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At least 1,765 records · Page 98Linked to original sources

USGS1993

Volcanic eruption of the mid-ocean ridge along the East Pacific Rise crest at 9°45-52'N: direct submersible observations of seafloor phenomena associated with an eruption event in April, 1991

In April, 1991, we witnessed from the submersible Alvin a suite of previously undocumented seafloor phenomena accompanying an in-progress eruption of the mid-ocean ridge on the East Pacific Rise crest at 9°45′N–52′N. The volume of the eruption could not be precisely determined, although comparison of pre- and post-eruption SeaBeam bathymetry indicate that any changes in ridge crest morphology resulting from the eruption were < 10 m high. Effects of the eruption included: (1) increased abundance and redistribution of hydrothermal vents, disappearance of numerous vent communities, and changes in characteristics of vent fauna and mineral deposits within the eruption area since December, 1989; (2) murkiness of bottom waters up to tens of meters above the seafloor due to high densities of suspended mineral and biogenic particulates; (3) destruction of a vent community by lava flows, mass wasting, and possible hydrovolcanic explosion at a site known as ‘Tubeworm Barbecue’ in the axial summit caldera (ASC) at 9°50.6′N; (4) near-critical temperatures of hydrothermal vent fluids, ranging up to 403°C; (5) temporal variations over a 2 week interval in both temperatures and chemical/isotopic compositions of hydrothermal fluids; (6) unusual compositions of end-member vent fluids, with pH values ranging to a record low of 2.5, salinities ranging as low as 0.3 wt% NaCl (one-twelfth that of seawater), and dissolved gases reaching high concentrations (> 65 mmol/l for both CO 2 and H 2 S); (7) venting at temperatures above 380°C of visually detectable white vapor that transformed to plumes of gray smoke a few centimeters above vent orifices; (8) disorganized venting of both high-temperature fluids (black and gray smoke) and large volumes of cooler, diffuse hydrothermal fluids directly from the basaltic seafloor, rather than from hydrothermal mineral constructions; (9) rapid and extensive growth of flocculent white bacterial mats (species unknown) on and under the seafloor in areas experiencing widespread venting of diffuse hydrothermal fluid; and (10) subseafloor downslope migration of magma normal to the ridge axis in a network of small-scale (1–5 m diameter) lava tubes and channels to distances at least 100–200 m outside the ASC. We suggest that, in April, 1991, intrusion of dikes in the eruption area to < 200 m beneath the ASC floor resulted in phase separation of fluids near the tops of the dikes and a large flux of vapor-rich hydrothermal fluids through the overlying rubbly, cavernous lavas. Low salinities and gas-rich compositions of hydrothermal fluids sampled in the eruption area are appropriate for a vapor phase in a seawater system undergoing subcritical liquid-vapor phase separation (boiling) and phase segregation. Hydrothermal fluids streamed directly from fissures and pits that may have been loci of lava drainback and/or hydrovolcanic explosions. These fissures and pits were lined with white mats of a unique fast-growing bacteria that was the only life associated with the brand-new vents. The prolific bacteria, which covered thousands of square meters on the ridge crest and were also abundant in subseafloor voids, may thrive on high levels of gases in the vapor-rich hydrothermal fluids initially escaping the hydrothermal system. White bacterial particulates swept from the seafloor by hydrothermal vents swirled in an unprecedented biogenic ‘blizzard’ up to 50 m above the bottom. The bacterial proliferation of April, 1991 is likely to be a transient bloom that will be checked quickly either by decline of dissolved gas concentrations in the fluids as rapid heat loss brings about cessation of boiling, and/or by grazing as other organisms are re-established in the biologically devastated area.

Earth and Planetary Science Letters↗

USGS2002

Data set of world phosphate mines, deposits, and occurrences: Part A. Geologic data. Part B. Location and mineral economic data

An inventory of more than 1,600 world phosphate mines, deposits, and occurrences was compiled from smaller data sets collected as part of multiple research efforts by Carlotta Chernoff, University of Arizona, and Greta Orris, U.S. Geological Survey. These data have been utilized during studies of black shale depositional environments and to construct phosphate deposit models. The compiled data have been edited for consistency and additional location information has been added where possible. The database of compiled phosphate information is being released in two sections; the geologic data in one section and the location and mineral economic data in the second. This report, U.S. Geological Survey Open-File Report 02–156–A, contains the geologic data and is best used with the complimentary data contained in Open-File Report 02–156–B. U.S. Geological Survey Open-File Report 02–156–B contains commodity data, location and analytical data, a variety of mineral economic data, reference information, and pointers to related records in the U.S. Geological Survey National mineral databases—MASMILS and MRDS.

Open-File Report↗

USGS2017

Geologic map of the northeast flank of Mauna Loa volcano, Island of Hawai'i, Hawaii

