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Holocene sediment, composed mainly of foram tests, occurs on the flanks of the Tanner and Cortes Banks, offshore southern California. The organic matter in this sediment differs in content and composition from the organic matter in nearby basins. Two sources of hydrocarbons are indicated: terrestrial plants and biodegraded or immature petroleum.
Middle Tertiary rift volcanism in a continental-rift valley in the Arabian-Nubian Shield was the first surface expression of active mantle convection beneath an axis that was to become the Red Sea. Investigation of the coastal plain of southwestern Saudi Arabia suggests that the rift valley was filled with basaltic and felsic to rhyolitic volcanic rocks (Ad Darb and Damad formations), cherty tuffaceous siltstones (Baid formation), and subordinate Nubian-type quartz sandstone (Ayyanah sandstone) between about 30 and 20 Ma ago. These rocks are named herein the Jizan group. At the same time, alkali-olivine basalt was erupted on the stable Precambrian craton at locations 100 to 200 km east of the rift valley axis. First-stage spreading of the Red Sea began about 20 Ma ago when diabasic dikes and gabbro and granophyre plutons (Tihamat Asir complex) of oceanic-tholeiitic parentage were intruded into the continental-rift deposits. The new oceanic crust was injected into a region of thinned continental crust. Because of thinning, the continental crust was extended and became fractured into a series of fault blocks. Crustal extension in the attenuated zone was accompanied by mafic and silicic volcanism producing a continental rift-valley tectonic environment. Fault blocks of the rift valley were initially rotated toward the Red Sea during the first-stage spreading episode. Inland from the continental rift, the thick continental crust was distended on long parallel fractures that were intruded by gabbroic to quartz syenitic magma to form continental dikes. This period of continental-margin extension was short lived, lasting perhaps only 1 or 2 Ma. The first-stage sea-floor spreading of the Red Sea continued until about 15 or 14 Ma ago at a half-spreading rate of about 2.2 cm/yr. Throughout early Tertiary time, the Arabian Shield erosion surface remained near sea level. First-stage uplift of the Red Sea Escarpment began during middle Miocene time, as evidenced by the coarse polymictic boulder conglomerate of the Bathan formation. Second-stage scarp uplift and second-stage sea-floor spreading followed during Pliocene, Pleistocene, and Holocene time.
The Cenozoic volcanic rocks of Saudi Arabia cover about 90,000 km 2 , one of the largest areas of alkali olivine basalt in the world. These volcanic rocks are in 13 separate fields near the eastern coast of the Red Sea and in the western Arabian Peninsula highlands from Syria southward to the Yemen Arab Republic. The initial phase of rifting of the Arabian Plate from the African Plate began as a wide zone of continental-crust extension manifested by basin and range topography. Freshwater lakes, northwest-trending marine gulfs, and alkali olivine basalt flows occupied these basins. Extensive dike swarms intruded parallel to the proto-Red Sea and marked the first phase of new mafic crust formed by volcanic processes. After a hiatus in volcanic activity, counterclockwise rotation of the Arabian Plate during middle Miocene time changed the stress pattern in the plate and a second phase of extrusion of alkali olivine basalt commenced along north-trending fractures. This stress pattern continues to influence Holocene volcanism. The earliest (pre-uplift) basalts to erupt on the Arabian Plate were predominantly undersaturated picrite and ankaramite, whereas those to erupt near the axis of the proto-Red Sea rift zone were tholeiite. The within-plate volcanic rocks evolved from picrite-ankaramite to alkali olivine basalt with minor volumes of fractionated, undersaturated felsic rocks. Continued crustal thinning and dike intrusion along the proto-Red Sea were accompanied by melting of the continental crust to produce silicic magma as part of a bimodal volcanic suite (tholeiite-rhyolite). These magmas were emplaced as dikes, sills, layered bodies, and flows that mark the early construction of the Red Sea crust. Second-phase lavas are predominantly fractionated hawaiites and alkali olivine basalts. Because undersaturated and oversaturated silicic magmas represent the second phase of activity, both fractional crystallization of the basaltic magma and melting of the crust are believed to have occurred. The historical record of volcanic activity in Saudi Arabia suggests that volcanism is dormant. The harrats should be evaluated for their potential as volcanic hazards and as sources of geothermal energy. The volcanic rocks are natural traps for groundwater; thus water resources for agriculture may be significant and should be investigated.
