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At least 145 records · Page 8Linked to original sources
USGS2010

After a century: Revised Paleogene coal stratigraphy, correlation, and deposition, Powder River Basin, Wyoming and Montana

The stratigraphy, correlation, mapping, and depositional history of coal-bearing strata in the Paleogene Fort Union and Wasatch Formations in the Powder River Basin were mainly based on measurement and description of outcrops during the early 20th century. Subsequently, the quality and quantity of data improved with (1) exploration and development of oil, gas, and coal during the middle 20th century and (2) the onset of coalbed methane (CBM) development during the late 20th and early 21st centuries that resulted in the drilling of more than 26,000 closely spaced wells with accompanying geophysical logs. The closeness of the data control points, which average 0.5 mi (805 m) apart, made for better accuracy in the subsurface delineation and correlation of coal beds that greatly facilitated the construction of regional stratigraphic cross sections and the assessment of resources. The drillhole data show that coal beds previously mapped as merged coal zones, such as the Wyodak coal zone in the Wyoming part of the Powder River Basin, gradually thinned into several discontinuous beds and sequentially split into as many as 7 hierarchical orders westward and northward. The thinning and splitting of coal beds in these directions were accompanied by as much as a ten-fold increase in the thicknesses of sandstone-dominated intervals within the Wyodak coal zone. This probably resulted from thrust loading by the eastern front of the Bighorn uplift accompanied by vertical displacement along lineaments that caused subsidence of the western axial part of the Powder River Basin during Laramide deformation in Late Cretaceous and early Tertiary time. Accommodation space was thereby created for synsedimentary alluvial infilling that controlled thickening, thinning, splitting, pinching out, and areal distribution of coal beds. Equally important was differential subsidence between this main accommodation space and adjoining areas, which influenced the overlapping, for example, of the Dietz coal zone in Montana, over the Wyodak coal zone in Wyoming. Correlation in a circular track of the Wyodak coal zone in the southern part of the basin also demonstrates overlapping with lower coal zones. Recognition of this stratigraphic relationship has led to revision of the correlations and nomenclature of coal beds because of inconsistency within these zones as well as those below and above them, which have long been subjects of controversy. Also, it significantly changes the traditional coal bed-to-bed correlations, and estimates of coal and coalbed methane resources of these coal zones due to thinning and pinching out of beds. More notably, thickness isopach, orientation, and distribution of the merged Wyodak coal bodies in the south-southeast part of the basin suggest that differential movement of lineament zones active during the Cretaceous was not a major influence on coal accumulation during the Paleocene. Improved knowledge of alluvial depositional environments as influenced by external and internal paleotectonic conditions within the Powder River Basin permits more accurate correlation, mapping, and resource estimation of the Fort Union and Wasatch coal beds. The result is a better understanding of the sedimentology of the basin infill deposits in relation to peat bog accumulation.

Montana, Wyoming↗
USGS2013

Stratigraphy of lower to middle Paleozoic rocks of northern Nevada and the Antler orogeny

Commonly accepted concepts concerning the lower Paleozoic stratigraphy of northern Nevada are based on the assumption that the deep-water aspects of Ordovician to Devonian siliceous strata are due to their origin in a distant oceanic environment, and their presence where we find them is due to tectonic emplacement by the Roberts Mountains thrust. The concept adopted here is based on the assumption that their deep-water aspects are the result of sea-level rise in the Cambrian, and all of the Paleozoic strata in northern Nevada are indigenous to that area. The lower part of the Cambrian consists mainly of shallow-water cross-bedded sands derived from the craton. The upper part of the Cambrian, and part of the Ordovician, consists mainly of deep-water carbonate clastics carried by turbidity currents from the carbonate shelf in eastern Nevada, newly constructed as a result of sea-level rise. Ordovician to mid-Devonian strata are relatively deep-water siliceous deposits, which are the western facies assemblage. The basal contact of this assemblage on autochthonous Cambrian rocks is exposed in three mountain ranges and is clearly depositional in all three. The western facies assemblage can be divided into distinct stratigraphic units of regional extent. Many stratigraphic details can be explained simply by known changes in sea level. Upper Devonian to Mississippian strata are locally and westerly derived orogenic clastic beds deposited disconformably on the western facies assemblage. This disconformity, clearly exposed in 10 mountain ranges, indicates regional uplift and erosion of the western facies assemblage and absence of local deformation. The disconformity represents the Antler orogeny.