Summary Mauna Loa, the largest volcano on Earth, has erupted 33 times since written descriptions became available in 1832. Some eruptions were preceded by only brief seismic unrest, while others followed several months to a year of increased seismicity. The majority of the eruptions of Mauna Loa began in the summit area (>12,000-ft elevation; Lockwood and Lipman, 1987); yet the Northeast Rift Zone (NERZ) was the source of eight flank eruptions since 1843 (table 1). This zone extends from the 13,680-ft-high summit towards Hilo (population ~60,000), the second largest city in the State of Hawaii. Although most of the source vents are farther than 30 km away, the 1880 flow from one of the vents extends into Hilo, nearly reaching Hilo Bay. The city is built entirely on flows erupted from the NERZ, most older than that erupted in 1843. Once underway, Mauna Loa's eruptions can produce lava flows that reach the sea in less than 24 hours, severing roads and utilities in their path. For example, lava flows erupted from the Southwest Rift Zone (SWRZ) in 1950 advanced at an average rate of 9.3 km per hour, and all three lobes reached the ocean within approximately 24 hours (Finch and Macdonald, 1953). The flows near the eruptive vents must have traveled even faster. In terms of eruption frequency, pre-eruption warning, and rapid flow emplacement, Mauna Loa poses an enormous volcanic-hazard threat to the Island of Hawai‘i. By documenting past activity and by alerting the public and local government officials of our findings, we can anticipate the volcanic hazards and substantially mitigate the risks associated with an eruption of this massive edifice. From the geologic record, we can deduce several generalized facts about the geologic history of the NERZ. The middle to the uppermost section of the rift zone were more active in the past 4,000 years than the lower part, perhaps due to buttressing of the lower east rift zone by Mauna Kea and Kīlauea volcanoes. The historical flows that erupted on the north flank of the rift zone, which is more vulnerable to inundation, advanced toward Hilo. Lockwood (1990) noted that the vents of historical activity are migrating to the south. The volcano appears to have a self-regulating mechanism that evenly distributes long-term activity across its flanks. The geologic record also supports this notion; the time prior to the historical period (Age Group 1, orange units, pre-A.D. 1843–1,000 yr B.P.; see map sheet 2) is dominated by activity on the south side of the NERZ. The NERZ trends N. 65° E. and is about 40 km long and 2–4 km wide, narrowing at the summit caldera. It becomes diffuse (6–7 km wide) at its down-rift terminus, at the approximately 3,400-ft elevation. Its constructional crest is marked by low spatter ramparts and by spatter cones as high as 60 m. Subparallel eruptive fissures and ground cracks cut vent deposits and flows in and near the rift crest. Lava typically flows to the north, east, or south, depending on vent location relative to the rift crest. Encompassing 1,140 km 2 of the northeast flank of Mauna Loa from the 10,880-ft elevation to sea level, the map covers the area from Hilo to Volcano on the east and includes the rift zone from Puu Ulaula quadrangle in the southwest to Hilo in the northeast. The distribution of 105 eruptive units (flows)—separated into 15 age groups ranging from more than 30,000 years B.P. to A.D. 1984—are shown, as well as the relations of volcanic and surficial sedimentary deposits. This map incorporates previously reported work published in generalized small-scale maps (Lockwood and Lipman, 1987; Buchanan-Banks, 1993; Lockwood, 1995; and Wolfe and Morris, 1996).

Hawaii↗

USGS1975

Reconnaissance engineering geology of the Ketchikan area, Alaska, with emphasis on evaluation of earthquake and other geologic hazards

