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At least 811 records · Page 45Linked to original sources

USGS2010

Radiocarbon dating of small terrestrial gastropod shells in North America

Fossil shells of small terrestrial gastropods are commonly preserved in wetland, alluvial, loess, and glacial deposits, as well as in sediments at many archeological sites. These shells are composed largely of aragonite (CaCO3) and potentially could be used for radiocarbon dating, but they must meet two criteria before their 14C ages can be considered to be reliable: (1) when gastropods are alive, the 14C activity of their shells must be in equilibrium with the 14C activity of the atmosphere, and (2) after burial, their shells must behave as closed systems with respect to carbon. To evaluate the first criterion, we conducted a comprehensive examination of the 14C content of the most common small terrestrial gastropods in North America, including 247 AMS measurements of modern shell material (3749 individual shells) from 46 different species. The modern gastropods that we analyzed were all collected from habitats on carbonate terrain and, therefore, the data presented here represent worst-case scenarios. In sum, ~78% of the shell aliquots that we analyzed did not contain dead carbon from limestone or other carbonate rocks even though it was readily available at all sites, 12% of the aliquots contained between 5 and 10% dead carbon, and a few (3% of the total) contained more than 10%. These results are significantly lower than the 20-30% dead carbon that has been reported previously for larger taxa living in carbonate terrain. For the second criterion, we report a case study from the American Midwest in which we analyzed fossil shells of small terrestrial gastropods (7 taxa; 18 AMS measurements; 173 individual shells) recovered from late-Pleistocene sediments. The fossil shells yielded 14C ages that were statistically indistinguishable from 14C ages of well-preserved plant macrofossils from the same stratum. Although just one site, these results suggest that small terrestrial gastropod shells may behave as closed systems with respect to carbon over geologic timescales. More work on this subject is needed, but if our case study site is representative of other sites, then fossil shells of some small terrestrial gastropods, including at least five common genera, Catinella, Columella, Discus, Gastrocopta, and Succinea, should yield reliable 14C ages, regardless of the local geologic substrate. ?? 2010.

Quaternary Geochronology↗

USGS2026

Hyperspectral narrowband imaging spectroscopy: A new paradigm for Earth observation

This editorial introduces the Special Issue entitled “Hyperspectral Narrowband Imaging Spectroscopy: A New Paradigm for Earth Observation” in the August 2026 issue of Photogrammetric Engineering & Remote Sensing (PE&RS), the flagship journal of the American Society for Photogrammetry and Remote Sensing (ASPRS). This volume represents the fourth dedicated hyperspectral special issue published in PE&RS, following earlier contributions by Thenkabail et al. (2025, 2024a, 2024b), and continues ASPRS’s commitment to advancing cutting‑edge imaging spectroscopy research and its applications across Earth system science. Remote sensing is undergoing one of the most profound transformations in its history. The emergence of hyperspectral narrowband (HNB) imaging spectroscopy data, capable of acquiring hundreds of contiguous, narrow spectral bands, has shifted the discipline from observing Earth in a handful of broad spectral windows to capturing continuous spectral signatures of the Planet. This transition marks a decisive break from the multispectral paradigm that has dominated satellite remote sensing for nearly five decades, driven by the advent of new orbital imaging spectrometers such as EnMAP, PRISMA, and NASA’s EMIT, and by the forthcoming Surface Biology and Geology (SBG) mission ((Pires Silva et al., 2026; Bourriz et al., 2025; Thenkabail et al., 2025; Chabrillat et al., 2024; Aneece et al., 2024; Dave et al., 2024; Thenkabail et al., 2024a; Thenkabail et al., 2024b; Thenkabail, 2024a; Thenkabail, 2024b; Thompson et al., 2022; Kokaly et al., 2022; Aneece & Thenkabail, 2022; Cawse Nicholson et al., 2021; Guanter et al., 2021; Vangi et al., 2021; Thenkabail et al., 2021). These missions (e.g., Table 1) deliver unprecedented spectral fidelity, improved signal to noise ratios, and global coverage capabilities, enabling a new era of quantitative, spectroscopy based Earth observation. Where multispectral broadbands (MBBs) provide only a few discrete measurements along the electromagnetic spectrum, HNB systems deliver rich, diagnostic information that enables scientists to characterize Earth’s surface with unprecedented biochemical, biophysical, and structural detail (Figure 1a, 1b). The implications for environmental monitoring, agriculture, water resources, and mineral exploration are profound. Several overarching themes emerge: • Spectral fidelity matters. The ability to preserve subtle absorption features is essential for mineral mapping, vegetation trait retrieval, and biochemical modeling. • AI and deep learning are indispensable. From destriping to classification, modern analytics must be scalable, label‑efficient, and capable of exploiting the full spectral–spatial richness of HNB data. • Physics‑based and data‑driven approaches must converge. Radiative transfer models such as PROSAIL, enhanced with localized soil parameterizations, remain foundational for biophysical retrievals and model‑based inference. • Dimensionality reduction and feature extraction are critical. Techniques such as L1‑ISOMAP demonstrate that intelligent manifold learning can unlock the structure of fused, high‑dimensional datasets. • Next‑generation architectures must be interactive and multimodal. ICTNet exemplifies the future of hyperspectral classification: hybrid, synergistic, and capable of modeling both local textures and global spectral dependencies.

