Sequence stratigraphy of tidally influenced deposits in a salt-withdrawal minibasin: Upper sandstone member of the Potrerillos Formation (Paleocene), La Popa basin, Mexico

Abstract

The Potrerillos minibasin of the La Popa basin, Mexico, is defined by the Carroza syncline and bounded by the El Gordo anticline and the La Popa salt weld. Stratigraphic geometries and facies distribution of the upper sandstone member of the Potrerillos Formation within the minibasin indicate that diapirism, shortening, and deposition were simultaneous and complexly interrelated during the Paleocene. The upper sandstone member is a regressive succession of marginal marine, siliciclastic deposits. Wave-dominated shoreface deposits consist of mudstone, siltstone, and sandstone and are interpreted to represent offshore to upper shoreface environments. Tide-dominated environments are heterogeneous and grouped into four broad classes based on the energy of the depositional environment. Lower delta-plain deposits range from mudstone to sandstone and are interpreted to represent channel, flood-plain, and lagoonal environments. Sedimentary structure orientations indicate asymmetrical, bidirectional paleocurrents with a dominant southeast trend parallel to regional structural trends. Unconformity-bounded strata onlap the El Gordo anticline, indicating syndepositional folding and control of the depositional system by detachment fold trends in the basin.The strata of the upper sandstone member are interpreted to contain six systems tracts that record three successive fourth-order eustatic cycles. These strata represent the deposits of a prograding, ebb-dominated deltaic system confined to the Carroza syncline. Maximum stratal accumulation in the synclinal hinge caused the migration of underlying salt into flanking structures. A balance between salt withdrawal and subsidence stabilized the position of both the synclinal hinge and the shoreline, leading to a positive deposition-subsidence feedback loop. During regional regression, the structural basin defined by the syncline formed a paleogeographic embayment and controlled shoreline evolution.