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At least 343 records · Page 19Linked to original sources
USGS1988

Geologic history and palynologic dating of Paleocene deposits, western Rock Springs uplift, Sweetwater County, Wyoming

During the latest Cretaceous or earliest Paleocene, a northwest-southeast trending anticline developed in the area of the present Rock springs uplift in southwestern Wyoming. This ancestral structure was eroded to a surface of fairly low relief on which a paleosol developed. The surface was formed on the Upper Cretaceous Almond Formation throughout the study area. In the early middle Paleocene (P3 palynomorph zone), topographic lows on the erosion surface were infilled by alluvial deposits that accumulated in channel, floodplain, and backswamp environments. An organic-rich facies contains numerous coal beds and is middle to late Paleocene in age (P3 to P5 zones). The assemblage of pollen that defines the late middle Paleocene (P4 zone) is absent from the area suggesting a hiatus, although no lithologic break was observed at this boundary. The younger organic-poor facies begins in the late Paleocene (P5 zone) and continues to the top of the studied sequence. This change in facies has been used to map the contact between the Fort Union Formation of Paleocene age in this area, and the Wasatch Formation which was though to be of Eocene age. This study demonstrates that, as currently mapped, the lower part of the Wasatch Formation is Paleocene in age. Stratigraphically higher parts of the Wasatch, which presumably contain rocks of latest Paleocene (P6 zone) and earliest Eocene age, were not studied. -Authors

Contributions to Geology - University of Wyoming, ↗
USGS1991

Late quaternary geologic framework, north-central Gulf of Mexico

The geologic framework of the north-central Gulf of Mexico shelf is composed of multiple, stacked, delta systems. Shelf and nearshore sedimentary facies were deposited by deltaic progradation, followed by shoreface erosion and submergence. A variety of sedimentary facies has been identified, including prodelta, delta fringe, distributary, lagoonal, barrier island, and shelf sand sheet. This study is based on the interpretation and the synthesis of > 6,700 km of high-resolution seismic profiles, 75 grab samples, and 77 vibracores. The nearshore morphology, shallow stratigraphy, and sediment distribution of the eastern Louisiana shelf are the products of transgressive sedimentary processes reworking the abandoned St. Bernard delta complex. Relatively recent Mississippi delta lobe consists primarily of fine sand, silt, and clay. In the southern portion of the St. Bernard delta complex, asymmetrical sand ridges (>5 m relief) have formed as the result of marine reworking of distributary mouth-bar sands. Silty sediments from the modern Mississippi Birdsfoot delta onlap the St. Bernard delta complex along the southern edge. The distal margin of the St. Bernard complex is distinct and has a sharp contact on the north near the Mississippi Sound barrier island coastline and a late Wisconsinan delta to the south. The Chandeleur Islands and the barrier islands of Mississippi Sound have been formed by a combination of Holocene and Pleistocene fluvial processes, shoreface erosion, and ravinement of the exposed shelf. Sediments underlying the relatively thin Holocene sediment cover are relict fluvial sands, deposited during the late Wisconsinan lowstand. Subsequent relative sea-level rise allowed marine processes to rework and redistribute sediments that formed the nearshore fine-grained facies and the shelf sand sheet.

Conference Paper↗
USGS2001

Applications of resistivity modeling in reservoir development: examples from Balder Field, Norwegian North Sea

The massive Paleocene oil sands of the Balder Field are overlain by several thinly bedded Eocene sand-prone packages of variable facies and reservoir quality. Although these sands have been penetrated by numerous exploration and development wells, uncertainty remains as to their extent, distribution, and ultimate effect on reservoir performance. The section is geologically complex (thin beds, injected sands, shale clasts and laminae, and faulting), and also contains a field-wide primary gas cap. With a depletion plan involving both gas and water injection, geologic/reservoir characterization of the Eocene is critical for prudent resource management during depletion. With this goal, resistivity modeling and core-based thin bed reservoir description from the first phase of development drilling have been integrated with seismic attribute mapping. Detailed core description, core permeability and grain size distribution data delineate six facies and help in distinguishing laterally continuous massive and laminated sands from potentially non-connected injection sands and non-reservoir quality siltstones and tuffs. Volumetric assessment of the thin sand resource has been enhanced by I-D forward modeling of induction log response using a commercial resistivity modeling program, R,BAN. After defining beds and facies with core and high resolution log data, the AHF60 array induction curve response was approximated using the 6FF40 response. Because many of the beds were thinner than 6FF40 resolution, the modeling is considered to provide a lower bound on R,. However, for most beds this model-based R, is significantly higher than that provided by one-foot vertical resolution shallow resistivity data, and is thought to be the best available estimate of true formation resistivity. Sensitivities in STOOIP were assessed with multiple R, earth models which can later be tested against production results. In addition, water saturation height functions, developed in vertical wells and thick beds, can be validated in deviated wells with thin beds. Sand thickness models constrained by this logand core-based petrophysical analysis were used to build impedance seismic synthetic sections from which seismic attributes could be extracted and calibrated. The model-based attribute calibration was then applied to the seismic impedance 3-D cube permitting sand thickness to be mapped and reservoir geology to be modeled with significantly more detail than previously possible. These results will guide the field''s reservoir management and assist in the delineation of new targets.