Photogrammetric Engineering and Remote Sensing (PE↗

USGS2006

The National Assessment of Shoreline Change: A GIS compilation of vector shorelines and associated shoreline change data for the sandy shorelines of the California coast

Introduction The Coastal and Marine Geology Program of the U.S. Geological Survey has generated a comprehensive data clearinghouse of digital vector shorelines and shoreline change rates for the sandy shoreline along the California open coast. These data, which are presented herein, were compiled as part of the U.S. Geological Survey's National Assessment of Shoreline Change Project. Beach erosion is a chronic problem along many open-ocean shores of the United States. As coastal populations continue to grow and community infrastructures are threatened by erosion, there is increased demand for accurate information including rates and trends of shoreline migration. There is also a critical need for shoreline change data that is consistent from one coastal region to another. One purpose of this work is to develop standard, repeatable methods for mapping and analyzing shoreline movement so that periodic, systematic, and internally consistent updates of shorelines and shoreline change rates can be made at a National Scale. This data compilation for open-ocean, sandy shorelines of the California coast is one in a series that already includes the Gulf of Mexico and the Southeast Atlantic Coast (Morton et al., 2004; Morton et al., 2005) and will eventually cover Washington, Oregon, and parts of Hawaii and Alaska. Short- and long-term shoreline change evaluations are determined by comparing the positions of three historical shorelines digitized from maps, with a modern shoreline derived from LIDAR (light detection and ranging) topographic surveys. Historical shorelines generally represent the following time-periods: 1850s-1880s, 1920s-1930s, and late 1940s-1970s. The most recent shoreline is from data collected between 1997 and 2002. Long-term rates of change are calculated by linear regression using all four shorelines. Short-term rates of change are end-point rate calculations using the two most recent shorelines. Please refer to our full report on shoreline change of the California coastline at http://pubs.usgs.gov/of/2006/1219/ for additional information regarding methods and results (Hapke et al., 2006). Data in this report are organized into downloadable layers by region (Northern, Central and Southern California) and are provided as vector datasets with metadata. Vector shorelines may represent a compilation of data from one or more sources and these sources are included in the dataset metadata. This project employs the Environmental Systems Research Institute's (ESRI) ArcGIS as it's GIS mapping tool and contains several data layers (shapefiles) that are used to create a geographic view of the California Coast. These vector data form a basemap comprised of polygon and line themes that include a U.S. coastline (1:80,000), U.S. cities, and state boundaries.

California↗

USGS2002

Subsurface and petroleum geology of the southwestern Santa Clara Valley ("Silicon Valley"), California

