13 Earth Life Sciences across the Cordillera

This session showcases interdisciplinary research that bridges geological sciences with allied fields including (but not limited to) genetics, ecology, biogeography, archaeology, informatics to emphasize innovative approaches to understand the interconnectedness of Earth systems.

Wednesday, 22 April 2026
1:30 PM - 5:30 PM
LMH, Fiesta Terrace Salon

Miocene to Present Paleogeography of the Central Baja California Peninsula (Mexico) Confirms No Transpeninsular Seaway

Paper number: 13-7
Program: Technical Sessions
Time: 3:50 PM – 4:10 PM

Authors

Abstract

A long-standing Earth-Life science hypothesis for the central Baja California peninsula (Mexico) is that a marine seaway transected the peninsula during Plio-Pleistocene time. Such a seaway would have created a physical barrier to floral and faunal gene flow between a shorter northern peninsula and a separate southern island. For decades, biologists have called upon this transpeninsular seaway hypothesis to explain the genetic divergence observed at the latitude of the central peninsula in dozens of low-dispersal plants and animals. To test this hypothesis, our interdisciplinary team (Baja GeoGenomics consortium) conducted detailed geologic mapping of a ~4,000 km2 region at the latitude of San Ignacio-Santa Rosalia (~27.4°N), obtaining ~150 geochronologic ages (Ar/Ar, U-Pb), ~350 XRF geochemical analyses, and paleocurrents in sedimentary and volcanic rocks. The study area encompasses the two lowest passes (405 m and 520 m asl) along the central peninsula topographic divide. We combine our new mapping, published mapping, and analysis of satellite imagery to construct paleogeographic maps of the central Baja California peninsula every 2 million years back to 16 Ma. At each time step, we delineate regions of eroding volcanic highlands, active volcanism, low-relief coastal plains, marine environments, active faulting and basin subsidence, and the evolving Pacific and Gulf of California shorelines. Since Miocene time, the western (Pacific) shoreline has remained west of Mesa San Regis, a site ~12 km northeast of San Ignacio that records only non-marine conditions (Gardner et al., this meeting). The eastern (Gulf of California) shoreline was established during 6.3-Ma marine flooding of the Gulf and has remained roughly co-located with fault systems that control the western rift margin. Detailed mapping confirms that marine deposits occur below ~200 m asl, except where locally uplifted up to ~300 m asl by magmatic inflation related to Quaternary volcanoes. Marine deposits do not exist at or near the 405 m and 520 m asl topographic passes. We therefore reject the transpeninsular seaway hypothesis at the latitude of San Ignacio-Santa Rosalia and conclude that climatic and/or topographic factors likely controlled the observed genetic divergence. This study demonstrates the importance of using geologic data to test hypotheses that make predictions about landscape evolution at geologic timescales, underscoring the need for cross-disciplinary collaboration to better understand co-evolution of life and Earth processes.

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

doi: 10.1130/abs/2026CD-410879

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.