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At least 37 records · Page 2Linked to original sources

USGS2006

Changes in the C storage in Las Tablas de Daimiel National Park (PNTD) in the last 1000 years [Cambios en el almacenamiento de C en el Parque Nacional de Las Tablas de Daimiel (PNTD) en los últimos 1000 años]

Las Tablas de Daimiel National Park has suffered too many modifications throughout its history, natural as well as anthropic, which have affected the carbon storage in different ways. The study of those variations has been carried out by the analysis of sedimentary record and historical data. The sedimentary record has been studied from the core Ciguela 4. It was sampled with a systematic high resolution method (0.7 cm thickness average) to analyze geochemistry and pollen. The analysis of all data shows that the natural changes (linked with the climate) have more variation ranges than the anthropic ones, are directly related with the climate and not with the concentration of the atmospheric CO2, showing a natural cyclicity with a fast mitigation (decades) of the variations. In the other hand the anthropogenic impacts depend on the proximity and intensity of the impact. The usage changes produced during the second half of the 19th century were an indirect impact with medium intensity. The environment had the capacity to recover the values of a normal storage in less than 50 years. Nevertheless the dissication and overexploitation of the groundwater (second half of 20th century) were direct and high intensity impacts. These impacts caused a fast loss of the water table and the salinization of the environment. Due to that the ecosystem lost capacity to store C. recovery of the normal values by a natural way is difficult now.

Las Tablas de Daimiel National Park↗

USGS2008

Holocene vegetation and fire regimes in subalpine and mixed conifer forests, southern Rocky Mountains, USA

Our understanding of the present forest structure of western North America hinges on our ability to determine antecedent forest conditions. Sedimentary records from lakes and bogs in the southern Rocky Mountains of Colorado and New Mexico provide information on the relationships between climate and vegetation change, and fire history since deglaciation. We present a new pollen record from Hunters Lake (Colorado) as an example of a high-elevation vegetation history from the southern Rockies. We then present a series of six sedimentary records from ???2600 to 3500-m elevation, including sites presently at the alpine?subalpine boundary, within the Picea engelmannii?Abies lasiocarpa forest and within the mixed conifer forest, to determine the history of fire in high-elevation forests there. High Artemisia and low but increasing percentages of Picea and Pinus suggest vegetation prior to 13 500 calendar years before present (cal yr BP) was tundra or steppe, with open spruce woodland to ???11 900 cal yr BP. Subalpine forest (Picea engelmannii, Abies lasiocarpa) existed around the lake for the remainder of the Holocene. At lower elevations, Pinus ponderosa and/or contorta expanded 11 900 to 10 200 cal yr BP; mixed conifer forest expanded ???8600 to 4700 cal yr BP; and Pinus edulis expanded after ???4700 cal yr BP. Sediments from lake sites near the alpine?subalpine transition contained five times less charcoal than those entirely within subalpine forests, and 40 times less than bog sites within mixed conifer forest. Higher fire episode frequencies occurred between ???12 000 and 9000 cal yr BP (associated with the initiation or expansion of south-west monsoon and abundant lightning, and significant biomass during vegetation turnover) and at ???2000?1000 cal yr BP (related to periodic droughts during the long-term trend towards wetter conditions and greater biomass). Fire episode frequencies for subalpine?alpine transition and subalpine sites were on average 5 to 10 fire events/1000 years over the Holocene, corresponding to one fire event every ???100 to 200 years. (5) Our Holocene-length sedimentary charcoal records provide additional evidence for the anomalous nature of the 20th-century fire regime, where fires were largely suppressed as a national policy. ?? IAWF 2008.

