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At least 127 records · Page 7Linked to original sources
USGS2023

Time-lapse seafloor surveys reveal how turbidity currents and internal tides in Monterey Canyon interact with the seabed at centimeter-scale

Here we show how ultra-high resolution seabed mapping using new technology can help to understand processes that sculpt submarine canyons. Time-lapse seafloor surveys were conducted in the axis of Monterey Canyon, ∼50 km from the canyon head (∼1,840 m water depth) over an 18-month period. These surveys comprised 5-cm resolution multibeam bathymetry, 1-cm resolution lidar bathymetry, and 2-mm resolution stereophotographic imagery. Bathymetry data reveal centimeter-scale textures that would be undetectable by more traditional survey methods. Upward-looking Acoustic Doppler Current Profilers at the site recorded the flow character of internal tides and the passage of three turbidity currents, while sediment cores collected from the site record flow deposits. Combined with flow and core data, the bathymetry shows how turbidity currents and internal tides modify the seabed. The turbidity currents drape sediment across the site, infilling bedform troughs and smoothing erosional features carved by the internal tides (e.g., rippled scours). Turbidity currents with speeds of 0.9–3.3 m/s failed to cause notable bedform movement, which is surprising given that flows with similar speeds produced rapid bedform migration elsewhere, including the upper Monterey Canyon. The lack of migration may be related to the character of the underlying substrate or indicate that turbidity currents at the site lack dense, near-bed layers. The scale of scours produced by the internal tides (≤0.7 m/s) approaches the scale of features recorded in the ancient rock record. Thus, these results illustrate how the scale gap between seabed mapping technology and the rock record may eventually be bridged.

California↗
USGS2012

Active transtensional intracontinental basins: Walker Lane in the western Great Basin

The geometry and dimensions of sedimentary basins within the Walker Lane are a result of Plio-Pleistocene transtensive deformation and partial detachment of the Sierra Nevada crustal block from the North American plate. Distinct morpho-tectonic domains lie within this active transtensive zone. The northeast end of the Walker Lane is partly buried by active volcanism of the southern Cascades, and adjacent basins are filled or poorly developed. To the south, the basin sizes are moderate, 25–45km × 15–10 km, with narrow 8-12km wide mountain ranges mainly oriented N-S to NNE. These basins form subparallel arrays in discrete zones trending about 300° and have documented clockwise rotation. This is succeeded to the south by a releasing stepover domain ∼85-100km wide, where the basins are elongated E-W to ENE, small (∼15-30km long, 5-15km wide), and locally occupied by active volcanic centers. The southernmost part of the Walker Lane is structurally integrated, with high to extreme relief. Adjacent basins are elongate, 50-200km long and ∼5 -20km wide. Variations in transtensive basin orientations in the Walker Lane are largely attributable to variations in strain partitioning. Large basins in the Walker Lane have 2-6km displacement across basin bounding faults with up to 3 km of clastic accumulation based on gravity and drill hole data. The sedimentary deposits of the basins may include interbedded volcanic deposits with bimodal basaltic and rhyolitic associations. The basins may include lacustrine deposits that record a wide range of water chemistry from cold fresh water conditions to saline-evaporative

Cascades;Great Basin;Sierra Nevada;Walker Lane↗
USGS2025

Shifting baselines of coral-reef species composition from the Late Pleistocene to the present in the Florida Keys

The ongoing global-scale reassembly of modern coral reefs is unprecedented compared with the observed stability of most late Quaternary reef assemblages. One notable exception is the marine isotope stage (MIS) 5e ( ca 130–116 thousand years ago [ka]) reefs in the Florida Keys, where the ubiquitous shallow-water coral, Acropora palmata , was near absent. Little is known, however, about reefs that grew during MIS5d–a ( ca 116–74 ka), between MIS5e and the Holocene. It is therefore unclear whether Florida's unique MIS5e coral assemblages represent a geologically brief anomaly or a more persistent departure from the western Atlantic coral-reef archetype. We addressed that question by reconstructing the composition of MIS5d–a reefs within 29 coral-reef cores collected throughout the Florida Keys. We then compared the relative composition of corals during MIS5d–a to existing datasets from MIS5e, Holocene and modern (1996 and 2022) reefs to evaluate how far today's reef assemblages have diverged from geological baselines. We show that although the proportion of reef frameworks built by corals was remarkably consistent ( ca 38%), species composition changed significantly through time. Acropora palmata was rare throughout MIS5, which we hypothesise was due to greater cold-temperature stress in Florida's subtropical reefs compared with the more climatically stable tropics. In contrast, the massive reef-building coral, Orbicella spp., was regionally dominant throughout the late Quaternary, but has become increasingly rare on modern reefs. By 2022, reefs in the Florida Keys were characterised by a truly novel coral assemblage dominated by Porites astreoides and Siderastrea siderea . In many ways, Florida's reefs defy the concept of a natural baseline; instead, their most persistent characteristic since the Late Pleistocene is their uniqueness. Yet, as reefs are increasingly subjected to unprecedented levels of environmental change, the exceptions to what was normal in the past could, paradoxically, provide the best geological analogues for the future.

Florida↗
USGS1986

Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, USA

Mount St. Helens has been a prolific source of tephra-fall deposits for about 40 000 years. These tephra deposits (1) record numerous explosive eruptions, (2) form important regional time-stratigraphic marker beds, and (3) record repeated changes in composition within and between eruptive periods. Recognized tephra strata record more than 100 explosive eruptive events at Mount St. Helens; those tephra strata are classified as beds, layers, and sets. Tephra sets, each of which consists of a group of beds and layers, define in part the nine eruptive periods recognized at the volcano. Individual tephra sets are distinguished from stratigraphically adjacent sets by differences in composition or by evidence of clapsed time. Several tephra units from Mount St. Helens form important marker beds at distances of hundreds of kilometers downwind from the volcano. Cummingtonite phenocrysts, which are known in ejecta from only Mount St. Helens in the Pacific Northwest, characterize some marker beds and readily identify their source. The tephra sequence also records eruption of the mafic andesites that mark the appearance of the modern Mount St. Helens and numerous changes in composition among dacite, basalt, and andesite since that time. ?? 1986 Springer-Verlag.

Bulletin of Volcanology↗
USGS1992

Rare earth, major, and trace element composition of Monterey and DSDP chert and associated host sediment: Assessing the influence of chemical fractionation during diagenesis

Chert and associated host sediments from Monterey Formation and Deep Sea Drilling Project (DSDP) sequences were analyzed in order to assess chemical behavior during diagenesis of biogenic sediments. The primary compositional contrast between chert and host sediment is a greater absolute SiO 2 concentration in chert, often with final SiO 2 ≥ 98 wt%. This contrast in SiO 2 (and Si Al "> SiAl ) potentially reflects precursor sediment heterogeneity, diagenetic chemical fractionation, or both. SiO 2 concentrations and Si Al "> SiAl ratios in chert are far greater than in modern siliceous oozes, however and often exceed values in acid-cleaned diatom tests. Compositional contrasts between chert and host sediment are also orders-of-magnitude greater than between multiple samples of the host sediment. Calculations based on the initial composition of adjacent host, observed porosity reductions from host to chert and a postulated influx of pure SiO 2 , construct a chert composition which is essentially identical to observed SiO 2 values in chert. Thus, precursor heterogeneity does not seem to be the dominant factor influencing the current chert composition for the key elements of interest. In order to assess the extent of chemical fractionation during diagenesis, we approximate the precursor composition by analyzing host sediments adjacent to the chert. The SiO 2 concentration contrast seems caused by biogenic SiO 2 dissolution and transport from the local adjacent host sediment and subsequent SiO 2 reprecipitation in the chert. Along with SiO 2 , other elements are often added (with respect to Al) to Monterey and DSDP chert during silicification, although absolute concentrations decrease. The two Monterey quartz chert nodules investigated, in contrast to the opal-CT and quartz chert lenses, formed primarily by extreme removal of carbonate and phosphate, thereby increasing relative SiO 2 concentrations. DSDP chert formed by both carbonate/phosphate dissolution and SiO 2 addition from the host. Manganese is fractionated during chert formation, resulting in MnO Al 2 O 3 "> MnOAl2O3 ratios that no longer record the depositional signal of the precursor sediment. REE data indicate only subtle diagenetic fractionation across the rare earth series. Ce Ce ∗ "> CeCe* values do not change significantly during diagenesis of either Monterey or DSDP chert. Eu Eu ∗ "> EuEu* decreases slightly during formation of DSDP chert. La n Yb n "> LanYbn is affected only minimally as well. During formation of one Monterey opal-CT chert lens, REE Al "> REEAl ratios show subtle distribution changes at Gd and to a lesser extent near Nd and Ho. REE compositional contrasts between diagenetic states of siliceous sediment and chert are of a vastly smaller scale than has been noted between different depositional environments of marine sediment, indicating that the paleoenvironmental REE signature is not obscured by diagenetic overprinting.

Geochimica et Cosmochimica Acta↗
USGS2026

Organic and isotopic indicators for sorting of sedimentary organic matter along a marginal submarine canyon

Submarine canyons are incised features of many continental margins that can have significant influence on the hydrodynamic distribution of sediments and organic matter eroded and deposited from the continents. Baltimore Canyon, on the mid-Atlantic margin of the United States, contains a complex set of sedimentary processes that simultaneously create unique benthic habitats and control the deposition of organic matter. Along the canyon axis, loci of net erosion, net deposition, and intense winnowing each host diverse faunal assemblages and varying mixtures of sedimentary organic matter derived both from production in the overlying water column and from mobilized sediments. Bioavailable components of this deposited organic matter sustain benthic communities, while recalcitrant components can contribute to long-term carbon burial in the deep sea. However, commonly employed bulk geochemical analyses provide little information about the relative bioavailability or depositional history of sedimentary organic matter. Here we employ a range of organic and isotopic analyses to explore in more detail how canyon-specific sediment dynamics determine the sorting of organic matter from shelf to open ocean. In combination with bulk geochemical characteristics, we subjected surface sediments from water depths of ∼200–1200 m in Baltimore Canyon to a sequential extraction procedure, isolating nonpolar and polar lipid classes, an acid-soluble fraction, and an acid-insoluble fraction. Each class was analyzed for carbon and nitrogen quantities and stable isotope ratios, and radiocarbon content where possible, along with compound-specific carbon and nitrogen isotope analysis of individual amino acids in the acid-hydrolysed fraction. We find different organic matter sources and depositional history recorded in the properties of younger, bioavailable organic matter components (polar lipids, amino acids) in comparison to the older, more recalcitrant components (nonpolar lipids, acid-insoluble fraction). These differences in source and bioavailability of organic matter vary along the canyon, correlating with grain size and erosion/deposition dynamics, and may help shape the benthic faunal assemblages. Additionally, our results suggest that determining the relative concentrations of acid-soluble and acid-insoluble organic matter may provide an easily accessible method to improve our understanding of the nutritional quality of sediments for benthic fauna than more commonly used bulk carbon or nitrogen concentrations.

Delaware, New Jersey↗
USGS2000

Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano-plutonic assemblages in the northern Sierra terrane

This field trip provides an overview of the stratigraphic and structural evolution of the northern Sierra terrane, which forms a significant part of the wall rocks on the western side of the later Mesozoic Sierra Nevada batholith in California. The terrane consists of a pre-Late Devonian subduction complex (Shoo Fly Complex) overlain by submarine arc-related deposits that record the evolution of three separate island-arc systems in the Late Sevonian-Early Mississippian, Permian, and Late Triassic-Jurassic. The two Paleozoic are packages and the underlying Shoo Fly Complex have an important bearing on plate-tectonic processes affecting the convergent margin outboard of the Paleozoic Cordilleran miogeocline, although their original paleogeographic relations to North America are controversial. The third arc package represents an overlap assemblage that ties the terrane to North America by the Late Triassic and helps constrain the nature and timing of Mesozoic orogenesis. Several of the field-trip stops examine the record of pre-Late Devonian subduction contained in the Shoo Fly Complex, as well as the paleovolcanology of the overlying Devonian to Jurassic arc rocks. Excellent glaciated exposures provide the opportunity to study a cross section through a tilted Devonian volcano-plutonic association. Additional stops focus on plutonic rocks emplaced during the Middle Jurassic arc magmatism in the terrane, and during the main pulse of Cretaceous magmatism in the Sierra Nevada batholith to the east.

California↗
USGS2002

Implications for evaporite tectonism in the Carbondale and Eagle collapse centers of west-central Colorado, based on reprocessed seismic reflection data

Reprocessing of approximately 64 km of seismic reflection data along five seismic lines has led to new interpretations of evaporite tectonism associated with the Pennsylvanian Eagle Valley Evaporite of the central Colorado trough. Evidence of the oldest evaporite tectonism in the region, imaged by the seismic data, occurs in the Eagle collapse center at Hardscrabble Mountain. Here, the Triassic-Permian State Bridge Formation is abnormally thick, reflecting an outflow of underlying evaporite. On the west side of the Carbondale collapse center, structural wedging formed the west-dipping Grand Hogback monocline during early Tertiary Laramide deformation close to the western margin of the late Paleozoic central Colorado trough. Uplimb thrusts beneath the steep face of the monocline provide evidence of backthrusting. The presence of the Roaring Fork diapir proximal to the point of greatest curvature of the Grand Hogback monocline at the Leadville reflector level suggests that diapirism may have begun during formation of the monocline. Evidence for late Cenozoic evaporite tectonism is observed in all the seismic lines in spite of the difficulty of imaging shallow, young deposits that record evidence of abundant late Cenozoic evaporite tectonism observed during geologic mapping.

Colorado↗
USGS2008

Devonian brachiopods of southwesternmost laurentia: Biogeographic affinities and tectonic significance

Three brachiopod faunas discussed herein record different depositional and tectonic settings along the southwestern margin of Laurentia (North America) during Devonian time. Depositional settings include inner continental shelf (Cerros de Los Murcielagos), medial continental shelf (Rancho Placeritos), and offshelf continental rise (Rancho Los Chinos). Ages of Devonian brachiopod faunas include middle Early (Pragian) at Rancho Placeritos in west-central Sonora, late Middle (Givetian) at Cerros de Los Murcielagos in northwestern Sonora, and late Late (Famennian) at Rancho Los Chinos in central Sonora. The brachiopods of these three faunas, as well as the gastropod Orecopia, are easily recognized in outcrop and thus are useful for local and regional correlations. Pragian brachiopods dominated by Acrospirifer and Meristella in the "San Miguel Formation" at Rancho Placeritos represent the widespread Appohimchi Subprovince of eastern and southern Laurentia. Conodonts of the early to middle Pragian sulcatus to kindlei Zones associated with the brachiopods confirm the ages indicated by the brachiopod fauna and provide additional information on the depositional setting of the Devonian strata. Biostratigraphic distribution of the Appohimchi brachiopod fauna indicates continuous Early Devonian shelf deposition along the entire southern margin of Laurentia. The largely emergent southwest-trending Transcontinental arch apparently formed a barrier preventing migration and mixing of many genera and species of brachiopods from the southern shelf of Laurentia in northern Mexico to the western shelf (Cordilleran mio-geocline) in the western United States. Middle Devonian Stringocephalus brachiopods and Late Devonian Orecopia gastropods in the "Los Murcielagos Formation" in northwest Sonora represent the southwest-ernmost occurrence of these genera in North America and date the host rocks as Givetian and Frasnian, respectively. Rhynchonelloid brachiopods (Dzieduszyckia sonora) and associated worm tubes in the Los Pozos Formation of the Sonora allochthon in central Sonora are also found in strati-form-barite facies in the upper Upper Devonian (Famennian) part of the Slaven Chert in the Roberts Mountains allochthon (upper plate) of central and western Nevada. Although these brachiopods and worm tubes occur in similar depositional settings along the margin of Laurentia in Mexico, they occur in allochthons that exhibit different tectonic styles and times of emplacement. Thus, the allochthons containing the brachiopods and worm tubes in Sonora and Nevada are parts of separate orogenic belts and have different geographic settings and tectonic histories. Devonian facies belts and faunas in northern Mexico indicate a continuous continental shelf along the entire southern margin of Laurentia. These data, in addition to the continuity of the late Paleozoic Ouachita-Marathon-Sonora orogen across northern Mexico, contradict the early Late Jurassic Mojave-Sonora megashear as a viable hypothesis for large-magnitude offset (600-1100 km) of Proterozoic through Middle Jurassic rocks from California to Sonora.

Special Paper of the Geological Society of America↗
USGS1999

Chapter 3: Development of the Santorini volcanic field in space and time

Santorini is one of the largest Quaternary volcanic centres of the Aegean Region. The caldera cliffs preserve well-exposed sequences of lavas and pyroclastic deposits, which record the long development of the volcano in space and time. These include the products of 12 major explosive eruptions and the dissected remains of several ancient lava shields, stratovolcanoes, and lava-dome complexes. The former existence of multiple eruptive centres scattered over the present-day islands shows that Santorini is best considered as a volcanic field , which probably also continues under the sea (Heiken & McCoy 1984). Santorini is best known for the Minoan eruption of the late Bronze Age (Bond & Sparks 1976; Heiken & McCoy 1984; Sparks & Wilson 1990), but some of the previous explosive eruptions may have been as large (Druitt et al . 1989). The occurrence of repeated explosive eruptions has triggered formation of at least four large calderas, such that the present-day caldera is a composite structure (Druitt & Francaviglia 1992). Santorini is potentially one of the most dangerous volcanoes in Europe, having had numerous eruptions in historic times, some of them with significant explosive components (Fytikas et al . 1990 a ).

Santorini↗
USGS2006

Sri Lanka field survey after the December 2004 Indian Ocean tsunami

An International Tsunami Survey Team (ITST) consisting of scientists from the United States, New Zealand, and Sri Lanka evaluated the impacts of the 26 December 2004 transoceanic tsunami in Sri Lanka two weeks after the event. Tsunami runup height, inundation distance, morphological changes, and sedimentary characteristics of deposits were recorded and analyzed along the southwest and east coasts of the country. Preliminary results show how local topography and bathymetry controlled the limits of inundation and associated damage to the infrastructure. The largest wave height of 8.71 m was recorded at Nonagama, while the greatest inundation distance of 390 m and runup height of 12.50 m was at Yala. At some sites, human alterations to the landscape increased the damage caused by the tsunami; this was particularly evident in areas of coral poaching and of sand dune removal.

Earthquake Spectra↗
USGS1939

Manganese in a thermal spring in west-central Utah

The hot spring north of Delta, Utah, is of particular interest because it has yielded commercial manganese ore; 715 tons of manganese oxide ore that averaged 20% manganese and 0.26% sulphur is recorded. The deposits occur as a thin bed and as lenses and nodules in a dome about 1,600 feet across and 15 feet high that has been formed subsequent to the dessication of Pleistocene Lake Bonneville. The alkaline hot waters, which reach temperatures of 182 degrees F. and have a total discharge of over 1,200 gallons a minute, average 3,900 parts per million in dissolved solids, with NaCl, CaSO 4 , MgCl 2 , and CaCO 3 . Five complete analyses show a manganese content of from 0 to 1.2 parts per million. Nevertheless, no appreciable manganese seems to be precipitating at present. The bed of manganese and iron oxides is scarcely more than a foot thick and is mostly covered by porous calcite. The ore is a porous aggregate of psilomelane and pyrolusite in which the vugs are lined with limonite. These minerals have been formed through the action of hot alkaline solutions over a long period; the original mineral was probably wad. The barium oxide is believed to be chemically combined with the manganese oxides. Probably all these materials have been leached from underlying rocks or deposits by hot circulating groundwaters and may not have a magmatic source.

Utah↗
USGS1996

January 1996 floods deliver large loads of nutrients and sediment to the Chesapeake Bay

The Blizzard of 1996 struck the Mid-Atlantic region in January, depositing a record amount of snowfall. Within two weeks of the paralyzing blizzard, warm and extremely humid air entered the region, followed by a major rainstorm. The combination of warm, humid air and heavy rainfall melted the snow at an unprecedented rate. In just over one day, two to five inches of water from snowmelt combined with two to five inches of rainfall, resulting in widespread major flooding throughout the Mid-Atlantic region, including the Chesapeake Bay watershed. The January 1996 storm caused severe flooding on many Chesapeake Bay tributaries. As a result of the flooding, large amounts of nutrients and sediment entered the Bay. The U.S. Geological Survey (USGS) monitored the amount of streamflow, nutrients, and sediment that entered the Chesapeake Bay as a result of the flood. This information is used to evaluate the effect of hydrologic events of this magnitude on the Bay's health and living resources.

Delaware, Maryland, New York, Pennsylvania, Virgin↗
USGS2002

Regional stratigraphic cross sections of Cretaceous rocks from east-central Arizona to the Oklahoma Panhandle

Sedimentary rocks of Cretaceous age along Transect DD'' in eastern Arizona, northern New Mexico, southern Colorado, and western Oklahoma consist mainly of sandstone, siltstone, shale, limestone, and bentonite. They accumulated as sediments in continental, nearshore marine, and offshore marine environments on the west side of a north-trending epicontinental sea. The rocks record intermittent deposition and erosion as well as regional and local subsidence and uplift possibly beginning in Aptian time (about 121-112 Ma) and occurring in Albian through Maastrichtian time (about 112-65.4 Ma). Most of the Lower Cretaceous (Berriasian through Aptian, 142-112 Ma) in this transect is represented by a basal unconformity. The Cretaceous rocks and unconformities along the transect are depicted on the attached lithostratigraphic cross sections (sheets 1 and 2); one extending from the Mogollon Rim in eastern Arizona to Pagosa Springs in southwestern Colorado and the other from Pagosa Springs, Colorado, to Kenton in western Oklahoma. The same rocks and unconformities are also represented on the attached chronostratigraphic profile (sheet 3), which was prepared mainly from surface and subsurface data shown on the lithostratigraphic cross sections.

Arizona, New Mexico, Oklahoma↗
USGS2006

Descriptions and preliminary report on sediment cores from the southwest coastal area, Part II: Collected July 2005, Everglades National Park, Florida

Twelve cores were collected from six sites in the southwest coastal area of Everglades National Park, Florida, in July 2005. These six sites create transects up three river systems that are part of the complex network of channels and bays that form the mangrove and coastal glades – Lostmans River system, Harney River system, and Shark River system. The three transects are linked to two cores collected in 2004 from Big Lostmans Bay and Tarpon Bay. A preliminary model of changes in flow through the southwest coastal zone is proposed based on an examination of the sediments and an initial assessment of key indicator species of mollusks within the cores. Throughout the time period recorded by deposition of these cores, flow to the southwest coastal area has been predominantly through the Shark River channels, diminishing to the north toward the Lostmans River system. The Lostmans system was less influenced by freshwater flow and more emergent than the two systems to the south. Freshwater flow has periodically reached the mouths of the Harney and Shark River systems, but these areas have persistently been zones of mixed estuarine environments, typical of transition zones. Evidence for a substantial change in the flow regime is found in the mid-system cores from the Harney and Shark Rivers. The lower portions of both cores were deposited in freshwater environments, with no indication of estuarine influence; however, a shift towards more estuarine conditions occurs in the upper portions of the cores and a loss of the larger freshwater fauna. These results are preliminary. The next step will be to develop age models and to conduct quantitative analyses of the fauna, flora, and sediment geochemistry at these sites. Results of the quantitative analyses will provide information on the natural and anthropogenic changes that have occurred in the southwest coastal system that will allow resource managers to set targets for restoration.

Florida↗
USGS2008

Geomorphic map of Worcester County, Maryland, interpreted from a LIDAR-based, digital elevation model

A recently compiled mosaic of a LIDAR-based digital elevation model (DEM) is presented with geomorphic analysis of new macro-topographic details. The geologic framework of the surficial and near surface late Cenozoic deposits of the central uplands, Pocomoke River valley, and the Atlantic Coast includes Cenozoic to recent sediments from fluvial, estuarine, and littoral depositional environments. Extensive Pleistocene (cold climate) sandy dune fields are deposited over much of the terraced landscape. The macro details from the LIDAR image reveal 2 meter-scale resolution of details of the shapes of individual dunes, and fields of translocated sand sheets. Most terrace surfaces are overprinted with circular to elliptical rimmed basins that represent complex histories of ephemeral ponds that were formed, drained, and overprinted by younger basins. The terrains of composite ephemeral ponds and the dune fields are inter-shingled at their margins indicating contemporaneous erosion, deposition, and re-arrangement and possible internal deformation of the surficial deposits. The aggregate of these landform details and their deposits are interpreted as the products of arid, cold climate processes that were common to the mid-Atlantic region during the Last Glacial Maximum. In the Pocomoke valley and its larger tributaries, erosional remnants of sandy flood plains with anastomosing channels indicate the dynamics of former hydrology and sediment load of the watershed that prevailed at the end of the Pleistocene. As the climate warmed and precipitation increased during the transition from late Pleistocene to Holocene, dune fields were stabilized by vegetation, and the stream discharge increased. The increased discharge and greater local relief of streams graded to lower sea levels stimulated down cutting and created the deeply incised valleys out onto the continental shelf. These incised valleys have been filling with fluvial to intertidal deposits that record the rising sea level and warmer, more humid climate in the mid-Atlantic region throughout the Holocene. Thus, the geomorphic details provided by the new LIDAR DEM actually record the response of the landscape to abrupt climate change. Holocene trends and land-use patterns from Colonial to modern times can also be interpreted from the local macro- scale details of the landscape. Beyond the obvious utility of these data for land-use planning and assessments of resources and hazards, the new map presents new details on the impact of climate changes on a mid-latitude, outer Coastal plain landscape.

Maryland↗
USGS2015

Geologic map of the Alamosa 30’ × 60’ quadrangle, south-central Colorado

The Alamosa 30'× 60' quadrangle is located in the central San Luis Basin of southern Colorado and is bisected by the Rio Grande. The Rio Grande has headwaters in the San Juan Mountains of Colorado and ultimately discharges into the Gulf of Mexico 3,000 kilometers (km) downstream. Alluvial floodplains and associated deposits of the Rio Grande and east-draining tributaries, La Jara Creek and Conejos River, occupy the north-central and northwestern part of the map area. Alluvial deposits of west-draining Rio Grande tributaries, Culebra and Costilla Creeks, bound the Costilla Plain in the south-central part of the map area. The San Luis Hills, a northeast-trending series of flat-topped mesas and hills, dominate the landscape in the central and southwestern part of the map and preserve fault-bound Neogene basin surfaces and deposits. The Precambrian-cored Sangre de Cristo Mountains rise to an elevation of nearly 4,300 meters (m), almost 2,000 m above the valley floor, in the eastern part of the map area. In total, the map area contains deposits that record surficial, tectonic, sedimentary, volcanic, magmatic, and metamorphic processes over the past 1.7 billion years.

Colorado↗
USGS2001

Fire and vegetation history of the Jemez Mountains

Historic patterns of fire occurrence and vegetation change in the Jemez Mountains of northern New Mexico have been described in detail by using multiple lines of evidence. Data sources include old aerial and ground-based photographs, historic records, charcoal deposits from bogs, fire-scarred trees (Figure 1), tree-ring reconstructions of precipitation, and field sampling of vegetation and soils. The forests and woodlands that cloak the Southwestern uplands provide the most extensive and detailed regional-scale network of fire history data available in the world (Swetnam and Baisan 1996, Swetnam et al. 1999, Allen 2002).

New Mexico↗