Paleoecology of a Lower Cretaceous (lower Albian) marine community of Cerro de Oro, central Sonora, Mexico

Abstract

The Early Cretaceous time is characterized by regression and transgression events in the oceans, which impulsed the radiation processes of species. In particular, these oscillation events controlled the distribution of marine invertebrates because they generated geographical barriers and the geographical connection between the different ecological niches. These events promote speciation of which there is a limited record in the state of Sonora. This work is the first quantitative paleoecological study of Early Cretaceous marine invertebrate fauna from central Sonora. The Mural Limestone exposed at the El Caloso Hill, located in the Cerro de Oro area, comprises 28 invertebrate taxa belonging to several groups such as corals, bivalves and gastropods, cephalopods, and echinoderms. These paleocommunities are part of the Early Cretaceous Mexican Sea, which covered the southwestern United States and Mexico during regressive/transgressive events. To evaluate and compare the diversity and richness of these paleocommunities, paleoecological indexes like the Simpson Dominance and Evenness index, Shannon index, Menhinick Species Richness, Total Chao Richness, and Pielou's Evenness index have been applied. In addition, the distribution described for these paleocommunities was defined as a clumped type. The limestone textures described for these environments comprises wackestone, and floatstone, typical of a shallow lagoon environment with low energy. Finally, the dominant guilds were represented by epifaunal sessile suspension, infaunal sessile suspension, and semi-infaunal facultative vagile suspension feeders.