Petrophysics↗
USGS1962

Generalized structure contour maps of the New Jersey coastal plain

Twelve generalized structural contour maps were prepared from a study of 169 well logs or sample logs of drill cuttings from the Coastal Plain of New Jersey, Delaware, and the E astern Shore of Maryland. The configuration of the tops of the nonmarine Cretaceous deposits (Patuxent , Patapsco, Raritan, and Magothy formations) and the Piney Point Formation (Eocene) show the known subsurface extent of these formations in both New Jersey and Delaware. The structural contour maps show the tops of the Merchantville Formation and Woodbury Clay, the Englishtown Formation, the Marshalltown Formation, the Wenonah Formation and Mount Laurel Sand, the Navesink Forma ti on, and the Red Bank Sand which are a ll of Late Cretaceous age. The maps of the Hornerstown Sand, the Vincentown Formation, and the Manasquan Formation and Shark River Marl of early Tertiary age show the subsurface extent of these formations only in New Jersey. Also included is an outline map showing the locations of wells and seismic station s and a structural contour map showing the configuration of the bedrock surface of the report area. Structural contours on top of the Magothy Formation, or on the top of the Raritan Formation where the Magothy formation is absent, show the configuration of the nonmarine deposits of Cretaceous age. Isopachs of the nonmarine deposits are derived by interpolation between contours on top of the bedrock and the top of either the Magothy Formation or the Raritan Formation where the Magothy is absent. The Merchantville Formation and Woodbury Clay are difficult to separate in the subsurface, and therefore the contour a re drawn on top of the Woodbury Clay. In New Jersey, the thickness of the combined Merchantville Form a ti on and Woodbury Clay ranges from ab out 100 to 140 feet near the outcrop, but exceeds 250 feet in the subsurface along the coast in Ocean County. The top of the Englishtown Formation is easy to recognize because it generally consists of a micaceous white and yellow sand, although locally it is a silty clay . The formation thins toward the southwest from about 160 feet in central Ocean County to less than 20 feet in Salem County . It has not been recognized in Delaware. The Marshalltown Formation varies from black clay to a glauconitic sand. It usually ranges in thickness from 20 to 60 feet . It is very thin or absent in Delaware. The Wenonah Formation and Mount Laurel and arc difficult to separate in New Jersey, and therefore are shown as a unit. The combined thickness range from 60 to 100) feet. In Delaware the two formations are easily separated. The Navesink Formation is generally highly glauconitc and it is difficult to determine the upper limit where overlain by the Hornerstown Sand which is also glauconitic. The contour map on the top of the Navesink is based upon relatively little control. The Red Bank Sand reaches a thickness of about 160 feet in Monmouth County. It thins southwestward and is absent in outcrop in the southern part of the Coastal Plain of New Jersey. A probable equivalent of the Reel Bank has be recognized in Delaware. The Tinton Sand Member is the topmost unit of the Red Bank and in Monmouth County. The Hornerstown Sand is most glauconitic and is about 30 feet thick in outcrop. This is overlain by the Vincentown Formation which consists of two facies (1) calcareous sand facies and (2) quartz sand facies. These a re overlain by the Manasquan Formation and Shark River Marl which are here treated as a unit . In outcrop the combined thickness of the Manasquan Formation and Shark River Marl is about 40 feet, but in the subsurface they thicken to about 200 feet. The Piney Point Formation of Jackson age occur in the subsurface in Cape May and Atlantic Counties, N.J. and in southern Delaware but is not exposed in these States. Brief notes are given on formation of later Tertiary and Pleistocene age , but no contour maps were constructed.

