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At least 1,279 records · Page 71Linked to original sources
USGS2014

Hydrologic conditions in urban Miami-Dade County, Florida, and the effect of groundwater pumpage and increased sea level on canal leakage and regional groundwater flow

The extensive and highly managed surface-water system in southeastern Florida constructed during the 20th Century has allowed for the westward expansion of urban and agricultural activities in Miami-Dade County. In urban areas of the county, the surface-water system is used to (1) control urban flooding, (2) supply recharge to production well fields, and (3) control seawater intrusion. Previous studies in Miami-Dade County have determined that on a local scale, leakage from canals adjacent to well fields can supply a large percentage (46 to 78 percent) of the total groundwater pumpage from production well fields. Canals in the urban areas also receive seepage from the Biscayne aquifer that is derived from a combination of local rainfall and groundwater flow from Water Conservation Area 3 and Everglades National Park, which are west of urban areas of Miami-Dade County. To evaluate the effects of groundwater pumpage on canal leakage and regional groundwater flow, the U.S. Geological Survey (USGS) developed and calibrated a coupled surface-water/groundwater model of the urban areas of Miami-Dade County, Florida. The model was calibrated by using observation data collected from January 1997 through December 2004. The model calibration was verified using observation data collected from January 2005 through December 2010. A 1-year warmup period (January 1996 through December 1996) was added prior to the start of the calibration period to reduce the effects of inaccurate initial conditions on model calibration. The model is designed to simulate surface-water stage and discharge in the managed canal system and dynamic canal leakage to the Biscayne aquifer as well as seepage to the canal from the aquifer. The model was developed using USGS MODFLOW–NWT with the Surface-Water Routing (SWR1) Process to simulate surface-water stage, surface-water discharge, and surface-water/groundwater interaction and the Seawater Intrusion (SWI2) Package to simulate seawater intrusion, respectively. Automated parameter estimation software (PEST) and highly parameterized inversion techniques were used to calibrate the model to observed surface-water stage, surface-water discharge, net surface-water subbasin discharge, and groundwater level data from 1997 through 2004 by modifying hydraulic conductivity, specific storage coefficients, specific yield, evapotranspiration parameters, canal roughness coefficients (Manning’s n values), and canal leakance coefficients. Tikhonov regularization was used to produce parameter distributions that provide an acceptable fit between model outputs and observation data, while simultaneously minimizing deviations from preferred values based on field measurements and expert knowledge. Analytical and simulated water budgets for the period from 1996 through 2010 indicate that most of the water discharging through the salinity control structures is derived from within the urban parts of the study area and that, on average, the canals are draining the Biscayne aquifer. Simulated groundwater discharge from the urban areas to the coast is approximately 7 percent of the total surface-water inflow to Biscayne Bay and is consistent with previous estimates of fresh groundwater discharge to Biscayne Bay. Simulated groundwater budgets indicate that groundwater pumpage in some surface-water basins ranges from 13 to 27 percent of the sum of local sources of groundwater inflow. The largest percentage of groundwater pumpage to local sources of groundwater inflow occurs in the basins that have the highest pumping rates (C–2 and C–100 Basins). The ratio of groundwater pumpage to simulated local sources of groundwater inflow is less than values calculated in previous local-scale studies. The position of the freshwater-seawater interface at the base of the Biscayne aquifer did not change notably during the simulation period (1996–2010), consistent with the similar positions of the interface in 1984, 1995, and 2011 under similar hydrologic and groundwater pumping conditions. Landward movement of the freshwater-seawater interface above the base of the aquifer is more prone to occur during relatively dry years. The model was used to evaluate the effect of increased groundwater pumpage and (or) increased sea level on canal leakage, regional groundwater flow, and the position of the freshwater-seawater interface. Permitted groundwater pumping rates, which generally exceed historical groundwater pumping rates, were used for Miami-Dade County Water and Sewer Department groundwater pumping wells in the base-case future scenario. Base-case future and increased pumping scenario results suggest seawater intrusion may occur at the Miami-Springs well field if the Miami Springs, Hialeah, and Preston well fields are operated using current permitted groundwater pumping rates. Scenario simulations also show that, in general, the canal system limits the adverse effects of proposed groundwater pumpage increases on water-level changes and saltwater intrusion. Proposed increases (up to a 7 percent increase) in groundwater pumpage do not have a notable effect on movement of the freshwater-seawater interface. Increased groundwater pumpage increased lateral groundwater inflow into basins subject to additional groundwater pumpage; however, most (55 percent) of the additional groundwater extracted from pumping wells was supplied by changes in canal seepage and leakage in urban areas of the model. Increased sea level caused increased water-table elevations in urban areas and decreased hydraulic gradients across the system; the largest increases in water-table elevations occurred seaward of the salinity control structures. The extent of flood-prone areas and the percentage of time water-table elevations in flood-prone areas were less than 0.5 foot below land surface increased with increased sea level. Increased sea level also resulted in landward migration of the freshwater-seawater interface; the largest changes in the position of the interface occurred seaward of the salinity control structures except in parts of the model area that were inundated by increased sea level. Decreased water-table gradients reduced groundwater inflow, groundwater outflow, canal exchanges, surface-water inflow, and surface-water outflow through salinity control structures. Results for the scenario that evaluated the combination of increased groundwater pumpage and increased sea level did not differ substantially from the scenario that evaluated increased sea level alone. Groundwater inflow, groundwater outflow, and canal exchanges were reduced in urban areas of the study area as a result of decreased water-table gradients across the system, although reductions were less than those in the increased sea-level scenario. The decline in groundwater levels caused by increased groundwater pumpage was less under the increased sea-level scenario than under the increased groundwater-pumpage scenario. The largest reductions in surface-water outflow from the salinity control structures occurred with increased sea level and increased groundwater pumpage. The model was designed specifically to evaluate the effect of groundwater pumpage on canal leakage at the surface-water-basin scale and thus may not be appropriate for (1) predictions that are dependent on data not included in the calibration process (for example, subdaily simulation of high-intensity events and travel times) and (or) (2) hydrologic conditions that are substantially different from those during the calibration and verification periods. The reliability of the model is limited by the conceptual model of the surface-water and groundwater system, the spatial distribution of physical properties, the scale and discretization of the system, and specified boundary conditions. Some of the model limitations are manifested in model errors. Despite these limitations, however, the model represents the complexities of the interconnected surface-water and groundwater systems that affect how the systems respond to groundwater pumpage, sea-level rise, and other hydrologic stresses. The model also quantifies the relative effects of groundwater pumpage and sea-level rise on the surface-water and groundwater systems.

