SEARCH · Geology Reports

Results for “Atlantic Geology”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

817 records · Page 46Linked to original sources

USGS1973

Geology and water resources of the Wharton Tract and the Mullica River basin in southern New Jersey

The Wharton Tract is an area of 150 square miles located in the Mullica River basin in southern New Jersey's Pine Barrens region. The tract is a relatively flat, low-lying, generally sandy area containing shallowly incised streams. The larger streams are commonly bordered by swamps. The tract was purchased by the State primarily as a water-supply preserve, but also for conservation and recreational purposes. Mean streamflow at three continuous record gaging stations in the Wharton Tract is: Mullica River near Batsto (46.1-square mile drainage area), 6 mgd (million gallons per day); Batsto River at Batsto (70.5-square mile drainage area), 81 mgd; Oswego River at Harrisville (64.0-square mile drainage area), 55 mgd. Thus mean discharge from this 180.6-sq mi (square mile) area is 202 mgd or 1.12 mgd per sq mi. Principal aquifers in the Wharton Tract and Mullic River basin are in the Kirkwood Formation of middle Miocene age, Cohansey Sand of Miocene(?) and Pliocene(?) age, and in overlying hydraulically connected deposits of Quaternary age. The Kirkwood Formation is composed of sand, silt, and clay. Diverse lithologies represent deposition in different environments such as nearshore marine, barrier bar, lagoonal, estuarine, and tidal marsh. Hydraulic characteristics of the Kirkwood in the Mullica River basin are virtually unknown. Most Kirkwood aquifers in the basin are believed to be hydraulically connected with the overlying Cohansey Sand. The Cohansey Sand is dominantly a quartz sand containing minor amounts of pebbly sand, silty sand, and interbedded clay. Almost all of the Wharton Tract and most of the Mullica River basin lie within the sandier area of the Cohansey, which contains approximately 75 percent sand beds and 25 percent silt and clay beds. Data from test drilling show that the upper 100 feet of sediments in the Wharton Tract contain about 93 percent sand beds, 3.5 percent clay beds, and 3.5 percent silt beds. The Cohansey in the Tract ranges in thickness from less than 50 feet to about 180 feet; the average thickness is about 125 feet. The Cohansey Sand is believed to be, in overall aspect, a deltaic deposit. It contains materials that were deposited locally in nearshore-marine, fluvial, estuarine, lagoonal, and beach environments. The hydraulic conductivity of Cohansey aquifer material ranges from about 90 to 250 feet per day (660 to 1,885 gallons per day per square foot) in southern New Jersey. One aquifer test in the Wharton Tract gives an average value of 130 feet per day (1,000 gallons per day per square foot). The transmissivity of the Cohansey Sand aquifer through most of the Wharton Tract is typically between 10,000 and 20,000 square feet per day (75,000 and 150,000 gallons per day per foot). Deposits of Quaternary age form a discontinuous veneer lying unconformably above the Cohansey Sand. The most important hydrologic function of most of these deposits is to absorb precipitation and transmit the water to the underlying Cohansey Sand. Thicker deposits of estuarine sand and clay of the Cape May Formation fill a channel in the underlying Cohansey Sand along the lower reaches of the Mullica River. This channel deposit is 85 feet thick near Batsto. Ground water and surface water in the Mullica River basin are low in dissolved solids, generally less than 50 mg/1 (milligrams per liter). Iron concentrations are generally high, up to 49,000 micrograms per liter (49 mg/1) in ground water and up to 7,100 micrograms per liter (7.1 mg/1) in the streams. The water is acidic as indicated by typical pH values of from 4.5 to 6.5. Color of the surface water is commonly high, ranging from 3 - 150 platinum-cobalt units. After appropriate treatment these waters are acceptable for most uses. The Wharton Tract is well situated to support the growing water needs of nearby New Jersey communities. Maximum development of water can be achieved by conjunctive use of ground and surface water. During most of the year, some water would be withdrawn either directly from streams or from adjacent wells. During periods of low flow during summer or fall water would be pumped from wells farther from the stream~. From analysis of flow-duration curves it is estimated that 70 mgd of water could be developed with minimal effect upon low flows in the half of the tract above the gaging stations on the Mullica and Batsto Rivers. The quantity available in the entire tract is greater, possibly in the order of 150 mgd. With augmentation of streamflow by pumping from ground water, it is likely that considerably more water could be safely used on a perennial basis. A possibility exists for multiple use of the water resources of the Mullica River through construction of an inexpensive tide barrier at the Garden State Parkway. This would create a fresh water lake in a State forest, park, and recreational area, which would also provide a flexible and economical water supply for much of the Atlantic coastal resort development.

