Paleoecology of Cambrian-Ordovician marine communities of Arivechi, eastern Sonora, Mexico: paleoenvironmental considerations

This work aims to study the preserved communities in rocks from the Cambrian-Ordovician, exposed west of the Arivechi, Sonora town in northwest Mexico. A total of 860 individuals from 70 species are analyzed, belonging to four Cambrian units (El Gavilán, El Mogallón, Milpillas, and La Huerta formations) and one Ordovician unit (El Santísimo formation), the latter one divided into three members. After a petrographic and paleoecological analysis, it is concluded that the El Gavilán and El Mogallón formations are characterized by deposits of an open and external platform dominated by epifaunal suspension feeders. The Milpillas formation is distinguished by rocks deposited in an open and restricted internal platform environment, where epifaunal organisms and suspension feeders prevail. The La Huerta formation is notable for its high content of brachiopods, epifaunal organisms, and suspension feeders. The first two members of the El Santísimo formation show a significant environmental change, as they are deposits from a deep-water cratonic basin. The change in biota includes planktonic organisms and suspension feeders. Finally, the upper member of the El Santísimo formation contains biota characteristics of a slope and a shallow marine platform environment near the coastline, with abundant nektobenthic organism life.