International Journal of Wildland Fire↗

USGS1999

Sediment color and reflectance record from Ocean Drilling Program Hole 625B, Gulf of Mexico (marine isotope stage 5 interval)

Analysis of climate indicators from the North Atlantic, California Margin, and ice cores from Greenland suggest millennial scale climate variability is a component of earth's climate system during the last interglacial period (marine oxygen isotope stage 5). The USGS is involved in a survey of high resolution marine records covering the last interglacial period (MIS 5) to further document the variability of climate and assess the rate at which climate can change during warm intervals. The Gulf of Mexico (GOM) is an attractive area for analysis of climate variability and rapid change. Changes in the Mississippi River Basin presumably are translated to the GOM via the river and its effect on sediment distribution and type. Likewise, the summer monsoon in the southwestern US is driven by strong southerly winds. These winds may produce upwelling in the GOM which will be recorded in the sedimentary record. Several areas of high accumulation rate have been identified in the GOM. Ocean Drilling Program (ODP) Site 625 appears to meet the criteria of having a well preserved carbonate record and accumulation rate capable of discerning millennial scale changes.

Open-File Report↗

USGS2016

Impacts of shore expansion and catchment characteristics on lacustrine thermokarst records in permafrost lowlands, Alaska Arctic Coastal Plain

Arctic lowland landscapes have been modified by thermokarst lake processes throughout the Holocene. Thermokarst lakes form as a result of ice-rich permafrost degradation, and they may expand over time through thermal and mechanical shoreline erosion. We studied proximal and distal sedimentary records from a thermokarst lake located on the Arctic Coastal Plain of northern Alaska to reconstruct the impact of catchment dynamics and morphology on the lacustrine depositional environment and to quantify carbon accumulation in thermokarst lake sediments. Short cores were collected for analysis of pollen, sedimentological, and geochemical proxies. Radiocarbon and 210 Pb/ 137 Cs dating, as well as extrapolation of measured historic lake expansion rates, were applied to estimate a minimum lake age of ~1400 calendar years BP. The pollen record is in agreement with the young lake age as it does not include evidence of the “alder high” that occurred in the region ~4000 cal yr BP. The lake most likely initiated from a remnant pond in a drained thermokarst lake basin (DTLB) and deepened rapidly as evidenced by accumulation of laminated sediments. Increasing oxygenation of the water column as shown by higher Fe/Ti and Fe/S ratios in the sediment indicate shifts in ice regime with increasing water depth. More recently, the sediment source changed as the thermokarst lake expanded through lateral permafrost degradation, alternating from redeposited DTLB sediments, to increased amounts of sediment from eroding, older upland deposits, followed by a more balanced combination of both DTLB and upland sources. The characterizing shifts in sediment sources and depositional regimes in expanding thermokarst lakes were, therefore, archived in the thermokarst lake sedimentary record. This study also highlights the potential for Arctic lakes to recycle old carbon from thawing permafrost and thermokarst processes.

Alaska↗

USGS2010

A 15 000-year record of climate change in northern New Mexico, USA, inferred from isotopic and elemental contents of bog sediments

Elemental (C, N, Pb) and isotopic ( δ 13 C, δ 15 N) measurements of cored sediment from a small bog in northern New Mexico reveal changes in climate during the Late Pleistocene and Holocene. Abrupt increases in Pb concentration and δ 13 C values ca. 14 420 cal. YBP indicate significant runoff to the shallow lake that existed at that time. Weathering and transport of local volcanic rocks resulted in the delivery of Pb-bearing minerals to the basin, while a 13 C-enriched terrestrial vegetation source increased the δ 13 C values of the sedimentary material. Wet conditions developed over a 300 a period and lasted for a few hundred years. The Younger Dryas period (ca. 12 700–11 500 cal. YBP) caused a reduction in terrestrial productivity reflected in decreasing C/N values, δ 15 N values consistently greater than 0‰ and low organic content. By contrast, aquatic productivity increased during the second half of this period, evidenced by increasing δ 13 C values at the time of highest abundance of algae. Dry conditions ca. 8 000–6 000 cal. YBP were characterised by low organic carbon content and high Pb concentrations, the latter suggesting enhanced erosion and aeolian transport of volcanic rock. The range in δ 13 C, δ 15 N and C/N values in the sedimentary record fall within the range of modern plants, except during the periods of runoff and drought. The sedimentary record provides evidence of natural climate variability in northern New Mexico, including short- (multi-centennial) and long-(millennial) term episodes during the Late Pleistocene and Holocene.