The Rio Grande region, New Mexico and Texas, includes most of the area east of the Rio Grande to the Sacramento Mountains. The Legion encompasses two large basins, the Jornada del Muerto and Tularosa basins, and the intervening San Andres Mountains. The altitude of the valley surfaces generally are from 600 to 1.500 meters. The mountain ranges generally have altitudes from 1,500 to 2,400 meters. About one-half the area is underlain by basin fill. Outcropping sedimentary rocks in the Rio Grande region range in age from Precambrian to Holocene. The oldest Precambrian rocks are metamorphosed and intruded by plutons. Paleozoic rocks are primarily carbonate rocks, with argillaceous beds, in the older Paleozoic units. Clastic and gypsum are in greater abundance in younger Paleozoic units of Pennsylvanian and Permian age. The Mesozoic rocks primarily are clastic rocks with some limestone. Cenozoic rocks consist of sequences of conglomerate, sandstone, mudstone, and siltstone derived from adjacent mountain masses, interbedded with basalt and andesite flows, and silicic tuffs. Volcanic activity continued into the Quaternary. Early to middle Tertiary volcanic and tectonic processes resulted in the implacement of plutonic bodies. Media considered to have potential for isolation of high-level radioactive waste include intrusive rocks, ash-flow tuff, and basaltic lava flows. Laharic and mudflow breccia and argillaceous beds also may be prospective host rocks. These and other rocks may be prospective media in areas where the unsaturated zone is thick. Quaternary faults are more common in the southern one-half of the region than in the northern one-half. Range-bounding faults with evidence of Quaternary movement extend northward into the central part of the region. Volcanic activity in the northern part of the region includes basalt flows of Quaternary age. Historical crustal uplift and seismicity have occurred in the vicinity of Socorro, New Mexico. The region is bordered on the west by an area with heat flow greater than 2.5 heat-flow units. A few measurements of this magnitude have been made within the region. Recharge to ground water in the Rio Grande region occurs in the higher altitudes where precipitation is greater, that is, in the San Andres and Sacramento Mountains and on the Chupadera Mesa. Ground-water flow from units west of the San Andres Mountains discharge to the Rio Grande. The ground-water flow unit of the Tularosa basin ultimately discharges to the Rio Grande or to wells in the vicinity of El Paso. Intermediate discharge points in the Tularosa basin include seepage to streams, springs, and evaporation to playas in the central part of the basin. Dissolved-solids concentations in ground water in the region generally are more than 1,000 milligrams per liter. The dissolved-solids concentrations in ground water in the recharge areas generally are less than 1,000 milligrams per liter. Dissolved-solids of concentrations ranging from 3,000 to 25,000 milligrams per liter are found in the ground water underlying the playa area in the central part of the Tularosa basin. The more than 43 mining districts in the region contain base metals and to a lesser extent, precious metals, in vein and replacement deposits. Four coal fields are located in the region.
The Barnwell low-level radioactive solid waste burial site is located in Barnwell County, South Carolina, 5 miles west of the city of Barnwell. Approximately 1,050 feet of stratified gravel, sand, silt, clay, and limestone, ranging in age from Late Cretaceous to Holocene, underlie the burial site. Ground water within the study area occurs under water table, semi-confined, and artesian conditions. Overland flow and most precipitation that recharges the ground-water system at the burial site is discharged to Marys Branch Creek. This creek originates as a spring about 3,000 feet south of the burial site and flows to the southwest into lower Three Runs. Lower Three Runs discharges into the Savannah River. Waste shipments to the site were reduced from 200,000 cubic feet per month for the period 1971 to 1979 to 100,000 cubic feet per month by October 1981. The wastes consist of both nonfuel cycle and nuclear fuel-cycle wastes. The standard trench dimensions at the burial site are 100 feet wide by 1,000 feet long and 22 feet deep. Trench bottoms are a minimum of 5 feet above the water table. Seven soil mapping units occur at the waste disposal facility. The three major soil types are all well drained and cover approximately 84 percent of the study area. (USGS)
This study characterizes the clay minerals in sediments associated with a plume of creosote-contaminated groundwater. The plume of contaminated groundwater near Pensacola, FL, is in shallow, permeable, Miocene to Holocene quartz sand and flows southward toward Pensacola Bay. Clay-size fractions were separated from 41 cores, chiefly split-spoon samples at 13 drill sites. The most striking feature of the chemical analyses of the clay fractions from uncontaminated site 2 and contaminated sites 4,5,6, and 7 is the variability of iron oxide (species in some samples as Fe2O3); total iron oxide abundance is lowest (2.5%) in uncontaminated sample 2-40, but is > 4.5% (4.5 to 8.5%) in the remaining assemblages. One feature suggesting interaction between the indigenous clays and the waste plume is the presence of nontronite-rich smectite. Nontronite commonly has been identified as the product of hydrothermal alteration and deep-sea weathering of submarine basalts; it is not a common constituent of Cenozoic Gulf Coast sediments. At the Pensacola site, relatively abundant nontronitic smectite is confined to contaminated sands or associated muds; it is least abundant or absent in sands and muds peripheral to the waste plume. The geochemistry of the waste plume, its substantial dissolved, (chiefly ferrous iron), mildly acidic (pH 5-6), and low redox composition, provides an environment similar to that previously determined for the low-temperature synthesis of nontronite. Data from clay-size fractions confirm conclusions that neoformed pyrite in some grain coatings occurs in an assemblage with excess iron over that required in the pyrite. Continuing studies to evaluate these tentative conclusions include: (1) chemical analysis of clay fractions from remaining sites to further examine the apparent relation between iron content and abundance of nontronitic smectite; (2) clay separation and analysis, and pore fluid extraction (squeezing or ultracentrifugation) and analysis from a continuous core through the mud lens to determine pore fluid composition (presence or absence of waste fluid), and character of associated clay minerals; and (3) clay separation and analysis in both permeable sands and the intervening mud lens that are clearly outside the limits of the waste plume to further document the effects of the plume. (See also W90-00022) (Lantz-PTT)
