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J.F. Wehmiller

Publications and source records attributed to J.F. Wehmiller.

11 recordsLinked to original sources
USGS2017

Comparison of amino acid racemization geochronometry with lithostratigraphy, biostratigraphy, uranium-series coral dating, and magnetostratigraphy in the Atlantic Coastal Plain of the southeastern United States

The results of an integrated study comprising litho- and biostratigraphic investigations, uranium-series coral dating, amino acid racemization in molluscs, and paleomagnetic measurements are compared to ascertain relative and absolute ages of Pleistocene deposits of the Atlantic Coastal Plain in North and South Carolina. Four depositional events are inferred for South Carolina and two for North Carolina by all methods. The data suggest that there are four Pleistocene units containing corals that have been dated at about 100,000 yr, 200,000 yr, 450,000 yr, and over 1,000,000 yr. Some conflicts exist between the different methods regarding the correlation of the younger of these depositional events between Charleston and Myrtle Beach. Lack of good uranium-series dates for the younger material at Myrtle Beach makes the correlation with the deposits at Charleston more difficult. ?? 1982.

Quaternary Research↗
USGS2012

Calibration of amino acid racemization (AAR) kinetics in United States mid-Atlantic Coastal Plain Quaternary mollusks using 87Sr/ 86Sr analyses: Evaluation of kinetic models and estimation of regional Late Pleistocene temperature history

The use of amino acid racemization (AAR) for estimating ages of Quaternary fossils usually requires a combination of kinetic and effective temperature modeling or independent age calibration of analyzed samples. Because of limited availability of calibration samples, age estimates are often based on model extrapolations from single calibration points over wide ranges of D/L values. Here we present paired AAR and 87 Sr/ 86 Sr results for Pleistocene mollusks from the North Carolina Coastal Plain, USA. 87 Sr/ 86 Sr age estimates, derived from the lookup table of McArthur et al. [McArthur, J.M., Howarth, R.J., Bailey, T.R., 2001. Strontium isotopic stratigraphy: LOWESS version 3: best fit to the marine Sr-isotopic curve for 0–509 Ma and accompanying Look-up table for deriving numerical age. Journal of Geology 109, 155–169], provide independent age calibration over the full range of amino acid D/L values, thereby allowing comparisons of alternative kinetic models for seven amino acids. The often-used parabolic kinetic model is found to be insufficient to explain the pattern of racemization, although the kinetic pathways for valine racemization and isoleucine epimerization can be closely approximated with this function. Logarithmic and power law regressions more accurately represent the racemization pathways for all amino acids. The reliability of a non-linear model for leucine racemization, developed and refined over the past 20 years, is confirmed by the 87 Sr/ 86 Sr age results. This age model indicates that the subsurface record (up to 80 m thick) of the North Carolina Coastal Plain spans the entire Quaternary, back to ∼2.5 Ma. The calibrated kinetics derived from this age model yield an estimate of the effective temperature for the study region of 11 ± 2 °C., from which we estimate full glacial (Last Glacial Maximum – LGM) temperatures for the region on the order of 7–10 °C cooler than present. These temperatures compare favorably with independent paleoclimate information for the region.

Delaware, Florida, Georgia, Maryland, New Jersey, ↗
USGS2008

Micropaleontologic record of late Pliocene and Quaternary paleoenvironments in the northern Albemarle Embayment, North Carolina, U.S.A.

