The paleobathymetric configuration of the early Gulf of Mexico is inferred from (1) Cretaceous carbonate shelf margins interpreted from seismic profiles and other stratigraphic data; (2) distribution of Jurassic and Cretaceous platform and basinal facies; and (3) hindcasting of subsidence history in the central basin. Substantial paleogeographic ambiguity results from uncertainty about (1) kinematics and timing of Late Triassic to Jurassic extensional opening of the Gulf basin, which probably involved major strike-slip faulting, (2) the magnitude of subsequent compressive deformation on the western and southern basin margins, and (3) possible accretion of allochthonous terranes. The initial sub-sea level topographic depression created by crustal extension is manifested by the distribution of Callovian (?) pre-marine salt and Oxfordian basinal marine facies. Late Jurassic sea-floor spreading split the main salt body and created a central deep-water (> 1 km) trough. From the Oxfordian to early Neocomian, ramp-like platform margins generally underwent net retreat, except in the northern Gulf, where major clastic progradation took place. Carbonate platform margins with sufficient paleorelief for geometric expression on seismic profiles developed early in the Cretaceous. These Cretaceous carbonate margins exhibit a variety of architectural styles, including (1) in the northwestern Gulf, two cycles of progradation (Coahuilan and Comanchean) terminated by drowning events; (2) in the southwestern Gulf, a single cycle of progradation; (3) continuous aggradation along the Florida and Campeche Escarpments. Paleobathymetric relief across Cretaceous carbonate margins ranges from high and steep, to low-relief, to ramplike. The close-of-Comanchean drowning event greatly and permanently reduced the extent of circum-Gulf carbonate platforms and especially rimmed margins. Locations of Cretaceous carbonate margins were influenced by basement hinge zones and paleohighs developed on attenuated continental crust, by the distribution of salt, and by clastic progradation. Eustacy is commonly invoked to explain behavior and architecture of carbonate margins in the Gulf, but other paleoenvironmental variables such as nutrient abundance are probably important as well.

Paleogeographic Evolution of Early Deep-Water Gulf of Mexico and Margins, Jurassic to Middle Cretaceous (Comanchean)

The geologic evolution of southeastern Mexico is analyzed in the regional context of the Gulf of Mexico, which starts it opening with the fragmentation and spreading of Pangea. The sedimentary record in this depression begins with the deposit of continental red beds during the Late Triassic and Early Jurassic, after which, during the Callovian, sea-waters from the Pacifi c invaded an extense area; low circulation and high evaporation of these waters allowed the deposition of large volumes of salt in the central part of the basin. From Late Jurassic to Late Cretaceous, carbonate deposition prevailed, changing to clastic at the beginning of the Paleogene, when the Laramide Orogeny formed the folds and faults of the Sierra Madre Oriental. During the rest of the Paleogene clastic sedimentation was deposited in large depocenters generated in the foreland of the Sierra Madre Oriental, and in the southern and southwestern parts of the Golf of Mexico, where the Chiapas Massif produced large volumes of sediments, whereas in the Yucatan Block the deposition of shallow water carbonates continued. In the Middle Miocene, during the Serravalian, compressive stresses resulting from the lateral movement of the Chortis Block and the subduction of the Cocos Plate, against the southern end of the North American Plate, formed the folds and faults of the Chiapas-Reforma-Akal belt over a decollement at the level of the Callovian salt; later, these structures were

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Evolución geológica del sureste mexicano desde el Mesozoico al presente en el contexto regional del Golfo de México

Tectonic setting and sandstone petrofacies of the Bisbee basin(USA–Mexico)

The Camargo volcanic field is the largest mafic alkalic volcanic field in the Mexican Basin and Range province, and the relationship between volcanism and normal faulting is especially strong. The Camargo volcanic field lies in the northern part of the province, midway between the Sierra Madre Occidental and Trans-Pecos Texas. It is formed by Pliocene–Pleistocene (4.7–0.09 Ma) intraplate mafic alkalic volcanic rocks, some of which contain peridotite, pyroxenite, and granulite xenoliths. The volcanic field covers ∼3000 km2 and has an estimated volume of ∼120 km3 erupted from >300 recognized vents. Twenty-six new 40Ar/39Ar age determinations for the Camargo volcanic field and its environs show that volcanic activity began in the southwest part of the field and shifted toward the northeast at ∼15 mm/yr. The average magmatic eruption rate during growth of the field was ∼0.026 km3/k.y.