The Alaska earthquake of March 27, 1964, dramatically emphasized the need for engineering geologic studies of urban areas in seismically active regions. A reconnaissance study of the Ketchikan area in southeastern Alaska is part of a program to evaluate earthquake and other geologic hazards in most of the larger Alaska coastal communities. These evaluations in the Ketchikan area should provide broad guidelines useful in city and land-use planning. Ketchikan, which had a population of approximately 7,000 in 1970, is built on the southwestern end of Revillagigedo Island along the northeastern coastline of Tongass Narrows. Altitudes reach 1,000 feet (305 m) within half a mile (0.8 km) of the coast and near-vertical cliffs characterize the terrain in places. The climate is predominantly marine. Average precipitation is approximately 152 inches (386 cm). The Ketchikan area was covered by glacier ice at least once and probably several times during the Pleistocene Epoch. The present topography, characterized by elongate lakes, U-shaped valleys, fiords, inlets, and passages, clearly reflects the effects of glaciation. The presence of emergent marine deposits, at least 300 feet (91 m) above sea level, shows that the land has been uplifted relative to sea level since the last deglaciation of the region. Bedrock is exposed or is near the surface throughout most of the mapped area. The bedrock consists chiefly of metamorphic rocks. In a few places these rocks have been intruded by igneous rocks. Exposed metamorphic rocks are mostly thinly foliated schists and phyllites, metamorphosed to greenschist facies. Foliation generally strikes northwest with moderate to steep dips to the northeast. Most of the rock is fairly competent and near-vertical cuts tend to be stable. The more indurated metamorphic rock can be used for riprap, but more durable blocks generally can be obtained from the igneous rock. The surficial deposits have been divided into the following map units on the basis of their time of deposition, mode of origin, and grain size: (1) undifferentiated drift (Qd), (2) elevated marine deposits (Qm), (3) stream alluvium (Qa), (4) fan-delta deposits (Qf), and (5) modern beach deposits (Qb). Manmade fill (f) also is mapped as a separate unit. Muskeg, colluvium, and offshore deposits are not included as map units but are discussed in the report under the heading "Surficial deposits (not shown on map)." The undifferentiated drift deposits consist mostly of till or other diamictons, generally less than 25 feet (7.6 m) thick. Exposed elevated marine deposits (Qm) generally consist of sand and gravel less than 5 feet (1.5 m) thick. Stream alluvium (Qa) is chiefly sand, gravel, cobbles, and boulders probably everywhere less than 15 feet (4.6 m) thick. Fan-delta deposits (Qf) consist mostly of loose sand, gravel, and boulders as much as 50 feet (15 m) thick. Modern beach deposits (Qb) are mostly loose sand and gravel generally less than 10 feet (3 m) thick. Two basically different types of manmade fill are present: (1) large fills along the waterfront, commonly 5 to 15 feet (1.5-4.6 m) thick, consisting of silt, sand, gravel, rock, and diverse other materials, and (2) fills, generally less than 10 feet (3 m) thick and consisting of sand, gravel, or crushed rock, placed inland from the waterfront and used as pads for buildings and parking areas. Fairly thick deposits of muskeg may be present in the southeastern part of the mapped area but have not been examined in the field. Colluvial deposits, locally 5 to 8 feet (1.5-2.4 m) thick, consist mostly of decomposing bedrock fragments. Offshore deposits are poorly known; near-shore loose sand and gravel rest on a sloping bedrock surface. Southeastern Alaska lies within the circum-Pacific seismic belt that rims the northern Pacific Basin and has been tectonically active since at least early Paleozoic time. Large-scale faulting has been common. The two most prominent fault systems in southeastern Alaska and surrounding regions are (1) the Denali fault system, and (2) the Fairweather-Queen Charlotte Islands fault system. Of the two, the Fairweather-Queen Charlotte Islands fault system is the more active and of most significance in relation to the Ketchikan area. Ketchikan lies within the northwest trend of the Gravina-Nutzotin belt of fault thrusting. The trends of at least some of the linear fiords near the mapped area are controlled by faults. However, it is not known whether a major fault extends up Tongass Narrows offshore from Ketchikan. Between 1899 and 1970, five earthquakes having magnitudes of 8 or greater occurred in or near southeastern Alaska or in adjacent offshore areas; three have occurred having magnitudes of between 7 and 8, at least eight with magnitudes of between 6 and 7, 15 with magnitudes of between 5 and 6, and about 140 have been recorded with magnitudes of less than 5 or of unassigned magnitudes. All of the earthquakes with magnitudes greater than 8, and a large proportion of the others, appear to be related to the Fair-weather-Queen Charlotte Islands fault system or to the connecting Chugach-St. Elias fault to the northwest. Within a 50-mile (80-km) radius of Ketchikan, epicenters of three earthquakes with magnitudes of 5 or less have been recorded. Within a radius of 100 miles (160 km), 10 epicenters have been recorded, two with magnitudes between 6 and 7 and eight with magnitudes of 5 or less. Although no instrumentally recorded earthquakes had epicenters in the mapped area, at least 32 earthquakes that had epicenters elsewhere were felt or possibly felt in Ketchikan. Most of these earthquakes probably had epicenters along the Queen Charlotte Islands fault. Ketchikan is tentatively assigned by me to seismic zone 2. This is a zone in which magnitudes of the largest expectable earthquake would range from 4.5 to 6.0 and where moderate damage could be expected. Large earthquakes of magnitude 8 or greater, however, can be expected to occur from time to time along the Queen Charlotte Islands fault. Ground motion from these earthquakes, although attenuated with distance, may still be sufficiently strong at Ketchikan to cause substantial damage. Possible future earthquake effects include: (1) land-level changes caused by local faulting or by large-scale regional deformation, (2) ground shaking, (3) compaction, (4) liquefaction, (5) subaerial and submarine sliding, (6) water-sediment ejection and ground fracturing, (7) reaction of sensitive and quick clays, and (8) effects of tsunamis, seiches, and other abnormal water waves. Although land-level changes due to local faulting are unlikely, large-scale regional deformation may cause uplift or subsidence in Ketchikan. Adverse effects would be confined mainly to the waterfront area. This area also would be most heavily damaged if Ketchikan were strongly shaken by an earthquake. Nonengineered, loose, manmade fills and fan-delta deposits in this area probably would be subject to the strongest shaking. These deposits probably also are most subject to compaction, liquefaction, sliding, and water-sediment ejection. Earthquake effects expectably would be considerably fewer and less severe for the part of Ketchikan upslope from the harbor area because bedrock is at or near the surface in large parts of the area. No sensitive clays have been identified but, if present, they probably are confined to the till and other diamicton deposits in the northeastern part of the mapped area. Tsunami waves are not expected to have a local generation source. Those arriving from a distant source, although potentially highly destructive, probably would be greatly attenuated before arriving at Ketchikan. Seiche waves may develop on lakes near the mapped area and possibly cause failure of earth-fill dams. Destructive waves generated by earthquake-induced local submarine sliding appear to be unlikely in the Ketchikan area. Geologic hazards in the area that are not caused by earthquakes are believed to be relatively minor. They include: (1) landsliding and subaqueous sliding, and (2) flooding. Only minor landsliding has occurred in the mapped area, but the potential for sliding may increase as the city expands and heavily timbered areas are cleared, with attendant accelerated erosion and mass wasting. The greatest potential for subaqueous sliding is along the shoreline, where fairly thick fan-delta deposits rest on a sloping bedrock surface. Periodic flooding has occurred on some creeks in the mapped area and can be expected to occur from time to time in the future. In order that more accurate evaluations of geologic hazards can be made in the future, several recommendations are made for additional studies.

Alaska↗

USGS1992

Net Late Holocene emergence despite earthquake-induced submergence, south-central Chile

Intertidal deposits show net Late Holocene emergence at three sites along the Pacific coast near Maulli??n and Carelmapu, Chile (latitude 41.6-41.7??S.). The maximum amount of net emergence is ca. 1 m in the past 1500 years and ca. 2 1 2 m in the past 4000 years. Emergence probably would have prevailed at a fourth site near Maulli??n were the site not underlain by easily compacted deposits; this site shows slight (< 1 m) net submergence in the past 3000 years. Despite net emergence, all four sites underwent 1-2 m of submergence from tectonic subsidence during a magnitude-9.5 earthquake in 1960, and two of the sites show evidence for earlier submergence events of Late Holocene age. The net emergence is probably due to some combination of cyclic uplift from elastic strain accumulation between earthquakes and monotonic uplift from postglacial loading of the Pacific Ocean floor. The small amount of the net emergence shows that neotectonics has had little net impact on Holocene relative sea level in part of the focal region of the largest earthquake recorded by seismograph. ?? 1992.