Nevada↗
USGS1916

Contributions to the geology and paleontology of San Juan County, New Mexico: 1. Stratigraphy of a part of the Chaco River valley

This preliminary paper is an attempt to set forth the principal features of the stratigraphy in a part of the San Juan Basin-to describe the succession of strata irrespective of possible correlations and thereby to establish a type section for the formations exposed and to bring out their relations to the strata immediately above and below. The paper presents only a part of the data collected by a field party of the United States Geological Survey in the season of 1915, in charge of the writer, and does not describe the economic resources of the area, such as coal, nor the general geologic problems.

New Mexico↗
USGS2008

Geologic map of upper cretaceous and tertiary strata and coal stratigraphy of the Paleocene Fort Union Formation, Rawlins-Little Snake River area, south-central Wyoming

This report provides a map and detailed descriptions of geologic formations for a 1,250 square mile region in the Rawlins-Little Snake River coal field in the eastern part of the Washakie and Great Divide Basins of south-central Wyoming. Mapping of geologic formations and coal beds was conducted at a scale of 1:24,000 and compiled at a scale of 1:100,000. Emphasis was placed on coal-bearing strata of the China Butte and Overland Members of the Paleocene Fort Union Formation. Surface stratigraphic sections were measured and described and well logs were examined to determine the lateral continuity of individual coal beds; the coal-bed stratigraphy is shown on correlation diagrams. A structure contour and overburden map constructed on the uppermost coal bed in the China Butte Member is also provided.

Scientific Investigations Map↗
USGS2014

Geologic map and upper Paleozoic stratigraphy of the Marble Canyon area, Cottonwood Canyon quadrangle, Death Valley National Park, Inyo County, California

This geologic map and pamphlet focus on the stratigraphy, depositional history, and paleogeographic significance of upper Paleozoic rocks exposed in the Marble Canyon area in Death Valley National Park, California. Bedrock exposed in this area is composed of Mississippian to lower Permian (Cisuralian) marine sedimentary rocks and the Jurassic Hunter Mountain Quartz Monzonite. These units are overlain by Tertiary and Quaternary nonmarine sedimentary deposits that include a previously unrecognized tuff to which we tentatively assign an age of late middle Miocene (~12 Ma) based on tephrochronologic analysis, in addition to the previously recognized Pliocene tuff of Mesquite Spring. Mississippian and Pennsylvanian rocks in the Marble Canyon area represent deposition on the western continental shelf of North America. Mississippian limestone units in the area (Tin Mountain, Stone Canyon, and Santa Rosa Hills Limestones) accumulated on the outer part of a broad carbonate platform that extended southwest across Nevada into east-central California. Carbonate sedimentation was interrupted by a major eustatic sea-level fall that has been interpreted to record the onset of late Paleozoic glaciation in southern Gondwana. Following a brief period of Late Mississippian clastic sedimentation (Indian Springs Formation), a rise in eustatic sea level led to establishment of a new carbonate platform that covered most of the area previously occupied by the Mississippian platform. The Pennsylvanian Bird Spring Formation at Marble Canyon makes up the outer platform component of ten third-order (1 to 5 m.y. duration) stratigraphic sequences recently defined for the regional platform succession. The regional paleogeography was fundamentally changed by major tectonic activity along the continental margin beginning in middle early Permian time. As a result, the Pennsylvanian carbonate shelf at Marble Canyon subsided and was disconformably overlain by lower Permian units (Osborne Canyon and Darwin Canyon Formations) representing part of a deep-water turbidite basin filled primarily by fine-grained siliciclastic sediment derived from cratonal sources to the east. Deformation and sedimentation along the western part of this basin continued into late Permian time. The culminating phase was part of a regionally extensive late Permian thrust system that included the Marble Canyon thrust fault just west of the present map area.

California↗
USGS2017

Field-trip guide to the vents, dikes, stratigraphy, and structure of the Columbia River Basalt Group, eastern Oregon and southeastern Washington

The Columbia River Basalt Group covers an area of more than 210,000 km 2 with an estimated volume of 210,000 km 3 . As the youngest continental flood-basalt province on Earth (16.7–5.5 Ma), it is well preserved, with a coherent and detailed stratigraphy exposed in the deep canyonlands of eastern Oregon and southeastern Washington. The Columbia River flood-basalt province is often cited as a model for the study of similar provinces worldwide. This field-trip guide explores the main source region of the Columbia River Basalt Group and is written for trip participants attending the 2017 International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly in Portland, Oregon, USA. The first part of the guide provides an overview of the geologic features common in the Columbia River flood-basalt province and the stratigraphic terminology used in the Columbia River Basalt Group. The accompanying road log examines the stratigraphic evolution, eruption history, and structure of the province through a field examination of the lavas, dikes, and pyroclastic rocks of the Columbia River Basalt Group.