The Butte quadrangle, in the Northern Rocky Mountains of southwestern Montana, has had a long, productive, and colorful mining history. Butte, the city from which the quadrangle takes its name, is located in the most famous mining district of the quadrangle. This district, the Butte or Summit Valley district, has been described as the "richest hill on earth" and is one of the richest and most productive mining districts of the world. The quantity of metals produced from this district alone are far greater than the combined total of all commodities from all other mining districts of the quadrangle. However, many districts other than Butte have had significant production as compared to other mining districts of the Northern Rocky Mountains. The dollar value of production from the Butte district is more than $6 billion (Miller, 1973) and that of the combined total of production from the other districts in the quadrangle is more than $400 million. These values are based on actual metal prices at the time of production. The totals would be many times larger if converted to present day commodity prices. Mineral occurrence data for a total of 1111 mines, prospects, and mineral occurrences have been compiled for the Butte quadrangle. These mineralized sites are found throughout the quadrangle but most are concentrated in the major mining districts; 78 percent are clustered in 46 established mining districts and the remaining 22 percent are more widely scattered in 24 geographic areas (fig. 1). Only small areas of the quadrangle lack significant mines, prospects, or mineral occurrences. The locations of mines and prospects are shown on maps (pl. 1 and 2) and a brief description of each site is given in a table arranged by mining district or geographic area (table 1) (all tables are at end of report). This table gives a brief description of each district or area and details of each site within the district or area including site number, name and alternate name(s), location by latitude and longitude, commodities present, description of the site, and sources of data. Data for this report come from the U.S. Geological Survey Mineral Resource Data System (MRDS; this was formerly known as the Computerized Resource Information Bank (CRIB)), from many published and unpublished sources, and from geologic field work. The Butte quadrangle is in southwestern Montana and is bounded by latitudes 46° and 47° N. and longitudes 112° and 114° W. The city of Butte is near the southern edge and in the southeastern corner of the quadrangle. Helena, the state capital of Montana, is located on the eastern edge and Missoula is located near the northwestern corner of the quadrangle. Most of the area of the quadrangle is in Granite, Powell, Lewis and Clark, and Jefferson Counties and the remaining area includes parts of Missoula, Ravalli, Deer Lodge, and Silver Bow Counties. The quadrangle includes a number of major and minor mountain ranges separated by intermontane valleys. The continental divide trends nearly north-south through the eastern part of the quadrangle to a point near Butte, then trends generally east-west near the southern boundary of the quadrangle, west of Butte. East of the divide the drainages are tributary to the Missouri River and west of the divide the drainages are tributary to the Clark Fork, which heads in the vicinity of Butte. The geology of the Butte quadrangle is very complex. Sedimentary and igneous rocks range in age from Proterozoic to Tertiary. Most of the pre-Tertiary sedimentary rocks are structurally complex due to widespread faulting and folding. Due to thrust faulting, complete sequences of these sedimentary units are not generally present in the quadrangle and the thicknesses and lithologies are variable from one thrust plate to another. The oldest rocks in the quadrangle are sedimentary rocks of the Belt Supergroup of Middle Proterozoic age. They form very thick sequences, are exposed over a large percentage of the area of the quadrangle, and include formations of the lower, middle, and upper parts of the Belt. Individual formations are as much as 13,000 ft thick (C. A. Wallace, unpub. data) and the maximum thickness of the Belt Supergroup in the quadrangle may be similar to that of the entire sequence near Alberton, Montana, to the northwest of the Butte quadrangle where it exceeds 67,000 ft (Harrison, 1972). In many areas of the quadrangle these Precambrian rocks are overlain by thin to moderately thick sequences of Cambrian to Permian sedimentary rocks. The maximum thickness of the Paleozoic section is about 8,000 ft (C. A. Wallace, unpub. data). A relatively thick sequence of Mesozoic sedimentary rocks, predominantly Cretaceous in age, which is found mostly in the central part of the quadrangle, overlies the Paleozoic rocks. If complete, the Mesozoic sequence would total about 28,000 ft (C. A. Wallace, unpub. data). The Butte quadrangle is located in a structurally complex region. Most of the Butte quadrangle is in the southern part of the Montana Disturbed Belt, a tectonic belt in the Northern Rocky Mountains characterized by northwest-trending faults and intense deformation. An element of the Disturbed Belt, called the Sapphire Thrust System occupies most of the western two-thirds of the quadrangle. Sedimentary rocks of Cretaceous and older ages in the Sapphire Thrust System have been complexly folded and faulted. Plutonic rocks, which intrude the sedimentary units, and volcanic rocks of Cretaceous and Tertiary ages are widespread in the quadrangle. Most of these are post-thrusting but some may be pre- or syn-tectonic and involved in the thrusting and folding. Most of the mineral wealth in the quadrangle, in the form of hydrothermal ore deposits, is genetically related to Cretaceous granitic plutonism. Igneous activity decreased but continued into Tertiary time, at least until the Oligocene. In the Butte quadrangle the Cenozoic Era was important for normal faulting, volcanism, sedimentation, glaciation, and the formation of many important mineral deposits. Many normal faults were especially active during the Miocene and Pliocene and some were active into the Quaternary. Volcanic rocks of Eocene and Oligocene age cover large areas and are genetically related to several important mining districts. During Cenozoic time, thick accumulations of Tertiary basin-fill sediments, Pleistocene glacial till and outwash, and Holocene alluvium and colluvium were deposited. The Cenozoic was important for the formation of placer deposits valuable mainly for gold but some have produced important quantities of sapphires and tungsten. This map is part of a folio of maps of the Butte 1° x 2°quadrangle, Montana, prepared under the Conterminous United States Mineral Assessment Program (CUSMAP). Other maps to be published as part of this folio are a geologic map, geochemical maps, geophysical maps, maps of linear features and limonitic alteration interpreted from satellite and airborne radar data, and mineral resource assessment maps.
