Characterization of Syn-Depositional Faulting of a Composite Type B Halokinetic Sequence along the La Popa Salt Weld, La Popa Basin, Nuevo Leon, Mexico

Halokinetic sequences are growth strata associated with passive diapirs and are bounded at the top and base by local angular unconformities. The unconformities are caused by drape-folding of the strata adjacent to a diapir as it rises topographically. The La Popa salt weld in the La Popa basin is a vertical salt-evacuation feature; the strata adjacent to the weld exhibit halokinetic sequences. Two types of halokinetic sequences (A & B) have been identified in the strata adjacent to the weld.

The definition and attributes of Type B halokinetic sequences are based on outcrops along the northeastern side of the weld where the Maastrichtian age Muerto Formation forms an onlap wedge onto the thick beam of Campanian age drape-folded Parras Shale. At this location there is a syn-depositional fault that cuts through the sequence. Documented slickensides on the fault surface indicate a normal fault sense of movement. Field mapping indicates faulting created a half-graben whose 3-D geometry is an elongate trough that parallels the trace of the weld. Field observations indicate that the hanging-wall strata is upper Parras Shale that is overlain by a growth stratal wedge of the Muerto Formation at the easternmost extent of the fault trace. This suggests that faulting was syn-depositional to the Muerto Formation and occurred late in the Type B halokinetic sequence formation. Faulting is thought to have occurred due two mechanisms: 1) as a response to extension associated with drape-folding of the thick beam of Parras Shale as diapirism progressed and 2) partial dissolution of the diapir allowing for graben formation with the Parras Shale forming the down-thrown block.