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.

During the past 15 yr, the global requirement for fertilizers has grown considerably, mainly due to demand by a larger and wealthier world population for more and higher-quality food. The demand and price for potash as a primary fertilizer ingredient have increased in tandem, because of the necessity to increase the quantity and quality of food production on the decreasing amount of available arable land. The primary sources of potash are evaporites, which occur mainly in marine salt basins and a few brine-bearing continental basins. World potash resources are large, but distribution is inequitable and not presently developed in countries where population and food requirements are large and increasing. There is no known substitute for potash in fertilizer, so knowledge of the world’s potash resources is critical for a sustainable future. The U.S. Geological Survey recently completed a global assessment of evaporite-hosted potash resources, which included a geographic information system–based inventory of known potash resources. This assessment included permissive areas or tracts for undiscovered resources at a scale of 1:1,000,000. Assessments of undiscovered potash resources were conducted for a number of the world’s evaporite-hosted potash basins. The data collected provide a major advance in our knowledge of global potash resources that did not exist prior to this study. The two databases include: (1) potash deposits and occurrences, and (2) potash tracts (basins that contain these deposits and occurrences and potentially undiscovered potash deposits). Data available include geology, mineralogy, grade, tonnage, depth, thickness, areal extent, and structure, as well as numerous pertinent references.