THE VIENTO FORMATION: SYNDEPOSITED DELTAIC SYSTEM RECORDS ADJACENT PASSIVE SALT RISE DIAPIR, LA POPA BASIN, MEXICO

The Paleocene Viento Formation, the youngest shallow marine unit in La Popa basin, Mexico, exposed on the side of a welded salt diapir that flanks a mini-basin margin, offer rare insight into the facies distribution and stacking pattern of siliciclastic strata, which are analogous for subsurface hydrocarbon-bearing rock-reservoir. Hidalgoan shortening initiated in Late Cretaceous and passive rise of La Popa salt diapir impacted sedimentology, depositional facies distribution, and structural geometry of the Viento Formation, and determined halokinetic sequence style and sequence boundary.

Along 4.5 km distance in contact with discontinuously outcropping remnant gypsum, Viento strata display broad zone of thinning from ~900 m to pinch-out to form a series of five stacked wedges, each ~130 m thick. Beds exhibit flatten dips basinward, but sit vertically at diapir. Sharp, subaqueous erosional surfaces and rare, low-angle unconformities that becomes conformable within tens of meters distance from the diapir characterize wedge halokinetic sequence boundaries. Seventeen sand-prone facies are consistent with deposition in a tide-influenced delta system and include prodelta, delta front and platform, and fluvio-deltaic assemblages. Gradual change and overall shallowing upward facies comprise shale, limestone buildup, oyster reef deposits, horizontal and inclined heterolithic bedding, bioturbated sandstone with Ophiomorpha and oyster-shells, mud-draped ripple-laminated sandstone, ball structure sandstone, trough-cross bedded sandstone, herringbone sandstone, sandstone with wood-fragments, logs and mud ripped-up clasts, and conglomeratic and pebbly sandstone. Conglomeratic and pebbly sandstone contain abundant well-rounded and well-sorted black chert and diapir-derived detritus – Jurassic metaigneous boulders that decrease abundance, size, and angularity in basinward direction.

Cyclical tectonic compressional events and continuous sediment loading controlled La Popa salt diapir rise and drove episodic diapiric extrusion. Viento stratal composition, distribution, and distinct geometry of halokinetic drape folding indicate that deposition and salt rise were coeval and reflect an overall increase in local third order net sediment accumulation rates relative to salt rise rates.