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At least 181 records · Page 10Linked to original sources
USGS2017

Paleowetlands and regional climate change in the central Atacama Desert, northern Chile

Widespread, organic-rich diatomaceous deposits are evidence for formerly wetter times along the margins of the central Atacama Desert, one of the driest places on Earth today. We mapped and dated these paleowetland deposits at three presently waterless locations near Salar de Punta Negra (24.5°S) on the western slope of the Andes. Elevated groundwater levels supported phreatic discharge into wetlands during two periods: 15,900 to ~ 13,800 and 12,700 to ~ 9700 cal yr BP. Dense concentrations of lithic artifacts testify to the presence of paleoindians around the wetlands late in the second wet phase (11,000?–9700 cal yr BP). Water tables dropped below the surface before 15,900 and since 8100 cal yr BP, and briefly between ~ 13,800 and 12,700 cal yr BP. This temporal pattern is repeated, with some slight differences, in rodent middens from the study area, in both paleowetland and rodent midden deposits north and south of the study area, and in lake level fluctuations on the adjacent Bolivian Altiplano. The regional synchroneity of these changes points to a strengthening of the South American Monsoon — which we term the "Central Andean Pluvial Event" — in two distinct intervals (15,900–13,800 and 12,700–9700 cal yr BP), probably induced by steepened SST gradients across the tropical Pacific (i.e., La Niña-like conditions).

Atacama Desert;Andes Mountains↗
USGS2017

50,000 years of vegetation and climate history on the Colorado Plateau, Utah and Arizona, USA

Sixty packrat middens were collected in Canyonlands and Grand Canyon National Parks, and these series include sites north of areas that produced previous detailed series from the Colorado Plateau. The exceptionally long time series obtained from each of three sites (> 48,000 14 C yr BP to present) include some of the oldest middens yet discovered. Most middens contain a typical late-Wisconsinan glaciation mixture of mesic and xeric taxa, evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria. Differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference. The oldest middens from Canyonlands NP, however, differ in containing strictly xeric assemblages, including middens incorporating needles of Arizona single-leaf pinyon, far north of its current distribution. Similar-aged middens from the eastern end of Grand Canyon NP contain plants more typical of glacial climates, but also contain fossils of one-seed juniper near its current northern limit in Arizona. Holocene middens reveal the development of modern vegetation assemblages on the Colorado Plateau, recording departures of mesic taxa from low elevation sites, and the arrival of modern dominant components much later.

Arizona, Utah↗
USGS2017

Environment and paleoecology of a 12 ka mid-North American Younger Dryas forest chronicled in tree rings

Until now, availability of wood from the Younger Dryas abrupt cooling event (YDE) in N. America ca. 12.9 to 11.6 ka has been insufficient to develop high-resolution chronologies for refining our understanding of YDE conditions. Here we present a multi-proxy tree-ring chronology (ring widths, “events” evidenced by microanatomy and macro features, stable isotopes) from a buried black spruce forest in the Great Lakes area (Liverpool East site), spanning 116 yr at ca. 12,000 cal yr BP. During this largely cold and wet period, the proxies convey a coherent and precise forest history including frost events, tilting, drowning and burial in estuarine sands as the Laurentide Ice Sheet deteriorated. In the middle of the period, a short mild interval appears to have launched the final and largest episode of tree recruitment. Ultimately the tops of the trees were sheared off after death, perhaps by wind-driven ice floes, culminating an interval of rising water and sediment deposition around the base of the trees. Although relative influences of the continental ice sheet and local effects from ancestral Lake Michigan are indeterminate, the tree-ring proxies provide important insight into environment and ecology of a N. American YDE boreal forest stand.

