Late and facies from northeastern : 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 –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 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 to western equatorial Pangea. Triassic marine prominent contribution from the Permian– and Cenozoic volcanic sequences of the 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 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 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 . Uncertainties regarding the age, tectonic zircon 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.

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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 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 A Bustamante Valle del Huizachal e E Sierra de 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- 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 in the in Nuevo León relation of Mesozoic rift basins in northeastern and minor carbonate rocks in La Ballena, in the and Tamaulipas (Michalzik, 1991). Some (i.e., Mexico with presumably coeval strata in north- central part of Sierra de Salinas, ~150 km east Jones et al., 1995) have sought to explain these eastern North America is also uncertain. of Zacatecas, as La Ballena formation (Figs. 1 seemingly incompatible tectonic settings by We report detrital zircon geochronology data and 3A). These strata contain a Late Triassic reference to the inferred allochthonous nature from key stratigraphic sections across northeast- fauna including Sirenites sp. (Chavez-Aguirre, of Mexico with respect to the North American ern Mexico. These data require a new model for 1968), Clionites sp., Paleoneilo sp., and Halo- craton, suggesting that early Mesozoic strata in the tectonic evolution and paleogeography of this via sp. (Silva-Romo, 1994), Meginoceras sp., north-central Mexico were displaced along the region. The stratigraphic sections studied (Fig. 1) and Clionitites sp. (Gómez-Luna et al., 1998). hypothetical Mojave-Sonora megashear. Those are distributed over an area of ~120,000 km2, Gómez-Luna et al. (1998) pointed out that this models were criticized by Molina-Garza and where ties between outcrops within this region, fauna is similar to those reported from Triassic Iriondo (2005), because early Mesozoic vol- based only in lithologic character, are tenuous Pacifi c provinces in Nevada and British Colum- canic rocks in north-central Mexico appear to (Barboza-Gudiño et al., 1999). Nevertheless, bia in the western Cordillera and, based on the overlie basement of a very different nature than detrital zircon provenance data are particularly presence of Clionitites sp. and Meginoceras

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MIXON et al. SILVA-ROMO CARRILLO- IMLAY CARRILLO- RUEDA-G. (1959) this work this work et al. (2000) BRAVO (1982) (1943) BRAVO (1961) et al. (1993) Zuloaga ZULOAGA ZULOAGA ZULOAGA ZULOAGA Zuloaga Zuloaga ZULOAGA Oxfordian Formation FORMATION FORMATION FORMATION FORMATION FORMATION Formation Formation

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Figure 2. Stratigraphic subdivisions proposed by different authors for the early Mesozoic successions exposed in the Sierra Madre Oriental from Nuevo León and Tamaulipas and the Mesa Central province in San Luis Potosí and Zacatecas. References for different stratigraphic nomenclature cited in text.

sp., assigned a Ladinian age for a lower fossil- and Silva-Romo, 1997). Cantú-Chapa (1969) graywacke beds contain internally graded bed- iferous horizon in the succession. For an upper reported early Carnian Juvavites sp., Cuevas- ding, as well as slump deposits; load and groove fossiliferous horizon, according to their fauna, Pérez (1985) reported Carnian conodonts, and casts are the most common sole marks (Figs. Gómez-Luna et al. (1998) considered an early Gallo-Padilla et al. (1993) reported the Carnian 5D, 5E). The components of the sandstones are Carnian age. A measured section is located ammonoids Anatomites aff. herbichi Mojsiso- monocrystalline quartz and minor polycrystal- 1.7 km to the north of the town of La Ballena vics and Aulacoceras sp. The best-preserved and line quartz, feldspar, as well as shale intraclasts (Fig. 4). Coordinates for the base of the section most extensive exposures of this area are located and detrital mica in a matrix of detrital and dia- are 22°28.150′N/101°42.499′W, and it consists a few kilometers west of the town of Charcas, in genetic quartz, muscovite + illite, and chlorite of interstratifi ed sandstone, siltstone, and shale an area also known as the San Rafael–La Trini- layers. The lithofacies identifi ed in the Charcas with uncommon occurrences of conglomeratic dad anticlinorium. Several isolated minor out- sections in order of their abundance in this area sandstone and quartzite. These rocks are dark crops are in the Presa de Santa Gertrudis area are facies A (channel), followed by facies B and gray on fresh surfaces and brown to grayish- and Sierra La Tapona, northwest of Charcas. In C (representing channel margin environments), yellow on weathered surfaces. The litho facies the Sierra de Charcas, an ~200-m-thick section and subordinate facies D, E, F, and G (suprafan succession (Figs. 4, 5A, and 5B) is interpreted was measured and described by Hoppe (2000). lobe, levee, and interchannel fl ats), correspond- as middle to lower fan facies associated with The same locality was studied by us, and fur- ing to a midfan or suprafan zone. well developed C and B facies, as well as ther described (Fig. 4) following the facies The succession at Sierra de Catorce (Figs. 1 A facies (after Mutti and Ricci-Lucchi, 1972); designations of Mutti and Ricci-Lucchi (1972). and 3C) consists of fi nely laminated shale and these lithofacies correspond to channel mar- Coordinates for the base of the section are intercalated thin siltstone and sandstone layers gins, suprafan lobes, and channel environments, 23°04.300′N/101°11.700′W. This succession (Fig. 5F). The main exposures in this area occur respectively. consists of turbiditic sandstones, commonly along the General and Ojo de Agua Canyons, At Sierra de Charcas in San Luis Potosí (Figs. with partial Bouma sequences, conglomeratic in the northwestern part of the sierra. In addi- 1 and 3B) the Triassic succession is called the sandstones, and graywacke, alternating with tion, there are outcrops of comparable strata Zacatecas Formation (Martínez-Pérez, 1972) siltstone and shale, although generally such in the southern Sierra de Catorce along the or La Ballena formation (Centeno-García pelitic layers are subordinate (Fig. 5C). The El Astillero Canyon. At this locality the Triassic

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22°32′ 22°32′

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Figure 3. Geologic sketch maps of the main localities with outcrops of marine Triassic rocks in San Luis Potosí and eastern Zacatecas state. (A) La Ballena area, northern Sierra de Salinas. (B) La Trinidad–San Rafael anticlinorium, west of Charcas. (C) Northwestern Sierra de Catorce.

age of the succession is inferred from lithologic Detrital zircon data and new geochronological are comparable with those of Charcas, with a similarities and stratigraphic position. There data obtained from pre–Late Jurassic rocks in few differences attributable to an evident pre- are no reports of Triassic fossils in this locality, Sierra de Catorce, described herein, demon- dominance in these outcrops of the inter channel and an older age has been suggested by a pos- strate that this inference is incorrect and are deposits (lithofaces D, E, and G), and subordi- sible late Paleozoic fossil fl ora (Franco-Rubio, consistent with a Late Triassic age of deposi- nate suprafan, levee, and channel deposits. For 1999) and late Paleozoic spores (Bacon, 1978). tion. The facies associations in this study a partial section of the succession

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Sierra de Salinas Sierra de Catorce Early Jurassic volcanics LITHOLOGY Early Jurassic volcanics Early Jurassic Volcanogenic products shallow marine BDE and fluvial cross-bedded orthoquartzite deposits Sierra de Charcas Conglomerate Early Jurassic volcanics DEG Thin-bedded shale and siltstone Medium to thick-bedded sandstone EDGF

A Thin-laminated sandstone and shale BDE Mudstone C BC A N Environments E 0 W

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Ichnofauna 0.0 W 0 E Intraclasts (clay) S Fossiliferous beds Unconformity

Figure 4. Lithologic sections of the Late Triassic marine sequence, measured in La Ballena, Sierra de Charcas, and Sierra de Catorce (see text for coordinates).

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A B

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Figure 5. Facies of Potosí fan. (A) Flute casts on base of fi ne-grained sandstone bed, La Ballena area. Hammer used for scale is 32 cm long. (B) Strongly deformed interchannel mudstone (facies G?) in La Ballena, Sierra de Salinas. Pen used for scale is 14 cm long. (C) Thick-bedded sandstone of facies B (facies designations after Mutti and Ricci-Lucchi, 1972) showing upward-thickening cycles, typical for channels or lobes at the base of distributary channels (normal position), Charcas area, San Luis Potosí. Persons are about 1.7 m. (D) Crossing groove casts at the base of thick-bedded turbidites, Charcas area. (E) Sandstone blocks fl oating in a fi ne-grained sandstone matrix. Inner fan slump deposits of facies F in the Charcas outcrops. Hammer used for scale is 32 cm long. (F) Upward- thinning fi ne-grained sandstone to siltstone cycles of facies D and E (top to the left) in the Sierra de Catorce area, San Luis Potosí. Hammer used for scale is 32 cm long.

