Abstract The Permian marine and continental sedimentary sequences in south central México and the biota contained in them are analyzed in this paper. The fossil flora and fauna are contained in Permian strata that correspond to the Guacamaya Formation in the states of Hidalgo and Veracruz; to the Patlanoaya, Los Hornos, Cuxtepeque, and Matzitzi Formations in the state of Puebla; to the Olinalá Formation in the state of Guerrero; to the Ihualtepec, Ixtaltepec, and Yododeñe Formations in the state of Oaxaca; and to the Paso Hondo Formation in the state of Chiapas. The microfaunistic association of Olinalá fusulinids can be correlated with the Guadalupe Mountains and the La Mar Formation of Texas in the U.S.A., and with the Difunta Formation of Coahuila and strata of the states of Sonora, Guerrero, and Oaxaca in Mexico. Fusulinids from the Olinalá, Ihualtepec, and Yododeñe Formations suggest that during the Late Permian (Wordian-Capitanian), these organisms were part of the same paleogeographic province that comprised Texas, Arizona, New Mexico, and California in the United States, and northern Sonora, Chihuahua, Coahuila, extending into central Mexico.

The Cosoltepec Formation consists of unfossiliferous phyllites and psammites with tectonic slices of basalt and forms a major part of the Acatlán Complex of southern México. It has traditionally been interpreted as part of either a Cambro-Ordovician accretionary prism or a passive margin deposited in the Iapetus Ocean. Although no reliable age data are available from the basaltic slices, their widespread tectonic interleaving with the Cosoltepec Formation suggests that some of the sedimentary rocks were originally deposited directly on the ocean-floor basalts. The age of the Cosoltepec metasediments ranges from Ordovician to uppermost Devonian (oldest unconformably overlying sediments: uppermost Devonian). The mafic rocks have been affected by greenschist- to sub-greenschist-facies metamorphism. The geochemistry indicates that they are mainly mid-ocean ridge basalt (MORB) tholeiites with flat or depleted rare earth element (REE) patterns and resemble MORB derived from heterogeneous sources. Another minor group consists of ocean island basalts and andesites, which have distinctly fractionated REE patterns, whereas their mantle-normalized trace element patterns do not show Nb-Ta or Ti negative anomalies. Thus, these mafic rocks appear to represent oceanic lavas that were tectonically incorporated into the clastic rocks of the Cosoltepec Formation during deformation that started immediately prior to deposition of late Fammenian sedimentary rocks and continued into the Mis-sissippian. Tectonic juxtaposition of these rocks with eclogitic rocks suggests that the deformation was related to exhumation following subduction: the Cosoltepec Formation and its mafic lenses derived from the overriding plate, whereas the eclogitic rocks represent parts of the subducting plate. The probable Middle Ordovician–Middle Devonian age of the oceanic rocks together with their initial deformation during the Devonian–Carboniferous suggest that they represent vestiges of the Rheic Ocean.

The Piaxtla Suite of the Acatlán Complex (southern México) has previously been considered a vestige of the Iapetus Ocean that underwent eclogite-facies metamorphism during Late Ordovician subduction and exhumation. Study of granitoid, mafic, and metasedimentary rocks of the Asis Lithodeme of the Piaxtla Suite reveals a complex tectonothermal history involving: (1) eclogite-facies syntectonic metamorphism preserved as aligned omphacite in mafic lenses dated at 346 ± 3 Ma (concordant U-Pb zircon age), which is inferred to result from subduction; (2) polyphase deformation involving WSW-ENE tectonic transport under amphibolite-facies conditions accompanied by migmatization due to decompression melting dated at ca. 347–330 Ma (SHRIMP [sensitive high-resolution ion microprobe] zircon ages); (3) continued deformation under greenschist facies; and (4) development of several phases of late folds and crenulation cleavage. Pressure, temperature, and time ( P-T-t ) data suggest rapid isothermal decompression from eclogite to upper amphibolite facies during the Visean (Middle Mississippian) followed by cooling. In the absence of age data for the latter stage, nearby unmetamorphosed latest Upper Devonian sedimentary rocks contain metamorphic, Piaxtla Suite clasts suggesting either diachronism in the exhumation process or synchronous exhumation and subsidence in adjacent areas. Such rapid exhumation of eclogites is typical of continent-continent collision zones, and the subhorizontal, WSW-ENE kinematics is compatible with either lateral thrust ramping or extension in the orogen. Devonian–Carboniferous subduction and exhumation are incompatible with an origin within the Iapetus Ocean, because that ocean had closed by Silurian times. However, they are consistent with oblique subduction of the leading edge of Gondwana along the southern flank of the Rheic Ocean during the amalgamation of Pangea.

