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At least 1,477 records · Page 82Linked to original sources

USGS2016

Geochemical characterization and dating of R tephra, a post-glacial marker bed in Mount Rainier National Park, Washington, U.S.A.

The oldest postglacial lapilli–ash tephra recognized in sedimentary records surrounding Mount Rainier (Washington State, USA) is R tephra, a very early Holocene deposit that acts as an important stratigraphic and geochronologic marker bed. This multidisciplinary study incorporates tephrostratigraphy, radiocarbon dating, petrography, and electron microprobe analysis to characterize R tephra. Tephra samples were collected from Tipsoo Lake and a stream-cut exposure in the Cowlitz Divide area of Mount Rainier National Park. Field evidence from 25 new sites suggests that R tephra locally contains internal bedding and has a wider distribution than previously reported. Herein, we provide the first robust suite of geochemical data that characterize the tephra. Glass compositions are heterogeneous, predominantly ranging from andesite to rhyolite in ash- to lapilli-sized clasts. The mineral assemblage consists of plagioclase, orthopyroxene, clinopyroxene, and magnetite with trace apatite and ilmenite. Subaerial R tephra deposits appear more weathered in hand sample than subaqueous deposits, but weathering indices suggest negligible chemical weathering in both deposits. Statistical analysis of radiocarbon ages provides a median age for R tephra of ∼10 050 cal years BP, and a 2σ error range between 9960 and 10 130 cal years BP.

Washington↗

USGS1989

Turbidity-current channels in Queen Inlet, Glacier Bay, Alaska

Queen Inlet is unique among Glacier Bay fjords because it alone has a branching channel system incised in the Holocene sediment fill of the fjord floor. Bathymetry and seismic-reflection profiles show that four channels begin on, or at the base of, the delta front of this marine-outwash fjord. By midpoint of the fjord, these channels have merged into one main channel that extends the length of the fjord. The main channel cuts deeply into the scarp that separates this hanging tributary from the West Arm of Glacier Bay. The Queen Inlet channel ends on the main fjord floor as several small distributaries that form part of a lobate-fan deposit. Sand from the channel and lobate fan, in contrast to fjord-floor mud, plus steep truncated channel walls indicate that turbidity currents created this apparently active channel system. Queen Inlet and other known channel-containing fjords are marine-outwash fjords; the tidewater glacial fjords do not have steep delta fronts on which slides are generated and may not have a sufficient reservoir of potentially unstable coarse sediment to generate channel-cutting turbidity currents. Presence or absence of channels, as revealed in the ancient rock record, may be one criterion for interpreting types of fjords.

Alaska↗

USGS2012

Offshore sand-shoal development and evolution of Petit Bois Pass, Mississippi-Alabama Barrier Islands, Mississippi, USA

Assessment of recently collected geophysical and sediment-core data identifies an extensive shoal field located off Dauphin and Petit Bois Islands. The shoals are the product of Pleistocene fluvial deposition and Holocene marine-transgressive processes, and their position and orientation oblique to the modern shoreline has been stable over the past century. The underlying stratigraphy has also influenced the evolution of the barrier platform and inlets. Buried distributary channels bisect the platform, creating erosion hotspots that breach during intense and repeated storms. Inlet growth inhibits littoral transport, and over time, reduces the down-drift sand supply. These relations demonstrate the role of the antecedent geologic framework on morphologic evolution. This study is part of the USGS Northern Gulf of Mexico Ecosystem Change and Hazard Susceptibility Project and the USACE Mississippi Coastal Improvements Program. These projects produced a wealth of information regarding coastal geology, geomorphology, and physical resources; some of the initial results are presented here.

Alabama;Mississippi↗

USGS2012

Geologic controls on sediment distribution and transport pathways around the Chandeleur Islands, LA., USA

Geophysical surveys around the Chandeleur Islands provide the necessary data to map the thickness and distribution of the Holocene deposit associated with this barrier island system. This system rests uncomformably on St. Bernard Delta deposits of the Mississippi Delta plain and is thinnest under the central part of the island chain and thickest at the northern and southern ends. The zone of divergence in the bidirectional littoral transport system coincides with the thin central part. An estimate of northward littoral transport rate based on lithosome age and the volume of sediment that has accumulated at the northern end of the transport cell suggests the average transport rate over the life of the system is greater than present day fair-weather estimates. This difference may be attributed to changes in transport rates through the life of the system, to changes in the rate of sea-level rise or to storms playing a more dominant role than fair-weather waves in littoral transport.

Louisiana↗

USGS2022

Quaternary fans and terraces in the Khumbu Himal south of Mount Everest: their characteristics, age and formation

Large fans and terraces are frequent in the Khumbu Himal within the high Himalayan valleys south of Mt. Everest. These features are composed of massive matrix- and clast-supported diamicts that were formed from both hyperconcentrated flows and coarse-grained debris flows. Cosmogenic radionuclide (CRN) exposure ages for boulders on fans and terraces indicate that periods of fan and terrace formation occurred at c. 16, c. 12, c. 8, c. 4 and c. 1.5 ka, and are broadly coincident with the timing of glaciation in the region. The dating precision is insufficient to resolve whether the surfaces formed before, during or after the correlated glacial advance. However, the sedimentology, and morphostratigraphic and geomorphological relationships suggest that fan and terrace sedimentation in this part of the Himalaya primarily occurs during glacier retreat and is thus paraglacial in origin. Furthermore, modern glacial-lake outburst floods and their associated deposits are common in the Khumbu Himal as the result of glacial retreat during historical times. We therefore suggest that Late Quaternary and Holocene fan and terrace formation and sediment transfer are probably linked to temporal changes in discharge and sediment load caused by glacier oscillations responding to climate change. The timing of major sedimentation events in this region can be correlated with fans and terraces in other parts of the Himalaya, suggesting that major sedimentation throughout the Himalaya is synchronous and tied to regional climatic oscillations. Bedrock incision rates calculated from strath terrace ages average c. 3.9 mm a −1 , suggesting that the overall rate of incision is set by regional uplift.

Imja Khola Valley, Khumbu Himal, Mount Everest↗

USGS1996

Deep-sea ostracode shell chemistry (Mg:Ca ratios) and late Quaternary Arctic Ocean history

The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for palaeoceanographic study. Shells from the Polar Surface Water (−1 to −1.5°C) had Mg:Ca molar ratios of about 0.006–0.008; shells from Arctic Intermediate Water (+0.3 to +2.0°C) ranged from 0.09 to 0.013. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation ( r 2 = 0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from Arctic and Nordic seas from water depths <900 m. Late Quaternary Krithe Mg:Ca ratios were analysed downcore using material from the Gakkel Ridge (water depths 3047 and 3899 m), the Lomonosov Ridge (water depth 1051 m) and the Amundsen Basin (water depth 4226 m) to test the core-top Mg:Ca temperature calibration. Cores from the Gakkel and Lomonosov ridges display a decrease in Mg:Ca ratios during the interval spanning the last glacial/deglacial transition and the Holocene, perhaps related to a decrease in bottom water temperatures or other changes in benthic environments.

Geological Society Special Publication↗

USGS2000

Tephrochronology of the Brooks River Archaeological District, Katmai National Park and Preserve, Alaska: What can and cannot be done with tephra deposits

The Brooks River Archaeological District (BRAD) in Katmai National Park and Preserve is a classical site for the study of early humans in Alaska. Because of proximity to the active Aleutian volcanic arc, there are numerous tephra deposits in the BRAD, which are potentially useful for correlating among sites of archaeological investigations. Microprobe analyses of glass separates show, however, that most of these tephra deposits are heterogeneous mixtures of multiple glass populations. Some glasses are highly similar to pyroclasts of Aniakchak Crater (160 km to the south), others are similar to pyroclasts in the nearby Valley of Ten Thousand Smokes, and some are similar to no other tephra samples from the Alaska Peninsula. Moreover, tephra deposits in any one archaeological study site are not always similar to those from nearby sites, indicating inconsistent preservation of these mainly thin, fine-grained deposits. At least 15, late Holocene tephra deposits are inferred at the BRAD. Their heterogeneity is the result of either eruptions of mixed or heterogeneous magmas, like the 1912 Katmai eruption, or secondary mixing of closely succeeding tephra deposits. Because most cannot be reliably distinguished from one another on the basis of megascopic properties, their utility for correlations is limited. At least one deposit can be reliably identified because of its thickness (10 cm) and colour stratification. Early humans seem not to have been significantly affected by these tephra falls, which is not surprising in view of the resilience exhibited by both plants and animals following the 1912 Katmai eruption.

Alaska↗

USGS2023

Canada Basin tectono-sedimentary element, Arctic Ocean

The Canada Basin (CB) formed during a short period of seafloor spreading inferred to be Early Cretaceous in age. Brookian strata of inferred Early Cretaceous–Holocene age comprise the sedimentary fill of the Canada Basin Tectono-Sedimentary Element (CB TSE). Although the CB has remained tectonically quiet since seafloor spreading ceased, both proximal and distal tectonism (Alpha Ridge magmatism, and the Cordilleran, Brooks Range and Eurekan orogenies) have influenced sediment source areas, dispersal paths and thicknesses in the basin. In the Neogene, the dominant source of sediments was the Mackenzie River, which drains northern portions of the Cordilleran orogen. The CB TSE is one of the most remote and challenging places on Earth to explore. Although regional seismic reflection and refraction data exist, there are no boreholes to constrain interpretations. Existing published estimates of hydrocarbon potential range from limited to moderate to significant.

Geological Society of London Monograph, Arctic Sed↗

USGS2009

Palaeoseismology of the Vilariça segment of the Manteigas-Bragança fault in northeastern Portugal

The Manteigas-Bragança fault is a major, 250-km-long, NNE-striking, sinistral strike-slip structure in northern Portugal. This fault has no historical seismicity for large earthquakes, although it may have generated moderate (M5+) earthquakes in 1751 and 1858. Evidence of continued left horizontal displacement is shown by the presence of Cenozoic pull-apart basins as well as late Quaternary stream deflections. To investigate its recent slip history, a number of trenches were excavated at three sites along the Vilariça segment, north and south of the Douro River. At one site at Vale Meão winery, the occurrence of at least two and probably three events in the past 14.5 ka was determined, suggesting an average return period of about 5–7 ka. All three events appear to have occurred as a cluster in the interval between 14.5 and 11 ka, or shortly thereafter, suggesting a return period of less than 2 ka between events within the cluster. In the same area, a small offset rill suggests 2–2.5 m of slip in the most recent event and about 6.1 m after incision below a c . 16 ka alluvial fill event along the Douro River. At another site along the Vilariça River alluvial plain, NE of the Vale Meão site, several trenches were excavated in late Pleistocene and Holocene alluvium, and exposed the fault displacing channel deposits dated to between 18 and 23 ka. In a succession of closely spaced parallel cuts and trenches, the channel riser was traced into and across the fault to resolve c . 6.5 m of displacement after 18 ka and c . 9 m of slip after c . 23 ka. These observations yield a slip rate of 0.3–0.5 mm/a, which is consistent with earlier estimates. Combining the information on timing at Vale Meão winery and displacement at Vilariça argues for earthquakes in the M7+ range, with coseismic displacements of 2–3 m. This demonstrates that there are potential seismic sources in Portugal that are not associated with the 1755 Lisbon earthquake or the Tagus Valley, and, although rare, large events on the Vilariça fault could be quite destructive for the region. This work provides an analogue for the study of active faulting in intracontinental settings and supports the view that earthquakes within intracontinental settings tend to cluster in time. In addition, this study highlights the usefulness and application of multiple field, remote sensing and geochronological techniques for seismic hazard mitigation.

Manteigas - Braganca fault↗

USGS2011

Cold-climate slope deposits and landscape modifications of the Mid-Atlantic Coastal Plain, Eastern USA

The effects of Pleistocene cold-climate geomorphology are distributed across the weathered and eroded Mid-Atlantic Coastal Plain uplands from the Wisconsinan terminal moraine south to Tidewater Virginia. Cold-climate deposits and landscape modifications are superimposed on antecedent landscapes of old, weathered Neogene upland gravels and Pleistocene marine terraces that had been built during warm periods and sea-level highstands. In New Jersey, sequences of surficial deposits define a long history of repeating climate change events. To the south across the Delmarva Peninsula and southern Maryland, most antecedent topography has been obscured by Late Pleistocene surficial deposits. These are spatially variable and are collectively described as a cold-climate alloformation. The cold-climate alloformation includes time-transgressive details of climate deterioration from at least marine isotope stage (MIS) 4 through the end of MIS 2. Some deposits and landforms within the alloformation may be as young as the Younger Dryas. Southwards along the trend of the Potomac River, these deposits and their climatic affinities become diffused. In Virginia, a continuum of erosion and surficial deposits appears to be the product of ‘normal’ temperate, climate-forced processes. The cold-climate alloformation and more temperate deposits in Virginia are being partly covered by Holocene alluvium and bay mud.

Geological Society Special Publication↗

USGS2020

Submarine canyons, slope failures and mass transport processes in southern Cascadia

The marine turbidite record along the southern Cascadia Subduction Zone has been used to interpret paleoseismicity and suggest a shorter recurrence interval for large (>M7) earthquakes along this portion of the margin; however, the sources and pathways of these turbidity flows are poorly constrained. We examine the spatial distribution of sediment storage, downslope transport, and slope failures across the margin using multibeam bathymetry, sparker multichannel seismic and chirp subbottom data. Although deep-sea seismoturbidites are often linked to turbidity flows in submarine canyons, the morphology and stratigraphy of southern Cascadia suggests few of the canyons have been active sediment conduits during the recent sea level highstand. Stepped, intraslope basins trap most of the sediment from Rogue and Sixes canyons. Smith and Klamath canyons appear to be isolated, lower slope incisions with no connection to upper slope canyons or gullies. Aggradation and infilling of channels on the upper slope of Trinidad Canyon indicate limited sediment bypass during the Holocene. In contrast, there is evidence of extensive mass wasting of the lower slope, and non-channelized downslope flows outside of the canyon systems that appear to be likely sources of seismoturbidites in southern Cascadia, rather than routing of shelf sediment through submarine canyon systems.

California, Oregon↗

USGS2019

The state of the world’s mangrove forests: Past, present, and future

Intertidal mangrove forests are a dynamic ecosystem experiencing rapid changes in extent and habitat quality over geological history, today and into the future. Climate and sea level have drastically altered mangrove distribution since their appearance in the geological record ∼75 million years ago (Mya), through to the Holocene. In contrast, contemporary mangrove dynamics are driven primarily by anthropogenic threats, including pollution, overextraction, and conversion to aquaculture and agriculture. Deforestation rates have declined in the past decade, but the future of mangroves is uncertain; new deforestation frontiers are opening, particularly in Southeast Asia and West Africa, despite international conservation policies and ambitious global targets for rehabilitation. In addition, geological and climatic processes such as sea-level rise that were important over geological history will continue to influence global mangrove distribution in the future. Recommendations are given to reframe mangrove conservation, with a view to improving the state of mangroves in the future.

Annual Review of Environment and Resources↗

USGS2024

Coastal wetlands in the Anthropocene

We review the functioning and sustainability of coastal marshes and mangroves. Urbanized humans have a 7,000-year-old enduring relationship to coastal wetlands. Wetlands include marshes, salt flats, and saline and freshwater forests. Coastal wetlands occur in all climate zones but are most abundant in deltas. Mangroves are tropical, whereas marshes occur from tropical to boreal areas. Quantification of coastal wetland areas has advanced in recent years but is still insufficiently accurate. Climate change and sea-level rise are predicted to lead to significant wetland losses and other impacts on coastal wetlands and the humans associated with them. Landward migration and coastal retreat are not expected to significantly reduce coastal wetland losses. Nitrogen watershed inputs are unlikely to alter coastal marsh stability because watershed loadings are mostly significantly lower than those in fertilization studies that show decreased belowground biomass and increased decomposition of soil organic matter. Blue carbon is not expected to significantly reduce climate impacts. The high values of ecosystem goods and services of wetlands are expected to be reduced by area losses. Humans have had strong impacts on coastal wetlands in the Holocene, and these impacts are expected to increase in the Anthropocene.

Annual Review of Environment and Resources↗

USGS2023

The Searsville Lake Site (California, USA) as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

Cores from Searsville Lake within Stanford University’s Jasper Ridge Biological Preserve, California, USA, are examined to identify a potential GSSP for the Anthropocene: core JRBP2018-VC01B (944.5 cm-long) and tightly correlated JRBP2018-VC01A (852.5 cm-long). Spanning from 1900 CE ± 3 years to 2018 CE, a secure chronology resolved to the sub-annual level allows detailed exploration of the Holocene-Anthropocene transition. We identify the primary GSSP marker as first appearance of 239,240 Pu (372–374 cm) in JRBP2018-VC01B and designate the GSSP depth as the distinct boundary between wet and dry season at 366 cm (6 cm above the first sample containing 239,240 Pu) and corresponding to October-December 1948 CE. This is consistent with a lag of 1–2 years between ejection of 239,240 Pu into the atmosphere and deposition. Auxiliary markers include: first appearance of 137 Cs in 1958; late 20th-century decreases in δ 15 N; late 20th-century elevation in SCPs, Hg, Pb, and other heavy metals; and changes in abundance and presence of ostracod, algae, rotifer and protozoan microfossils. Fossil pollen document anthropogenic landscape changes related to logging and agriculture. As part of a major university, the Searsville site has long been used for research and education, serves users locally to internationally, and is protected yet accessible for future studies and communication about the Anthropocene.

California↗

USGS2023

The San Francisco Estuary, USA as a reference section for an Anthropocene series

A San Francisco Estuary core was analysed at high resolution to assess its component stratigraphic signatures of the Anthropocene in the form of non-native species, Hg, spheroidal carbonaceous particles, δ 13 C org , δ 15 N, radiogenic materials, and heavy metals. Time series analysis of the core using Ti data provides a chronology to depth 167 cm into the 1960s. Below this, to depth 230 cm, the lowermost part of the core may extend to the 1950s or potentially a little earlier. The earliest anthropogenic marker recorded in the core is the excursion in Hg (beginning at 190 cm) which may denote the early 1960s and is the closest stratigraphic marker in the core to the proposed mid-20th century timing for the onset of the Anthropocene. Biostratigraphical signatures of non-native species arriving in the 1970s–1980s are widespread key markers and are significant tools for the correlation of Anthropocene deposits across the estuary. The absence of signals that indicate pre-1950s deposits precludes the use of the core to mark the Holocene–Anthropocene boundary. However, the core provides an important reference section to demonstrate the palaeontological distinctiveness of Anthropocene series deposits.

California↗

USGS2018

Towards coordinated regional multi-satellite InSAR volcano observations: Results from the Latin America pilot project

Within Latin America, about 319 volcanoes have been active in the Holocene, but 202 of these volcanoes have no seismic, deformation or gas monitoring. Following the 2012 Santorini Report on satellite Earth Observation and Geohazards, the Committee on Earth Observation Satellites (CEOS) developed a 4-year pilot project (2013-2017) to demonstrate how satellite observations can be used to monitor large numbers of volcanoes cost-effectively, particularly in areas with scarce instrumentation and/or difficult access. The pilot aims to improve disaster risk management (DRM) by working directly with the volcano observatories that are governmentally responsible for volcano monitoring as well as with the international space agencies (ESA, CSA, ASI, DLR, JAXA, NASA, CNES). The goal is to make sure that the most useful data are collected at each volcano following the guidelines of the Santorini report that observation frequency is related to volcano activity, and to communicate the results to the local institutions in a timely fashion. Here we highlight how coordinated multi-satellite observations have been used by volcano observatories to monitor volcanoes and respond to crises. Our primary tool is measurements of ground deformation made by Interferometric Synthetic Aperture Radar (InSAR), which have been used in conjunction with other observations to determine the alert level at these volcanoes, served as an independent check on ground sensors, guided the deployment of ground instruments, and aided situational awareness. During this time period, we find 26 volcanoes deforming, including 18 of the 28 volcanoes that erupted - those eruptions without deformation were less than 2 on the VEI scale. Another 7 volcanoes were restless and the volcano observatories requested satellite observations, but no deformation was detected. We describe the lessons learned about the data products and information that are most needed by the volcano observatories in the different countries using information collected by questionnaires. We propose a practical strategy for regional to global satellite volcano monitoring for use by volcano observatories in Latin America and elsewhere to realize the vision of the Santorini report.

Journal of Applied Volcanology↗

USGS2000

Active Fault Near-Source Zones Within and Bordering the State of California for the 1997 Uniform Building Code

The fault sources in the Project 97 probabilistic seismic hazard maps for the state of California were used to construct maps for defining near-source seismic coefficients, N a and N v , incorporated in the 1997 Uniform Building Code (ICBO 1997). The near-source factors are based on the distance from a known active fault that is classified as either Type A or Type B. To determine the near-source factor, four pieces of geologic information are required: (1) recognizing a fault and determining whether or not the fault has been active during the Holocene, (2) identifying the location of the fault at or beneath the ground surface, (3) estimating the slip rate of the fault, and (4) estimating the maximum earthquake magnitude for each fault segment. This paper describes the information used to produce the fault classifications and distances.

California↗

USGS2004

Geotechnical reconnaissance of the 2002 Denali fault, Alaska, earthquake

The 2002 M7.9 Denali fault earthquake resulted in 340 km of ruptures along three separate faults, causing widespread liquefaction in the fluvial deposits of the alpine valleys of the Alaska Range and eastern lowlands of the Tanana River. Areas affected by liquefaction are largely confined to Holocene alluvial deposits, man-made embankments, and backfills. Liquefaction damage, sparse surrounding the fault rupture in the western region, was abundant and severe on the eastern rivers: the Robertson, Slana, Tok, Chisana, Nabesna and Tanana Rivers. Synthetic seismograms from a kinematic source model suggest that the eastern region of the rupture zone had elevated strong-motion levels due to rupture directivity, supporting observations of elevated geotechnical damage. We use augered soil samples and shear-wave velocity profiles made with a portable apparatus for the spectral analysis of surface waves (SASW) to characterize soil properties and stiffness at liquefaction sites and three trans-Alaska pipeline pump station accelerometer locations. ?? 2004, Earthquake Engineering Research Institute.

Earthquake Spectra↗