9 Sedimentary Systems and Provenance in the Western Cordillera (Posters)

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 - 5:30 PM
LMH, 5th Floor Chapel

Characterization of Cenozoic conglomerate successions in the eastern margin of the Yanhuitlán Basin, Oaxaca, Southern Mexico, and reconstruction of the depositional environments

Paper number: 9-5
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

Extensive conglomerate deposits are exposed along the eastern edge of the Cenozoic Yanhuitlán sedimentary basin, near Asunción Nochixtlán, Oaxaca. This study aims to characterize these clastic successions to identify their depositional environments and clast sources, and to develop a model for the basin fill's evolution. It also seeks to understand their connection with regional tectonic events and to establish a new lithostratigraphic classification.

The distribution of facies and clast composition shows systematic lateral variations that allow the identification of two sedimentary domains. To the north, the Cántaros Formation consists of clast-supported to matrix-supported conglomerate with subangular to subrounded clasts, poor sorting, and a coarse sandstone matrix, interpreted as debris flow deposits with channelized facies spanning 100 meters in thickness. These features indicate deposition in a proximal alluvial-fan system. Clasts are mostly made of limestone and chert, with fewer metamorphic and andesite clasts. The conglomerate unconformably overlies Paleocene–Early Eocene floodplain and lacustrine rocks (Yanhuitlán Formation) and Cretaceous limestone (Ocotlán Formation). Therefore, the Cántaros Formation is interpreted as post–Lower Eocene in age. Sedimentation was influenced by paleorelief, as no syn-sedimentary faults were identified.

To the south, the Sosola Formation (Schlaepfer, 1970) consists of conglomerate, conglomeratic sandstone, and sandstone, with a thickness of 60 meters. Facies are characterized by hyperconcentrated-flow deposits, well-developed channel fills, and sandstone strata with planar-parallel lamination. These features suggest deposition in the medial-to-distal parts of an alluvial fan system. The conglomerate unconformably overlies the Yanhuitlán Formation and Proterozoic gneiss of the Oaxaca Complex. Clasts mainly consist of andesite and tuff, with smaller amounts of limestone and metamorphic rocks. The Sosola Formation is cut by regional left-lateral strike-slip faults that place the conglomerate in tectonic contact with the Oaxaca Complex. Fault activity and basement uplift-controlled accommodation space and influenced the depositional architecture of the conglomerates in the Sosola Formation.

Overall, the successions record two distinct alluvial fan systems, whose facies distribution, provenance variations, and stratigraphic relationships reflect different source areas and tectonic control during the evolution of the Yanhuitlán basin. The geometry and distribution of the Sosola Formation clastic rocks, along-with the geometry of the faults, suggest that they may be the southern extension of the Santa Lucía Fault (Oligocene) located further north of-the Yanhuitlán basin.

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

doi: 10.1130/abs/2026CD-410905

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