Boletín de la Sociedad Geológica Mexicana
Volumen 67, núm. 2, 2015, p. 123-143
Geología y estratigrafía del pozo profundo San Lorenzo Tezonco y de sus alrededores, sur de la Cuenca de México
José Luis Arce1,*, Paul Layer2, Isela Martínez3, José Iván Salinas4, María del Consuelo Macías-Romo1, Eric Morales-Casique1, Jeff Benowitz2, Oscar Escolero1, Nils Lenhardt5
1 Instituto de Geología, UNAM, Cd. Universitaria Coyoacán, México, D.F., 04510. Tel. 52 + 55-56224288 ext. 108 FAX. 52 + 55-56224289.
2 Department of Geology and Geophysics and Geophysical Institute, University of Alaska, Fairbanks, AK, USA.
3 Escuela Superior de Ingeniería y Arquitectura, IPN, Ticomán, México, D.F.
4 Facultad de Ingeniería, UNAM, Cd. Universitaria Coyoacán, México, D.F., 04510.
5 Department of Geology, University of Pretoria, Pretoria 0002, South Africa.
The underground stratigraphy of the San Lorenzo Tezonco deep well records intense volcanic activity in the Mexico Basin and surrounding areas during the past 20.1 Ma. The lithological column of the 2008 m deep well is dominated by volcanic material, either as lava flows or pyroclastic deposits (97 %), and only the uppermost 70 m are composed of lacustrine deposits (3 %). Based on field descriptions and laboratory analyses (petrography, whole-rock chemistry, and radiometric dating), it was possible to recognize four lithological packages throughout the well, which were then correlated with exposed rocks. The lower part of the drill core is represented by rocks belonging to the Tepoztlán Formation (876 – 2008 m depth) that vary in composition from basaltic-andesite to rhyolite, with ages ranging from 13 to 20.1 Ma. On the surface this formation outcrops around the towns of Malinalco and Tepoztlán. Between depths of 581 and 875 m, rocks interpreted as being part of the Sierra de las Cruces that vary in composition from andesite to dacite and in age from 0.9 to 5 Ma. Upward in the drill core (510 – 580 m) are andesitic rocks of Cerro de la Estrella volcano, dated at 0.25 Ma. The last volcanic package found in the well is represented by Santa Catarina basaltic-andesitic rocks (70 – 120 m) that are younger than 0.25 Ma, and probably Holocene. Lacustrine deposits crown the stratigraphic column of the drill core with ages probably younger than 34 ka.
Additionally, we conclude that the rocks belonging to the Xochitepec Formation, outcropping around Xochimilco, in Mexico City, have an age of 1.23 to 1.66 Ma, in contrast with the Oligocene age proposed in previous works for these rocks. These new ages plus the chemical composition data allow us to correlate the Xochitepec rocks with those from Sierra de las Cruces
Keywords: San Lorenzo Tezonco deep well, Basin of Mexico, volcanic stratigraphy, geochronology.