New Jersey↗

USGS2013

Estimating irrigation water use in the humid eastern United States

Accurate accounting of irrigation water use is an important part of the U.S. Geological Survey National Water-Use Information Program and the WaterSMART initiative to help maintain sustainable water resources in the Nation. Irrigation water use in the humid eastern United States is not well characterized because of inadequate reporting and wide variability associated with climate, soils, crops, and farming practices. To better understand irrigation water use in the eastern United States, two types of predictive models were developed and compared by using metered irrigation water-use data for corn, cotton, peanut, and soybean crops in Georgia and turf farms in Rhode Island. Reliable metered irrigation data were limited to these areas. The first predictive model that was developed uses logistic regression to predict the occurrence of irrigation on the basis of antecedent climate conditions. Logistic regression equations were developed for corn, cotton, peanut, and soybean crops by using weekly irrigation water-use data from 36 metered sites in Georgia in 2009 and 2010 and turf farms in Rhode Island from 2000 to 2004. For the weeks when irrigation was predicted to take place, the irrigation water-use volume was estimated by multiplying the average metered irrigation application rate by the irrigated acreage for a given crop. The second predictive model that was developed is a crop-water-demand model that uses a daily soil water balance to estimate the water needs of a crop on a given day based on climate, soil, and plant properties. Crop-water-demand models were developed independently of reported irrigation water-use practices and relied on knowledge of plant properties that are available in the literature. Both modeling approaches require accurate accounting of irrigated area and crop type to estimate total irrigation water use. Water-use estimates from both modeling methods were compared to the metered irrigation data from Rhode Island and Georgia that were used to develop the models as well as two independent validation datasets from Georgia and Virginia that were not used in model development. Irrigation water-use estimates from the logistic regression method more closely matched mean reported irrigation rates than estimates from the crop-water-demand model when compared to the irrigation data used to develop the equations. The root mean squared errors (RMSEs) for the logistic regression estimates of mean annual irrigation ranged from 0.3 to 2.0 inches (in.) for the five crop types; RMSEs for the crop-water-demand models ranged from 1.4 to 3.9 in. However, when the models were applied and compared to the independent validation datasets from southwest Georgia from 2010, and from Virginia from 1999 to 2007, the crop-water-demand model estimates were as good as or better at predicting the mean irrigation volume than the logistic regression models for most crop types. RMSEs for logistic regression estimates of mean annual irrigation ranged from 1.0 to 7.0 in. for validation data from Georgia and from 1.8 to 4.9 in. for validation data from Virginia; RMSEs for crop-water-demand model estimates ranged from 2.1 to 5.8 in. for Georgia data and from 2.0 to 3.9 in. for Virginia data. In general, regression-based models performed better in areas that had quality daily or weekly irrigation data from which the regression equations were developed; however, the regression models were less reliable than the crop-water-demand models when applied outside the area for which they were developed. In most eastern coastal states that do not have quality irrigation data, the crop-water-demand model can be used more reliably. The development of predictive models of irrigation water use in this study was hindered by a lack of quality irrigation data. Many mid-Atlantic and New England states do not require irrigation water use to be reported. A survey of irrigation data from 14 eastern coastal states from Maine to Georgia indicated that, with the exception of the data in Georgia, irrigation data in the states that do require reporting commonly did not contain requisite ancillary information such as irrigated area or crop type, lacked precision, or were at an aggregated temporal scale making them unsuitable for use in the development of predictive models. Confidence in the reliability of either modeling method is affected by uncertainty in the reported data from which the models were developed or validated. Only through additional collection of quality data and further study can the accuracy and uncertainty of irrigation water-use estimates be improved in the humid eastern United States.