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cropping out in the Sierra de Catorce was also line basement is believed to end to the west, lowed Early Jurassic magmatic arc activity measured in detail (coordinates of the base: where the submarine fan deposits (Potosí fan) (Fastovsky et al., 2005; Barboza-Gudiño et al., 23.42.099′N/100°54.750′W (Fig. 4). have been interpreted to overlie 2008). Rocks of the La Boca Formation also A relatively poorly understood succession of in Zacatecas (Centeno-García and Silva-Romo, interfi nger with volcanogenic deposits at sev- intensely deformed fi ne-grained siltstone, shale, 1997; Centeno-García, 2005), changing to an eral localities, including Huizachal and La Boca lithic sandstone, and minor conglomerate and ophiolitic complex in Guerrero-Michoacán and Canyons, and contain a fossil assemblage of carbonate rocks exposed along the Arroyo del Baja California (Centeno-García, 2005). At the vertebrate fauna, which allows assignment to Taray in the Sierra de Teyra (Fig. 1) of north- different localities the Triassic successions were an Early to Middle Jurassic age for redbeds that ern Zacatecas was named the Taray Formation defi ned as lithostratigraphic units or in some crop out in the Huizachal Canyon (Clark et al., (Córdoba-Méndez, 1964). The age of the Taray cases as structural complexes. We propose to 1994). Typically, the La Joya Formation uncon- Formation has been interpreted as late Paleozoic retain the name Zacatecas Formation for all the formably overlies the La Boca Formation and (Córdoba-Méndez, 1964), Late Triassic (Silva- successions of the Potosí fan that can be distin- represents the basal strata of the marine Late Romo et al., 2000), and Jurassic (Anderson guished as a lithostratigraphic unit (e.g., Zaca- Jurassic through Cretaceous succession. et al., 2005). Because of similar lithology and tecas, La Ballena, Charcas, and Real de Catorce) By the last revision of the early Mesozoic stratigraphic position, this unit or part of it can and to use the term “complex” associated with stratigraphy from the region, Rueda-Gaxiola be correlated with the Triassic rocks described a local name for highly deformed rock bodies et al. (1993, 1999) proposed the Los San Pedros in the Mesa Central and considered part of the consisting of a heterogeneous mixture of two or allogroup, which includes a basal volcanogenic Potosi fan. more rock types, in some cases without a pri- unit in the Rio Blanco allomember, which is Using information provided by PEMEX mary stratifi cation preserved (e.g., Taray com- overlain by a volcano-sedimentary allo member, (in Tristán-González et al., 1995) from the plex, Arteaga complex). conforming both the Rhaetian–Hettangtian Tapona-1 well, north of Charcas (Fig. 1), it is Huizachal alloformation. The overlying thought that there is a structural increase in the EL ALAMAR FLUVIAL SYSTEM: Sinemurian–Pliensbachian redbed succession thickness of this rock body, because several CONTINENTAL FACIES OF THE was defi ned by Rueda-Gaxiola et al. (1993) as folds and imbrications affect these strata and the SIERRA MADRE ORIENTAL the La Boca alloformation. However, the type more than 4640 m drilled (the total depth of locality of the Rio Blanco allomember was the well represents the Triassic turbidite sequence) Late Triassic and Early Jurassic strata in the defi ned north of Aramberri Nuevo León. At without reaching the base. We estimate, without a Sierra Madre Oriental in northeastern Mexico are this locality, 65 km away from the type local- palinspastic reconstruction, a possible area extent referred to as the Huizachal Group (Mixon et al., ity of the La Boca alloformation, the volcanic of the Potosí fan system of >120,000 km2. Sev- 1959), consisting of the Late Triassic to Early rocks yielded a U-Pb zircon age of 193 ± 0.2 Ma eral paleofl ow patterns observed from groove Jurassic La Boca Formation and the unconform- (Barboza-Gudiño et al., 2008) directly overly- casts, fl ute casts, and cross-lamination in the ably overlying La Joya Formation of Middle to ing Paleozoic schist (Meiburg et al., 1987), and different localities (Fig. 4) show west-southwest Late Jurassic age. These strata have been stud- the Triassic succession was not deposited. paleocurrent patterns. ied since the 1920s and stratigraphic nomencla- Late Triassic continental strata in Nuevo It is also important to point out that in several ture has evolved (Fig. 2). Heim (1940) assigned León and Tamaulipas (Figs. 1 and 6) consist of places, such as the Sierra de Teyra in northern a pre–Late Jurassic age for redbeds exposed in sandstone, conglomeratic sandstone, siltstone, Zacatecas, or possible localities in Guanajuato the Huizachal, Peregrina, and Novillo Canyons, and mudstone. The facies associations corre- and Querétaro, such Triassic successions occur in the Huizachal-Peregrina uplift, and the areas spond to proximal alluvial fan, braided stream, as structural complexes interlayered with ophio- of Miquihuana and Aramberri in Tamaulipas and and distal meandering stream deposits, showing litic rocks and older sedimentary and meta- Nuevo León (Fig. 1). A Huizachal Formation several west-southwest paleocurrent patterns morphic olistoliths. These exotic rocks are consisting of continental hematitic sandstone, that are in accordance with channel and trunk enclosed in Triassic sand and mudstone-siltstone conglomerate, mudstone, and minor volcanic orientations (Fig. 7). Such Triassic successions strongly deformed matrix, a mélange indicating rocks was formally defi ned by Imlay et al. (1948) in Tamaulipas (Fig. 6A) unconformably over- ancient or accretionary complexes at the type locality in the Huizachal Canyon lie Paleozoic strata or Precambrian–Paleozoic ( Centeno-García, 2005). 20 km southwest of Ciudad Victoria, Tamaulipas. basement, and are overlain by the Jurassic Unconformably overlying the Triassic strata Mixon et al. (1959) reported, in the lower redbeds considered as the upper part of the in all localities in the Mesa Central, there is a unit of their Huizachal Group, defined as La Boca Formation. In Nuevo Leon their volcanic and volcaniclastic succession includ- La Boca Formation, a fl oral assemblage of Late base is not exposed and there is no evidence ing basaltic andesites, rhyolites, and redbeds Triassic age containing Pterophylum fragile, of deposition of Early Jurassic redbeds in this assigned to the Nazas Formation (Pantoja- Pterophylum inaequalle Fontaine, Cephalo- area. This suggests a complex paleogeographic Alor, 1972) as well as a poorly understood taxopsis carolinensis, and Podozamites, which distribution of basement uplift areas or horsts Early Jurassic succession of fl at marine sedi- were revised by Weber (1997) to Laurozamites during early Mesozoic time. Uplifts were prob- mentary rocks interlayered in the Sierra de yaqui, “Ctenophylum braunianum,” Elato- ably separated by elongate grabens occupied Catorce with the basal part of the Nazas For- cladus ex gr. Carolinensis, and questionable by trunk streams of the fl uvial systems, as pro- mation (Barboza-Gudiño et al., 2004; Venegas- fragments of Podosamites, respectively. Weber posed by Michalzik (1991). The best-exposed Rodriguez et al., 2009). (1997) suggested that the fl ora is indicative of and best-preserved of these depocenters is the The Triassic succession is inferred to overlie the Late Triassic and more precisely of the Car- San Marcos–El Alamar area of southern Nuevo Grenvillian granulitic basement on the basis of nian or Norian. León, near the town of Galeana (Fig. 6B). Tri- several xenoliths contained in Cenozoic vol- The continental redbeds assigned to the upper assic fl uvial successions are well exposed along canic rocks in western San Luis Potosí (Ruiz part of the La Boca Formation were deposited federal highway 58 (San Roberto-Linares). et al., 1988; Schaaf et al., 1994). This crystal- during a period of crustal extension that fol- Other exposures are also located near Santa

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TO LINARES

24°°00′ 24°°00′ NUEVO MÉXICO LEÓN NUEVO TAMAULIPAS

LEÓN ′ GOLFO B

DE 30 C ° MÉXICO

A 99° A

AMAULIPAS N A. San Marcos Area T LB06-1 La Boca B. El Alamar Canyon HUIZACHAL-PEREGRINA ANTICLINORIUM Nogales C. Huizachal-Peregrina Anticlinorium La Crucita 24°52′

′ ′ Santa Ana

00 14

° ° ′ GALEANA 24°°52

100° 101° Rancho Rancho B Nuevo Nuevo

CIUDAD VICTORIA

SAN MARCOS El Carrizo

′ SM06-1 14 ° Francisco

Cenozoic cover 101°

5 km ′ I. Madero 00

SANTA CLARA ° 100 24°° ′ 24°°37′ 24°°36′ 37 24°°36′ Late Jurassic-Cretaceous limestones

Río de Lower to Middle Jurassic redbeds San José C El Encinal 400 km Pablillo El Taray SIERRA PABLILLO Lower Jurassic volcanic rocks Joya

0 50 Verde ′

30 Huizachal ° Triassic fluvial succession

99° (TS = El Alamar Formation Type Section) Independencia ′ Precambrian and Paleozoic rocks Puerto de

00

° El Alamar ′ 5km Arrazola San Felipe 52

100° 2.5 km ° SM06-1 =Sample

99°

24°31′ 24°31′ 23°°33′ 23°°33′

Figure 6. Geologic sketch maps of the Late Triassic continental sequence that crops out in the Sierra Madre Oriental, northeastern Mexico. (A) San Marcos area, south of Galeana, Nuevo León. (B) El Alamar Canyon, Nuevo León. (C) Huizachal-Peregrina anticlinorium, Tamaulipas (for key, see Fig. 3).