Oregon, Washington↗
USGS1954

Stratigraphy of parts of De Soto and Hardee Counties, Florida

The late Cenozoic stratigraphy of part of central Florida immediately south of the land-pebble phosphate district was studies in detail to determine the southern limit of the economically important Bone Valley formation and its relations with marine rocks of late Miocene and Pliocene age in south-central Florida. In addition a reconnaissance type appraisal of the phosphate and uranium resources of this area was desired. The upper Tertiary and Quaternary rocks were mapped, and the economic geology was studied in a general manner. The Hawthorn formation of middle Miocene age, is the oldest rock Exposed. Undifferentiated phosphatic sand and clay may be composed of the Bone Valley formation, of late Miocene to Pliocene age; a combination of Bone Valley formation and residuum of weathered Hawthorn formation; or Hawthorn residuum alone. The Bone Valley formation and residuum of Hawthorn formation appear almost identical in cuttings from auger drilling in this area. It was not feasible nor practical to map these two units separately. The undifferentiated phosphatic sand and clay interfingers with a marine sand of late Miocene age, The Caloosahatchee marl of Pliocene age, is present in the southeast corner of the area investigated. It is apparent that the undifferentiated phosphatic sand and clay was undergoing subaerial erosion and reworking during deposition or the Caloosahatchee marl. Stratified sand and clayey sand containing scattered thin lenses of fresh-water limestone and marl of Pleistocene age are either floodplain deposits or subaerial topset beds of a delta made by the Pleistocene Peace River. Sediments of Recent age are local stream deposits. Bars and shoals in the Peace River south of Brownville, De Soto County, contain appreciable tonnages of low grade "river-pebble" phosphate. The phosphate and uranium content of the undifferentiated phosphatic sand and clay in Hardee County is too low to be of economic significance.

Florida↗
USGS2001

Stratigraphy and vertical hydraulic conductivity of the St. Francois confining unit in townships 25-27 N. and ranges 01-02 W., southeastern Missouri

