Initial Alleghenian (Western Pangean} South America)

TECTONICS, VOL. 4, NO. 1, PAGES 1-39, JANUARY 1985 ALLEGHENIAN RECONSTRUCTION AND SUBSEQUENT EVOLUTION OF THE GULF OF MEXICO, BAHAMAS, AND P ROTO-CARI B BEAN 1 James L. Pindell Exploration Research Division, Pennzoil Company, Houston, Texas Abstract. A detailed model for the of Mexico from Late Triassic to earliest evolution of the Gulf of Mexico, the Cretaceous time, but seafloor spreading Bahamas and the Proto-Caribbean is built was delayed until the Late Callovian. This within the framework provided by a detailed divided a single Gulf-wide salt basin into initial Alleghenian (western Pangean} the Louann and Campeche salt provinces. reconstruction and an accurate subsequent The Yucatan block progressively rotated relative-motion history between North about 43 degrees counterclockwise away America and Gondwana (northern Africa and from the Texas-Louisiana margin around a South America). The Alleghenian pole in northern Florida. The reconstruction closes all pre-Jurassic Tamaulipas-Golden Lane-Chiapas fault zone oceans; accounts for Jurassic attenuation of of eastern Mexico is interpreted as the continental crust by restoring that remains of an initially intracontinental attenuation to original pre-rift continental transform system along which Yucatan thicknesses; incorporates an improved migrated. Attenuated continental crust Equatorial Atlantic fit between northern beneath southern Florida and the western Brazil and the Guinea margin of Africa; Bahamas, termed here the Florida Straits quantitatively removes changes in shape of block, migrated approximately 300 km out northern South America due to Late of the eastern Gulf, approximately along Cretaceous and Cenozoic accretion and Central Atlantic flow lines. These internal deformation; includes pre-Mesozoic rotations are consistent with recently continental crust presently underlying the suggested magnetic anomaly trends in the western Bahamas and southern Florida; and Gulf of Mexico (Shepherd et al., 1982; S. correlates Late Paleozoic geology of Hall, personal communication, 1984). The Yucatan with its neighboring continental Proto-Caribbean formed synchronously by a masses. Extension occurred within the Gulf fan-like rotation of Yucatan away from Venezuela. 1 Now at Department of Geological INTRODUCTION Sciences, Durham University, United Kingdom. Evolutionary models of the Gulf of Mexico must integrate the geology of the Copyright 1985 circum-Gulf region (Figure 1) into a by the American Geophysical Union. quantitative kinematic framework defined by a Late Paleozoic continental reconstruction Paper number 4T1357. of western Pangea (North and South 0278-7407/85/004T- 1357510.00 America, Africa and Yucatan} and an Pindell: AlleghenianReconstruction, Gulf of Mexico Evolution 88 s s LIMIT OF SALT c c LOWER CRETACEOUS MAFIC EDGE OF BLAKE MARATHON PRE-MESOZOIC c KEY WELLS TO BASEMENT LOU•NN OVERTHRUST 72 s s s s s GOLDEN LANE c c ß CHORTIS KM 500 1000 Fig. ]. General inctonic and locality map of the Gulf region, features described in text. MSM, Mojave-Sonora Megashear; TMVBL, Trans-Mexican Volcanic Belt Lineament; SU, Sabine Uplift; MU, Monroe Uplifq JD, Jackson Dome; WA, WigginsArch; MOA, Florida Middle Grounds Arch; SO, Sierra Guaniguanico,presently western Cuba but was northeastern corner of Yucatan block prior to Paleogene;BSMA, Blake Spur Magnetic Anomaly; M-25, M-2], M-J6, M-l], Central North Atlantic magnetic anomalies. accurate subsequent relative motion history common prior to collision, and the majority between North and South America. The of Triassic deposition upon each consists of absence of any indication of Upper red beds that are lithologically similar and Permian-Triassic marine conditions in the difficult to correlate biostratigraphically. circum-Gulf region suggests that the initial Because of repeated Paleozoic orogeny reconstruction must recognize complete in the Appalachians, and because the terms Paleozoic ocean closure. In turn, the way Appalachian, Ouachita, Marathon and in which closure is achieved in the Huastecan describe geographic portions of a reconstruction must provide an internally single continuous, but diachronous, belt of consistent rearrangement of interpreted Late Paleozoic deformation, the term tectonic provinces and metamorphic zones Alleghenian orogenesis is used here to from the various continental blocks. The describe collectively the diachronous event rearrangement of provinces is made that produced the Alleghenides, those Late difficult by the fact that Jurassic Mississippian-Middle Permian tectonic continental breakup has followed features and metamorphism that were approximately the lines of Late Paleozoic created by final ocean closure between continental suturing; only rarely can Gondwana and American portions of