The Camargo volcanic field lies within an accommodation zone with west-dipping faults and east-tilted blocks to the north and east-dipping faults and west-tilted blocks to the south. These faults are expressed in the volcanic field by a N30°W-trending graben with scarps up to ∼100 m high through its central part. Volcanism and faulting were at least in part coeval, and younger volcanic products commonly drape fault scarps that cut earlier lavas. Normal faulting is bracketed between 4.7 and 2.1 Ma and may have also migrated northeastward. Estimated vertical slip rates on four Pliocene faults range from 0.03 mm/yr, a likely long-term rate, to 1.67 mm/yr, interpreted as a short-term rate operative during periods of active faulting. Northwest-striking normal faults that cut alluvial-fan deposits and Pleistocene lavas in the northern Camargo volcanic field and geomorphic evidence for recent uplift to the south of the volcanic field suggest that the region is still extending.

Synextensional Pliocene–Pleistocene eruptive activity in the Camargo volcanic field, Chihuahua, México

La porcion suroriental del terreno Cuicateco, entre Matias Romero y Juchitan, Oaxaca, esta
compuesta por una secuencia vulcanosedimentaria de bajo grado metamorfi co que presenta por lo menos
tres eventos de deformacion, D1: plegamiento recumbente a isoclinal F1 de la superfi cie de estratifi cacion
S0, con una vergencia general hacia el noreste y desarrollo de una esquistosidad de plano axial S1 con
echado hacia el suroeste. Paralelo a las superfi cies S1 se observa el desarrollo de hornblenda, epidota,
clorita, moscovita y cuarzo. Este deformacion esta relacionada a un evento transcurrente con cinematica
sinestral de edad post-maastrichtiana. D2: evento paleocenico? caracterizado por cabalgaduras
con direccion de desplazamiento al norte-noreste, como la falla Vista Hermosa, y el desarrollo de la
superfi cie de esquistosidad S2 sin una aparente recristalizacion asociada. D3: evento miocenico defi nido
por fallamiento de tipo normal y lateral.
La composicion quimica de las rocas anfi boliticas del terreno Cuicateco es de basalto toleitico
(SiO2 de 45 a 50%), con empobrecimientos relativos en tierras raras ligeras y patrones casi planos
de tierras raras pesadas. Los elementos en traza muestran un patron empobrecido en elementos mas
incompatibles con respecto a los menos incompatuble y anomalias negativas de Th y Nb en algunas
muestras. Una componente de magmas relacionados con subduccion es tambien evidente por su relacion
Ta/Yb vs. Th/Yb.
Los fechamientos de U-Pb por LA-MC-ICPMS en zircones de una anfi bolita arrojaron una edad
de 65.7 ± 1.2 Ma (Maastrichtiano) interpretada como la edad de cristalizacion del protolito basaltico.
De igual manera, los zircones detriticos de una fi lita vulcanoclastica indican una edad maxima de
deposito maastrichtiana (78 Ma) con picos signifi cativos en 113 Ma, 542 Ma, 1198 Ma, 1662 Ma, 2791
y 3062 Ma. Los zircones de una arenisca de la Formacion Todos Santos arrojaron una edad maxima del
deposito posterior al Triasico Medio - Superior (228 Ma) con picos importantes en 571 Ma, 1026 Ma,
1530 Ma, 1978 Ma y 2909 Ma.
Los resultados petrologicos, estructurales y geocronometricos sugieren el desarrollo de un
vulcanismo basico en un ambiente de cuenca oceanica con infl uencia de subduccion durante el Cretacico
Superior que sufrio los efectos de dos deformaciones, una transpresiva y otra compresiva, durante el
Cretacico Superior?Paleoceno, seguido por un fallamiento normal y lateral miocenico que se asocia a
la dinamica del sistema de fallas Polochic-Motagua.

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El terreno Cuicateco: ¿cuenca oceánica con influencia de subducción del Cretácico Superior en el sur de México? Nuevos datos estructurales, geoquímicos y geocronológicos

Se muestra la evolucion sedimentaria mesozoica del noreste de Mexico a traves de varios mapas paleogeograficos regionales. Tambien, con base en diferentes estilos de plegamiento, se propone un modelo alternativo para la deformacion del Terciario Temprano del noreste de Mexico, asi como una serie de paleorreconstrucciones de tectonica de placas, basados principalmente en la existencia de varias fallas sinistrales de transcurrencia, orientadas al noroeste y una falla dextral transcurrente (Falla Tamaulipas-Oaxaca) orientada al nor-noroeste, a lo largo de la cual el bloque de Yucatan se movio hacia el Sur (Jurasico Tardio) desde su antigua position en el sitio que hoy ocupa el Golfo de Mexico.

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R. J. Padilla

Papers

Post-paleozoic tectonics of northeast mexico and its role in the evolution of the gulf of mexico