Abstract Approximately 5 km of Cretaceous and Paleogene strata are exposed in the Serranfa del Lnlerior of northeastern Venezuela, and the depositional settings and paleoenvironmental conditions of these strata have been investigated, leading to paleogeographic reconstructions spanning approximately 90 my of passive-margin sedimentation. Exposed Lower Cretaceous strata are generally shallow marine in origin and vary between siljciclasUc shelf deposits and bioherm-dominated, impure carbonate platform deposits. Neocomian-Aptian shelfal and carbonate-platform facies are widespread and comprise the Barranqufn Formation. A major, Early Cretaceous siliciclasiic fiuvio-deltaic system emanated from southwest of the Serranfa del Interior and was the source of the commonly coarse-grained Lower Cretaceous strata. In Early Albian time, a short-lived transgressive/regressive cycle led to deposition of the shaley, deep-shelf deposits of the Garcfa Formation. The E) Cantil Formation was deposited on a Early to early Middle Albian carbonate platform that had significant and variable silicjclaslic contamination (particularly in the southern Serranfa del Interior). The carbonate platform started retrograding southward in Early Albian time and was eventually succeeded by deeper marine deposition of glauconitic sand and shale of the Cbimana Formation. After a brief, Middle Albian progradational event (upper Chimana Formation), regional transgression led to primarily pelagic deposition in the Querecual Formation. Upper Cretaceous strata are notably more homogeneous and of deeper marine origin than Lower Cretaceous strata, and consist primarily of organic-rich, calcareous siltstone and muddy, micritic limestone. These slope deposits of the Querecual and San Antonio Formations are the petroleum source rocks for the Eastern Venezuela Basin. Deep-water (>200 m) sedimentation continued almost continuously from Late Albian until mid-Maastrichtian time, with (he exception of a minor, Santonian- Early Campanian influx of sand at the base of the San Antonio Formation. A voluminous influx of submarine fan sediments occurred in Late Maastrichtian time during deposition of the San Juan Formation. After transgression and monotonous dark shale deposition in the Vidono Formation, renewed progradation in Early Eocene time led to deposition of the glauconitic submarine fan deposits of the Caratas Formation. Shallowing of the depositional surface locally led to shelfal carbonate deposition at the top of the Caratas Formation in Middle Eocene time (the Tinajitas limestone). Passive-margin sedimentation was finished by the close of the Eocene Epoch, and was followed by foredeep sedimentation and eventually by uplift and exposure of the passive-margin strata within the Serranfa del Interior.

Abstract The deposition of organic carbon–rich sediments during the Late Cretaceous in northern South America was controlled by global and local oceanographic, climatic, and tectonic variables. Key in establishing “source rock” depositional systems across the region were eustatic sea-level rise, warming global sea-surface temperatures, the formation of low-latitude saline bottom waters, and a relatively constant supply of fine-grained hemipelagic sediment (mostly derived from the south and east). Specific paleobathymetric conditions enhanced the development of stagnant water masses from the proto-Caribbean plate to Suriname. Organic-matter preservation was aided by the presence of these water masses across the region. Primary productivity was elevated above “normal” marine levels only in the protocentral Caribbean and along the ancestral Costa Rica/Panama island arc, or during seasonal upwelling in northern South America. Cooler, wetter climatic conditions that began in the late Santonian also were modified by regional and local variables. The development of new intermediate/bottom-water masses, increased polar heat transport caused by improved deep-ocean circulation, and fluctuations in volcanogenic CO 2 provided a background effect for local variables such as bathymetry and topography. The development of oxygenated high-latitude water masses provided a means for ventilation of stagnant, low-oxygen bottom waters across northern South America and the central Caribbean. Stronger seasonal upwelling (increased wind stress caused by better polar heat transport, and northward movement of the South American Plate into the zone of northward Ekman transport), more frequent fluvial outflow and deltaic deposition, and the submergence of key paleobathymetric barriers aided ventilation and subsequently diminished organic-matter preservation. Most of these variables had a positive impact on primary productivity and caused rapid changes in the diversity of planktonic foraminifera through the end of the Cretaceous.