The St. Francois confining unit (DerbyDoerun Dolomite and Davis Formation) lies beneath the Ozark aquifer (Jefferson City Dolomite to the Potosi Dolomite) and impedes the circulation of water between the overlying Ozark aquifer and the underlying St. Francois aquifer (Bonneterre Formation and Lamotte Sandstone). The Bonneterre Formation is the potential host formation for lead-zinc deposits in the area. There is concern that mine dewatering in the Bonneterre Formation could lower water levels in the Ozark aquifer. To address this concern, the vertical hydraulic conductivity of the St. Francois confining unit in six townships (T. 25-27 N. and R. 01- 02 W.) of Oregon, Carter, and Ripley Counties of southeastern Missouri was evaluated by describing the stratigraphy and measuring the vertical hydraulic conductivity of core samples. The Davis Formation is an intrashelf basin facies consisting of a series of shales interbedded with shaley limestones, shale-free limestones, and local dolostones, and ranges from 24 to 320ft (feet) thick, but typically the thickness is 100 to 200 ft. Shale-dominant sequences can be tens of feet thick, and contain as much as 90 percent shale. Carbonate-dominant zones may be 70 ft thick or greater. The top of the Davis Formation (based on 56 data points) ranges from 620 to 2,022 ft deep and ranges in altitude from 40ft below sea level in the northern part of the study area to 1, 182 ft below sea level in the southern part of the study area. The Derby-Doerun Dolomite represents a pair of superimposed carbonate ramp cycles. Where present, the basal shaley sequence represents a transition with the Davis Formation. The formation (based on 50 data points) ranges from 50 to 386ft thick, but typically is 120 to 180ft thick in the study area. The top of the DerbyDoerun Dolomite ranges from 495 to 2,020 ft deep (based on 53 data points), and ranges in altitude from 85 ft above sea level to 94 7 ft below sea level. The St. Francois confining unit is thickest in the central and southern parts of the study area. The thickness, as determined by 51 core logs that completely penetrate the unit, ranges from less than 200ft in the northwestern and east-central parts of the study area to 411 ft in the central part, but typically ranges from 270 to 340 ft. The net shale thickness of the confining unit (based on 29 data points) ranges from 1. 7 ft in the east -central part of the study area to 89 ft in the southwest part. These net shale thickness values include the cumulative shale thickness of rock from the top of the Derby-Doerun Dolomite to the base of the False Davis. Vertical hydraulic conductivities of 35 rock core samples from the St. Francois confining unit in the study area range from 7.6 x 10 -15 to 2.1 x 10 -10 ft/s (foot per second). The logarithmic transformed vertical hydraulic conductivities of the Derby-Doerun Dolomite and Davis Formation are similar (p-value = 0.073) using the statistical twosample t-test; however, this p-value approaches the level of significance value of 0.05. The vertical hydraulic conductivity of the Derby-Doerun Dolomite is larger and less variable than the Davis Formation. When grouped by rock type, the vertical hydraulic conductivity of samples that contain carbonate, shale, or both carbonate and shale, are similar. A comparison on the ranked data using the Mann-Whitney test shows the confining unit in the study area is statistically different (p-value = 0.020) from the confining unit in the prospecting area (west and adjacent to the study area). The median value of the vertical hydraulic conductivity data from the study area (6.7 x 10 -13 ft/s) is three times larger than the median vertical hydraulic conductivity value for the prospecting area (2.2 x 10 -13 ft/s ). The interquartile range shows that the variability of the study area data spans one order of magnitude (2.0 x 10 -13 to 2.2 x 10 -12 ft/s) and that the corresponding data from the prospecting area spans nearly two orders of magnitude (3.2 x 10 -14 to 1.1 x 10 -12 ft/s). The ranked vertical hydraulic conductivities of the Derby-Doerun Dolomite in the two areas are statistically similar (p-value = 0.514). The median vertical hydraulic conductivity of the study area data ( 1.2 X 10 -12 ft/s) is about three times greater than the median value of the prospecting area data (4.4 x 10 -13 ft/s). The variability of the data, as shown by the interquartile range, is less in the study area (5.5 x 10 -13 to 2.2 x 10 -12 ft/s; spanning less than one order of magnitude) as compared to the prospecting area (3.2 x 10 -14 to 6.3 x 10 -10 ft/s; spanning over four orders of magnitude). The ranked vertical hydraulic conductivities of the Davis Formation in the two areas show these data sets are statistically similar (p-value = 0.076). The median vertical hydraulic conductivity value of study area samples ( 4.5 x 10 -13 ft/s) is three times greater than the median value of the prospecting area data (1.6 x 10 -13 ft/s). The interquartile range of the study area data spans one order of magnitude (1.2 x 10 -13 to 1.4 x 10 -12 ft/s) and the corresponding data from the prospecting area spans nearly 1.5 orders of magnitude (3.2 x 10 -14 to 7.4 x 10 -13 ft/s). The Mann-Whitney test shows the ranked vertical hydraulic conductivities of each rock type from the study area are statistically similar to the same rock type in the prospecting area [carbonates (p-value = 0.225), shales (p-value = 0.668), and carbonates and shales (p-value = 0.227)]. However, in each of the three cases the study area samples have larger median values and less variability than the prospecting area samples. Because the vertical hydraulic conductivity of the various rock types of the confining unit in the study area are statistically similar, the entire carbonate-shale thickness is the primary factor determining the effectiveness of the confining unit. The range of effective vertical hydraulic conductivity of the St. Francois confining unit in the study area using appropriate minimum and maximum thickness, net shale thickness, and vertical hydraulic conductivities is 3 X 10 -13 to 2 X 10 -12 ft/s. The vertical hydraulic conductivity of the confining unit is small, and the confining unit effectively impedes the ground-water flow between the Ozark aquifer and the St. Francois aquifer, unless preferred- path secondary permeability has developed along faults and fractures that extend through the confining unit.

Missouri↗
USGS2003

Stratigraphy and vertical hydraulic conductivity of the St. Francois Confining Unit in the Viburnum Trend and evaluation of the Unit in the Viburnum Trend and exploration areas, southeastern Missouri

