Abstract

An elongate, arcuate structure consisting of a fault-like displacement surface, 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 structure resulted from hanging-wall subsidence during evacuation of salt along a formerly diapiric salt wall. The La Popa weld has an exposed length of ∼25 km and superficially resembles a growth fault. The displacement surface is convex to the southwest and dips south to southwest. Stratigraphic displacement at the surface is zero at either end and increases to ∼5 km halfway along the trace of the structure. The La Popa structure had a two-phase history: (1) a diapiric phase marked by rise of an elongate salt wall flanked by parallel withdrawal synclines and (2) a subsequent evacuation phase recorded by hanging-wall subsidence and stratigraphic welding of footwall and hanging wall as salt evacuated from the former diapir. During diapirism, thick siliciclastic strata accumulated in the salt-withdrawal synclines that formed by downbuilding adjacent to the rising salt wall. Siliciclastic units thinned toward the salt wall, near which they were upturned and developed numerous angular unconformities. Thick biohermal carbonate 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 synkinematic strata toward the developing weld. This is the first exposed example of a secondary salt weld described as such in the literature.

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