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

  • Ismael Ferrusquía-Villafranca Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.
  • José Ramón Torres-Hernández Instituto de Geología, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava 5, San Luis Potosí, C.P. 78000, Mexico.
  • José E. Ruiz-González Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.
  • Enrique Martínez-Hernández Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.
Keywords: Mexico, Oaxaca, Yolomécatl Formation, Eocene, depositional systems

Abstract

The 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.

Author Biographies

Ismael Ferrusquía-Villafranca, Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.

Instituto de Geología

José Ramón Torres-Hernández, Instituto de Geología, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava 5, San Luis Potosí, C.P. 78000, Mexico.

Instituto de Geología

José E. Ruiz-González, Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.

Instituto de Geología

Enrique Martínez-Hernández, Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación s/n, Ciudad Universitaria, Coyoacán, Ciudad de México, C.P. 04510, Mexico.

Instituto de Geología

Published
2018-07-25
Section
Articles