Delaware;New Jersey↗
USGS2016

Proposed Auxiliary Boundary Stratigraphic Section and Point (ASSP) for the base of the Ordovician System at Lawson Cove, Utah, USA

T he Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System is at the First Appearance Datum (FAD) of the conodont Iapetognathus fluctivagus at Green Point in Newfoundland, Canada. Strata there are typical graptolitic facies that were deposited near the base of the continental slope.We propose establishing an Auxiliary boundary Stratotype Section and Point (ASSP) at the FAD of I. fluctivagus at the Lawson Cove section in the Ibex area of Millard County, Utah, USA. There, strata consist of typical shelly facies limestones that were deposited on a tropical carbonate platform and contain abundant conodonts, trilobites, brachiopods, and other fossil groups. Cambrian and Ordovician strata in this area are ~5300m thick, with the Lawson Cove section spanning 243m in three overlapping segments. Six other measured and studied sections in the area show stratigraphic relationships similar to those at Lawson Cove. Faunas have been used to divide these strata into 14 conodont and 7 trilobite zonal units. The widespread olenid trilobite Jujuyaspis occurs ~90cm above the proposed boundary at Lawson Cove; this genus is generally regarded as earliest Ordovician. Rhynchonelliform and linguliform brachiopods are common to abundant and are useful for correlation. The FAD of Iapetognathus fluctivagus and occurrences of Jujuyaspis and the Lower Ordovician planktonic graptolite Anisograptus matanensis all occur within a 2.4m interval of strata at a nearby section. Non-biological correlation tools include a detailed sequence stratigraphic classification and a detailed carbon-isotope profile. Especially useful for correlation is a positive 13C excursion peak ~15cm below the proposed boundary horizon. All of these correlation tools form an integrated framework that makes the Lawson Cove section especially useful as an ASSP for global correlation of strata with faunas typical of shallow, warm-water, shelly facies.

Utah↗
USGS2016

Petrology and tectonic history of the Green Bay Schist, Portmore, St. Catherine Parish, Jamaica

There are three occurrences of medium- to high-grade metamorphic rocks in Jamaica: amphibolite facies Westphalia Schist, blueschist/greenschist facies Mt. Hibernia Schist, and the hitherto poorly characterized amphibolite facies Green Bay Schist. New trace element data and thermodynamic calculations show that Green Bay Schist is closely related to Westphalia Schist. The protoliths for both are very similiar (basalt-andesitic basalt, C-MORB), consistent with a subducted ocean-ridge tectonic environment, hence arc-related. The protolith for Mt. Hibernia Schist is quite different (basalt, P-MORB), related to the Caribbean Large Igneous Province. Whereas the P-T-t paths for Green Bay Schist and Westphalia Schist prior to the middle Campanian (>78 Ma) are inferred to be similar, the late Campanian, Maastrichtian and Cenozoic P-T-t paths are very different. New 40Ar/39Ar age determinations show the following: (1) While the difference in the late Campanian and Maastrichtian remains problematic, (2) the difference in the Cenozoic clearly reflects the location relative to the NW-trending, NE-dipping Wagwater Fault: Westphalia Schist to the NE (hanging wall); Green Bay Schist to the SW (foot wall). The Cenozoic P-T-t paths are complementary, and consistent with the behavior of the Wagwater Fault: 65-50 Ma, normal motion (transtension); 50-10 Ma, inactive (quiescent); 10 Ma-present, reverse motion (transpression).

