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At least 73 records · Page 4Linked to original sources
USGS2009

Sedimentology and hydrodynamic implications of a coarse-grained hurricane sequence in a carbonate reef setting

Storms and associated surges are major coast-shaping processes. Nevertheless, no typical sequences for storm surge deposits in different coastal settings have been established. This study interprets a coarse-grained hurricane ridge deposit on the island of Bonaire, Netherlands Antilles. The sequence was deposited during Hurricane Lenny in November 1999. Insight is gained into the hydrodynamics of surge flow by interpreting textural trends, particle imbrication, and deposit geometry. Vertical textural variations, caused by time-dependent hydrodynamic changes, were used to subdivide the deposit into depositional units that correspond to different stages of the surge, such as setup, peak, and return flow. Particle size and imbrication trends and geometry of the units reflect landward bed-load transport of components during the setup, a nondirectional flow with sediment falling out of suspension during the peak, and a seaward bedload transport during the return flow. Formation of a ridge during setup affected the texture of the return flow unit. Changing angles of imbrication reflect alternating flow velocities during each phase. Normal grading during setup and inverse grading during return flow are caused by decelerating and accelerating flow, respectively. Hence, the interpreted deposit seems to represent the first described complete hurricane surge sequence from a carbonate environment. ?? 2009 Geological Society of America.

Geology↗
USGS1981

Paleogeography and sedimentology of Upper Cretaceous turbidites, San Diego, California

Upper Cretaceous (Campanian and Maestrichtian) marine strata of the Rosario Group in the San Diego area include the Point Loma Formation and overlying Cabrillo Formation. These units contain six facies associations: (1) shelf and lagoonal sandstone, (2) slope and basin-plain(?) mudstone, (3) outer-fan lobe sandstone, (4) middle-fan channel-fill sandstone, (5) middle-and inner-fan interchannel and channel-margin thin-bedded turbidites and mudstone, and (6) inner-fan channel-fill conglomerate and sandstone. The facies associations define a deep-sea fan deposited by westward-flowing sediment gravity flows that transported sediments derived chiefly from batholithic and prebatholithic metamorphic rocks of the Peninsular Ranges. The sedimentary basin initially deepened abruptly, partly aided by eustatic sea-level rise. The fan then prograded westward into the basin, with a retrogradational phase recorded in the uppermost part of the sequence, which is erosionally truncated by transgressive lower Eocene conglomerate. The fan was deposited along the eastern edge of a forearc basin similar to that of the Great Valley sequence in northern California. The western part of the fan, which probably contained mostly outer-fan lobe and associated basin-plain deposits, appears to have been truncated by late Cenozoic strike-slip faulting associated with the San Andreas fault system. The fan and remnants of the western part of the basin and associated subduction complex may be present on the northwest in the Channel Islands region or still farther north.

California↗
USGS1990

Sedimentology and petroleum occurrence, Schoolhouse Member, Maroon Formation (Lower Permian), northwestern Colorado

The Lower Permian Schoolhouse Member of the Maroon Formation forms a partly exhumed petroleum reservoir in the Eagle basin of northwestern Colorado. The Schoolhouse consists mainly of yellowish gray to gray, low-angle to parallel bedded, very fine to fine-grained sandstone of eolian sand-sheet origin; interbedded fluvial deposits are present in most sections. Geological and geochemical data suggest that Schoolhouse Member oils have upper Paleozoic sources, including the intrabasinal Belden Formation. Late Paleozoic faults have served as local conduits for vertical petroleum migration. Large-scale (>200 km) lateral migration from sources in the Permian Phosphoria Formation is also possible but less likely. Belden oil was generated and migrated before about 75 Ma. Subsequently, the Schoolhouse Member reservoir was uplifted, then partly exhumed on the monoclinal flank of the Laramide (latest Cretaceous-Paleogene) White River uplift. -from Authors

Colorado↗
USGS1983

Sedimentology of Southwestern Roads region, U.S. Virgin Islands: origin and rate of sediment accumulation

Sand deposits on southern insular shelf of St. Thomas, U.S. Virgin Islands, were investigated to determine their origin, environmental processes and accumulation rates. Sea-floor samples show that the sand has been derived (in situ) mainly from calcareous algae and molluscs. Zonation of the dominant sand producers is related to the present environmental setting; water depth has the greatest influence. Carbon-14 data (bulk sample) of cores indicate accumulation rates of slightly less than 1 mm/year for the last 5,000 years. Faunal studies show that the climate has remained constant over the past 5,000 years. The only changes in environmental conditions appear to have been an increase in water depth, changes in the patterns of water movement, and an increase in water temperature.

