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At least 487 records · Page 27Linked to original sources
USGS1970

Seismic-reflection records from a survey at the Rocky Mountain Arsenal near Denver, Colorado

During July 1966, after competitive bidding, a contract was awarded by the U.S. Geological Survey to GeoData Corporation and Geo Prospectors, Inc., both of Tulsa, Oklahoma, for 18 miles of continuous seismic-reflection profiling in the vicinity of a deep injection disposal well (IDW) at the Rocky Mountain Arsenal near Denver, Colorado. The purpose of this survey was to determine if structure exists in the 12,000-ft sedimentary section or in the Precambrian basement that might be related to the series of earthquakes that occurred in the area starting in the spring of 1962. A paper on the seismic-reflection profiling by Ben R. Rummerfield, A. Peter Olson, and D. B. Hoover (1968) reported the major conclusions of the survey.

Colorado↗
USGS1998

Compilation of 29 sonic and density logs from 23 oil test wells in western Washington State

Three-dimensional velocity models for Puget Sound provide a means for better understanding the lateral variations in strong ground motions recorded during local earthquakes in Puget Lowland. We have compiled 29 sonic and density logs from 23 oil test wells to help us determine the geometry and physical properties of the Cenozoic basins in western Washington. The maximum depths sampled by the test wells are between 0.47 and 4.04 km. These well logs sample Quaternary to Eocene sedimentary and volcanic rocks. This report presents the locations, elevations, depths, stratigraphic and other information about the test wells, and provides plots showing the density and sonic velocities as a function of depth for each well log. We also present two-way travel times calculated from the sonic velocities.

Washington↗
USGS1987

Sedimentary processes on the northwestern Iberian continental margin viewed by long-range side-scan sonar and seismic data

The effects of an eastern boundary current in the North Atlantic have been mapped from about 39° north latitude along the Iberian margin to as far north as 43°30 north latitude at the western margin of Galicia Bank. The geostrophic current has produced sediment drifts that are covered with bedforms. The sediment drifts are difficult to detect on Gloria long-range side-scan sonar data but are easily resolved on seismic-reflection records as anomalously thick accumulations of sediment banked against either buried or outcropping basement highs. The bedforms ornamenting the drift surfaces were subdivided into 1,000-m water-depth intervals, and their dimensions were tabulated. There are few bedforms in water depths less han 2,000 m, but from depths between 2,000 and 4,000 m they are numerous and have a mean wavelength of 695 m. Bedforms from depths greater than 4,000 m have a mean wavelength of 999 m. The different wavelengths from different water depths suggest two distinct and separated boundary flows. The wave heights of all bedforms found in water depths greater than 2,000 m are less than 10 m. In order to investigate the continuity of sediment drifting through geological time, the stratigraphic section drilled at DSDP Site 398 was reinterpreted and, using seismic-reflection profiles, was traced throughout the northern Iberian margin. Together, the lithostratigraphic and seismic data indicate that sediment drifting developed along this margin in the Eocene. The lithofacies of the Eocene section is t e oldest to have numerous layers of sand and silt. An unconformity separates the Eocene section from the latest Miocene-Pliocene section. The unconformity is interpreted to be the result of the initial pulses of Mediterranean outflow that followed the Messinian desiccation events. A second period of sediment drifting commenced during the Pliocene once the Mediterranean basin filled and the flow out of the Strait of Gibraltar resumed.

Journal of Sedimentary Petrology↗
USGS1992

Lithology, stratigraphy, and paleoenvironments of the Mobil 312-1 well, Georges Bank Basin, US North Atlantic outer continental shelf

The Mobil 312-1 hydrocarbon exploratory well, southeastern Georges Bank Basin penetrated a section entirely composed of sedimentary rocks that range from Middle to Pliocene age. Carbonates are the dominant lithologies in the intervals at 6096-3444 m, 2560-2096 m and 1067-887 m; siliciclastics make up most of the remaining section. Although inferred paleoenvironments range primarily from supratidal to outer neritic, thin lignitic coal beds at 2204-2195 m and 1929-1920 m record brief periods of nonmarine sedimentation. Middle and Upper Jurassic calcarenites, the drilling targets of the well, have little or no visible porosity and underwent at least three episodes of cementation.

