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Boletín de la Sociedad Geológica Mexicana
http://dx.doi.org/10.18268/BSGM2003v56n1a4 |
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Los ammonites del Caloviano de la región Mixteca, Oaxaca, México
Raúl Sabino Carrasco-Ramírez
Instituto Nacional de Estadística, Geografía e Informática Dirección Regional Noreste Pino Suárez # 790 Sur, 64000 Monterrey, N. L., México
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Abstract
In the Mixteca region, in northwestern Oaxaca state, Mexico, crop out Middle Jurassic rocks with a rich fossil fauna, consisting mostly of ammonoids. The CallovianYucuñuti Member of the Yucuñuti Formation, consists of nearshore to shelf siltstone, sandstone grit and biomicrite. Ammonoids present in this unit belong in the Reineckeia–Neuqueniceras Assemblage Zone (nov.), which is coeval to the European Anceps Zone, Stuebeli Subzone (base of the middle Callovian). They belong to the Perisphinctidae and Reineckeidae families, and include the following species: Ch. cf. suborion (Burckhardt), Ch. Praecursor (Mangold), N. inermis (Burckhardt), R. anceps (Reinecke) and R. tuberosa (Burckhardt). Reineckeia anceps, the index species of the European Anceps Zone of the early middle Callovian, is described for the first time for Mexico.
Keywords: ammonoids, Formación Yucuñuti, assemblage, Callovian, Mexico.