The confining ability of the St. Francois confining unit (Derby-Doerun Dolomite and Davis Formation) was evaluated in ten townships (T. 31?35 N. and R. 01?02 W.) along the Viburnum Trend of southeastern Missouri. Vertical hydraulic conductivity data were compared to similar data collected during two previous studies 20 miles south of the Viburnum Trend, in two lead-zinc exploration areas that may be a southern extension of the Viburnum Trend. The surficial Ozark aquifer is the primary source of water for domestic and public-water supplies and major springs in southern Missouri. The St. Francois confining unit lies beneath the Ozark aquifer and impedes the movement of water between the Ozark aquifer and the underlying St. Francois aquifer (composed of the Bonneterre Formation and Lamotte Sandstone). The Bonneterre Formation is the primary host formation for lead-zinc ore deposits of the Viburnum Trend and potential host formation in the exploration areas. For most of the more than 40 years the mines have been in operation along the Viburnum Trend, about 27 million gallons per day were being pumped from the St. Francois aquifer for mine dewatering. Previous studies conducted along the Viburnum Trend have concluded that no large cones of depression have developed in the potentiometric surface of the Ozark aquifer as a result of mining activity. Because of similar geology, stratigraphy, and depositional environment between the Viburnum Trend and the exploration areas, the Viburnum Trend may be used as a pertinent, full-scale model to study and assess how mining may affect the exploration areas. Along the Viburnum Trend, the St. Francois confining unit is a complex series of dolostones, limestones, and shales that generally is 230 to 280 feet thick with a net shale thickness ranging from less than 25 to greater than 100 feet with the thickness increasing toward the west. Vertical hydraulic conductivity values determined from laboratory permeability tests were used to represent the St. Francois confining unit along the Viburnum Trend. The Derby-Doerun Dolomite and Davis Formation are statistically similar, but the Davis Formation would be the more hydraulically restrictive medium. The shale and carbonate values were statistically different. The median vertical hydraulic conductivity value for the shale samples was 62 times less than the carbonate samples. Consequently, the net shale thickness of the confining unit along the Viburnum Trend significantly affects the effective vertical hydraulic conductivity. As the percent of shale increases in a given horizon, the vertical hydraulic conductivity decreases. The range of effective vertical hydraulic conductivity for the confining unit in the Viburnum Trend was estimated to be a minimum of 2 x 10-13 ft/s (foot per second) and a maximum of 3 x 10-12 ft/s. These vertical hydraulic conductivity values are considered small and verify conclusions of previous studies that the confining unit effectively impedes the flow of ground water between the Ozark aquifer and the St. Francois aquifer along the Viburnum Trend. Previously-collected vertical hydraulic conductivity data for the two exploration areas from two earlier studies were combined with the data collected along the Viburnum Trend. The nonparametric Kruskal-Wallis statistical test shows the vertical hydraulic conductivity of the St. Francois confining unit along the Viburnum Trend, and west and east exploration areas are statistically different. The vertical hydraulic conductivity values generally are the largest in the Viburnum Trend and are smallest in the west exploration area. The statistical differences in these values do not appear to be attributed strictly to either the Derby-Doerun Dolomite or Davis Formation, but instead they are caused by the differences in the carbonate vertical hydraulic conductivity values at the three locations. The calculated effective vertical hydraulic conductivity range for the St. Franc

Water-Resources Investigations Report↗
USGS1999

Stratigraphy and hydrologic conditions at the Brookhaven National Laboratory and vicinity, Suffolk County, New York, 1994-97

