Depositional systems of the late Eocene Yolomécatl Formation, northwestern Oaxaca, southeastern Mexico: a first approach

Abstract

Ferrusquía-Villafranca, I., Torres-Hernández, J.R., Ruiz-González, J.E., Martínez-Hernández, E., 2018, Depositional systems of the late Eocene Yolomécatl Formation, northwestern Oaxaca, southeastern Mexico: a first approach: Revista Mexicana de Ciencias Geológicas, v. 35, núm. 2, p. 142-157. ABSTRACTThe discrimination/characterization of depositional systems recorded in formal lithostratigraphic, Cenozoic, continental, epiclastic units of Mexico, is largely a pending task, notwithstanding its great academic and economic importance. Contributing to fill this gap, we present a first approach to discriminate and characterize the depositional systems of the late Eocene Yolomécatl Formation, which fills the namesake, triangle-shaped tectonic basin, and carries the southernmost Paleogene vertebrate fauna of North America. The study area lies between 17°25'-17°30' North Latitude and 97°29'-97°36' West Longitude, and between 2000-2500 m a.s.l.; the federal highway 125 traverses it; Santiago Yolomécatl is the main town.The Yolomécatl Formation is at least 650 m thick, although the continuous thickness measured in the principal reference section is much less (~250 m); it includes fluvial and lake depositional systems sparsely interbedded by tuff sheets (a system per se). The fluvial system consists of 1) Gmm, Gmg, Gcm lithofacies: alluvial fans and related deposits; 2) Gm, Gh, Gp, Gt, St, Sp lithofacies: channel lag deposits; 3) Sr, Sh, Sl, Fl lithofacies: floodplain deposits. The (clastic) lacustrine system includes: 1) Ll, Lsm, Lm lithofacies: offshore deposits; 2) Ll, Lsm lithofacies: playa lake and mud flats deposits. This large thickness of this unit indicates superposition of fluvial/lacustrine systems, and sparse pyroclastic emplacements that took place in a basin gradually subsiding with sedimentation, under humid to subhumid conditions, probably interrupted by seasonal dryness.Finally, the tectonic setting of the Yolomécatl Basin, indicates that its genesis and development are related to the dynamics of the regional, left-lateral strike-slip Tamazulapam fault, which is also regarded as the boundary between the Mixteca (west) and Oaxaca (east) terranes. INTRODUCTIONAfter ~130 years of geologic research in Mexico, important tasks have been barely touched, such as the discrimination and characterization of depositional systems registered in formal, continental, epiclastic, Cenozoic lithostratigraphic units of this country, in spite of their academic and economic importance. Only a few papers on this subject have been published (e.g. Chávez-Cabello et al., 2007;Ferrusquía-Villafranca and Ruiz-González, 2011;Ferrusquía-Villafranca et al., 2016a;Puy-Alquiza et al., 2017

Polish Polar Research

“…-The genus Striatolamia is characterized by stronger irregular striations on the lingual face of the central cusp in comparison to Carcharias. Anterior teeth of Striatolamia are characterized by greatly reduced or even absent cusplets, a less pronounced sigmoidal profile than Carcharias, and more massive roots that form an acute diverging angle (see Ferrusquia-Villafranca et al 1999;Cunningham 2000). The taxonomy and systematic position of Striatolamia is still under debate due to similar dental morphology of the sand tiger shark Carcharias (for a more elaborate discussion, see Kriwet et al 2016).…”