Clara, 2 km west of state highway 2, and at Alamar Canyon, Nuevo León (coordinates: eral of the sandstones contain basal gravelly El Alamar Canyon in the Sierra de Pablillo 24°55.130′N/099°55.000′W), and in La Boca to pebbly conglomeratic lag horizons, chang- (Fig. 6C). Triassic fl uvial strata in the Galeana Canyon, Tamaulipas (Fig. 7). The section ing upward into fi nely laminated sandstones area are the oldest rocks exposed in this region at San Marcos has a minimum thickness of and siltstones, commonly overlain by mud- and there are no exposures of their bases or 180 m, and the El Alamar Canyon section stones. The most abundant sedimentary struc- of any older strata. We measured three par- is more than 350 m thick. The succession tures are trough cross-beds and channel scours tial sections of continental strata in San Mar- exposed consists of thick-bedded, medium- to (Figs. 8A, 8B); tabular burrows are common cos (coordinates of the bottom of measured coarse-grained arkosic sandstone, predomi- in fi ne-grained facies. These lithologies rep- section: 24°40.750′N/100°06.000′W) and El nantly gray, light green, or brownish-red. Sev- resent fi ning-upward cycles, tens of meters in

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El Alamar Canyon La Boca Canyon Early Jurassic Upper Jurassic fluvial and LITHOLOGY La Casita Fm. Volcano- shallow marine Upper Jurassic genic deposits Volcanogenic products La Joya Fm. deposits N ? Limestone and marl W 0 E Fl Gm Limestone and gypsum Fl n = 66 S Sp Mudstone San Marcos area Siltstone St Sl Medium- to thick-bedded sandstone Gm St Gt Sp Structureless pebbly sandstone

Sp Cross-bedded sandstone Fl St Conglomerate Fm Sp St Gm

Sl Environments Gm P St Floodplain Fl Fm Sand flats Sh St Gt Minor channel system Sp

Mafic sills Gm Gm Major channel system Fm St Structures Gm Gt Sl Graded bedding Gt Sp Gm Trough cross-beds Small trough cross-beds St Gt Sl Trench 100 m P Plants and rootlets Sl Sp Concretions Gm Sl Sp Tubular burrows Sh 50 Fining upward

Gm Chanel, scour and fill Permo-Triassic (?) magmatic rocks Intraclasts (clay) Fossiliferous beds 0 Facies code after Miall (1977, 1978) Unconformity

Figure 7. Lithologic sections of the Late Triassic continental sequence, measured in La Boca Canyon, El Alamar Canyon, and San Marcos area (see text for exact location).

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A B

C D

E F

Figure 8. Facies of El Alamar River. (A) Trough cross-bedding, developed in coarse-grained sandstone (facies St after Miall, 1977, 1978). (B) Channel-fi ll sandstones incising mudstones in a road outcrop at San Marcos area. (C) Poorly sorted conglomerate of the Gm facies, composed mainly of quartz, chert, quartzite greenstone, and black shale pebbles, cropping out in La Boca Canyon, Tamaulipas. (D) Facies P of silicifi ed concretions in mud- stones, El Alamar Canyon. (E) Petrifi ed trunk (chert and carbonate) in a conglomeratic sandstone, El Alamar Canyon, Nuevo León. (F) Rhizoliths (fi ve circular sections around the hammer) in fi ne-grained sandstone to siltstone facies of the fl ood-plain deposits in the San Marcos area, Nuevo León. Hammer for scale is 32 cm long. All facies designations herein are after Miall (1977, 1978).

thickness , interpreted as basal channels over- using the codes of Miall (1977): conglomerate and mudstone to siltstone facies with carbon- lain by sand fl ats and overbank deposits, (Fig. 8C) facies (Gm, Gt), trough and planar ate concretions (Fig. 8D) (Fm, P). There is a formed in low sinuosity streams and braided cross-beds as well as horizontal-bedded coarse notable abundance of petrifi ed wood (Fig. 8E) channels. Michalzik (1991) interpreted this sandstone (St, Sp, Sh), horizontal bedded and in the form of centimeter-long fragments of cyclic deposition as Donjek-type fl uvial sedi- planar cross-bedded sandstone (Sh, Sl), lami- tree trunks as much as 10 m long identifi ed mentation, and recognized different lithofacies nated and massive siltstone facies (Fl, Fm), as Araucarioxylon sp. (R.A. Scott, personal

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commun., in Carrillo-Bravo, 1961). The pet- STRATIGRAPHIC REVISION istics and stratigraphic position. The name El rifi ed wood is commonly associated with Alamar formation is derived from El Alamar Gm and Gt conglomerates and St, Sp coarse- The Late Triassic–Early Jurassic continen- Canyon in the Sierra de Pablillo, Nuevo León, grained sandstone, which represent channel tal facies, included in the La Boca Forma- where the proposed unit stratotype is located. and channel bar deposits, principally in the tion of Nuevo Leon and Tamaulipas, requires The defi ned type section is located in the west- sequences exposed in La Boca canyon, in stratigraphic revision. New fi eld and analytical ern wall of El Alamar Canyon, 1.5 km north of Tamaulipas, and El Alamar Canyon, in Nuevo evidence demonstrate the existence of a Late El Alamar de Abajo Ranch (Fig. 6C). El Ala- León (Fig. 7). The section at La Boca canyon is Triassic fl uvial succession, separated from an mar Canyon is located in the source area of the ~350 m in thickness. Its base is not exposed as overlying Early Jurassic volcanic-sedimentary Rio Pablillo, which drains the internal part of it is in fault contact with Permian(?) intrusive redbed succession. Interlayered volcanic rocks the Sierra Madre to the Gulf of Mexico coastal rocks (base of the measured section at coordi- yielded a 189.0 ± 0.2 Ma age (U-Pb, zircon) in plain in the region of Linares, Nuevo León. nates 23°54.500′N/099°20.280′W). the basal part of the Jurassic redbeds exposed This locality may be accessed via an 11 km Several decimeter-sized cylindrical burrow in the Huizachal Valley (Fastovsky et al., 2005) route through the sierra, departing from the casts are associated with the siltstone and mud- and a 193 ± 0.2 Ma U-Pb zircon age (Barboza- town of Pablillo at the Nuevo León highway 2, stone facies, which represent fl oodplain depos- Gudiño et al., 2008) for an ignimbrite of the with good accessibility for a fi eld vehicle. The its. Such structures are common in the upper Aramberri area; both ages are younger than the base of the sequence is not exposed, but the part of the sequence exposed in Cerro La Nieve, Triassic redbeds that crop out in the western and measured section from the top at the coordinates in the San Marcos area. The burrows are per- northern part of the Huizachal Peregrina anti- 24°33.083′N/099°55.500′W to bottom at the pendicular to bedding, as cylindrical 20–30-cm- clinorium and the El Alamar–San Marcos area coordinates 24°55.133′N/099°55.000′W, con- long casts 5–15 cm in diameter. The casts are in Nuevo León. In consequence, the basal Rio sists of more than 350 m of siliciclastic fl uvial fi lled by gray, green, and yellow siltstone and Blanco allomember of the Huizachal alloforma- deposits as described in Table 1 (see also Fig. 7). mudstone, similar to the surrounding rocks tion, as defi ned by Rueda-Gaxiola et al. (1993), In the Huizachal-Peregrina anticlinorium (Figs. 7 and 8F). Michalzik (1991) interpreted is evidently Early Jurassic in age. in Tamaulipas incomplete sections of El Ala- these trace fossils as lungfi sh burrows, similar Considering the confusion generated by the mar formation unconformably overlie Paleo- to those reported in Late Triassic strata of the inclusion of the studied Triassic succession zoic metamorphic, sedimentary, and magmatic Colorado Plateau (Dubiel et al., 1987). There within a formally defi ned stratigraphic unit of rocks; the formation is in turn unconformably has been discussion on the origin of such similar Late Triassic–Early Jurassic age (La Boca For- overlain by Jurassic redbeds and volcanogenic structures described from the Colorado Plateau mation sensu Mixon et al., 1959), we formally rocks (upper La Boca Formation sensu Mixon (McAllister et al., 1988), that were later inter- propose a new stratigraphic unit, named the El et al., 1959) and/or Late Jurassic redbeds of the preted as crayfi sh burrows and fi nally as rhizo- Alamar formation, for the Late Triassic succes- La Joya Formation (upper Huizachal Group liths (Tanner and Lucas, 2006). Burrows are sion. The purpose of this newly defi ned unit is sensu Mixon et al., 1959). common in mudstones, and in silicifi ed pedo- to differentiate the Late Triassic succession, The Triassic sequence of the El Alamar genic gray to light green calcretes. which is identifi able by lithologic character- formation was considered by Carrillo-Bravo

