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At least 811 records · Page 45Linked to original sources
USGS2025

Using high-resolution geospatial imagery and data to document the evolution of the Wilderness Breach that was created by Hurricane Sandy in 2012 at Fire Island National Seashore, New York

The U.S. Geological Survey’s National Civil Applications Center obtained remote sensing data and imagery collected from 1939 through 2023 to monitor changes at Fire Island National Seashore, New York. On October 29, 2012, an inlet was created during Hurricane Sandy on Fire Island that remained open for 10 years. This inlet, named the “Wilderness Breach,” formed at the same location where an inlet had previously existed and remained open from 1763 to 1825. This report documents the morphological changes that occurred at the Wilderness Breach during the 10-year existence of this feature.

New York↗
USGS1970

Paleozoic and Precambrian rocks of Alaska and their role in its structural evolution

Acknowledging that there are large gaps in the knowledge of the geology of Alaska, the following threefold subdivision of Alaska into Paleozoic tectonic elements is proposed: Southern Alaska--the Alaska Range and farther south--is the northern end of the Paleozoic Cordilleran geosyncline that rims the eastern Pacific. Northern Alaska--the northeastern Brooks Range and the Arctic Coastal Plain--is underlain by a pre-Upper Devonian fold belt that may continue around the rim of the Canada Basin into the Franklinian geosyncline of the Canadian Arctic Islands. East-central Alaska, with a thinner, mainly carbonate rock section, seems to be a western extension of the Yukon shelf that separates the circum-Arctic geosynclinal trend from the Cordilleran geosyncline along the Pacific margin of southern Alaska.

Alaska↗
USGS1979

Uranium, thorium, and mercury distribution through the evolution of the McDermitt Caldera complex

The McDermitt caldera complex developed over a period of 5 m.y. years during which ash-flow tuff sheets anomalous in mercury, uranium, and thorium were emplaced. The moat portions of the caldera complex were subsequently filled with tuffaceous sediments. Late in the caldera development near-surface intrusives and domes were emplaced along the margins of the complex and mineralized with uranium. Seven large hydrothermal systems developed at this time and formed large areas of alteration within the caldera-fill volcanics and sediments. Five of the altered zones are associated with economic concentrations of uranium, and or mercury.

Nevada, Oregon↗
USGS1983

Middle Tertiary continental rift and evolution of the Red Sea in southwestern Saudi Arabia

Middle Tertiary rift volcanism in a continental-rift valley in the Arabian-Nubian Shield was the first surface expression of active mantle convection beneath an axis that was to become the Red Sea. Investigation of the coastal plain of southwestern Saudi Arabia suggests that the rift valley was filled with basaltic and felsic to rhyolitic volcanic rocks (Ad Darb and Damad formations), cherty tuffaceous siltstones (Baid formation), and subordinate Nubian-type quartz sandstone (Ayyanah sandstone) between about 30 and 20 Ma ago. These rocks are named herein the Jizan group. At the same time, alkali-olivine basalt was erupted on the stable Precambrian craton at locations 100 to 200 km east of the rift valley axis. First-stage spreading of the Red Sea began about 20 Ma ago when diabasic dikes and gabbro and granophyre plutons (Tihamat Asir complex) of oceanic-tholeiitic parentage were intruded into the continental-rift deposits. The new oceanic crust was injected into a region of thinned continental crust. Because of thinning, the continental crust was extended and became fractured into a series of fault blocks. Crustal extension in the attenuated zone was accompanied by mafic and silicic volcanism producing a continental rift-valley tectonic environment. Fault blocks of the rift valley were initially rotated toward the Red Sea during the first-stage spreading episode. Inland from the continental rift, the thick continental crust was distended on long parallel fractures that were intruded by gabbroic to quartz syenitic magma to form continental dikes. This period of continental-margin extension was short lived, lasting perhaps only 1 or 2 Ma. The first-stage sea-floor spreading of the Red Sea continued until about 15 or 14 Ma ago at a half-spreading rate of about 2.2 cm/yr. Throughout early Tertiary time, the Arabian Shield erosion surface remained near sea level. First-stage uplift of the Red Sea Escarpment began during middle Miocene time, as evidenced by the coarse polymictic boulder conglomerate of the Bathan formation. Second-stage scarp uplift and second-stage sea-floor spreading followed during Pliocene, Pleistocene, and Holocene time.

Open-File Report↗
USGS1986

Genesis and evolution of the Baid al Jimalah tungsten deposit, Kingdom of Saudi Arabia

The Baid al Jimalah tungsten deposit flat 25°09 N., long 42°41' E.) is a swarm of steeply dipping, sheeted, tungsten-bearing quartz veins. It is spatially, temporally, and genetically associated with a 569 Ma, highly differentiated, porphyritic granite that intrudes late Proterozoic, immature sandstones of the Murdama group. The bulk of the vein constituents came from hydrothermal fluids exsolved from a granite cupola at a depth of about 3.1 km during a single cycle of magma intrusion and hydrothermal mineralization. Hypogene mineralization can be divided into 3 main periods: early quartz-molybdenite stockwork veins, wolframite- and scheelite-bearing greisen veins, and late, barren veins. Each of the three periods can be divided into several stages that are transitional to each other. The greisen veins, in particular, show replacement of earlier mineral assemblages by later ones. The veins at Baid al Jimalah East, approximately 1.5 km to the east of the Baid al Jimalah tungsten deposit, are genetically related to it and probably formed while the greisen mineralization was being deposited. Early stockwork mineralization was formed near magmatic temperatures (580°-700°C) from low salinity fluids (1-2 weight percent NaCl equivalent). Two fluids were present, one low density and CO 2 rich, the other high density and H 2 O rich. Greisen mineralization was formed from fluids in the liquid state at temperatures mostly between 390° and 430°C with salinities between 4.5 and 10.9 weight percent NaCl equivalent. Late, barren mineralization formed from liquids with salinities between 0.5 and 3.0 weight percent NaCl equivalent and at temperatures at least as low as 238°C. The veins at Baid al Jimalah East formed from liquids between 0 and 4.2 weight percent NaCl equivalent at temperatures largely between 300° and 375°C. Depth of mineralization was greater than 3.1 km. The temperatures given above have been corrected for pressure assuming this depth, and are 75-80°C higher than the fluid inclusion filling temperatures. Important volatile constituents of the hydrothermal fluids were CO 2 and CH 4 , in addition to H 2 O and HF. Baid al Jimalah is similar in character and origin to other tungsten-tin greisen deposits in the world, especially the Hemerdon deposit in Devon, England. It is also analogous to Climax-type molybdenum deposits, which contain virtually identical mineral assemblages, but with the relative intensities of the molybdenum and tungsten mineralization reversed.

Open-File Report↗