14 Lost Oceans, Shifting Continents: Interdisciplinary Records of Paleo-Pacific Plate Histories in the American Cordilleras

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.

Wednesday, 22 April 2026
1:30 PM - 4:00 PM
LMH, Meeting Room

Calcareous nannofossils as proxies for paleoclimatic conditions across the paleocene–eocene boundary in the Tepetate Formation, arroyo El Conejo, Baja California Sur, Mexico

Paper number: 14-5
Program: Technical Sessions
Time: 3:10 PM – 3:30 PM

Authors

Abstract

Calcareous nannofossils are marine microfossils widely used in biostratigraphic and paleoclimatic studies due to their rapid evolutionary rates and broad geographic distribution. In the Tepetate Formation, located at Arroyo El Conejo, Baja California Sur, Mexico, a taxonomic analysis was conducted to determine the relative age of the sedimentary rocks and to evaluate their correlation with the Paleocene-Eocene (P-E) boundary.

Two stratigraphic sections were measured, and systematic sampling was carried out for micropaleontological analysis. Smear-slide preparations were produced using the simple smear-slide technique and examined under transmitted light microscopy with both natural and polarized light. Species identification was based on specialized literature and supported by the Nannotax online database.

A total of 25 calcareous nannofossil species were identified, belonging to genera characteristic of the Paleogene, including Coccolithus, Discoaster, Sphenolithus, Rhomboaster, Toweius, and Fasciculithus. The occurrence of biostratigraphically significant index species such as Discoaster lodoensis, Sphenolithus primus, and Tribrachiatus orthostylus allows the assignment of a late Paleocene-early Eocene age, corresponding to the NP9-NP10 biozones of Martini (1971).

These results contribute to the biostratigraphic characterization of the Tepetate Formation and provide valuable data for the regional correlation of Paleogene stratigraphic sequences in Baja California Sur. Furthermore, the recognition of key nannofossil assemblages associated with the P-E transition strengthens the understanding of micropaleontological records and their application to paleoclimatic reconstructions in northwestern Mexico.

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

doi: 10.1130/abs/2026CD-411046

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