Northeastern Geology↗
USGS1981

Seismic stratigraphic characteristics of upper Louisiana continental slope: an area east of Green Canyon

A high-resolution seismic reflection survey was conducted in a small area of the upper Louisiana Continental Slope known as Green Canyon Area. This area includes tracts 427, 428, 471, 472, 515, and 516, that will be offered for sale in March 1982 as part of Lease Sale 67. The sea floor of this region is, slightly hummocky and is underlain by salt diapirs that are mantled by early Tertiary shale. Most of the shale is overlain by younger Tertiary and Quaternary deposits, although locally some of the shale protrudes the sea floor. Because of proximity to older Mississippi River sources, the sediments are thick. The sediment cover shows an abundance of geologic phenomena such as horsts, grabens, growth faults, normal faults, and consolidation faults, zones with distinct and indistinct parallel reflections, semi-transparent zones, distorted zones, and angular unconformities. The major feature of this region is a N-S linear zone of uplifted and intruded sedimentary deposits formed due to diapiric intrusion. Small scale graben development over the crest of the structure can be attributed to extension and collapse. Large scale undulations of reflections well off the flanks of the uplifted structure suggest sediment creep and slumping. Dipping of parallel reflections show block faulting and tilting. Air gun (5 and 40 cubic inch) records reveal at least five major sequences that show masked onlap and slumping in their lower parts grading into more distinct parallel reflections in their upper parts. Such sequences can be related to local uplift and sea level changes. Minisparker records of this area show similar sequences but on a smaller scale. The distinct parallel reflections often onlap the diapir flanks. The highly reflective parts of these sequences may represent turbidite-type deposition, possibly at times of lower sea level. The acoustically more transparent parts of each sequence may represent deposits containing primarily hemipelagic and pelagic sediment. A complex ridge system is present along the west side of the area and distinct parallel reflections onlap onto this structure primarily from the east. Much of this deposition may be ascribed to sedimentation within a submarine canyon whose position is controlled by this ridge.

Louisiana Continental Slope↗
USGS1982

Uranium and thorium enrichment in rocks from the base of DSDP Hole 465A, Hess Rise, central North Pacific

Uranium and thorium are concentrated in Cretaceous limestone, chert, ash, basalt, and other rock types at Deep Sea Drilling Project Site 465 located on the southern Hess Rise in the central North Pacific. U concentrations, up to 194 ppm on a carbonate-free basis, are among the highest recorded for any deep-sea deposits. U was initially derived from seawater and concentrated by absorption on terrigenous (humic) organic matter in limestone in a shallow marine environment. U and Th were probably concentrated further by low-temperature hydrothermal fluids emanating from the basaltic basement. Mainly montmorillonite, an alteration product of basalt and ash, and organic matter in sedimentary rocks acted as hosts for U and Th. The unique combination of sediments rich in humic organic matter, abundant smectite in altered ash and basalt, and warm hydrothermal solutions provided the necessary conditions for migration and concentration of U and Th. To better understand the conditions limiting the migrating and concentration of U and Th, other rocks deposited during the ocean-wide Cretaceous anoxic events should be analyzed for these elements. ?? 1982.