Brookhaven National Laboratory (BNL) has installed many test borings as part of an effort to delineate the extent of ground-water contamination at the site. In 1994, the U.S. Geological Survey began a study in cooperation with BNL to define the stratigraphy in the 28-square-mile area encompassing BNL, and to monitor ground-water levels in the 300 squaremile area of central Suffolk County that surrounds BNL. The uppermost geologic units at BNL are of Pleistocene age. These sediments are underlain unconformably by the Matawan Group-Magothy Formation, undifferentiated (referred to as the Magothy Formation), of Cretaceous age, which typically consists of light- to dark-gray, variably sorted sand interbedded with light- to dark-gray clay layers; it also contains beds of grayish-brown to brownish-gray sand. Bed thicknesses differ substantially within each boring and tend to be laterally discontinuous as a result of their terrestrial deltaic depositional environment, although a prominent clay unit, referred to as the ?grayish-brown clay? in this report, was encountered at many borings. Pollen-sample analyses confirm that this unit is of Cretaceous age and is the uppermost unit of Cretaceous sediments in several parts of the study area. The upper surface of the Cretaceous deposits is irregular within the 28-square-mile study area and has relief of about 120 feet. Several prominent channels and ridges in the surface are aligned generally northwest-southeast. The Cretaceous surface beneath BNL is characterized more by local erosional features than by the regional cuesta shape that was suggested by previous authors. The overlying Pleistocene-aged units include (1) a sand layer overlain by the Gardiners Clay, (2) the Gardiners Clay, and (3) upper Pleistocene deposits, which include the Upton unit, glacial outwash, glaciolacustrine deposits, and terminal moraine deposits. The sand unit below the Gardiners Clay was the first Pleistocene unit to be deposited atop the irregular surface of the Cretaceous deposits in this area. The Gardiners Clay was deposited during a major rise in sea level as the sea encroached into parts of the present-day BNL study area. The shallow part of the upper Pleistocene deposits generally consists of light-brown sand and gravel but overlies green to grayish-green, variably sorted sand, silt, and clay at altitudes of 50 to 70 feet below sea level in some parts of the study area. This lower part of the upper Pleistocene deposits in the study area was referred to by previous investigators as the unidentified unit and has been designated as the Upton unit in this report. The discharge of ground water to the Peconic and Carmans Rivers locally affects the water-table configuration. The main ground-water divide on Long Island is about 0.5 miles north of the site; a secondary divide originates near the start of flow of the Peconic River and extends east-southeastward toward the South Fork. The water-table configuration on the BNL site is affected by pumping from supply wells and remediation wells, by infiltration of the water through recharge basins, by discharge from the sewage-treatment plant, and by local near-surface clay units. The horizontal hydraulic gradient at BNL typically is 0.001 foot per foot but can steepen near recharge basins and pumping wells. Vertical flow gradients within the upper Pleistocene deposits (upper glacial aquifer) were as large as 0.007 foot per foot (downward) in the northern part of BNL and were negligible in the southern part. Downward vertical gradients between the lower part of the upper glacial aquifer and the upper part of the Magothy Formation (Magothy aquifer) were about 0.018 foot per foot throughout the site.

Water-Resources Investigations Report↗
USGS2022

Stratigraphy and eruption history of maars in the Clear Lake Volcanic Field, California

The Clear Lake Volcanic Field (CLVF) is the northernmost and youngest field in a chain of volcanic provinces in the California Coast Range mountains. Effusive and explosive volcanic activity in the field has spanned at least 2.1 million years, with the youngest eruptions comprising a series of maar craters at the edges of, and within, Clear Lake itself. This work documents the first direct ages for many of these maar deposits, and builds the stratigraphic basis for interpreting eruptive processes and dynamics of the young eruptions which produced them. Detailed stratigraphy has distinguished maar eruption products from pyroclastic deposits (monolithologic falls and flows, previously mapped together with maars as a single unit), and established a set of 6 eruption facies from maar deposit lithology, grain size parameters, and depositional structures. Radiocarbon dates from carbon films found on clasts at 3 outcrops have constrained several of these maar eruptions to ~8500-13,500 years BP, coinciding with eruptive periods previously estimated based on lake core tephrachronology. Part of this period also coincides with indigenous occupation (< 12,000 years BP), which suggests that oral histories of Pomo and other local tribes may contain descriptions of volcanic phenomena experienced by local residents of the CLVF. Collaboration between volcanologists and indigenous historians may add a valuable human dimension to the youngest eruptions of the Clear Lake Volcanic Field; combined, geologic and ethnographic avenues of research will help build a richer eruption history for future volcanic hazard assessment.

California↗
USGS1986

Pre-Wisconsin glacial stratigraphy of the central plains region in Iowa, Nebraska, Kansas, and Missouri

Recent investigations have documented the presence of several tills and interglacial paleosols that were not recognized in the simple Kansan-Aftonian-Nebraskan stratigraphic sequence. Also, the single 'Pearlette ash' recognized by early workers now is known to be three different Pearlette family ash beds of greatly contrasting ages. The complexity of the stratigraphy, as it is currently understood, and the miscorrelations of early work necessitate abandonment of the archaic terms Kansan, Aftonian, and Nebraskan in stratigraphic terminology. Continued use of those terms will only promote confusion of stratigraphic nomenclature and erroneous correlations of stratigraphic units. The limited chronometric control available within the early and middle Pleistocene stratigraphic sequence is provided directly by dating or by correlation of buried soils and volcanic ash beds and it is provided inferentially by interpretation of magnetic polarity data. These controls provide, at best, a general time framework to begin a new synthesis of the Quaternary history of the region. New methods of dating are needed to facilitate long-distance correlation of early and middle Pleistocene deposits. ?? 1986.

