Late Triassic stratigraphy and facies from northeastern Mexico: Tectonic setting and provenance José Rafael Barboza-Gudiño* Aurora Zavala-Monsiváis* Gastón Venegas-Rodríguez* Luís Daniel Barajas-Nigoche* Universidad Autónoma de San Luis Potosí, Instituto de Geología, Manuel Nava No. 5, Zona Universitaria, 78240, San Luis Potosí, México ABSTRACT 900 Ma); (2) Pan-African (700–500 Ma); A generalized stratigraphic framework for both and (3) dominant Permian–Triassic (280– provinces is illustrated in Figure 2. Triassic strata in northeastern Mexico dis- 240 Ma). The presence of these zircons dis- Shortening deformation during the Laramide tributed over an area of ~120,000 km2 have plays evidence of sources in Grenvillian orogeny and mid-Cenozoic extensional tec- received relatively little attention in paleo- Oaxaquia block, Pan-African terrains such tonics widely affected these rocks, and they geographic and tectonic reconstructions of as Yucatan and southeastern Texas, and a are extensively covered by Late Jurassic to western equatorial Pangea. Triassic marine prominent contribution from the Permian– Cretaceous limestones and Cenozoic volcanic sequences of the Zacatecas Formation in Triassic east Mexico magmatic arc. Notable rocks and alluvial deposits, thereby rendering western San Luis Potosí and Zacatecas is the absence of detrital contributions from facies interpretations, basin-wide correlations, constitute facies corresponding to different the southwestern North American cra- and paleogeographic reconstructions diffi cult. sections of a submarine fan system previ- ton. The geochronological data thus argue Much discussion exists regarding their precise ously described as the Potosí fan and were against proposed southeastward displace- age, correlation, environments of deposition, deposited on the paleo-Pacifi c margin of ment of Triassic successions and their base- sediment provenance, and tectonic setting. This Pangea. New geochronologic data and fi eld ment to their current position as proposed by uncertainty limits our ability to test tectonic observations permit revision of the stratig- the Mojave-Sonora megashear hypothesis. models for the evolution of this region during raphy from Late Triassic to Early Jurassic We propose that continental Triassic strata the early Mesozoic (Anderson and Schmidt, fl uvial deposits of the Huizachal Group that were deposited in eastern Mexico before the 1983; Salvador, 1987), which was an important crop out in Nuevo León and Tamaulipas and opening of the Gulf of Mexico basin, and are time of tectonic transition on the western mar- indicate a link between the lower part of this thus autochthonous and transported detritus gin of Pangea. Furthermore, Triassic and Early succession (Triassic strata) and the Potosí toward the ancient Pacifi c margin into the Jurassic strata in northeastern Mexico contain a fan. This work proposes and defi nes the Potosí fan, which is also autochthonous. record of a variety of sedimentary environments El Alamar formation, which represents the in western equatorial Pangea that may improve only Triassic strata of the Huizachal Group INTRODUCTION our understanding of paleoclimatic, paleobio- (lower part of the Late Triassic–Early Juras- logic, and paleoceanographic events during this sic La Boca Formation), and is interpreted as Triassic successions in northeastern Mex- particular period of Earth history. a continental succession that records a major ico have been known for more than 100 years The age has been established in several fl uvial system draining equatorial Pangea (Burckhardt and Scalia, 1905), but they are localities by means of their fossil fauna (Burck- and fl owing west into the Potosí fan. Petro- still poorly understood. Outcrops of Trias- hardt and Scalia, 1905; Cantú-Chapa, 1969; graphic and geochemical studies indicate sic strata are isolated across the Mesa Central Gómez-Luna et al., 1998) or fl ora (Mixon et al., that both Triassic successions, the Zacatecas province in the states of Zacatecas and San Luis 1959; Weber, 1997; Silva-Pineda and Buitrón- Formation (marine) and El Alamar forma- Potosí and in the core of anticlines or related Sanchez, 1999), but in many other localities tion (continental) have continental block and to basement uplifts of the Sierra Madre Ori- age relations remain unknown due to a lack of recycled orogenic provenances. U-Pb detrital ental in Nuevo León and Tamaulipas, Mexico fossils. Uncertainties regarding the age, tectonic zircon geochronology by laser ablation– (Fig. 1). The Triassic strata in the Mesa Central setting, and transport history of these strata cre- multicollector –inductively coupled plasma– province (marine) have been assigned to the ate opposing models for