STRATIGRAPHIC RESPONSE OF THE MAASTRICHTIAN MUERTO FORMATION TO PASSIVE RISE OF THE EL GORDO DIAPIR, LA POPA BASIN, NORTHEASTERN MEXICO

In the La Popa basin, a part of the deformed Hidalgoan foreland located in Nuevo León, Mexico, the Maastrichtian Muerto Formation is exposed adjacent to the El Gordo diapir in the limbs of the El Gordo anticline, a detachment fold that cross-cuts the diapir. Eight measured sections document lateral thinning of the Muerto Formation from ~700 m thick at a distance 2 km away from the diapir to an erosional pinch out directly adjacent to the diapir. However, the strata of the Muerto Formation to not vary with respect to the hinge of the El Gordo anticline, establishing the lower limit of the age of deformation in the La Popa basin as post-Muerto Formation. The Muerto Formation was deposited by a large, west-to-east progradational deltaic system composed of four depositional facies assemblages: shoreface, tidal, lagoonal, and lower delta plain. The distribution and abundance of each depositional facies assemblage and systems tract geometries within the Muerto Formation adjacent to the diapir are controlled by the passive rise of the El Gordo diapir and the relationship between sediment accumulation rate and diapir rise rate. Transgressive systems tracts within the Muerto Formation typically contain parasequences that onlap toward the diapir. The onlap geometry is caused by a decrease in sediment accumulation rate relative to diapir rise rate during initiation of the transgressive systems tract, which drove the locus of deposition away from the diapir crest. As the sediment accumulation rate increased during deposition of the transgressive systems tract, onlapping parasequence geometries developed. Development of the highstand systems tract was accompanied by erosion and truncation of the underlying transgressive systems tract within a 1 km radius of the diapir crest due to the combined effect of a high sediment accumulation rate and reduced accommodation space development associated with rise of the diapir in this area. Diapir inflation associated with reduced sediment accumulation rates during the final stage of deposition slightly rotated the strata of the Muerto Formation directly adjacent to the diapir, producing a localized low-angle unconformity between the Muerto Formation and the overlying Potrerillos Formation.