AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Laramide Episodic Documentation in Architecture and Depofacies of Viento Formation: Consequence of La Popa Salt Weld Evolution, La Popa Basin, Northeastern Mexico
(1) Geological Sciences, University of Alabama, Tuscaloosa, AL.
The stratigraphic architecture of the Eocene Viento Formation was investigated in southwest of La Popa secondary salt-weld, adjacent to the prominent bend zone located at its midpoint. Seven stratigraphic sections, measured perpendicular to the strike of the weld, along a 4.3 km SE-NW transect document lateral erosional thinning from 880 m to zero and exhibit bedding orientations from moderately dipping (35°) distal to the weld to slightly overturned adjacent to the weld, rare, minor faults (<2 m displacement) and rare, intraformational angular unconformities (≤20°).
Viento deposits include voluminous bioturbated siltstone and sandstone containing abundant Ophiomorpha burrows and wood fragments. Depofacies consistent with deltaic deposition comprise coarsening -upward parasequences: fissile shale, ripple to plane-laminated sandstone with mud rip-up clasts, oyster bank, low angle trough cross-bedded sandstone, heterolithic mud-draped sandstone to siltstone, and conglomeratic facies. Conglomeratic facies exhibit abundant 1-15 cm large, disarticulated oysters and well-rounded, well-sorted, pebbles to cobbles composed of chert and meta-igneous clasts. Clast size and angularity both increase with increasing proximity to the weld.
Facies analysis reveals Viento deposits represent a tidally influenced, river-dominated prograding delta system. Massive input of sand continuously discharged by Viento system synchronous with episodic Laramide compression events activated beneath evaporite layer and drove evaporite diapiric rise. Extrusion of diapiric evaporates to the surfaces is demarcated by the presence of conglomerate clasts composed of exotic lithologies found incorporated within Eocene Viento deposits. These exotic clasts were incorporated into the evaporate, transported upward during diapiric rise, exhumed at seafloor, reworked, and redeposited within the Viento Formation. Depofacies composition together with their vertical succession relationship and lateral geometry unequivocally indicates that deposition and shortening were simultaneous with salt rise.