Quaternary Research↗
USGS2017

Major- and trace-element characterization, expanded distribution, and a new chronology for the latest Pleistocene Glacier Peak tephras in western North America

The Glacier Peak tephra beds are among the most widespread and arguably some of the most important late Pleistocene chronostratigraphic markers in western North America. These beds represent a series of closely-spaced Plinian and sub-Plinian eruptions from Glacier Peak, Washington. The two most widespread beds, Glacier Peak 'G' and 'B', are reliably distinguished by their glass major and trace element abundances. These beds are also more broadly distributed than previously considered, covering at least 550,000 and 260,000??km2, respectively. A third bed, the Irvine bed, known only from southern Alberta, is similar in its major-element composition to the Glacier Peak G bed, but it shows considerable differences in trace element concentrations. The Irvine bed is likely considerably older than the G and B tephras and probably records an additional Plinian eruption, perhaps also from Glacier Peak but from a different magma than G through B. A review of the published radiocarbon ages, new ages in this study, and consideration in a Bayesian framework suggest that the widespread G and B beds are several hundred years older than widely assumed. Our revised age is about 11,600??14C yr BP or a calibrated age (at 2 sigma) of 13,710-13,410??cal yr BP. ?? 2008 University of Washington.

Quaternary Research↗
USGS2017

Late Pleistocene eolian features in southeastern Maryland and Chesapeake Bay region indicate strong WNW-NW winds accompanied growth of the Laurentide Ice Sheet

Inactive parabolic dunes are present in southeastern Maryland, USA, along the east bank of the Potomac River. More elongate and finer-grained eolian deposits and paha-like ridges characterize the Potomac River-Patuxent River upland and the west side of Chesapeake Bay. These ridges are streamlined erosional features, veneered with eolian sediment and interspersed with dunes in the low-relief headwaters of Potomac- and Patuxent-river tributaries. Axis data for the dunes and ridges indicate formation by WNW-NW winds. Optically stimulated luminescence and radiocarbon age data suggest dune formation from ??? 33-15??ka, agreeing with the 30-13??ka ages Denny, C.S., Owens, J.P., Sirkin, L., Rubin, M., 1979. The Parsonburg Sand in the central Delmarva Peninsula, Maryland and Delaware. U.S. Geol. Surv. Prof. Pap. 1067-B, 16??pp. suggested for eolian deposits east of Chesapeake Bay. Age range and paleowind direction(s) for eolian features in the Bay region approximate those for late Wisconsin loess in the North American midcontinent. Formation of midcontinent loess and Bay-region eolian features was coeval with rapid growth of the Laurentide Ice Sheet and strong cooling episodes (?? 18 O minima) evident in Greenland ice cores. Age and paleowind-direction coincidence, for eolian features in the midcontinent and Bay region, indicates strong mid-latitude WNW-NW winds for several hundred kilometers south of the Laurentide glacial terminus that were oblique to previously simulated anticyclonic winds for the last glacial maximum.

Quaternary Research↗
USGS2017

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 14 C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 14 C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 14 C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon ( Mammut americanum ) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 14 C yr BP and 10,032 ± 40 14 C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.

Quaternary Research↗
USGS2017

Marine tephrochronology of the Mt. Edgecumbe volcanic field, southeast Alaska, USA

The Mt. Edgecumbe Volcanic Field (MEVF), located on Kruzof Island near Sitka Sound in southeast Alaska, experienced a large multiple-stage eruption during the last glacial maximum (LGM)-Holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well-dated dacite (MEd) tephra. Marine sediment cores collected from adjacent basins to the MEVF contain both tephra-fall and pyroclastic flow deposits that consist primarily of rhyolitic tephra and a minor dacitic tephra unit. The recovered dacite tephra correlates with the MEd tephra, whereas many of the rhyolitic tephras correlate with published MEVF rhyolites. Correlations were based on age constraints and major oxide compositions of glass shards. In addition to LGM-Holocene macroscopic tephra units, four marine cryptotephras were also identified. Three of these units appear to be derived from mid-Holocene MEVF activity, while the youngest cryptotephra corresponds well with the White River Ash eruption at not, vert, similar 1147 cal yr BP. Furthermore, the sedimentology of the Sitka Sound marine core EW0408-40JC and high-resolution SWATH bathymetry both suggest that extensive pyroclastic flow deposits associated with the activity that generated the MEd tephra underlie Sitka Sound, and that any future MEVF activity may pose significant risk to local population centers.

Alaska↗
USGS2017

New optically stimulated luminescence ages provide evidence of MIS3 and MIS2 eolian activity on Black Mesa, northeastern Arizona, USA

Eolian deposition on the semiarid southern Colorado Plateau has been attributed to episodic aridity during the Quaternary Period. However, OSL ages from three topographically controlled (e.g. falling) dunes on Black Mesa in northeastern Arizona indicate that eolian sediments there were deposited in deep tributary valleys as early as 35–30 ka, with most sand deposited before 20 ka. In contrast, the oldest OSL ages for sand sheets fall within the Pleistocene-Holocene climatic transition (~ 12–8 ka). Thus most eolian sediment accumulated on Black Mesa under climatic conditions that were in general cooler, moister, and more variable than today, not more arid, pointing to a considerable increase in sediment supply.

Arizona↗
USGS2017

Vegetation history along the eastern, desert escarpment of the Sierra San Pedro Mártir, Baja California, Mexico

Plant macrofossils from 38 packrat middens spanning the last ~ 33,000 cal yr BP record vegetation between ~ 650 and 900 m elevation along the eastern escarpment of the Sierra San Pedro Mártir, northern Baja California. The middens span most of the Holocene, with a gap between ~ 4600 and 1800 cal yr BP, but coverage in the Pleistocene is uneven with a larger hiatus between 23,100 and 14,400 cal yr BP. The midden flora is relatively stable from the Pleistocene to Holocene. Exceptions include Pinus californiarum , Juniperus californica and other chaparral elements that were most abundant > 23,100 cal yr BP and declined after 14,400 cal yr BP. Despite being near the chaparral/woodland-desertscrub ecotone during glacial times, the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record, and this is corroborated by a nearby semi-continuous pollen stratigraphy from lake sediments. Regular appearance of C 4 grasses and summer-flowering annuals since 13,600 cal yr BP indicates occurrence of summer rainfall equivalent to modern (JAS average of ~ 80–90 mm). This casts doubt on the claim, based on temperature proxies from marine sediments in the Guaymas Basin, that monsoonal development in the northern Gulf and Arizona was delayed until after 6200 cal yr BP.

Baja California, Sierra San Pedro Mártir↗
USGS2017

Terrestrial sensitivity to abrupt cooling recorded by aeolian activity in northwest Ohio, USA

Optically stimulated luminescence dated sand dunes and Pleistocene beach ridges in northwest Ohio are used to reconstruct landscape modification more than 5000. yr after deglaciation. Four of the OSL ages (13.3-11.1. ka) cluster around the Younger Dryas cold event, five ages (10.8-8.2. ka) cluster around the Preboreal, one young age (0.9-0.7. ka) records more recent aeolian activity, and one age of 15.1-13.1. ka dates a barrier spit in Lake Warren. In northwest Ohio, both landscape instability recorded by aeolian activity and a vegetation response recorded by pollen are coeval with the Younger Dryas. However, the climate conditions during the Preboreal resulting in aeolian activity are not recorded in the available pollen records. From this, we conclude that aeolian dunes and surfaces susceptible to deflation are sensitive to cooler, drier episodes of climate and can complement pollen data. Younger Dryas and Preboreal aged aeolian activity in northwestern Ohio coincides with aeolian records elsewhere in the Great Lakes region east of the prairie-forest ecotone. ?? 2011 University of Washington.

Quaternary Research↗
USGS2017

Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages

Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907 ± 31 to 11,650 ± 50 14 C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520 + 95/−20 cal yr BP. Ages of shells juxtaposed with the logs are 12,850 ± 65 14 C yr BP ( Mytilus edulis ) and 12,800 ± 55 14 C yr BP ( Balanus sp.), indicating a marine reservoir age of about 1000 yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England.

Maine↗
USGS2017

A loess–paleosol record of climate and glacial history over the past two glacial–interglacial cycles (~ 150 ka), southern Jackson Hole, Wyoming

Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric 10 Be accumulation in soils, and cosmogenic 10 Be surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8, 7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (~ 76–69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (~ 43–51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada.

Wyoming↗
USGS2017

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000. yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500. cal. yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting. ?? 2011 University of Washington.