Portmore↗
USGS2015

Field trip guidebook for the post-meeting field trip: The Central Appalachians

The lower Paleozoic rocks to be examined on this trip through the central Appalachians represent an extreme range of depositional environments. The lithofacies we will examine range from pelagic radiolarian chert and interbedded mudstone that originated on the deep floor of the Iapetus Ocean, through mud cracked supratidal dolomitic laminites that formed during episodes of emergence of the long-lived Laurentian carbonate platform, to meandering fluvial conglomerate and interstratified overbank mudstone packages deposited in the latest stages of infilling of the Taconic foredeep. In many ways this field trip is about contrasts. The Upper Cambrian (Furongian) and Lower Ordovician deposits of the Sauk megasequence record deposition controlled primarily by eustatic sea level sea level fluctuations that influenced deposition along the passive, southern (Appalachian) margin of the paleocontinent of Laurentia. The only tectonic influence apparent in these passive margin deposits is the expected thickening of the carbonate stack toward the platform margin as compared to the thinner (and typically shallower) facies that formed farther in toward the paleoshoreline. Carbonates overwhelmingly dominate the passive margin succession. Clastic influx was minimal and consisted largely of eastward transport of clean cratonic sands across the platform from the adjacent inner detrital belt to the west during higher order (2nd and 3rd order) regressions. In contrast, Middle and Upper Ordovician deposits of the Tippecanoe megasequence record the strong influence of tectonics, specifically Iapetus closure. The first signal of this tectonic transformation was the arrival of arc-related ash beds that abound in the active margin carbonates. Subsequent intensification of Taconic orogenesis resulted in the foundering of the carbonate platform under the onslaught of fine siliciclastics arriving from offshore tectonic sources to the east, creating a deep marine flysch basin where graptolitic shale and sandstone turbidites accumulated. The foreland basin thus created would fill with progressively coarser and more shallow/proximal clastic facies through the Upper Ordovician, culminating in deposition of fluvial redbeds that cap the Taconic clastic wedge. Arguably the most controversial rocks within the Tippecanoe Sequence in this area are unusual, Lower Ordovician deep marine facies that are associated with the much younger flysch of the Martinsburg Formation in the Great Valley of eastern Pennsylvania. Long considered the erosional remnants of a Taconic-style thrust sheet, and referred to as the Hamburg Klippe, these deep marine deposits have recently been reinterpreted as olistostromal deposits that were introduced by gravity sliding into the flysch basin contemporaneous with Martinsburg deposition. Besides their constituent lithofacies, rocks of the Sauk and Tippecanoe megasequences also present a stark contrast in faunas. Cambrian and Lower Ordovician faunas predate the Great Ordovician Biodiversification Event (GOBE), a global event that saw unprecedented diversification within many major invertebrate groups (mollusks, corals, and bryozoans to name a few) that previously were only minor components of the marine fauna. Unfortunately, the much higher diversity of Middle and Upper Ordovician faunas wrought by the GOBE is somewhat muted in this region by the stresses introduced by conversion of the Appalachian shelf into a flysch basin. Another noteworthy difference between the Cambrian and Ordovician biota related to the paleogeographic setting of the rocks to be examined on this trip derives from their evolution in the shallow marine environments of Laurentia. Several shelf-wide extinctions decimated the shallow marine faunas of the Laurentian shelf through the late Cambrian producing stage-level biostratigraphic units known as biomeres. The biomere phenomenon is discussed in this guidebook and a few stops to examine Cambrian faunas and one biomere boundary extinction are included to provide contrast with stage boundary extinctions that occurred later, in the Ordovician, that lack the defining attributes of the biomere boundary extinctions. Again, it’s all about contrast.

Central Appalachians↗
USGS2020

Extension directions in the Colorado River extensional corridor compared to fragmentation of a structurally disrupted caldera in the Sacramento Mountains, southeastern California

The northwest trend of the southern Colorado River extensional corridor in the southwestern USA veers northward between 34° and 35° north latitude. The tilt axes of early Miocene west-tilted volcanic strata in the west-central Sacramento Mountains mirror this bend. Steeply dipping early Miocene strata and volcanics north and south of the bend indicate the strong respectively westward to southwestward tilt of detached fault blocks and probably of the detachment fault on which they are superposed. These fault panels include fragments of the 18.8 Ma Peach Spring Tuff’s (PST) source caldera. The PST occurs in two major detached fault domains in the Sacramento Mountains where outflow facies ignimbrite grades southward into intracaldera facies. The facies transitions, interpreted as part of the PST’s source caldera’s northeastern margin, lie on a northeast extensional azimuth that would restore them to continuity with the Silver Creek caldera in the Black Mountains, AZ, 50 km to the northeast. This extensional vector agrees with some but not other indicators of extension azimuth such as fault striae, ductile lineations, tilt axes, and elongated plutons. The new results imply spatial variability of extension direction and raise questions about the how this variability may relate to the bend in the Colorado River extensional corridor.