Florida↗
USGS1952

Stratigraphic sections of the Phosphoria formation in Idaho, 1947-48, Part I

The Permian Phosphoria formation of the western states contains one of the world's largest reserves of phosphate. Although previous investigations (see especially Mansfield, 1927), including reconnaissance geologic mapping and sampling, established the location of most of the important deposits and their quality of scattered localities, they were not sufficiently detailed to permit a comparison of the merits of individual deposits or an appraisal of the reserves of phosphate rock that might be available under present economic conditions. Because the growing importance of the western phosphate deposits requires a better, more detailed understanding of their distribution and quality, the Geological Survey began in 1947 a comprehensive investigation, including (1) reconnaissance geologic mapping, mostly in Montana, of areas in which the Phosphoria formation could occur but where it had not previously been looked for or found; (2) geologic mapping, mostly in Montana, at a scale no smaller than 1:62,500, of several areas known to contain the Phosphoria formation but not previously mapped except in reconnaissance fashion; (3) geologic and topographic mapping, at a scale of 1:12,000, of some of the richest, thickest, and most accessible deposits; (4) measuring, describing, and sampling all beds of the phosphatic and shaly parts, and in some places the full thickness, of the Phosphoria formation and its stratigraphic equivalents at one or two localities per township over the entire field; (5) chemical and spectrographic analysis of the samples for phosphate, fluorine, minor metals, oil, and rock-forming constituents; and (6) petrologic and geochemical studies of the rocks and minerals of the formation. These studies are designed to define the regional and local geologic structures in which the phosphate bed lie, to provide a basis for the estimation of reserves of the inferred class over the entire region, and to determine the origin of the rocks and the elements contained in them. The data collected are not of the detail required to plan actual mining operations, but it is hoped they will guide industry in the selection of individual deposits worthy of further exploration. Most of the field work contemplated as a part of this investigation is now completed. Although the data will not be compiled or published in final form for some years to come, segments of the data, accompanied by little or no interpretation, will be published as preliminary maps or reports as they are assembled. The present report is the first of a series presenting in abbreviated form the description and analyses of the beds measured and sampled at various localities in southeastern Idaho (pl. 1). Companion reports presenting segments of the data from Montana, Wyoming, and Utah (Swanson and others, 1952, and McKelvey and others, 1952a and 1952b) are being released at the same time as this report, and others are in preparation.

Idaho↗
USGS1995

Types of secondary porosity of carbonate rocks in injection and test wells in southern peninsular Florida