Quaternary International↗

USGS2012

Origin of an unusual monazite-xenotime gneiss, Hudson Highlands, New York: SHRIMP U-Pb geochronology and trace element geochemistry

A pod of monazite-xenotime gneiss (MXG) occurs within Mesoproterozoic paragneiss, Hudson Highlands, New York. This outcrop also contains granite of the Crystal Lake pluton, which migmatized the paragneiss. Previously, monazite, xenotime, and zircon from MXG, plus detrital zircon from the paragneiss, and igneous zircon from the granite, were dated using multi-grain thermal ionization mass spectrometry (TIMS). New SEM imagery of dated samples reveals that all minerals contain cores and rims. Thus TIMS analyses comprise mixtures of age components and are geologically meaningless. New spot analyses by sensitive high resolution ion microprobe (SHRIMP) of small homogeneous areas on individual grains allows deconvolution of ages within complexly zoned grains. Xenotime cores from MXG formed during two episodes (1034 ± 10 and 1014 ± 3 Ma), whereas three episodes of rim formation are recorded (999 ± 7, 961 ± 11, and 874 ± 11 Ma). Monazite cores from MXG mostly formed at 1004 ± 4 Ma; rims formed at 994 ± 4, 913 ± 7, and 890 ± 7 Ma. Zircon from MXG is composed of oscillatory-zoned detrital cores (2000-1170 Ma), plus metamorphic rims (1008 ± 7, 985 ± 5, and ∼950 Ma). In addition, MXG contains an unusual zircon population composed of irregularly-zoned elongate cores dated at 1036 ± 5 Ma, considered to be the time of formation of MXG. The time of granite emplacement is dated by oscillatory-zoned igneous cores at 1058 ± 4 Ma, which provides a minimum age constraint for the time of deposition of the paragneiss. Selected trace elements, including all REE plus U and Th, provide geochemical evidence for the origin of MXG. MREE-enriched xenotime from MXG are dissimilar from typical HREE-enriched patterns of igneous xenotime. The presence of large negative Eu anomalies and high U and Th in monazite and xenotime are uncharacteristic of typical ore-forming hydrothermal processes. We conclude that MXG is the result of unusual metasomatic processes during high grade metamorphism that was initiated at about 1035 Ma. This rock was then subjected to repeated episodes of dissolution/reprecipitation for about 150 m.y. during regional cooling of the Hudson Highlands.

New York↗

USGS2010

Landslide inventory for the Little North Santiam River Basin, Oregon

This geodatabase is an inventory of existing landslides in the Little North Santiam River Basin, Oregon (2009). Each landslide feature shown has been classified according to a number of specific characteristics identified at the time recorded in the GIS database. The classification scheme was developed by the Oregon Department of Geology and Mineral Industries (Burns and Madin, 2009). Several significant landslide characteristics recorded in the database are portrayed with symbology on this map. The specific characteristics shown for each landslide are the activity of landsliding, landslide features, deep or shallow failure, type of landslide movement, and confidence of landslide interpretation. These landslide characteristics are determined primarily on the basis of geomorphic features, or landforms, observed for each landslide. This work was completed as part of the Master's thesis "Turbidity Monitoring and LiDAR Imagery Indicate Landslides are Primary Source of Suspended-Sediment Load in the Little North Santiam River Basin, Oregon, Winter 2009-2010" by Steven Sobieszczyk, Portland State University and U.S. Geological Survey. Data layers in this geodatabase include: landslide deposit boundaries (Deposits); field-verfied location imagery (Photos); head scarp or scarp flanks (Scarp_Flanks); and secondary scarp features (Scarps).The geodatabase template was developed by the Oregon Department of Geology and Mineral Industries (Burns and Madin, 2009).

Oregon↗

USGS1975

Ground-water reconnaissance in the Fresno Northeast area, Fresno County, California

The Fresno northeast area includes about 133 square miles (344 square kilometres) in the central part of California. Four physiographic units occur in the area, the largest of which is the compound alluvial fan of the intermittent streams north of the Kings River. Geologic units consist of consolidated rocks and unconsolidated deposits. The consolidated rocks yield only small quantities of fresh water to wells. The unconsolidated deposits immediately overlie the consolidated rocks and, within their upper part, yield large quantities of water to wells. The dominant structure of the unconsolidated deposits is that of a homocline. Although the deposits are inferred to be faulted, the fault does not have any demonstrated effect on the movement of ground water. Total storage capacity in the area in the upper 200 feet (61metres) is about 1,100,000 acre-feet (1,360 cubic hectometres). The total volume of ground-water underflow moving out of the area was estimated to be about 60,000 to 70,000 acre-feet per year (74 to 86 cubic hectometres per year). Two water-level contour maps indicate that changes in water use over a 12-year period have not greatly affected the direction of ground-water movement. Long-term records show that rises and declines in water level, indifferent parts of the area, often occur during the same period of time. The records also show that most of the storage changes in the reservoir have occurred in the upper 100 feet (30 metres) through a long-term water-level fluctuation of less than 40 feet (12 metres). Short-term trends show that, in general, water levels rise during winter, level off during spring, and decline from summer through autumn.