Arizona, California↗
USGS2023

Geology of the Mount Rogers area, revisited: Evidence of Neoproterozoic continental rifting, glaciation, and the opening and closing of the Iapetus Ocean, Blue Ridge, VA–NC–TN

Recent field and geochronological studies in eight 7.5-minute quadrangles near Mount Rogers in Virginia, North Carolina and Tennessee recognize (1) important stratigraphic and structural relationships for the Neoproterozoic Mount Rogers and Konnarock Formations, and the northeast end of the Mountain City window; (2) the separation of Mesoproterozoic rocks of the Blue Ridge into three age groups; and (3) the timing and emplacement of the Blue Ridge thrust sheet. The study area includes folded and faulted Paleozoic strata of the Valley and Ridge in the northwest juxtaposed by metamorphic and igneous rocks of the Blue Ridge to the southeast. In the Valley and Ridge, Cambrian to Middle Ordovician carbonate and clastic rocks are exposed in a syncline in the Pulaski thrust sheet; these rocks are overridden by the Blue Ridge thrust sheet. The northeast end of the Mountain City window is interpreted as a simple window; the Stone Mountain fault is folded and continues as the Iron Mountain fault on the NW-side of the window. The Stone Mountain fault does not exist at the surface to the NE near the Razor Ridge volcanic center. Instead, a continuous section of Proterozoic gneisses, Mount Rogers Formation, Konnarock Formation and Chilhowee Group is now recognized. Rhyolites of the Mount Rogers Formation range from 760–749Ma, with detrital zircon age populations from associated volcaniclastic rocks indicating magmatism and rifting began by ~780 Ma. Rhyolite outliers in the Konnarock Formation and a change from rift-related clastic rocks of the Mount Rogers Formation transitioning to maroon laminites, mudstones and laminites with dropstones, suggest that the Konnarock Formation may be as old as ~751 Ma. Mesoproterozoic crystalline rocks of the Blue Ridge, previously referred to as the Cranberry Gneiss, are distinguished based on field relationships and SHRIMP U–Pb zircon geochronology: (1) ~1.33 Ga pre-Grenvillian crust; (2) 1190–1140 Ma granitoids (early magmatic suite); and (3) 1075–1030 Ma granitoids (late magmatic suite). Multiple greenschist-facies high-strain zones, including the 2–11 km wide Fries high-strain zone, occur in the Blue Ridge thrust sheet. Fabrics across the Fries and Gossan Lead faults have similar orientations and NW–directed contractional deformation. 40 Ar/ 39 Ar hornblende, muscovite, and K-feldspar ages indicate the western and eastern Blue Ridge had different thermal histories. The eastern Blue Ridge (Gossan Lead thrust sheet) experienced a 360–340 Ma amphibolite facies event prior to juxtaposition with the western Blue Ridge. 40 Ar/ 39 Ar muscovite ages in western Blue Ridge rocks document greenschist facies metamorphism and deformation and emplacement of the Blue Ridge thrust sheet at ~340 Ma; the Catface and Fries faults are tentatively interpreted to be contemporaneous. After initial emplacement of the Blue Ridge thrust sheet at ~340 Ma, shortening was accommodated by westward translation along the basal decollement, which carried the Blue Ridge thrust sheet to its current position.

North Carolina, Tennessee, Virginia↗
USGS2008

The experimental basis for interpreting particle and magnetic fabrics of sheared till

Particle fabrics of basal tills may allow testing of the bed-deformation model of glacier flow, which requires high bed shear strains (>100). Field studies, however, have not yielded a systematic relationship between shear-strain magnitude and fabric development. To isolate this relationship four basal tills and viscous putty were sheared in a ring-shear device to strains as high as 714. Fabric was characterized within a zone of shear deformation using the long-axis orientations of fine-gravel and sand particles and the anisotropy of magnetic susceptibility (AMS) of small (???5-8 cm3) intact samples. Results indicate that till particles rotate toward the plane of shearing with long-axis orientations that become tightly clustered in the direction of shear (0??78 < S1 < 0??94 for three-dimensional data). These strong, steady-state fabrics are attained at shear strains of 7-30, with no evidence of fabric weakening with further strain, regardless of the specific till or particle-size fraction under consideration. These results do not support the Jeffery model of particle rotation, which correctly describes particle rotation in the viscous putty but not in the tills, owing to fluid-mechanical assumptions of the model that are violated in till. The sensitivity of fabric development to shear-strain magnitude indicates that, for most till units where shear-strain magnitude is poorly known, attributing fabric variations to spatial differences in other variables, such as till thickness or water content, will be inherently speculative. Attributing fabric characteristics to particular basal till facies is uncertain because shear-strain magnitude is unlikely to be closely correlated to till facies. Weak or spatially variable fabrics, in the absence of post-depositional disturbance or major deviations from unidirectional simple shear, indicate that till has not been pervasively sheared to the high strains required by the bed-deformation model. Strong flow-parallel fabrics are a necessary but insufficient criterion for confirming the model. Copyright ?? 2008 John Wiley & Sons, Ltd.