The types of secondary porosity present in carbonate injection intervals and in the overlying carbonate rocks were determined at 11 injection well sites and 3 test well sites in southern peninsular Florida. The hydrogeologic system consists of a thick sequence of carbonate rocks overlain by clastic deposits. Principal hydrogeologic units are the surficial aquifer system, the intermediate aquifer system or the intermediate confining unit,the Floridan aquifer system, and the sub-Floridan confining unit.The concept of apparent secondary porosity was used in this study because the secondary porosity features observed in a borehole television survey could have been caused by geologic processes as well as by drilling activities. The secondary porosity features identified in a television survey were evaluated using driller's comments and caliper, flowmeter, and temperature logs. Borehole intervals that produced or received detectable amounts of flow, as shown by flowmeter and temperature logs, provided evidence that the secondary porosity of the interval was spatially distributed and interconnected beyond the immediate vicinity of a borehole and, thus, was related to geologic processes. Features associated with interconnected secondary porosity were identified as effective secondary porosity. Fracture porosity was identified as the most common type of effective secondary porosity and was observed predominantly in dolomite and dolomitic limestone. Cavity porosity was the least common type of effective secondary porosity at the study sites. In fact, of the more than 17,500 feet of borehole studied a total of only three cavities constituting effective secondary porosity were identified at only two sites. These cavities were detected in dolomite rocks. Most apparent cavities were caused by drilling-induced collapse of naturally fractured borehole walls. Also, fractures usually were observed above and below cavities. The majority of vugs observed in the television surveys did not constitute effective secondary porosity. No effective secondary porosity was evident in the limestone or dolomitic limestone in the 300-foot interval immediately above the injection interval at six sites on the southeastern coast of Florida. Injection wells commonly are cased through the 300-foot interval. Fractures or cavities that contribute to effective secondary porosity may be present in this interval, but were not detectable with the methods used. Widely dispersed, inter- connected fractures or cavities can be present beyond the rock column intersected by the borehole and can provide local pathways for vertical migration of injected wastewater or the displaced saltwater. In the interval between the top of the Floridan aquifer system and a point 300 feet above the top of the injection interval, fractured rocks having effective secondary porosity were observed at five of six sites along the southeastern coast. Borehole characteristics usually are related to the drilling characteristics of the rock type. In limestone, borehole diameters are consistently larger than the bit diameter whereas in dolomite, borehole diameters are intermittently larger than the bit diameter. The large borehole diameters associated with dredging probably are caused by the presence of intensively fractured dolomite which collapses during drilling.

Water-Resources Investigations Report↗
USGS1952

Present and past ground-water conditions in the Morrison Formation in southwestern Colorado and southeastern Utah

Field and laboratory studies of ground-water conditions in the carnotite-bearing Morrison formation in southwestern Colorado and southeastern Utah were undertaken to determine possible relations between ground waters and the carnotite deposits. The ore-bearing sandstone consists of lenticular sandstone strata, interbedded within discontinuous layers of mudstone; these strata were deposited in a stream environment. The porosity and permeability of the ore-bearing sandstone in one area are relatively low, porosity averaging about 15 percent and permeability ranging between 30 and 3300 millidarcys. Permeability studies in this same area show that sandstone classed as favorable for ore is slightly more permeable than and has nearly twice the transmissibility of sandstone classed as semifavorable; outcrop studies also suggest a lower transmissibility for sandstone that is unfavorable. Samples of water from the ore-bearing and associated strata show considerable variation in chemical charter. These water samples are generally low in uranium, vanadium, copper, and lead, most samples containing less than 1 part per million (ppm) of each metal. General geologic relations suggest that ground-water movement probably was active through the ore-bearing strata during their deposition and shortly afterward. Movement during this time probably occurred largely through the more permeable sand strata and in the general direction of initial dip and stream flow. During Cretaceous time, when several thousand feet of marine sediments accumulated over the Morrison, the water contained in the ore-bearing strata probably was immobile or nearly so and was protected from escape or contamination. Following Tertiary deformation and erosion, active ground-water circulation no doubt was restored, but because of the low permeability and the lenticular character and therefore low transmissibility of the ore-bearing sandstone, ground-water movement probably was slow. Faulting probably also influenced the direction and rate of ground-water movement during Tertiary time. Movement and localization of ground water would permit the concentration of metal-bearing solutions during Salt Wash and early Brushy Basin time in the beds that now contain ore deposits. It is more difficult to explain the formation of these deposits, which have a wide geographic distribution at a restricted stratigraphic position, from solutions circulating through the rocks at a later date. Whatever mode of origin is used to explain the deposits, geologists almost without exception, agree that the metals were transported by solutions that have migrated through the sediments for considerable distances. For this reason, a study of the horizontal and vertical transmissibility characteristics of all exposed sedimentary formations on the Colorado Plateau is planned.

Colorado, Utah↗
USGS1995

Proterozoic low-Ti iron-oxide deposits in New York and New Jersey: Relation to Fe-oxide (Cu-U-Au-rare earth element) deposits and tectonic implications

Low-Ti iron-oxide deposits in exposed Grenville-age rocks of New York and New Jersey belong to a distinct class of iron-oxide (Cu-U-Au–rare earth element [REE]) deposits that includes similar iron deposits in southeastern Missouri and the Kiruna district of Sweden, the giant Olympic Dam U-Cu-Au-Ag deposit (Australia), and the Bayan Obo REE-Nb deposit (China). Most of the New York–New Jersey deposits exhibit features consistent with a hydrothermal origin and define a regionally significant metallogenic event that provides important clues to the evolution of this part of the Grenville orogen. In the Adirondacks, the tectonic setting of these deposits is consistent with postorogenic uplift and extensive crustal melting at 1070–1050 Ma that was accompanied by late tectonic to posttectonic deposition of iron.

