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At least 199 records · Page 11Linked to original sources
USGS2011

Geology and petroleum potential of the Eurasia Basin

The Eurasia Basin petroleum province comprises the younger, eastern half of the Arctic Ocean, including the Cenozoic Eurasia Basin and the outboard part of the continental margin of northern Europe. For the USGS petroleum assessment (CARA), it was divided into four assessment units (AUs): the Lena Prodelta AU, consisting of the deep-marine part of the Lena Delta; the Nansen Basin Margin AU, comprising the passive margin sequence of the Eurasian plate; and the Amundsen Basin and Nansen Basin AUs which encompass the abyssal plains north and south of the Gakkel Ridge spreading centre, respectively. The primary petroleum system thought to be present is sourced in c . 50–44 Ma (Early to Middle Eocene) condensed pelagic deposits that could be widespread in the province. Mean estimates of undiscovered, technically recoverable petroleum resources include <1 billion barrels of oil (BBO) and about 1.4 trillion cubic feet (TCF) of nonassociated gas in Lena Prodelta AU, and <0.4 BBO and 3.4 TCF nonassociated gas in the Nansen Basin Margin AU. The Nansen Basin and Amundsen Basin AUs were not quantitatively assessed because they have less than 10% probability of containing at least one accumulation of 50 MMBOE (million barrels of oil equivalent).

Book chapter↗
USGS2009

Ultra-deep oxidation and exotic copper formation at the late pliocene boyongan and bayugo porphyry copper-gold deposits, surigao, philippines: Geology, mineralogy, paleoaltimetry, and their implications for Geologic, physiographic, and tectonic controls

The Boyongan and Bayugo porphyry copper-gold deposits are part of an emerging belt of intrusion-centered gold-rich deposits in the Surigao district of northeast Mindanao, Philippines. Exhumation and weathering of these Late Pliocene-age deposits has led to the development of the world's deepest known porphyry oxidation profile at Boyongan (600 m), and yet only a modest (30-70 m) oxidation profile at adjacent Bayugo. Debris flows, volcanic rocks, and fluviolacustrine sediments accumulating in the actively extending Mainit graben subsequently covered the deposits and preserved the supergene profiles. At Boyongan and Bayugo, there is a vertical transition from shallower supergene copper oxide minerals (malachite + azurite + cuprite) to deeper sulfide-stable assemblages (chalcocite ?? hypogene sulfides). This transition provides a time-integrated proxy for the position of the water table at the base of the saturated zone during supergene oxidation. Contours of the elevation of the paleopotentiometric surface based on this min- eralogical transition show that the thickest portions of the unsaturated zone coincided with a silt-sand matrix diatreme breccia complex at Boyongan. Within the breccia complex, the thickness of the unsaturated zone approached 600 in, whereas outside the breccia complex (e.g., at Bayugo), the thickness averaged 50 m. Contours of the paleopotentiometric surface suggest that during weathering, groundwater flowed into the breccia complex from the north, south, and east, and exited along a high permeability zone to the west. The high relief (>550 m) on the elevation of the paleopotentiometric surface is consistent with an environment of high topographic relief, and the outflow zone to the west of the breccia complex probably reflects proximity to a steep scarp intersecting the western breccia complex margin. Stable isotope paleoaltimetry has enabled estimation of the elevation of the land surface, which further constrains the physiographic setting during supergene oxidation. Isotopic measurements of oxygen in supergene kaolinite from Boyongan suggest that local paleometeoric water involved in weathering had a ??180 composition of approximately -5.7 per mil. At the latitude of the southern Philippines, this value corresponds to Pleistocene rain water condensing at elevations between 750 and 1,050 m above contemporary sea level, providing a maximum estimate for the surface elevation during weathering of the porphyry systems. Physiographic reconstuctions suggest that the deep oxidation profile at Boyongan formed in an environment of high topographic relief immediately east of a prominent (>550 m) escarpment. The high permeability contrast between the breccia complex and the surrounding wall rocks, coupled with the proximity of the breccia complex to the escarpment, led to a depressed groundwater table and a vertically extensive unsaturated zone in the immediate vicinity of Boyongan. This thick vadose zone and the low hypogene pyrite/copper sulfide ratios (0.6) at Boyongan promoted in situ oxidation of copper sulfides with only modest (<200 m) supergene remobilization of copper. In contrast, higher hypogene pyrite/chalcopyrite ratios (2.3) at Bayugo led to greater acid production during weathering and more complete leaching of copper above the base of oxidation. This process promoted significant (600 m) lateral dispersion of copper down the paleohydraulic gradient into the diatreme breccia comple, ultimately leading to the formation of an exotic copper deposit. ?? 2009 Society of Economices Geologists, Inc.