Eastern United States↗

USGS1975

Sediments, structural framework, petroleum potential, environmental conditions, and operational considerations of the United States South Atlantic Outer Continental Shelf

The area designated for possible oil and gas lease sale in Bureau of Land Management memorandum 3310 #43 (722) and referred to therein as part of the United States South Atlantic Outer Continental Shelf (OCS) contains about 98,000 square kilometres of the continental margin seaward of the 3 mile offshore limit and within the 600 metre isobath. The designated area, offshore of North Carolina, South Carolina, Georgia, and Florida, encompasses parts of three physiographic provinces: the Continental Shelf, the Florida-Hatteras Slope, and the Blake Plateau. The structural framework of the U.3. South Atlantic region is dominated by the Southeast Georgia Embayment --an east-plunging depression recessed into the Atlantic Coastal Plain and shelf between Cape Fear, North Carolina and Jacksonville, Florida. The embayment is bounded to the north by the Cape Fear Arch and to southeast by the Peninsular Arch. Refraction data indicate a minor basement(?) ridge beneath the outer shelf between 30° and 32°N at 80°W. Drill hole data also suggest a gentle fold or accretionary structure (reef?) off the east coast of Florida. Several other structural features have been identified by refraction and reflection techniques and drilling. These are the Yamacraw Uplift, Burton High, Stone Arch, and the Suwannee Channel. Gravity and magnetic anomalies within the area probably result from emplacement of magma bodies along linear features representing fundamental crustal boundaries. Of these anomalies, the most prominent, is a segment of the East Coast Magnetic Anomaly which crosses the coast at Brunswick, Georgia. This anomaly has been interpreted as representing an ancient continental boundary where two formerly separate continental plates collided and were welded together. There may be as much as 5,000 m of sedimentary rocks in the Southeast Georgia Embayment out to the 600 m isobath. Basement rocks beneath the Southeast Georgia Embayment are expected to be similar to those exposed in the Appalachian Piedmont province. Triassic deposits are likely to exist beneath the inner Continental Shelf, and probably consist of nonmarine arkosic sandstones, shales, basalt flows, and diabase intrusions deposited in relatively narrow northeast-trending grabens. Jurassic marine carbonates in the Bahamas grade northward to carbonates, shales, sand, and arkose in North Carolina. Salt may be present in the basal Jurassic section in the Southeast Georgia Embayment. Up to 4,000 m of Jurassic-Lower Cretaceous rocks are expected out to the 600 m water depth. Lower Cretaceous rocks in southern Florida are shallow-water marine limestone and dolomites with beds of anhydrite. In coastal North Carolina the Lower Cretaceous is a marine section made up of shales, sand, and sandy limestone. The Upper Cretaceous is composed almost entirely of marine carbonates in southern Florida grading northward to nonmarine to marginal marine, sandstones and shales with minor amounts of carbonates. In general, Upper Cretaceous rocks will probably maintain a fairly constant thickness (600 m) on the Continental Shelf and grade downdip from terrigeneous sands and shales to more marine chalks, limestones, and dolomites. The Cenozoic rocks are predominantly shallow-water marine carbonates in Florida grading northward into a marginal marine to marine clastic facies composed of sands, marls, and limestones. The offshore Cenozoic section is expected to range in thickness from 600 to 1100 m.

Florida, Georgia, South Carolina↗

USGS1997

Transgressive systems tract development and incised-valley fills within a quaternary estuary-shelf system: Virginia inner shelf, USA

