Permian succession from Sierra La Flojera, Sonora, Mexico: Stratigraphy and correlation with Laurentia

Upper Paleozoic rocks crop out in the central part of Sonora, northwestern Mexico. The Sierra La Flojera, located southeast of Hermosillo City, is an isolated hill with a north-south orientation whose age remains controversial due to the scarcity of well-preserved fossils. However, previous information points out the occurrence of rocks from the Pennsylvanian-Permian and the Upper Triassic (Carnian). This paper focuses on the Permian rocks and describes a stratigraphic succession mainly composed of sandstone, conglomerate, limestone, and fossiliferous limestone with abundant fusulinids, and bryozoan, brachiopod, gastropod, and crinoid remains deposited on a shallow marine shelf. The Permian (early Leonardian) age was determined based on the occurrence of the fusulinids Paraskinnerella sp., Skinnerella sp., and Chalaroschwagerina sp., and Paraschwagerina sp. (reworked), which were associated with crinoid-isolated columnar plates of Preptopremnum cf. laeve. The fossil record studied points out that the Sierra La Flojera section was deposited during the early Leonardian and is coeval with other localities of Sonora, Chihuahua, and Coahuila (Mexico), and California and Texas (USA).