Micropaleontological data provide a strong actualistic basis for detailed interpretations of Quaternary paleoenvironmental change. The 90 m-thick Quaternary record of the Albemarle Embayment in the mid-Atlantic coastal plain of the USA provides an excellent opportunity to use such an approach in a region where the details of Quaternary environmental change are poorly known. The foraminiferal record in nine cores from the northern Outer Banks, east of Albemarle Sound, North Carolina, indicates the deposition of subhorizontal, mostly open-marine early to late Pleistocene units unconformably upon a basement of late Pliocene reduced-oxygen, fine-grained, shelf-basin deposits. Pollen data record several warm–cool fluctuations within the early to mid-Pleistocene deposits. Diatom data indicate that some fresh and brackish-water units occur within the generally open-marine Pleistocene succession. A channel cut by the paleo-Roanoke River during the last glacial sea-level lowstand occurs in the northern part of the study area. Pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest Pleistocene. Overlying silts and muds accumulated under cool climatic, estuarine conditions according to diatom and pollen data. Radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest Pleistocene. The estuarine channel-fill deposits are overlain by Holocene open-marine sands deposited as the rising sea transgressed into the estuary approximately 8.5 to 9.0 kyr BP. Within the barrier island drill cores of this study, fully marine sedimentation occurred throughout the Holocene. However, immediately west of the present barrier island, mid- to late Holocene estuarine deposits underlie the modern Albemarle Sound. The islands that currently form a continuous barrier across the mouth of Albemarle Sound have a complex history of Holocene construction and destruction and large portions of them may be less than 3 kyr old. The barrier island sands overlie open-marine sands of Colington Shoal in the north and to the south overlie fluvial and marine sand filling paleo-Roanoke tributary valleys. The Pleistocene sediments underlying the northern Outer Banks study area are mainly of open inner to mid-shelf origin. If, as is likely, sea level continues to rise, a return to such environmental conditions is likely in the near future.

North Carolina↗
USGS2005

Late Neogene and Quaternary evolution of the northern Albemarle Embayment (mid-Atlantic continental margin, USA)

Seismic surveys in the eastern Albemarle Sound, adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern North Carolina coastal system. Litho- and chronostratigraphic data are derived from eight drill sites on the Outer Banks barrier islands, and the Mobil #1 well in eastern Albemarle Sound. Within the study area, parallel-bedded, gently dipping Miocene beds occur at 95 to > 160 m below sea level (m bsl), and are overlain by a southward-thickening Pliocene unit characterized by steeply inclined, southward-prograding beds. The lower Pliocene unit consists of three seismic sequences. The 55–60 m thick Quaternary section unconformably overlies the Pliocene unit, and consists of 18 seismic sequences exhibiting numerous incised channel-fill facies. Shallow stratigraphy (< 40 m bsl) is dominated by complex fill patterns within the incised paleo-Roanoke River valley. Radiocarbon and amino-acid racemization (AAR) ages indicate that the valley-fill is latest Pleistocene to Holocene in age. At least six distinct valley-fill units are identified in the seismic data. Cores in the valley-fill contain a 3–6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards. Organic materials within the interlaminated deposits have ages of 13–11 cal. ka. The interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments (bay-mouth and shoreface environments) that consist of silty, fine- to medium-grained sands containing open neritic foraminifera, suggesting that this area lacked a fronting barrier island system and was an open embayment from ∼10 ka to ∼4.5 ka. Seismic data show that initial infilling of the paleo-Roanoke River valley occurred from the north and west during the late Pleistocene and early Holocene. Later infilling occurred from the south and east and is characterized by a large shoal body (Colington Island and Shoals) and adjacent inlet fill. Establishment of a continuous barrier island system across the bay-mouth resulted in deposition of the latest phase of valley-fill, characterized by estuarine organic-rich muds.

Albemarle Embayment↗
USGS2004

Uranium-series coral ages from the US Atlantic Coastal Plain-the "80 ka problem" revisited

Uranium series coral ages for emergent units from the passive continental margin US Atlantic Coastal Plain (ACP) suggest sea level above present levels at the end of marine oxygen isotope stage (MIS) 5, contradicting age-elevation relations based on marine isotopic or coral reef models of ice equivalent sea level. We have reexamined this problem by obtaining high precision 230Th/238U and 231Pa/235U thermal ionization mass spectrometric ages for recently collected and carefully cleaned ACP corals, many in situ. We recognize samples that show no evidence for diagenesis on the basis of uranium isotopic composition and age concordance. Combining new and earlier data, among those ages close to or within the age range of MIS 5, over 85% cluster between 65 and 85 ka BP. Of the corals that we have analyzed, those that show the least evidence for diagenesis on the basis of uranium isotopic composition and age concordance have ages between 80 and 85 ka BP, consistent with a MIS 5a correlation. The units from which these samples have been collected are all emergent and have elevations within ???3-5m of those few units where early stage 5 (???125,000 ka BP) coral ages have been obtained. The ACP appears to record an unusual history of relative sea level throughout MIS 5, a history that is also apparent in the dated coral record for Bermuda. We speculate that this history is related to the regional (near-to intermediate-field) effects of ancestral Laurentide Ice sheets on last interglacial shorelines of the western North Atlantic. ?? 2004 Elsevier Ltd and INQUA. All rights reserved.

Quaternary International↗
USGS1989

Stetson Pit, Dare County, North Carolina: An integrated chronologic, faunal, and floral record of subsurface coastal quaternary sediments

Continuous split spoon samples from a drill hole penetrating 34 m of coastal plain sediments at Stetson Pit in Dare County, North Carolina were taken for lithologic, aminostratigraphic, faunal (ostracodes) and floral (pollen) analyses. Three distinct aminozones are recognized in the subsurface section based upon D-alloisoleucine/L-isoleucine (A/I) values in each of the molluscan species Mulinia lateralis and Mercenaria sp. Ostracode zonations in the subsurface section are based on percentages of 80 thermophilic and cryophilic species (those living today south and north of Cape Hatteras) and the percentages of brackish water species. Five assemblage zones are delineated. Six pollen assemblage zones are also delineated within the subsurface section based upon study of 48 sediment samples. The subsurface record at Stetson Pit is interpreted to represent portions of four interglacials based upon the combined faunal, floral and aminostratigraphic data. The two younger aminozones, with amino acid age estimates of 100,000±20,000 yr (−7.2 to −11.2 m MSL) and 300,000–500,000 yr (−13 to −14.2 m MSL), represent portions of middle/late Pleistocene interglacials. The lower aminozone (−17.4 to −33 m MSL) spans an interval that probably includes at least two interglacials (based upon faunal and floral records) and has an age estimated to be between 800,000 and 1,300,000 yr. Boundaries delineated by faunal, floral, and amino acid methods do not always coincide, due to sampling constraints and phase lags between the different records. One major unconformity (at −17.4 m MSL) in the Stetson Pit section is easily recognized from lithologic characteristics and may represent a hiatus of as much as 800,000 yr. Lithologic changes associated with all other zone boundaries are subtle and would probably not be considered significant in the absence of faunal, floral, or amino acid data.

North Carolina↗
USGS1982

Aminostratigraphy and faunal correlations of late Quaternary marine terraces, Pacific Coast, USA

Recent studies using the extent of racemization of amino acids to date fossil mollusc shells in the Arctic1, the British Isles2 and on the Atlantic3,4 and Pacific5-13 coasts of North America have relied mainly on theoretical kinetic models of racemization. Ages generated in this fashion are highly model dependent and require estimates of integrated long-term diagenetic temperatures. We present here an alternative, empirical approach to aminostratigraphy in which we plot amino acid enantiomeric ratios versus latitude (for localities along the Pacific coast of the United States), and generate isochronal correlations by connecting data points of geographically proximal localities that have similar D:L ratios and zoogeographic aspect. Isochrons are calibrated at a few localities by independent radiometric dates. The diagenetic temperature effect on racemization is reflected in the slope of the isochrons, but the need to quantify temperature is eliminated. ?? 1982 Nature Publishing Group.

Nature↗
USGS1982

Stratigraphy, structure, absolute age, and paleontology of the upper Pleistocene deposits at Sankaty Head, Nantucket Island, Massachusetts

The Sankaty Head cliff exposes drift of at least two glaciations and interglacial marine deposits. Radiocarbon, amino-acid- racemization, and uranium-thorium analyses were used to determine the absolute ages of the beds. The results indicate that 1) the Sankaty Sand correlates with oxygen-isotope stage 5 (Sangamonian), 2) the underlying drift is older than stage 5 (Illinoian or older) , and 3) the overlying drift is Wisconsinan in age. -from Authors

Massachusetts↗
USGS1979

Quaternary crustal deformation along a major branch of the San Andreas fault in central California