Earth Surface Processes and Landforms↗
USGS2007

Geoarchaeology of stratified paleoindian deposits at the Big Eddy site, Southwest Missouri, U.S.A

The Big Eddy site (23CE426) in the Sac River valley of southwest Missouri is a rare recorded example of distinctly stratified Early through Late Paleoindian cultural deposits. Early point types recovered from the site include Gainey, Sedgwick, Dalton (fluted and unfluted), San Patrice, Wilson, and Packard. The Paleoindian record at Big Eddy represents only a fraction of the site's prehistoric cultural record; stratified cultural deposits in alluvium above the Paleoindian components span the entire known prehistoric sequence, and terminal Pleistocene alluvium may contain pre-Early Paleoindian cultural deposits. This study focused on the paleogeomorphic setting, stratigraphy, depositional environments, pedology, geochronology, and history of landscape evolution of the late Pleistocene and early Holocene alluvium at the site. The Paleoindian sequence is associated with a complex buried soil 2.85 m below the modern surface (T1a) of the first terrace of the Sac River valley in the site vicinity. This soil formed at the top of the early submember of the Rodgers Shelter Member (underlying the T1c paleogeomorphic surface) and contains at least 70 cm of stratified Paleoindian cultural deposits, all in floodplain and upper point-bar facies. A suite of 36 radiocarbon ages indicates that the alluvium hosting the Paleoindian sequence aggraded between ca. 13,250 and 11,870 cal yr B.P. (11,380 and 10,180 14C yr B.P.). Underlying deposits accumulated between ca. 15,300 and 13,250 cal yr B.P. (12,950 and 11,380 14C yr B.P.). By ca. 11,250 cal yr B.P. (9,840 14C yr B.P.) the T1c paleogeomorphic surface was buried by the earliest increment of a thick sequence of overbank sheetflood facies, ultimately resulting in deep burial and preservation of the Paleoindian record. The landform-sediment assemblage that hosts the Paleoindian and possibly earlier cultural deposits at Big Eddy is both widespread and well preserved in the lower Sac River valley. Moreover, the terminal Pleistocene and early Holocene depositional environments were favorable for the preservation of the archaeological record. ?? 2007 Wiley Periodicals, Inc.

Geoarchaeology↗
USGS2012

Varying sediment sources (Hudson Strait, Cumberland Sound, Baffin Bay) to the NW Labrador Sea slope between and during Heinrich events 0 to 4

Core HU97048-007PC was recovered from the continental Labrador Sea slope at a water depth of 945 m, 250 km seaward from the mouth of Cumberland Sound, and 400 km north of Hudson Strait. Cumberland Sound is a structural trough partly floored by Cretaceous mudstones and Paleozoic carbonates. The record extends from ∼10 to 58 ka. On-board logging revealed a complex series of lithofacies, including buff-colored detrital carbonate-rich sediments [Heinrich (H)-events] frequently bracketed by black facies. We investigate the provenance of these facies using quantitative X-ray diffraction on drill-core samples from Paleozoic and Cretaceous bedrock from the SE Baffin Island Shelf, and on the < 2-mm sediment fraction in a transect of five cores from Cumberland Sound to the NW Labrador Sea. A sediment unmixing program was used to discriminate between sediment sources, which included dolomite-rich sediments from Baffin Bay, calcite-rich sediments from Hudson Strait and discrete sources from Cumberland Sound. Results indicated that the bulk of the sediment was derived from Cumberland Sound, but Baffin Bay contributed to sediments coeval with H-0 (Younger Dryas), whereas Hudson Strait was the source during H-events 1–4. Contributions from the Cretaceous outcrops within Cumberland Sound bracket H-events, thus both leading and lagging Hudson Strait-sourced H-events.

Hudson Strait;Cumberland Sound;Baffin Bay↗
USGS2017

Evidence for Regional Stream Aggradation in the Central Oregon Coast Range during the Pleistocene-Holocene Transition

Low, nearly continuous terraces of similar age are present along streams in drainage basins that range in size from Drift Creek (190 km2) to the Umpqua River (11,800 km2) in the Oregon Coast Range. Radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000-11,000 14C yr B.P. Beveled bedrock surfaces (straths) that underlie the fluvial sediments are 1-8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied. Where exposed, the bedrock straths are overlain by 2-11 m of fluvial sediment that consists of a bottom-stratum (channel) facies of sandy pebble-cobble gravel and a top-stratum (overbank) facies of sandy silt or silt. Eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in Coast Range drainage basins during the Pleistocene-Holocene transition. The cause of such widespread aggradation is unknown but may be related to climate-induced changes in the frequency of evacuation of colluvium from hollows, which are common in all drainage basins in the region.