Journal of Quaternary Science↗

USGS2007

Ensuring confidence in radionuclide-based sediment chronologies and bioturbation rates

Sedimentary records of naturally occurring and fallout-derived radionuclides are widely used as tools for estimating both the ages of recent sediments and rates of sedimentation and bioturbation. Developing these records to the point of data interpretation requires careful sample collection, processing, analysis and data modeling. In this work, we document a number of potential pitfalls that can impact sediment core records and their interpretation. This paper is not intended as an exhaustive treatment of these potential problems. Rather, the emphasis is on potential problems that are not well documented in the literature, as follows: (1) the mere sampling of sediment cores at a resolution that is too coarse can result in an apparent diffusive mixing of the sedimentary record at rates comparable to diffusive bioturbation rates observed in many locations; (2) 210 Pb profiles in slowly accumulating sediments can easily be misinterpreted to be driven by sedimentation, when in fact bioturbation is the dominant control. Multiple isotopes of different half lives and/or origin may help to distinguish between these two possible interpretations; (3) apparent mixing can occur due simply to numerical artifacts inherent in the finite difference approximations of the advection diffusion equation used to model sedimentation and bioturbation. Model users need to be aware of this potential problem. Solutions to each of these potential pitfalls are offered to ensure the best possible sediment age estimates and/or sedimentation and bioturbation rates can be obtained.

Estuarine, Coastal and Shelf Science↗

USGS2014

Late Holocene sedimentary environments of south San Francisco Bay, California, illustrated in gravity cores

Data are reported here from 51 gravity cores collected from the southern part of San Francisco Bay by the U.S. Geological Survey in 1990. The sedimentary record in the cores demonstrates a stable geographic distribution of facies and spans a few thousand years. Carbon-14 dating of the sediments suggests that sedimentation rates average about 1 mm/yr. The geometry of the bay floor and the character of the sediment deposited have remained about the same in the time spanned by the cores. However, the sedimentary record over periods of centuries or decades is likely to be much more variable. Sediments containing a few bivalve shells and bivalve or oyster coquinas are most often found west of the main channel and near the San Mateo Bridge. Elsewhere in the south bay, shells are rare except in the southernmost reaches where scattered gastropod shells are found.

California↗

USGS2013

Differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes

Records of ancient intraoceanic arc activity, now preserved in continental suture zones, are commonly used to reconstruct paleogeography and plate motion, and to understand how continental crust is formed, recycled, and maintained through time. However, interpreting tectonic and sedimentary records from ancient terranes after arc–continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others. In this synthesis we examine what is lost, and what is preserved, in the translation from modern processes to the ancient record of intraoceanic arcs. Composition of accreted arc terranes differs as a function of arc–continent collision geometry. ‘Forward-facing’ collision can accrete an oceanic arc on to either a passive or an active continental margin, with the arc facing the continent and colliding trench- and forearc-side first. In a ‘backward-facing’ collision, involving two subduction zones with similar polarity, the arc collides backarc-first with an active continental margin. The preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case. Preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision, rather than tectonic erosion. The prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent. Arc systems are most likely to undergo tectonic accretion shortly before forward-facing collision with a continent, and thus most forearc and accretionary-prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity, when sediment flux to the trench was greatest and tectonic accretion prevailed. Collision geometry and tectonic erosion vs. accretion are important controls on the ultimate survival of material from the trench, forearc, arc massif, intra-arc basins, and backarc basins, and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts, oblique plate convergence, and arc rifting. Forward-facing collision involves substantial recycling, melting, and fractionation of continent-derived material during and after collision, and so produces melts rich in silica and incompatible trace elements. As a result, forward-facing collision can drive the composition of accreted arc crust toward that of average continental crust.

