TROPICAL MARINE MOLLUSK ASSEMBLAGES FROM THE PLEISTOCENE OF OAXACA, SOUTHERN MEXICO

Inglés

Abstract

The Colotepec Formation crops out along the southern Pacific coast of Oaxaca, Mexico. This unit harbors a notable diversity of
mollusks from the Pleistocene, mainly taxa of Bivalvia and Gastropoda. The malacological assemblage of both localities consists of 53 taxa of Bivalvia and 71 of Gastropoda; all of them are currently distributed in the southern part of Mexico. Also, specimens of rhodoliths, echinoids, and crustaceans were identified. All the identified taxa inhabit shallow and warm tropical waters, and some are from coastal lagoons. Both localities share 16 taxa of Bivalvia and 11 of Gastropoda. The assemblages are considered para-autochthonous. Most taxa inhabit subtidal environments, on both hard and soft substrates. Bivalves with thick shells display a variety of associated sclerobionts, including bivalves, gastropods, sponges, serpulids, and bryozoans. The ichnodiversity comprises Thalassinoides, Psilolichnus, and Ophiomorpha nodosa. According to the rate of subsidence, the maximal age of the Pleistocene sequences may range from 248,000 to 112,000 years BP (Marine Isotope Stage 8 to Marine Isotope Stage 5). The information on the Pleistocene assemblages provides valuable evidence for conservation strategies for modern taxa. Despite their paleontological value, the localities are at risk of natural hazards and anthropogenic pressures.