High-frequency Quaternary glacioeustasy resulted in the incision of six moderate- to high-relief fluvial erosion surfaces beneath the Virginia inner shelf and coastal zone along the updip edges of the Atlantic continental margin. Fluvial valleys up to 5 km wide, with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level, cut through underlying Pleistocene and Mio-Pliocene strata in response to drops in baselevel on the order of 100 m. Fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments (ancestral generations of the Chesapeake Bay). Complex incised-valley fill successions are bounded by, or contain, up to four stacked erosional surfaces (basal fluvial erosion surface, bay ravinement, tidal ravinement, and ebb-flood channel-base diastem) in vertical succession. These surfaces, combined with the transgressive oceanic ravinement that generally caps incised-valley fills, control the lateral and vertical development of intervening seismic facies (depositional systems). Transgressive stratigraphy characterizes the Quaternary section beneath the Virginia inner shelf where six depositional sequences (Sequences I-VI) are identified. Depositional sequences consist primarily of estuarine depositional systems (subjacent to the transgressive oceanic ravinement) and shoreface-shelf depositional systems; highstand systems tract coastal systems are thinly developed. The Quaternary section can be broadly subdivided into two parts. The upper part contains sequences consisting predominantly of inner shelf facies, whereas sequences in the lower part of the section consist predominantly of estuarine facies. Three styles of sequence preservation are identified. Style 1, represented by Sequences VI and V, is characterized by large estuarine systems (ancestral generations of the Chesapeake Bay) that are up to 40 m thick, have hemicylindrical wedge geometries, and occur within large, coast-oblique trending depressions (paleo-estuaries). Style 1 is dominated by fluvial through estuary-mouth depositional systems (Seismic Facies 1-4). Style 2 sequence preservation, represented by Sequences III and II, is dominantly an inner shelf and shoreface succession with a seaward-thickening tabular wedge geometry that does not exceed 15 m in thickness. These shoreface and inner shelf depositional systems of the upper transgressive systems tract (Seismic Facies 9) and highstand systems tract (Seismic Facies 7 and 11) are not associated with paleo-estuaries. Style 3 sequence preservation is represented by Sequence 1, the Holocene Sequence. It consists of lower transgressive systems tract fluvial-estuarine, lagoonal, and tidal-inlet fill deposits (Seismic Facies 1-6, and 8) overlain by upper transgressive systems tract shelf and shoreface sands (Seismic Facies 9). Style 3 has a crenulated wedge geometry, and is thickest beneath and seaward of the modern Chesapeake Bay mouth. It thins northward and landward onto Late Pleistocene interfluvial highs on the basinward side of the southern Delmarva Peninsula.

Marine Geology↗

USGS1997

Ground Water Atlas of the United States: Segment 11, Delaware, Maryland, New Jersey, North Carolina, Pennsylvania, Virginia, West Virginia