Virgin Islands↗
USGS1984

Macrotidal subarctic environment of Turnagain and Knik Arms, Upper Cook Inlet, Alaska: sedimentology of the intertidal zone

An extensive sheet of silty sand crossed by tidal channels is exposed at low tide in Turnagain and Knik Arms, Alaska. Transportation and deposition of sediment composing this sheet is the result of strong tidal currents due to the maximum spring tidal range of approximately 11.4 m. In Turnagain and Knik Arms, the initiation of the floodtide is accompanied by the occurrence of a tidal bore that travels at a speed of 4 m/sec or more up the tidal channels. In intertidal environments in many parts of the world, physical processes of sedimentation are typically influenced by surface fauna; sedimentary structures in some zones are altered or obliterated by the activities of the infauna. However, in Turnagain and Knik Arms, virtually no macrofauna exist, and so the area provides an opportunity to study depositional processes and sedimentary structures without the masking effects of bioturbation. Suspended-sediment values for Turnagain and Knik Arms are greatest in the summer months and nearest low-tide stages. Ice floes form during winter months and, in combination with the freezing of intertidal sediment to several meters of depth, have a significant effect on sediment dispersal and on the deepening and increased stability of the tidal channels. The intertidal sediment is mainly very well sorted, medium to very fine sand and coarse silt, with a notable paucity of gravel, coarse sand, and clay. Sediment accumulates in sandbars oriented parallel to the axis of the estuary. Textural and facies patterns reflect decreasing current energy, first, as a function of distance from the mouth of the estuary and, second, as a function of topographic elevation on the sandbars. The intertidal deposits in Turnagain Arm contain a transitional upward-fining sequence which is analogous to point-bar and channel-bar successions described by other workers. The base of the sequence contains parallel-laminated sand that is overlain by mixed parallel- and cross-laminated silty sand overlain by cross-laminated silty sand. At the top of the sequence is a unit of organically rich parallel-laminated silt and sandy silt. This suite of sedimentary features and textures indicates changing current velocities and directions as bars emerge or are modified during ebb tide, and the vertical sequences could potentially be used to record intertidal bar erosion and aggradation by point- and channel-bar migration, a process carried out primarily by bed-load currents.

Journal of Sedimentary Petrology↗
USGS1986

Sedimentology and clast orientations of the 18 May 1980 southwest- flank lahars, Mount St. Helens, Washington

Three lahars that resulted from the flow transformation of an inflated pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic Mount St . Helens eruption of 18 May 1980 deposited about 1 x 10 6 m 3 of massive, poorly sorted, poorly graded volcaniclastic sediment on the SW flank (SWF). Downflow changes in mean grain size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4mm, and occur only in the basal portion of the deposits; both mean grain size and sorting coefficient increase slightly with distance. The deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting, but lahar clast fabric may be more complex and variable than previously suggested.

Washington↗
USGS1987

Fabric and its relation to sedimentologic and physical properties of near-surface sediment, Shelikof Strait and Alsek prodelta, Alaska

To investigate the possible relation between the fabric (microstructural arrangement of particles) of a fine-grained sedimentary deposit and the depositional and environmental processes of that deposit, the fabric of sediment samples from the sea floor of two different depositional settings, Shelikof Strait and the Alsek prodelta, Alaska, were studied by using scanning electron microscopy (SEM). Sediment of both areas is texturally similar, consisting of a muddy sand that grades to a mud with increasing water depth. Mineralogically, both areas are characterized by a clay-size fraction dominated by illite, chlorite, and rock flour. The dominant fabric of undisturbed sediment from both study areas consists of a sand- and coarse-silt-size agranular fraction surrounded by an open matrix of clay- and fine-silt-size platelets arranged in a combination of randomly oriented flocs and many single grain contacts. The similarity of the fabric of sediment from the two study areas suggests that the fabric is not controlled by the different depositional settings but rather by the dominant clay mineralogy and sediment texture. The most noticeable alteration of the original fabric of Shelikof Strait and Alsek prodelta sediment occurs as a result of high levels of consolidation and the shearing process.