Deformed marine terraces and alluvial deposits record Quaternary crustal deformation along segments of a major, seismically active branch of the San Andreas fault which extends 190 km SSE roughly parallel to the California coastline from Bolinas Lagoon to the Point Sur area. Most of this complex fault zone lies offshore (mapped by others using acoustical techniques), but a 4-km segment (Seal Cove fault) near Half Moon Bay and a 26-km segment (San Gregorio fault) between San Gregorio and Point Ano Nuevo lie onshore. At Half Moon Bay, right-lateral slip and N—S horizontal compression are expressed by a broad, synclinal warp in the first (lowest: 125 ka?) and second marine terraces on the NE side of the Seal Cove fault. This structure plunges to the west at an oblique angle into the fault plane. Linear, joint0controlled stream courses draining the coastal uplands are deflected toward the topographic depression along the synclinal axis where they emerge from the hills to cross the lowest terrace. Streams crossing the downwarped part of this terrace adjacent to Half Moon Bay are depositing alluvial fans, whereas streams crossing the uplifted southern limb of the syncline southwest of the bay are deeply incised. Minimum crustal shortening across this syncline parallel to the fault is 0.7% over the past 125 ka, based on deformation of the shoreline angle of the first terrace. Between San Gregorio and Point Ano Nuevo the entire fault zone is 2.5–3.0 km wide and has three primary traces or zones of faulting consisting of numerous en-echelon and anastomozing secondary fault traces. Lateral discontinuities and variable deformation of well-preserved marine terrace sequences help define major structural blocks and document differential motions in this area and south to Santa Cruz. Vertical displacement occurs on all of the fault traces, but is small compared to horizontal displacement. Some blocks within the fault zone are intensely faulted and steeply tilted. One major block 0.8 km wide east of Point Ano Nuevo is downdropped as much as 20 m between two primary traces to form a graben presently filling with Holocene deposits. Where exposed in the sea cliff, these deposits are folded into a vertical attitude adjacent to the fault plane forming the south-west margin of the graben. Near Point Ano Nuevo sedimentary deposits and fault rubble beneath a secondary high-angle reverse fault record three and possibly six distinct offset events in the past 125 ka. The three primary fault traces offset in a right-lateral sense the shoreline angles of the two lowest terraces east of Point Ano Nuevo. The rates of displacement on the three traces are similar. The average rate of horizontal offset across the entire zone is between 0.63 and 1.30 cm/yr, based on an amino-acid age estimate of 125 ka for the first terrace, and a reasonable guess of 200–400 ka for the second terrace. Rates of this magnitude make up a significant part of the deficit between long-term relative plate motions (estimated by others to be about 6 cm/yr) and present displacement rates along other parts of the San Andreas fault system (about 3.2 cm/yr). Northwestward tilt and convergence of six marine terraces northeast of Ano Nuevo (southwest side of the fault zone) indicate continuous gentle warping associated with right-lateral displacement since early or middle Pleistocene time. Minimum local crustal shortening of this block parallel to the fault is 0.2% based on tilt of the highest terrace. Five major, evenly spaced terraces southeast of Ano Nuevo on the southwest flank of Mt. Ben Lomond (northeast side of the fault zone) rise to an elevation of 240 m, indicating relatively constant uplift (about 0.19 m/ka and southwestward tilt since Early or Middle Pleistocene time (Bradley and Griggs, 1976).

California↗
USGS1979

Anomalously high uplift rates along the Ventura-Santa Barbara coast, California-tectonic implications

The NW—SE trending segments of the California coastline from Point Arena to Point Conception (500 km) and from Los Angeles to San Diego (200 km) generally parallel major right-lateral strike-slip fault systems. Minor vertical crustal movements associated with the dominant horizontal displacements along these fault systems are recorded in local sedimentary basins and slightly deformed marine terraces. Typical maximum uplift rates during Late Quaternary time are about 0.3 m/ka, based on U-series ages of corals and amino-acid age estimates of fossil mollusks from the lowest emergent terraces. In contrast, the E–W-trending segments of the California coastline between Point Conception and Los Angeles (200 km) parallel predominantly northward-dipping thrust and high-angle reverse faults of the western Transverse Ranges. Along this coast, marine terraces display significantly greater vertical deformation. Amino-acid age estimates of mollusks from elevated marine terraces along the Ventura—Santa Barbara coast imply anomalously high uplift rates of between 1 and 6 m/ka over the past 40 to 100 ka. The deduced rate of terrace uplift decreases from Ventura to Los Angeles, conforming with a similar trend observed by others in contemporary geodetic data. The more rapid rates of terrace uplift in the western Transverse Ranges reflect N—S crustal shortening that is probably a local accommodation of the dominant right-lateral shear strain along coastal California.

California↗