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At least 37 records · Page 2Linked to original sources
USGS2008

Geochemical correlation and 40Ar/39Ar dating of the Kern River ash bed and related tephra layers: Implications for the stratigraphy of petroleum-bearing formations in the San Joaquin Valley, California

The Kern River ash (KRA) bed is a prominent tephra layer separating the K and G sands in the upper part of the Kern River Formation, a major petroleum-bearing formation in the southern San Joaquin Valley (SSJV) of California. The minimum age of the Kern River Formation was based on the tentative major-element correlation with the Bishop Tuff, a 0.759??0.002 Ma volcanic tephra layer erupted from the Long Valley Caldera. We report a 6.12??0.05 Ma 40Ar/39Ar date for the KRA, updated major-element correlations, trace-element correlations of the KRA and geochemically similar tephra, and a 6.0??0.2 Ma 40Ar/39Ar age for a tephra layer from the Volcano Hills/Silver Peak eruptive center in Nevada. Both major and trace-element correlations show that despite the similarity to the Bishop Tuff, the KRA correlates most closely with tephra from the Volcano Hills/Silver Peak eruptive center. This geochemical correlation is supported by the radiometric dates which are consistent with a correlation of the KRA to the Volcano Hills/Silver Peak center but not to the Bishop Tuff. The 6.12??0.05 Ma age for the KRA and the 6.0??0.2 Ma age for the tephra layer from the Volcano Hills/Silver Peak eruptive center suggest that the upper age of the Kern River Formation is over 5 Ma older than previously thought. Re-interpreted stratigraphy of the SSJV based on the new, significantly older age for the Kern River Formation opens up new opportunities for petroleum exploration in the SSJV and places better constraints on the tectonostratigraphic development of the SSJV. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2008

Late Pleistocene Hansel Valley basaltic ash, northern Lake Bonneville, Utah, USA

The Hansel Valley ash bed lies within 5 cm of the base of deposits of Lake Bonneville (???28 ka) in the vicinity of Great Salt Lake and provides a useful stratigraphic marker for this area of the lake basin. However, it has not been matched to an eruptive edifice, presumably because such an edifice was eroded by waves of Lake Bonneville. We present data for the chemical composition of the tephra and for possible matching lavas and tephras of the region, as well as grain size data for the tephra in an attempt to identify the location of the eruption. Matches with other tephras are negative, but lavas near the coarsest ash deposits match well with the distinctive high values of TiO2 and P2O5 of the ash. Neither chemistry nor grain size data points uniquely to a source area, but an area near the northwest shore of Great Salt Lake and within Curlew Valley is most likely. The Hansel Valley ash is an example of an ash that has no direct numerical date from proximal deposits, despite considerable study, yet nonetheless is useful for stratigraphic studies by virtue of its known stratigraphic position and approximate age. Basaltic tephras commonly are not as widespread as their rhyolitic counterparts, and in some cases apparently are produced by eruptive sources that are short lived and whose edifices are not persistent. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2008

A 2650-year-long record of environmental change from northern Yellowstone National Park based on a comparison of multiple proxy data

Geochemical, stable-isotope, pollen, charcoal, and diatom records were analyzed at high-resolution in cores obtained from Crevice Lake, a varved-sediment lake in northern Yellowstone National Park. The objective was to reconstruct the ecohydrologic, vegetation, and fire history of the watershed for the last 2650 years to better understand past climate variations at the forest-steppe transition. The data suggest a period of limited bottom-water anoxia, relatively wet winters, and cool springs and summers from 2650 to 2100 cal yr BP (700-150 BC). Dry warm conditions occurred between 2100 and 850-800 cal yr BP (150 BC and AD 1100-1150), when the lake was anoxic, winter precipitation was low, and summer stratification was protracted. The data are consistent with overall warmer/drier conditions during the Medieval Climate Anomaly, although they suggest a shift towards wetter winters within that period. The period from 850 to 800 cal yr BP (AD 1100-1150) to 250 cal yr BP (AD 1700) was characterized by greater water-column mixing and cooler spring/summer conditions than before. In addition, fire activity shifted towards infrequent large events and pollen production was low. From 250 to 150 cal yr BP (AD 1700-1800), winter precipitation was moderate compared to previous conditions, and the lake was again stratified, suggesting warm summers. Between 150 and 42 cal yr BP (AD 1800-1908), winter precipitation increased and spring and summer conditions became moderate. Metal pollution, probably from regional mining operations, is evident in the 1870s. Large fires occurred between ca. 1800-1880, but in general the forests were more closed than before. The Crevice Lake record suggests that the last 150 years of Yellowstone's environmental history were characterized by intermediate conditions when compared with the previous 2500 years. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2008