Gravity anomalies, historical records of exploratory oil wells and oil seeps, new organic-geochemical results, and new stratigraphic and structural data indicate the presence of a concealed, oil-bearing sedimentary basin beneath a highly urbanized part of the Santa Clara Valley, Calif. A conspicuous isostatic-gravity low that extends about 35 km from Palo Alto southeastward to near Los Gatos reflects an asymmetric, northwest-trending sedimentary basin comprising low-density strata, principally of Miocene age, that rest on higher-density rocks of Mesozoic and Paleogene(?) age. Both gravity and well data show that the low-density rocks thin gradually to the northeast over a distance of about 10 km. The thickest (approx 4 km thick) accumulation of low-density material occurs along the basin's steep southwestern margin, which may be controlled by buried, northeast-dipping normal faults that were active during the Miocene. Movement along these hypothetical normal faults may been contemporaneous (approx 17–14 Ma) with sedimentation and local dacitic and basaltic volcanism, possibly in response to crustal extension related to passage of the northwestward-migrating Mendocino triple junction. During the Pliocene and Quaternary, the normal faults and Miocene strata were overridden by Mesozoic rocks, including the Franciscan Complex, along northeastward-vergent reverse and thrust faults of the Berrocal, Shannon, and Monte Vista Fault zones. Movement along these fault zones was accompanied by folding and tilting of strata as young as Quaternary and by uplift of the modern Santa Cruz Mountains; the fault zones remain seismically active. We attribute the Pliocene and Quaternary reverse and thrust faulting, folding, and uplift to compression caused by local San Andreas Fault tectonics and regional transpression along the Pacific-North American Plate boundary. Near the southwestern margin of the Santa Clara Valley, as many as 20 exploratory oil wells were drilled between 1891 and 1929 to total depths as great as 840 m. At least one pump unit is still standing. Although no lithologic or paleontologic samples are available from the wells, driller's logs indicate the presence of thick intervals of brown shale and sandstone resembling nearby outcrops of the Miocene Monterey Formation. Small amounts of oil and gas were observed in several wells, but commercial production was never established. Oil from the Peck well in Los Gatos is highly biodegraded, contains biomarkers commonly found in oils derived from the Monterey Formation, and has a stable-C-isotopic (d13C) composition of –23.32 permil, indicating derivation from a Miocene Monterey Formation source rock. Preliminary calculations suggest that about 1 billion barrels of oil may have been generated from source rocks within the Monterey Formation in the deepest part of the subsurface sedimentary basin between Los Gatos and Cupertino. Most of this oil was probably lost to biodegradation, oxidation, and leakage to the surface, but some oil may have accumulated in as-yet-undiscovered structural and stratigraphic traps along the complex structural boundary between the Santa Clara Valley and the Santa Cruz Mountains. Although some of these undiscovered accumulations of oil may be of commercial size, future petroleum exploration is unlikely because most of the area is currently devoted to residential, recreational, commercial, and industrial uses.

California↗

USGS2008

TSPP - A collection of FORTRAN programs for processing and manipulating time series

This report lists a number of FORTRAN programs that I have developed over the years for processing and manipulating strong-motion accelerograms. The collection is titled TSPP, which stands for Time Series Processing Programs. I have excluded 'strong-motion accelerograms' from the title, however, as the boundary between 'strong' and 'weak' motion has become blurred with the advent of broadband sensors and high-dynamic range dataloggers, and many of the programs can be used with any evenly spaced time series, not just acceleration time series. This version of the report is relatively brief, consisting primarily of an annotated list of the programs, with two examples of processing, and a few comments on usage. I do not include a parameter-by-parameter guide to the programs. Future versions might include more examples of processing, illustrating the various parameter choices in the programs. Although these programs have been used by the U.S. Geological Survey, no warranty, expressed or implied, is made by the USGS as to the accuracy or functioning of the programs and related program material, nor shall the fact of distribution constitute any such warranty, and no responsibility is assumed by the USGS in connection therewith. The programs are distributed on an 'as is' basis, with no warranty of support from me. These programs were written for my use and are being publicly distributed in the hope that others might find them as useful as I have. I would, however, appreciate being informed about bugs, and I always welcome suggestions for improvements to the codes. Please note that I have made little effort to optimize the coding of the programs or to include a user-friendly interface (many of the programs in this collection have been included in the software usdp (Utility Software for Data Processing), being developed by Akkar et al. (personal communication, 2008); usdp includes a graphical user interface). Speed of execution has been sacrificed in favor of a code that is intended to be easy to understand, although on modern computers speed of execution is rarely a problem. I will be pleased if users incorporate portions of my programs into their own applications; I only ask that reference be made to this report as the source of the programs.