TABLE 1. SIMPLIFIED MEASURED SECTION OF THE EL ALAMAR FORMATION AT TYPE SECTION IN EL ALAMAR CANYON, STATE OF NUEVO LEÓN Depth Lithology (m) Unconformity, breccia (La Joya Formation) top Siltstone to mudstone, red-brown, fi ne planar cross-lamination 24 Sandstone to siltstone, red, mica rich, fi ne laminated, medium- bedded, small trough cross-bedding 43 Pebbly sandstone, red, structureless, conglomeratic sandstone 23 Coarse-grained to medium-grained sandstone to laminated, gray to red-brown siltstone, structureless 20 Conglomerate to conglomeratic sandstone with abundant white quartz pebbles 5 Siltstone to mudstone, red-purple and gray-green with conglomeratic lenses 45 Conglomeratic sandstone 3 Fine- to medium-grained sandstone, green 23 Coarse-grained and conglomeratic sandstone, gray-pink, mica rich, petrifi ed wood, red-brown siltstone layers 1 5 Medium- to coarse-grained sandstone and siltstone, black shale intraclasts 14 Poorly sorted conglomerate, medium- to coarse-grained sandstone, conglomeratic sandstone 10 Siltstone, gray-green to medium-grained structureless sandstone 8 Poorly sorted conglomerate, well-rounded pebbles, quartz, quartzite, gray-black chert, and greenstone 5 Medium-grained sandstone, siltstone to mudstone, green to red-purple, medium- bedded, structureless 20 Conglomeratic sandstone 1 Medium-grained sandstone, laminated 8 Fine-grained sandstone to siltstone, red-purple, including chert and oxide concretions 5 Medium- to coarse-grained sandstone and conglomeratic sandstone, petrifi ed wood fragments 1 0 Fine-grained sandstone and fi ne laminated siltstone, gray-green 12 Medium-grained, structureless sandstone and interbedded poorly sorted conglomerates, petrifi ed wood 6 Conglomeratic sandstone changing upward to fi ne-grained and fi ne- laminated gray mica-rich sandstone 2 Medium- to coarse-grained sandstone, cross-bedding 8 Fine-grained sandstone, purple-red, thick- bedded, planar cross-lamination 10 Thick-bedded red conglomeratic to medium-grained sandstone, large planar cross-bedding 30 Base not exposed bottom Total thickness 350 Note: See text and Figure 6C for location.

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(1961) as the basal part of the Huizachal For- succession of continental redbeds (La Boca tion and analysis techniques described in detail mation following the fi rst defi nition of Imlay Formation) was generated during arc activity in in Gehrels et al. (2006). The analysis involves et al. (1948), and this corresponds to member B northeastern Mexico. The La Boca Formation the ablation of zircon with a New Wave/Lambda of La Boca Formation as described by Mixon was deposited in an extensional period during Physic DUV193 Excimer laser (operating at a (1963) and originally defi ned by Mixon et al. and after the magmatic arc activity. The La Boca wavelength of 193 nm) using a spot diameter of (1959). Member A of Mixon (1963) also cor- Formation is in turn unconformably overlain by 15–35 µm. LA-ICPMS analysis is particularly responds to his member C, and appears as a the La Joya Formation (Mixon et al., 1959), well suited for detrital zircon studies because of basal unit as a result of stratigraphic repetition which represents the base of the marine Late the rapid generation of large data sets; we ana- caused by normal and strike-slip faults. Strata Jurassic transgressive sequence coeval with lyzed ~100 zircon crystals from each sample. of the Triassic El Alamar formation were prob- opening of the Gulf of Mexico. For each analysis, the errors in determining ably included in the Jurassic redbed succession 206Pb/238U and 206Pb/204Pb result in a measure- of the La Boca alloformation as defi ned by ANALYTICAL RESULTS ment error of ~1%–2% (at 2σ level) in the Rueda-Gaxiola et al. (1993). 206Pb/238U age. The errors in measurement of The El Alamar formation was identifi ed on U-Pb geochronology of detrital zircons was 206Pb/207Pb and 206Pb/204Pb also result in ~1%– the basis of similar lithology and a comparable performed to determine the maximal deposi- 2% (at 2σ level) uncertainty in age for grains fl uvial facies and subfacies along the western tion age as well as the provenance of four sand- that are older than 1.0 Ga, but are substantially fl ank of the Huizachal-Peregrina anticlinorium. stone samples. The samples CH06–1 (Charcas, larger for younger grains due to low intensity of El Alamar strata are not exposed in the Huizachal San Luis Potosí), RC06–31 (Sierra de Catorce, the 207Pb signal. For most analyses, the cross- Valley south of Ciudad Victoria. In the San Mar- San Luis Potosí), SM06–1 (San Marcos, over in precision of 206Pb/238U and 206Pb/207Pb cos area, south of Galeana, Nuevo León, it is Nuevo León), and LB06–1 (La Boca Canyon, ages occurs at 0.8–1.0 Ga. well exposed along the federal highway 58, km Tamaulipas) were analyzed by laser ablation– The resulting ages are plotted in concordia 76.5, but is absent in the Miquihuana-Aramberri multicollector–inductively coupled plasma diagrams (Fig. 9) and are also shown on age- area in southern Nuevo León and Tamaulipas, mass spectrometry (LA-MC-ICPMS) at the Ari- probability plots (Ludwig, 2003). These plots where Paleozoic schist and phyllites are well zona LaserChron Center, following the separa- show each age and its uncertainty (measurement exposed, underlying Jurassic redbeds or vol- canic rocks and Cretaceous marine beds. The main criterion that permits discrimination of the El Alamar and La Boca fl uvial successions 2600 CHARCAS is the conspicuous absence of volcanic rocks or volcanogenic layers in the Triassic succession

(El Alamar Formation), in contrast to a common U occurrence of volcanogenic strata in the overlay- 238 2200 ing deposits of the Jurassic succession (La Boca R DE CATORCE

Formation). In addition, a general gray-green Pb/

and occasionally yellow to dark brown color is 206 distinctive of the El Alamar formation. This is in 1800 contrast to a consistent red-purple and red-brown SAN MARCOS color of the overlying Jurassic strata. The pres- ence of abundant petrifi ed wood is also charac- 1400 teristic of the Triassic unit. BOCA The biostratigraphic age of the El Alamar for- LA mation is determined on the basis of Carnian– 1000 Norian fl oras fi rst reported by Mixon et al. (1959) and reinterpreted by Weber (1997). A Late Triassic age of deposition is also in agree- 600 ment with an Early Triassic (245 Ma) maximum depositional age indicated by the zircon geo- chronology described in the following. The El 200 Alamar formation is thus the same age as the Late Triassic Zacatecas Formation, which rep- resents the marine counterpart of the El Alamar fl uvial system. We show here that they also have very similar provenance characteristics. Volcanic and volcaniclastic strata overlying the Triassic successions throughout the Mesa Central and at several localities in the Sierra 207Pb/235U Madre Oriental have been interpreted as rem- nants of the Early Jurassic Nazas continental arc Figure 9. U/Pb concordia-diagrams for the analyzed samples (2σ error ellipses). Locations (Jones et al., 1995; Barboza-Gudiño et al., 1998; of samples are shown in Figures 3 (Potosí fan: RC06–31, CH06–1) and 6 (El Alamar River: Bartolini, 1998; Bartolini et al., 2003). A coeval LB06–1, SM06–1).