Quaternary Science Reviews↗
USGS1997

Fluvial-deltaic sedimentation and stratigraphy of the ferron sandstone

East-central Utah has world-class outcrops of dominantly fluvial-deltaic Turonian to Coniacian aged strata deposited in the Cretaceous foreland basin. The Ferron Sandstone Member of the Mancos Shale records the influences of both tidal and wave energy on fluvial-dominated deltas on the western margin of the Cretaceous western interior seaway. Revisions of the stratigraphy are proposed for the Ferron Sandstone. Facies representing a variety of environments of deposition are well exposed, including delta-front, strandline, marginal marine, and coastal-plain. Some of these facies are described in detail for use in petroleum reservoir characterization and include permeability structure.

Brigham Young University Geology Studies↗
USGS2004

Sequence stratigraphy of the Kingak Shale (Jurassic-Lower Cretaceous), National Petroleum Reserve in Alaska

Beaufortian strata (Jurassic-Lower Cretaceous) in the National Petroleum Reserve in Alaska (NPRA) are a focus of exploration since the 1994 discovery of the nearby Alpine oil field (>400 MMBO). These strata include the Kingak Shale, a succession of depositional sequences influenced by rift opening of the Arctic Ocean Basin. Interpretation of sequence stratigraphy and depositional facies from a regional two-dimensional seismic grid and well data allows the definition of four sequence sets that each displays unique stratal geometries and thickness trends across NPRA. A Lower to Middle Jurassic sequence set includes numerous transgressive-regressive sequences that collectively built a clastic shelf in north-central NPRA. Along the south-facing, lobate shelf margin, condensed shales in transgressive systems tracts downlap and coalesce into a basinal condensed section that is likely an important hydrocarbon source rock. An Oxfordian-Kimmeridgian sequence set, deposited during pulses of uplift on the Barrow arch, includes multiple transgressive-regressive sequences that locally contain well-winnowed, shoreface sandstones at the base of transgressive systems tracts. These shoreface sandstones and overlying shales, deposited during maximum flooding, form stratigraphic traps that are the main objective of exploration in the Alpine play in NPRA. A Valanginian sequence set includes at least two transgressive-regressive sequences that display relatively distal characteristics, suggesting high relative sea level. An important exception is the presence of a basal transgressive systems tract that locally contains shoreface sandstones of reservoir quality. A Hauterivian sequence set includes two transgressive-regressive sequences that constitute a shelf-margin wedge developed as the result of tectonic uplift along the Barrow arch during rift opening of the Arctic Ocean Basin. This sequence set displays stratal geometries suggesting incision and synsedimentary collapse of the shelf margin.

Alaska↗
USGS2008

Hierarchy of sedimentary discontinuity surfaces and condensed beds from the middle Paleozoic of eastern North America: Implications for cratonic sequence stratigraphy

Sedimentological analyses of middle Paleozoic epeiric sea successions in North America suggest a hierarchy of discontinuity surfaces and condensed beds of increasing complexity. Simple firmgrounds and hardgrounds, which are comparatively ephemeral features, form the base of the hierarchy. Composite hardgrounds, reworked concretions, authigenic mineral crusts and monomictic intraformational conglomerates indicate more complex histories. Polymictic intraformational conglomerates, ironstones and phosphorites form the most complex discontinuity surfaces and condensed beds. Complexity of discontinuities is closely linked to depositional environments duration of sediment starvation and degree of reworking which in turn show a relationship to stratigraphic cyclicity. A model of cratonic sequence stratigraphy is generated by combining data on the complexity and lateral distribution of discontinuities in the context of facies successions. Lowstand, early transgressive and late transgressive systems tracts are representative of sea-level rise. Early and late transgressive systems tracts are separated by the maximum starvation surface (typically a polymictic intraformational conglomerate or condensed phosphorite), deposited during the peak rate of sea-level rise. Conversely the maximum flooding surface, representing the highest stand of sea level, is marked by little to no break in sedimentation. The highstand and falling stage systems tracts are deposited during relative sea-level fall. They are separated by the forced-regression surface, a thin discontinuity surface or condensed bed developed during the most rapid rate of sea-level fall. The lowest stand of sea level is marked by the sequence boundary. In subaerially exposed areas it is occasionally modified as a rockground or composite hardground.