North Carolina↗
USGS2017

Rapid late Pleistocene/Holocene uplift and coastal evolution of the southern Arabian (Persian) Gulf

The coastline along the southern Arabian Gulf between Al Jubail, Kingdom of Saudi Arabia, and Dubai, UAE, appears to have risen at least 125 m in the last 18,000 years. Dating and topographic surveying of paleo-dunes (43–53 ka), paleo-marine terraces (17–30 ka), and paleo-marine shorelines (3.3–5.5 ka) document a rapid, > 1 mm/a subsidence, followed by a 6 mm/a uplift that is decreasing with time. The mechanism causing this movement remains elusive but may be related to the translation of the coastal area through the backbasin to forebulge hinge line movement of the Arabian plate or, alternatively, by movement of the underlying Infracambrian-age Hormuz salt in response to sea-level changes associated with continental glaciation. Independent of the mechanism, rapid and episodic uplift may impact the design of engineering projects such as nuclear power plants, airports, and artificial islands as well as the interpretation of sedimentation and archeology of the area.

Quaternary Research↗
USGS2012

Holocene alluvial stratigraphy and response to climate change in the Roaring River valley, Front Range, Colorado, USA

Stratigraphic analyses and radiocarbon geochronology of alluvial deposits exposed along the Roaring River, Colorado, lead to three principal conclusions: (1) the opinion that stream channels in the higher parts of the Front Range are relics of the Pleistocene and nonalluvial under the present climate, as argued in a water-rights trial USA v. Colorado, is untenable, (2) beds of clast-supported gravel alternate in vertical succession with beds of fine-grained sediment (sand, mud, and peat) in response to centennial-scale changes in snowmelt-driven peak discharges, and (3) alluvial strata provide information about Holocene climate history that complements the history provided by cirque moraines, periglacial deposits, and paleontological data. Most alluvial strata are of late Holocene age and record, among other things, that: (1) the largest peak flows since the end of the Pleistocene occurred during the late Holocene; (2) the occurrence of a mid- to late Holocene interval (~2450–1630(?) cal yr BP) of warmer climate, which is not clearly identified in palynological records; and (3) the Little Ice Age climate seems to have had little impact on stream channels, except perhaps for minor (~1 m) incision. Published

Colorado↗
USGS2012

Sea-level history of past interglacial periods: New evidence from uranium-series dating of corals from Curaçao, Leeward Antilles islands

Curaçao has reef terraces with the potential to provide sea-level histories of interglacial periods. Ages of the Hato (upper) unit of the “Lower Terrace” indicate that this reef dates to the last interglacial period, Marine Isotope Stage (MIS) 5.5. On Curaçao, this high sea stand lasted at least 8000 yr (~ 126 to ~ 118 ka). Elevations and age of this reef show that late Quaternary uplift rates on Curaçao are low, 0.026–0.054 m/ka, consistent with its tectonic setting. Ages of ~ 200 ka for corals from the older Cortalein unit of the Lower Terrace correlate this reef to MIS 7, with paleo-sea level estimates ranging from − 3.3 m to + 2.3 m. The estimates are in agreement with those for MIS 7 made from other localities and indicate that the penultimate interglacial period was a time of significant warmth, on a par with the present interglacial period. The ~ 400 ka (MIS 11) Middle Terrace I on Curaçao, dated by others, may have formed from a paleo-sea level of + 8.3 to + 10.0 m, or (less likely) + 17 m to + 20 m. The lower estimates are conservative compared to previous studies, but still require major ice sheet loss from Greenland and Antarctica.

Leeward Antilles↗
USGS2012

Holocene dune formation at Ash Meadows National Wildlife Area, Nevada, USA

Small isolated dune fields in the northern Mojave Desert are important centers of biodiversity and archaeological occupation sites. Currently dunes at Ash Meadows, Nevada, are stabilized by vegetation and are experiencing erosion of their upwind margins, indicating a negative sediment budget. New OSL ages from dunes at Ash Meadows indicate continuous eolian accumulation from 1.5 to 0.8 ka, with further accumulation around 0.2 ka. Prior studies (e.g., Mehringer and Warren, 1976) indicate periods of dune accumulation prior to 3.3 ka; 1.9–1 ka; and after 0.9 ka. These periods of eolian accumulation are largely synchronous with those identified elsewhere in the Mojave Desert. The composition of the Ash Meadows dunes indicates their derivation from regional fluvial sources, most likely during periods when axial washes were active as a result of enhanced winter precipitation.

Quaternary Research↗