Geology↗
USGS1967

Time and space relationships of the taconic allochthon and autochthon

The Taconic rock sequence extends from near Sudbury, Vermont, to near Poughkeepsie, New York, a length of about 150 miles; and from just west of the Green Mountain Range and Berkshire Highlands to the valleys of the Hudson River and Lake Champlain, a width of about 20 miles. The Taconic rocks are now in the axial region of the Middlebury synclinorium and its southward extension. The Taconic sequence consists of about 2000 feet of slate, with subsidiary graywacke, quartzite, and limestone; many of the rock units are turbidites. Fossils from the rocks include forms of Early, Middle, and Late Cambrian and Early and Middle Ordovician age. Evidence of stratigraphic tops derived from the fossils and from primary sedimentary features agrees with structural data and demonstrates that the Taconic rocks are geometrically the highest strata within the Middlebury synclinorium. The underlying rocks of the synclinorium (the synclinorium sequence) are right side up; they also range in age from Early Cambrian to Middle Ordovician but belong to a different sedimentary lithofacies (dominantly carbonate and orthoquartzite). The relation between the Taconic sequence and the synclinorium sequence, therefore, is a baffling problem. Lithostratigraphically, the Taconic sequence falls into three groups: (1) the pre- Normanskill "low Taconic " sequence, occurring in the area between the main Taconic Range and the Hudson River, as far south as Rhinebeck, New York; (2) the Normanskill Shale in the same area, as well as in the area south of Rhinebeck at least as far as Poughkeepsie, New York, and also west of the Hudson River; and (3) the "high Taconic " sequence, occupying the main Taconic Range from Dorset Mountain, Vermont, south to Indian Mountain in Sharon, Connecticut, as well as Mount Greylock in Massachusetts. Rocks of (1) and (2) are fossiliferous, but to date no fossil has been found in (3). Rocks of (1) and that part of (2) areally coextensive with (1) thus are of known age but uncertain three-dimensional geometric configuration, whereas rocks of (3) are of known configuration (in the centers of open synclinoria) but unknown age. Only that part of (2) beyond the areal confines of (1) is both of known age and known configuration; these rocks are in sedimentary contact above the older rocks of the synclinorium sequence and are autochthonous. At the north end of the Taconic sequence in western Vermont, rocks of group (1) are beyond reasonable doubt allochthonous. Because of the southward geometric continuity of the structural elements, all the Taconic rocks of group (1), and that part of group (2) areally coextensive with it, are interpreted as allochthonous. The structure of group (3), the high Taconic sequence, is inferred by topography and by detailed lithostratigraphic matching with rocks of the east Vermont sequence; on this basis, as well as on the basis of the broad lithic similarity with rocks of group (1), rocks of group (3) are concluded to be also allochthonous. A discontinuous polymict conglomerate underlies and surrounds the allochthon on all sides and is interpreted here as a record that dates the imminent arrival of the allochthon at each locality. The conglomerate contains unsorted blocks of rocks of both the Taconic sequence and the synclinorium sequence; the matrix is the autochthonous upper Normanskill Shale or its equivalent. Fossils from the matrix shale date the event as Trenton, probably Sherman Fall in age. The geologic history of the area is reconstructed as follows: The pre-Normanskill Taconic rocks were deposited in the area of the present Precambrian massifs of the Green Mountains-Berkshire Highlands belt between the clastic, eugeosynclinal east Vermont sequence to the east and the miogeosynclinal synclinorium sequence to the west; they constitute the transitional facies between these two belts. Conditions were relatively stable until early Middle Ordovician time , when the Green Mountain- Berkshire Highlands area began to rise and the area of the present Middlebury synclinorium began to subside. Subsidence took place largely by a series of high-angle longitudinal faults that, as a whole, step down to the west. Argillaceous sediments (the Normanskill Shale) began to inundate the former miogeosynclinal area; because the conditions of sedimentation had become similar, the sediments resembled, in facies, the synchronous Taconic rocks that were being deposited to the east. Continued rise of the Green Mountains-Berkshire Highlands area led in middle Trenton time to the decollement of the Cambrian and Ordovician sediments into the area of the present Middlebury synclinorium in a series of giant submarine slides. Sedimentation continued at the receiving site throughout the event; sedimentation may also have persisted on the moving slides. The record is found today in the turbidite-laden shale and graywacke in the upper part of the Normanskill Shale of both the allochthon and the autochthon . Restoration of the allochthonous rocks to the original site of deposition leads to correlations between rocks of the Taconic sequence and of the largely autochthonous east Vermont sequence. The lithic correlation can be carried to the level of individual formations and is confirmed by a few known ages in the east Vermont sequence. Several lines of reasoning lead to a plausible correlation of part of the Cavendish Formation of southeastern Vermont with the oldest part of the Taconic sequence. This correlation leads further to the conclusion that in this area the contacts between the Green Mountain massif and the Cavendish Formation and between the Cavendish and the overlying east Vermont sequence must both be thrust faults of large displacements. This conclusion is in fact inevitable because one of the Taconic thrust slices that extends without interruption between the latitudes corresponding to the gap in the Precambrian massifs has been shown by local structural evidence to be allochthonous; an outside original depositional site must be found for it. The present Taconic allochthon is coextensive with an area of marked negative Bouguer gravity anomaly; the Green Mountains-Berkshire massifs constitute a belt of positive anomaly. It is here proposed that these anomalies resulted from a deepseated transfer of material; subcrustal addition of material caused the rise of the Green Mountains-Berkshire Highlands area, and the concurrent subtraction of material caused subsidence in the Middlebury synclinorium area through a series of faults which were the near-surface expression of an episode of crustal collapse. If this interpretation is correct, then the regional gravity anomaly represents an uncompensated feature that has persisted since Middle Ordovician time .