Journal of Sedimentary Petrology↗
USGS1989

Whitings, a sedimentologic dilemma

Whitings, drifting clouds of water, milky because of suspended carbonate, have been claimed to originate from either the action of bottom-feeding fish or direct precipitation of calcium carbonate. Five cruises during different seasons were made to the Great Bahama Bank to collect data pertinent to the controversy. Measurements of particulate concentrations average 10 mg/liter with a maximum of 20 mg/liter of carbonate sediment suspended in whiting water, compared with an average of 1.5 mg/liter for clear water outside the whitings. The particles are dominantly acicular aragonite, but Mg calcite composes as much as 20 percent of some whitings. Sedimentation rates, measured with fixed and drifting sediment traps, were as great as 34 g/m 2 /hr. Sediment suspended in whitings aggregated into silt- and sand-size fioccules and settled to the bottom of settling tanks within six hours, even on a rocking ship. Sediment in artificial whitings, created by stirring sediment from the bottom with a shrimp trawl, settled to the bottom in about the same time. Natural whitings, on the other hand, were never observed to dissipate. Because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours, we conclude that the natural whitings are continually replenished by direct precipitation. The search for fish in whitings utilized sidescan sonar and fathometer imaging, shrimp trawls, rotenone, remote video, and direct scuba observation. These methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most Bahamian whitings. Several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend. The distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish. Stable carbon- and oxygen-isotopic analyses and Delta 14 C activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension. Estimates indicate that the amount of new carbonate produced in whitings on the Great Bahama Bank is substantially higher than that arising from algal production. Consequently, the amount of sediment transported to deep water may be much greater than previously thought.

Journal of Sedimentary Petrology↗
USGS1987

Marine and nonmarine gas-bearing rocks in Upper Cretaceous Blackhawk and Neslen Formations, eastern Uinta Basin, Utah: Sedimentology, diagenesis, and source rock potential

The Upper Cretaceous Blackhawk and Neslen Formations in the eastern Uinta basin contain large amounts of thermogenic gas that was generated from interbedded humic-rich source rocks. The geometry and distribution of hydrocarbon source and reservoir rocks are controlled by depositional environment. The Blackhawk, composed of laterally extensive sandstone and locally interbedded carbonaceous siltstone and minor coal, reflects deposition in nearshore marine and backshore environments. The Neslen contains organic-rich siltstone and mudstone with lesser amounts of carbonaceous shale, coal, and lenticular sandstone that formed in coastal and lower alluvial-plain depositional settings. Potential reservoir sandstones are composed dominantly of monocrystalline quartz grains and sedimentary lithic fragments. Mechanical compaction during early burial was followed by the precipitation of quartz, carbonate, and barite later in the burial history. Variations in porosity and permeability (2-10%; < 1 md) reflects the presence of authigenic clay, mineral cements, and dissolved lithic grains. Natural fractures, cemented with carbonate, barite, and kaolinite, occur locally. Active hydrocarbon generation occurred in the Neslen and Blackhawk during the Oligocene and Miocene when these units were near their maximum burial depth and temperature. The rate of hydrocarbon generation decreased from the late Miocene to the present, owing to widespread cooling that occurred in response to regional uplift and erosion associated with the development of the Colorado Plateau. Temporally equivalent rocks in other areas of the basin may have experienced similar diagenetic and hydrocarbon generation histories.

Colorado, Utah↗
USGS2007

Sedimentology, stratigraphy, and depositional environment of the Crystal Geyser Dinosaur Quarry, east-central Utah

The Crystal Geyser Dinosaur Quarry, near Green River, Utah, is located at the base of the Lower Cretaceous (Barremian) Yellow Cat Member of the Cedar Mountain Formation. The quarry preserves a nearly monospecific accumulation of a new basal therizinosauroid, Falcarius utahensis. We used field descriptions and petrographic analysis to determine the depositional environment and development of the quarry strata. Results of these analyses suggest that the quarry represents multiple episodes of bone accumulation buried by spring and overbank flood deposits. Evidence for these previously undescribed spring deposits includes calcite macroscopic structures within the quarry strata - such as pisolites and travertine fragments - and calcite micromorphologies - including radial-fibrous, feather, and scandulitic dendrite morphologies and tufa clasts. At least two episodes of bone incorporation are preserved in the quarry based on their stratigraphic position and lithologic associations. The unique depositional setting in and around the Crystal Geyser Dinosaur Quarry appears to have been favorable for the preservation of vertebrate fossils and provides insight into early Cretaceous environments in North America. Copyright ?? 2007, SEPM (Society for Sedimentary Geology).