Associations of multi-decadal sea-surface temperature variability with US drought

Recent research suggests a link between drought occurrence in the conterminous United States (US) and sea surface temperature (SST) variability in both the tropical Pacific and North Atlantic Oceans on decadal to multidecadal (D2M) time scales. Results show that the Atlantic Multidecadal Oscillation (AMO) is the most consistent indicator of D2M drought variability in the conterminous US during the 20th century, but during the 19th century the tropical Pacific is a more consistent indicator of D2 M drought. The interaction between El Nin??o-Southern Oscillation (ENSO) and the AMO explain a large part of the D2M drought variability in the conterminous US. More modeling studies are needed to reveal possible mechanisms linking low-frequency ENSO variability and the AMO with drought in the conterminous US. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2008

Geochemical evidence for hydroclimatic variability over the last 2460 years from Crevice Lake in Yellowstone National Park, USA

A 2460-year-long hydroclimatic record for Crevice Lake, Yellowstone National Park, Montana was constructed from the ??18O values of endogenic carbonates. The ??18O record is compared to the Palmer Hydrologic Drought Index (PHDI) and Pacific Decadal Oscillation (PDO) indices, as well as inferred discharge of the Yellowstone River. During the last century, high ??18O values coincide with drought conditions and the warm phase of the PDO index. Low ??18O values coincide with wet years and a negative PDO index. Comparison of tree-ring inferred discharge of the Yellowstone River with the ??18O record over the last 300 years indicates that periods of high discharge (i.e., wet winters with significant snow pack) correspond with low ??18O values. Extrapolating this relationship we infer wet winters and high river discharge for the periods of 1090-1030, 970-870, 670-620, and 500-430 cal years BP. The wet intervals at 670 and 500 cal BP are synchronous with similar events in Banff, Canada and Walker Lake, Nevada. The wet intervals at 970 and 670 cal BP overlap with wet intervals at Walker Lake and major drought events identified in the western Great Basin. These results suggest that the northern border of Yellowstone National Park straddles the boundary between Northern Rocky Mountains and Great Basin climate regimes. ?? 2007 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2010

Santa Barbara Basin diatom and silicoflagellate response to global climate anomalies during the past 2200 years

Santa Barbara Basin (SBB) diatom and silicoflagellate assemblages are quantified from a box core record spanning AD 1940-2001 and an Ocean Drilling Program Hole 893A record from ???220 BC to AD 1880. The combined relative abundance of the diatoms Fragilariopsis doliolus and Nitzschia interrupteseriata from continuous two-year sampling intervals in the box core varies with sea surface temperature (SST), suggesting its utility in SST reconstruction. The assemblage data from the ODP 893A record indicate a broad interval of generally cooler SSTs between ???AD 800 and 1350, which corresponds to the Medieval Climate Anomaly (MCA), a period of generally warmer temperatures across other regions of the northern hemisphere. The assemblages also indicate an interval of generally warmer SSTs between ???AD 1400 and 1800, a period of otherwise global cooling referred to as the Little Ice Age (LIA). The changes in assemblages of diatoms and silicoflagellates support the hypothesis that the widespread droughts of the Medieval Climate Anomaly in the Western US were associated with cooler eastern North Pacific SST. The box core assemblages have higher percentages of tropical and subtropical compared to temperate and subpolar species than the ODP samples, reflecting a response of phytoplankton communities to an unusual 20th century warming. Pseudonitzschia australis, a diatom linked with domoic acid production, begins to become more common (>3% of the diatom assemblage) in the box core only after AD 1985, suggesting a link to anthropogenic activity. ?? 2008 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2009

Use of OSL dating to establish the stratigraphic framework of Quaternary eolian sediments, Anton scarp upper trench, Northeastern Colorado High Plains, USA

This paper contains the results of the optically stimulated luminescence (OSL) dating used to establish stratigraphic ages and relationships of eolian sediments in a trench in northeastern Colorado, USA. This trench was located in the upper face of the Anton scarp, a major topographic lineament trending NW-SE for a distance of 135 km, in anticipation of intersecting near-surface faulting. The trench was 180 m long, 4.5-6.0 m deep, and exposed 22 m of stratigraphic section, most of which dipped gently west and was truncated by gulley channeling at the face of the scarp. No direct evidence of faulting was found in the upper trench. The stratigraphy from the trench was described, mapped and dated using OSL on quartz and potassium feldspar, and 14 C obtained from woody material. OSL dating identified two upper loess units as Peoria Loess and Gilman Canyon Loess, deposited between 16 and 30 ka ago. The bottom layers of the trench were substantially older, giving OSL ages in excess of 100 ka. These older ages are interpreted as underestimates, owing to saturation of the fast component of OSL. Using OSL and 14 C dating, we can constrain the erosion and down cutting of the scarp face as occurring between 16 and 5.7 ka. As the trenching investigation continues in other parts of the scarp face, the results of this preliminary study will be of importance in relating the ages of the strata that underlie different parts of the scarp, and in determining whether Quaternary faulting was a mechanism that contributed to the formation of this regional geomorphic feature.

Quaternary International↗
USGS2010

Mass spectrometric U-series dating of the Chaoxian hominin site at Yinshan, eastern China

The fossils of Chaoxian hominin, widely accepted as representing archaic Homo sapiens in eastern China, were recovered from the middle or slightly higher levels of Layer 2 deposits of a collapsed cave at Yinshan, Anhui Province. Results of mass spectrometric U-series dating of intercalated speleothem calcites are presented. Based mainly on four broadly coeval calcite samples, the hominin fossils should be bracketed in the range of 310–360 ka or somewhat older. These ages are much older than the previous estimate at 160–200 ka based on the U-series dating of fossil teeth and bones, and may be cited as supporting evidence for an earlier H. erectus –archaic H. sapiens interface in China.

Yinshan↗
USGS2010

Paradigms and proboscideans in the southern Great Lakes region, USA

Thirteen new chronometric dates for Illinois proboscideans are considered in relation to well-dated pollen records from northeastern and central Illinois. These dates span an interval from 21,228 to 12,944 cal BP. When compared to pollen spectra, it is evident that Mammut americanum inhabited spruce (Picea) and black ash (Fraxinus nigra) forest during the B??lling-Aller??d (14,700-12,900 cal BP) and early Younger Dryas (12,900-11,650 cal BP) chronozones. Both Mammuthus jeffersonii and Mammuthus primigenius inhabited spruce dominated open-woodland during the Oldest Dryas chronozone, while M.??primigenius persisted in a forest of predominantly black ash during the Aller??d chronozone. A newly discovered specimen from Lincoln, IL, clarifies the taxonomic distinction between M. primigenius and M.??jeffersonii. Hitherto, a paradigm of proboscidean succession during the full- to late-glacial periods was based on the vegetation succession of steppe tundra-like vegetation to spruce forest to spruce-deciduous forest. The presumed proboscidean succession was that of cold, dry steppe-adapted M. primigenius succeeded by more mesic-tolerant M. jeffersonii that in turn was succeeded by the wet forest-adapted M.??americanum. Reported data do not support this view and indicate a need for re-evaluation of assumptions of proboscidean ecology and history, e.g., the environmental tolerances and habits of M.??primigenius in regions south of 55??N, and its dynamic relationship with other proboscidean taxa. ?? 2009 Elsevier Ltd and INQUA.

Quaternary International↗
USGS2010

Holocene landscape response to seasonality of storms in the Mojave Desert

New optically stimulated and radiocarbon ages for alluvial fan and lake deposits in the Mojave Desert are presented, which greatly improves the temporal resolution of surface processes. The new Mojave Desert climate-landscape record is particularly detailed for the late Holocene. Evidence from ephemeral lake deposits and landforms indicates times of sustained stream flow during a wet interval of the latter part of the Medieval Warm Period at ca. AD 1290 and during the Little Ice Age at ca. AD 1650. The former lakes postdate megadroughts of the Medieval Warm Period, whereas the latter match the Maunder Minimum of the Little Ice Age. Periods of alluvial fan aggradation across the Mojave Desert are 14–9 cal ka and 6–3 cal ka. This timing largely correlates to times of increased sea-surface temperatures in the Gulf of California and enhanced warm-season monsoons. This correlation suggests that sustained alluvial fan aggradation may be driven by intense summer-season storms. These data suggest that the close proximity of the Mojave Desert to the Pacific Ocean and the Gulf of California promotes a partitioning of landscape-process responses to climate forcings that vary with seasonality of the dominant storms. Cool-season Pacific frontal storms cause river flow, ephemeral lakes, and fan incision, whereas periods of intense warm-season storms cause hillslope erosion and alluvial fan aggradation. The proposed landscape-process partitioning has important implications for hazard mitigation given that climate change may increase sea-surface temperatures in the Gulf of California, which indirectly could increase future alluvial fan aggradation.

California↗
USGS2010

The 23rd Pacific Climate Workshop (PACLIM)

The 23rd Pacific Climate Workshop (PACLIM) was held May 13–16, 2007 at the Asilomar Conference Grounds in Pacific Grove, California, in what turned out to be a relatively dry spring on the central California coast. What a change from 2006, which was the sixth wettest year of the 101 years for which records have been kept. The special session at the 2007 gathering was entitled “Abrupt Climate Change: Causes and Ecosystem Responses”, reflecting the increasing evidence for rapid climate shifts in marine and terrestrial environments.

California↗
USGS2010

Palaeoenvironmental significance of diatom and vertebrate fossils from Late Cenozoic tectonic basins in west-central México: A review

Pronounced lacustrine sedimentation developed in west-central México during the late Miocene, between approximately 11 and 7 Ma. This was in response to tectonic extension associated with the initial emplacement of the late Miocene substrata of the Trans-Mexican Volcanic Belt. Climatic conditions in west-central México during this interval were relatively warm and humid based on the widespread distribution of interpreted lacustrine beds. Following a latest Miocene (8.0–5.4 Ma) stage of arid conditions and greatly reduced deposition of fine-grained lacustrine sediments, extensive, east–west oriented, relatively deep, perennial lakes ensued. They mark the early Pliocene (5.3–4.0 Ma). Lower Pliocene diatomites contain the same diatom species (e.g., Stephanodiscus carconensis and Tertiarius aff. baikalensis) found in rocks of this age in the western United States. The relatively warm and humid conditions that characterized this interval in central México coincide with a period of high-latitude warming, higher global sea level, and a reduction in size of the Antarctic Ice sheets. Because the Central American Seaway persisted until at least the latest Miocene, it might have acted to increase precipitation in central Mexico. This could have continued into the earliest Pliocene. Mexican Pliocene mammalian faunas also support a savanna setting with moist and warm conditions prevailing at the time. Shallow lakes and fluvial conditions dominate after 4.0 Ma, until the end of Pleistocene. A combination of reduced precipitation, due to general global cooling and drying, as well as volcanic and tectonic processes, are presumed to have been the cause for this mid-Pliocene reduction in lake size and extent in central México.

Chincua, Ixtlahuaca↗
USGS2011

Enhanced Late Holocene ENSO/PDO expression along the margins of the eastern North Pacific

Pacific climate is known to have varied during the Holocene, but spatial patterns remain poorly defined. This paper compiles terrestrial and marine proxy data from sites along the northeastern Pacific margins and proposes that they indicate 1) suppressed ENSO conditions during the middle Holocene between ∼8000 and 4000 cal BP with a North Pacific that generally resembled a La Niña-like or more negative PDO phase and 2) a climate transition between ∼4200 and 3000 cal BP that appears to be the teleconnected expression to a more modern-like ENSO Pacific. Compared to modern day conditions, the compiled data suggest that during the middle Holocene, the Aleutian Low was generally weaker during the winter and/or located more to the west, while the North Pacific High was stronger during the summer and located more to the north. Coastal upwelling off California was more enhanced during the summer and fall but suppressed during the spring. Oregon and California sea surface temperatures (SSTs) were cooler. The Santa Barbara Basin had an anomalous record, suggesting warmer SSTs. Late Holocene records indicate a more variable, El Niño-like, and more positive PDO Pacific. The Aleutian Low became more intensified during the winter and/or located more to the east. The North Pacific High became weaker and/or displaced more to the south. Coastal upwelling off California intensified during the spring but decreased during the fall. Oregon and California SSTs became warmer, recording the shoreward migration of sub-tropical gyre waters during the fall, while spring upwelling (cooler SST) increased in the Santa Barbara Basin. The high-resolution proxy records indicate enhanced ENSO and PDO variability after ∼4000 cal BP off southern California, ∼3400 cal BP off northern California, and by ∼2000 cal BP in southwestern Yukon. A progressively northward migration of the ENSO teleconnection during the late Holocene is proposed.

Quaternary International↗
USGS2011

The rise and fall of Lake Bonneville between 45 and 10.5 ka

A sediment core taken from the western edge of the Bonneville Basin has provided high-resolution proxy records of relative lake-size change for the period 45.1–10.5 calendar ka (hereafter ka). Age control was provided by a paleomagnetic secular variation (PSV)-based age model for Blue Lake core BL04-4. Continuous records of δ18O and total inorganic carbon (TIC) generally match an earlier lake-level envelope based on outcrops and geomorphic features, but with differences in the timing of some hydrologic events/states. The Stansbury Oscillation was found to consist of two oscillations centered on 25 and 24 ka. Lake Bonneville appears to have reached its geomorphic highstand and began spilling at 18.5 ka. The fall from the highstand to the Provo level occurred at 17.0 ka and the lake intermittently overflowed at the Provo level until 15.2 ka, at which time the lake fell again, bottoming out at ∼14.7 ka. The lake also fell briefly below the Provo level at ∼15.9 ka. Carbonate and δ18O data indicate that between 14.7 and 13.1 ka the lake slowly rose to the Gilbert shoreline and remained at about that elevation until 11.6 ka, when it fell again. Chemical and sedimentological data indicate that a marsh formed in the Blue Lake area at 10.5 ka. Relatively dry periods in the BL04-4 records are associated with Heinrich events H1–H4, suggesting that either the warming that closely followed a Heinrich event increased the evaporation rate in the Bonneville Basin and (or) that the core of the polar jet stream (PJS) shifted north of the Bonneville Basin in response to massive losses of ice from the Laurentide Ice Sheet (LIS) during the Heinrich event. The second Stansbury Oscillation occurred during Heinrich event H2, and the Gilbert wet event occurred during the Younger Dryas cold interval. Several relatively wet events in BL04-4 occur during Dansgaard-Oeschger (DO) warm events. The growth of the Bear River glacier between 32 and 17 ka paralleled changes in the values of proxy indicators of Bonneville Basin wetness and terminal moraines on the western side of the Wasatch Mountains have ages ranging from 16.9 to 15.2 ka. This suggests a near synchroneity of change in the hydrologic and cryologic balances occurring in the Bonneville drainage system and that glacial extent was linked to lake size.

Quaternary International↗
USGS2011

Stratigraphy of the Younger Dryas Chronozone and paleoenvironmental implications: Central and Southern Great Plains

The Great Plains of the United States was the setting for some of the earliest research in North America into patterns and changes in the character of late Pleistocene environments and their effects on contemporary human populations. Many localities in the region have well-stratified records of terminal Pleistocene and early Holocene human (Paleoindian) activity and past environments. These have proven important in debates over the character of the Younger Dryas Chronozone (YDC; 11,000–10,000 14 C BP; 12,900–11,700 cal BP) in the continental interior. This paper reviews the lithostratigraphic record of the YDC on the Central and Southern Great Plains and summarizes paleobiological records (largely isotopic). The goal is to determine if there is any uniformity in the timing, character, direction and/or magnitude of changes in depositional environments or broader geomorphic systems before, during or after the YDC in order to address the question of the character of environments through this time. The stratigraphic records of the late Pleistocene to early Holocene transition, and in particular, the stratigraphic records of the YDC vary through time and space. The data clearly show that a host of geomorphic processes produced the terminal Pleistocene and early Holocene stratigraphic records of the Great Plains. Moreover, the YDC is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils. The various geomorphic systems of the Great Plains did not behave synchronously in response to any common climate driver. These stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid-latitude climates in the terminal Pleistocene and early Holocene.

Montana, Wyoming, Colorado, New Mexico, Texas, Okl↗