2019 AAPG Annual Convention and Exhibition:

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Strontium Isotope Dating of Evaporites and the Breakup of the Gulf of Mexico and Proto-Caribbean Seaway

Abstract

New and existing Strontium isotope ratio data are presented for seven areas of evaporite deposition within western equatorial Pangea (middle America). The data show that halite was deposited on the proximal margins of the northern and southern Gulf of Mexico (GoM) at about 169-170 Ma (Bajocian), whereas a thick anhydrite was deposited in Trinidad at 166 Ma (Callovian). This Callovian age probably also applies to evaporites in northern coastal Cuba (i.e., the overthrust southern Bahamian margin), the conjugate to Trinidad. The data constrain numerous problems such as: (1) the Couva Evaporite in Trinidad pertains to rifting rather than to Cretaceous carbonate platform deposition; (2) the salt drilled in Mata Espino-101B (Veracruz Basin) is Bajocian (halite) or Bathonian (gypsum), but the depositional site was probably beneath the Sierra Madre Oriental thrustbelt west of Veracruz Basin before that area was part of the GoM; (3) a 3-9 m.y. hiatus appears to exist in proximal areas around the GoM, above salt and below Late Oxfordian marine sequences (Norphlet “window”), caused by either marginal uplift (thermal?) or by the water level failing to fill the basin to paleo-sea level again (probably producing an offlapping architecture); (4) based on detrital zircon dating, salt deposition in parts of Mexico, at least, appears to have proceeded from continental deposition immediately, but this looks less likely for the US sector; (5) we strongly suspect, but cannot yet prove, that salt youngs basinward in the GoM and is Callovian-Early Oxfordian in distal areas, correlative with more proximal Norphlet deposition, because models of Atlantic opening suggest the GoM basin was still smaller at 169 Ma than the mapped expanse of autochthonous salt deposition.