37 Cordilleran Margin Evolution and Supercontinent Tectonics: From Pangea Assembly to North American Orogenesis (Posters)

This session integrates tectonics, petrology, geochronology, stratigraphy, and paleontology to illuminate how Paleo-Pacific plates drove subduction dynamics, crustal evolution, and paleogeographic reconstructions across the complex geological architecture of the American Cordilleras.

Friday, 24 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Tectonosedimentary evolution of the Concordia Basin: Implications for the Early Jurassic rifting and rotation of the Yucatán Block

Paper number: 37-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Upper Triassic–Middle Jurassic basins of Mexico provide a critical record of lithospheric extension associated with the break-up of Pangea, the subduction of the Farallon plate, and the opening of the Gulf of Mexico. Their tectonic origin remains debated, with interpretations ranging from back-arc settings related to the Nazas Arc to intra-arc basins, rifts, or transtensional troughs. While previous models often assume a uniform origin for these basins—whether situated along the Mexican "backbone" or within the Yucatán Block—this study provides evidence of a distinct structural evolution for the Concordia Basin.

We present an integrated analysis based on field observations, stratigraphy, facies analysis, provenance, structural data, and detrital zircon (DZ) U-Pb geochronology to unravel the basin evolution. Our results indicate that Concordia Basin development was controlled by a North-South fault system (specifically the Motozintla, Nectá, and Flores Magón structures) accommodating an East-West extensional regime. The sedimentary and magmatic record reveals three distinct stages:

1.      Rhaetian–Sinemurian: The Nueva Independencia Formation documents a transition from marine to lagoonal environments, coeval with localized magmatism (ca. 200 Ma). Facies continuity suggests that internal structural highs, such as the Chicomuselo High, had not yet developed.

2.      Pliensbachian: Represented by the La Silla Formation and the El Diamante member (ca. 191 Ma), lava flows interbedded with thick alluvial fans mark a shift to continental deposition, indicating major tectonic unroofing. The El Diamante deposits reflect floodplains draining eastward from the uplifted Chiapas Massif Complex.

3.      Toarcian–Aalenian: The Jericó and Concordia members record a transition from high-energy braided fluvial systems to low-energy systems. Fault migration from the southern Motozintla Shear Zone toward the northern La Pinada-Nectá and Flores Magón faults facilitated the development of the Chicomuselo High.

Paleogeographically, the evidence suggests the Yucatán Block remained coupled to the southern margin of Laurentia prior to its southward drift. Contrary to previous models, we find no evidence of significant dextral strike-slip faulting during early basin formation. Instead, the data support an initial East-West extension that was sustained during the Jurassic. This path marks the transition of the Yucatán Block from a part of Pangea into a distinct microplate, where basins developed under a predominant Atlantic influence—distinct from the hybrid Atlantic-Pacific influence proposed for basins in the Mexican backbone.

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

doi: 10.1130/abs/2026CD-410850

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