Special Paper of the Geological Society of America↗
USGS2017

Nutrient and sediment concentrations and loads in the Steele Bayou Basin, northwestern Mississippi, 2010–14

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers-Vicksburg District, monitored streamflow, water quality, and sediment at two stations on the Steele Bayou in northwestern Mississippi from October 2010 through September 2014 to characterize nutrient and sediment concentrations and loads in areas where substantial implementation of conservation efforts have been implemented. The motivation for this effort was to quantify improvements, or lack thereof, in water quality in the Steele Bayou watershed as a result of implementing large- and small-scale best-management practices aimed at reducing nutrient and sediment concentrations and loads. The results of this study document the hydrologic, water-quality, and sedimentation status of these basins following over two decades of ongoing implementation of conservation practices. Results from this study indicate the two Steele Bayou stations have comparable loads and yields of total nitrogen, phosphorus, and suspended sediment when compared to other agricultural basins in the southeastern and central United States. However, nitrate plus nitrite yields from basins in the Mississippi River alluvial plain, including the Steele Bayou Basin, are generally lower than other agricultural basins in the southeastern and central United States. Seasonal variation in nutrient and sediment loads was observed at both stations and for most constituents. About 50 percent of the total annual nutrient and sediment load was observed during the spring (February through May) and between 25 and 50 percent was observed during late fall and winter (October through January). These seasonal patterns probably reflect a combination of seasonal patterns in precipitation, runoff, streamflow, and in the timing of fertilizer application. Median concentrations of total nitrogen, nitrate plus nitrite, total phosphorus, orthophosphate, and suspended sediment were slightly higher at the upstream station, Steele Bayou near Glen Allan, than at the downstream station, Steele Bayou at Grace Road at Hopedale, MS, although the differences typically were not statistically significant. Mean annual loads of nitrate plus nitrite and suspended sediment were also larger at the upstream station, although the annual loads at both stations were generally within the 95-percent confidence intervals of each other.

Mississippi↗
USGS1980

Evolution of the continental margin of southern Spain and the Alboran Sea

Seismic reflection profiles and magnetic intensity measurements were collected across the southern continental margin of Spain and the Alboran basin between Spain and Africa. Correlation of the distinct seismic stratigraphy observed in the profiles to stratigraphic information obtained from cores at Deep Sea Drilling Project site 121 allows effective dating of tectonic events. The Alboran Sea basin occupies a zone of motion between the African and Iberian lithospheric plates that probably began to form by extension in late Miocene time (Tortonian). At the end of Miocene time (end of Messinian) profiles show that an angular unconformity was cut, and then the strata were block faulted before subsequent deposition. The erosion of the unconformity probably resulted from lowering of Mediterranean sea level by evaporation when the previous channel between the Mediterranean and Atlantic was closed. Continued extension probably caused the block faulting and, eventually the opening of the present channel to the Atlantic through the Strait of Gibraltar and the reflooding of the Mediterranean. Minor tectonic movements at the end of Calabrian time (early Pleistocene) apparently resulted in minor faulting, extensive transgression in southeastern Spain, and major changes in the sedimentary environment of the Alboran basin. Active faulting observed at five locations on seismic profiles seems to form a NNE zone of transcurrent movement across the Alboran Sea. This inferred fault trend is coincident with some bathymetric, magnetic and seismicity trends and colinear with active faults that have been mapped on-shore in Morocco and Spain. The faults were probably caused by stresses related to plate movements, and their direction was modified by inherited fractures in the lithosphere that floors the Alboran Sea.

Alboran Sea↗
USGS1977

Spherulitic rhyolite dike from Goat Island, southeastern Alaska

Spherulites, as much as 4 mm in diameter, locally constitute almost 50 percent by volume of a dark-red rhyolite dike that intrudes porphyritic pyroxene gabbro along the northeast coast of Goat Island, 3.2 km northwest of Hydaburg, southeastern Alaska. The largest spherulites are composed mainly of o-quartz, whereas the smallest consist of a microcrystalline intergrowth of tridymite and alkali feldspar. Textural relations indicate that the radial and concentrically zoned structures are the products.of devitrification of glassy lava. The mineralogy of the dike is similar to that of other spherulitic rhyolites except that quartz occurs to the exclusion of cristobalite. The posteruptive formation of the spherulites has also resulted in alkali transfer, the groundmass of the dike being enriched in both sodium and potassium relative to the spherulites.