Quaternary Research↗
USGS1978

Distribution of rutile in metamorphic rocks and implications for placer deposits

Pelitic units in the eastern Great Smoky Mountains of the North Carolina Blue Ridge contain rutile grains only in kyanite and higher zones. Adjacent non-pelitic rocks do not contain rutile at kyanite grade but commonly contain sphene. Detrital rutile breaks down at metamorphic grades lower than those at which metamorphic rutile forms. Similarly, pelitic rocks in southeastern Connecticut contain rutile grains above, but not below, the sillimanite isograd. Most non-pelitic rocks there contain rutile only in the hypersthene zone. The slight difference in behavior of rutile in the two terranes is attributed primarily to a slight difference in calcium content of the pelites. In both areas, rutile commonly appears first as inclusions in garnet. Geologic maps showing metamorphic and stratigraphic or compositional information should be useful as prospecting tools for placer deposits. A variety of rocks at granulite facies and pelitic rocks of the upper amphibolite facies contain rutile and these could provide an extensive source for rutile in rutile placer deposits. ?? 1978 Springer-Verlag.

Mineralium Deposita↗
USGS1988

Geochemistry and origin of albite gneisses, northeastern Adirondack Mountains, New York

Albite gneisses containing up to 8.7 percent Na2O and as little as 0.1% K2O comprise a significant part of the Proterozoic Lyon Mountain Gneiss in the Ausable Forks Quadrangle of the northeastern Adirondacks, New York State. Two distinct types of albite gneisses are present. One is a trondhjemitic leucogneiss (LAG) consisting principally of albite (Ab95-Ab98) and quartz with minor magnetite and, locally, minor amounts of amphibole or acmiterich pyroxene. LAG probably originated by metamorphism of a rhyolitie or rhyodacitic ash-flow tuff with A-type geochemical affinities, following post-depositional analcitization in a saline or saline-alkaline environment. The other type is a mafic albite gneiss (MAG) containing albite and pyroxene along with 0-45 percent quartz, minor amphibole, and titanite. MAG locally displays pinstripe banding and contains albite (Ab98) megacrysts up to 5 cm across. Its precursor may have been a sediment composed of diagenetic analcite or albite, dolomite, and quartz. Both types of albite gneiss are interlayered with granitic gneisses (LMG) of variable composition derived from less altered tuffs. A potassium-rich (up to 9.7% K2O) microcline gneiss facies may have had a protolith rich in diagenetic K feldspar. We propose that the albite gneisses and associated granitic gneisses are the granulite-facies metamorphic equivalent of a bimodal, dominantly felsic, volcanic suite with minor intercalated sediments, probably including evaporites. The volcanics were erupted in an anorogenic setting, such as an incipient or failed intracontinental rift. Deposition took place in a closed-basin, playa lake environment, where diagenetic alteration resulted in redistribution of the alkalis and strong oxidation. ?? 1988 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1971

Distribution of elements in biotite-hornblende pairs and in an orthopyroxene-clinopyroxene pair from zoned plutons, northern Sierra Nevada, California

Distribution of major and minor elements has been determined for five hornblende-biotite pairs from hornblende-biotite quartz diorite and monzotonalite and for a clinopyroxene-orthopyroxene pair from pyroxene diorite collected from the border zones and centers of zoned plutons in the northern Sierra Nevada, California. The distribution coefficients K d [Mg/Fe] for biotite/hornblende are of the same magnitude (0.61–0.67) for both the mafic border zone and the silicic center. For comparison, K D [Mg/Fe] values for biotite/hornblende from plutonic rocks of the central Sierra Nevada and the southern California batholith were calculated from data published by others. Rocks of the oldest age group (ca. 150 m.y.) in the central Sierra Nevada have an average distribution coefficient, K D , of 0.64, close to the average K D in the study area, where K-Ar dates are 143 to 129 m.y. The intermediate age group has an average K D =0.81, and the youngest group has K D =0.77. K D [Mg/Fe] for biotite/hornblende from the southern California batholith is 0.83, close to the average of the intermediate age group in the central Sierra Nevada. The calculated difference in pressure of crystallization between rocks of the Feather River area and the southern California batholith is 1 kb; the rocks of the Feather River area being crystallized at a higher pressure. This is in good agreement with the low-pressure contact metamorphism in the south (pyroxene hornfels facies), as compared with a medium-pressure metamorphism around the northern plutons, where andalusitesillimanite-cordierite and andalusite-staurolite subfacies of the amphibolite facies indicate pressures of about 4 kb. Trace elements Cr, V, Ni, Co, Ga are distributed equally between biotite and hornblende, whereas Ba and possibly Cu are concentrated in biotite and Sr and Sc and possibly Zr in hornblende.

