Evolution of Cupido and Coahuila carbonate platforms, Early Cretaceous, northeastern Mexico Christoph Lehmann* Department of Earth Sciences, University of California, Riverside, California 92521 David A. Osleger Department of Geology, University of California, Davis, California 95616 Isabel P. Montañez } William Sliter† U.S. Geological Survey, Menlo Park, California 94025 Annie Arnaud-Vanneau Institut Dolomieu, rue Maurice Gignoux, 38031 Grenoble cedex, France Jay Banner Department of Geological Sciences, University of Texas, Austin 78712-1101 ABSTRACT is a discontinuous rudist-coral reef. A broad tributing to the determination of global versus shelf lagoon developed in the lee of the Cupido regional controls on carbonate platform evolu- The Cupido and Coahuila platforms of margin, where as much as 660 m of cyclic per- tion during middle Cretaceous time. northeastern Mexico are part of the extensive itidal deposits accumulated. During middle to carbonate platform system that rimmed the late Aptian time, a major phase of flooding INTRODUCTION ancestral Gulf of Mexico during Barremian to forced a retrograde backstep of the Cupido Albian time. Exposures of Cupido and platform, shifting the locus of shallow-marine Lower Cretaceous epicontinental carbonates Coahuila lithofacies in several mountain ranges sedimentation northwestward toward the provide reservoirs for enormous volumes of hy- spanning an ~80 000 km2 area reveal informa- Coahuila block. This diachronous flooding drocarbons along the Gulf of Mexico coast and tion about platform morphology and composi- event records both the demise of the Cupido in the Middle East. Some of the largest carbon- tion, paleoenvironmental relations, and the shelf and the consequent initiation of the ate platforms developed in northeastern Mexico chronology of platform evolution. New biostra- Coahuila ramp. and Texas, specifically during Barremian to Al- tigraphic data, integrated with carbon and The backstepped Coahuila ramp (Aptian- bian time, when carbonate platforms reached strontium isotope stratigraphy, significantly Albian) consisted of a shallow shoal margin their maximum extent around the Gulf of Mex- improve chronostratigraphic relations across separating an interior evaporitic lagoon from a ico coast (Scott, 1990; Wilson and Ward, 1993). the region. These data substantially change low-energy, muddy deep ramp. More than For this reason, Cretaceous carbonate platforms previous age assignments of several formations 500 m of cyclic carbonates and evaporites ac- of Texas and eastern Mexico have been the focus and force a revision of the longstanding stratig- cumulated in the evaporitic lagoon during of numerous regional studies (e.g., Coogan et al., raphy in the region. The revised stratigraphy early to middle Albian time. Restriction of the 1972; Enos, 1974; Wilson, 1975; Bebout and and enhanced time control, combined with re- platform interior dissipated by middle to late Loucks, 1974; Scott, 1990; Minero, 1991; Enos gional facies associations, allow the construc- Albian time with the deposition of peloidal, mil- and Stephens, 1993). Recent research on the Cu- tion of cross sections, isopach maps, and time- iolid-rich packstones and grainstones of the Au- pido and Coahuila platforms has focused on slice paleogeographic maps that collectively rora Formation. The Coahuila platform was spectacular outcrops in the Sierra Madre Orien- document platform morphology and evolution. drowned during latest Albian to early Ceno- tal near Monterrey and Saltillo (Wilson and Pialli, The orientation of the Cupido (Barremian- manian time, and the deep-water laminites of 1977; Conklin and Moore, 1977; Goldhammer Aptian) shelf margin was controlled by the the Cuesta del Cura Formation were deposited. et al., 1991; Wilson and Ward, 1993). These im- emergent Coahuila basement block to the This study fills in a substantial gap in the portant studies have documented the composi- northwest. The south-facing margin is a high- Cretaceous paleogeography of the eastern Gulf tion and orientation of the Cupido reefal plat- energy grainstone shoal, whereas the margin of Mexico coast, improving regional correla- form margin and have established the character facing the ancestral Gulf of Mexico to the east tions with adjacent hydrocarbon-rich plat- of the peritidal facies belt immediately behind forms. The enhanced temporal relations and the margin. However, critical questions remain chronology of events recorded in the Cupido about the vast interior of the Cupido platform *Present address: BP Amoco Exploration and Pro- duction, 501 WestLake Park Boulevard, Houston, Texas and Coahuila platforms significantly improve and its paleogeographic and genetic relationship 77079-2696; e-mail: [email protected]. global correlations with coeval, economically with the younger Coahuila platform. Further- †Deceased. important platforms worldwide, perhaps con- more, the current stratigraphic framework in the Data Repository item 9956 contains additional material related to this article. GSA Bulletin; July 1999; v. 111; no. 7; p. 1010–1029; 12 figures. 