Cruces, NM
ABSTRACT: Sand, Salt, And Orogenesis on The Paleocene Western Margin of The Gulf of Mexico: The Upper Sandstone Member of The Potrerillos Formation, La Popa Basin, Mexico
The Upper Sandstone Member (USM) of the Potrerillos Formation records a thick, sandy, Paleocene tidal system deposited in La Popa foreland basin. The Potrerillos Formation is part of the Difunta Group, an interval of Cretaceous to Cenozoic clastics associated with Hidalgoan (Mexican Laramide equivalent) orogenesis and shoreline progradation around the western Gulf of Mexico. Depositional facies and geometries reflect the influence of intrabasinal halokenesis as well as local Hidalgoan orogenesis.
Facies of the USM indicate a complex assemblage of intertidal to subtidal environments. Fossils and ichnofossils indicate an estuarine environment. Stratal thinning and low energy facies are common adjacent to El Papalote evaporite diapir. Stratal thinning is also observed in relation to a major intrabasinal fold. Paleocurrent data suggest a dominantly ebb-tidal current which flowed southeast; eastward accretion of tidal bundles, however, suggests oblique migration of sand bodies. Current directions were parallel to regional structural trends, intrabasinal folds, and the La Popa salt weld, which lay ~4km to the north. These data suggest that the USM was deposited in a structurally confined, elongate basin. The high net sand, depositional facies, and basin geometry are consistent with a macrotidal system. The average sand is a lithic arkose with Fp:Fk=24. Lithic grains indicate a variety of volcanic, metamorphic, and sedimentary sources. Locally, these sands likely represent tidally redistributed nearshore sands. Regionally, these were derived from volcanic terranes and Hidalgoan uplifts to the (north)west; some transport is inferred along structure-parallel fluvial systems on the northeast of the Coahuila block.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado