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Mary McGann

Publications and source records attributed to Mary McGann.

At least 55 records · Page 3Linked to original sources
USGS2013

The timing of sediment transport down Monterey Submarine Canyon, offshore California

While submarine canyons are the major conduits through which sediments are transported from the continents out into the deep sea, the time it takes for sediment to pass down through a submarine canyon system is poorly constrained. Here we report on the first study to couple optically stimulated luminescence (OSL) ages of quartz sand deposits and accelerator mass spectrometry 14 C ages measured on benthic foraminifera to examine the timing of sediment transport through the axial channel of Monterey Submarine Canyon and Fan, offshore California. The OSL ages date the timing of sediment entry into the canyon head while the 14 C ages of benthic foraminifera record the deposition of hemipelagic sediments that bound the sand horizons. We use both single-grain and small (∼2 mm area) single-aliquot regeneration approaches on vibracore samples from fining-upward sequences at various water depths to demonstrate relatively rapid, decadal-scale sand transport to at least 1.1 km depth and more variable decadal- to millennial-scale transport to a least 3.5 km depth on the fan. Significant differences between the time sand was last exposed at the canyon head (OSL age) and the timing of deposition of the sand (from 14 C ages of benthic foraminifera in bracketing hemipelagic sediments) are interpreted as indicating that the sand does not pass through the entire canyon instantly in large individual events, but rather moves multiple times before emerging onto the fan. The increased spread in single-grain OSL dates with water depth provides evidence of mixing and temporary storage of sediment as it moves through the canyon system. The ages also indicate that the frequency of sediment transport events decreases with distance down the canyon channel system. The amalgamated sands near the canyon head yield OSL ages that are consistent with a sub-decadal recurrence frequency while the fining-upward sand sequences on the fan indicate that the channel is still experiencing events with a 150–250 year recurrence frequency out to 3.5 km water depths.

Geological Society of America Bulletin↗
USGS2013

Geologic history of the summit of Axial Seamount, Juan de Fuca Ridge

Multibeam (1 m resolution) and side scan data collected from an autonomous underwater vehicle, and lava samples, radiocarbon-dated sediment cores, and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on Axial Seamount's summit and upper rift zones. The maps show 52 post-410 CE lava flows and 20 precaldera lava flows as old as 31.2 kyr, the inferred age of the caldera. Clastic deposits 1–2 m thick accumulated on the rims postcaldera. Between 31 ka and 410 CE, there are no known lava flows near the summit. The oldest postcaldera lava (410 CE) is a pillow cone SE of the caldera. Two flows erupted on the W rim between ∼800 and 1000 CE. From 1220 to 1300 CE, generally small eruptions of plagioclase phyric, depleted, mafic lava occurred in the central caldera and on the east rim. Larger post-1400 CE eruptions produced inflated lobate flows of aphyric, less-depleted, and less mafic lava on the upper rift zones and in the N and S caldera. All caldera floor lava flows, and most uppermost rift zone flows, postdate 1220 CE. Activity shifted from the central caldera to the upper S rift outside the caldera, to the N rift and caldera floor, and then to the S caldera and uppermost S rift, where two historical eruptions occurred in 1998 and 2011. The average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions.

Geochemistry, Geophysics, Geosystems↗
USGS2013

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

Over 150 million m 3 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 to the outer coast. This integrative program is based on comprehensive surficial sediment sampling of the San Francisco Bay Coastal System, including the seabed, Bay floor, area beaches, adjacent rock units, and major drainages. Analyses of sample morphometrics and biological composition (e.g., Foraminifera) were then integrated with a suite of tracers including 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopes, rare earth elements, semi-quantitative X-ray diffraction mineralogy, and heavy minerals, and with process-based numerical modeling, in situ current measurements, and bedform asymmetry to robustly determine the provenance of beach-sized sand in the region.

California↗
USGS2013

Distribution of biologic, anthropogenic, and volcanic constituents as a proxy for sediment transport in the San Francisco Bay Coastal System

Although conventional sediment parameters (mean grain size, sorting, and skewness) and provenance have typically been used to infer sediment transport pathways, most freshwater, brackish, and marine environments are also characterized by abundant sediment constituents of biological, and possibly anthropogenic and volcanic, origin that can provide additional insight into local sedimentary processes. The biota will be spatially distributed according to its response to environmental parameters such as water temperature, salinity, dissolved oxygen, organic carbon content, grain size, and intensity of currents and tidal flow, whereas the presence of anthropogenic and volcanic constituents will reflect proximity to source areas and whether they are fluvially- or aerially-transported. Because each of these constituents have a unique environmental signature, they are a more precise proxy for that source area than the conventional sedimentary process indicators. This San Francisco Bay Coastal System study demonstrates that by applying a multi-proxy approach, the primary sites of sediment transport can be identified. Many of these sites are far from where the constituents originated, showing that sediment transport is widespread in the region. Although not often used, identifying and interpreting the distribution of naturally-occurring and allochthonous biologic, anthropogenic, and volcanic sediment constituents is a powerful tool to aid in the investigation of sediment transport pathways in other coastal systems.

California↗
USGS2013

Heavy mineral analysis for assessing the provenance of sandy sediment in the San Francisco Bay Coastal System

Heavy or high-specific gravity minerals make up a small but diagnostic component of sediment that is well suited for determining the provenance and distribution of sediment transported through estuarine and coastal systems worldwide. By this means, we see that surficial sand-sized sediment in the San Francisco Bay Coastal System comes primarily from the Sierra Nevada and associated terranes by way of the Sacramento and San Joaquin Rivers and is transported with little dilution through the San Francisco Bay and out the Golden Gate. Heavy minerals document a slight change from the strictly Sierran-Sacramento mineralogy at the confluence of the two rivers to a composition that includes minor amounts of chert and other Franciscan Complex components west of Carquinez Strait. Between Carquinez Strait and the San Francisco Bar, Sierran sediment is intermingled with Franciscan-modified Sierran sediment. The latter continues out the Gate and turns southward towards beaches of the San Francisco Peninsula. The Sierran sediment also fans out from the San Francisco Bar to merge with a Sierran province on the shelf in the Gulf of the Farallones. Beach-sand sized sediment from the Russian River is transported southward to Point Reyes where it spreads out to define a Franciscan sediment province on the shelf, but does not continue southward to contribute to the sediment in the Golden Gate area.

California↗
USGS2012

The FOBIMO (FOraminiferal BIo-MOnitoring) initiative—Towards a standardised protocol for soft-bottom benthic foraminiferal monitoring studies

The European Community Marine Strategy Framework Directive (MSFD) was established to provide guidelines for monitoring the quality of marine ecosystems. Monitoring the status of marine environments is traditionally based on macrofauna surveys, for which standardised methods have been established. Benthic foraminifera are also good indicators of environmental status because of their fast turnover rates, high degree of specialisation, and the preservation of dead assemblages in the fossil record. In spite of the growing interest in foraminiferal bio-monitoring during the last decades, no standardised methodology has been proposed until today. The aim of the FOraminiferal BIo-MOnitoring (FOBIMO) expert workshop, held in June 2011 at Fribourg, Switzerland, which assembled 37 scientists from 24 research groups and 13 countries, was to develop a suite of standard methods. This paper presents the main outcome of the workshop, a list of motivated recommendations with respect to sampling devices, sample storage, treatment, faunal analysis and documentation. Our recommendations fulfil the criteria imposed both by scientific rigour and by the practical limitations of routine studies. Hence, our aim is to standardise methodologies used in bio-monitoring only and not to limit the use of different methods in pure scientific studies. Unless otherwise stated, all recommendations concern living (stained) benthic foraminiferal assemblages. We have chosen to propose two types of recommendations. Mandatory recommendations have to be followed if a study wants to qualify as sound and compatible to the norms. The most important of these recommendations are the interval from 0 to 1 cm below the sediment surface has to be sampled, and an interface corer or box corer that keeps the sediment surface intact is to be used for offshore surveys. A grab sampler must not be deployed in soft sediments. Three replicate samples are to be taken and analysed separately. Samples are to be washed on a 63-μm screen, and the living benthic foraminiferal fauna of the > 125 μm fraction is to be analysed. Splits are to be picked and counted entirely, and all counted foraminifera from at least one replicate per station have to be stored in micropalaeontological slides. Census data, supplementary laboratory data and microslides have to be archived. Advisory recommendations are to sample in autumn, to have a sample size of 50 cm 2 or a tube of 8 cm inner diameter, to use > 70% ethanol as a preservative, rose Bengal at a concentration of 2 grams per litre for staining, and a staining time of at least 14 days. The split size should be defined by a target value of 300 specimens, heavy liquid separation should be avoided, and the 63–125 μm fraction or deeper sediment levels may be considered in some environments. We are convinced that the application of this protocol by a large number of scientists is a necessary first step to a general acceptance of benthic foraminifera as a reliable tool in bio-monitoring studies.

Marine Micropaleontology↗
USGS2012

Arrival and expansion of the invasive foraminifera Trochammina hadai Uchio in Padilla Bay, Washington

Trochammina hadai Uchio, a benthic foraminifera native to Japanese estuaries, was first identified as an invasive in 1995 in San Francisco Bay and later in 16 other west coast estuaries. To investigate the timing of the arrival and expansion of this invasive species in Padilla Bay, Washington, we analyzed the distribution of foraminifera in two surface samples collected in 1971, in nine surface samples collected by Scott in 1972–1973, as well as in two cores (Padilla Flats 3 and Padilla V1/V2) obtained in 2004. Trochanimina hadai , originally identified as the native Trochammina pacifica Cushman in several early foraminiferal studies, dominates the assemblage of most of the surface samples. In the Padilla V1/V2 and Padilla Flats 3 cores, the species' abundance follows a pattern of absence, first appearance, rapid expansion commonly seen shortly after the arrival of a successful biological invasion, setback, and second expansion. Using Q-mode cluster analysis, pre-expansion and expansion assemblages were identified. Pb-210 dating of these cores proved unsuccessful. However, based on T. hadai's first appearance occurring stratigraphically well above sedimentological changes in the cores that reflect deposition of sediments in the bay due to previous diversions of the Skagit River, and its dominance in the early 1970s surface samples, we conclude that the species arrived in Padilla Bay somewhere between the late 1800s and 1971. Trochammina hadai may have been introduced into the bay in the 1930s when oyster culturing began there or, at a minimum, ten years prior to its appearance in San Francisco Bay.

Washington↗
USGS2010

Submarine mass transport within Monterey Canyon: Benthic disturbance controls on the distribution of chemosynthetic biological communities

Documenting mass transport within Monterey Canyon and Fan has been a focus of remotely operated vehicle (ROV) observations, sampling, monitoring, and multibeam mapping studies. These efforts indicate that major mass transport events occur within upper Monterey Canyon (<2 km water depths) with a sub-annual recurrence frequency. However, 14 C-stratigraphies indicate that a sand carrying event has not penetrated through lower Monterey Canyon (>2 km water depths) and onto Monterey Fan for ~100 years. Simultaneous efforts to document the distribution of benthic taxa observed in the video records from 668 ROV dives conducted by the Monterey Bay Aquarium Research Institute (MBARI) provide a uniquely detailed record of the occurrence of chemosynthetic biological communities (CBC). The combined results of these studies provide an understanding of the relationship between disturbance caused by episodic mass wasting events and the distribution of CBC. CBC are common within the canyon's axis below ~2.5 km water depth, but have not been found within the canyon's axis at depths shallower than 2 km. Moreover, CBC occur on the canyon walls at essentially any depth, primarily within young (~hundreds of years old) slump scars. The distribution of CBC provides evidence about the disturbance history of the seafloor. Major mass transport events will destroy communities that lie in their path. Erosion associated with major mass transport events can create environments to support CBC by exposing methane-bearing strata. This can happen as a result of slumping events on the sidewalls of the canyon or where major gravity flow events have excavated the base of canyon walls. Once fresh strata are exposed, geochemical conditions to support CBC will persist for a few centuries. Because CBC are composed of slow-growing and long-lived organisms, it will take decades for these communities to be established. Their existence indicates that environmental stability has occurred over a similar time scale.

California↗
USGS2010

Estuarine sedimentation, sediment character, and foraminiferal distribution in central San Francisco Bay, California

Central San Francisco Bay is the deepest subembayment in the San Francisco Bay estuary and hence has the largest water volume of any of the subembayments. It also has the strongest tidal currents and the coarsest sediment within the estuary. Tidal currents are strongest over the west-central part of central bay and, correspondingly, this area is dominated by sand-size sediment. Much of the area east of a line from Angel Island to Alcatraz Island is characterized by muddy sand to sandy mud, and the area to the west of this line is sandy. The sand-size sediment over west-central bay furthermore is molded by the energetic tidal currents into bedforms of varying sizes and wavelengths. Bedforms typically occur in water depths of 15-25 m. High resolution bathymetry (multibeam) from 1997 and 2008 allow for subdivision of the west-central bayfloor into four basic types based on morphologic expression: featureless, sand waves, disrupted/man-altered, and bedrock knobs. Featureless and sand-wave morphologies dominate the bayfloor of west-central bay. Disrupted bayfloor has a direct association with areas that are undergoing alteration due to human activities, such as sand-mining lease areas, dredging, and disposal of dredge spoils. Change detection analysis, comparing the 1997 and 2008 multibeam data sets, shows that significant change has occurred in west-central bay during the roughly 10 years between surveys. The surveyed area lost about 5.45 million m3 of sediment during the decade. Sand-mining lease areas within west-central bay lost 6.77 million m3 as the bayfloor deepened. Nonlease areas gained 1.32 million m3 of sediment as the bayfloor shallowed slightly outside of sand-mining lease areas. Furthermore, bedform asymmetry did not change significantly, but some bedforms did migrate some tens of meters. Gravity cores show that the area east of Angel and Alcatraz Islands is floored by clayey silts or silty sand whereas the area to the west of the islands is floored dominantly by sand- to coarse sand-sized sediment. Sandy areas also include Raccoon Strait, off Point Tiburon, and on the subtidal Alcatraz, Point Knox, and Presidio Shoals. Drab-colored silty clays are the dominant sediment observed in gravity cores from central bay. Their dominance along the length of the core suggests that silty clays have been deposited consistently over much of this subembayment for the time period covered by the recovered sediments (Woodrow and others, this report). Stratification types include weakly-defined laminae, 1-3 mm thick. Few examples of horizontal lamination in very fine sand or silt were observed. Cross lamination, including ripples, was observed in seven cores. Erosional surfaces were evident in almost every core where x-radiographs were available (they are very difficult to observe visually). Minor cut-and-fill structures also were noted in three cores and inclined strata were observed in three cores. Textural patterns in central bay indicate that silts and clays dominate the shallow water areas and margins of the bay. Sand dominates the tidal channel just east of Angel and Alcatraz Islands and to the west of the islands to the Golden Gate. The pattern of sand-sized sediment, as determined by particle-size analysis, suggests that sand movement is easterly from the west-central part of the bay. A second pattern of sand movement is to the south from the southwestern extremity of San Pablo Bay (boundary approximated by the location of the Richmond-San Rafael Bridge). Age dates for central bay sediment samples were obtained by carbon-14 radiometric age dating. Age dates were determined from shell material that was interpreted to be largely in-place (not transported). Age dates subsequently were reservoir corrected and then converted to calendar years. Sediments sampled from central bay cores range in age from 330 to 4,155 years before present. Foraminiferal distribution in the San Francisco Bay estuary is fairly well

Open-File Report↗
USGS2009

Review of impacts of contaminated sediment on microfaunal communities in the Southern California Bight

A comparison of foraminiferal faunal trends in pristine and impacted regions on the continental shelf and slope of the Southern California Bight, as well as variations in the temporal foraminiferal distribution patterns from 1955 to 1998, suggest that the benthic microfaunal communities have been greatly affected by the presence of contaminated sediment near the major outfall sites. Six species were most impacted: Trochammina pacifica, Bulimina denudata, Eggerella advena, Buliminella elegantissima, Nonionella stella, and Nonionella basispinata. The silver contaminant-tolerant and organic-waste indicating species Trochammina pacifica and Bulimina denudata dominated the outfall regions in the mid-century but declined in abundance in the 1990s after sewage treatment and sludge disposal activities improved. Over the same time period, the abundance of Eggerella advena, a pioneer colonizer of formerly impacted waste-discharge sites tolerant of most trace-metal and organic contaminants, increased dramatically on the shelf, whereas Buliminella elegantissima, a nitrogen-favoring taxon, dominated the nearshore regions except at the pristine site. In contrast, the contaminant-sensitive species Nonionella stella and Nonionella basi-spinata dominated the shelf assemblages in pristine to low-impacted areas in the late 1950s and early 1960s but were rare to absent near the outfalls, even after remediation efforts were put into effect. Although most other species patterns, as well as the amphipod survival and sea urchin fertilization tests, show that the enhanced sewage treatment programs improved sediment conditions, the inability of Nonionella stella and Nonionella basispinata to reinhabit formerly colonized areas suggests that not all faunal trends have returned to pre- or early-outfall levels even with remediation. The sensitivity of foraminifers to the presence of contaminated sediments suggests that they are a useful tool in evaluating the impact of anthropogenic contamination on microfaunal communities.

California↗
USGS2008

Interferometric Sidescan Bathymetry, Sediment and Foraminiferal Analyses; a New Look at Tomales Bay, California

The United States Geological Survey (USGS) in collaboration with Point Reyes National Sea Shore (PRNS), and the Tomales Bay Watershed Council [http://www.tomalesbaywatershed.org/] has completed a detailed bathymetric survey, and sediment and foraminiferal analyses of the floor of Tomales Bay, California. The study goals are to detail the submarine morphology, the sediment distribution, sedimentary features, and distribution of foraminifera to provide a framework for future studies. The USGS collected swath bathymetric data with a SEA SWATHplus interferometric sidescan sonar system (2004, 2005) and an echo sounder system (2006). The data were processed into continuous mosaic images that show bathymetric detail of the bay floor with 0.2-m vertical and 4.0-m horizontal resolution. Acoustic backscatter data from the 2004 and 2005 surveys were processed into 2-m resolution grids. In addition, 27 sediment samples were collected from various parts of the bay for grain size analyses and a comprehensive study of the distribution of foraminifera in Tomales Bay. The foraminiferal analysis determined that the invasive foraminifera Trochammina hadai from Japan was present in Tomales Bay. The project was conducted in response to a request from the National Park Service, and the Tomales Bay Watershed Council who voiced a need to look at the environmental impacts of human input to the surrounding watersheds that ultimately flow into the bay. The mapping, sediment, and foraminiferal data establish a baseline survey for future comparisons of possible geologic and anthropogenic changes that might occur due to changes in land use or development in the surrounding watershed. These data may also aid in determining the possible pathways of pollutants entering the bay from the surrounding watersheds.

Open-File Report↗
USGS2008

Comments on potential geologic and seismic hazards affecting proposed liquefied natural gas site in Santa Monica Bay, California

In a letter to the U.S. Geological Survey (USGS) dated March 25, 2008, Representative Jane Harman (California 36th district) requested advice on geologic hazards that should be considered in the review of a proposed liquefied natural gas (LNG) facility off the California coast in Santa Monica Bay. In 2004, the USGS responded to a similar request from Representative Lois Capps, regarding two proposed LNG facilities offshore Ventura County, Calif., with a report summarizing potential geologic and seismic hazards (Ross and others, 2004). The proposed LNG Deepwater Port (DWP) facility includes single point moorings (SPMs) and 35 miles of underwater pipelines. The DWP submersible buoys, manifolds, and risers would be situated on the floor of the southern Santa Monica Basin, in 3,000 feet of water, about 23 miles offshore of the Palos Verdes Peninsula. Twin 24-inch diameter pipelines would extend northeastward from the buoys across the basin floor, up the basin slope and across the continental shelf, skirting north around the Santa Monica submarine canyon. Figure 1 provides locations of the project and geologic features. Acronyms are defined in table 1. This facility is being proposed in a region of known geologic hazards that arise from both the potential for strong earthquakes and geologic processes related to sediment transport and accumulation in the offshore environment. The probability of a damaging earthquake (considered here as magnitude 6.5 or greater) in the next 30 years within about 30 miles (50 km) of the proposed pipeline ranges from 16% at the pipeline's offshore end to 48% where it nears land (Petersen, 2008). Earthquakes of this magnitude are capable of producing strong shaking, surface fault offsets, liquefaction phenomena, landslides, underwater turbidity currents and debris flow avalanches, and tsunamis. As part of the DWP license application for the Woodside Natural Gas proposal in Santa Monica Bay (known as the OceanWay Secure Energy Project), Fugro West, Inc., had already prepared a document discussing geologic hazards in the area, titled 'Exhibit B Topic Report 6 - Geological Resources' (Fugro West, Inc., 2007); hereafter, this will be called the 'Geological Resources document'. The USGS agreed to evaluate the information in the Geological Resources document regarding (1) proximity of active faults to the proposed project, (2) potential magnitude of seismic events from nearby faults, (3) thoroughness of the assessment of earthquake hazards in general, (4) potential hazards from ground rupture and strong shaking, (5) potential hazards from tsunamis, and (6) other geologic hazards including landslides and debris flows. Because two new earthquake probability reports were scheduled to be released in mid-April, 2008, by the USGS and the California Geological Survey (CGS), the USGS suggested a 6-month review period to enable a thorough incorporation of this new information. Twenty-seven scientists from the USGS and the CGS reviewed various sections of the Geological Resources document. This report outlines our major conclusions. The appendix is a longer list of comments by these reviewers, grouped by section of the Geological Resources document. Before discussing our reviews, we first provide a brief overview of geologic hazards in the proposed site area. This report is a snapshot in time and any future work in the area will need to take into account ongoing research efforts. For example, USGS scientists collected seismic reflection data in the spring of 2008 to study the structure and seismic potential of several faults in the area. Their interpretations (Conrad and others, 2008a and 2008b) are too preliminary to be included in this report, but their final results, along with other researchers' studies in the project area, should be considered in any future work on the Deepwater Port project.

California↗
USGS2006

Geomorphological, depositional, and foraminiferal indicators of late Quaternary tectonic uplift in Iskenderun Bay, Turkey

Iskenderun Bay is a major shallow embayment in the eastern part of the Mediterranean Sea, where the African and Anatolian Plates converge. This tectonically active basin was investigated for oceanographic, sedimentological, geochemical, and foraminiferal parameters. On the basis of the data acquired, the distribution of living and fossil foraminifera in 284 grab and 54 gravity core samples was determined, the basin floor bathymetry of the bay constructed, radiocarbon ages of sediments and fossils ascertained, and depositional environments reconstructed. It has been discovered that for the last 13.5 k.y., water masses were stratified and sedimentation was discontinuous within the basin, which is characterized by irregular sea bottom morphology. The sedimentation rate was very slow, varying in time and space from 0 to 0.012 cm yr −1 . The foraminiferal distributions were spatially varied and discontinuous and indicate a reversal from deep to shallow marine conditions in the cores. These irregularities were attributed to active tectonics in the bay and a major tectonic uplift of the bay since the late Pleistocene.

Iskenderun Bay↗
USGS2004

Late Quaternary deposition in the inner basins of the California continental borderland — Part A. Santa Monica Basin

Radiocarbon dating of sediment core samples from Santa Monica Basin document Holocene (younger than approximately 11 ka) landslides and fault offsets along the basin margin. The new dates include 17 from six piston cores on the continental slope and 11 from Ocean Drilling Program Site 1015 on the basin floor. The dates, which are based on data from pelagic and benthic foraminifera in addition to several dates from mollusk shells, are used to provide chronostratigraphic control for a previously determined basin-wide seismic stratigraphy. The geologic setting at the core sites and a sediment log for each core are shown. In addition, each sediment log is accompanied by a color core photograph as well as P-wave velocity and gamma-ray density profiles. The primary purpose of the report is to make the radiocarbon dates available for other studies in the Santa Monica Basin. A comparison of sediment accumulation rates between the late Pleistocene and Holocene provides insight to the effects of sea-level change on sediment input to the basin. In addition, the results can be used to evaluate the effectiveness of wire-line piston coring in providing age control for earthquake hazard and sedimentologic studies.

California↗
USGS1999

Benthic foraminifers in the regional monitoring program’s San Francisco Estuary samples

For over three decades, sand-sized protozoans known as foraminifers have made contributions to our understanding of environmental problems in urban areas (Alve, 1991; Clark, 1971; Ellison et al., 1986; Watkins, 1961). Benthic foraminiferal assemblages are particularly sensitive pollution indicators in estuarine and coastal areas (Alve, 1995) because they vary spatially and temporally in relation to environmental variables and can respond to almost imperceptible physical change in the environment due to pollutants. Foraminifers also have similar distributions to those of shallow marine invertebrates (Buzas and Culver, 1991, 1993), and can therefore act as proxies for larger organisms in polluted environments. In addition, the ability of foraminifers to respond to environmental degradation is enhanced because they reproduce quickly, as often as every three months to one year (Murray, 1991).

Report↗