Chemical Geology↗
USGS2007

Neogene transpressional foreland basin development on the north side of the central alaska range, usibelli group and nenana gravel, tanana basin

Neogene strata of the Tanana basin provide a long-term record of a northwardpropagating, transpressional foreland-basin system related to regional shortening of the central Alaska Range and strike-slip displacement on the Denali fault system. These strata are ???2 km thick and have been deformed and exhumed in thrust faults that form the foothills on the north side of the Alaska Range. The lower part of the sedimentary package, the Usibelli Group, consists of 800 m of mainly Miocene strata that were deposited in fluvial, lacustrine, and peat bog environments of the foredeep depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as recycled Upper Cretaceous palynomorphs, indicate that the Miocene foreland-basin system was supplied increasing amounts of sediment from lithologies currently exposed in thrust sheets located south of the basin. The upper part of the sedimentary package, the Nenana Gravel, consists of 1200 m of mainly Pliocene strata that were deposited in alluvial-fan and braidplain environments in the wedge-top depozone of the foreland-basin system. Compositional data from conglomerate and sandstone, as well as 40 Ar/ 39 Ar dating of detrital feldspars in sandstone and from granitic clasts in conglomerate, indicate that lithologies exposed in the central Alaska Range provided most of the detritus to the Pliocene foreland-basin system. 40Ar/39Ar dates from detrital feldspar grains also show that two main suites of plutons contributed sediment to the Nenana Gravel. Detrital feldspars with an average age of 56 Ma are interpreted to have been derived from the McKinley sequence of plutons located south of the Denali fault. Detrital feldspars with an average age of 34 Ma are interpreted to have been derived from plutons located north of the Denali fault. Plutons located south of the Denali fault provided detritus for the lower part of the Nenana Gravel, whereas plutons located north of the Denali fault began to contribute sediment during deposition of the upper part of the Nenana Gravel. This age distribution documented in detrital feldspars of the Nenana Gravel is interpreted as representing a progressive northward exhumation of plutons that were located south of the Pliocene Tanana basin. In contrast to previous studies, we interpret the Usibelli Group and Nenana Gravel to represent a continuum in the evolution of a transpressional foreland basin that began during Miocene time on the north side of the Alaska Range. Copyright ?? 2007 The Geological Society of America.

Special Paper of the Geological Society of America↗
USGS2022

Characteristics, relationships and precision of direct acoustic-to-seismic coupling measurements from local explosions

Acoustic energy originating from explosions, sonic booms, bolides and thunderclaps have been recorded on seismometers since the 1950s. Direct pressure loading from the passing acoustic wave has been modelled and consistently observed to produce ground deformations of the near surface that have retrograde elliptical particle motions. In the past decade, increased deployments of colocated seismometers and infrasound sensors have driven efforts to use the transfer function between direct acoustic-to-seismic coupling to infer near-surface material properties including seismic velocity structure and elastic moduli. In this study, we use a small aperture (≈600 m) array of broadband seismometers installed in different manners and depths in both granite and sedimentary overburden to understand the fundamental nature and repeatability of seismic excitation from 1 to 15 Hz using horizontally propagating acoustic waves generated by 97 local (2–10 km) explosions. In agreement with modelling, we find that the ground motions induced by acoustic-to-seismic coupling attenuate rapidly with depth. We confirm the modelled relation between acoustic and ground motion amplitudes, but show that within one acoustic wavelength, the uncertainty in the transfer coefficient between seismic and acoustic energy at a given seismic station increases linearly with separation distance between the seismic and acoustic sensor. We attribute this observation to the rapid decorrelation of the infrasonic wavefield across small spatial scales and recommend colocating seismic and infrasound sensors for use in studies seeking to invert for near-surface material properties. Additionally, contrary to acoustic-to-seismic coupling theory and prior observations, we find that seismometers emplaced in granite do not record retrograde elliptical particle motions in response to direct pressure loading. We rule out seismometer tilt effects as a likely source of this observations and suggest that existing models of acoustic-to-seismic excitation may be too simplistic for seismometers placed in high rigidity materials.