Alaska↗
USGS1998

The Chesapeake Bay bolide impact: a new view of coastal plain evolution

A spectacular geological event took place on the Atlantic margin of North America about 35 million years ago in the late part of the Eocene Epoch. Sea level was unusually high everywhere on Earth, and the ancient shoreline of the Virginia region was somewhere in the vicinity of where Richmond is today (fig. 1). Tropical rain forests covered the slopes of the Appalachians. To the east of a narrow coastal plain, a broad, lime (calcium carbonate)- covered continental shelf lay beneath the ocean. Suddenly, with an intense flash of light, that tranquil scene was transformed into a hellish cauldron of mass destruction. From the far reaches of space, a bolide (comet or asteroid), 3-5 kilometers in diameter, swooped through the Earth's atmosphere and blasted an enormous crater into the continental shelf. The crater is now approximately 200 km southeast of Washington, D.C., and is buried 300-500 meters beneath the southern part of Chesapeake Bay and the peninsulas of southeastern Virginia (fig. 1). The entire bolide event, from initial impact to the termination of breccia deposition, lasted only a few hours or days. The crater was then buried by additional sedimentary beds, which accumulated during the following 35 million years.

Fact Sheet↗
USGS2000

Timing of the Acadian Orogeny in northern New Hampshire

New U-Pb geochronology constrains the timing of the Acadian orogeny in the Central Maine Terrane of northern New Hampshire. Sixteen fractions of one to six grains each of zircon or monazite have been analyzed from six samples: (1) an early syntectonic diorite that records the onset of the Acadian, (2) a schist, a migmatite, and two granites that together record the peak of the Acadian; and (3) a postkinematic pluton that records the end of the Acadian. Zircon from the syntectonic Wamsutta Diorite gives a 207Pb/206Pb age of circa 408 Ma, the time at which the boundary between the deforming orogenic wedge and the foreland basin was in the vicinity of the Presidential Range. This age agrees well with the Emsian position of the northwest migrating Acadian orogenic front and records the beginning of the Acadian in this part of the Central Maine Terrane. We propose a possible Acadian tectonic model that incorporates the geochronologic, structural, and stratigraphic data. Monazite from the schist, migmatite, Bigelow Lawn Granite, and Slide Peak Granite gives 207Pb/206U ages, suggesting the peak of Acadian metamorphism and intrusion of two-mica granites occurred at circa 402-405 Ma, the main pulse of Acadian orogenesis. Previously reported monazite ages from schists that likely record the peak metamorphism in the Central Maine Terrane of New Hampshire and western Maine range from circa 406-384 Ma, with younger ages in southeastern New Hampshire and progressively older ages to the west, north, and northeast. Acadian orogenesis in the Presidential Range had ended by circa 355 Ma, the 207Pb/235U age of monazite from the Peabody River Granite. From 408 to perhaps at least 394 Ma, Acadian orogenesis in the Presidential Range was typical of the tectonic style, dominated by synkinematic metamorphism, seen in central and southern New Hampshire, Massachusetts, and Connecticut. From no earlier than 394 Ma to as late as 355 Ma, the orogenesis was typical of the style in parts of Maine dominated by postkinematic metamorphism.

Journal of Geology↗
USGS2002

Drainage reversals in Mono Basin during the late pliocene and Pleistocene

Mono Basin, on the eastern flank of the central Sierra Nevada, is the highest of the large hydrographically closed basins in the Basin and Range province. We use geomorphic features, shoreline deposits, and basalt-filled paleochannels to reconstruct an early to middle Pleistocene record of shorelines and changing spillways of Lake Russell in Mono Basin. During this period of time, Lake Russell repeatedly attained altitudes between 2205 and 2280 m-levels far above the present surface of Mono Lake (~1950 m) and above its last overflow level (2188 m). The spill point of Lake Russell shifted through time owing to late Tertiary and Quaternary faulting and volcanism. During the early Pleistocene, the lake periodically discharged through the Mount Hicks spillway on the northeastern rim of Mono Basin and flowed northward into the Walker Lake drainage basin via the East Walker River. Paleochannels recording such discharge were incised prior to 1.6 Ma, possibly between 1.6 and 1.3 Ma, and again after 1.3 Ma (ages of basaltic flows that plugged the paleochannels). Faulting in the Adobe Hills on the southeastern margin of the basin eventually lowered the rim in this area to below the altitude of the Mount Hicks spillway. Twice after 0.76 Ma, and possibly as late as after 0.1 Ma, Lake Russell discharged southward through the Adobe Hills spillway into the Owens-Death Valley system of lakes. This study supports a pre-Pleistocene aquatic connection through Mono Basin between the hydrologically distinct Lahontan and Owens-Death Valley systems, as long postulated by biologists, and also confirms a probable link during the Pleistocene for species adapted to travel upstream in fast-flowing water.