The hydrogeologic framework of the North Carolina Coastal Plain aquifer system consists of ten aquifers separated by nine confining units. From top to bottom the aquifers are: the surficial aquifer, Yorktown aquifer, Pungo River aquifer, Castle Hayne aquifer, Beaufort aquifer, Peedee aquifer, Black Creek aquifer, upper Cape Fear aquifer, lower Cape Fear aquifer, and the Lower Cretaceous aquifer. The uppermost aquifer (the surficial aquifer in most places) is a water-table aquifer and the bottom of the system is underlain by crystalline bedrock. The sedimentary deposits forming the aquifers are of Holocene to Cretaceous age and are composed mostly of sand with lesser amounts of gravel and limestone. Confining units between aquifers are composed primarily of clay and silt. The thickness of the aquifers ranges from zero along the Fall Line to more than 10,000 feet at Cape Hatteras. Prominent structural features are the increasing easterly homoclinal dip of the sediments and the Cape Fear arch, the axis of which trends in a southeast direction. The stratigraphic continuity is determined from correlations of 161 geophysical logs along with data from drillers' and geologists' logs. Aquifers were defined by means of these logs plus water-level and water-quality data and evidence of the continuity of pumping effects. Eighteen hydrogeologic sections depict the correlation of these aquifers throughout the Coastal Plain.
A complex, multilayered ground-water flow system exists in the Coastal Plain sediments of Texas. The Tertiary and Quaternary clastic deposits have an areal extent of 114,000 square miles onshore and in the Gulf of Mexico. Two distinct aquifer systems are recognized within the sediments, which range in thickness from a few feet to more than 12,000 feet The older system--the Texas coastal uplands aquifer system-consists of four aquifers and two confining units in the Claiborne and Wilcox Groups. It is underlain by the practically impermeable Midway confining unit or by the top of the geopressured zone. It is overlain by the nearly impermeable Vicksburg-Jackson confining unit, which separates it from the younger coastal lowlands aquifer system. The coastal lowlands aquifer system consists of five permeable zones and two confining units that range in age from Oligocene to Holocene. The hydrogeologic units of both systems are exposed in bands that parallel the coastline. The units dip and thicken toward the Gulf. Quality of water in the aquifer systems is highly variable, with dissolved solids ranging from less than 500 to 150,000 milligrams per liter. Substantial withdrawal from the aquifer systems began in the early 1900's and increased nearly continuously into the 1970's. The increase in withdrawal was relatively rapid from about 1940 to 1970. Adverse hydrologic effects, such as saltwater encroachment in coastal areas, land-surface subsidence in the Houston-Galveston area, and long-term dewatering in the Whiter Garden area, were among some of the factors that caused pumping increases to slow or to cease in the 1970's and 1980's. Ground-water withdrawals in the study area in 1980 were about 1.7 billion gallons per day. Nearly all of the withdrawal was from four units: Permeable zones A, B, and C of Miocene age and younger, and the lower Claiborae-upper Wilcox aquifer. Ground-water levels have declined hundreds of feet in the intensively pumped areas of Houston-Galveston, Kingsville, Winter Garden, and Lufkin-Nacogdoches. Water-level declines have caused inelastic compaction of clays which, in turn, has resulted in land-surface subsidence of more than one foot in an area of about 2,000 square miles. Maximum subsidence of nearly 10 feet occurs in the Pasadena area east of Houston. A three-dimensional, variable-density digital model was developed to simulate predevelopment and transient flow in the aquifer systems. The modeled area is larger than the study area, and includes adjacent parts of Louisiana and Mexico. The transient model calibration period was from 1910 (predevelopment) to 1982. Model-generated head distributions, water-level hydrographs, and land-surface subsidence were matched to measured data in selected, intensively pumped areas. For the study area, mean horizontal hydraulic conductivity in the calibrated model ranges from 10 feet per day for the middle Wilcox aquifer to 25 feet per day for permeable zone A. Mean transmissivity ranges from about 4,600 feet squared per day for the middle Claiborne aquifer to about 10,400 feet squared per day for permeable zone D. Mean vertical hydraulic conductivity ranges from 1.1x10 -5 feet per day for the Vicksburg-Jackson confining unit, to 3.8x10 -3 feet per day for permeable zone A. Mean values of calibrated storage coefficient range from 52x10 -4 for the middle Claiborne aquifer to 1.7x10 -3 for the middle Wilcox aquifer and permeable zone C. Calibrated inelastic specific storage values for clay beds in permeable zones A, B, and C in the Houston-Galveston area are 8.5x10 -5 , 8.0x10 -5 , and 8.0x10 -6 feet -1 , respectively. These values are 85, 80, and 8 times greater than the estimated elastic specific storage value for the clays in permeable zones A, B, and C, respectively. Recharge rates were mapped for predevelopment conditions as determined from a steady-state model calibration. A maximum rate of 3 inches per year was simulated in small areas, and the average rate for the study area was 034 inch per year. Total simulated recharge was 85 million cubic feet per day in the outcrop area. Recharge was equal to discharge in outcrop areas (79 