Segment 11 consists of the States of Delaware, Maryland, New Jersey, North Carolina, West Virginia, and the Commonwealths of Pennsylvania and Virginia. All but West Virginia border on the Atlantic Ocean or tidewater. Pennsylvania also borders on Lake Erie. Small parts of northwestern and north-central Pennsylvania drain to Lake Erie and Lake Ontario; the rest of the segment drains either to the Atlantic Ocean or the Gulf of Mexico. Major rivers include the Hudson, the Delaware, the Susquehanna, the Potomac, the Rappahannock, the James, the Chowan, the Neuse, the Tar, the Cape Fear, and the Yadkin-Peedee, all of which drain into the Atlantic Ocean, and the Ohio and its tributaries, which drain to the Gulf of Mexico. Although rivers are important sources of water supply for many cities, such as Trenton, N.J.; Philadelphia and Pittsburgh, Pa.; Baltimore, Md.; Washington, D.C.; Richmond, Va.; and Raleigh, N.C., one-fourth of the population, particularly the people who live on the Coastal Plain, depends on ground water for supply. Such cities as Camden, N.J.; Dover, Del.; Salisbury and Annapolis, Md.; Parkersburg and Weirton, W.Va.; Norfolk, Va.; and New Bern and Kinston, N.C., use ground water as a source of public supply. All the water in Segment 11 originates as precipitation. Average annual precipitation ranges from less than 36 inches in parts of Pennsylvania, Maryland, Virginia, and West Virginia to more than 80 inches in parts of southwestern North Carolina (fig. 1). In general, precipitation is greatest in mountainous areas (because water tends to condense from moisture-laden air masses as the air passes over the higher altitudes) and near the coast, where water vapor that has been evaporated from the ocean is picked up by onshore winds and falls as precipitation when it reaches the shoreline. Some of the precipitation returns to the atmosphere by evapotranspiration (evaporation plus transpiration by plants), but much of it either flows overland into streams as direct runoff or enters streams as base flow (discharge from one or more aquifers). The distribution of average annual runoff (fig. 2) is similar to the distribution of precipitation; that is, runoff is generally greatest where precipitation is greatest. Runoff rates range from more than 50 inches per year in parts of western North Carolina to less than 12 inches in parts of North Carolina, Virginia, and West Virginia. Parts of the seven following physiographic provinces are in Segment 11: the Coastal Plain, the Piedmont, the Blue Ridge, the New England, the Valley and Ridge, the Appalachian Plateaus, and the Central Lowland. The provinces generally trend northeastward (fig. 3). The northeastern terminus of the Blue Ridge Province is in south-central Pennsylvania, and the southwestern part of the New England Province, the Reading Prong, ends in east-central Pennsylvania. The topography, lithology, and water-bearing characteristics of the rocks that underlie the Blue Ridge Province and the Reading Prong are similar. Accordingly, for purposes of this study, the hydrology of the Reading Prong is discussed with that of the Blue Ridge Province. The Coastal Plain Province is a lowland that borders the Atlantic Ocean. The Coastal Plain is as much as 140 miles wide in North Carolina but narrows northeastward to New Jersey where it terminates in Segment 11 at the south shore of Raritan Bay. Although it is generally a flat, seaward-sloping lowland, this province has areas of moderately steep local relief, and its surface locally reaches altitudes of 350 feet in the southwestern part of the North Carolina Coastal Plain. The Coastal Plain mostly is underlain by semiconsolidated to unconsolidated sediments that consist of silt, clay, and sand, with some gravel and lignite. Some consolidated beds of limestone and sandstone are present. The Coastal Plain sediments range in age from Jurassic to Holocene and dip gently toward the ocean. The boundary between the Coastal Plain and the Piedmont Provinces is called the Fall Line (fig. 3) because falls and rapids commonly form where streams cross the contact between the consolidated rocks of the Piedmont (fig. 4) and the soft, semiconsolidated to unconsolidated sediments of the Coastal Plain. The increase in stream gradient at the Fall Line provided favorable locations for mills and other installations that harnessed water power during the early years of the Industrial Revolution, and on most major rivers, the Fall Line coincides with the head of navigation. The Piedmont Province is an area of varied topography that ranges from lowlands to peaks and ridges of moderate altitude and relief. The metamorphic and igneous rocks of this province range in age from Precambrian to Paleozoic and have been sheared, fractured, and folded. Included in this province, however, are sedimentary basins that formed along rifts in the Earth's crust and contain shale, sandstone, and conglomerate of early Mesozoic age, interbedded locally with basaltic lava flows and minor coal beds. The sedimentary rocks and basalt flows are intruded in places by diabase dikes and sills. The mountain belt of the Blue Ridge Province forms the northwestern margin of the Piedmont in most of Segment 11. This belt consists mostly of igneous and high-rank metamorphic rocks but also includes low-rank metamorphic rocks of late Precambrian age and small areas of sedimentary rocks of Early Cambrian age along its western margin. In this report, the Reading Prong of the New England Province, which is an upland that extends from east of the Susquehanna River in Pennsylvania northeastward into New Jersey (fig. 3), is treated as part of the Blue Ridge Province. Part of the Reading Prong in Pennsylvania and New Jersey and a small part of the Piedmont Province in northeastern New Jersey have been glaciated. Glacial deposits completely or partly fill some of the valleys, and the eroding action of the glacial ice removed some of the rock from the ridges. Thus, the glaciated parts of the province have a smoother topography and less relief than other parts. The Valley and Ridge Province is characterized by layered sedimentary rock that has been complexly folded and locally thrust faulted. As the result of repeated cycles of uplift and erosion, resistant layers of well-cemented sandstone and conglomerate form elongate mountain ridges and less resistant, easily eroded layers of limestone, dolomite, and shale form valleys. The rocks of the province range in age from Cambrian to Pennsylvanian. Parts of this province from central Pennsylvania into New Jersey have been glaciated, and glacial deposits fill or partially fill some of the valleys. The Appalachian Plateaus Province is underlain by rocks that are continuous with those of the Valley and Ridge Province, but in the Appalachian Plateaus the layered rocks are nearly flat-lying or gently tilted and warped, rather than being intensively folded and faulted. The boundary between the two provinces is a prominent southeast-facing scarp called the Allegheny Front in most of the northern part of Segment 11 (fig_ 5) and the Cumberland Escarpment in the southern part. The scarp faces the Valley and Ridge Province, and throughout most of the segment, the eastern edge of the Appalachian Plateaus Province is higher than the ridges in the Valley and Ridge. Like parts of the Reading Prong and the Valley and Ridge Province, the northern part of the Appalachian Plateaus Province in Pennsylvania has been glaciated. In the glaciated section, the surface is mantled by glacial drift, and the valleys are partly filled with glacial deposits. The northwestern corner of Segment 11 contains a small part of the Central Lowland Province. This flat lowland is underlain by gently dipping sedimentary rocks, some of which are the same geologic formations as those of the Appalachian Plateaus Province. The two provinces are separated by a northwest- facing scarp. Because of the small area of the Central Lowland Province within the segment and the similarity of aquifer properties with those of the glaciated part of the Appalachian Plateaus Province, the two provinces are discussed together in this report.

