Abstract In the search for unconventional reservoirs, one of the geological formations most studied in the United States is the Eagle Ford (Upper Cretaceous), which extends from the state of Texas in United States to the northeastern portion of the Mexican republic. The Eagle Ford Formation consists of argillaceous limestones and calcareous siltstone deposited in a mixed environment. These lithologies have petrophysical and geochemical characteristics sufficient to be considered as producing gas and/or oil, depending on the content of organic matter and the degree of maturity thermal reached. In the northeast of the State of Coahuila, based on lithology, paleontological content, and TOC, Eagle Ford formation can be divided into three units: Biozone A: Heterohelix sigali and Helvetoglobotruncana helvética , dominated by limestone, in platform environments, thicknesses of 16 to 100m, and TOC content of 0.56% to 1.65%. Biozone B: Whiteinella archaeocretacea , limestone and calcareous shales, interbedded lithologies, deposited Biozone C: Rotalipora , black shales deposited in suboxic basin, thicknesses of 60 to 95m, and TOC content of 1.86% to 5.2. With the thickness distribution of the proposed units, it can be interpreted that the variation in the water depth depends on the topographic relief that prevailed in the Late Cretaceous (Cenomanian–Turonian) in the northeastern portion of Mexico: in a shelf and basin environment, influenced by Maverick Basin. Geochemical data analyzed and the proposed subdivision, indicates that Biozone C drive is the thickest, and has more TOC content in the northeastern part of the Burro-Picachos Basin; the predominant type of kerogen in the area is the type III. Using the Dykstra-Parson method to determine the homogeneity of the distribution of values of each proposed unit, Biozone A has a higher degree of homogeneity than Biozone C. However, based on TOC and degree of homogeneity, Biozone B has a lower degree of exploration.

Abstract A thin, discontinuous, fluvial, locally conglomeratic sandstone at the base of the Dakota Sandstone in the vicinity of the southeastern San Juan basin, New Mexico has been named the Encinal Canyon Member of the Dakota Sandstone. In the past, the sandstone beds, placed here in the Encinal Canyon, have been included in the Jackpile sandstone, (an economic unit in the Morrison Formation), in the Burro Canyon Formation, or in the Oak Canyon Member of the Dakota Sandstone. Distinction between the Encinal Canyon Member and the Jackpile sandstone, which are separated by an unconformity that probably spans most of the Early Cretaceous, is economically important. The Jackpile is a primary uranium exploration target, whereas the Dakota contains little known uranium. In the past, the sub-Dakota erosional surface in the southeastern San Juan basin generally was thought to be at the base of the marine and paralic Oak Canyon Member of the Dakota Sandstone, which overlies the Encinal Canyon Member. The unconformity is shown here to be at the base of the fluvial rocks of the Encinal Canyon Member. Local relief at the base of the Encinal Canyon indicates that the sub-Dakota erosional surface formed during a time of regional degradation. Easterly flowing streams scoured underlying units and in some places cut completely through the Jackpile sandstone and the Burro Canyon Formation. The Encinal Canyon was deposited in response to the initial transgression of the Dakota sea. As the sea inundated the area, a transgressive erosional surface formed, and the overlying paralic and marine sediments of the Oak Canyon Member were deposited.

ABSTRACT Within coastal outcrop sections west of Santa Barbara, California, the upper part of the Middle Miocene is condensed into a narrow stratigraphic interval that is characterized by phosphatic hardgrounds. Foraminiferal biostratigraphy shows that the base of the condensed interval is diachronous, varying from a position within the Luisian Stage at Gaviota Beach, to a position just above the Luisian-Mohnian boundary at Naples Beach and probably at El Capitan Beach. Termination of the main episode of hardground deposition occurred within the Early Mohnian, and is synchronous within the resolution of the biostratigraphic correlations. Phosphatic hardground sections at Gaviota Beach, El Capitan Beach, and Naples Beach correlate to a biogenic silica-rich interval characterized by chert, porcelanite, and organic phosphatic shale at Arroyo Burro Beach. The Upper Luisian to Lower Mohnian siliceous sediments at Arroyo Burro Beach correlate in part or in whole to the massive chert member of the Monterey Formation, the main fractured chert reservoir interval of Monterey oil fields in Santa Barbara Channel.

ABSTRACT The understanding of the plate tectonic interactions between the Caribbean, South America, and Atlantic plates and their integration with the timing of the basin configurations, its source rock deposition, and thermal maturation provides important insights to interpret the Venezuelan petroleum systems. The different tectonic settings in northern Venezuela offered the right environmental conditions for the deposition of world-class–Cretaceous organic-rich source rocks all through its northern margin, allowing the generation, expulsion, migration, entrapment, and geographical distribution for most of the 1.8 trillion bls of original oil in place and 200 TCFG in discovered-proven resources in the 14 main basins of Venezuela. The integrated and comprehensive approach of this study allowed the proposal of an orogenic float partitioning tectonic model that couples the development of the southern Caribbean plate along oblique terrane accretions and subduction below northern South America concurrently with the Atlantic oceanic-crust subduction below the Caribbean plateau. The orogenic float glides on the underlying Caribbean–South American lithosphere coupling, along a basal decollement surface with two deformation fronts that forced a foreland basin to the south in the arc–continent collision (“A” subduction) and coeval forearc basins on Caribbean oceanic-crust subductions under Caribbean terranes or “B” subduction. Right-lateral–strike-slip fault activity along the Oca, San Sebastian, El Pilar, and Arima systems occurs synchronously with the eastward rejuvenation of Caribbean accretion and thrusting. These offsets are the consequence of the oblique convergence between the plates to balance the eastward displacement with the southward thrusting and foredeep subsidence. We report evidence for 100 km (60 mi) of right-lateral displacement along the Oca fault. In our model, the orogenic float used the weakness of the crust along old transform system that formed during the Mesozoic rifting event, to create internal strain-partitioning and displace the arc–continent deformation front along northwest–southeast right-lateral transfer-fault systems of Barquisimeto, Burro Negro, Guárico, Margarita, Urica, and Tobago to name the most important. This succession of tectonic events had implications for basin development north and south of the suture, on the autochthonous side and on the transported terranes. The understanding of the Andean orogenesis as well as the rest of the northern ranges, and the timing and subsidence of adjacent basins, along with the related petroleum systems allowed us to identify and locate from Eocene to present the main oil and gas kitchens for the Cretaceous and Cenozoic source rocks in northern onshore and offshore Venezuela. This facilitated the identification of remaining exploration potential even on mature and explored basins, such as the Cretaceous and Eocene-subcrop plays in Golfo de Venezuela, the foreland subthrust belt play in Ensenada de Barcelona with autochthonous Cretaceous to Paleogene reservoirs, a possible pre-Cretaceous source rock within Espino graben, and several transtensional and transpressional plays in the offshore basins of Blanquilla, Cariaco, Bonaire, and northeastern Falcón basins.