Geophysical Journal International↗
USGS1994

Evidence from xenoliths for a dynamic lower crust, eastern Mojave Desert, California

Garnet-rich xenoliths in a Tertiary dike in the eastern Mojave Desert, California, preserve information about the nature and history of the lower crust. These xenoliths record pressures of ∼ 10–12 kbar and temperatures of ∼ 750–800°C. Approximately 25% have mafic compositions and bear hornblende + plagioclase + clinopyroxene + quartz in addition to garnet. The remainder, all of which contain quartz, include quartzose, quartzofeldspathic, and aluminous (kyanite±sillimanite-bearing) varieties. Most xenoliths have identifiable protoliths—mafic from intermediate or mafic igneous rocks, quartzose from quartz-rich sedimentary rocks, aluminous from Al-rich graywackes or pelites, and quartzofeldspathic from feldspathic sediments and/or intermediate to felsic igneous rocks. However, many have unusual chemical compositions characterized by high FeO(t), FeO(t)/MgO, Al 2 O 3 , and Al 2 O 3 /CaO, which correspond to high garnet abundance. The mineralogy and major-and trace-element compositions are consistent with the interpretation that the xenoliths are the garnet-rich residues of high-pressure crustal melting, from which granitic melt was extracted. High 87 Sr/ 86 Sr and low 143 Nd/ 144 Nd, together with highly discordant zircons from a single sample with Pb/Pb ages of ∼ 1.7 Ga, demonstrate that the crustal material represented by the xenoliths is at least as old as Early Proterozoic. This supracrustal-bearing lithologic assemblage may have been emplaced in the lower crust during either Proterozoic or Mesozoic orogenesis, but Sr and Nd model ages> 4 Ga require late Phanerozoic modification of parent/daughter ratios, presumably during the anatectic event. Pressures of equilibration indicate that peak metamorphism and melting occurred before the Mojave crust had thinned to its current thickness of <30 km. The compositions of the xenoliths suggest that the lower crust here is grossly similar to estimated world-wide lower-crustal compositions in terms of silica and mafic content; however, it is considerably more peraluminous, has a lower mg -number, and is distinctive in some trace element concentrations, reflecting its strong metasedimentary and restitic heritage.

Journal of Petrology↗
USGS2006

Recognizing the Albian-Cenomanian (OAE1d) sequence boundary using plant carbon isotopes: Dakota Formation, Western Interior Basin, USA

Analysis of bulk sedimentary organic matter and charcoal from an Albian-Cenomanian fluvial-estuarine succession (Dakota Formation) at Rose Creek Pit (RCP), Nebraska, reveals a negative excursion of ???3???, in late Albian strata. Overlying Cenomanian strata have ??13C values of -24???, to -23???, that are similar to pre-excursion values. The absence of an intervening positive excursion (as exists in marine records of the Albian-Cenomanian boundary) likely results from a depositional hiatus. The corresponding positive ??13C event and proposed depositional hiatus are concordant with a regionally identified sequence boundary in the Dakota Formation (D2), as well as a major regressive phase throughout the globe at the Albian-Cenomanian boundary. Data from RCP confirm suggestions that some positive carbon-isotope excursions in the geologic record are coincident with regressive sea-level phases. We estimate using isotopic correlation that the D2 sequence boundary at RCP was on the order of 0.5 m.y. in duration. Therefore, interpretations of isotopic events and associated environmental phenomena, such as oceanic anoxic events, in the shallow-marine and terrestrial record may be influenced by stratigraphic incompleteness. Further investigation of terrestrial ??13C records may be useful in recognizing and constraining sea-level changes in the geologic record. ?? 2006 Geological Society of America.

Geology↗
USGS1983

Reconnaissance geology of the Jabal Saq Quadrangle, sheet 26/43 C, Kingdom of Saudi Arabia

The Jabal Saq quadrangle is located in the northeastern part of the Arabian Shield at the northern end of the Najd region between lat 26?00' and 26?30' N. and long 43?00' and 43?30' E. The northeastern two-thirds of the quadrangle is underlain by Paleozoic sedimentary rocks, the southwestern one-third by Proterozoic metamorphic and igneous rocks. The oldest rocks in the quadrangle are weakly metamorphosed immature sandstones that may correlate with the Murdama group. They have been intruded by several large plutons ranging in composition from mafic granodiorite to syenogranite. A densely developed fracture cleavage cuts the metamorphic rocks; otherwise, no structural features were recorded. The quadrangle has low mineral potential; no ancient mines were identified. The Dharaymeeah syenogranite forms a large pluton and bears some petrologic resemblance to alkali granites identified elsewhere in the Arabian Shield that have documented potential for containing deposits of lithophile rare metals. Analyses of wadi sediment samples collected in the quadrangle suggest that the syenogranite may also be enriched in some of these elements. The anomalously radioactive Usba monzogranite resembles highly evolved peraluminous granite plutons that elsewhere in the world are associated with deposits of tin and tungsten.