million cubic feet per day) plus net lateral flow out of the study area (6 million cubic feet per day). Rates of inflow and outflow to the ground-water system have nearly tripled from predevelopment to 1982 (85 to 276 million cubic feet per day) based on model simulation. Withdrawal of 231 million cubic feet per day was supplied principally by an increase in outcrop recharge and, to a lesser extent, from a decrease in natural discharge and release of water from storage in aquifers and compacting clay beds. The average simulated 1982 recharge rate for the study area was 0.52 inch per year, with a maximum simulated rate of 6 inches per year in Jackson and Wharton Counties. Because withdrawal has caused problems such as saltwater intrusion, land-surface subsidence, and aquifer dewatering, the Texas Department of Water Resources has projected that ground-water use will decline substantially in most of the study area by the year 2030. Some areas remain favorable for development of additional ground-water supplies. Pumping from older units that are farther inland and in areas where potential recharge is greater will minimize adverse hydrologic effects.
The Gulf Coast Regional Aquifer-System Analysis includes all major aquifer systems in Cenozoic deposits in the Gulf Coastal Plain in the States of Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, Tennessee, Texas, and small areas in Alabama and Florida (western panhandle area), an area of about 290,000 square miles. The Gulf Coast geosyncline and the Mississippi embayment were the major depocenters for the Tertiary and Quaternary deposits that form the framework for the aquifer systems. FoiiDation of the Gulf Coast geosyncline and the Mississippi embayment began with downwarping and downfaulting at the end of the Paleozoic Era. Sedimentation caused the geosyncline to continue to subside throughout Mesozoic and Cenozoic time. During the Late Cretaceous, at the close of the Mesozoic Era, the sea advanced northward and eventually inundated the Mississippi embayment. Marine cycles persisted throughout the Paleocene and Eocene Epochs of the Tertiary Period, as the sea alternately advanced and retreated over the Mississippi embayment. The resulting sediments form a series of dense marine clays separated by terrigenous sands. The Gulf Coast geosyncline remained submerged during marine regressions in the embayment. After withdrawal of the last Tertiary sea from the Mississippi embayment at the end of the Eocene Epoch, deposition continued along the Gulf Coastal Plain under a shifting variety of nonmarine, marine, near-marine, and deltaic environments. Deposition resumed in the Mississippi embayment during the Quaternary with glacially related terraces and aggradation of streams. Fluvial deposition continues. Structural features in the Gulf Coastal Plain and Mississippi embayment significantly affected Cenozoic deposition. The Desha basin, for example, is a pronounced Tertiary synclinal depocenter in southeastern Arkansas. Three large uplifts are approximately aligned along the latitude of the northern boundary of Louisiana. These are, from west to east, the Sabine, Monroe, and Jackson uplifts. A belt of three major fault zones, the Luling-Mexia-Talco, Arkansas, and Pickens-Gilbertown, generally follows the strike of sediments across the Coastal Plain and more or less forms the northern updip extent of the Gulf Coast geosyncline. An alternating series of gentle synclines and anticlines is oriented perpendicular to the coastline along the Gulf Coast in Texas. Beginning at the southwestern end, these are the Rio Grande embayment, San Marcos arch, Houston embayment, and Sabine arch. The Wiggins anticline is oriented approximately along strike of the sediments in southern Mississippi. Salt domes are numerous in the Gulf Coastal Plain and may penetrate thousands of feet of sediments. Although the degree of salt intrusion can be very great, disruption of adjacent strata is limited to the vicinity of the dome. The physiography of the Gulf Coastal Plain is a direct result of the nature of the strata at land surface and physical forces that act upon them. Different terrains typify the lithologies that underlie them. The sands and clays that are the predominant rock types each produce characteristic geomorphologic patterns; sands tend to produce ridges, and clays produce topographic lows. Although Cenozoic deposits are not uniformly differentiated, interstate correlations of major Paleocene and Eocene units are generally established throughout the area. Younger deposits are not as well differentiated. Some stratigraphic designations made at surface exposures cannot be extended into the sub-surface, and the scarcity of distinct geologic horizons has hampered differentiation on a regional scale. The complexities of facies development in Oligocene and younger coastal deposits preclude the development of extensive recognizable horizons needed for stratigraphic applications. Coastal deposits are a heterogeneous assemblage of deltaic, lagoonal, lacustrine, palustrine, eolian, and fluvial clastic facies and local calcareous reef facies. Even major time boundaries, as between geologic series, are not fully resolved. Surficial Quaternary deposits overlie the truncated subcrops of Tertiary strata and generally are distinguishable, although some contacts between Pleistocene and underlying Pliocene deposits have been a ?lstoncal source of controversy. Glacially related terraces are characteristic of the Pleistocene Epoch, and alluvium of aggrading streams typifies the Holocene.
