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Seaward-dipping strata of carbonate-cemented shell debris located along the coast of Siesta Key on the Gulf Coast of the Florida peninsula have long been interpreted to be beachrock equivalent in age to the Pleistocene Anastasia Formation (Stage 5e) of the east coast of Florida. Detailed examination of thin sections along with radiometric dating and isotopic analyses demonstrates clearly that this is a Holocene deposit that is not beachrock but was lithified in a meteoric environment. Whole rock dates, dates from shells only, and from cement only demonstrate that these beach deposits were in place by at least 1800 yr BP and might have been there as long ago as 4300 yr BP. This means that some type of barrier island...
Categories: Publication; Types: Citation; Tags: Marine Geology
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High-resolution seismic-reflection data have been used to a varying degree by geoscientists to interpret the history of marine sediment accumulations around Antarctica. Reconnaissance analysis of 1-, 3.5-, and 12-kHz data collected by the U.S. Geological Survey in the western Ross Sea has led to the identification of eight echo-character facies and six microtopographic facies in the sediment deposits that overlie the Ross Sea unconformity. Three depositional facies regions, each characterized by a particular assemblage of echo-character type and microtopographic facies, have been identified on the continental shelf. These suites of acoustic facies are the result of specific depositional processes that control type...
Categories: Publication; Types: Citation; Tags: Marine Geology
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We present detailed bathymetry, remotely operated vehicle (ROV) and submersible observations, and sedimentary and radiocarbon age data from carbonate deposits recovered from two submerged terraces at − 150 m (T1) and − 230 m (T2) off Lanai, Hawaii. The tops of the terraces are veneered by relatively thin (<5 m) in situ accumulations of coralline algal nodule, coralgal nodule, Halimeda and a derived oolitic facies deposited in intermediate (30–60 m) to deep fore-reef slope settings (60–120 m). The data are used to develop a sedimentary facies model that is consistent with eustatic sea-level variations over the last 30 ka. Both nodule facies on T1 and T2 initiated growth 30–29 ka following a fall in sea level of ∼50...
Categories: Publication; Types: Citation; Tags: Marine Geology
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A new instrumented tripod, the GEOPROBE system, has been constructed and used to collect time-series data on physical and geological parameters that are important in bottom sediment dynamics on continental shelves. Simultaneous in situ digital recording of pressure, temperature, light scattering, and light transmission, in combination with current velocity profiles measured with a near-bottom vertical array of electromagnetic current meters, is used to correlate bottom shear generated by a variety of oceanic processes (waves, tides, mean flow, etc.) with incipient movement and resuspension of bottom sediment. A bottom camera system that is activated when current speeds exceed preset threshold values provides a unique...
Categories: Publication; Types: Citation; Tags: Marine Geology
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A radiographic scanning technique (RST) can produce single continuous radiographs of cores or core sections up to 1.5 m long and up to 30 cm wide. Changing a portable industrial X-ray unit from the normal still-shot mode to a scanning mode requires simple, inexpensive, easily constructed, and highly durable equipment. Additional components include a conveyor system, antiscatter cylinder-diaphragm, adjustable sample platform, developing tanks, and a contact printer. Complete cores, half cores, sample slabs or peels may be scanned. Converting the X-ray unit from one mode to another is easy and can be accomplished without the use of special tools. RST provides the investigator with a convenient, continuous, high quality...
Categories: Publication; Types: Citation; Tags: Marine Geology
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In exposures of Pleistocene rocks on the east coast of South Africa, eight sedimentary facies were distinguished on the basis of petrology, grain size, internal structures and field relationships. These are interpreted as deposits of surf zone, breaker zone, swash zone, backbeach, boulder beach and dune environments. Three phases of deposition and diagenesis are recognized. As a result of the stabilising effect of pre-existing coastal facies, the deposits from successive sea level stands are stacked vertically in a narrow coast-normal strip. Early cementation prevented erosion of the deposits during subsequent transgressions. Deposition of subsequent facies took place on an existing coastal dune (Facies 1). A terrace...