ABSTRACT The Eastern Venezuelan foreland basin (EVB) has been filling from the southwest by the Orinoco River since the late Miocene–early Pliocene. The easternmost part of the Eastern Venezuelan Basin (EEVB) became overfilled by clastic sedimentation since the Pliocene. The EEVB now consists of a 10 km (33,000 ft) thick delta system formed by the Orinoco River, which has spilled over the shelf edge onto the Atlantic margin of northeastern Venezuela. The Eastern Venezuelan foreland basin is the second largest hydrocarbon-producing basin in Venezuela, with proven reserves of 36 billion barrels. To improve our understanding of the paleogeography and hydrocarbon potential of the EEVB, 620 km 2 (385 mi 2 ) of 3-D seismic, 4000 km (2485 mi) of 2-D seismic, and six wells with well logs were interpreted from the Punta Pescador area of the EEVB. We integrate the results from this study with the results of previous workers around the Orinoco Delta. Based on the integration of these data, the following sequence of Cenozoic events affecting the study area are proposed: (1) passive margin setting since the Cretaceous to Paleogene; (2) oblique collision of the Caribbean plate causing an underfilled, foreland basin stage that initiated during the late Oligocene; (3) during the Oligocene and early Miocene, south–north-flowing fluvial systems and associated deltas prograded northward and filled the foreland-basin-related depocenter; (4) late Miocene eustatic sea level lowering produced a major erosional surface and submarine canyons that allowed sediments to suddenly prograde eastward; and (5) early Pliocene to Holocene overfilling of the EEVB with eastward progradation of the Orinoco Delta into the Atlantic Ocean. Using the new information presented in this chapter, several hydrocarbon prospects were identified within the clastic Miocene–Pliocene–Pleistocene sequence.

Abstract An integrated, testable chronostratigraphic database of Late Cretaceous bioevents in numerous reference sections was constructed in order to test the global synchrony of Upper Cretaceous oceanic redbeds—CORBs—and to measure precisely their rates of sediment accumulation. Graphic correlation was the method of choice because it is based on species checklists and because the range projections are transparent and testable. Stage boundaries are defined by GSSP or key reference sections with ammonites, planktic foraminifera, and nannofossils, as well as with magnetochrons. Sequence boundaries and other sedimentary markers as defined in reference sections are projected into the database by graphic correlation of the co-occurring fossils. The database scale is calibrated to radiometric ages of Upper Cretaceous stages that are generally similar to those of the 2004 time scale. This database is used in three areas to interpret deposition of CORBs, the North Atlantic, the Swiss Pre-Alps, and the Eastern Austrian Alps. North Atlantic CORB intervals in six cores range in age from Turonian to Maastrichtian. This succession was deposited within two distinct deep water masses. A Turonian–Santonian oxygenated water mass with a relatively shallow calcite compensation depth (CCD) hosted red-bed deposition and diversification of benthic foraminifera. Deep-water, low pH conditions existed in the North Atlantic during Late Cretaceous submarine volcanism. The well oxygenated Campanian–Maastrichtian water mass was above the CCD, and calcareous fossils were preserved during a second benthic foraminifer diversification event. Red marine clay and turbidites alternated with gray and green beds. Rates of sediment accumulation generally were higher during the Campanian–Maastrichtian period than during the earlier period. CORB strata in the Swiss Pre-Alps were deposited at different times in different places for varying durations and at different rates beginning in the Aptian and continued sporadically into the Santonian. In the Eastern Alps Upper Cretaceous marine red beds are interbedded with siliciclastic and calcareous facies deposited in the Penninic Ocean between colliding plates. Oldest CORB deposition is recorded in the Albian and became persistent during the Campanian. Interbedded red and gray strata record climatic forcing during tectonically controlled transgressive events. The duration of CORB deposition generally was shorter in epicontinental basins than in oceanic basins, but the average rate of sediment accumulation tended to be similar in epicontinental and oceanic basins. Even-bedded CORBs were deposited at the sameaverage duration as homogeneously bedded deposits, but even-bedded CORBs accumulated faster than homogeneous deposits. Many repetitively interbedded oceanic red beds were deposited at rates close to orbital frequencies and may have been related to climatic forcing.