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error only) as a normal distribution, and add all 25 ages from a sample into a single curve (Fig. 10; 254 Ma CHARCAS Supplemental Table File1). eaieprobabilityRelative Maximal depositional ages between 216 and 20 214 Ma (sample collected in La Boca Canyon) and 230 and 225 Ma (sample collected in the Sierra de Charcas) correspond to the Late Trias- 15 sic. The absence of Early Jurassic zircons also indicates deposition of the succession prior to 10 the presence of the Early Jurassic volcanic arc

in the region, so that a real depositional age for 527 Ma the analyzed samples in the Late Triassic may 5 423 Ma 1242 Ma 1025 Ma be inferred, as also known from biostratigraphic 687 Ma data for the marine sequence (Cantú-Chapa, 1969; Cuevas-Pérez, 1985; Gómez-Luna, 1998; 0 9 Gallo-Padilla et al., 1993) and the Late Triassic 254 Ma REAL DE CATORCE fl ora found in the fl uvial sequence exposed in 8 Nuevo León and Tamaulipas (Carrillo-Bravo, 7 1961; Mixon et al., 1959; Mixon, 1963; Weber, probabilityRelative 960 Ma 1997). The maximum age of deposition for the 6 turbiditic succession exposed in the Sierra de Catorce, San Luis Potosí, is 230–225 Ma (three 5 zircon ages between 237 and 209 Ma) and con- 4

fi rms a post–Late Permian age for these strata, 583 Ma 1167 Ma consistent with an interpreted Late Triassic age 3 508 Ma (Martínez-Perez, 1972; López-Infanzón, 1986; Figure 10. Probability density 2

Cuevas Perez, 1985; Barboza-Gudiño et al., distribution histogram plots of 1524 Ma1788 Ma 1999), but incompatible with an interpreted detrital zircons; all the sam- 1

late Paleozoic age (e.g., Bacon, 1978; Bartolini, ples show a main pick by 245– 0 1998; Franco-Rubio, 1999). 269 Ma, corresponding with the 12 SAN MARCOS A fundamental goal of the detrital zircon Permian–Triassic magmatic arc, 269 Ma geochronology was also the comparison of the There are present also as main 977 Ma populations, Pan-African (600– 10

results between the analyzed samples in order probabilityRelative to correlate their maximal age of deposition, as 450 Ma) and Grenvillian (1250– well as to compare provenance similarities. As 900 Ma) zircons. 8 shown in Figures 9 and 10, there are notable

contributions of a Permian–Triassic detrital 6 1200 Ma zircon age population (280–245 Ma) in all of

the samples, corresponding with the eastern 4 598 Ma Mexico Permian–Triassic magmatic arc, which 1315 Ma yields K-Ar ages from 284 to 232 Ma (Torres 2 et al., 1999; Dickinson and Lawton, 2001). Other Paleozoic ages (467–420 Ma) probably correspond to – magmatic 0 rocks described in peri-Gondwanan terranes of 245 Ma Mexico, like the Acatlán Complex (Miller et al., 60 LA BOCA 2007) or detrital zircon age populations present

in the Granjeno Schist in northeastern Mexico 50 (Nance et al., 2007) or the El Fuerte Formation Relative probability

in Sinaloa (Vega-Granillo et al., 2008). There 40 are other populations present that correspond

to the Pan-African (700–500 Ma) and Gren- 30 villian (1300–900 Ma) events, as well as sub-

ordinate Paleoproterozoic–Archean zircon age 20 populations. In sample LB06–1, collected in

10 1Supplemental Table File. Excel fi le of four tables. If you are viewing the PDF of this paper or read- ing it offl ine, please visit http://dx.doi.org/10.1130/ 0 0 400 800 1200 1600 2000 2400 2800 GES00545.S1 or the full-text article on www.gsapubs Ma .org to view the supplemental table fi le.

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Qt Qm Craton Real de Catorce interior Craton Charcas interior La Ballena Quartzose La Boca recycled Transitional Transitional Cañón del Novillo continental continental Recycled Cañón del Alamar orogenic San Marcos Peregrina

Mixed

Transitional recycled Dissected arc Basement Dissected arc uplift Basement uplift Lithic Transitional arc Transitional arc recycled undissected arc undissected arc F L F Lt Figure 11. Ternary diagram (after Dickinson 1985), based on monocrystalline quartz (Qm), total feldspar (F), and lithic grains (Lt), show- ing provenance of the Triassic rocks from several localities in northeastern Mexico. Qm—monocrystalline quartz; F—feldspar—potassium feldspar (K)+plagioclase (Pl); L—lithic fragments; Lt—L+ polycrystalline quartz (Qp).

La Boca Canyon, >70% of the zircons yielded In order to correlate the studied sequences, populations, the sandstone petrology sug- ages in the range 300–200 Ma, corresponding sediment-petrographic and geochemical stud- gests similar source areas. This is shown by to the Permian–Triassic arc, with an age pick ies were performed to defi ne provenances applying petrographic and geochemical tech- near 245 Ma and subordinate Pan-African and and a possible link between the Late Trias- niques such as the provenance triangles (after Grenvillian zircon populations. This is probably sic fl uvial deposits of El Alamar River (El Dickinson, 1985) that show continental block a result of the proximity of several outcrops of Alamar formation) and the Potosí fan (Zaca- and recycled orogen provenances (Fig. 11; the Permian magmatic rocks observed in the tecas Formation). Like the distinct zircon age Table 2) and geochemical methods as shown Huizachal-Peregrina anticlinorium, close to the depocenters of the fl uvial facies. TABLE 2. POINT COUNTING DATA OF 16 SANDSTONE SAMPLES FROM THE The Charcas locality, the most western sam- EL ALAMAR FORMATION (NUEVO LEÓN AND TAMAULIPAS) AND 9 SAMPLES pled locality, is also characterized by a promi- FROM THE ZACATECAS FORMATION (SAN LUIS POTOSÍ–ZACATECAS) nent Late Permian peak (centered at 254 Ma Sample Qp Qm K P Ls Lv Lm Mx Total Qt Lt and accounting for 35% of the grains analyzed), El Alamar Formation CAL.01 38 549 179 44 49 0 16 114 989 587 65 small populations of a few grains each for the CAL.04 18 150 35 20 22 4 8 0 257 168 34 Mesoproterozoic (1300–900 Ma), Pan-African CAL1.1. 14 552 278 56 7 0 19 72 998 566 26 (700–500 Ma), early Paleozoic (Silurian), and CAL1.1.1. 9 205 26 15 8 3 12 3 281 214 23 CAL1.1.4.075500001292 75 0 isolated grains of Archean and Paleoproterozoic CAL1.1.8. 21 489 175 4 26 0 10 268 993 510 36 age. The Real de Catorce locality shares the CAL1.1.3. 10 35 10 15 5 4 8 5 92 45 17 abundance of Late Permian grains (20 grains CAL1.2.4. 15 417 352 87 15 0 17 28 931 432 32 CN-2.1. 37 569 10 0 39 0 51 186 892 606 90 making 20% of the analyzed grains), but also CN-2.2 64 225 5 0 27 0 12 99 432 289 39 contains distinct peaks of Pan-African (508 and LBP03 37 502 297 99 4 2 34 108 1083 539 40 PRGRI 101 665 0 0 54 0 103 259 1182 766 157 583 Ma), Grenville (960 and 1167 Ma), and few SMP2.1 51 417 164 14 56 13 65 169 949 468 134 Paleoproterozoic grains. The section of the El SMP2.3 32 363 178 30 34 4 7 147 795 395 45 Alamar formation at the San Marcos locality is SMP2.4 80 677 124 24 94 10 82 182 1273 757 186 SMP2.6 78 413 211 22 74 4 76 187 1065 491 154 nearly identical to the Real de Catorce locality. Perhaps as notable as the presence of Zacatecas Formation CHR3.03. 60 482 258 61 23 3 49 94 1030 542 75 Permian , Pan-African, and Grenvillian zircons CHR6.03. 59 559 271 87 29 20 34 40 1099 618 83 is the absence of Yavapai (ca. 1.7 Ga), Mazatzal CHR8.03 68 475 226 48 54 5 27 65 968 543 86 (ca. 1.6 Ga), and Mesoproterozoic (1.45–1.40 Ga) CHR9.03 66 492 261 73 27 2 64 44 1029 558 93 ENC-1 0 35 25 10 5 4 3 7 89 35 12 zircons that might have been derived from base- LB01 40 472 369 57 21 0 6 54 1019 512 27 ment typical of the American southwest (Amato RC23 30 461 80 0 35 0 6 123 735 491 41 RC25 32 490 20 0 11 0 15 13 581 522 26 et al., 2008), and are present in Triassic strata RC27 177 277 20 0 29 0 26 158 687 454 55 of the Colorado Plateau (Dickinson et al., 2007) Note: Qp—polycrystalline quartz; Qm—monocrystalline quartz; K—potassic feldspar; P—plagioclase; and Sonora (e.g., Gehrels and Stewart, 1998; Ls—sedimentary lithic fragments; Lv—volcanic lithic fragments; Lm—metamorphic lithic fragments; Mx—matrix; Gonzalez-León et al., 2005, 2009). Qt—total quartz; Lt—total lithic fragments,

