GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 172-5
Presentation Time: 9:00 AM-6:30 PM


SCHORR, Marissa Rose, Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, IN 47401, HARTKE, Samantha, Department of Geosciences, University of Texas at Dallas, 800 W. Campbell Road, MC17, Richardson, TX 75080, PUGH, Andrew, Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, 1664 N. Virginia Street, Reno, NV 89557, CAMACHO, Daniel, Earth Sciences, Universidad Autonoma de Baja California Sur, Carretera al sur km 5.5, La Paz, 23080, Mexico, NAVARRETE, Gabriela Marie, Geosciences, California State University of Bakersfield, 9001 Stockdale Highway, Bakersfield, CA 93311, TJARKS, Dulaney, Department of Geological Sciences, University of Kansas City-Missouri, 5100 Rockhill Rd, Kansas City, MO 64110, MARTÍNEZ GUTIÉRREZ, Genaro, Universidad Autónoma de Baja California Sur, La Paz, 23080, Mexico, NIEMI, Tina M., Department of Geosciences, University of Missouri - Kansas City, 5100 Rockhill Road, Flarsheim Hall 420, Kansas City, MO 64110 and ANTINAO, José Luis, Indiana Geological and Water Survey, Indiana University, 611 North Walnut Grove Ave., Bloomington, IN 47405

The Santa Rosalía basin in Mexico’s central Baja California Peninsula records sedimentation during Gulf of California rifting and subsequent tectonic uplift of the basin. Gravel and calcareous fossiliferous conglomerate and sandstone at the top of the sedimentary sequence have been included in the Pleistocene Santa Rosalía Formation. Distinct marine terraces within this formation, at 10 m, 25–30 m, 100 m, and ~200 m (above sea level [asl]) are identified near the town of Santa Rosalía. The height of these terraces increases towards the NW and decreases towards the SE. Four distinct fluvial terraces with top elevations ranging from 2 m to 50 m above the modern stream level were observed in the Santa Agueda, Boleo, Montado, and Providencia arroyos. Soil profiles in the higher elevation terraces were observed to be deeper and more developed than the soil profiles in the lower elevation terraces.

To constrain abandonment and stabilization of the observed marine and fluvial terraces, we dated them using a combination of cosmogenic exposure dating using 36Cl and luminescence dating of feldspars. Preliminary results indicate that the oldest and highest marine terrace (at >200 m asl) contains boulders having exposure ages between 480 ± 64 ka and 720 ± 150 ka (36Cl exposure age). The youngest uplifted fluvial terrace (2 m above the modern stream) is dated at 15 ± 3 ka (post IR–IRSL on feldspar). These results indicate that the basin stopped subsiding and began uplifting ca. 800 ka. This is consistent with local geomorphological evidence for uplift such as stream capture and the presence of stream knickpoints.