Depositional Setting and Distribution of Sands Within Type a Halokinetic Sequences: From Example from the Paleocene Upper Mudstone Member, Potrerillos Formation, La Popa Basin, Mexico

Jordayna J. Druke and Katherine A. Giles
Geological Sciences, New Mexico State University, Las Cruces, NM

La Popa basin of northeastern Mexico contains exceptional exposures of structural and stratigraphic features associated with passive diapirism. The strata of the Potrerillos Formation exposed adjacent to El Papalote and El Gordo diapirs can be arranged into stacked packages of Type A halokinetic sequences. Type A halokinetic sequences are characterized by the high degree of local folding, significant amount of fault reactivation at sequence boundaries, and low sediment accumulation rates. The general facies progression within a single Type A halokinetic sequence is basal carbonate debris flow containing diapir/roof derived detritus overlain by fine-grained homogenous sandstone deposited by hyperpycnal flows in a lower shoreface to middle shelf setting, capped by massive offshore black shale. The individual halokinetic sequences are separated by sequence boundaries marked by syn-depositional deformation of the strata through drape folding associated with halokinesis, which creates a steep, near 90 degree angular unconformity. Debris flows thin and fine away from the diapir, grading into calciturbidites that are onlapped by hyperpycnal flows. The sandstone and black shale thin by onlap toward the diapir and are thicker on the down-dip side of the diapir. Within the stacked composite Type A halokinetic sequences the percentage of sand decreases upward . These sequences form when sediment accumulation rate is lower than diapir rise rate resulting in diapir inflation. This is typical of conditions on the shelf during the transgressive systems tract. The topography of the inflated diapir causes up-dip ponding and winnowing of siliciclastics resulting in thinner, sand-prone sequences and higher net to gross percentage, whereas as down-dip in the sediment shadow zone are thin, isolated sands separated by thick shale horizons.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas