Attributes and History of the Cretaceous-Eocene La Popa Salt Weld Derived from Halokinetic Sequence Stratigraphy

Daniel M. Loera¹ and Katherine A. Giles^2
1 New Mexico State University, Las Cruces, NM
² Institute of Tectonic Studies, New Mexico State University, Las Cruces, NM

An exhumed vertical salt weld in the Cretaceous–Eocene La Popa basin of northeastern Mexico provides a rare opportunity for resolving the detailed structural and stratigraphic attributes of welds. The La Popa weld is a 25 km long arcuate structure formerly interpreted as a reverse fault and has a fault-like displacement surface with the greatest stratigraphic and structural displacement occurring halfway along the trace of the structure. The NW end of the structure merges gradually with the La Popa salt wall and the SE end diverges into a horsetail splay of small displacement right-lateral strike-slip surfaces. Maximum stratigraphic displacement across the weld juxtaposes Lower Cretaceous (Albian) carbonate strata against Lower Eocene siliciclastic strata. Previous estimates for maximum structural throw are approximately 6 km based on regional stratigraphic thicknesses; however, two-thirds less offset (2.5 km) was determined utilizing halokinetic sequence stratigraphy of strata adjacent to the weld. Halokinetic sequence stratigraphy also indicates that the weld was formerly occupied by the SE continuation of the La Popa salt wall and that progressive welding of the SE end during the Late Cretaceous roughly coincided with initiation of Hidalgoan shortening across the basin. Hidalgoan shortening trends NE-SW, which is slightly oblique to the trend of the SE end of the structure and may explain why welding preferentially occurred there. In contrast, the NW end of the system continued as a salt wall with increased halokinetic rise rates progressing through to the Eocene.