California↗

USGS2010

Remote telemetered and time-lapse cameras at Augustine Volcano: Chapter 12 in The 2006 eruption of Augustine Volcano, Alaska

Before and during the 2006 eruption of Augustine Volcano, the Alaska Volcano Observatory (AVO) installed a network of telemetered and nontelemetered cameras in Homer, Alaska, and on Augustine Island. On December 1, 2005, a network camera was installed at the Homer Field Station, a University of Alaska Fairbanks Geophysical Institute (UAF/GI) facility on a bluff near Homer, where telemetered Augustine data are received. The camera placed there provides observations of the volcano from a distance of 126 km (78 miles) in daylight hours during clear sky conditions. On January 9, 2006, a radio-telemetered network camera was installed on the lower eastern flank of the volcano at 'Mound,' 4.4 km (2.7 miles) from the summit. The proximity of this camera provided for near-field images of the volcano. A nontelemetered camera with onsite recording was installed 3.8 km (2.4 miles) north of the volcano's summit near Burr Point on December 17, 2005. This camera recorded high-resolution images at a rate of 4 images per hour through much of the eruptive sequence. A low-light camera was installed on February 8, 2006, at the Homer facility to augment the extreme low-light camera installed by the UAF/GI (Sentman and others, this volume). On September 10, 2006, a second radio-telemetered network camera was installed at Lagoon camp on the west side of Augustine Island, 5.4 km (3.3 miles) west-northwest of the summit. The installation of these camera systems proved valuable for assessing volcanic activity, determining ground hazards and on-island weather for visiting field teams, and deciphering depositional history after the eruption.

Alaska↗

USGS1989

Procedure for evaluating observation-well networks in Wyoming, and application to northeastern Wyoming, 1986

A sequence of steps was developed for evaluating and modifying the existing, long-term, observation-well network in any part of Wyoming. The State was subdivided geographically into nine groundwater areas, including the northeastern Wyoming groundwater area, based on major structural features. Northeastern Wyoming was the first of the nine areas to be evaluated using these procedures. The stratigraphic units of Wyoming were grouped into five rock units on the basis of age, similar depositional environments, and water-yielding properties. Activities likely to affect groundwater in northeastern Wyoming were evaluated. The most important monitoring needs in the area are related to: (1) Oil-field waterflooding; (2) surface mining of coal; (3) increasing municipal use of groundwater, and (4) need for general resource information. The 18 observation wells in the existing (1986) network meet most of the needs identified. Seven additional wells need to be added to the network, whereas four wells in the network can be discontinued. Water level data from the 18 observation wells are presented by county. Maps and hydrographs are accompanied by brief discussions of information related to the records obtained. (USGS)

Water-Resources Investigations Report↗

USGS1959

Ground-water resources of the lower Niobrara River and Ponca Creek basins, Nebraska and South Dakota

This report describes the area in north-central Nebraska and south-central South Dakota drained by Ponca Creek and by the Niobrara River below Valentine, Nebr. The Niobrara River and Ponca Creek are neighboring eastward flowing tributaries of the Missouri River. The Dakota sandstone of Cretaceous age is the oldest formation tapped by wells; the water it yields to wells in small to moderate quantities is rather highly mineralized and very hard; it is unsuitable for irrigation and most domestic uses. Overlying the Dakota, in ascending order, are the following formations of Cretaceous age: the Graneros shale, Greenhorn limestone, Carlile shale, Niobrara formation, and Pierre shale. None of these is a source of water supply. The Niobrara is the oldest formation exposed, cropping out in only the deeper valleys at the eastern end of the area. The Pierre shale, which is exposed much more extensively, crops out in the deeper valleys throughout nearly all the area. Except where the Niobrara River, its major tributaries, and Ponca Creek have cut their valleys into them, the Cretaceous rocks are overlain by semiconsolidated rocks of Tertiary age. Two Tertiary formations, the Brule and the Ogallala, are present in the area. The Brule formation underlies all the western part of the area and is exposed in the valleys of both the Niobrara and Keya Paha Rivers. The Ogallala formation, which overlaps the Brule, forms the upland on both sides of the river and is exposed in many places. The Brule is not a source of water supply, whereas the Ogallala yields small to moderately large quantities of water to many wells on the upland. The water in the Ogallala is of the calcium bicarbonate type and is moderately mineralized and hard. Unconsolidated deposits of Quaternary age mantle the Tertiary rocks throughout nearly all the upland area south of the Niobrara River and in parts of the upland area north of the river. They also floor the Niobrara River valley. Where saturated, these sediments, which consist of stream-deposited sand and gravel and wind-deposited sand, yield small to large amounts of water to wells. The water in the Quaternary deposits is of the calcium bicarbonate type but is less mineralized and softer than that in the Ogallala. The only significant source of recharge to the Dakota sandstone in the report area is underflow from the west. Except for waiter yielded to wells tapping the Dakota, water in the formation is discharged from the area by underflow to the east. In the upland part of the area, the Ogallala formation and the overlying deposits of Quaternary age constitute a single aquifer, water moving from one Into the other without apparent hindrance. This aquifer is recharged principally by the direct infiltration of precipitation but in part also by underflow from the west and south and by seepage from intermittent streams and ponds. Water is discharged from the upland aquifer by outflow through springs or seepage into streams, through the process of evapotranspiration, and by wells when they are pumped. Ground water leaves the report area by underflow where the Quaternary deposits in the valleys of the Niobrara River and Ponca Creek merge with the Quaternary deposits in the Missouri River valley. In places where the Niobrara formation, the Pierre shale, or the Brule formation is at the surface or is mantled by thin deposits of the Ogallala or thin deposits of Quaternary age, only meager amounts of ground water can be obtained unless wells are deep enough to tap the Dakota sandstone. Elsewhere the Ogallala formation and the deposits of Quaternary age generally yield ample water for domestic and stock supplies, and in some places, notably in the vicinity of Ainsworth, they yield enough water for irrigation. Additional large supplies of ground water could be obtained on the upland in the southwestern and west-central parts of the area. The report contains an annotated bibliography of previous publications on the geology and ground-water resources of the area, brief descriptions of the Cretaceous, Tertiary, and Quaternary rocks, a map showing the contour of the water table, logs of test holes and wells not published elsewhere, results of analyses of ground- and surface-water samples, and records of all wells of large discharge and representative wells of small discharge.