Open-File Report↗

USGS2000

Titanium mineral resources of the western U.S.: An update

Thirteen deposits or districts in the western U.S. have been examined in which titanium mineral resources have been reported or implied. These deposits are of the following general types (in probable order of importance): 1) Cretaceous shoreline placer deposits, 2) silica-sand deposits of California, 3) fluvial monazite placers of Idaho, 4) anorthosite related deposits, and 5) clay and bauxite deposits of the northwestern U.S. Relative to previous reports, this one shows some greater and some lesser resources (table 1). In any case, titanium-mineral resources of the western U.S. (west of 103° longitude) remain modest at world scale except as unconventional (especially perovskite) and by-product (especially porphyry) resources. Some deposits, however, have enhanced value to the titanium explorationist for the geologic relations they illustrate. Among the new conclusions are: a) Loci of Cretaceous shoreline placers form linear patterns, nested as a function of age, that can be traced for thousands of kilometers, permitting focused exploration in whole new mountain ranges. b) Medial hematite-ilmenite solid-solution, which is highly magnetic, is a major carrier of TiO 2 values in the Cretaceous deposits of Wyoming. This phase was previously thought to be relatively rare. c) Regressive shoreline placer deposits in indurated Cretaceous sequences expose intricate facies relations, such as the construction of shoreface sequences by long-shore drift over tidal-channel fill, without much loss of paleogeographic information. d) Due to deep weathering, virtually every Eocene sediment that accumulated in the Ione basin at the foot of the Sierra Nevada has economic value, permitting recovery of altered ilmenite and zircon along with silica, clay, coal, and gold. Ilmenite is most abundant in newly recognized shoreline sands. e) Upper Tertiary fluvial placers of Idaho formed in and filled fault-bounded basins and thus are far more voluminous than deposits in the modern valley system. Previously reported resources are thus far too low. f) Mafic igneous rocks of Proterozoic age near Bagdad, Arizona are of ophiolitic affinity, but contain nelsonitic ilmenite enrichments associated with anorthositic layers.

Open-File Report↗

USGS2019

Calcrete uranium deposits in the Southern High Plains, USA

The Southern High Plains (SHP) is a new and emerging U.S. uranium province. Here, uranyl vanadates form deposits in Pliocene to Pleistocene sandstone, dolomite, and limestone. Fifteen calcrete uranium occurrences are identified; two of these, the Buzzard Draw and Sulfur Springs Draw deposits, have combined in-place resources estimated at about 4 million pounds of U 3 O 8 . Ore minerals carnotite and finchite are hosted in dolomite at the Sulfur Springs Draw deposit, with accessory fluorite, celestine, smectite/illite, autunite, and strontium carbonate. Host carbonate at the Sulfur Springs Draw deposit is ∼190 ka and mineralization mobilized as recently as 3.8 ka. Ash collected near the deposit is 631 ka and erupted from the Yellowstone caldera complex. The Triassic Dockum Group that contains sandstone-hosted uranium deposits throughout the region and underlies the SHP is a potential source for uranium and vanadium. Regional uplift and dissection reintroduced oxygenated groundwater into the Dockum Group, mobilizing uranium. Additional uranium may have been contributed to groundwater by weathering of volcanic ash in Pliocene and Pleistocene host rocks. The locations of the uranium occurrences are mostly in modern drainage systems in the southeast portion of the SHP. Modelling of modern groundwater in the SHP carried out in a parallel study shows that a single fluid could form carnotite through evaporation, and that fluids of the requisite composition are more prevalent in the southern portion of the SHP. The southeastern portion of the SHP hosts more uranium occurrences due to a variety of factors including (1) upward transport of groundwater and connectivity between source and host rock, (2) higher uranium and vanadium content of groundwater, (3) higher rates of groundwater recharge in this region to drive the mineralizing system, and (4) shallower groundwater facilitating surface evaporation. Ongoing erosion of host rocks challenges preservation of deposits and may limit their size.

Southern High Plains↗

USGS2022

Groundwater resources of the Harney Basin, southeastern Oregon

Groundwater development has increased substantially in southeastern Oregon’s Harney Basin since 2010, mainly for the purpose of large-scale irrigation. Concurrently, some areas of the basin experienced groundwater-level declines of more than 100 feet, and some shallow wells have gone dry. The Oregon Water Resources Department has limited new groundwater development in the basin until an improved understanding of the groundwater-flow system is available. This report describes the results of a hydrologic investigation undertaken to provide that understanding. The investigation encompasses the groundwater hydrology of the entire 5,240-square-mile Harney Basin. Most of the precipitation in the Harney Basin falls in the higher-elevation areas of the Blue Mountains and Steens Mountain. Although considerable groundwater recharge occurs in these upland areas, most (83 percent) re-emerges as streams and springs in the uplands. Groundwater recharge in the lowlands is provided through infiltration of surface water flowing onto the lowlands from rivers and streams leaving the uplands and as groundwater flow from the surrounding upland rocks. Water-balance calculations indicate that the rate of groundwater recharge to the Harney Basin lowlands (where most groundwater is withdrawn) averages 173,000 acre-feet per year (acre-ft/yr). Groundwater in the Harney Basin lowlands mainly discharges through evapotranspiration from groundwater-irrigated (supplied from wells) crops or from natural vegetation drawing groundwater from the shallow water table and capillary fringe. Groundwater discharge in the lowlands is estimated to be about 283,000 acre-ft/yr, which exceeds the estimated groundwater recharge to the lowlands by about 110,000 acre-ft/yr. This imbalance results in removal of groundwater from storage in the aquifer system and is evidenced by the large declines observed in groundwater levels in the areas of greatest groundwater pumpage. To a large degree, the location and depth of pumpage dictate the timing and distribution of the effects of groundwater use in the Harney Basin. Pumpage is commonly greatest in the areas where higher-permeability geologic units allow for higher well yields. However, many of these higher-permeability units are bounded by lower-permeability units that cannot supply groundwater at a sufficient rate to replenish the areas of greatest pumpage, resulting in groundwater-level declines. Three Harney Basin areas with a combined area exceeding 140 square miles have experienced groundwater-level declines exceeding 40 feet compared to pre-development conditions: near the Weaver Spring/Dog Mountain area, in the northeastern floodplains along Highway 20, and near Crane. Areas of more modest groundwater-level decline (about 10 feet) were identified in the Virginia Valley area and the Silver Creek floodplain north of Riley. Smaller localized areas of groundwater-level depression have also formed around individual wells or groups of wells throughout the Harney Basin lowlands. Most groundwater being pumped from the Harney Basin lowlands, including all three areas experiencing large groundwater-level declines, was recharged more than 12,000 years ago, near the end of the last glacial period when the climate in the basin was cooler and wetter than today. Geochemical evidence indicates that modern recharge generally circulates to a depth no greater than 100 feet below the floodplains of major rivers and streams in the lowlands. Away from the major river and stream corridors, pre-modern water commonly is found at the water table. Recharge to groundwater and recovery of groundwater levels in the most heavily pumped areas in the Harney Basin lowlands are restricted by the limited spatial extent and depth of modern recharge in the Harney Basin lowlands and the relatively fine-grained deposits underlying most of the lowland areas.

Oregon↗

USGS2004

Delineation of tectonic provinces of New York state as a component of seismic-hazard evaluation

Seismic-hazard evaluations in the eastern United States must be based on interpretations of the composition and form of Proterozoic basement-rock terranes and overlying Paleozoic strata, and on factors that can cause relative movements among their units, rather than Phanerozoic orogenic structures, which may be independent of modern tectonics. The tectonic-province concept is a major part of both probabilistic and deterministic seismic-hazard evaluations, yet those that have been proposed to date have not attempted to geographically correlate modern earthquakes with regional basement structure. Comparison of basement terrane (megablock) boundaries with the spatial pattern of modern seismicity may lead to the mechanically sound definition of tectonic provinces, and thus, better seismic-hazard evaluation capability than is currently available. Delineation of megablock boundaries will require research on the many factors that affect their structure and movement. This paper discusses and groups these factors into two broad categories-megablock tectonics in relation to seismicity and regional horizontal-compressive stresses, with megablock tectonics divided into subcategories of basement, overlying strata, regional lineaments, basement tectonic terranes, earthquake epicenter distribution, and epeirogeny, and compressive stresses divided into pop-ups and the contemporary maximum horizontal-compressive stress field. A list presenting four to nine proposed research topics for each of these categories is given at the end.

Northeastern Geology and Environmental Sciences↗

USGS2014

Surficial geologic map of the Charleston region, Berkeley, Charleston, Colleton, Dorchester, and Georgetown Counties, South Carolina

This map portrays the surface and shallow subsurface geology of the greater Charleston, S.C. region east of 80°30′ west and south of 33°15′ north. The region covers the entirety of Charleston County and portions of Berkeley, Colleton, Dorchester, and Georgetown Counties. Units locally exposed at the surface range in age from middle Eocene to Holocene, but most of the area is covered by Quaternary interglacial deposits. These are, from oldest to youngest, the Okefenokee, Waccamaw(?), Penholoway, Ladson, Ten Mile Hill, and Wando Formations and the Silver Bluff beds. Two cross sections, one running southeast from Harleyville to the coastline on James Island and the other running along the coastal barrier islands from the town of Edisto Beach to the northeast end of Bull Island at the southwest edge of Bull Bay, portray the complex geometry of the Paleogene and Neogene marine units that directly lie beneath the Quaternary units. These older units include the Santee Limestone, Tupelo Bay, Parkers Ferry, Ashley, Chandler Bridge, Edisto, Parachucla, and Marks Head Formations, the Goose Creek Limestone, and the Raysor Formation. The estimated locations of deeply buried active basement faults are shown which are responsible for ongoing modern seismicity in the Charleston, S.C. area.

South Carolina↗

USGS2019

Encylopedia of Caves

For many people, a visit to a cave is a wondrous event directing our minds to ponder the mysteries presented by these unique places and inspiring questions: How old is the cave? What was the role of water in forming the cave and where did the water come from? How is the cave connected to the surface environment? These are intriguing questions to ask, and karst scientists use isotope geochemistry to help solve these mysteries. Isotopes are atoms of the same chemical element that have the same number of protons but vary in their number of neutrons. As a result of their atomic mass difference, isotopes of a single element may exhibit slightly different chemical behavior. Radioisotopes are unstable and the nucleus of a parent isotope will spontaneously break apart (decay), releasing energy and changing into another element (daughter product) by loss or gain of protons, neutrons, or electrons. Stable isotopes, as implied by the name, are stable and do not spontaneously decay. These two types of isotopes are used widely by scientists to understand ancient and modern karst systems. Generally, radioisotopes are used for absolute dating karst water, cave sediments, cave formations (speleothems), and other material preserved in caves (such as bones). Stable isotopes can provide information about relative ages of cave water and speleothems. An absolute age provides a numeric date—such as 100,000 years old—whereas a relative age provides information that something is older or younger than something else—such as cave art is younger than a speleothem found in the same cave. Stable isotopes are used to study ancient karst systems because isotopic signals of past climate (paleoclimate) and environmental conditions (paleoenvironment) are preserved in speleothems and sediments. Stable isotopes are also used to understand modern systems, primarily through studies that distinguish sources of karst water, cave air, or contaminants, mixing of those sources, and biologic or chemical reactions that process compounds, such as breakdown of contaminants or organic matter. The variation in mass among isotopes is small, and isotope abundances are measured as a ratio of a common isotope to its less common isotopic counterparts (stable isotopes) or the abundance of a parent compared to daughter isotope (radioisotopes). As an example, hydrogen (H) has three naturally occurring isotopes. Most H comprises one proton (1H), but the rarer stable isotope (called deuterium) comprises one proton and one neutron (2H), and the radioisotope (called tritium) comprises one proton and two neutrons (3H). Because scientists use the minute differences in isotopes to test hypotheses, a scientist must understand the accuracy, precision, and error of the available methods, the assumptions about the chemical conditions of interest, and the limitations of the isotopic method being used. Many isotopic studies employ multiple isotopic tracers to better leverage the strengths and offset the limitations of using a single isotope. This article focuses on isotopes used to study the geology and hydrology of caves, but much additional isotopic work has been used to characterize the biology of caves.

Book chapter↗

USGS1969

Errors in using modern stream-load data to estimate natural rates of denudation

The practice of calculating natural rates of denudation from routinely collected data on the loads of suspended and dissolved matter in modern rivers is subject to several significant errors. The sources of these errors are demonstrated by examples from the Atlantic drainage of the United States, where their total effect has apparently doubled the natural rate of erosion. The largest error is caused by assuming that modern sediment loads in populated areas represent natural erosion, whereas in fact they mainly reflect the influence of man. Conversion of forests to croplands in the middle Atlantic states causes about a tenfold increase in sediment yield. Coal mining, urbanization, and highway construction have added extra loads of sediment to the streams. Modern sediment loads in the Atlantic-draining rivers are probably 4 to 5 times greater than they would be if the area had remained undisturbed by man. Errors in calculating the chemical denudation are caused by atmospheric contributions to the dissolved loads of streams and by pollutants that are added directly to stream waters. About one-quarter of the salts in Atlantic-draining streams were contributed from the atmosphere, either as recycled sea salts or as pollutants and soil dust that originally became airborne as a result of the activities of man. Perhaps another one-tenth of the dissolved load consists of industrial and agricultural wastes or acid mine waters that have been added directly to the streams.

Connecticut, Delaware, Georgia, Maryland, Massachu↗

USGS2009

Postglacial sedimentary record of the Southern California continental shelf and slope, Point Conception to Dana Point

Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13-11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8-9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate ca. 15-10 ka, a consequence of coastal ravinement and downslope resedimentation, perhaps in conjunction with climatic increases in fluvial sediment delivery. Grain sizes and accumulation rates then decreased after 12-10 ka when the shelf flooded and backfilled under rising sea level. The Santa Barbara coastal cell contains the largest mass of postglacial sediment at 32-42 ?? 10 9 metric tons, most of which occurs between offshore Santa Barbara and Hueneme Canyon. The San Pedro cell contains the second largest quantity of sediment, 8-11 ?? 10 9 metric tons, much of which is present on the eastern Palos Verdes and outer San Pedro shelves. By comparison, the mass of sediment sequestered within the Santa Monica cell is smaller at ??6-8 ?? 10 9 metric tons. The postglacial sediment mass distribution among coastal cells reflects the size of local fluvial sediment sources, whereas intracell accumulation patterns reflect antecedent bathymetric features conducive for sediment bypass or trapping. ?? 2009 The Geological Society of America.