Palaios↗
USGS1997

The paradox of nonmarine ichnofaunas in tidal rhythmites; integrating sedimentologic and ichnologic data from the Late Cretaceous of eastern Kansas, USA

The occurrence of trace fossil assemblages dominated by arthropod trackways and surface grazing trails within Carboniferous tidal rhythmites has puzzled sedimentologists and ichnologists, who interpreted them either as marine or nonmarine. The Virgilian (Stephanian) Tonganoxie Sandstone Member (Stranger Formation) at Buildex Quarry (eastern Kansas) consists, for the most part, of planar-laminated coarse-grained siltstones deposited on an upper tidal flat, close to or at the fluvial-estuarine transition of a macrotidal estuarine paleovalley. Recurrent thickness fluctuations demonstrate the strong influence of tidal processes and provide evidence that these deposits are tidal rhythmites, with thicker strata representing spring tides and thinner ones recording neap tides. The Buildex sequence hosts a moderately diverse ichnofauna composed of arthropod trackways (Dendroidichnites irregulare, Diplichnites gouldi, Diplopodichnus bifurcus, Kouphichnium isp., Mirandaichnium famatinense, Stiallia pilosa, Stiaria intermedia), grazing traces (Gordia indianaensis, Helminthoidichnites tenuis, Helminthopsis hieroglyphica), subsurface feeding traces (Treptichnus bifurcus, T. pollardi, irregular networks), apterygote insect resting and feeding traces (Tonganoxichnus buildexensis, T. ottawensis), fish traces (Undichna britannica, U. simplicitas), and tetrapod trackways. In contrast to trace fossil assemblages from brackish-water estuarine settings, the Buildex ichnofauna is characterized by moderate to relatively high ichnodiversity, ichnotaxa commonly present in terrestrial/freshwater environments, dominance of surface trails and absence of burrows, dominance of temporary structures produced by a mobile deposit-feeder fauna, a mixture of traces belonging to the Scoyenia and Mermia ichnofacies, moderate density of individual ichnotaxa, and absence of monospecific suites. This ichnofauna is thought to record the activity of a typical freshwater/terrestrial benthos. The presence of this mixed freshwater/terrestrial ichnofauna in tidal rhythmites is regarded as indicative of tidal flats that were developed in the most proximal zone of the inner estuary under freshwater conditions, more precisely in a zone between the maximum limit of landward tidal currents and the salinity limit further towards the sea. Although lithofacies distribution in estuarine valleys is mainly salinity-independent, the distribution of benthos is not. Accordingly, ichnologic studies have the potential to provide a high-resolution delineation of fluvio-estuarine transitions.

Kansas↗
USGS1990

Site 765: Sedimentology

Various techniques were used to decipher the sedimentation history of Site 765, including Markov chain analysis of facies transitions, XRD analysis of clay and other minerals, and multivariate analysis of smear-slide data, in addition to the standard descriptive procedures employed by the shipboard sedimentologist. This chapter presents brief summaries of methodology and major findings of these three techniques, a summary of the sedimentation history, and a discussion of trends in sedimentation through time.

Proceedings of the Ocean Drilling Program: Initial↗
USGS1987

Petrology and sedimentology of the Horlick Formation (Lower Devonian), Ohio Range, Transantarctic Mountains

The Horlick Formation of Early Devonian age is as thick as 50 m and consists of subhorizontal, interbedded subarkosic sandstone and chloritic shale and mudstone. The Horlick overlies an erosion surface cut into Ordovician granitic rocks and is, in turn, overlain by Carboniferous and Permian glacial and periglacial deposits. Textures, sedimentary structures, and ubiquitous marine body fossils and animal traces suggest that the Horlick was deposited on a shallow shelf having moderate wave energy and a moderate tidal range. The source terrane probably lay to the north, and longshore transport was toward the west.

Bulletin↗