634 Geosphere, October 2010

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in the chondrite-normalized rare earth ele- 1000 El Alamar C. ment (REE) plot (Fig. 12A). All REE patterns Novillo C. show a negative Eu anomaly. This is indica- La Boca C.

e

t San Marcos

tive of provenance from igneous rocks, which i

r

are formed by intracrustal differentiation with d 100

n

plagioclase fractionation in the upper conti- o

h

nental crust. There is a notable similarity with C

/

k

light REE enrichment and a fl at heavy REE c sector in all the cases. The Th/Sc versus Zr/Sc o R 10 plots (Fig. 12B) shows a zircon addition as a result of sediment recycling; this is typical for trailing-edge turbidites in a passive margin A (McLennan et al., 1993). Chemical data of the Figure 12. (A) Chondrite- six analyzed samples are shown in Table 3. 1000 1 normalized rare earth element Real de Catorce (REE) patterns of 17 analyzed The only available isotopic data for Triassic La Ballena sediments are whole-rock Sm-Nd analyses of Charcas samples. All rocks show very

sandstones collected in La Ballena and Zaca- e similar patterns with light REE

t

i

tecas, reported by Centeno-García and Silva- r enrichment and a fl at heavy

d 100

ε n REE pattern, characteristic for Romo (1997); the initial Nd ratios are –5.2 and

o

–5.5, respectively, and are indicative of an old h a passive margin setting and a

C upper continental crust provenance, as well as / negative Eu anomaly, typi cal for

k c upper continental crust with the Nd-model ages of 1.6–1.3 Ga, in agree- o ment with a model with an old continental R 10 an old upper continental crust block. Likely sources are thus the Precambrian provenance (McLennan et al., Oaxaquia block and Pan-African basement in 1993). (B) Th/Sc versus Zr/Sc the east-northeast part of the region. (after McLennan et al., 1993) 1 for fine-grained sandstones DISCUSSION La Ce Pr NdSm Eu Gd Tb Dy Ho Er Tm Yb Lu to mudstones from continental to marine Triassic rocks from The age, correlation, and tectonic and northeastern Mexico. All ana- lyzed rocks show a high Zr/Sc paleogeographic settings of Triassic strata in 10 north-central and northeastern Mexico have Sediment Recycling ratio, typical for turbidite sands

d i (Zircon Addition) been the subject of considerable debate (see c from passive margins or for a recycling sediment because of Bartolini et al., 2001, and references therein). 1 A key observation is that volcanic and volcani- zircon addition. C.—canyon. clastic rocks of Early Jurassic age overlie Tri-

c

assic marine strata in north-central Mexico S / .1 B Charcas

(Fig. 13), for example at Sierra de Charcas, h La Boca

T La Ballena source rock Compositional Sierra de Catorce (Real de Catorce), and Sierra Novillo Canyon de Salinas (La Ballena). Comparable Early Variations El Alamar Canyon .01 San Marcos

Jurassic strata also containing volcanic detritus c i R. de Catorce

s

and fl ows overlie the Triassic fl uvial succes- a b composition sion assigned here to the El Alamar formation mafic felsic in Nuevo León and Tamaulipas. Thus the Tri- .001 assic redbeds of the El Alamar formation in .1 1 10 100 1000 the region can be distinguished from younger Zr / Sc La Boca redbeds by the absence of volcanic components and its distinct Triassic fl ora. Fos- sil fl ora indicate a Late Triassic age for the El Alamar formation, which is thus at least in part of contemporaneous magmatism. Furthermore, other exposed Triassic successions, such as correlative with Late Triassic marine strata in our results suggest that a gap in arc magma- pelagic strata and associated ophiolites of the Zacatecas and San Luis Potosí, for which a tism existed between the Early Triassic and the San Hipólito Formation in Baja California Ladinian–Carnian age is indicated by ammo- Early Jurassic in northern Mexico. Admittedly, (Sedlock and Yukio, 1990), Triassic conti- noide fauna. The fact that Early Jurassic vol- our data set is small and Triassic magmatism nental to transitional marine strata of the Bar- canic rocks overlie Triassic rocks and the lack is evident in Coahuila (Molina-Garza and ranca Group in central Sonora (Stewart and of Middle or Late Triassic detrital zircons in Iriondo, 2005); therefore our data suggest at Roldán-Quintana, 1991), and Triassic shallow Triassic strata studied suggest that a continen- least a signifi cant decrease in magmatic activ- to deep marine strata of the Antimonio and tal volcanic arc was not established in north- ity, if not a complete gap in magmatism. Río Asunción Formations in northwest Sonora central and northeastern Mexico until Early A large distance separates Triassic strata in (González-León et al., 2005). Thus estab- Jurassic time. Triassic strata show no evidence north-central and northwestern Mexico from lishing any relationship (paleogeographic,

Geosphere, October 2010 635

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l E a c o aster, Ontario, Canada). For sample locations, see Figures 3 and 6. aster, B

a L r a m a l A

l E s o c r a M

n a S e c r o t a C

TABLE 3. MAJOR AND TRACE ELEMENT COMPOSITION OF TRIASSIC SEDIMENTS FROM NORTHEASTERN MEXICO TRIASSIC SEDIMENTS FROM NORTHEASTERN COMPOSITION OF TRACE ELEMENT AND 3. MAJOR TABLE e d