California↗
USGS1989

Depositional history of the Lagniappe Delta, northern Gulf of Mexico

The northern Gulf of Mexico continental shelf is characterized by superimposing deltas. One such delta, informally named Lagniappe, extends east of the Mississippi Delta from mid-shelf to the continental slope. This late Wisconsinan delta is adjacent to, but not associated with the Mississippi Delta complex: the fluvial source was probably the ancient Pearl and/or Mobile Rivers. The fluvially dominated Lagniappe Delta is characterized by complex sigmoid-oblique seismic-reflection patterns, indicating delta switching of high-energy sand-prone facies to low-energy facies. The areal distribution and sediment thickness of the delta were partially controlled by two diapirs. ?? 1989 Springer-Verlag New York Inc.

Geo-Marine Letters↗
USGS2006

Geology and geochemistry of jasperoids from the Gold Bar district, Nevada

Gold Bar is one of several Carlin-type gold mining districts located in the Battle Mountain-Eureka trend, Nevada. It is composed of one main deposit, Gold Bar; five satellite deposits; and four resources that contain 1.6 Moz (50 t) of gold. All of the deposits and resources occur at the intersection of north-northwest- and northeast-trending high-angle faults in slope facies limestones of the Devonian Nevada Group exposed in windows through Ordovician basin facies siliciclastic rocks of the Roberts Mountains allochthon. Igneous intrusions and magnetic anomalies are notably absent. The Gold Bar district contains a variety of discordant and stratabound jasperoid bodies, especially along the Wall Fault zone, that were mapped and studied in some detail to identify the attributes of those most closely associated with gold ore and to constrain genetic models. Four types of jasperoids, J0, J1, J2, and J3, were distinguished on the basis of their geologic and structural settings and appearance. Field relations suggest that J0 formed during an early event. Petrographic observations, geochemistry, and ??18O values of quartz suggest it was overprinted by the hydrothermal event that produced ore-related J1, J2, and J3 jasperoids and associated gold deposits. The greater amount of siliciclastic detritus present in J0 jasperoids caused them to have higher ??18O values than J1,2,3 jasperoids hosted in underlying limestones. Ore-related jasperoids are composed of main-ore-stage replacements and late-ore-stage open-space filling quartz with variable geochemistry and an enormous range of ??18O values (24.5 and -3.7???). Jasperoids hosted in limestones with the most anomalous Au, Ag, Hg, ??(As, Sb, Tl) concentrations and the highest ??18O values are associated with the largest deposits. The 28??? range of jasperoid ??18O values is best explained by mixing between an 18O-enriched fluid and an 18O-depleted fluid. The positive correlation between the sizes of gold deposits and the ??18O composition of jasperoids indicates that gold was introduced by the 18O-enriched fluid. The lowest calculated ??18O value for water in equilibrium with late-ore-stage quartz at 200??C (-15???) and the measured ??D value of fluid inclusion water extracted from late-ore-stage orpiment and realgar (-116???) indicate that the 18O-depleted fluid was composed of relatively unexchanged meteoric water. The source of the 18O-enriched ore fluid is not constrained. The ??34S values of late-ore-stage realgar, orpiment, and stibnite (5.7-15.5???) and barite (31.5-40.9???) suggest that H2S and sulfate were derived from sedimentary sources. Likewise, the ??13C and ??18O values of late-stage calcite (-4.8 to 1.5??? and 11.5 to 17.4???, respectively) suggest that CO2 was derived from marine limestones. Based on these data and the apparent absence of any Eocene intrusions in the district, Gold Bar may be the product of a nonmagmatic hydrothermal system. ?? Springer-Verlag 2006.

Mineralium Deposita↗