1,721,012 research outputs found
Pedogenic features of marine inundation in coastal soils and their formation and preservation in coastal and near-coastal paleosols.
No full textMorphologic and geochemical features of paleosols are frequently used for paleoenvironmental interpretations. This study considers potential effects of sea-level rise on pedogenic overprinting in coastal soils and early diagenetic alteration in paleosols subjacent to marine deposits. Suites of hydromorphic traits were visualized statistically using hierarchical clustering and dimensionality reduction methods to identify environmental controls on pedogenesis. Vertic soils forming on the Texas Gulf Coast provided a potential modern analog for pedogenic overprinting prior to permanent inundation. Finally, geochemical depth trends of major oxides in the B-horizons of Upper Mississippian paleosols in eastern Tennessee, subjacent to marine deposits are examined, and the effects of additions of early diagenetic alteration prior to lithification are quantified and discussed. Ultimately, this study confirms that pedogenic drivers in coastal ecosystems are extremely complex and interrelated, and although identifying site-specific controls from paleosols may be limited by preservation and burial diagenesis, a thorough understanding of sea-level history improves the interpretive power of paleosols
Miocene paleoenvironments and paleosol pH proxies.
No full textPaleoenvironmental analysis is an interdisciplinary endeavor that draws on sedimentology, stratigraphy, geochemistry, and geostatistics. This dissertation includes two paleoenvironmental case studies and the development of a new suite of proxies for soil pH. The first case study was performed at Coffee Ranch, the site of a late Miocene (6.6 Ma) bonebed in the Texas Panhandle. Using sedimentology, stratigraphy, and paleopedology, the depositional environments at Coffee Ranch were reconstructed as a fluvial system with seasonally-variable discharge, alluvial paleosols with seasonal water deficit, and intermittent eolian deposits. Climate state was constrained using a combination of paleosol morphological properties, micromorphological associations, pedotransfer functions for climate variables, and elemental mass-balance trends, all of which were consistent with a mean annual precipitation (MAP) nearly double modern values and a much warmer and less seasonally variable mean annual temperature (MAT) than modern conditions. An early Miocene (ca. 17.5 Ma) fossil site located at Ngira, western Kenya, was also analyzed using fluvial geomorphologic and paleopedologic techniques. The Ngira fossil locality preserves a large number of vertebrate fossils, but has a conspicuous lack of primate remains, unlike nearby contemporaneous fossil sites that contain some of the world’s best preserved early Miocene fossil apes. Using pedotransfer functions for climate variables, as well as elemental mass-balance and paleosol morphological indices, the site was reconstructed as having a strongly seasonal, dry subhumid climate. Stable carbon isotopes from pedogenic carbonates are consistent with a surprisingly large amount of C4 biomass, which was used in conjunction with the presence of microcharcoal grains and rodent community paleoecology to interpret an open-canopy habitat for the site. Finally, a soil database was analyzed, with the goal of producing predictive models for soil pH using elemental oxides as input variables. It was found that large-scale vegetation and climate patterns correlate with soil pH; however, elemental ratios traditionally used to predict MAP and MAT were shown to more closely predict pH than climate. Three new pH pedotransfer functions were applied on succession of middle and late Triassic paleosols from western Pangea, and the results indicate that a paleosols became progressively more alkaline as the megamonsoon climate system gradually diminished
Late quaternary Alaskan paleoclimate : geoarchaeological insights into the Pleistocene-Holocene transition.
No full textEastern Beringia is a region which has undergone dramatic changes since the end of the Last Glacial Maximum, environmentally and climatically. These changing conditions likely contributed to the changes in human behavior observed in the earliest human inhabitants who migrated into the region sometime within this time period. In order to better understand the relationship between shifting paleoenvironmental conditions and human behavior, it is crucial to have a detailed understanding of what those climatic changes looked like in the regions these early Beringians were inhabiting. To accomplish this goal, this dissertation uses modern pedological, micromorphological, and sedimentological analyses to reconstruct paleoclimate and the site formation history of three archaeological sites in Alaska: Dry Creek in the Nenana River Valley, Owl Ridge in the Teklanika River Valley, and Serpentine Hot Springs on the Seward Peninsula. This work reveals a progressive transition from cold, dry, open tundra conditions following the Last Glacial Maximum to cool, moist, boreal forest conditions in the middle to late Holocene, though this transition was not a smooth one
Rise of the Givetian (385 Ma) Forests, Northern Appalachian Basin, Catskill State Park, New York, U.S.A.
No full textForestation on Earth may have profoundly changed fluvial sedimentary patterns, increased the release of bio-limiting nutrients to marine systems and increased the consumption of atmospheric CO₂ through biologic productivity and silicate mineral weathering. Evidence is presented for occurrences of forested ecosystems in swamplands in deltaic coastal settings, across a range of seasonally-drained floodplain overbank environments, and even in what were likely terraced interfluve landscapes during the Givetian in the Appalachian basin. Evidence is also presented that chemical weathering in paleosols on alluvial plains in the Appalachian basin may have increased from the Ordovician through the Middle Devonian. Temporal correlation of terrestrial and marine strata is essential in order to understand the potential cause and effect relationships between changes in Devonian weathering systems and marine environmental, ecological and geochemical conditions. Over 450 m of nearly continuous outcrop exposure along Plattekill Creek in West Saugerties, New York, was measured in order to develop a sequence-stratigraphic framework, using alluvial stacking-pattern analysis. The analysis reveals several orders of cyclicity that correspond with Acadian tectophases and previously documented marine depositional sequences. Paleo-precipitation for 37 paleosol profiles was estimated using the CALMAG proxy, a geochemical ratio from bulk soil material in vertic paleosols, which suggests dominantly wet paleoclimates throughout the Middle Devonian, an interpretation also supported by micromorphological data. The paleosol calcite paleobarometer was used to estimate atmospheric CO₂ decline related to the development of forested ecosystems, as well as determine the initial atmospheric pCO₂ at the onset of forestation. The timing of calcite precipitation in relation to the soil saturation state and soil-atmosphere connectivity was investigated in a modern Vertisol (smectitic, clay-rich soil, seasonally saturated) in Brazoria County, Texas, U.S.A., which is an excellent modern analog to forested paleosols in the Appalachian basin. A luminescent phase of calcite formed during the water-saturated portion of the year, negating its use for pCO₂ estimations. A non-luminescent phase formed during the well-drained portion of the year when atmospheric CO₂ mixed with soil-respired CO₂ and is therefore useful for pCO₂ estimation. From these results a model is presented that independently tests the saturation state of a paleosol at the time of pedogenic carbonate precipitation
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Late Mississippian (Chesterian) high-frequency climate change in the Pennington Formation at Pound Gap, KY USA.