Geological Society of America Bulletin↗
USGS1976

Cenozoic deposits of southeastern New Mexico and an outline of the history of evaporite dissolution

Sedimentary records of Cenozoic history in southeastern New Mexico begin with the Ogallala Formation of Miocene and Pliocene age. Later records include the Gatuna Formation of early or middle Pleistocene age, Mescalero caliche, an informal term, of middle Pleistocene age, and fluvial deposits of late Pleistocene age but there are many gaps in the record. The modern landscape is the result of erosion and deposition in climates that have ranged from semihumid to semiarid as well as dissolution of soluble rocks in Permian formations in the subsurface. This dissolution may have begun as early as Jurassic time and has continued intermittently to the present.

New Mexico↗
USGS2026

Cenozoic distributed volcanism of the Arabia Plate—A review

Cenozoic volcanic rocks of the Arabia Plate cover about 140,000 square kilometers across a distance of about 3,000 kilometers from southern Yemen to southeastern Turkey. The majority of volcanic products are alkali basalts that erupted in restricted areas, commonly over periods of a million or more years, building mafic lava fields, each known in Arabic as a “harrat.” Harrat volcanism commenced following the Oligocene flood-lava effusions that blanketed the (now) Ethiopian highlands, southern Sudan, and western Yemen, and overlapped the latest Oligocene to early Miocene initial riftings of the Red Sea and Gulf of Aden, but the majority of harrat volcanism has been since approximately 13–10 million years ago. Persistent harrat magmatism in restricted locations led to the development of intermediate and evolved magmas (hawaiites, mugearites, benmoreites, trachytes, comendites, and phonolites) mainly through intracrustal crystallization-differentiation. Most of these intermediate and evolved magmas erupt at sites of the greatest aggregate volcanic relief, reflecting sites of the greatest overall magmatic fluxes. Production of fractionated magmas at these sites negates “monogenetic” as an appropriate descriptor of harrat volcanism. This chapter summarizes the geologic, eruptive, and tectonic history and aspects of the petrogenesis of the Cenozoic Arabian alkalic province. Particular emphasis is placed on results of a joint study of Ḩarrat Rahat adjacent to the city of Al Madīnah al Munawwarah, Kingdom of Saudi Arabia, published as U.S. Geological Survey Professional Paper 1862 and Saudi Geological Survey Special Report SGS–SP–2021–1. A goal of this chapter is to provide an introduction to those unfamiliar with this vast, enigmatic, and fascinating region of distributed continental volcanism.

Arabia Plate↗
USGS2016

Geologic framework, age, and lithologic characteristics of the North Park Formation in North Park, north-central Colorado