Economic Geology↗
USGS1997

Geologic age: using radioactive decay to determine geologic age

At the close of the 18th century, the haze of fantasy and mysticism that tended to obscure the true nature of the Earth was being swept away. Careful studies by scientists showed that rocks had diverse origins. Some rock layers, containing clearly identifiable fossil remains of fish and other forms of aquatic animal and plant life, originally formed in the ocean. Other layers, consisting of sand grains winnowed clean by the pounding surf, obviously formed as beach deposits that marked the shorelines of ancient seas. Certain layers are in the form of sand bars and gravel banks -- rock debris spread over the land by streams. Some rocks were once lava flows or beds of cinders and ash thrown out of ancient volcanoes; others are portions of large masses of once-molten rock that cooled very slowly far beneath the Earth's surface. Other rocks were so transformed by heat and pressure during the heaving and buckling of the Earth's crust in periods of mountain building that their original features were obliterated.

General Information Product↗
USGS1976

Geology of central Costa Rica and its implications in the geologic history of the region

The oldest rocks in Costa Rica, the Nicoya Complex, crop out in an arcuate belt along the Pacific coast and outside the mapped area. The complex is an ophiolite assemblage and indicates that a Late Cretaceous arc-trench system, probably a southerly extension of the Middle America Trench, lay along and west of the present Pacific coast. Polarity of the system is indicated by the presence of a volcanic olivine basalt arc east of the ophiolite belt and by a younger magmatic arc farther east. Relative lack of metamorphism of the ophiolite assemblage suggests that the rocks were obducted rather than subducted. Fossil evidence indicates that the complex was emplaced no later than the late Campanian. By the late Eocene both the ophiolite assemblage and the olivine basalt arc had been established as major sediment sources for basins that lay to the east, and they continued as such through the Oligocene and possibly into the middle Miocene. Widespread deposition of trachyandesite lava and volcaniclastic sediments, local marine planation, uplift, and renewed volcanism mark what is presumed to be the end of the Miocene. Extreme south-to-north coarsening of the unconformably superposed Doan Formation and the presence of corals in the shaly facies of the Doan in the southern part of the mapped areas suggest that marine sedimentation there was undisturbed by orogeny and that intrusion of the Talamancan magmatic rocks must have followed deposition of the Doan. Volcaniclastic block breccia, characteristic of northern exposures of the Doan, indicates that volcanism in the proto- Cordillera Central had begun by at least Doan time. Volcanism has been a dominant process in central Costa Rica since that time.

Journal of Research of the U.S. Geological Survey↗
USGS2007

Geologic controls on movement of produced-water releases at US geological survey research Site A, Skiatook lake, Osage county, Oklahoma

Highly saline produced water was released from multiple sources during oil field operations from 1913 to 1973 at the USGS research Site A on Skiatook Lake in northeastern Oklahoma. Two pits, designed to hold produced water and oil, were major sources for release of these fluids at the site. Produced water spills from these and other features moved downslope following topography and downdip by percolating through permeable eolian sand and colluvium, underlying permeable sandstone, and, to a lesser extent, through shales and mudstones. Saline water penetrated progressively deeper units as it moved through the gently dipping bedrock to the north and NW. A large eroded salt scar north of the pits coincides with underlying fine-grained rocks that have retained substantial concentrations of salt, causing slow revegetation. Where not eroded, thick eolian sand or permeable sandstone bedrock is near the surface, and vegetation has been little affected or has reestablished itself after the introduced salt was flushed by precipitation. The extent of salt-contaminated bedrock extends well beyond existing surface salt scars. These results indicate that one of the legacies of surface salt spills can be a volume of subsurface salinization larger than the visible surface disturbance.

Oklahoma↗