Attributes and evolution of an exhumed salt weld, La Popa basin, northeastern Mexico

An elongate, arcuate structure consisting of a fault-like displacement surf ace, previously regarded as a reverse fault, and parallel synclines within the Late Cretaceous-Eocene La Popa basin of northeastern Mexico are herein reinterpreted as a salt weld and its flanking withdrawal synclines, The str ucture resulted from hanging-wall subsidence during evacuation of salt alon g a formerly diapiric salt wall. The La Popa weld has an exposed length of similar to 25 km and superficially resembles a growth fault. The displaceme nt surface is convex to the southwest and dips south to southwest. Stratigr aphic displacement at the surface is zero at either end and increases to si milar to 5 km halfway along the trace of the structure. The La Popa structu re had a two-phase history: (1) a diapiric phase marked by rise of an elong ate salt wall flanked by parallel withdrawal synclines and (2) a subsequent evacuation phase recorded by hanging-wall subsidence and stratigraphic wel ding of footwall and hanging wall as salt evacuated from the former diapir, During diapirism, thick siliciclastic strata accumulated in the salt-withd rawal synclines that formed by downbuilding adjacent to the rising salt wal l. Siliciclastic units thinned toward the salt wall, near which they were u pturned and developed numerous angular unconformities. Thick biohermal carb onate lentils accumulated episodically on topographic highs associated with the rising salt wall. Evacuation of the salt wall caused lateral migration of the hanging-wall synclinal hinge and a consequent shift of thickest syn kinematic strata toward the developing weld. This is the first exposed exam ple of a secondary salt weld described as such in the literature.