35 The Mesozoic Convergent Margin of Alta and Baja California (Posters)
This session will cover aspects including the structure, petrology, geochronology, and stratigraphy of the Mesozoic convergent margin of North America from Alta California to Baja California Sur.
Friday, 24 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel
Structural and Stratigraphic Architecture of the Magdalena Forearc Basin (Baja California Sur): Unconformities and Waning Contraction during Late-Stage Farallon Subduction
Paper number: 35-4
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
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Mario Gonzalez-EscobarCICESE - Departamento de Ciencias de la Tierra, Ensenada, Baja California
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Luca FerrariUNAM - Campus Juriquilla, Centro de Geociencias, Juriquilla, QRO
Abstract
The onshore sector of the Magdalena Basin in Baja California Sur preserves a forearc-basin record of the Mesozoic convergent margin of western North America. We integrate 2D seismic reflection profiles, Bouguer gravity data, and well logs from the Villa Constitución area (UTM Zone 12N) to define five tectonostratigraphic units (M1–M5; Early Cretaceous–Eocene) and two regionally traceable unconformities (D-1 and D-2).
Basement (M1) is overlain by Lower–Upper Cretaceous successions (M2–M3) separated by an intra-Cretaceous unconformity (D-1). A second angular unconformity (D-2) truncates M3 and is overlain by onlapping Paleocene–Eocene strata (M4–M5), recording forearc uplift and erosion followed by renewed accommodation. Cretaceous units dip landward and are cut by a NW–SE-striking reverse fault with clear displacement in M1–M3 and diminished or unresolved offset upward, indicating that contraction waned markedly by Eocene times. Time-structure mapping of D-2 defines a western marginal high adjacent to the former accretionary prism, with increasing depth toward the basin interior; post-D-2 strata thicken basinward and partially infill inherited relief, producing an asymmetric forearc geometry.
We interpret D-1 as a mid-Cretaceous reorganization within the forearc system and D-2 as an upper-plate response to Farallon subduction, recording a discrete Paleocene uplift event that preceded reduced deformation and Eocene subsidence. This interpretation is consistent with published evidence for exhumation of the Peninsular Ranges Batholith and detrital-zircon provenance constraints showing that Eocene formations (El Salto, El Cien, and San Gregorio) are dominated by Late Cretaceous age populations.
These results highlight how forearc basins along Baja California preserve episodic uplift and basin reorganization during convergent-margin evolution.
Geological Society of America Abstracts with Programs. Vol. 58, No. 3
doi: 10.1130/abs/2026CD-410967
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