Earth-Science Reviews↗

USGS2021

Sedex hydrothermal systems triggered upheavals to marine chemistry and mass extinctions: Applications for ore genesis research and mineral exploration

New USGS research reveals that the discharge of metal-rich brine that formed sedex deposits on ancient seafloors had profound effects on global ocean chemistry and biologic evolution. For example, brine expulsion caused short-duration positive excursions (“spikes”) in the global marine Sr isotope record. While these spikes are unexplained by conventional oceanic models, our chronostratigraphic correlations of major sedex events, combined with mass balance evidence and oceanographic modeling, confirm that the flux of radiogenic Sr from sedex brines during ore formation was sufficient to cause these once enigmatic 87Sr/86Sr spikes. Recognition that the timing of peak 87 Sr/ 86 Sr spikes correlates exactly with global δ 13 C (and δ 18 O) spikes, climate change, deposition of metal-rich black shales and ironstones, metal-induced malformation (teratology) of marine organisms, and mass extinctions, establishes a causal relationship between sedex deposits and these dramatic events in earth history. The relationships among these features are not fully understood. However, our new model demonstrates that the flux of key biolimiting nutrients and metals contained in sedex brines exceeds that of the total modern riverine flux to the ocean. Undoubtably, these immense nutrient fluxes spurred ocean eutrophication, which, ultimately, through a series of positive feedback mechanisms, may be a previously unrecognized trigger of global ocean anoxic events (OAEs) that produced these chemical and biological perturbations. A derivative result from this integrative research is the recognition that OAEs resulted in the formation of “bathtub rim” deposits at redox boundaries along continental margins that concentrated various redox sensitive critical minerals. For example, we have identified midcontinent phosphorite deposits that contains heavy REE grades and tonnages that rival any REE deposit in the world. The recognition that sedex-forming fluid expulsion events are recorded in the global marine isotopic, geologic, and biological records, defines a new approach to the study of and exploration for sedex deposits. Traditional ore genesis research, coupled with chronostratigraphic correlation and high-resolution 87 Sr/ 86 Sr isotope chemostratigraphy can be used to answer long-standing questions about geologic processes responsible for formation of these extraordinary deposits. This approach allows us to constrain, for the first time, the age, duration, and fluxes of fluids and metals vented into the ocean by these giant hydrothermal systems. Accordingly, the fact that large mineralizing events are recorded in the marine sedimentary record opens the tantalizing prospect that we have the ability to conduct effective resource assessments and define prospective basins anywhere in the world. This innovative approach allows for identification of favorable stratigraphic ages and basins and remote evaluation of the size (and, thus, the mineral potential) of undiscovered mineral deposits. This methodology could be applied on regional basin-wide assessments, to evaluate sedimentary basin prospectivity, resource favorability of specific horizons therein, and to the evaluation of the potential of early-stage prospects.

Geological Society of Nevada Newsletter↗

USGS2003

Trends in chemical concentration in sediment cores from three lakes in New Jersey and one lake on Long Island, New York

Sediment cores were extracted from three lakes in northeastern New Jersey and one lake on western Long Island, New York, as part of the U.S. Geological Survey National Water-Quality Assessment Program. Sediment layers were dated by use of cesium-137 (137Cs), copper, lead, or dichlorodiphenyl-trichloroethane (DDT) profiles. Sediment layers were analyzed for seven selected trace elements, including arsenic, cadmium, chromium, lead, mercury, nickel, and zinc, and five hydrophobic organochlorine compounds, including chlordane, dieldrin, total DDT, total polychlorinated biphenyls (PCBs), and total polycyclic aromatic hydrocarbons (PAHs). All seven trace elements were detected throughout the cores from all four lakes. Concentrations of all elements, except arsenic, were elevated in the three cores from lakes within urbanized watersheds (Packanack Lake, Orange Reservoir, and Newbridge Pond) relative to the concentrations in the lake core collected below the largely forested, reference watershed (Clyde Potts Reservoir). Results of trend analyses indicate that concentrations of all trace elements, with the exception of arsenic and lead, were relatively constant throughout the core from the minimally urbanized Clyde Potts Reservoir. In urban lakes, significant upward trends in concentrations from deeper to shallower sediments were observed either to peak concentrations or throughout the core for all elements, with the exception of chromium at all lakes and arsenic and nickel at Orange Reservoir. This finding indicates that changes in population and land use in the urbanized watersheds over the period of sedimentary record have contributed to upward trends in trace-element concentrations. Although downward trends in concentrations were observed for some trace elements in the years after their concentrations peaked, concentrations of all trace elements in urban lake cores were higher in the most recently deposited sediments than at the base of each respective core. Lead concentrations over time were highly correlated with the population in the vicinity of the lake until the concentration peak in sediment deposited in the mid-1970’s. Concentrations of lead in lake sediment appear to be closely related to the use of leaded gasoline because lead concentrations generally decreased after the use of leaded gasoline was phased-out in the mid-1970’s. Zinc concentrations were highly correlated with population over the entire length of the core. In general, zinc concentrations increased in the three urbanized watersheds, probably in response to increasing population and vehicular use. This trend was not evident at Clyde Potts Reservoir, however, where vehicular traffic in the watershed is minimal. Detectable concentrations of chlordane, total DDT, and total PCBs were present in cores from all lakes; however, dieldrin was detected only in the Newbridge Pond and Packanack Lake cores. Concentrations generally were higher in cores from the urbanized Newbridge Pond and Orange Reservoir watersheds than in those from the minimally urbanized Clyde Potts Reservoir watershed. With the exception of chlordane in the Clyde Potts and Orange Reservoir cores, concentrations of the four organochlorine compounds had significant downward trends from peak concentrations to recently deposited sediment or non-significant trends throughout the core. On the basis of these findings and as a result of regulatory actions prohibiting the production and use of these compounds, downward trends in sedimentary concentrations are expected to continue; however, the persistence of these compounds indicates that a substantial amount of time may be required to purge them from the watersheds. Concentrations of PAHs in sediment generally increased with population growth and urbanization, probably as a result of increased fossil-fuel combustion (gasoline and home-heating fuels and other uses (roads and parking lots paved with asphalt) associated with increased urban development and vehicular traffic. This finding is supported by low concentrations of PAHs in Packanack Lake sediments in the 1930’s, before the watershed was urbanized and when automobiles were comparatively rare. As vehicular use and urbanization increase in these watersheds, the general increase of PAH concentrations in lake sediments can be expected to continue. Data from this study indicate that changes in population, land use, and chemical use in the urbanized watersheds over the period of sedimentary record have contributed to upward trends in concentrations of trace elements and hydrophobic organic compounds. Although downward trends were observed for some constituents in the years after their concentrations peaked, concentrations of most constituents in urban lake cores were higher in the most recently deposited sediments than at the base of each respective core and in the reference lake cores. Similar trends in concentrations of these constituents have been observed in sediment cores from other urban lakes across the United States.

New Jersey, New York↗

USGS2008

Paired charcoal and tree-ring records of high-frequency Holocene fire from two New Mexico bog sites

Two primary methods for reconstructing paleofire occurrence include dendrochronological dating of fire scars and stand ages from live or dead trees (extending back centuries into the past) and sedimentary records of charcoal particles from lakes and bogs, providing perspectives on fire history that can extend back for many thousands of years. Studies using both proxies have become more common in regions where lakes are present and fire frequencies are low, but are rare where high-frequency surface fires dominate and sedimentary deposits are primarily bogs and wetlands. Here we investigate sedimentary and fire-scar records of fire in two small watersheds in northern New Mexico, in settings recently characterised by relatively high-frequency fire where bogs and wetlands (Chihuahuen??os Bog and Alamo Bog) are more common than lakes. Our research demonstrates that: (1) essential features of the sedimentary charcoal record can be reproduced between multiple cores within a bog deposit; (2) evidence from both fire-scarred trees and charcoal deposits documents an anomalous lack of fire since ???1900, compared with the remainder of the Holocene; (3) sedimentary charcoal records probably underestimate the recurrence of fire events at these high-frequency fire sites; and (4) the sedimentary records from these bogs are complicated by factors such as burning and oxidation of these organic deposits, diversity of vegetation patterns within watersheds, and potential bioturbation by ungulates. We consider a suite of particular challenges in developing and interpreting fire histories from bog and wetland settings in the Southwest. The identification of these issues and constraints with interpretation of sedimentary charcoal fire records does not diminish their essential utility in assessing millennial-scale patterns of fire activity in this dry part of North America. ?? IAWF 2008.