the early Mesozoic mass spectrometry show three main zircon Zacatecas Formation (Carrillo-Bravo, 1968, in paleogeography of western Pangea, resulting age populations: (1) Grenvillian (1300– Silva-Romo et al., 2000), La Ballena forma- in an association of presumably coeval strata tion (Silva-Romo, 1994) and Taray Formation from highly contrasting tectonic settings, now ( Córdoba-Méndez, 1964), and in the Sierra in close geographic proximity. Subaerial vol- *E-mails: Barboza-Gudiño: [email protected]; Zavala-Monsiváis: [email protected]; Madre Oriental (continental), to the Huizachal canic rocks and redbeds interpreted as depos- Venegas-Rodríguez: [email protected] Formation (sensu Carrillo-Bravo, 1961) or its of a continental magmatic arc (Jones et al., .mx; Barajas-Nigoche: [email protected]. La Boca Formation (sensu Mixon et al., 1959). 1995; Bartolini et al., 2003; Barboza-Gudiño Geosphere; October 2010; v. 6; no. 5; p. 621–640; doi: 10.1130/GES00545.1; 14 fi gures; 3 tables; 1 supplemental table fi le. For permission to copy, contact [email protected] 621 © 2010 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/6/5/621/3342154/621.pdf by guest on 26 September 2021 Barboza-Gudiño et al. 101° useful in this region because they permit corre- TEXAS lation of strata from different coeval sedimen- tary environments. In addition, they are useful in deciphering contrasting possible source regions COAHUILA NUEVO LEON for detritus in the Late Triassic strata. REYNOSA MONTERREY POTOSÍ FAN: THE TRIASSIC MARINE FACIES OF THE MESA CENTRAL PARRAS N S It is well established that Middle to Late IE SALTILLO R Triassic marine rocks are exposed across the R GALEANA Sierra de Teyra A Mesa Central. Triassic outcrops of siliciclastic M LINARES A San Marcos sedimentary rocks in the vicinity of the city of D TAMAULIPAS Zacatecas (Fig. 1) were fi rst reported by Burck- R E hardt and Scalia (1905), who described Triassic CONCEPCIÓN DEL ORO El Alamar Huizachal-Peregrina fossils including several ammonites (Sirenites 24° O Smithi n. sp., Trachyceras sp., Clionites sp., anticlinorium G R Aramberri 24° o Juvavites sp.) as well as bivalves (23 species of ZACATECAS I l E f Miquihuana Palaeoneilo and unidentifi ed Aviculids) from Tapona 1 CIUDAD VICTORIA o N f a classic locality at Arroyo La Pimienta. This well M T fauna is considered of Carnian age (Burckhardt M O MATEHUALA A Bustamante Valle del Huizachal e E Sierra de Catorce x and Scalia, 1905; Gutierrez-Amador, 1908; S L i A c Maldonado-Koerdell, 1948). Although never C o E CHARCAS formally defi ned, these rocks were fi rst named N TULA T N-America Triásico de Zacatecas ( Gutierrez-Amador , R ront A chita f 1908), and are currently known as the Zaca- L Oua Cortéz uila Coah tecas Formation (Carrillo-Bravo, 1968, in Silva- S. M SAN LUIS POTOSÍ Oaxaquia Romo et al., 2000; Martínez-Pérez, 1972; ZACATECAS adre north south Carrillo-Bravo, 1982). There are no known 100 km SAN LUIS POTOSÍ Guerrero Cuicateco exposures of the base of this unit or other pre- La Ballena composite terrane ya Ma Triassic rocks in the Mesa Central region, their (Sierra de Salinas) 101° Mixteca total thickness anywhere is not known, and Late Triassic (marine) Areas of Precambrian-Paleozoic nowhere can a continuous section of >300 or outcrops without Triassic deposits 400 m be measured, because intense folding Late Triassic (continental) Jurassic redbeds and numerous thrust and normal faults affect and volcanic rocks the succession. The most recent studies of the Triassic rocks Figure 1. Pre-Late Jurassic localities in central to northeastern Mexico (modifi ed after in western San Luis Potosí and Zacatecas are Barboza-Gudiño et al., 1999). Shown are Late Triassic exposures of the marine and conti- sedimentologic, stratigraphic, and tectonic nental facies, post-Triassic redbeds, exposures of pre-Mesozoic crystalline rocks, in some studies interpreting such successions as part cases interpreted as areas of no deposition during the Triassic, and the main volcanic centers of a submarine fan system at the paleo-Pacifi c of the Early Jurassic volcanic arc that crop out. margin of North America (Centeno-García and Silva-Romo, 1997; Silva-Romo et al., 2000; Hoppe et al., 2002; Centeno-García, 2005), named the Potosí fan by Centeno-García (2005). et al., 2008) are near roughly coeval volcanic their inferred counterparts in northwest Sonora, Silva-Romo (1994) informally referred to a rocks and redbeds interpreted as a continental where they are inferred to have formed. The cor- sequence of marine siliciclastic turbiditic layers rift in the Sierra Madre Oriental in Nuevo León relation of Mesozoic rift basins in northeastern and minor carbonate rocks in La Ballena, in the and Tamaulipas (Michalzik,