The average number of archeologic sites along the Colorado River in eastern Grand Canyon between River Miles 65-72 exceeds 12 km -1 ; the largest concentration from Glen Canyon Dam to the mouth of Grand Canyon. The sites are mostly of Anasazi affiliation, dating from the Pueblo Ito Pueblo II periods (A.D. 800-1200), although older sites of Basketmaker II affinity (about 200 B.C. to A.D. 400) and younger sites of Native American and Anglo affiliation are also present. All of the sites are closely associated with late-Holocene alluvial, debris-flow, and eolian deposits that accumulated in the river corridor during the past 2,500 years. The majority of sites occur on or beneath the surface of ancient alluvial deposits of the Colorado River, which form distinctive high terraces. Lateral shifts of the river extensively eroded these deposits and associated archeologic sites twice in prehistoric times, between A.D.300700 and between A.D. 1200-1400. In late historic times, numerous sites have been damaged or destroyed by erosion, which has accelerated since 1965-73. The daily operation of Glen Canyon Dam probably did not cause accelerated erosion in eastern Grand Canyon, although the presence of the dam indirectly effects erosion. Generally, sites are eroded by arroyo cutting in the short, ephemeral streams that drain the terraces of the river corridor. These streams are small; 90 percent have catchment area less than 20,000-30,000 m 2 and channel length of less than 300-400 m. Driven by excessive rainfall, arroyo cutting deepens, widens, and expands the channel system. The extent of arroyo cutting is related to past and present depositional levels of the river, which are local baselevels of erosion. The post-dam level is 3-4 m below the lowest pre-dam level; this decrease resulted from elimination of the annual flood and a six-fold reduction of sediment load. Eighty percent of tributary streams end above or on the post-dam depositional level, but during large runoff the channels are free to extend upslope as well as downslope toward the river. These channels will eventually extend downslope to the river, where the channel gradient will be lowered 3-4 m. Arroyo cutting will be intensified until channel gradients adjust to the post-dam baselevel.
The sea-floor of a dumpsite area offshore New York and New Jersey (Deep-water dumpsite 106) was studied using detailed bathymetry, sidescan-sonar images, subbottom profiles, bottom photographs, and bottom-sediment samples. These data show that this continental rise area contains deposits of submarine landslides and pathways of sediment gravity flows. Images of the sea floor obtained with a deep-towed high-resolution sidescan sonar system show offshore-trending furrowed surfaces over parts of the area. If such furrows are old, one might expect them to have been obliterated by sediment resuspension and redeposition due to the mostly gentle contour-parallel bottom currents that are measured in the present day. While most of the sea-floor features were probably formed during Pleistocene or early Holocene (glacial or early post-glacial) times, our information suggests that vigorous present-day episodes of offshore-directed transport may continue to occur, at unknown intervals.
Surficial deposits on northern Adak Island, Alaska include a variety of volcanic, glacial, eolian, and beach sediments. These deposits are the primary water-bearing units on the island and their distri- bution is shown on the accompanying surficial geologic map. An extensive sequence of volcanic debris-flow deposits (lahars) was identified on the eastern slope of Mount Moffett. The sedimentary characteristics of the lahar deposits indicate that they are related to volcanic eruptions of Mount Moffett and are evidence for Holocene volcanic activity at this volcano. Similar lahar deposits also are present on the southern slopes of Mount Adagdak. The surficial geologic map units described in the report are a basis for island-wide assess- ments of ground-water conditions, aquifer proper- ties, and general hydrogeologic conditions, and will be useful for determining the availability of potential construction materials.