Categories: Publication; Types: Citation; Tags: Marine Geology
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The surficial sediments have been mapped and the shallow geologic framework outlined of the Maryland inner continental shelf. The initial study encompassed a small area offshore of Assateague Island but was extended northward to include the Ocean City area and eastward across several linear shoals. The surficial sediments are predominantly sand with mean grain sizes ranging from 0.40 to 2.89???. Mud and gravel are the mappable components of the surficial sediments. Muds are distributed along a N-S-trending band seaward of the shoreface. Gravels are mapped farther offshore in 18-22 m of water. Four distinct seismic units are identified from seismic reflection profiles. The lowermost unit, T1, exhibits high-angle...
Categories: Publication; Types: Citation; Tags: Marine Geology
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Recent geophysical surveys off northern California reveal patterns of gullies on the sea floor and preserved within continental-slope deposits that represent both erosional and aggradational processes. These surveys, conducted as part of the STRATAFORM project, combined multibeam bathymetry and backscatter with high-resolution seismic profiles. These data provide a new basis for evaluating gully morphology, distribution, and their significance to slope sedimentation and evolution. The continental margin off northern California exhibits an upper slope that has undergone both progradation and aggradation. The slope surface, which dips at <2??to 4.0??, contains a set of straight, evenly spaced, and parallel to sub-parallel...
Categories: Publication; Types: Citation; Tags: Marine Geology
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The orientations and termination directions of newly formed ice gouges, identified in a 5-year study of two offshore corridors in eastern Harrison Bay, Alasaka, indicate a bimodal distribution of sediment transport directions: west-southwest and southeast, due to ice-keel bulldozing. The westerly sediment transport results from the dominant westward drift of sea ice and ocean currents, whereas the southeasterly transport results from episodic fall storms with winds from the northwest. Transport associated with ice gouging occurs by bulldozing and by resuspension during the bulldozing processes. Fine-grained (< 63 ??m) sediment transport may also involve transport of resuspended sediment by intensified currents found...
Categories: Publication; Types: Citation; Tags: Marine Geology
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As sea level rises and hurricanes become more intense, barrier islands around the world become increasingly vulnerable to conversion from self-sustaining migrating landforms to submerging or subaqueous sand bodies. To explore the mechanism by which such state changes occur and to assess the factors leading to island disintegration, we develop a suite of numerical simulations for the Chandeleur Islands in Louisiana, U.S.A., which appear to be on the verge of this transition. Our results suggest that the Chandeleurs are likely poised to change state, leading to their demise, within decades depending on future storm history. Contributing factors include high rates of relative sea level rise, limited sediment supply,...
Categories: Publication; Types: Citation; Tags: Marine Geology
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Biannual beach profiles were collected at 42 Oahu and 36 Maui Locationsbetween August 1994 and August 1999. Surveys were conducted atapproximately summer-winter intervals and extend from landward of the activebeach to about -4 meters water depth. Profile data on this CDROM arepresented in both Microsoft EXCEL 97/98 & 5.0/95 Workbook (.xls) format andcomma separated value (.csv) format. Graphical representation of the surveys (xvs. z and x vs. y) are presented in EXCEL format only. Site descriptions, includingbeach location, directions to site, GPS information, and a description ofReference Points used, are available in both EXCEL and ADOBE ACROBAT .pdfformat.
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Biannual beach profiles were collected at 42 Oahu and 36 Maui Locationsbetween August 1994 and August 1999. Surveys were conducted atapproximately summer-winter intervals and extend from landward of the activebeach to about -4 meters water depth. Profile data on this CDROM arepresented in both Microsoft EXCEL 97/98 & 5.0/95 Workbook (.xls) format andcomma separated value (.csv) format. Graphical representation of the surveys (xvs. z and x vs. y) are presented in EXCEL format only. Site descriptions, includingbeach location, directions to site, GPS information, and a description ofReference Points used, are available in both EXCEL and ADOBE ACROBAT .pdfformat.
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The influences of wave climate and sediment supply on the depths of sand-mud transitions (hSMT) are investigated. Depths of sand-mud transitions (SMT) are based on published granulometric data from surface samples gathered from 14 sites in different wave-dominated coastal environments with fluvial input, including high energy (Columbia, Eel, Russian, San Lorenzo, Copper, and Nepean rivers), moderate energy (Ebro, Nile, Santa Clara, Tseng-wen and Kao-ping rivers), and low energy (Po, Pescara and Tronto rivers) regimes. Geometric mean diameter (GMD) and mud percent are compiled from samples along shore-normal transects, and significant correlation is found between these two textural descriptors. Nominally, the SMT...
Categories: Publication; Types: Citation; Tags: Marine Geology
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High-resolution multichannel minkisparker seismic-reflection (MCS) profiles were collected by the U.S. Geological Survey in September and October of 2016 from the northern portion of the Santa Barbara Basin offshore southern California. Data were collected aboard the USGS R/V Parke Snavely and NOAA R/V Shearwater during field activity 2016-666-FA. Data were acquired to support USGS geologic hazards projects to aide hazard assessment within the Santa Barbara Basin. High-resolution multichannel minisparker seismic-reflection, multibeam-bathymetry and acoustic-backscatter data were collected to investigate the causes and consequences of submarine landslides in the Santa Barbara Basin. These data and information are...
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Combined EM-300 multibeam bathymetric data and satellite photography reveal the physiography of the continental margin between 35°50′ and 37°03′N and from the shoreline west of 122°40′ and 122°37′W, which includes Monterey Bay, in a previously unprecedented detail. Patterns in these images clearly reveal the processes that are actively influencing the current geomorphology of the Monterey Bay region, including the Monterey Bay National Marine Sanctuary (MBNMS). Our data indicates that seafloor physiography within the MBNMS results from plate margin tectonic deformation, including uplift and erosion along structural lineaments, and from fluid flow. Mass wasting is the dominant process active within the Ascension–Monterey...
Categories: Publication; Types: Citation; Tags: Marine Geology
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Over 150 million m3 of sand-sized sediment has disappeared from the central region of the San Francisco Bay Coastal System during the last half century. This enormous loss may reflect numerous anthropogenic influences, such as watershed damming, bay-fill development, aggregate mining, and dredging. The reduction in Bay sediment also appears to be linked to a reduction in sediment supply and recent widespread erosion of adjacent beaches, wetlands, and submarine environments. A unique, multi-faceted provenance study was performed to definitively establish the primary sources, sinks, and transport pathways of beach-sized sand in the region, thereby identifying the activities and processes that directly limit supply...
Categories: Publication; Types: Citation; Tags: Marine Geology
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The mineralogical compositions of 119 samples collected from throughout the San Francisco Bay coastal system, including bayfloor and seafloor, area beaches, cliff outcrops, and major drainages, were determined using X-ray diffraction (XRD). Comparison of the mineral concentrations and application of statistical cluster analysis of XRD spectra allowed for the determination of provenances and transport pathways. The use of XRD mineral identifications provides semi-quantitative compositions needed for comparisons of beach and offshore sands with potential cliff and river sources, but the innovative cluster analysis of XRD diffraction spectra provides a unique visualization of how groups of samples within the San Francisco...
Categories: Publication; Types: Citation; Tags: Marine Geology
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Observed morphodynamic changes over multiple decades were coupled with storm-driven run-up characteristics at Fire Island, New York, to explore the influence of wave processes relative to the impacts of other coastal change drivers on the near-term evolution of the barrier island. Historical topography was generated from digital stereo-photogrammetry and compared with more recent lidar surveys to quantify near-term (decadal) morphodynamic changes to the beach and primary dune system between the years 1969, 1999, and 2009. Notably increased profile volumes were observed along the entirety of the island in 1999, and likely provide the eolian source for the steady dune crest progradation observed over the relatively...
Categories: Publication; Types: Citation; Tags: Marine Geology


map background search result map search result map Beach profile data for Maui, Hawaii Beach profile data for Oahu, Hawaii Improving understanding of near-term barrier island evolution through multi-decadal assessment of morphologic change Integration of bed characteristics, geochemical tracers, current measurements, and numerical modeling for assessing the provenance of beach sand in the San Francisco Bay Coastal System Sand sources and transport pathways for the San Francisco Bay coastal system, based on X-ray diffraction mineralogy Improving understanding of near-term barrier island evolution through multi-decadal assessment of morphologic change Beach profile data for Oahu, Hawaii Beach profile data for Maui, Hawaii Integration of bed characteristics, geochemical tracers, current measurements, and numerical modeling for assessing the provenance of beach sand in the San Francisco Bay Coastal System Sand sources and transport pathways for the San Francisco Bay coastal system, based on X-ray diffraction mineralogy