Biostratigraphy and depositional history of the tepetate formation at Arroyo Colorado (Early-Middle Eocene), Baja California Sur, Mexico

Abstract

An integrated study of Foraminifera, Ostracoda and lithostratigraphy was conducted on samples of the Tepetate Formation from the Arroyo Colorado locality, Baja California Sur (Mexico). Based on the planktonic Foraminifera, Acarinina pentacamerata (latest lower Eocene) and Hantkenina nuttalli (earliest middle Eocene) zones were recognized that indicate an age range from 51.2 to 48.4 Ma. Benthic Foraminifera suggest correlation with the Penutian to Narizian California stages, which agrees with the planktonic foraminiferal biozones. The sedimentary structures and microfossils throughout the sequence indicate deposition within a transgressive-regressive-transgressive cycle, including environments from the inner to outer marine shelf in depths shallower than 150 m. Gravity flows dominate the sequence, and storm-deposited beds are present in the middle of the section. Considering the nature of this formational unit, we recommend the designation of a composite stratotype, according to the North American Stratigraphic Code.

Ridge-trench interactions and the Neogene tectonic evolution of the Magdalena shelf and southern Gulf of California: Insights from detrital zircon U-Pb ages from the Magdalena fan and adjacent areas

“…Based on early micropaleontologic studies, the Tepetate Forma tion was assigned a Late Cretaceous-early Eocene age (Fulwider, 1976;Coleman, 1979). However, abundant reworked Late Cretaceousearly Tertiary microfossils are found throughout the section and become more prevalent toward the top (Carreño, 2000;Garcia-Cordero and Carreño, 2005). Although the Tepetate Formation may be as old as Late Cretaceous, the most recent micropaleontologic studies conclude that most outcrops were deposited in the early-middle Eocene (Carreno, 2000;Garcia-Cordero and Carreno, 2005).…”

New Crabs From the Eocene and Oligocene of Baja California Sur, Mexico and an Assessment of the Evolutionary and Paleobiogeographic Implications of Mexican Fossil Decapods

“…Mina-Uhink (1957) considered the Arroyo Colorado section as the type locality for the Tepetate Formation, although he did not describe the rocks or the upper and lower boundaries of the unit. Subsequently, numerous other studies have been conducted on the Tepetate Formation (Knappe, 1974;Fulwider, 1976;Minch and Leslie, 1979;Coleman, 1979;Galli-Oliver et aI., 1986;Lopez-Ferreira et aI., 1991;Demetrion, 1991, 1994;Vasquez-Garcia et aI., 1995;Perrilliat, 1996;Carreno, 2000;Gonzalez and Thies, 2000;Ledesma-Vazquez et aI., 2001). Knappe (1974) considered the unit to be early Eocene to early middle Eocene in age based upon planktic and benthic foraminiferans.…”

“…Knappe (1974) considered the unit to be early Eocene to early middle Eocene in age based upon planktic and benthic foraminiferans. In her work, Carreno (2000) defined a latest lower Eocene age for the outcrops of the Tepetate Formation at the Arroyo Colorado locality, based on the planktic foraminifers Acarinina pentacamerata and Hantkenina nuttalli,…”

“…suggesting an age range of 51.2-48.4 Ma. Carreno (2000) also suggested the Arroyo Colorado section as the formal type section for the Tepetate Formation. Demetrion (1992, 1994) considered the Tepetate Formation to be very similar to the Bateque Formation, also located in Baja California Sur, and correlated the Tepetate Formation with the middle part of the Bateque Formation.…”