5 The southern margin of the North American cordillera through time

This session deals with the geologic evolution of the southeastern Cordillera of the North American Plate, its role during ancient orogenic cycles, opening of the Gulf of Mexico, and its interaction with the Caribbean Plate.

Wednesday, 22 April 2026
8:00 AM - 12:00 PM
LMH, Meeting Room

The Mesozoic Breakup of Western Pangea: Triassic Rifting, Role of Paleo-dynamic Topography, and North Oaxaca Transfer

Paper number: 5-2
Program: Technical Sessions
Time: 8:30 AM – 8:50 AM

Authors

Abstract

We have updated the Jurassic–Early Cretaceous (195–121 Ma) paleo-tectonic maps of Pindell et al. (2020), adding a 230 Ma map to begin the series and to address Triassic rifting. Here we address 3 of the most significant points from the revision. First, the regional azimuth of Late Triassic (230–195 Ma) inter-continental extension appears best defined by the 345° trend of a short basement segment along the Guyana margin. This trend is more north–south than the 312° initial Atlantic opening vector, and hence compression would be expected (not observed), suggesting a distinct stage of 345° extension prior to 195 Ma Atlantic spreading. This stage encompasses Eagle Mills and Newark deposition and created what we call the South Florida–Suriname Basin (SFB), within which the region’s best developed SDR sets formed in Early Jurassic. Second, via global analogues, we view the SDR accumulations within the SFB as the center of a regional syn-rift dynamic high that affected predicted isostatic base levels for some 50 Myrs (200–150 Ma), and we show a practical method of incorporating syn-rift dynamic elevation into isostatic basin analysis. Implications are significant, including creation of syn-rift basins 1–2 km higher than expected, often above global sea level, and seafloor spreading commencing at only ~1 km subsea. Third, we present the case that the Cuicateco Belt is the locus of intra-continental sinistral shear, rather than the Mojave–Sonora Megashear, that is required for continental crust in southern Mexico (especially greater Oaxaca to the south of the Trans-Mexico Volcanic Belt) to avoid overlap with continental crust in Colombia. This “North Oaxaca Transfer” is parallel to Atlantic opening, and our reconstructions suggest it connected the Arperos Basin with the Proto-Caribbean Seaway. Sub-horizontal mylonite stretching lineations affect Cuicateco rocks from Early Jurassic to 133 Ma in age, consistent with the predicted period of shear along the transfer. Further, mylonite clasts occur within occurrences of conglomeratic Todos Santos Fm. adjacent to Cuicateco, suggesting the shearing was complex enough to bring mid-crustal rocks to the surface.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410824

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