Open-File Report↗
USGS2020

Major hydrostratigraphic contacts of the Truxton basin and Hualapai Plateau, northwestern Arizona, developed from airborne electromagnetic data

The area surrounding the Grand Canyon has spectacular outcrop exposure in the modern canyon walls, leading to stratigraphic contact delineations that are well constrained near canyons yet poorly constrained where the terrain remains undissected and relatively unexplored by boreholes. An airborne electromagnetic and magnetic survey of the western Hualapai Indian Reservation and surrounding areas was undertaken to support the development of a three-dimensional hydrostratigraphic framework of the Truxton basin and Hualapai Plateau. These data were used to develop models of the resistivity structure with total depths of investigation ranging from 200 meters in the most conductive parts of the Truxton basin to more than 600 meters in the higher resistivity areas underlying the Hualapai Plateau. The modeled resistivity structure was used in conjunction with geologic maps, well lithologic records, and results from gravity models of the depth to bedrock to develop high-resolution regional interpretations of the elevation of the Muav Limestone-Bright Angel Shale contact and the top of the crystalline basement. These contacts are conceptualized to serve as the base of the Paleozoic limestone aquifers primarily underlying the Hualapai Plateau and the Tertiary-Quaternary sedimentary and volcanic aquifers of the Truxton basin, respectively.

Arizona↗
USGS2023

Insights into the metamorphic history and origin of flake graphite mineralization at the Graphite Creek graphite deposit, Seward Peninsula, Alaska, USA

Graphite Creek is an unusual flake graphite deposit located on the Seward Peninsula, Alaska, USA. We present field observations, uranium-lead (U–Pb) monazite and titanite geochronology, carbon (C) and sulfur (S) stable isotope geochemistry, and graphite Raman spectroscopy data from this deposit that support a new model of flake graphite ore genesis in high-grade metamorphic environments. The Graphite Creek deposit is within the second sillimanite metamorphic zone of the Kigluaik Mountains gneiss dome. Flake graphite, hosted in sillimanite-gneiss and quartz-biotite paragneiss, occurs as disseminations and in sets of very high grade (up to 50 wt.% graphite), semi-massive to massive graphite lenses 0.2 to 1 m wide containing quartz, sillimanite, inclusions of garnet porphyroblasts, K-feldspar, and tourmaline. Restitic garnet, sillimanite, graphite, and biotite accumulations indicate a high degree of anatexis and melt loss. Strong yttrium depletion in monazite, high europium ratios (Eu/Eu*), and excursions of high strontium and thorium concentrations are consistent with biotite dehydration melting. Monazite and titanite U–Pb ages record peak metamorphism from ~ 97 to 92 million years ago (Ma) and a retrograde event at ~ 85 Ma. Raman spectroscopy confirms the presence of carbonaceous material and highly ordered, crystalline graphite. Graphite δ 13 C VPDB values of − 30 to − 12‰ and pyrrhotite δ 34 S VCDT values of − 14 to 10‰ are consistent with derivation from organic carbon and sulfur in sedimentary rocks, respectively. These data collectively suggest that formation of massive graphite lenses occurred approximately synchronously with high-temperature metamorphism and anatexis of a highly carbonaceous pelitic protolith. Melt extraction and fluid release associated with anatexis were likely crucial for concentrating graphite. High-temperature, graphitic migmatite sequences within high-strain shear zones may be favorable for the occurrence of high-grade flake graphite deposits.