Special Paper of the Geological Society of America↗

USGS2009

Implications of estimated magmatic additions and recycling losses at the subduction zones of accretionary (non-collisional) and collisional (suturing) orogens

Arc magmatism at subduction zones (SZs) most voluminously supplies juvenile igneous material to build rafts of continental and intra-oceanic or island arc (CIA) crust. Return or recycling of accumulated CIA material to the mantle is also most vigorous at SZs. Recycling is effected by the processes of sediment subduction, subduction erosion, and detachment and sinking of deeply underthrust sectors of CIA crust. Long-term (>10-20 Ma) rates of additions and losses can be estimated from observational data gathered where oceanic crust underruns modern, long-running (Cenozoic to mid-Mesozoic) ocean-margin subduction zones (OMSZs, e.g. Aleutian and South America SZs). Long-term rates can also be observationally assessed at Mesozoic and older crust-suturing subduction zone (CSSZs) where thick bodies of CIA crust collided in tectonic contact (e.g. Wopmay and Appalachian orogens, India and SE Asia). At modern OMSZs arc magmatic additions at intra-oceanic arcs and at continental margins are globally estimated at c. 1.5 AU and c. 1.0 AU, respectively (1 AU, or Armstrong Unit,= 1 km 3 a -1 of solid material). During collisional suturing at fossil CSSZs, global arc magmatic addition is estimated at 0.2 AU. This assessment presumes that in the past the global length of crustal collision zones averaged c. 6000 km, which is one-half that under way since the early Tertiary. The average long-term rate of arc magmatic additions extracted from modern OMSZs and older CSSZs is thus evaluated at 2.7 AU. Crustal recycling at Mesozoic and younger OMSZs is assessed at c. 60 km 3 Ma -1 km -1 (c. 60% by subduction erosion). The corresponding global recycling rate is c. 2.5 AU. At CSSZs of Mesozoic, Palaeozoic and Proterozoic age, the combined upper and lower plate losses of CIA crust via subduction erosion, sediment subduction, and lower plate crustal detachment and sinking are assessed far less securely at c. 115 km 3 Ma -1 km -1 . At a global length of 6000 km, recycling at CSSZs is accordingly c. 0.7 AU. The collective loss of CIA crust estimated for modern OMSZs and for older CSSZs is thus estimated at c. 3.2 AU. SZ additions (2.7 AU) and subtractions (23.2 AU) are similar. Because many uncertainties and assumptions are involved in assessing and applying them to the deep past, the net growth of CIA crust during at least Phanerozoic time is viewed as effectively nil. With increasing uncertainty, the long-term balance can be applied to the Proterozoic, but not before the initiation of the present style of subduction at c. 3 Ga. Allowing that since this time a rounded-down rate of recycling of 3 AU is applicable, a startlingly high volume of CIA crust equal to that existing now has been recycled to the mantle. Although the recycled volume (c. 9 ?? 10 9 km 3 ) is small (c. 1%) compared with that of the mantle, it is large enough to impart to the mantle the signature of recycled CIA crust. Because subduction zones are not spatially fixed, and their average global lengths have episodically been less or greater than at present, recycling must have contributed significantly to creating recognized heterogeneities in mantle geochemistry. ?? The Geological Society of London 2009.

Geological Society Special Publication↗

USGS2018

The 1952 Kern County, California earthquake: A case study of issues in the analysis of historical intensity data for estimation of source parameters

Seismic intensity data based on first-hand accounts of shaking give valuable insight into historical and early instrumental earthquakes. Comparing an observed intensity distribution to intensity-prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes. Magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available. However, the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties. In this paper, we illustrate these challenges and possible solutions using the 1952 Kern County, California, earthquake as a case study. Published estimates of its magnitude vary from M W 7.2–7.5, making it possibly the second largest in California during the 20th century. We considered over 1100 first-hand reports of shaking, supplemented with other data, and inferred the magnitude in several ways using intensity prediction equations, yielding a preferred intensity magnitude M I 7.2 ± 0.2, where the uncertainty reflects our judgement. The revised intensity distribution reveals stronger shaking on the hanging wall, south of the surface expression of the White Wolf fault, than on the footwall. Characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region. Such reinterpreted intensities for historic earthquakes, combined with U.S. Geological Survey (USGS) Did You Feel It? data for more recent events, can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed.