pre-Permian geology be tied across Laurussia [Graham et al., 1975; Kluth and Alleghenian sutures in the reconstruction Coney, 1981; Pindell and Dewey, 1982; because the opposing continents had little in Dewey, 1982; Bradley, 1982]. Pindell: Alleghenian Reconstruction, Gulf of Mexico Evolution 3 Before a plausible Alleghenian Venezuela in order to match the Louann and reconstruction may be attempted, one must Campeche rift-related salt provinces in the (1) identify all pre-Mesozoic continental Gulf (Figure 1). This positioning of Yucatan crust involved in Alleghenian orogenesis, (2) provides the necessary geometry of res tore to original crustal thickness the opposing margins for a tight fit between attenuation undergone by each margin during Gondwana and Laurussia. Discussed below Late Triassic and Jurassic rifting, and (3} are considerations that constrain and retract, where possible, post-Permian substantiate reconstructions of western offsets on intracontinental fault systems Pangea in the complex area between North such as those in Mexico [Anderson and and South America. These collectively Schmidt, 1983] and in northwest South produce the Alleghenian paleoreconstruction America [Dewey and Pindell, 1984]. In of Figure 2. Table 1 defines abbreviations, addition, proper realignment of the and interprets geological features, circum-Atlantic continents by closure of the portrayed in Figure 2. Central-North and the South Atlantic The Florida Straits Block Oceans is critical to Alleghenian paleogeography, by providing the primary Several lines of evidence suggest that framework on which to build more detailed southern Florida and much of the Bahamas aspects of the western Pangean Platform are underlain by pre-Mesozoic reconstruction. continental crust, a block (or blocks} In this study, a detailed Alleghenides referred to here as the Florida Straits reconstruction is derived, following the block (Figure 1). above methodology, which serves as a The nature and age of basement beneath starting point from which is modeled the Bahamas has been debated for decades, subsequent evolution of the Gulf of Mexico, the Bahamas and the Proto-Caribbean Sea. as geophysical and well data have not yet provided a conclusive answer. However, The evolutionary model is based upon a framework of relative motions between gravimetric, magnetic, and seismic data North America and South America-Africa [Uchupi et al., 1971] suggest that presumably pre-Mesozoic, attenuated [Klitgord and Schouten, 1982], the latter of continental crust underlies the western half which remained a single continent of the platform, whereas the eastern half throughout the opening of the Gulf. is oceanic. Basement of the oceanic Basement geology, intracontinental extension, and general Jurassic portion must have been raised to the photic sedimentation patterns of the Gulf region zone early on to initiate carbonate bank are reviewed and interpreted, and are development, presumably by plate motions integrated into the evolving plate kinematic along transform faults, or by volcanism, framework. The evolutionary model is during the separation of North America and Gondwana. Recently acquired seismic data discussed, and implications are derived. along the northern Bahamian margin (J. W. THE ALLEGHENIAN RECONSTRUCTION Ladd, personal communication, 1984} indicate that the western Bahamas are underlain by A consensus is emerging that the Late attenuated continental crust as far east as Paleozoic reconstruction of circum-Atlantic Tongue of the Ocean. A similar eastward continents and blocks in the Gulf and extent is suggested by the Punta Alegre Caribbean realm must achieve total closure evaporites of northern Cuba [Pardo, 1975] in the Gulf of Mexico area [Pindell and and by the possible salt occurrence [Lidz, Dewey, 1982; Buffler et al., 1980, 1981; 1973] beneath Exuma Sound (Figure 1), if it Dewey, 1982; Dietz and Holden, 1970; is assumed that evaporite sequences Freeland and Dietz, 1972; Salvador and pertaining to continental breakup are Green, 1980; Pilger, 1978; Walper, 1980; formed primarily in shallow water, on White, 1980]. The reconstruction must attenuated continental crust due to initial explain deformation patterns in the subsidence during rifting. The southern Alleghenian orogenic belt and the apparent margin of the Bahamas was imbricated in absence of Upper Permian to Late Triassic thrusts as Cuba collided with the Bahamas marine sedimentary rocks in the in the Paleogene [Gealey, 1980; Dickinson s tratigraphies of the margins involved. and Coney, 1980], providing surface Further, it seems most probable that the exposures in northern Cuba of early Yucatan block, but not the Chortis block, Bahamian stratigraphy. The eastward fit between the U.S. Gulf Coast and extent

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