International Journal of Wildland Fire↗

USGS2015

Trans-Amazon Drilling Project (TADP): origins and evolution of the forests, climate, and hydrology of the South American tropics

This article presents the scientific rationale for an ambitious ICDP drilling project to continuously sample Late Cretaceous to modern sediment in four different sedimentary basins that transect the equatorial Amazon of Brazil, from the Andean foreland to the Atlantic Ocean. The goals of this project are to document the evolution of plant biodiversity in the Amazon forests and to relate biotic diversification to changes in the physical environment, including climate, tectonism, and the surface landscape. These goals require long sedimentary records from each of the major sedimentary basins across the heart of the Brazilian Amazon, which can only be obtained by drilling because of the scarcity of Cenozoic outcrops. The proposed drilling will provide the first long, nearly continuous regional records of the Cenozoic history of the forests, their plant diversity, and the associated changes in climate and environment. It also will address fundamental questions about landscape evolution, including the history of Andean uplift and erosion as recorded in Andean foreland basins and the development of west-to-east hydrologic continuity between the Andes, the Amazon lowlands, and the equatorial Atlantic. Because many modern rivers of the Amazon basin flow along the major axes of the old sedimentary basins, we plan to locate drill sites on the margin of large rivers and to access the targeted drill sites by navigation along these rivers.

Amazon region↗

USGS2025

Evaluating Laramide orogenesis via flexural basin response in the San Juan basin, New Mexico and Colorado

A challenge in interpreting the location, timing, and magnitude of ancient orogenic events is that ongoing uplift and erosion in the hinterlands often destroys much of the primary record of these events. However, basin-thickness patterns in the sedimentary record can provide complimentary evidence of uplift via flexural effects. Here, we deploy well-log correlation, isochores, basin modeling, flexural modeling, and subcrop mapping to evaluate the Late Cretaceous to Paleogene basin response to Laramide tectonism in the San Juan basin. A wedge of upper Campanian to Maastrichtian sedimentary rock thickens from 200 to 800 meters from southeast to northwest in the basin. This pattern can be successfully simulated via flexural modeling if we infer early Laramide uplift along the northwest basin flank that produced a 0.8 km high topographic load. The Laramide unconformity bounds the top of this Upper Cretaceous sedimentary wedge and truncates progressively older strata to the east, further supporting a westward tilt of the basin. The onset of Campanian Laramide flexure may have also contributed to the profound transgression from the upper Menefee Formation to the Lewis Shale. The Paleocene isochore map displays an approximately symmetrical pattern, with thickening towards the center of the basin. This suggests the possibility of competing flexural loads. The base Eocene structure indicates an asymmetric deep on the northeast flank of the basin, providing flexural evidence of contemporaneous uplift/loading of the Nacimiento uplift and Archuleta arch; this has been modeled as ~2.1 km load height. Both Cretaceous and Paleocene sedimentary wedges are narrow, suggesting low flexural rigidity; modeled effective elastic thicknesses (EET) are 20-30 km, comparable to estimates of modern EET for the region.

Colorado, New Mexico↗

USGS2023

The Far-Field imprint of the late Paleozoic Ice Age, its demise, and the onset of a dust-house climate across the Eastern Shelf of the Midland Basin, Texas

The late Paleozoic is a period of pronounced climatic and tectonic change, characterized by the onset and disappearance of continental-scale glaciers across polar Gondwana, the formation of Pangea, and widespread large igneous province volcanism. The low-latitude equatorial tropics are assumed to be places of persistent warm and wet climatic conditions throughout the Phanerozoic, which through intense silicate weathering, exert a major influence on Earth’s climate via the consumption of atmospheric carbon through carbonic hydrolytic weathering, formation of clay minerals and deliverability of alkalinity to ocean basins. Here we investigate the late Paleozoic sedimentary record of the Eastern Shelf of the Midland Basin in order to refine the climatic and provenance record of this region. The Eastern Shelf of the Midland Basin was situated within the equatorial tropics throughout the late Paleozoic and was connected to the open ocean through a network of fluvial systems that drained into the marine Midland Basin. We present new U-Pb zircon geochronology (19 samples, 2591 analyses) and sedimentary petrography (11 samples, 5800 grain counts), which we integrate with previously published paleobotany, paleosol chemistry and clay mineralogy to provide a holistic climate and tectonic record from this region. We observe major changes in sedimentary processes that we attribute to the formation of Pangea, eustatic changes linked to a dynamic high-latitude glaciation and teleconnections with low latitude hydrology, and a long-term shift in the Earth climate system all of which result in a dynamic sediment provenance history. Late Pennsylvanian and earliest Permian deposits are enriched in zircons with local affinity and interpreted to reflect local uplift and repeat incision across the basin margin, the latter a result of glacioeustatic forcing during an “everwet” climate. A major paleoenvironmental shift occurs in the late early Permian, which is reflected by the transition from fluvial to mixed fluvial-aeolian and ultimately aeolian dominant sedimentation by the late Permian. The transition from fluvial to aeolian dominant sedimentation is accompanied by a change in clay chemistry, sedimentary rock textual maturity, paleosol morphology and a threefold increase in Paleozoic zircons in the mid to late Permian strata. Widespread loess deposits across equatorial Pangea during the Permian have been used to argue for the possibility of equatorial glaciers situated in highland settings during the early Permian. Conversely, our data suggest initiation of a substantial component of aeolian deposition across the field areas, which is coincident with widespread ice loss across high latitude Gondwana, and ultimately highlights the teleconnections between high latitude glaciation and the low latitude hydrologic cycle.

Texas↗

USGS1995

Jurassic thrusting of Precambrian basement over Paleozoic cover in the Clipper Mountains, southeastern California

The Clipper Mountains in the eastern Mojave Desert expose evidence of Jurassic plutonic intrusion along what was an active thrust at the east fringe of the exposed Cordilleran Jurassic magmatic arc. This event occurred during a period of widespread arc magmatism and intra-arc thrusting in the Cordillera related to subduction under the west edge of North America. Jurassic plutons in the eastern Mojave Desert are compositionally more diverse and more K 2 O-rich than Cretaceous plutons. Late-kinematic intrusion of the Jurassic Goldhammer pluton, exposed in the Clipper Mountains, was along an active ductile thrust fault that put Proterozoic basement gneiss over Paleozoic strata by the time of intrusion. U-Pb geochronology and hornblende geobarometry are interpreted to indicate that the pluton was emplaced at 161 ± 10 Ma at a pressure approximately 0.46 GPa or more. This pressure corresponds to approximately a 17-km depth or more, at least 13 km greater than inferred stratigraphic overburden (2–4 km) at the time of intrusion. The excess we attribute to pre-intrusion tectonic burial from overthrusting of the observed allochthon of Proterozoic basement and (or) from earlier Mesozoic overthrusting. Ductile deformation continued along the observed thrust system during intrusion of the Goldhammer pluton. Fabrics in the pluton and country-rock record ductile shearing that was partly top westward but mostly top-eastward; the shearing began before or during the intrusion and continued during and after intrusion. The Jurassic burial history in the Clipper Mountains parallels that in adjacent ranges to the east, but contrasts with that in ranges to the south and west where exposed Paleozoic rocks were at colder and shallower crustal levels in Jurassic time. The tectonic record in the Clipper Mountains suggests large crustal thickening and topographic uplift that would be expected to leave a sedimentary record in Jurassic basins.

GSA Special Papers↗

USGS2012

Ecological controls on the shell geochemistry of pink and white Globigerinoides ruber in the northern Gulf of Mexico: implications for paleoceanographic reconstruction

