Tectonostratigraphic data derived from ongoing biostratigraphic, chronostratigraphic, paleobathymetric, paleobiogeographic, and lithostratigraphic investigations in west-central and east-central Mexico suggest that the Gulf of Mexico formed in two phases:

Phase 1: Rifting and subsequent sea-floor spreading during the Late Jurassic (middle Oxfordian). All but the southwestern portion of the Gulf of Mexico formed during Phase 1.

Phase 2: Northwest-to-southeast tectonic transport of allochthonous San Pedro del Gallo terrane remnants along the west side of Walper Megashear during the Middle Jurassic to Early Cretaceous.

Where the stratigraphic successions are complete, megafossil data indicates that the San Pedro del Gallo terrane was situated at Southern Boreal paleolatitudes (30 N) in the Nevadan back arc domain during the Middle Jurassic (late Bathonian to early Callovian) and was subsequently carried to lower paleolatitudes during the Late Jurassic and Early Cretaceous. For example, in the Huayacocotla remnant, the Boreal ammonite Kepplerites was recovered in the subsurface from the Palo Blanco Formation by Cant-Chapa. In North America, Kepplerites is known from the Izee terrane (east-central Oregon), Western Interior (Montana and Saskatchewan), and northward to southern Alaska. Radiolarian, calpionellid, ammonite, and bivalve faunal data indicate that the Huayacocotla remnant had been transported to Northern Tethyan paleolatitudes (23 N to 29 N) during the Kimmeridgian and Tithonian and to Central Tethyan paleolatitudes (23 N) by the beginning of the Early Cretaceous.