California↗

USGS2025

Mitigation of human cognitive bias in volcanic eruption forecasting

Modern operational eruption forecasting methods rely heavily on human judgment in the face of uncertainty and are thus susceptible to myriad cognitive biases and errors by the scientist-forecasters. Recent developments in the behavioral sciences have elucidated cognitive biases across a wide spectrum of human behaviors and found ways to mitigate them. These insights have led to significant gains in human forecast accuracy across a range of disciplines. However, such gains have yet to widely penetrate volcanic eruption forecasting efforts. In this study, we review recent progress in these fields as relevant to improving current eruption forecasting methods as practiced by volcano observatories worldwide. We group cognitive biases into 1) information and selection biases, 2) group effects and social-emotional biases, and 3) framing and decision biases and highlight the numerous places in which these biases may permeate eruption forecasts. We present a framework for improving group discussion and forecasting processes at volcano observatories, considering recent gains from behavioral sciences along with a mitigation checklist to effectively reduce bias in operational eruption forecasts. Finally, we present an updated forecasting methodology for use in our own group, the US Geological Survey (USGS) Volcano Disaster Assistance Program, based on previous “multiple datasets” methods, that includes clear and deliberate efforts to minimize cognitive biases and thus improve eruption forecasting accuracy.

Journal of Applied Volcanology↗

USGS2002

Variations in sediment texture on the northern Monterey Bay National Marine Sanctuary continental shelf

The storm-protected continental shelf of Monterey Bay, part of the Monterey Bay National Marine Sanctuary, north-central California, is subject to abundant, episodic sediment input from fluvial sources. North of Monterey Bay, conditions of reduced sediment supply combined with the exposed nature of the shelf provide an effective laboratory for studying the contrasting effects of storm- versus fluvial-dominated conditions on modern sedimentation. Textural analyses performed on surface sediment samples collected from more than 380 box cores and MultiCores??? document the existence of a clearly defined mud belt occupying the mid-shelf throughout the region. Inshore sands combined with these mid-shelf muds represent deposits from modern sedimentation processes. In Monterey Bay, where episodic fluvial input from winter storms dominates sedimentation, the mid-shelf mud belt extends across the shelf to the shelf break. North of Monterey Bay, where sediment loads are reduced and both oceanographic and storm processes dominate, the mid-shelf mud belt is bordered by relict sediments occupying the outer shelf. In the study area, mass accumulation rates established by radiochemical studies support the contention that storm-induced along-shelf processes result in northward transport of sediment within the mud belt. The continuity of transport, however, is interrupted by topographic highs which are barriers or inhibitors to sediment transport created by wrench-style tectonics associated with the San Andreas fault system.

Marine Geology↗

USGS2007

First documentation of tidal-channel sponge biostromes (upper Pleistocene, southeastern Florida)

Sponges are not a common principal component of Cenozoic reefs and are more typically dominant in deep-water and/or cold-water localities. Here we report the discovery of extensive upper Pleistocene shallow-marine, tropical sponge biostromes from the Mami Limestone of southeastern Florida built by a new ceractinomorph demosponge. These upright, barrel- to vase-shaped sponges occur in monospecific aggregations constructed within the tidal channels of an oolitic tidal-bar belt similar to modern examples on the Great Bahama Bank. The biostromes appear to have a ribbon-like geometry, with densely spaced sponges populating a paleochannel along a 3.5 km extent in the most lengthy biostrome. These are very large (as high as 2 m and 1.8 m in diameter), particularly well-preserved calcified sponges with walls as hard as concrete. Quartz grains are the most common particles agglutinated in the structure of the sponge walls. Where exposed, sediment fill between the sponges is commonly a highly burrowed or cross-bedded ooid-bearing grainstone and, locally, quartz sand. It is postulated that the dense, localized distribution of these particular sponges was due to a slight edge over competitors for food or energy supply and space in a stressed environment of tidal-influenced salinity and nutrient changes, strong currents, and frequently shifting submarine sand dunes. To our knowledge, this represents the first documentation of sponge biostromes composed of very large upright sponges within high-energy tidal channels between ooid shoals. The remarkably well-preserved accumulations provide an alternative example of sponge reefs for comparative paleoenvironmental studies. ?? 2007 The Geological Society of America.

Geology↗