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

A series of Pleistocene beach rides are the rocky substrate for the Cabo Pulmo reef, Gulf of California

Paper number: 4-10
Program: Technical Sessions
Time: 11:00 AM – 11:15 AM

Authors

Abstract

Cabo Pulmo Bay contains the northernmost eastern Pacific reef. Lately, it has been suggested that Cabo Pulmo is a rocky reef rather than a true reef. However, there is uncertainty about the type of rocky substrate supporting the reef. The reef is within Cabo Pulmo Bay, which is slightly concave with a N-S orientation. Mean while the reef shows alignments in the NE40°SW direction; the colonies develop from just below low tide to a gradually increasing depth of approximately 30m. This paper presents information supporting that the type of rocky substrate is a Late Pleistocene beach conglomerate. The coastline of Cabo Pulmo Bay is affected by erosion, which has exposed a beach conglomerate composed of gravels and cobbles predominantly of volcanic origin, with few granitic rock clasts and abundant bivalve fossils in life position, as well as corals and other fossils, similar to the fauna currently inhabiting the reef. Matrix of the conglomerate is dominantly siliceous carbonate sand. Due to its stratigraphic position and composition, this beach conglomerate is related to the marine terrace deposits in the southern part of the bay, which have been dated to approximately 125,000 years ago (Muhs et al., 1994). The beach conglomerate, which outcrops in parts of the coastline, continues offshore and forms the series of rocky ridges that are the substrate of the modern reef. In satellite images, these beach conglomerate ridges show a concave curvature, similar to that is developed on beaches due to the direction of wave approach. Finaly, based on the stratigraphic position of the beach conglomerate, its lithological and textural characteristics, as well as the morphology observed in satellite images, it was determined that the conglomerate ridges are ancient coastlines developed during the sea level rise following the glacial period of isotopic stage 6 and prior to the interglacial period 5e.

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

doi: 10.1130/abs/2026CD-411073

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