Introduction A series of short piston cores (< 2m) were taken from eleven stations in Florida Bay in May, 1994 by researchers from the U.S. Geological Survey (St. Petersburg, FL., Woods Hole, MA., and Denver CO.) in cooperation with South Florida Water Management District, and the Everglades National Park, and the National Oceanic and Atmospheric Administration (NOAA). Core 6A from Bob Allen Keys (25° 1.391” N, 80°39.41” W) penetrated 172 cm of Holocene sediments in 0.6 m of water on a grass covered mud bank, approximately 1.75 miles (2.82 km) east of the water monitoring station on the southern end of the Bob Allen Keys. Core 6A was sampled for particle size, insoluble residue, water content, loss on ignition, Pb 210 , Rasup>222, and paleontologic analyses. Here we present the results of the preliminary paleontologic analyses of the biotic components from core #6A. The Everglades/Florida Bay ecosystem has formed over the last 5000 years at the southern tip of peninsular Florida. Here it has been influenced by Atlantic, Caribbean and Gulf of Mexico waters, and by tropical and subtropical climatic regimes. This location ensures that over time the ecosystem has undergone climatic changes on both a seasonal and long term basis, and that it has been subjected to many major storms. Additionally, in the last century, the hydrologic regime of the region has been altered profoundly through construction of a canal system to control flooding in southern Florida. This system regulates the timing and amount of freshwater flow into Florida Bay. Recently, algal blooms, seagrass, and sponge die-offs, and declining numbers of shellfish, have been reported in Florida Bay; although it has been assumed that these changes have resulted from human alteration of freshwater flow into the bay, this assumption has not been rigorously tested. The research described here is part of a project designed to examine the history of the Everglades/Florida Bay ecosystem over the last 150 years and to test assumptions of cause and effect. The purpose of the project is two-fold; first, to determine the characteristics of the ecosystem prior to significant human-induced alteration, including the natural range of variation in the ecosystem. This information will establish a baseline for restoration of the system. Second, the project aims to establish the extent, range, and timing of changes to the ecosystem over the last 150 years, and to determine whether these changes correlate with human alteration of the environment, or meteorological patterns, such as precipitation and major storms, or a combination of factors.
This report summarizes data acquired from 1990 to 1994 for the gas-hydrate portion of the USGS project 'Permafrost and gas hydrate as possible sources of methane' of the USGS Global Change and Climate History program. The objective of this project has been to test the hypothesis that gas hydrate deposits of the Beaufort Sea continental shelf are destabilized by the ~10?C temperature increase that has resulted from the Holocene transgression of the Arctic Ocean. To test this idea we have selected an area off the north coast of Alaska centered on Harrison Bay. We have measured the concentration of methane in surficial sediments, in the water column when ice is present and absent, and in seasonal sea ice. Our results show that more methane is present in the water when ice is present than when ice is absent, and that methane is also present within the ice itself, often at higher concentrations than in the water. Thus the Beaufort Sea shelf of Alaska is a seasonal source of methane. The primary source of this methane has not yet been defined, but gas hydrate is a reasonable candidate.
An investigation of the geohydrology and of the potential for water-supply development on several of the Boston Harbor Islands, eastern Massachusetts, was conducted to evaluate the possibility of developing a permanent small-capacity water supply to support recreational activities, such as camping, hiking, and swimming. The Boston Harbor Islands, including Bumkin, Gallops, Georges, Grape, Lovell, and Peddocks Islands are part of a larger group of glacially deposited drumlins, which are composed of thick, dense, homogeneous till in their core that are overlain by a thin layer of stratified-beach deposits. The surficial materials over-lie a weathered zone of the metasedimentary Cambridge Argillite in the Boston Harbor area and were deposited by continental ice sheets that covered New England twice during the late Pleistocene Epoch, and by near-shore processes in the Holocene Epoch. The thickness of these materials range from less than 1 to about 300 feet where present. The till was deposited by glacial ice and is characterized as an unsorted matrix of sand, silt, and clay with variable amounts of stones and large boulders. The stratified deposits primarily consist of sorted and layered sand and gravel that accumulated and formed the beaches and tombolos of the harbor islands. These deposits overlie the till at altitudes generally less than 10 feet above sea level. A cross-sectional, ground-water-flow model was developed to estimate depth to the water table for a hypothetical drumlin-island flow system, which was assumed to be representative of the drumlin islands in Boston Harbor. Areas were identified in each island flow system with the greatest potential for small-capacity water-supply development based on the model-calculated depth to water and surficial geology of the islands. Model-calculated depth to water estimates were used because of the lack of available hydrologic data for the islands. Model results indicate that the simulated depth to water is less than 20 feet within 240 feet from the shore of the hypothetical drumlin-island flow system. This area on the topographic maps of the six Boston Harbor Islands roughly coincides with the high transmissivity zones of stratified-beach deposits and weathered till on the lower slopes of the drumlins where ground-water discharge and surface and subsurface runoff occurs.