Abstract Detrital zircon age populations from Palaeozoic sedimentary and metasedimentary rocks in Mexico support palinspastic linkages to the northwestern margin of Gondwana (Amazonia) during the late Proterozoic–Palaeozoic. Age data from: (1) the latest Cambrian-Pennsylvanian cover of the c . 1 Ga Oaxacan Complex of southern Mexico; (2) the ?Cambro-Ordovician to Triassic Acatlán Complex of southern Mexico's Mixteca terrane; and (3) the ?Silurian Granjeno Schist of northeastern Mexico's Sierra Madre terrane, collectively suggest Precambrian provenances in: (1) the c . 500–650 Ma Brasiliano orogens and c . 600–950 Ma Goias magmatic arc of South America, the Pan-African Maya terrane of the Yucatan Peninsula, and/or the c . 550–600 Ma basement that potentially underlies parts of the Acatlán Complex; (2) the Oaxaquia terrane or other c . 1 Ga basement complexes of the northern Andes; and (3) c . 1.4–3.0 Ga cratonic provinces that most closely match those of Amazonia. Exhumation within the Acatlán Complex of c . 440–480 Ma granitoids prior to the Late Devonian–early Mississippian, and c . 290 Ma granitoids in the early Permian, likely provided additional sources in the Palaeozoic. The detrital age data support the broad correlation of Palaeozoic strata in the Mixteca and Sierra Madre terranes, and suggest that, rather than representing vestiges of Iapetus or earlier oceanic tracts as has previously been proposed, both were deposited along the southern, Gondwanan (Oaxaquia) margin of the Rheic Ocean and were accreted to Laurentia during the assembly of Pangaea in the late Palaeozoic.

The Acatlán Complex of southern México comprises metasedimentary and metaigneous rocks that represent the vestige of a Paleozoic ocean. Juxtaposed against granulite-facies gneisses of Mesoproterozoic (ca. 1 Ga) age, the complex has previously been related to the Iapetus Ocean and interpreted to preserve a tectonostratigraphic record linked to that of the Appalachian orogen: (1) Cambro-Ordovician deposition of a trench or forearc sequence (the Petlalcingo Group: the Magdalena, Chazumba, and Cosoltepec Formations) and an oceanic assemblage (the Piaxtla Group), (2) polyphase Late Ordovician–Early Silurian deformation (the Acatecan orogeny) during which the Piaxtla Group underwent eclogite-facies metamorphism synchronous with megacrystic granitoid emplacement, (3) deposition of the arc-related Tecomate Formation and intrusion of megacrystic granitoid plutons during the Devonian, and (4) deformation under greenschist-facies conditions during the Late Devonian Mixtecan orogeny. However, recent structural, geochronological, and geochemical studies have shown that (1) the Cosoltepec Formation is bracketed between ca. 455 Ma and the latest Devonian and may be part of a continental rise prism with slivers of oceanic basalt; (2) the Magdalena and Chazumba Units represent a clastic wedge assemblage of Permo-Triassic age; (3) the eclogitic metamorphism is locally Mississippian in age; (4) the Tecomate Formation is an arc complex of latest Pennsylvanian–Middle Permian age; (5) the megacrystic granitoid rocks span the Ordovician and have a calc-alkaline geochemistry, whereas accompanying mafic units have mixed continental arc–tholeiitic affinities and are locally as young as the earliest Silurian; (6) the greenschist-facies tectonothermal event occurred in the Permo-Triassic; and (7) the complex records a Jurassic tectonothermal event that resulted in local high-grade metamorphism and migmatization. This revised geological history precludes any linkage to Iapetus, but is consistent with that of the Rheic and paleo-Pacific Oceans and is interpreted to record (1) development of a rift or passive margin on the southern flank of the Rheic Ocean in the Cambro-Ordovician, (2) formation of either an arc or an extensional regime along the formerly active northern margin of Gondwana throughout the Ordovician, (3) ocean closure documented by subduction-related eclogite-facies metamorphism and exhumation during the Late Devonian–Mississippian, (4) Permo-Triassic convergent tectonics on the paleo-Pacific margin of Pangea, and (5) overriding of a Jurassic plume.

Abstract In the last decade, Paleozoic rocks have been recognized as having potential for future resources of oil and gas in several countries around the world. The petroleum potential of the upper Paleozoic strata in northern South America is noteworthy in view of the correlations with hydrocarbon-bearing strata and source rocks in neighboring Brazil and Peru–Bolivia, and the southern United States, for both conventional and unconventional oil and gas reservoirs. In the northern part of South America, specifically in Venezuela and Colombia, the upper Paleozoic stratigraphic record is poorly documented and understood, but the succession there reveals major changes in facies, which can be related to global-scale events. These changes have been described through detailed fieldwork in the Venezuelan Andes, supported by petrographic and geochemical studies. This dataset forms the basis for the interpretation of the potential petroleum systems in this area, along with the available published information. Sedimentation during the Permian occurred on an extensive ramp, which dipped basinward, probably toward the north, toward the open ocean within the foreland basin, which has been named the Mucuchachi Basin (MB). The Permian rocks in the MB extend through Colombia to the west and southwest, where a few sections of limestone and shale with fusulinids occur. The MB may well have been connected to the basins in Peru and Bolivia to the southwest and with those in the Mexican and Guatemala areas to the north, where a similar stratigraphic succession is developed. Elements of the petroleum system for these Permian rocks include the presence of source rocks since values of total organic carbon reach 5% in some shales. However, indicators of thermal maturity suggest an over-mature level. On the other hand, a thermal simulation derived from basin modeling software and clumped isotopes thermometry suggests that strata could have been in the oil and gas window during the Cenozoic. Thus there is the likelihood of hydrocarbons having been expelled upward into stratigraphically younger reservoirs, where fractured fine-grained clastic facies and sandstone horizons could have the potential to provide reservoir rocks. The presence of fine-grained facies with low permeability suggests that these Permian rocks could have the potential to provide a sealing capacity as well as the possibility of being part of stratigraphic traps. In addition, several authors have pointed out potential structural traps in the Barinas–Apure Basin and these could have extended to the western areas of the Los Llanos Basin in Colombia are restricted to the Tachira Graben.