Alaska↗
USGS2019

Age of the dacite of Sunset Amphitheater, a voluminous Pleistocene tephra from Mount Rainier (USA), and implications for Cascade glacial stratigraphy

The dacite of Sunset Amphitheater, Mount Rainier (USA), illustrates the difficulties in establishing accurate ages of Pleistocene tephra eruptions. Nearly uniform whole-rock, glass, and mineral compositions, texture, and phenocryst assemblage establish that certain conspicuous dissected pumice exposures scattered from Mount Rainier to southern Puget Sound are products of the same Pleistocene Plinian eruption . Deposit thicknesses and pumice sizes support an eruption on the order of low Volcanic Explosivity Index (VEI) 5, atypically explosive for dominantly lava-producing Mount Rainier. Statistically permissible 40 Ar/ 39 Ar plateau ages of plagioclase phenocryst separates are 138 ± 20 ka and 101 ± 11 ka (2σ). A previously published result of 206 ± 11 ka is herein shown to result from a sample selection error. Zircon from the pumice yields a U-Th crystallization age of 147 ± 8 ka if the isochron is required to pass through the tephra U-Th isotopic composition . In contrast, pooled (U-Th)/He measurements on the zircon yield an age of 85 ± 6 ka (2σ), which accords with well-behaved 40 Ar/ 39 Ar ages of stratigraphically associated lavas high on Mount Rainier, and is the best estimate of the pumice's true eruption age. Inclusions of undegassed melt (glass) in the plagioclase separates are proposed as biasing apparent 40 Ar/ 39 Ar plateau ages to old values through coupling of undegassed magmatic excess Ar with radiogenic Ar that accumulated post-eruptively from relatively K-rich glass. U-Th ages record zircon growth prior to eruption, consistent with a possible complex history of advanced solidification followed by remobilization . The ca. 85 ka eruption age confirms that bracketing glacial tills on the flanks of Mount Rainier were products of the Penultimate Glaciation (MIS 6) and Last Glacial Maximum (MIS 2). This eruption age also provides an important time marker for glacial and other sedimentary deposits in southern Puget Sound lowland that, excepting the Vashon Drift (MIS 2), generally lack reliable age determinations.

Washington↗
USGS2002

High-resolution seismic-reflection investigation of the northern Gulf of Mexico gas-hydrate-stability zone

We recorded high-resolution seismic-reflection data in the northern Gulf of Mexico to study gas and gas-hydrate distribution and their relation to seafloor slides. Gas hydrate is widely reported near the seafloor, but is described at only one deep drill site. Our data show high-reflectivity zones (HRZs) near faults, diapirs, and gas vents and interbedded within sedimentary sections at shallow depth (<1 km). The HRZs lie below the gas-hydrate-stability zone (GHSZ) as well as within the zone (less common), and they coincide with zones of shallow water-flows. Bottom simulating reflections are rare in the Gulf, and not documented in our data. We infer HRZs result largely from free gas in sandy beds, with gas hydrate within the GHSZ. Our estimates for the base BHSZ correlate reasonably with the top of HRZs in some thick well-layered basin sections, but poorly where shallow sediments are thin and strongly deformed. The equivocal correlation results from large natural variability of parameters that are used to calculate the base of the GHSZ. The HRZs may, however, be potential indicators of nearby gas hydrate. The HRZs also lie at the base of at least two large seafloor slides (e.g. up to 250 km2) that may be actively moving along decollement faults that sole within the GHSZ or close to the estimated base of the GHSZ. We suspect that water/gas flow along these and other faults such as 'chimney' features provide gas to permit crystallization of gas hydrate in the GHSZ. Such flows weaken sediment that slide down salt-oversteepened slopes when triggered by earthquakes. Published by Elsevier Science Ltd.