The city of San Fernando sits atop a structurally complex, sedimentologically diverse, and tectonically evolving late Tertiary-Quaternary basin situated within the Transverse Ranges of southern California. The surrounding San Fernando Valley (SFV) contains the headwaters of the Los Angeles River and its tributaries. Prior to the advent of flood control, the valley floor was composed of active alluvial fans and floodplains. Seasonal streams emanating from Pacoima and Big Tujunga Canyons drain the complex western San Gabriel Mountains and deposit coarse, highly permeable alluvium that contains generally high-quality ground water. The more shallow western part derives mainly from Tertiary and pre-Tertiary sedimentary rocks, and is underlain by less permeable, fine-grained deposits containing persistent shallow ground water and poorer water quality. Home of the 1971 San Fernando and the 1994 Northridge earthquakes, the SFV experienced near-record levels of strong ground motion in 1994 that caused widespread damage from strong shaking and ground failure. A new map of late Quaternary deposits of the San Fernando area shows that the SFV is a structural trough that has been filled from the sides, with the major source of sediment being large drainages in the San Gabriel Mountains. Deposition on the major alluvial fan of Tujunga Wash and Pacoima Wash, which issues from the San Gabriel Mountains, and on smaller fans, has been influenced by ongoing compressional tectonics in the valley. Late Pleistocene deposits have been cut by active faults and warped over growing folds. Holocene alluvial fans are locally ponded behind active uplifts. The resulting complex pattern of deposits has a major effect on liquefaction hazards. Young sandy sediments generally are highly susceptible to liquefaction where they are saturated, but the distribution of young deposits, their grain size characteristics, and the level of ground water all are complexly dependent on the tectonics of the valley. The San Fernando area lies on the southern slopes of the San Gabriel Mountains. The basement rocks here include high-grade metamorphic rocks of Precambrian age. The mountains are largely composed of crystalline basement that includes the Pelona Scist of probable Mesozoic age that has been overthrust by Precambrian gneisses; the gneisses were subsequently intruded by Mesozoic plutons prior to overthrusting along the latest Cretaceous Vincent thrust. Gneisses of somewhat variable composition and possibly varying ages are found in four terranes, but not all are in contact with Pelona Schist. Large tracts of Precambrian (1.2 billion years old) andesine anorthosite are intrusive into 1.7 billion year-old Mendenhall gneiss, and are found in the western part of the San Gabriels. Mixed with these are younger marble, limestone, and schist of possible Paleozoic age found in association with plutons along the southern margin of the range. The older rocks are intruded by diorite, quartz diorite, and granodiorite of Jurassic age. Also present are siliceous sedimentary rocks of Jurassic age. A thick section of Tertiary sedimentary and volcanic rocks overlie these units. The sediments located south of the San Gabriel Fault are totally different in character from those on the northern range flank, and mostly resemble the western Transverse Ranges due to their deposition in the southeastern Ventura basin; approximately 3,000 m of these sediments are exposed north and west of the city of San Fernando in the Tujunga syncline. Some of the Tertiary rocks are Paleocene and Eocene in age, but the bulk of these rocks are Oligocene and Miocene in age. The Vasquez and Sespe Formations of basal basaltic volcanic and sandstone are Oligocene and lower Miocene in age. These are overlain by clastic rocks of Tick Canyon and Mint Canyon Formations of middle to late Miocene age. Above these rocks are the Castaic, Modelo, and Santa Margarita Formations of fossiliferous marine shale, sand
A continuous core was recovered from a 961-foot- deep stratigraphic corehole at Robins Point, located at the southeastern tip of the Gunpowder Neck Peninsula, Harford County, Maryland. A 2-inch- diameter ground-water-quality observation well was installed with the screen set at a depth of 392 to 402 feet (ft). Geophysical logs obtained from thecorehole include: natural gamma, multipoint normal resistivity (16-inch and 64-inch), 4-ft-guard focused resistivity, acoustic (sonic) velocity, and caliper. Pollen analysis of 34 samples provided relativestratigraphic ages. Lithologies encountered in ascending order (surface elevation 4 ft above mean sea level), include: 72.4 ft of weatheredmetamorphic rock and saprolie, 711.4 ft of lower and upper Cretaceous fluvio-deltaic deposits, and 145.9 ft of Pleistocene and 31.3 ft of Holocene(?) fluvial and estuarine deposits. Aquifers and confining units identified include, in descending order: 41.8 ft of surficial aquifer, 90.9 ft of upper paleochannel confining unit, 28.8 ft of paleochannel confined aquifer, 15.7 ft of lower paleochannel confining unit, 123.7 ft of Upper Patapsco aquifer, 44.6 ft of Upper Patapsco confining unit, 92.8 ft of Middle Patapsco aquifer, 57.3 ft of Lower Patapsco confining unit, 151.7 ft of Lower Patapsco aquifer, 115.4 ft of Potomac confining unit, 126.4 ft of Patuxent aquifer, an aquifer of 23.4 ft of saprolite, and 48.7 ft of weathered-rock/saprolite confining unit.