HON, KEVIN D., New Mexico State University, Dept. of Geological Sciences, Las Cruces, NM

ABSTRACT: Structural and Depositional Analysis of the Muerto Formation Adjacent to an Ancient Secondary Salt Weld, Nuevo Leon, Mexico

Diapirism and subsequent salt weld development produced growth stratal geometries, progressive unconformities and faulting within the Late Cretaceous to early Tertiary La Popa foreland basin. Sourced from the developing Sierra Madre orogen, the La Popa basin sediments consists of about 5,500 meters of an overall regressive sequence of deltaic and shelf sediments with subordinate limestone lenses that are penetrated by several salt bodies, including a salt weld. A salt weld is a planar, fault-like feature formerly occupied by salt that separates two bodies of strata.

Two stages of development, a diapiric stage and an evacuation stage, created complex geometries associated with the salt weld and are preserved in the terrigenous sandstones of the Maastrichtian Muerto Formation. During the diapiric stage, rising Jurassic evaporite created a local topographic high on the basin floor. Over time, sediment onlapped the rising surface and older strata became steeper adjacent to the salt body. During periods when diapiric rise rate exceeded rate of deposition, local erosional truncations formed within the adjacent strata. Normally conformable with the underlying Parras Shale and the siltstones and mudstones of the overlying Potrerillos Formation, the Muerto Formation becomes unconformable with these two formations within a few 100 meters of the diapirweld. Also, the rising diapir created local growth faults, one of which is in the Parras Shale and truncated by the Muerto Formation, that dip toward the salt body. During the evacuation stage in the Eocene, salt weld development resulted in synthetic and antithetic faulting throughout the La Popa strata.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid