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ABSTRACT

New and existing strontium isotope data are given for several widespread evaporites from western equatorial Pangea. The data indicate evaporite deposition occurred on proximal margins of the Gulf of Mexico at ca. 169 Ma (Bajocian, not Callovian as commonly thought) and 166 Ma in Trinidad (Bathonian-Callovian boundary). The 166 Ma age may also apply to undated evaporite on the Bahamian margin, conjugate rift of Trinidad, and now in Cuba. We show that: (1) the Trinidadian (and Bahamian?) evaporite pertains to rifting rather than to Late Jurassic–Cretaceous carbonate platform deposition; (2) the Mata Espino-101B evaporite (a borehole in Veracruz Basin, Mexico) is not Paleocene but Bajocian (halite) or Bathonian (gypsum) and hence is not related to possible Paleogene Gulf of Mexico desiccation; (3) evaporite deposition may have offlapped basinward in the Gulf of Mexico (Bathonian–early Oxfordian in more distal areas), because most Atlantic opening models preclude the Gulf of Mexico from being large enough by 169 Ma to accommodate the mapped expanse of autochthonous salt deposition; and (4) a 3–9 m.y. hiatus (the Norphlet window) is apparent in proximal areas around the Gulf of Mexico between evaporite and upper Oxfordian marine successions, caused perhaps by proximal margin uplift (flexural or thermal) or by Gulf of Mexico water level remaining below paleo–sea level (evaporation?) during Bathonian–early Oxfordian time. Although a 20–30 m.y. hiatus may exist below evaporite in the U.S. coast, cordilleran Mexico was tectonically active into the Middle Jurassic, and pre-salt continental deposits are closer in age to salt deposition there. Pre-salt strata along Campeche–northern Yucatán remain undated. Our data do not resolve if the evaporite was sourced from the Atlantic, the Pacific, or both, but the fact that the Trinidadian evaporite is younger than Gulf of Mexico evaporite, and the presence of Bajocian marine and evaporite sections across Mexico perhaps favor the Pacific as the source.

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