Delaware, Maryland, New Jersey, North Carolina, Pe↗

USGS1947

Minor floods of 1938 in the North Atlantic States

Five noteworthy floods occurred during 1938 in the North Atlantic States. The first flood was in January, the others were in June, July, August, and September. The floods of January, June, and August were relatively local events in Connecticut, New Jersey, and New York, respectively. The floods of July and September were widespread, reaching from New Jersey and New York to New Hampshire in generally coincident locations. The flood of September, the most severe, is described in appropriate detail in Water-Supply Paper 867; the others in this volume are in separate sections arranged chronologically. Extraordinary floods in Connecticut during January 1938 resulted from a critical combination of warm rainfall and virtual overnight melting of the accumulated snowfall of winter. Seven small streams in central and western Connecticut rose to levels on January 25 higher than those reached during the great floods of March 1936. Crest discharge of these streams approximated 100 second-feet per square mile. Ice cover was loosened and sent downstream in recurrent jams. In general, the larger rivers did not attain extraordinary stages. The Connecticut River at Hartford peaked at a stage 3.6 feet above ordinary flood level. Direct damage by the flood was relatively small. Snow cover on January 20, at the beginning of the rains, varied from 0.25 inch along the coast to 2.75 inches water equivalent in the northern part of the State. Precipitation between January 24 and 26 exceeded 2.75 inches in only three small areas. Total supply as water in snow and precipitation did not exceed 4.8 inches over any tributary area. Maximum measured flood run-off was 2.7 inches. The flood of June 1938 in New Jersey was the immediate result of a 30-hour rainstorm on June 26-27 that centered along a line extending from Odessa, Del., to Milton, N. J. Storm rainfall exceeded 5 inches over a total area of 2,900 square miles. River stages in the central parts of the storm area rose to levels that approached and on a few rivers exceeded previous maxima of record. Damage was extensive throughout the storm area, especially in Burlington, N. J., where Sylvan Lake Dam failed. The highest rate of flow per unit of area measured was 88 second-feet per square mile. However, all peak discharges were exceeded during the later floods of 1938 or by the flood of September 1, 1940, which produced discharges over 1,000 second-feet per square mile in southern New Jersey. The maximum volume of direct runoff during the flood, expressed in mean depth in inches on the drainage area, was 2.1 inches. From July 17 to 25, 1938, there was an irregular series of rainstorms over the eastern seaboard that brought more than 10 inches of rain over an area of 2,000 square miles and more than 6 inches over 23,000 square miles. Nearly 14 inches of rain fell at Long Branch, N. J. Extraordinary floods occurred mainly in the smaller tributary streams. Damage to highways, homes, factories, and crops, particularly the tobacco co-op in Connecticut, was extensive. Crest discharges at 12 gaging stations exceeded those previously observed. Maximum rates of discharge varied from 601 second-feet per square mile for an area of 2.91 square miles in New Jersey to 35 second-feet per square mile for an area of 711 square miles in Connecticut. Antecedent soil moisture prior to the storm was probably normal or a little above. The maximum volume of direct runoff was 4.75 inches in Massachusetts, 5.6 inches in eastern Connecticut, 6.75 inches in the Catskill Mountain region of New York, and 4.95 inches in the Raritan River Basin of New Jersey. Infiltration indices from 0.09 .to 0.21 inch per hour were computed, such rates being within the range defined for basins in the same areas during the floods of September 1938. The flood of August 6-11, 1938, in the Catskill Mountain region of New York resulted from heavy rains with a maximum of 8 inches at two centers. Rainfall exceeded 3 inches over more than 3,000

