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ABSTRACT: Facies Assemblages of the Tidally-Influenced Deltaic System of the Maastrichtian Muerto Formation, La Popa Basin, Mexico: An Analogue for the Gulf of Mexico Subsurface

WEISLOGEL, AMY L., and TIMOTHY F. LAWTON , Institute of Tectonic Studies, Las Cruces, NM

The Maastrichtian Muerto Formation was deposited in the distal part of the once-contiguous Sierra Madre foreland, which developed over the rifted eastern margin of Mexico. In a segment of the now deformed foreland known as La Popa basin, the Muerto is presently exposed in the Coahuila marginal fold belt of the Rio Grande embayment, and also crops out adjacent to an evaporite diapir known as El Gordo diapir. Muerto strata represent the first significant influx (600 m) of sediment derived from the growing thrust belt to the west and transported eastward by a large deltaic system. The Muerto Formation contains three facies assemblages: shelfal/shoreface, tidal and lagoonal. The shelfal/shoreface facies assemblage ranges from offshore shales to middle shoreface sandstones. The tidal facies assemblage includes an ebb tidal delta, flood and ebb tidal channel lithofacies. The lagoonal facies assemblage includes oyster banks and bioturbated washover facies. The Muerto system is progradational; however, no lower delta plain or terrestrial sedimentation is recorded in the vicinity of El Gordo diapir. Local subsidence and uplift resulting from salt withdrawal and diapiric rise influenced thickness and facies distribution of the Muerto Formation adjacent to El Gordo diapir. The Muerto Formation exhibits lateral shallowing and thins from 695 m to 67 m over 6 km towards the diapir. The Jackson Gas Rock (informal unit of the Selma Group) adjacent to the Jackson dome in the Mississippi embayment, although of different lithology than the Muerto Formation, is of comparable age and exhibits similar thickness trends in the subsurface.

 

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas