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Jeffrey S. Pigati

Publications and source records attributed to Jeffrey S. Pigati.

At least 37 records · Page 2Linked to original sources
USGS2020

Climatically driven displacement on the Eglington fault, Las Vegas, Nevada

The Eglington fault is one of several intrabasinal faults in the Las Vegas Valley, Nevada and is the only one recognized as a source for significant earthquakes. Its broad warp displaces late Pleistocene paleo-spring deposits of the Las Vegas Formation, which record hydrologic fluctuations that occurred in response to millennial and submillennial-scale climate oscillations throughout the late Quaternary. The sediments allow us to constrain the timing of displacement on the Eglington fault and identify hydrologic changes that are temporally coincident with that event. The fault warps deposits that represent widespread marshes that filled the valley between 31.7 and 27.6 ka. These marshes desiccated abruptly in response to warming and groundwater lowering during Dansgaard-Oeschger (D-O) events 4 and 3, resulting in the formation of a pervasive, hard carbonate cap by 27.0 ka. Vertical offset by as much as 4.2 meters occurred after the cap hardened, and most likely after younger marshes desiccated irreversibly due to a sudden depression of the water table during D-O 2, beginning at 23.3 ka. The timing of displacement is further constrained to before 19.5 ka as evidenced by undeformed spring deposits that are inset into the incised topography of the warp. Coulomb stress calculations validate the hypothesis that the significant groundwater decline during D-O 2 triggered fault displacement through unloading of vertical stress of the water column. The synchroneity of this abrupt hydrologic change and warping on the Eglington fault suggests that climatically modulated tectonics operated in the Las Vegas Valley during the late Quaternary.

Nevada↗
USGS2019

Fluvial sedimentary history of Arlington Canyon, Channel Islands National Park, California

Arlington Canyon, in the northwest part of Santa Rosa Island, Channel Islands National Park, California, has been the setting for important scientific discoveries over the past half century, including the oldest human remains in North America, several vertebrate fossil sites, and purported evidence of a catastrophic extinction event at the end of the Pleistocene. The canyon is filled with alluvial sediments that date to between 16.4 and 1.1 ka (thousands of calibrated years before present), representing accumulation that occurred primarily in response to rising sea levels during the late Pleistocene and Holocene. The deposits are laterally discontinuous, exhibit a high degree of sedimentary complexity, and contain evidence of past climates and environments, including fossil bones, burned plant macrofossils, and invertebrate microfossils. Here, we show that it is critical to view the observations, data, and conclusions of scientific studies conducted in the canyon within this larger context so that localized facets of the spatially and temporally extensive alluvial deposits are not misinterpreted or misrepresented. By improving the baseline understanding of processes and drivers of sediment accumulation in Arlington Canyon, we hope to offer a solid foundation and better underpinning for future archeological, paleontological, and geochemical studies here and throughout the northern Channel Islands.

California↗
USGS2019

Late Quaternary paleohydrology of desert wetlands and pluvial lakes in the Soda Lake basin, central Mojave Desert, California (USA)

Sediment cores taken near extant springs along the western margin of Soda Lake playa, as well as from the playa center, reveal dramatic hydrologic changes that occurred in the central Mojave Desert during the late Quaternary. Results of stratigraphic, chronologic, physical, chemical, and microfossil analyses of seven cores, ranging in length from 5 to 23 m, help refine the timing and character of the final stages of pluvial Lake Mojave during the late Pleistocene and define distinct periods of wetland development in the early and late Holocene. Evidence shows that an incipient lake occupied the central Soda Lake basin by at least 25.0 ka (ka = thousands of calibrated 14 C years before present), and a fully developed Lake Mojave was present between 20.5 and 12.8 ka, before receding and ultimately yielding to playa conditions by 11.0 ka. Organic-rich “black mats” appear in several cores along the playa margin between 10.7 and 9.0 ka, suggesting that spring-fed wetlands persisted in this area long after the lake had regressed. The basin remained relatively dry throughout most of the Holocene until wetland ecosystems expanded along the margins between 0.73 and 0.18 ka, coincident with part of the Medieval Climate Anomaly and Little Ice Age. Overall, our results demonstrate that buried sediments surrounding extant and extinct springs can be used to reconstruct past hydrologic conditions in desert environments on a variety of spatial and temporal scales, and provide important baseline information for effective management of limited desert resources.

California↗
USGS2018

The geology and paleontology of Tule Springs Fossil Beds National Monument, Nevada

On December 19, 2014, Tule Springs Fossil Beds National Monument, located in the Las Vegas Valley of southern Nevada, was established by Congress as the 405th unit of the National Park Service to “conserve, protect, interpret, and enhance for the benefit of present and future generations the unique and nationally important paleontological, scientific, educational, and recreational resources and values of the land” (P.L. 113-291, sec. 3092). Vertebrate fossils have been known from the region for more than a century, and recent work has established the Tule Springs local fauna as one of the most significant Pleistocene vertebrate faunas in the American Southwest. The sedimentary sequence that entombs the fossils represents a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Work in Tule Springs Fossil Beds National Monument continues today through the efforts of scientists from the U.S. Geological Survey, National Park Service, and academic institutions across the country.

Nevada↗
USGS2018

The Las Vegas Formation

The Las Vegas Formation was established in 1965 to designate the distinctive light-colored, fine-grained, fossil-bearing sedimentary deposits exposed in and around the Las Vegas Valley, Nevada. In a coeval designation, the sediments were subdivided into informal units with stratigraphic and chronologic frameworks that have persisted in the literature. Use of the Las Vegas Formation name over the past half century has been hampered because of the lack of a robust definition and characterization of the entire lithostratigraphic sequence, its geographic distribution, and chronology. This study evaluates and describes deposits attributed to the Las Vegas Formation with detailed stratigraphy, sedimentology, and field relations. A large suite of radiocarbon and luminescence ages facilitates revision and temporal expansion of the geochronology. In all, we characterize 17 informal geologic units within the formation, each dating to a unique period of geologic time, with stratigraphically ascending members X, A, B, D, and E and attendant beds in members B, D, and E. The age of the Las Vegas Formation spans at least the middle Pleistocene to early Holocene (from approximately 573 to 8.53 kilo-annum [thousands of years before present]) and is related to past episodes of groundwater discharge in the Las Vegas Valley. The contextual information derived from this new framework is dually noteworthy because the sediments entomb one of the most significant Pleistocene vertebrate faunas in the American Southwest, the Tule Springs local fauna, and represent a paleohydrologic system that responded dynamically to abrupt changes in climate throughout the late Quaternary. Characterizing the nature of these important deposits stabilizes the nomenclature, promotes the continued use of the informal units within the formation, and facilitates studies of similar deposits associated with desert wetland ecosystems elsewhere in the southwestern United States.

Nevada↗
USGS2018

Overview of the oxygen isotope systematics of land snails from North America

Continental paleoclimate proxies with near-global coverage are rare. Land snail δ 18 O is one of the few proxies abundant in Quaternary sediments ranging from the tropics to the high Arctic tundra. However, its application in paleoclimatology remains difficult, attributable in part to limitations in published calibration studies. Here we present shell δ 18 O of modern small (<10 mm) snails across North America, from Florida (30°N) to Manitoba (58°N), to examine the main climatic controls on shell δ 18 O at a coarse scale. This transect is augmented by published δ 18 O values, which expand our coverage from Jamaica (18°N) to Alaska (64°N). Results indicate that shell δ 18 O primarily tracks the average annual precipitation δ 18 O. Shell δ 18 O increases 0.5–0.7‰ for every 1‰ increase in precipitation δ 18 O, and 0.3–0.7‰ for every 1°C increase in temperature. These relationships hold true when all taxa are included regardless of body size (ranging from ~1.6 to ~58 mm), ecology (herbivores, omnivores, and carnivores), or behavior (variable seasonal active periods and mobility habits). Future isotopic investigations should include calibration studies in tropical and high-latitude settings, arid environments, and along altitudinal gradients to test if the near linear relationship between shell and meteoric precipitation δ 18 O observed on a continental scale remains significant.

Quaternary Research↗
USGS2018

Origin of last-glacial loess in the western Yukon-Tanana Upland, central Alaska, USA

Loess is widespread over Alaska, and its accumulation has traditionally been associated with glacial periods. Surprisingly, loess deposits securely dated to the last glacial period are rare in Alaska, and paleowind reconstructions for this time period are limited to inferences from dune orientations. We report a rare occurrence of loess deposits dating to the last glacial period, ~19 ka to ~12 ka, in the Yukon-Tanana Upland. Loess in this area is very coarse grained (abundant coarse silt), with decreases in particle size moving south of the Yukon River, implying that the drainage basin of this river was the main source. Geochemical data show, however, that the Tanana River valley to the south is also a likely distal source. The occurrence of last-glacial loess with sources to both the south and north is explained by both regional, synoptic-scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the Brooks Range to the north and the Alaska Range to the south. Based on a comparison with recent climate modeling for the last glacial period, seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources.

Alaska↗
USGS2018

Desert wetlands record hydrologic variability within the Younger Dryas chronozone, Mojave Desert, USA

One of the enduring questions in the field of paleohydrology is how quickly desert wetland ecosystems responded to past episodes of abrupt climate change. Recent investigations in the Las Vegas Valley of southern Nevada have revealed that wetlands expanded and contracted on millennial and sub-millennial timescales in response to changes in climate during the late Quaternary. Here, we evaluate geologic evidence from multiple localities in the Mojave Desert and southern Great Basin that suggests the response of wetland systems to climate change is even faster, occurring at centennial, and possibly decadal, timescales. Paleowetland deposits at Dove Springs Wash, Mesquite Springs, and Little Dixie Wash, California, contain evidence of multiple wet and dry cycles in the form of organic-rich black mats, representing periods of past groundwater discharge and wet conditions, interbedded with colluvial, alluvial, and aeolian sediments, each representing dry conditions. Many of these wet-dry cycles date to within the Younger Dryas (YD) chronozone (12.9–11.7 ka), marking the first time intra -YD hydrologic variability has been documented in paleowetland deposits. Our results illustrate that desert wetland ecosystems are exceptionally sensitive to climate change and respond to climatic perturbations on timescales that are relevant to human society.

Arizona, California, Nevada↗
USGS2018

Quaternary sea-level history and the origin of the northernmost coastal aeolianites in the Americas: Channel Islands National Park, California, USA

Along most of the Pacific Coast of North America, sand dunes are dominantly silicate-rich. On the California Channel Islands, however, dunes are carbonate-rich, due to high productivity offshore and a lack of dilution by silicate minerals. Older sands on the Channel Islands contain enough carbonate to be cemented into aeolianite. Several generations of carbonate aeolianites are present on the California Channel Islands and represent the northernmost Quaternary coastal aeolianites on the Pacific Coast of North America. The oldest aeolianites on the islands may date to the early Pleistocene and thus far have only been found on Santa Cruz Island. Aeolianites with well-developed soils are found on both San Miguel Island and Santa Rosa Island and likely date to the middle Pleistocene. The youngest and best-dated aeolianites are located on San Miguel Island and Santa Rosa Island. These sediments were deposited during the late Pleistocene following the emergence of marine terraces that date to the last interglacial complex (~ 120,000 yr to ~ 80,000 yr). Based on radiocarbon and luminescence dating, the ages of these units correspond in time with marine isotope stages [MIS] 4, 3, and 2. Sea level was significantly lower than present during all three time periods. Reconstruction of insular paleogeography indicates that large areas to the north and northwest of the islands would have been exposed at these times, providing a ready source of carbonate-rich skeletal sands. These findings differ from a previously held concept that carbonate aeolianites are dominantly an interglacial phenomenon forming during high stands of sea. In contrast, our results are consistent with the findings of other investigators of the past decade who have reported evidence of glacial-age and interstadial-age aeolianites on coastlines of Australia and South Africa. They are also consistent with observations made by Darwin regarding the origin of aeolianites on the island of St. Helena, in the South Atlantic Ocean, more than a century and a half ago.

California↗
USGS2018

Examining the relationship between portable luminescence reader measurements and depositional ages of paleowetland sediments, Las Vegas Valley, Nevada

Portable luminescence readers are exciting new tools that have the potential to rapidly determine the age structure of late Quaternary stratigraphic columns. This is important because high-resolution age profiling can reveal details about the temporal dynamics of climate cause and ecosystem effect, often while researchers are still in the field. In this paper, we compare new portable luminescence reader measurements of total photon counts with a suite of robust, highly resolved ages from middle to late Pleistocene-age paleowetland deposits in the Las Vegas Valley of southern Nevada. Our results show that total photon counts correlate with age, with a quadratic equation providing the best fit to the data. Significant scatter is present in the data, which is likely the result of dose rate variations, multiple sediment sources, and transport mechanisms that include both eolian and fluvial processes. The observed scatter can be reduced significantly using a simple pretreatment procedure involving a 250 μm sieve and neodymium hand magnet to normalize particle sizes and remove magnetic grains. Following this treatment, age estimates based on the reader measurements have an average error of 30 ± 18% when compared against known ages. These findings confirm that portable reader measurements scale with age in paleowetland deposits, allowing its use in establishing rapid, albeit approximate, chronologies for these deposits throughout the American Southwest.

Nevada↗
USGS2018

Juke Box trench: A valuable archive of late Pleistocene and Holocene stratigraphy in the Bonneville basin, Utah

A backhoe trench in deposits of Pleistocene Lake Bonneville and Holocene wetlands below the mouth of Juke Box Cave, near Wendover, Utah, provides an excellent view of the late Pleistocene and Holocene geologic history of the area. The following stratigraphic units are exposed (ascending): preBonneville gravel (fluvial or lacustrine) and oolitic sand (ages greater than 30,000 yr B.P.); Lake Bonneville marl (30,000 to ~13,000 yr B.P.); an unconformity stratigraphically above the Bonneville marl marked by lacustrine gravel of probable Gilbert-episode age (~11,500 yr B.P.); and poorly sorted sand and carbonate mud deposited in post-Bonneville spring-fed wetlands. The wetland deposits include layers of poorly sorted sand, peat composed of bulrush remains and other organic-rich muds, and the Mazama volcanic ash (~7600 yr B.P.). Four calibrated 14C ages suggest the wetland deposits span nearly the entire Holocene, from about 10,700 to at least 1200 yr B.P. The spring and wetland are now dry.

Utah↗
USGS2017

The Great Acceleration and the disappearing surficial geologic record

The surficial geologic record is the relatively thin veneer of young (<~1 Ma) and mostly unconsolidated sediments that cover portions of Earth’s terrestrial surface (Fig. 1). Once largely ignored as “overburden” by geologists, surficial deposits are now studied to address a wide range of issues related to the sustainability of human societies. Geologists use surficial deposits to determine the frequency and severity of past climatic changes, quantify natural and anthropogenic erosion rates, identify hazards, and calculate recurrence intervals associated with earthquakes, landslides, tsunamis, and volcanic eruptions. Increasingly, however, humans are eradicating the surficial geologic record in many key areas through progressive modification of Earth’s surface.

GSA Today↗
USGS2017

Activation of a small ephemeral lake in southern Jordan during the last full glacial period and its paleoclimatic implications

Playas, or ephemeral lakes, are one of the most common depositional environments in arid and semiarid lands worldwide. Playa deposits, however, have mostly been avoided as paleoclimatic archives because they typically contain exceptionally low concentrations of organic material, making 14 C dating difficult. Here, we describe a technique for concentrating organic matter in sediments for radiocarbon dating and apply it to playa sediments recovered from a 2.35 m sediment core from a small playa in southern Jordan. Based on 14 C ages of the organic concentrate fraction, the playa was active from ~29 to 21 ka, coincident with the last major high stand of Paleolake Lisan and wet conditions recorded by other paleoclimatic proxies in the southernmost Levant during the last full glacial period (35–20 ka). The timing and spatial pattern of these records suggests that the increased moisture was likely derived from more frequent and deeper eastern Mediterranean (EM) cyclones associated with the intensification of the westerlies. The presence of full glacial pluvial deposits in southern Jordan (29°N), and the lack of similarly aged deposits in the northern Arabian Peninsula to the south, suggests that the southerly limit of the incursion of EM cyclones during last full glacial period was ~28°N.

Khabrat Ratiya↗
USGS2017

Radiocarbon ages of terrestrial gastropods extend duration of ice-free conditions at the Two Creeks forest bed, Wisconsin, USA

Analysis of terrestrial gastropods that underlie the late Pleistocene Two Creeks forest bed (~ 13,800–13,500 cal yr BP) in eastern Wisconsin, USA provides evidence for a mixed tundra-taiga environment prior to formation of the taiga forest bed. Ten new AMS 14 C analyses on terrestrial gastropod shells indicate the mixed tundra-taiga environment persisted from ~ 14,500 to 13,900 cal yr BP. The Twocreekan climatic substage, representing ice-free conditions on the shore of Lake Michigan, therefore began near the onset of peak warming conditions during the Bølling–Allerød interstadial and lasted ~ 1000 yr, nearly 600 yr longer than previously thought. These results provide important data for understanding the response of continental ice sheets to global climate forcing and demonstrate the potential of using terrestrial gastropod fossils for both environmental reconstruction and age control in late Quaternary sediments.

Wisconsin↗
USGS2017

A geochronologic framework for the Ziegler Reservoir fossil site, Snowmass Village, Colorado

The Ziegler Reservoir fossil site near Snowmass Village, Colorado, provides a unique opportunity to reconstruct high-altitude paleoenvironmental conditions in the Rocky Mountains during the last interglacial period. We used four different techniques to establish a chronological framework for the site. Radiocarbon dating of lake organics, bone collagen, and shell carbonate, and in situ cosmogenic 10 Be and 26 Al ages on a boulder on the crest of a moraine that impounded the lake suggest that the ages of the sediments that hosted the fossils are between ~ 140 ka and > 45 ka. Uranium-series ages of vertebrate remains generally fall within these bounds, but extremely low uranium concentrations and evidence of open-system behavior limit their utility. Optically stimulated luminescence (OSL) ages (n = 18) obtained from fine-grained quartz maintain stratigraphic order, were replicable, and provide reliable ages for the lake sediments. Analysis of the equivalent dose (D E ) dispersion of the OSL samples showed that the sediments were fully bleached prior to deposition and low scatter suggests that eolian processes were likely the dominant transport mechanism for fine-grained sediments into the lake. The resulting ages show that the fossil-bearing sediments span the latest part of marine isotope stage (MIS) 6, all of MIS 5 and MIS 4, and the earliest part of MIS 3.

Colorado↗
USGS2017

A high-elevation, multi-proxy biotic and environmental record of MIS 6-4 from the Ziegler Reservoir fossil site, Snowmass Village, Colorado, USA

In North America, terrestrial records of biodiversity and climate change that span Marine Oxygen Isotope Stage (MIS) 5 are rare. Where found, they provide insight into how the coupling of the ocean&ndash;atmosphere system is manifested in biotic and environmental records and how the biosphere responds to climate change. In 2010&ndash;2011, construction at Ziegler Reservoir near Snowmass Village, Colorado (USA) revealed a nearly continuous, lacustrine/wetland sedimentary sequence that preserved evidence of past plant communities between ~ 140 and 55 ka, including all of MIS 5. At an elevation of 2705 m, the Ziegler Reservoir fossil site also contained thousands of well-preserved bones of late Pleistocene megafauna, including mastodons, mammoths, ground sloths, horses, camels, deer, bison, black bear, coyotes, and bighorn sheep. In addition, the site contained more than 26,000 bones from at least 30 species of small animals including salamanders, otters, muskrats, minks, rabbits, beavers, frogs, lizards, snakes, fish, and birds. The combination of macro- and micro-vertebrates, invertebrates, terrestrial and aquatic plant macrofossils, a detailed pollen record, and a robust, directly dated stratigraphic framework shows that high-elevation ecosystems in the Rocky Mountains of Colorado are climatically sensitive and varied dramatically throughout MIS 5.

Colorado↗
USGS2017

Reply to the discussion of Pinter et al. on ‘Fluvial system response to late Pleistocene-Holocene sea-level change on Santa Rosa Island, Channel Islands National Park, California’ by Schumann et al. (2016)

We appreciate the thoughtful discussion offered by Pinter et al. (2017) because it gives us an opportunity to elucidate some of the main points of our study, address some apparent misinterpretations, and recapitulate one of our conclusions. Pinter et al.’s discussion emphasizes and reinforces some of the important concepts we presented but also raises questions regarding specific aspects of our study, including that: (1) base level is the dominant control on fluvial system change on Santa Rosa Island (SRI); (2) post-Last Glacial Maximum (LGM) fluvial aggradation on SRI occurred at uniform rates; and (3) the transition from aggradation to incision on SRI occurred during the last 500 to ≤150 years.

California↗