Marine and Petroleum Geology↗
USGS1978

Geologic map of the Mare Australe area of Mars

The south polar region of Mars is among the most geologically diverse on the planet. The areas is within the heavily cratered hemisphere of Mars bu t is distinguished by a variety of younger, regionally extensive deposits and a n a ssemblage of unique erosional forms. The spectrum of units varies from the oldest to the youngest on the planet. The oldest unit, typif ying t h e cratered hemisphere, is the material of ancient large craters, most of which have undergone advanced degradation. These ancient crater materials are overlain by a variety of regional deposits, including extensive intercrater debris blankets, r i dged volcanic flows, and massive eolian deposits that eroded to form complex cliff-rimmed pits. In the central zone of the polar region, south of roughly 75 ˚ S., these depositional units are, in turn, unconformably overlain by a t remendous sedimentary complex 1,500-2,000 km in diameter, consisting of 40 or more regularly spaced horizontal starta . Each stratum retains apparently uniform thickness (several tons of meters) over hundreds of kilometers; erosional unconformities between starta have not as yet been identified. Resting on the uppermost surface of this layered terrain is the perm anent residual polar ice cap. This complex stratigraphic record may ultimately hold the keys t o the initial atmospheric evolution, climatological fluctuations, and the history, budget, and mobility of wate r on the planet.

IMAP↗
USGS2014

Hydrogeology and water quality of the stratified-drift aquifer in the Pony Hollow Creek Valley, Tompkins County, New York

The lithology, areal extent, and the water-table configuration in stratified-drift aquifers in the northern part of the Pony Hollow Creek valley in the Town of Newfield, New York, were mapped as part of an ongoing aquifer mapping program in Tompkins County. Surficial geologic and soil maps, well and test-boring records, light detection and ranging (lidar) data, water-level measurements, and passive-seismic surveys were used to map the aquifer geometry, construct geologic sections, and determine the depth to bedrock at selected locations throughout the valley. Additionally, water-quality samples were collected from selected streams and wells to characterize the quality of surface and groundwater in the study area. Sedimentary bedrock underlies the study area and is overlain by unstratified drift (till), stratified drift (glaciolacustrine and glaciofluvial deposits), and recent post glacial alluvium. The major type of unconsolidated, water-yielding material in the study area is stratified drift, which consists of glaciofluvial sand and gravel, and is present in sufficient amounts in most places to form an extensive unconfined aquifer throughout the study area, which is the source of water for most residents, farms, and businesses in the valleys. A map of the water table in the unconfined aquifer was constructed by using (1) measurements made between the mid-1960s through 2010, (2) control on the altitudes of perennial streams at 10-foot contour intervals from lidar data collected by Tompkins County, and (3) water surfaces of ponds and wetlands that are hydraulically connected to the unconfined aquifer. Water-table contours indicate that the direction of groundwater flow within the stratified-drift aquifer is predominantly from the valley walls toward the streams and ponds in the central part of the valley where groundwater then flows southwestward (down valley) toward the confluence with the Cayuta Creek valley. Locally, the direction of groundwater flow is radially away from groundwater mounds that have formed beneath upland tributaries that lose water where they flow on alluvial fans on the margins of the valley. In some places, groundwater that would normally flow toward streams is intercepted by pumping wells. Surface-water samples were collected in 2001 at four sites including Carter, Pony Hollow (two sites), and Chafee Creeks, and from six wells throughout the aquifer. Calcium dominates the cation composition and bicarbonate dominates the anion composition in groundwater and surface-water samples and none of the common inorganic constituents collected exceeded any Federal or State water-quality standards. Groundwater samples were collected from six wells all completed in the unconfined sand and gravel aquifer. Concentrations of calcium and magnesium dominated the ionic composition of the groundwater in all wells sampled. Nitrate, orthophosphate, and trace metals were detected in all groundwater samples, but none were more than U.S. Environmental Protection Agency or New York State Department of Health regulatory limits.

New York↗
USGS1987

15N/14N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (“black shales”) were found to have significantly lower δ 15 N values (lower 15 N/ 14 N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ° 15 N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15 N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15 N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N 2 -fixing blue-green algae, a possible source of this sediment 15 N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.

Earth and Planetary Science Letters↗