Conference Paper↗
USGS2012

Geology and sequence stratigraphy of undiscovered oil and gas resources in conventional and continuous petroleum systems in the Upper Cretaceous Eagle Ford Group and related strata, U.S. Gulf Coast Region

The U.S. Geological Survey (USGS) recently assessed the technically recoverable undiscovered oil and gas onshore and in State waters of the Gulf Coast region of the United States. The USGS defined three assessment units (AUs) with potential undiscovered conventional and continuous oil and gas resources in Upper Cretaceous (Cenomanian to Turonian) strata of the Eagle Ford Group and correlative rocks. The assessment is based on geologic elements of a total petroleum system, including hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (sequence stratigraphy and petrophysical properties), and traps (formation, timing, and seals). Conventional oil and gas undiscovered resources are in updip sandstone reservoirs in the Upper Cretaceous Tuscaloosa and Woodbine Formations (or Groups) in Louisiana and Texas, respectively, whereas continuous oil and continuous gas undiscovered resources reside in the middip and downdip Upper Cretaceous Eagle Ford Shale in Texas and the Tuscaloosa marine shale in Louisiana. Conventional resources in the Tuscaloosa and Woodbine are included in the Eagle Ford Updip Sandstone Oil and Gas AU, in an area where the Eagle Ford Shale and Tuscaloosa marine shale display vitrinite reflectance (Ro) values less than 0.6%. The continuous Eagle Ford Shale Oil AU lies generally south of the conventional AU, is primarily updip of the Lower Cretaceous shelf edge, and is defined by thermal maturity values within shales of the Eagle Ford and Tuscaloosa that range from 0.6 to 1.2% Ro. Similarly, the Eagle Ford Shale Gas AU is defined downdip of the shelf edge where source rocks have Ro values greater than 1.2%. For undiscovered oil and gas resources, the USGS assessed means of: 1) 141 million barrels of oil (MMBO), 502 billion cubic feet of natural gas (BCFG), and 4 million barrels of natural gas liquids (MMBNGL) in the Eagle Ford Updip Sandstone Oil and Gas AU; 2) 853 MMBO, 1707 BCFG, and 34 MMBNGL in the Eagle Ford Shale Oil AU; and 3) 50,219 BCFG and 2009 MMBNGL in the Eagle Ford Shale Gas AU.

Louisiana;Texas↗
USGS1991

Late Quaternary stratigraphy and depositional history of the Long Island Sound basin

The stratigraphy of Late Quaternary geologic units beneath Long Island Sound (LIS) is interpreted from 3,500 km of high-resolution, seismic-reflection profiles supplemented by vibracore data. Knowledge gained from onshore regional geologic studies and previous offshore investigations is also incorporated in these interpretations. Glacial deposits overlie and nearly fill an Inner Lowland which is floored by crystalline rocks in the north and bounded to the south by an irregular, north-facing cuesta scarp in Cretaceous Coastal-Plain strata. The thick glacial section consists largely of sediment that was deposited in glacial Lake Connecticut during the retreat of the last (late Wisconsin) ice sheet. Ice-marginal lacustrine fan deposits and submerged extensions of the southeastern Connecticut recessional moraines mark positions of the ice margin during systematic northward retreat. When the ice margin stood at positions just north of the present shoreline of Connecticut (17.6-16.5 ka), glacial Lake Connecticut was slightly larger than Long Island Sound is today. Ice-marginal deltas and near-ice marginal fluviodeltaic deposits occur along coastal Connecticut. Delta-building was diachronous; progressively younger deltas record northwesterly retreat of the ice margin and lowering lake levels. Distally from the deltas, varied lake-clays (up to 150 m thick) drape the underlying topography. The lake spillway cut across the Harbor Hill-Roanoke Point-Fishers Island-Charlestown end moraine at its lowest point just west of Fishers Island (The Race). Lake levels fell as the spillway notch was erosionally deepened, and gradually the lakebed became subaerially exposed. A largely preserved channel system cuts the lake-deposit surface; fluvial channel-fill sediments are overlain by estuarine sediments in the channel system. Perhaps as early as 15 ka, but no later than 13 ka, the sea entered the Basin through the channel at The Race and quickly transgressed westward via the lakebed channel system. As the sea rose further and spread throughout the Basin, a wave-cut surface was formed. Extensive marine deltaic deposits, up to 40 m thick, overlie the wave-cut marine unconformity in the east-central part of the Basin. These sediments were derived from erosion of the drained bed of Lake Hitchcock, in the Connecticut valley to the north, and were deposited in a -40-m relative sea at about 12.4 ka. Where quiet waters prevail, marine mud generally less than 15 m thick blankets the older deposits of the Basin. Elsewhere, especially in eastern LIS, tidal currents are actively reworking and transporting glacial and postglacial deposits.

Connecticut, New York↗