We evaluate the relationship between foraminiferal test size and shell geochemistry (δ 13 C, δ 18 O, and Mg/Ca) for two of the most commonly used planktonic foraminifers for paleoceanographic reconstruction in the subtropical Atlantic Ocean: the pink and white varieties of Globigerinoides ruber. Geochemical analyses were performed on foraminifera from modern core-top samples of high-accumulation rate basins in the northern Gulf of Mexico. Mg/Ca analysis indicates a positive relationship with test size, increasing by 1.1 mmol/mol (~ 2.5 °C) from the smallest (150–212 μm) to largest (> 500 μm) size fractions of G. ruber (pink), but with no significant relationship in G. ruber (white). In comparison, oxygen isotope data indicate a negative relationship with test size, decreasing by 0.6‰ across the size range of both pink and white G. ruber. The observed increase in Mg/Ca and decrease in δ 18 O are consistent with an increase in calcification temperature of 0.7 °C per 100 μm increase in test size, suggesting differences in the seasonal and/or depth distribution among size fractions. Overall, these results stress the necessity for using a consistent size fraction in downcore paleoceanographic studies. In addition, we compare downcore records of δ 18 O and Mg/Ca from pink and white G. ruber in a decadal-resolution 1000-year sedimentary record from the Pigmy Basin. Based on this comparison we conclude that pink G. ruber is calcifying in warmer waters than co-occurring white G. ruber, suggesting differences in the relative seasonal distribution and depth habitat of the two varieties.

Marine Micropaleontology↗

USGS2019

Late Miocene to Pleistocene source to sink record of exhumation and sediment routing in the Gulf of Alaska from detrital zircon fission-track and U-Pb double dating

We investigate the late Miocene‐Pleistocene offshore sedimentary record of the Yakutat microplate to evaluate the spatial and temporal variations in rock exhumation and sediment routing patterns at the heavily glaciated and actively converging plate boundary in southeast Alaska. We present 1,456 new fission track ages and 1,372 new U‐Pb ages from double‐dated detrital zircons derived from fourteen samples collected from offshore. We integrate our results with published geochronology and thermochronology data onland and offshore in order to constrain grain provenance. We find that offshore strata deposited east of the fold and thrust belt are sourced from the rapidly exhuming areas along the entire Fairweather Fault, the northeastern part of the syntaxial region, as well as the slowly exhuming Insular superterrane. In contrast, the western strata are sourced from the emerging fold and thrust belt and the Chugach Metamorphic Complex located north of the plate boundary. In these samples we identified a change in sediment provenance, which we suggest marks the capture of the Bagley Ice Valley by the proto‐Bering Glacier at the transition from the early to late Pliocene. This implies that the modern Bagley‐Bering Glacier System is much older than previously known. Strata deposited at ~8.6 Ma suggest that extreme rapid exhumation was already ongoing in the late Miocene, which supports previous findings in deep‐sea deposits. Overall, the data help discern several stages in the evolution of sediment routing patterns in response to dynamic tectonic and surficial processes along this active convergent margin.

Alaska↗

USGS2019

Multiproxy Cretaceous-Paleogene boundary event stratigraphy: An Umbria-Marche basin-wide perspective

The complete and well-studied pelagic carbonate successions from the Umbria-Marche Basin (Italy) permit the study of the event-rich stratigraphical interval around the Cretaceous-Paleogene (K-Pg) boundary (e.g., Deccan volcanism, boundary impact, Paleocene recovery and climate). To test the robustness of various proxy records (bulk carbonate δ13C, δ18O, 87Sr/86Sr and Ca, Fe, Sr and Mn concentrations) inside the Umbria-Marche basin, several stratigraphically equivalent sections were investigated (Bottaccione Gorge, Contessa Highway, Fornaci East quarry, Frontale, Morello and Petriccio Core). Besides the classical Gubbio sections of Bottaccione and Contessa, the new Morello section is put forward as an alternative location for this stratigraphical interval as it is less altered by burial diagenesis. Elemental profiles (Ca, Fe, Sr, Mn) acquired by handheld X-Ray Fluorescence (pXRF) efficiently provide regional chemostratigraphical and paleoenvironmental information. The Deccan volcanism, the K-Pg boundary, the characteristic pattern of the Sr/Ca profile across the boundary driven by the extinction and recovery of coccolithophores, and the Dan-C2 hyperthermal event are examples of such recorded paleoenvironmental events. Moreover, cyclostratigraphic analyses of proxies of detrital input (magnetic susceptibility and Fe concentrations) show the imprint in the sedimentary record of a 2.4 Myr eccentricity minimum around 66.45-66.25 Ma and suggest that the occurrence of the Dan-C2 hyperthermal event was astronomically paced.

Umbria-Marche basin↗