Nebraska, North Dakota↗

USGS2016

Geologic history of Martian regolith breccia Northwest Africa 7034: Evidence for hydrothermal activity and lithologic diversity in the Martian crust

The timing and mode of deposition for Martian regolith breccia Northwest Africa (NWA) 7034 were determined by combining petrography, shape analysis, and thermochronology. NWA 7034 is composed of igneous, impact, and brecciated clasts within a thermally annealed submicron matrix of pulverized crustal rocks and devitrified impact/volcanic glass. The brecciated clasts are likely lithified portions of Martian regolith with some evidence of past hydrothermal activity. Represented lithologies are primarily ancient crustal materials with crystallization ages as old as 4.4 Ga. One ancient zircon was hosted by an alkali-rich basalt clast, confirming that alkalic volcanism occurred on Mars very early. NWA 7034 is composed of fragmented particles that do not exhibit evidence of having undergone bed load transport by wind or water. The clast size distribution is similar to terrestrial pyroclastic deposits. We infer that the clasts were deposited by atmospheric rainout subsequent to a pyroclastic eruption(s) and/or impact event(s), although the ancient ages of igneous components favor mobilization by impact(s). Despite ancient components, the breccia has undergone a single pervasive thermal event at 500–800°C, evident by groundmass texture and concordance of ~1.5 Ga dates for bulk rock K-Ar, U-Pb in apatite, and U-Pb in metamict zircons. The 1.5 Ga age is likely a thermal event that coincides with rainout/breccia lithification. We infer that the episodic process of regolith lithification dominated sedimentary processes during the Amazonian Epoch. The absence of pre-Amazonian high-temperature metamorphic events recorded in ancient zircons indicates source domains of static southern highland crust punctuated by episodic impact modification.

Journal of Geophysical Research E: Planets↗

USGS2026

Differentiating persistent and intermittent euxinia from the molecular derivatives of green sulfur bacteria carotenoids

Green sulfur bacteria biomarkers that indicate euxinia within the photic zone sometimes co-occur with evidence of contradictory depositional redox conditions, such as oxygen-requiring fossils or bioturbation. Intermittent euxinia may explain this apparent contradiction, and recent studies of modern environments show that green sulfur bacteria dwell in transiently euxinic settings. As a result, new approaches are needed to distinguish green sulfur bacteria biomarkers indicative of persistent versus intermittent euxina in ancient sedimentary samples, which this study addresses by investigating how the distribution of isorenieratene derivatives relates to depositional redox conditions. To accomplish this objective, this study focuses on two drill cores through the Upper Cretaceous Mowry Shale and the Eagle Ford Group. These drill cores are comparably thermally immature according to vitrinite reflectance data, and these formations in these cores capture a spectrum of depositional redox conditions according to multiple organic and inorganic proxies, including newly acquired iron speciation and kerogen organic sulfur data. The results presented here reveal that higher molecular weight diagenetic products of isorenieratene are preferentially preserved under persistent euxinia compared to intermittently euxinic intervals that contain isorenieratene derivatives that are shifted to lower molecular weights. Further, the total inventory of aromatic carotenoid diagenetic products contains features that can be used to identify green sulfur bacteria biomarkers from reworked petrogenic sources. Accordingly, the diagenetic fate of isorenieratene and the distribution of its diagenetic products distinguish persistent versus intermittent euxinia, which can be used to sharpen our evaluation of euxinia in the geologic record.

Geochemica et Cosmochimica Acta↗

USGS2017

The 2014 eruptions of Pavlof Volcano, Alaska

Pavlof Volcano is one of the most frequently active volcanoes in the Aleutian Island arc, having erupted more than 40 times since observations were first recorded in the early 1800s . The volcano is located on the Alaska Peninsula (lat 55.4173° N, long 161.8937° W), near Izembek National Wildlife Refuge. The towns and villages closest to the volcano are Cold Bay, Nelson Lagoon, Sand Point, and King Cove, which are all within 90 kilometers (km) of the volcano (fig. 1). Pavlof is a symmetrically shaped stratocone that is 2,518 meters (m) high, and has about 2,300 m of relief. The volcano supports a cover of glacial ice and perennial snow roughly 2 to 4 cubic kilometers (km 3 ) in volume, which is mantled by variable amounts of tephra fall, rockfall debris, and pyroclastic-flow deposits produced during historical eruptions. Typical Pavlof eruptions are characterized by moderate amounts of ash emission, lava fountaining, spatter-fed lava flows, explosions, and the accumulation of unstable mounds of spatter on the upper flanks of the volcano. The accumulation and subsequent collapse of spatter piles on the upper flanks of the volcano creates hot granular avalanches, which erode and melt snow and ice, and thereby generate watery debris-flow and hyperconcentrated-flow lahars. Seismic instruments were first installed on Pavlof Volcano in the early 1970s, and since then eruptive episodes have been better characterized and specific processes have been documented with greater certainty. The application of remote sensing techniques, including the use of infrasound data, has also aided the study of more recent eruptions. Although Pavlof Volcano is located in a remote part of Alaska, it is visible from Cold Bay, Sand Point, and Nelson Lagoon, making distal observations of eruptive activity possible, weather permitting. A busy air-travel corridor that is utilized by a numerous transcontinental and regional air carriers passes near Pavlof Volcano. The frequency of air travel across the region results in a relatively large number of airborne observations of eruptive activity. During the 2014 Pavlof eruptions, the Alaska Volcano Observatory received observations and photographs from pilots and local observers, which aided evaluation of the eruptive activity and the areas affected by eruptive products. This report outlines the chronology of events associated with the 2014 eruptive activity at Pavlof Volcano, provides documentation of the style and character of the eruptive episodes, and reports briefly on the eruptive products and impacts. The principal observations are described and portrayed on maps and photographs, and the 2014 eruptive activity is compared to historical eruptions.

