Filters: Tags: Radiocarbon Dating (X)10 results (216ms)
This map illustrates extents and types of unconsolidated deposits and bedrock in the Big Delta A-4 Quadrangle, Alaska. This map is based on field observations begun by P�w� in 1949 and by Reger in 1976. Unit characteristics and extents were determined during field visits and by interpreting 1:40,000-scale black-and-white aerial photographs taken in August 1949 and 1:63,360-scale, false-color infrared aerial photographs taken in July 1978, August 1980, and August 1981.
Note: No formal accuracy tests were conducted and these data are disseminated to allow discussion related to methods. Sample Analyses: Samples were processed at both the USGS in Menlo Park, CA, and at UC Berkeley following established methodology for separating organic material from sinter (Howald et al., 2014; Lowenstern et al., 2016; Slagter et al., 2019). First, the exterior surface of each sample was removed using a rock saw, and then any further material was removed if there was any visible algal material in the interior of the sample. Second, samples underwent a series of chemical baths. Samples were crushed and soaked in 30% hydrogen peroxide for 48 hours to remove any remaining modern algae. Once cleaned,...
Data release for Independent age estimates resolve the controversy of ancient human footprints at White Sands
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected from the same stratigraphic horizons as those of the Ruppia seeds, along with optically stimulated luminescence ages of sediments from within the human footprint–bearing sequence, to evaluate the veracity of the seed ages. The results show that the chronologic framework originally established for the White Sands footprints is robust...
Between 27 and 11 kyr ago, during the last major (Naptowne) glaciation, the northwestern and western Kenai Peninsula and the Cook Inlet trough were covered by ice except for local nunataks and small refugia, like the Caribou Hills. Landforms related to four glacial stades are recognized and paleogeographic maps document ice limits, drainage systems, glacial-impounded lakes, and glaciomarine terraces. Numerous multidisciplinary studies of glacial, vegetation, and insect histories document Holocene climatic changes.
Archaeologists and researchers in allied fields have long sought to understand human colonization of North America. Questions remain about when and how people migrated, where they originated, and how their arrival affected the established fauna and landscape. Here, we present evidence from excavated surfaces in White Sands National Park (New Mexico, United States), where multiple in situ human footprints are stratigraphically constrained and bracketed by seed layers that yield calibrated radiocarbon ages between ~23 and 21 thousand years ago. These findings confirm the presence of humans in North America during the Last Glacial Maximum, adding evidence to the antiquity of human colonization of the Americas and providing...
Radiocarbon ages, age-model code, and other supplemental data for Nelson et al. (2021), A maximum rupture model for the central and southern Cascadia subduction zone—assessing ages for coastal evidence of megathrust earthquakes and tsunamis
This data release contains supplemental data for the following paper: Nelson, A.R., DuRoss, C.B., Mahan, S.A., Gray, H.J., Engelhart, S.E., Witter, R.C., Hawkes, A.D., Horton, B.P., Kelsey, H.M., and Padgett, J.S., 2021, A maximum rupture model for the central and southern Cascadia subduction zone—assessing ages for coastal evidence of megathrust earthquakes and tsunamis: Quaternary Science Reviews 261, https://doi.org/10.1016/j.quascirev.2021.106922. The data include a compilation of new and previously published radiocarbon ages from the original cores from Bradley Lake of Kelsey et al. (2005; odt format), and tables of new and previously published radiocarbon data for 7 of the 13 tidal wetland sites along the...
We assessed a construction site in the northern Las Vegas Valley that was initially reported as an "ice age" deposit. Alluvial deposits exposed at the site were inset into the Las Vegas Formation and contained semi-articulated Equus remains. Calibrated radiocarbon dates on two different materials associated with the remains centered on 1957, thus rendering the horse bones as modern.
Surficial geology of the Dalton Highway (Itkillik-Sagavanirktok rivers) area, southern Arctic foothills, Alaska
This report provides detailed (1:63,360-scale) surficial-geologic mapping in the Dalton Highway area, from the Sagavanirktok to the Itkillik Rivers, in the west-central Philip Smith Mountains quadrangle. The map area extends from the northern flank of the Endicott Mountains into the Arctic Foothills province.
Core names are in the format: SitecodeYear-Core#, i.e. TJE12-01 is Tijuana, 2012, 1st core. cm are the lower depth interval of the cm from which sample was taken, i.e. a sample from 50 cm would be from 49-50 cm depth. Radiocarbon data processed at the UCI Keck CCAMS Laboratory, Earth System Science Department, 2222B Croul Hall, University of California, Irvine, Irvine, CA 92697-3100, +1 949 824 3674. 137 Cs activity data analysis by Core Scientific International, 154 Red Lily Road, Winnipeg, Manitoba, Canada R3X 0G1, (204) 479-9821, (204)694-4130. Site Codes: TJE - Tijuana Estuary, UNB - Upper Newport Bay, SB - Seal Beach, MGL - Mugu Lagoon, MOB - Morro Bay, BOL - Bolinas Lagoon, BOD - Bodega Bay, JCB - Jacoby Marsh...
During 2006 and 2007 the Alaska Division of Geological & Geophysical Surveys conducted reconnaissance surficial-geologic mapping in segment 1 of the Alaska Highway corridor, which straddles the Alaska Highway through the Tanana River valley from Delta Junction to the eastern boundary of the Mt. Hayes Quadrangle. Surficial-geologic deposits were initially mapped by interpreting ~1:63,360-scale, false-color infrared aerial photographs taken in August 1980 and field verified in 2006-2007.