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.

Abstract Eastern Venezuelan basin (EVB) is located in the northern South America, in the easternmost part of Venezuela, and it has been filling from the southwest by the Orinoco River since late Miocene – early Pliocene (?), forming the 12-km- thick Orinoco Delta in the Atlantic Ocean. To improve our understanding of the paleogeography and hydrocarbon potential of the eastern Venezuelan basin and the adjacent, thickly-buried segment of the South American passive margin, we use 620 km2 of 3D seismic, 650 km of 2D seismic, and five wells with well logs from the Punta Pescador area of northeastern Venezuela near the Columbus Channel and the border with Trinidad. The following sequence of Cenozoic events affecting the passive margin are proposed: (1) during the Oligocene and early Miocene, south to north flowing fluvial systems and associated deltas progradated northward from the Guyana shield; (2) the late Miocene Messinian event lowered eustatic sea level along the passive margin and produced a major erosional event that breached a continental high which allowed the Orinoco Delta to prograde rapidly into the deeper water Atlantic area in the earliest Pliocene; and (3) early Pliocene to recent progradation of the Orinoco Delta is well documented into the deeper water areas of Trinidad and offshore Venezuela. The onset of major input of the Orinoco River in this area is thought by most workers to be late Miocene in age, which is supported by a change in the flow direction interpreted in the seismic data, from south-north in the pre-late Miocene–early Pliocene section to southwest to northeast direction in the Pliocene to Recent sequence. Through the Cenozoic time, a superposition of fluvial system over deltaic and deep water facies evidences the progradation of the facies and the filling of the basin.