4 Sedimentary Systems and Provenance in the Western Cordillera

This session invites contributions on sedimentary processes, depositional environments, stratigraphic frameworks, and provenance evolution across western North America. Topics may include basin analysis, source-to-sink studies, and applications of stratigraphy to energy and environmental questions.

Wednesday, 22 April 2026
8:00 AM - 12:00 PM
LMH, Fiesta Terrace Salon

Sedimentation in the Forearc Basin During the Eocene in the Vizcaino and Laguna San Ignacio Region, Baja California Sur, Mexico

Paper number: 4-7
Program: Technical Sessions
Time: 10:00 AM – 10:20 AM

Authors

Abstract

In the region between Vizcaino and San Juanico, Cretaceous to Paleogene sedimentary rocks are exposed, representing the sedimentary fill of the forearc basin (Vizcaino basin) generated by the subduction of the Farallon plate beneath North America. During much of the Late Cretaceous and Paleocene, sedimentation in the basin occurred in bathyal and neritic environments (Valle Group). This study focus on the stratigraphy of the marine strata overlying the Valle Group, which correspond to the Bateque Formation. Due to discrepancies among previous authors, we reviewed in the field its geographic distribution. The formation is exposed around and to the east-southeast of San Ignacio Lagoon, extending to the San Juanico area. The stratigraphic relationship between the Valle Group and the Bateque Formation was clarified. Our sedimentological, structural, and biostratigraphic data (calcareous nanofossils) indicate that around 48 Ma, a gradual shift in sedimentation occurred from bathyal to shelf, marking the transition from the Valle Group to the Bateque Formation. We measured a 190 m thick column, which we propose as the type section of this formation. The Bateque Formation is mostly composed of siltstone, sandstone, and bioclastic sandstone with some mudstone packages. Several facies can be distinguished, suggesting deposition on the middle to inner continental shelf with the influence of storms. The fossils, particularly mollusks and macroforaminifera, reflect warm water conditions. Along the column, we detected five levels with stratigraphic condensation or erosion: Level 1 is an unconformity (48.0–47.5 Ma), where bored clasts indicate a considerable hiatus. Levels 2, 3, and 4 reflect stratigraphic condensation characterized by glauconitic sandstones with an erosional base. Rb-Sr dating of glauconite grains for levels 2 and 3 indicates ages of 47.3 and 45.2 Ma, respectively. Level 4 is estimated to be 45 to 44.5 Ma. Level 5 corresponds to one or more conglomeratic layers where detrital zircons indicate an age of 43 Ma. The youngest deposits of the Bateque Formation have a biostratigraphic age of NP16 (late middle Eocene). The Bateque Formation is overlain by several stratigraphic units of varying ages. Despite being deposited in a forearc basin, there are no volcanic rocks, and the petrographic composition of the sandstones indicates a recycled orogenic origin.

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

doi: 10.1130/abs/2026CD-411075

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