l a e R a n e l l a B

a L 0.7905.62 0.627 3.37 0.475 0.584 5.150.13 0.710 4.71 0.10 0.839 6.71 0.11 0.951 4.78 0.13 0.657 5.18 0.14 0.770 0.464 3.69 0.11 0.569 5.77 0.12 0.577 11.31 0.07 0.996 4.38 0.07 0.537 0.47 0.14 0.874 8.42 0.804 0.32 0.902 3.74 0.05 5.43 0.05 2.14 0.08 3.83 0.15 0.08 0.09 61.6917.61 79.88 9.21 76.95 63.33 9.58 69.07 11.34 73.13 14.24 69.42 11.77 77.26 10.07 69.82 10.36 28.33 13.43 66.13 11.46 81.25 14.81 65.31 12.22 74.86 15.69 62.07 11.58 66.87 18.54 64.45 14.81 17.65 LOI—loss on ignition. Analyses performed by inductively coupled plasma–mass spectrometry at Activation Laboratories, Ltd. (Anc Analyses performed by inductively coupled plasma–mass spectrometry at LOI—loss on ignition. y t i 3 l 3 2 5 2 O 0.64 3.00 2.29 1.63 1.25 2.44 1.40 1.50 0.16 0.17 0.23 0.20 0.40 2.64 0.71 0.87 0.46 a O 2 O 2 c OO 3.72 0.79 0.67 2.26 2.57 1.67 1.59 1.23 2.98 1.47 3.63 1.70 2.96 1.68 4.37 3.43 4.33 Note: 2 2 2 o Ti O Fe Trace elements (ppm) Trace K Al MgO 1.87LOI 0.60 1.10 6.91 1.51 1.79 1.49 3.21 0.95 8.03 2.11 3.41 2.06 3.20 2.19 5.20 4.44 3.00 3.51 4.04 0.17 19.96 1.86 4.59 1.20 2.38 1.92 4.28 0.77 2.40 1.42 5.39 9.55 6.31 P RbBaThU 179 1,040Ta 12.4 197 35 3.15 0.90 9.10 139 30 1.83 0.59 5.73 411 1.53 0.49 91 6.89 606 1.80 0.65 84 9.68 2.04 653 0.67 7.90 53 1.57 582 0.59 5.21 57 1.25 325 0.61 6.21 1.61 37 0.53 927 9.82 2.12 0.78 108 634 7.19 1.83 0.48 13.9 905 62 2.73 0.93 10.4 557 126 2.89 1.05 7.66 773 71 1.15 0.56 6.98 411 2.00 92 0.50 15.4 927 3.01 1.02 67 11.2 721 3.44 0.80 14.3 198 1,010 3.27 1.01 138 190 SiO c9 711131113915131272010211619 YSc198 V 34.0 206 17.0 60 22.4 54 26.9 19.9 82 17.5 101 25.0 78 17.9 82 21.4 48.9 62 45.6 104 22.5 81 17.4 59 15.7 53 36.1 116 27.9 28.8 70 152 141 149 Major elements (wt%) MnOCaONa 0.013 0.39Total 0.040 0.60 0.031 99.37 0.42 0.061 100 0.030 6.51 99.98 0.036 0.36 100 0.119 1.34 99.97 0.058 100 3.92 0.036 0.28 100 0.501 0.26 0.155 100 21.13 0.003 99.53 0.036 1.74 99.37 0.044 0.05 100 0.035 0.14 99.07 0.017 100 0.46 0.018 0.43 99.21 0.80 99.92 100 0.33 99.78 EuTl1.120.280.260.760.600.400.420.290.810.460.930.540.900.451.280.781.01 Gd 1.16 5.55 0.992 4.14 1.04 4.79 1.39 6.49 1.07 4.07 1.36 4.71 1.41 5.31 0.893 3.59 0.661 2.50 3.25 10.3 2.03 1.01 9.45 1.68 4.40 0.641 5.30 1.66 3.37 1.21 7.19 1.20 4.79 4.95 b91555–––86 8 6 513612 NbPb1911–5–5–55–5–5–58 Sr70504715024406248189923699662384834 ZrHf 10.8 156 7.6 3.9 362 6.7 9.3 206 9.1 6.4 151 9.4 4.5 343 9.3 8.2 380 9.5 9.5 297 7.7 396 7.7 10.6 188 9.8 7.1 85 5.7 11.4 237 2.8 11.8 278 6.6 9.0 274 7.5 7.9 178 7.3 13.1 198 11.6 4.9 212 13.1 5.3 237 5.7 6.4 L Sample 02 LBP 03 LBP RC 23 RC 17 2.3B SMP 2.6B SMP 1.1 CAL 1.1.1 CAL 1.1.4 CAL 1.17 CAL LB 3 CN 2.1 CN 1.3 CHR 1-3 CHR 2-3 CHR 5-3 CHR 7-3 CoNiCs 6 35Pr 10.5NdSm –20 6 1.8 5.59 21.2Tb 28 4.78 6 4.2Dy 6.40Ho 25.2Er 5.15 27 7.1 1.00 4.24 17.1 9 5.72 3.94 1.16 –20 0.64 7.68 3.72 5.8 31.9 3.38 17 6.52 0.64 –20 0.83 6.82 2.11 25.5 2.4 4.65 4.52 0.87 9 0.92 6.05 2.66 24.9 40 4.97 6.4 5.56 0.91 0.67 16 7.02 2.86 28.5 –20 3.89 5.92 3.4 0.76 0.71 4.62 2.51 18.4 3.61 7 26 3.89 0.69 9.4 0.88 3.89 2.18 15.3 4.82 3.16 0.93 13 77 5.2 0.63 9.07 3.03 38.2 3.51 9.61 0.69 –20 13.2 43 0.61 5.0 2.17 52.0 3.94 11.0 0.83 –20 1.72 7.83 2.87 29.9 17 2.9 9.24 5.99 1.68 12.0 1.49 5.08 31 49.6 8.18 –1 9.0 8.82 1.61 0.79 4.88 5.39 19.2 –20 4.48 15.8 3.82 16 0.86 0.73 9.44 2.84 38.1 3.81 28.0 24 8.06 0.71 0.54 7 7.26 2.30 28.5 3.12 17.3 –20 5.67 0.60 1.25 8.32 1.99 32.0 10 6.95 30.9 6.39 –20 1.35 0.87 4.29 5.25 1.04 6 0.91 3.38 5.52 1.09 6 3.58 Cr 139ZnLaCe 35 127 28.2 50.4 –30 34 26.6 55.4 –30 57 17.8 36.8Tm –30Yb 39.3 46 49.1Lu 52 29.9 0.579 59.8 42 3.42 0.544 0.316 22.9 32 50.4 2.04 92 0.324 0.377 26.0 55.1 54 2.18 0.334 0.415 32 18.7 38.5 0.392 0.377 2.53 56 18.5 57 0.391 34.6 0.315 2.47 90 34.2 0.329 0.450 84.1 61 2.05 0.426 0.314 57.8 202 101 –20 2.89 0.297 0.459 32.0 110 68.1 1.90 0.458 31 0.703 43.1 –30 107 0.627 0.848 2.96 77 20.3 0.829 0.442 47 41.3 4.19 36.5 0.406 36 0.347 79.1 –30 5.08 0.362 29.9 0.302 83 62.1 2.60 58 0.298 0.645 33.3 70.5 2.26 64 0.585 0.521 –30 0.489 1.81 0.565 81 55 0.541 3.77 3.04 3.30

636 Geosphere, October 2010

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LA BALLENA CHARCAS REAL DE MIQUIHUANA ARAMBERRI CAÑÓN DEL VALLE DEL CAÑÓN DE SAN MARCOS CAÑÓN DEL CATORCE NOVILLO HUIZACHAL LA BOCA ALAMAR Cretaceous Carbonates La Joya Formation Zuloaga Formation Olvido Gyps Zuloaga Formation Zuloaga Formation Minas Viejas Gyps La Joya Formation Zuloaga Group NazasFormation Red beds La Boca Formation Huizachal Volcanic rocks Group Marginal marine facies (Huayacocotla Formation) Precambrian-Paleozoic metamorphic basement El Alamar formation

Zacatecas Formation

Figure 13. Correlation of pre-Cretaceous units of the studied areas in central to northeastern Mexico. Late Triassic El Alamar formation overlies Paleozoic magmatic, metamorphic, and sedimentary rocks in the northern part of the Huizachal-Peregrina anticlinorium and is absent in the Aramberri-Miquihuana high. The base of the marine turbiditic sequence (Zacatecas Formation) of the Potosí Fan is unknown, and probably overlies continental crust at the western margin of nuclear Mexico and far to the west on ancient oceanic crust.