Deposits of the North Park Formation of late Oligocene and Miocene age are locally exposed at small, widely spaced outcrops along the margins of the roughly northwest-trending North Park syncline in the southern part of North Park, a large intermontane topographic basin in Jackson County in north-central Colorado. These outcrops suggest that rocks and sediments of the North Park Formation consist chiefly of poorly consolidated sand, weakly cemented sandstone, and pebbly sandstone; subordinate amounts of pebble conglomerate; minor amounts of cobbly pebble gravel, siltstone, and sandy limestone; and rare beds of cobble conglomerate and altered tuff. These deposits partly filled North Park as well as a few small nearby valleys and half grabens. In North Park, deposits of the North Park Formation probably once formed a broad and relatively thick sedimentary apron composed chiefly of alluvial slope deposits (mostly sheetwash and stream-channel alluvium) that extended, over a distance of at least 150 kilometers (km), northwestward from the Never Summer Mountains and northward from the Rabbit Ears Range across North Park and extended farther northwestward into the valley of the North Platte River slightly north of the Colorado-Wyoming border. The maximum preserved thickness of the formation in North Park is about 550 meters near the southeastern end of the North Park syncline. The deposition of the North Park Formation was coeval in part with local volcanism, extensional faulting, development of half grabens, and deposition of the Browns Park Formation and Troublesome Formation and was accompanied by post-Laramide regional epeirogenic uplift. Regional deposition of extensive eolian sand sheets and loess deposits, coeval with the deposition of the North Park Formation, suggests that semiarid climatic conditions prevailed during the deposition of the North Park Formation during the late Oligocene and Miocene. The North Park Formation locally contains a 28.1-mega-annum (Ma, million years ago) ash-flow tuff near its base at Owl Ridge and is interbedded with 29-Ma rhyodacite lava flows and volcanic breccia at Owl Mountain. The formation locally contains vertebrate fossils at least as young as Barstovian age (about 15.9–12.6 Ma) and overlies rocks as young as the White River Formation, which contains vertebrate fossils of Chadronian age (about 37–33.8 Ma) in North Park and a bed of 36.0-Ma volcanic ash in the upper part of the Laramie River valley about 30 km northeast of Walden, Colorado. Based on the ages of the vertebrate fossils, folding of the rocks and sediments in the North Park syncline may be much younger than about 16 Ma. Bedding characteristics of the North Park Formation suggest that (1) some or much of the sand, sandstone, and pebbly sandstone may have been deposited as sheetwash alluvium; (2) much of the siltstone may have been deposited as sheetwash alluvium or ephemeral pond or marsh deposits; (3) beds of sandy limestone probably were deposited as ephemeral pond or marsh deposits; and (4) altered tuff probably was deposited in ephemeral ponds or marshes. Most of the conglomerate and gravel in the North Park Formation are stream-channel deposits that were deposited by high-energy ephemeral or intermittent streams that issued from volcanic terrain rather than debris-flow deposits in relatively near-source fan deposits dominated by sediment gravity flow. Laccolithic doming, uplift, and tilting in the Never Summer Mountains near the Mount Richthofen stock, as well as the formation of volcanic edifices in the Never Summer Mountains and the Rabbit Ears Range during the late Oligocene and Miocene, significantly steepened stream gradients and greatly increased the erosive power and transport capacity of streams that transported large rock fragments and finer sediment eroded from volcanic and sedimentary sources and deposited them in the North Park Formation. Much of the material that makes up the rocks and sediments of the North Park Formation was derived from the erosion of volcanic, intrusive, and sedimentary rocks. Clasts in the North Park Formation were derived chiefly from the erosion of volcanic and intrusive igneous rocks of late Oligocene and Miocene age that range in composition from rhyolite to trachybasalt. These rocks are locally exposed along the west flank of the Never Summer Mountains, the north flank of the Rabbit Ears Range, and the east flank of the Park Range at and near Rabbit Ears Peak. The minor amount of igneous and metamorphic clasts of Proterozoic age in the North Park Formation are commonly composed of durable rock types that are resistant to both physical and chemical weathering. Many of these clasts may have been derived from the erosion of conglomerate and conglomeratic sandstone in the Coalmont Formation rather than from basement rocks currently at or near the ground surface in the Never Summer Mountains. Much of the sand and finer grained particles in the North Park Formation probably were derived from the erosion of sandstone, shale, and sandy claystone of the Coalmont Formation. Likewise, much of the abundant sand-sized quartz and feldspar in sand, sandstone, and pebbly sandstone of the North Park Formation probably was derived from the erosion of sandstone, conglomeratic sandstone, and conglomerate of the Coalmont Formation. Some of the fine sand, very fine sand, and silt in very fine grained sandstone and siltstone of the North Park Formation may be derived from the erosion of coeval eolian sand and loess in the Browns Park Formation that was transported across the Park Range by westerly or southwesterly winds.

Colorado↗
USGS2002

Historical and modern distributions of benthic foraminifers on the continental shelf of Monterey Bay, California

Historical (early 1930s) and modern samples provide a detailed account of the spatial distribution of benthic foraminifers on the continental shelf of Monterey Bay, California. Ten species among a total of 110 present dominated the 110 samples investigated in the historical study. A cluster analysis of the foraminiferal abundances in the historical study identified five assemblages: Inner Shelf, Middle Shelf, Outer Shelf, Southeastern Shelf and Southwestern Shelf. Specimens with calcareous tests were most prevalent in all the assemblages. A cluster analysis of the modern foraminiferal frequencies from 95 samples also defined five assemblages: Inner Shelf, Middle Shelf, Middle/Outer Shelf Arenaceous, Outer Shelf, and Southern Shelf. Although arenaceous taxa dominate much of the modern fauna, the spatial distribution of the modern assemblages is similar to that of the historical record when presumably unrecognized taxa are eliminated from the data. Both the historical and, to a greater degree, the modern foraminiferal assemblages exhibit a strong correlation with the sediment grain size distribution. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗
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↗
USGS1978

Origin of two clay-mineral facies of the Potomac Group (Cretaceous) in the Middle Atlantic States

Sedimentary clay that crops out in the coastal plains of New Jersey, Delaware, the part of Maryland north and east of Washington, B.C., and the northeast half of Washington, D.C., in the nonmarine Cretaceous Potomac Group is predominantly kaolinite and illite. In contrast, in part of southeastern Maryland, the southwest half of Washington, D.C., and most of eastern Virginia, Potomac Group clay is predominantly montmorillonite. Kaolinite and illite were probably derived by intense acid weathering of metamorphic and granitic rocks to the west during the Cretaceous and were deposited in a well-drained basin. Montmorillonite was most likely produced by deep weathering of a mainly granitic source. Poor drainage and alkaline surface- and ground-water conditions probably accompanied the production, transportation, deposition, and burial of the montmorillonite. Kaolinization of the montmorillonite is taking place now at the surface in northern Virginia.

Delaware, Maryland, New Jersey, Pennsylvania, Virg↗