1010 LOWER CRETACEOUS CARBONATE PLATFORM EVOLUTION, STRATIGRAPHY, MEXICO study area is marked by equivocal age assign- and on the south by the left-lateral Torreon- Formations (Smith and Bloxsom, 1974; Loucks, ments, and thus there may be miscorrelations. Monterrey lineament (parallel with the trend of 1977; Tinker, 1985; Goldhammer et al., 1991). To attain a more complete regional under- the Sonora-Mojave megashear) (Anderson and The second major episode of carbonate plat- standing of these two platforms, we focused on Schmidt, 1983). The Sonora-Mojave megashear form evolution in the region, the Coahuila remote and relatively uninvestigated exposures to is inferred to have extended to the east, bisecting platform (Acatita-Aurora Formations; Fig. 2), de- the west and northwest in the Sierra de Parras and the Tamaulipas block and the Picachos block veloped on top of the Coahuila basement block above the Coahuila basement block. The objec- (Wilson, 1990). Left-lateral shear zones are inter- during Aptian through Albian time. The Coahuila tives of this study were to (1) document paleo- preted to have been major intracontinental trans- platform margin manifests a significant backstep geographic and large-scale facies relationships form faults that were active during Late Triassic to from the preceding Cupido margin, a result of across northeastern Mexico for Barremian to Al- Middle Jurassic time, but were likely inactive dur- long-term sea-level rise through Early Cretaceous bian strata, (2) obtain new biostratigraphic and ing carbonate deposition in Barremian through time that culminated during Cenomanian time chemostratigraphic information to refine chrono- Albian time (Wilson, 1990; Goldhammer and (Haq et al., 1988). Deeper water carbonates of the stratigraphic relationships, and (3) use these data Wilson, 1991). Upper Tamaulipas Formation were deposited on to interpret the evolutionary development of During Late Jurassic time, sea-floor spreading the more rapidly subsiding portions of the plat- these Lower Cretaceous platforms. started in the Gulf of Mexico (Buffler and form surrounding the Coahuila block. The The results of this study have important im- Sawyer, 1985; Winker and Buffler, 1988), and Coahuila platform was ultimately drowned during plications for our understanding of the Early nearshore siliciclastic and carbonate deposits (La latest Albian–earliest Cenomanian time, as Cretaceous evolution of the Gulf of Mexico Gloria and Zuloaga Formations) accumulated recorded by diachronous deposition of thinly in- coast region. First, the new biostratigraphic near basement highs, passing into offshore car- terbedded cherty lime mudstones and argillaceous data, integrated with carbon and strontium iso- bonate shoals and outer-ramp muds (Zuloaga rhythmites of the Sombreretillo and Cuesta del tope stratigraphy, dictate a substantial revision Formation; Meyer and Ward, 1984; Johnson, Cura Formations (Fig. 2; Bishop, 1972; Ice, 1981; of the longstanding stratigraphic framework in 1991). Evaporites and mudstones of the Olvido Longoria and Monreal, 1991). Deposition of the study area. In addition, this study fills in a Formation were deposited conformably on the pelagic mudstones, shales, and coarser siliciclas- substantial hole in the data for the Cretaceous Zuloaga Formation during continuous flooding. tic strata of younger Cretaceous formations indi- paleogeography of the eastern Gulf of Mexico These initial marine carbonate deposits were cates the transition to foreland basin sedimenta- coast, improving regional correlations with ad- terminated with deposition of siliciclastics and tion and the beginning of Laramide orogenesis. jacent hydrocarbon-rich platforms to the south lime mudstones of the La Casita Formation dur- in eastern Mexico (Valles–Golden Lane) and to ing Late Jurassic and earliest Cretaceous time METHODS AND DATABASE the north in Texas (Sligo-Comanche). Perhaps (Fortunato and Ward, 1982). most important, the high-resolution chronology The rift phase of the Gulf of Mexico was com- There were 37 sections totaling 17 000 m of the evolution of the Cupido and Coahuila pleted by the beginning of Cretaceous time, and logged on a decimeter scale throughout the platforms can be compared to coeval platforms the region underwent cooling and continuous >80 000 km2 study area (Fig. 3). Most sections worldwide to search for connections and dis- subsidence throughout Early Cretaceous