Alaska↗

USGS2019

Insights into the mechanisms of phreatic eruptions from continuous high frequency volcanic gas monitoring: Rincón de la Vieja volcano, Costa Rica

Understanding the trigger mechanisms of phreatic eruptions is key to mitigating the effects of these hazardous but poorly forecastable volcanic events. It has recently been established that high-rate volcanic gas observations are potentially very suitable to identifying the source processes driving phreatic eruptions, and to eventually detecting precursory changes prior to individual phreatic blasts. In February-May 2017, we deployed a Multi-GAS instrument to continuously monitor gas concentrations in the crater lake plume of Rincón de la Vieja, a remote and poorly monitored active volcano in Costa Rica, site of frequent phreatic/phreatomagmatic eruptions. Forty-two phreatic/phreatomagmatic eruptions were seismically recorded during our investigated period, 9 of which were also recorded for gas by the Multi-GAS. To the best of our knowledge, these represent the first instrumentally measured gas compositions during individual phreatic/phreatomagmatic explosions at an active volcano. Our results show that during background quiescent degassing the Rincón de la Vieja crater lake plume was characterized by high CO 2 /SO 2 ratios of 64 ± 59 and H 2 S/SO 2 ratios of 0.57 ± 0.20. This composition is interpreted as reflecting hydrothermal (re)processing of magma-sourced gas in the sub-limnic environment. Phreatic blasts were recorded by the Multi-GAS as brief (1–2 min long) pulses of elevated gas mixing ratios (up to ~52 ppmv SO 2 and >3,000 ppmv CO 2 ), or more than an order of magnitude higher than during background degassing (~1 ppmv SO 2 and ~450 ppmv CO 2 ). During the phreatic eruption(s), the H 2 S/SO 2 ratio was systematically lower (<0.18) than during background degassing, but the CO 2 /SO 2 ratio remained high (and variable), ranging from 37 to 390. These S-poor compositions for the eruptive gas imply extensive processing of the source magmatic gas during pre-eruptive hydrothermal storage, likely by deposition of native S and/or sulfate. Our gas results are thus overall consistent with a mechanism of phreatic eruptions triggered by accumulation of magmatic-hydrothermal gases beneath a hydrothermal seal. We claim that real-time Multi-GAS monitoring is urgently needed at other crater lake-hosting volcanoes (e.g., Ruapehu, Aso), where phreatic eruptions may similarly be preceded by phases of reduced S degassing at the surface.

Rincón de la Vieja Volcano↗

USGS2018

Chapter 7: Structural configuration of the Central African Copperbelt: Roles of evaporites in structural evolution, basin hydrology, and ore location

The Central African Copperbelt is the world’s premier sediment-hosted Cu province. It is contained in the Katangan basin, an intracratonic rift that records onset of growth at ~840 Ma and inversion at ~535 Ma. In the Copperbelt region, the basin has a crudely symmetrical form, with a central depocenter maximum containing ~11 km of strata positioned on the northern side of the border of the Democratic Republic of Congo and Zambia, and marginal condensed sequences <2 km in thickness. This fundamental extensional geometry was preserved through orogenesis, although complex configurations related to halokinesis are prevalent in central and northern parts of the basin, whereas to the south, relatively high-grade metamorphism occurred as a result of basement-involved thrusting and burial. The largest Cu ± Co ores, both stratiform and vein-controlled, are known from the periphery of the basin and transition to U-Ni-Co and Pb-Zn-Cu ores toward the depocenter maximum. Most ore types are positioned within a ~500-m halo to former near-basin-wide salt sheets or associated halokinetic structures, the exception being that located in extreme basin marginal positions, where primary salt was not deposited. Stratiform Cu ± Co ores occur at intrasalt (Congolese-type), subsalt (Zambian-type), and salt-marginal (Kamoa-type) positions. Bulk crush-leach fluid inclusion data from the first two of these deposit types reveal a principal association with residual evaporitic brines. A likely signature of the ore fluids, the brines were generated during deposition of the basin-wide salt-sheets and occupied voluminous sub and intrasalt aquifers from ~800 Ma. Associated intense Mg ± K metasomatism was restricted to these levels, indicating that capping and enclosing salt remained impermeable for prolonged periods of the basin’s history, isolating the deep-seated aquifers from the upper part of the basin fill. From ~765 to 740 Ma, the salt sheets in the Congolese part of the basin were halokinetically modified. Salt was withdrawn laterally to feed diapirs, ultimately leading to localized welding or breaching of the former hydrological seal. At these points, deeper-level residual brines were drawn into the intrasalt stratigraphy to interact with reducing elements and form the stratiform ores. It is probable that salt welding occurred diachronously across the northern and central parts of the basin, depending upon the interplay of original salt thickness, rates and volumes of sediment supply during accumulation of salt overburden, and tectonism. The variable timing of this fundamental change in hydrologic architecture is poorly constrained to the period of halokinetic onset to the earliest stages of orogenesis; however, the geometry of the ores and associated alteration patterns demands that mineralization preceded the characteristically complex fragmentation of the host strata. Thus, while an early orogenic timing is permissible, mineralization during the later stages of extensional basin development was more likely. In situ reducing elements that host Zambian-type stratiform Cu ± Co ores were in continuous hydrological communication with subsalt aquifers, such that ore formation could have commenced from the ~800 Ma brine introduction event. The nonhalokinetic character of the salt in this region allowed the intact seal to have maintained suprahydrostatic pore pressures, facilitating fluid circulation until late stages of basin growth and possibly early stage orogenesis. Leachate data from ores positioned in the depocenter maximum and southern parts of the basin that underwent relatively high grade metamorphism record mixing of residual and halite dissolution-related brines. Salt dissolution was likely triggered by emergence of diapirs or thermally and/or mechanically induced increased permeability of halite. While it is certain that halite dissolution occurred during and after orogenesis, conditions favorable for salt dissolution may have existed locally during extension in the depocenter maximum. The permeability of salt increased to a point where it became the principal aquifer. The salt’s properties as an aquiclude lost, originally deep-seated residual brine mixed with new phases of evaporite dissolution-related brine to produce ores at middle levels of the basin fill. During the final stages of ore formation, recorded by postorogenic Pb-Zn-Cu mineralization in the depocenter maximum, the salinity of fluids was dominantly derived from the dissolution of remnant bodies of salt.