tectonic, or other) between the Triassic suc- Detrital zircons typical of the American The Triassic strata of northeastern Mexico cessions in northeastern Mexico and other Southwest are absent from both marine and have important implications for the exis- Triassic sections along in the Pacifi c margin continental Triassic rocks studied. In contrast, tence of the Mojave-Sonora megashear, a is diffi cult. Nonetheless, all Triassic sections zircons in the Barranca Group, in Sonora, show great buried left-lateral strike-slip fault that across northern Mexico are consistent with the a distinct peak of grains with ages near 1.42 Ga is inferred to have displaced ~800 km most proposal that Mexico faced an open oceanic (Gehrels and Stewart, 1998; González-León of northern Mexico, including the Ouachita basin to the west in Triassic time (Ortega- et al., 2009), consistent with its close relation- and the Jurassic continental arc of Gutiérrez et al., 1994). ship with the western Cordillera. northern Sonora, southeastward in Jurassic Nearly half of the detrital zircons in each of Strata of the Zacatecas Formation and asso- time (Anderson and Silver, 1979; Anderson the four samples were likely derived from the ciated strata in Charcas and Real de Catorce and Schmidt, 1983; Jones et al., 1995). The eastern Mexico Permian arc, which encom- are interpreted as part of a large-scale sub- Triassic marine strata in Zacatecas and San passes outcrops near Las Delicias in Coahuila, marine fan system, the Potosí fan (Centeno- Luis Potosí and Triassic continental strata subsurface plutonic rocks in Tamaulipas, the La García, 2005). Submarine fans are typically in Tamaulipas and Nuevo León are south Mixtequita massif in Oaxaca, and the Chiapas associated with extensive fl uvial systems that of the inferred trace of the Mojave-Sonora massif (Torres et al., 1999; Weber et al., 2003). drain a large continental basin. Thus, as a fi rst megashear. Had this displacement existed, A large component was derived from bedrock approximation we hypothesize the relation- these units should have been located 800 km sources of Grenvillian age (1250–900 Ma) of ship between the El Alamar fl uvial system to the northwest of their present position in the Oaxaquian subcontinent (Ortega-Gutiérrez and the Potosí fan probably as the result of Triassic time. Detrital zircon geochronology et al., 1995) or possibly reworked from the river valley draining an extensive portion for Triassic rocks does not support the model Ouachita rock assemblages. A potential source of western equatorial Pangea during Triassic of large left-lateral displacement. Besides the for Pan-African zircons exists in basement time, with fl ow to the paleo-Pacifi c margin absence of detrital zircons from Precambrian rocks of the Yucatan Peninsula (then positioned to the west (Fig. 14). Paleocurrent geochemi- provinces such as Yavapai and Mazatzal, and against the Texas and Louisiana coast (Molina- cal and detrital zircon data all support this Mesoproterozoic zircons (1.45–1.40 Ga), we Garza et al., 1992), Coahuila (Lopez et al., hypothesis, which is based on their zircon note that a suitable source for Pan-African zir- 2001), southeast Texas, and Florida (Dallmeyer provenance from Grenvillian and Pan-African cons could not be easily found had these rocks et al., 1987; Mueller et al., 1994), although they basement rocks as well as the Permian– been in a position suggested by reconstruc- may also have been recycled from Paleozoic Triassic magmatic arc. In addition, the con- tion of displacement by the Mojave-Sonora strata of the Ouachita orogen. Detrital zircons sistent directions of sediment transport based megashear. Furthermore, Grenvillian zircon in Triassic rocks in north-central and northeast- in some types of measured directional struc- sources in northwest Mexico are restricted to ern Mexico show some similarity with Triassic tures (e.g., fl ute casts and groove casts) in ages of ca. 1.2–1.1 Ga (Barbeau et al., 2005; rocks of the Dockum Group. The Trujillo For- the marine facies, represented in Figure 4, or Dickinson et al., 2007), whereas zircons in mation contains important populations of Pan- cross-bedding, and channel and trunk orienta- the Zacatecas Formation and the El Alamar African (700–380 Ma) and Grenvillian (1250– tion in the continental facies (Fig. 7), agree in formation are more typical of Oaxaquia Gren- 900 Ma; Fox et al., 2005; Dickinson and all the cases with paleocurrent patterns toward villian ages (1250–900 Ma; Keppie et al., Gehrels , 2008) zircons. the west and southwest. 2001; Solari et al., 2003, 2004).

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Barboza-Gudiño, J.R., Tristan-Gónzalez, M., and Torres- Hernández, J.R., 1999, Tectonic setting of pre- Oxfordian units from central and northeastern Mexico: North America A review, in Bartolini, C., et al., eds., Mesozoic sedi- mentary and tectonic history of north-central Mexico: () Geological Society of America Special Paper 340, Florida p. 197–210, doi: 10.1130/0-8137-2340-X.197. Barboza-Gudiño, J.R., Torres-Hernández, J.R., and Tristán- González, M., 1998, The Late Triassic–Early Jurassic Ouachita belt active continental margin of western North America in northeastern México: Geofísica Internacional, v. 37, p. 283–292. Alamar Yucatán Barboza-Gudiño, J.R., Hoppe, M., Gómez-Anguiano, M., and Martínez-Macías, P.R., 2004, Aportaciones para la River interpretación estratigráfi ca y estructural de la porción noroccidental de la Sierra de Catorce, San Luis Potosí, México: Revista Mexicana de Ciencias Geológicas, Potosí Fan v. 21, p. 299–319. Oaxaquia Barboza-Gudiño, J.R., Orozco-Esquivel, M.T., Gómez- Anguiano, M., and Zavala-Monsiváis, A., 2008, The South America Early Mesozoic volcanic arc of western North Amer- ica in northeastern Mexico: Journal of South Ameri- Granj () can Earth Sciences, v. 25, p. 49–63, doi: 10.1016/ eno-Acatlán belt j.jsames.2007.08.003. Bartolini, C., 1998, Stratigraphy, geochemistry, geochronol- Permo-Triassic ogy and tectonic setting of the Mesozoic Nazas For- arc mation, north-central Mexico [Ph.D. thesis]: El Paso, University of Texas, 557 p. Bartolini, C., Lang, H., Cantú-Chapa, A., and Barboza- Nascent Early Gudiño, J.R., 2001, The Triassic Zacatecas Formation Late Paleozoic in central Mexico: Paleotectonic, paleogeographic Mesozoic subduction and paleobiogeographic implications, in Bartolini, C., subduction et al., eds., The western Gulf of Mexico Basin: Tecton- Permo-Triassic plutons ics, sedimentary basins and petroleum systems: Ameri- can Association of Petroleum Geologists Memoir 75, Pan-African blocks p. 295–315. Paleo-Pacific Bartolini, C., Lang, H., and Spell, T., 2003, Geochronology, geochemistry, and tectonic setting of the Mesozoic Grenvillean basement Nazas arc in north-central Mexico, and its continua- tion to northern South America, in Bartolini, C., et al., eds., The Circum-Gulf of Mexico and the Caribbean: Figure 14. Paleogeographic reconstruction of Mexico for the time during deposition of the Hydrocarbon habitats, basin formation and plate tec- tonics: American Association of Petroleum Geologists Potosí fan (Late Triassic) indicating provenance from Grenvillian (Oaxaquia block), Pan- Memoir 79, p. 427–461. African (Yucatan, actual southeasternmost United States, and Gondwana), and Permian– Burckhardt, C., and Scalia, S., 1905, La faune marine du Triassic (east Mexico magmatic arc) sources. Detrital zircon geochronology, paleo-fl ow pat- Trias Supérieur de Zacatecas: Instituto de Geología de México Boletín 21, 44 p. terns, petrography, and geochemical studies support such sources as well as sources from Cantú-Chapa, A., 1969, Una nueva localidad del Triásico the Ouachita collisional belt. Superior marino en México: Instituto Mexicano del Petróleo Revista, v. 1, p. 71–72. Carrillo-Bravo, J., 1961, Geología del Anticlinorio Huizachal- Peregrina al NW de Ciudad Victoria, Tamaulipas: Asociación Mexicana de Geólogos Petroleros Boletin ACKNOWLEDGMENTS Anderson, T.H., and Schmidt, V.A., 1983, A model of the (Instituto de Estudios de Poblacion y Desarrollo, evolution of Middle America and the Gulf of Mexico– Dominican Republic), v. 13, p. 1–98. We acknowledge support from projects CONACYT Caribbean Sea region during Mesozoic time: Geologi- Carrillo-Bravo, J., 1982, Exploración petrolera de la Cuenca 2002-CO2-41239 (Consejo Nacional de Ciencia cal Society of America Bulletin, v. 94, p. 941–966, doi: Mesozoica del Centro de México: Boletín de la Asoci- y Tecnología), Programa de Apoyo al Desarrollo 10.1130/0016-7606(1983)94<941:TEOMAA>2.0 ación Mexicana de Geólogos Petroleros, v. 34, p. 21–46. .CO;2. Centeno-García, E., 2005, Review of upper Paleozoic and Universitario (PROADU) 2003-01-24-001-53, and Anderson, T.H., and Silver, L.T., 1979, The role of the Mesozoic stratigraphy and depositional environments Fondo de Apoyo a las Investigación FAI/UASLP Mojave-Sonora megashear in the tectonic evolution of of central and west Mexico: Constraints on terrane C06-FAI-11-33.70 (Universidad Autónoma de San northern Sonora, in Anderson, T.H., and Roldán Quin- analysis and paleogeography, in Anderson, T.H., Luis Potosí). We thank Victor Valencia and Alexander tana, J., eds., Geology of northern Sonora Guidebook, et al., eds., The Mojave-Sonora megashear hypothesis: Pullen (LaserChron Laboratory, University of Ari- Annual Meeting of the Geological Society of America: Development, assessment and alternatives: Geological zona) for technical support and suggestions, Kelly Estación Noroeste, Instituto de Geología, Universidad Society of America Special Paper 393, p. 233–258, doi: Hayes and Delfi no Ruvalcaba for revision of the Nacional Autónoma de México and the University of 10.1130/0-8137-2393-0.233. English text, and Roberto Molina Garza for revi- Pittsburgh, p. 59–68. Centeno-García, E., and Silva-Romo, G., 1997, Petrogenesis Anderson, T.H., Jones, N.W., and McKee, J.W., 2005, The and tectonic evolution of central Mexico during sion and suggestions. We appreciate the constructive Taray Formation: Jurassic(?) mélange in northern Triassic–Jurassic time: Revista Mexicana de Ciencias reviews of Timothy F. 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