Water Supply Paper↗

USGS1975

Sediments, structural framework, petroleum potential, environmental conditions, and operational considerations of the United States North Atlantic Outer Continental Shelf

The area designated for possible oil and gas lease sale as modified from BLM memorandum 3310 #42 (722) and referred to therein as the North Atlantic Outer Continental Shelf (OCS) contains about 58,300 sq km of shelf beneath water depths of less than 200 m and lies chiefly within the Georges Bank basin. The oldest sediments drilled or dredged on the bordering Continental Slope are sandstone, clay, and silt of Upper Cretaceous age. In Upper Cretaceous exposures, on Marthas Vineyard and nearby New England islands, the predominant lithology appears to be clay. About 125 km northeast of the eastern tip of Georges Bank, the Shell B-93 well penetrated clays and silts of Upper and Lower Cretaceous age above dense Jurassic carbonate rocks which overlie a basement of lower Paleozoic slate, schist, quartzite, and granite. Structurally, the Georges Bank basin is a westerly trending trough which opens to the west-southwest. Post-Paleozoic sediments are more than 8 km thick in parts of the basin. Major structural features appear to be directly related to basement structures. Local anticlines, probably caused by differential compaction over basement flexures and horst blocks or by later uplift along basement faults are reflected principally in Lower Cretaceous and older sediments, though some of these features continue upward to within 0.7 of a second (about 650 m) of the seafloor. Tertiary deposits in the Georges Bank basin are probably up to a kilometre thick and are made up of poorly consolidated sand, silt, and clay. The Cretaceous section is inferred to be up to 3.5 km thick and to be mainly clastics -- shale, siltstone, calcareous shale, changing to limestone in the lowest part of the system. Jurassic rocks in the deepest part of the basin appear to be about 3.6 to 4.0 km thick and probably consist mainly of dense carbonates. Potential source rocks in the Georges Bank basin may include organic-rich Cretaceous shale and carbonaceous Jurassic limestone. By analogy with the Scotian Shelf, Cretaceous sandstones are considered to be potential reservoir rocks. Local zones of porous dolomite are believed to be present in carbonate rocks of Jurassic age and should not be overlooked as potential reservoirs. Structural highs related to draping and differential compaction over basement blocks could be important potential petroleum traps. Additional traps may include reef structures near the shelf edge, updip pinchouts, and stratigraphic traps in both clastic and carbonate sediment. A statistical mean for the undiscovered recoverable petroleum resources is calculated to be 0.9 billion barrels of oil and 4.2 trillion cubic feet of gas. At the 5 percent probability level (1 in 20 chance) the undiscovered recoverable petroleum resources are calculated to be 2.4 billion barrels of oil and 12.5 trillion cubic feet of gas. These undiscovered recoverable petroleum resources are those quantities of oil and gas that may be reasonably expected to exist in favorable settings, but which have not yet been identified by drilling. Such estimates, therefore, carry a high degree of uncertainty. Environmental studies of Georges Bank indicated a low-moderate risk from petroleum development. However, the risk estimate is based on very limited data. Drift bottle returns used to infer oil spill trajectories show about a 2% overall recovery rate. Meteorologic data comes mainly from nearby land areas and from ships attempting to avoid storms. Seismicity on Georges Bank is low. This may reflect, in large part, the difficulty of land-based stations in recording earthquakes far from the coast. Direct data on the engineering properties of shallow buried sediment comes mainly from two Texas Tower surveys of limited areas on Georges Shoal and Nantucket Shoals made in the early 1950's. The 17 holes (most less than 30 m deep) reveal some silty layers below loose sand and much lateral variability in sediment type over short distances. The technology for exploration at the required water depths (20 m - 200 m) is available. Mobil drilling units are in great demand around the world and will have to be brought in from other areas along with skilled manpower. Our highest estimates indicate 50 platforms, 800 producing wells, 1,100 km of pipeline, and 5 onshore terminals may be needed. The time frame for production, using our high estimates (5% probability) for the undiscovered recoverable resources, could include 4-5 years for significant development, 6-7 years until production commences, and 18 years until peak production.

Open-File Report↗