Central African Copperbelt↗

USGS1993

Stable isotope study of fluid inclusions in fluorite from Idaho: Implications for continental climates during the Eocene

Isotopic studies of fluid inclusions from meteoric water-dominated epithermal ore deposits offer a unique opportunity to study paleoclimates because the fluids can provide direct samples of ancient waters. The oxygen and hydrogen isotope compositions of meteoric waters vary because of changes in climatic variables such as mean annual temperature of precipitation, relative humidity, origin and history of air masses, and the isotope composition of the oceans. Inclusion fluids found in fluorite (CaF 2 ) are especially useful because their host is devoid of oxygen or hydrogen, thus precluding postentrapment isotope exchange. Fluorite-hosted fluid inclusions from the Eocene (51-50 Ma) epithermal deposits of the Bayhorse mining district, northeastern Idaho, have low salinities, most less than 0.6 equivalent wt% NaCl, and low to moderate homogenization temperatures (98 to 146 °C), indicating meteoric origins for the fluids. Oxygen and hydrogen isotope data on inclusion fluids are almost identical to those of modern meteoric waters in the area. The equivalence of the isotope composition of the Eocene inclusion fluids and modern meteoric waters indicates that the Eocene climatic conditions were similar to those today. This conclusion supports the climate modeling of Sloan and Barron, who suggested that the climates of continental interiors do not reflect the magnitude of warming preserved by the deep-ocean paleoclimate record during the Eocene.

Geology↗

USGS2011

The Edwardsburg Formation and related rocks, Windermere Supergroup, central Idaho, USA

In central Idaho, Neoproterozoic stratified rocks are engulfed by the Late Cretaceous Idaho batholith and by Eocene volcanic and plutonic rocks of the Challis event. Studied sections in the Gospel Peaks and Big Creek areas of west-central Idaho are in roof pendants of the Idaho batholith. A drill core section studied from near Challis, east-central Idaho, lies beneath the Challis Volcanic Group and is not exposed at the surface. Metamorphic and deformational overprinting, as well as widespread dismembering by the younger igneous rocks, conceals many primary details. Despite this, these rocks provide important links for regional correlations and have produced critical geochronological data for two Neoproterozoic glacial periods in the North American Cordillera. At the base of the section, the more than 700-m-thick Edwardsburg Formation (Fm.) contains interlayered diamictite and volcanic rocks. There are two diamictite-bearing members in the Edwardsburg Fm. that are closely related in time. Each of the diamictites is associated with intermediate composition tuff or flow rocks and the diamictites are separated by mafic volcanic rocks. SHRIMP U–Pb dating indicates that the lower diamictite is about 685±7 Ma, whereas the upper diamictite is 684±4 Ma. The diamictite units are part of a cycle of rocks from coarse clastic, to fine clastic, to carbonate rocks that, by correlation to better preserved sections, are thought to record an older Cryogenian glacial to interglacial period in the northern US Cordillera. The more than 75-m-thick diamictite of Daugherty Gulch is dated at 664±6 Ma. This unit is preserved only in drill core and the palaeoenvironmental interpretation and local stratigraphic relations are non-unique. Thus, the date for this diamictite may provide a date for a newly recognized glaciogenic horizon or may be a minimum age for the diamictite in the Edwardsburg Fm. The c. 1000-m-thick Moores Lake Fm. is an amphibolite facies diamictite in which glacial features have not been observed. However, it is part of a sedimentary cycle from unsorted siliclastic deposits to mud and carbonate deposits. Using lithostratigraphy and available geochronology, the Moores Lake Fm. is correlated with a younger succession of Cryogenian glaciogenic rocks in southeastern Idaho. Traditional correlations of Neoproterozoic rocks in the Cordillera recognize two levels of Cryogenian diamictites. The Edwardsburg and Moores Lake diamictites along the middle Cordillera fit well into the scenario of two glacial events. Because of the correlations, dates that provide ages for the diamictites in central Idaho (and corroborated in southeastern Idaho, Link & Fanning 2008) could constrain the age of correlated glaciogenic deposits elsewhere in the Cordillera. However, in the absence of dates for the glaciogenic diamictites in Canadian and southern US Cordilleran sections, the correlations are considered possible but uncertain.

Idaho↗