Get PDFClimate during the Late Mississippian (Late Chesterian) in the southern Appalachian Basin was characterized by periods of aridity and humidity. The Pennington Formation, exposed at Pound Gap, KY, USA records these changing climatic conditions. The climate signal, however, is partially obscured by longer-term eustatic fluctuations throughout the Late Chesterian. In this clastic-dominated formation, evidence for several orders of cyclicity point to tectonic, glacio-eustatic, and climate controlled-cyclicity. Pennington Formation paleosols provide a record of climate and ecological changes for latest Chesterian time. Forty paleosols were identified, described, and assigned to seven pedotypes ranging from Vertisols to Oxisols. Field and micromorphological evidence suggests a polygenetic character of the Vertisols, resulting from changing soil drainage through time. Using the CIA-K proxy, mean annual precipitation (MAP) estimates range from 519 to 1361 mm/yr. Variations in MAP and quantified soil processes correspond with variation s in soil drainage, resulting from high-frequency paleoclimate change. The temporal distribution of trace elements in paleosols is also related to soil-forming processes and climate. The trace element chemistry (Ti, Ga, Ge, Y, Zr, Nb, Cs, La, Hf, Ta, W, Ce, Th) of the paleosols is controlled by either organic matter content or lessivage (clay formation and accumulation by feldspar weathering). Climate changes are inferred from the trace element chemistry, which is related to changing MAP and intensity of chemical weathering. This study provides greater resolution of changing climate, controls on sedimentation, and pedogenic processes than what is provided in previous studies of the Late Mississippian. The documented variability in fluvial cyclicity, paleosol types, soil drainage, and trace element chemistry might represent the record of high-frequency climate changes likely associated with expansion and contraction of the paleo-Intertropical Convergence Zone (ITCZ)
Taphonomic and mass-extinction research from an ichnological perspective.
No full textThe assemblage of Pleistocene megafauna at Waco Mammoth National Monument (WMNM) and the terrestrial Cretaceous-Paleogene (K-Pg) boundary at Big Bend National Park are just two examples that demonstrate the peril effects of an extreme environmental perturbation on ancient ecosystems. Ichnology is the study of traces that are generated by organismal behavior; therefore, analyzing major die-offs through an ichnological lens can provide a unique perspective to understand the ethology of the survivors. At WMNM trace-fossil analysis was combined with taphonomy, which revealed that the Columbian mammoth herd was subjected to extensive vertebrate and invertebrate scavenging. These findings necessitated a re-evaluation of the causal mechanisms responsible for the death of the herd, as well as demonstrated that scavenging organisms out-survived, at least for some time, the large herbivores in this case. The application of ichnology to the terrestrial K-Pg boundary revealed new findings about the surviving organisms in response to the end-Cretaceous extinction. Herbivorous, soil-dwelling insects, as evidenced from analogous traces, were significantly reduced in body size (Lilliput effect) following the aftermath of the event. These findings, in conjunction with research on marine-organism responses, provide empirical evidence that the Lilliput effect was a phenomenon that affected surviving organisms across highly disparate trophic levels and ecosystems. Lastly, a hybrid approach of ichnology and zooarchaeology was used to develop morphological criteria for taphonomic analysts to differentiate between carnivore traces and unintentional, preparator air-scribe marks, which can be more similar than one might imagine. Utilization of an ichnological perspective to study survival behaviors from the ancient past may one day help address some of the decisions regarding our current mass extinction
Paleoclimate and paleoenvironments of the Late Paleozoic Ice Age : the UNESCO World Heritage Joggins Fossil Cliffs of Nova Scotia revisited.
No full textDuring the late Paleozoic ice age, the fault-bounded equatorial Cumberland Basin of Nova Scotia experienced rapid subsidence, accumulating kilometer-thick fluvial sedimentary units derived from two highlands to the northwest and southeast. Major variations are recorded in the paleosols exposed at the Joggins Fossil Cliffs, ranging from oxidized and well-drained paleosols with recognizable vertic features to highly reduced organic-rich paleosols. These different soil lithologies suggest alternating conditions between well-drained floodplain environments and water saturation associated with overall poor soil development. Although halokinetic subsidence of the Cumberland Basin is known to have been operative during deposition of these units, previous research favored glacio-eustatic processes as the primary forcing mechanism of sedimentation. A total of 474 fluvial aggradational cycles were identified within a kilometer-thick interval and show a fluctuating accommodation history with a very abrupt nature. The series of fluvial aggradational cycles was used to develop threshold autoregressive models based on (1) their thickness, (2) their paleosol thickness, (3) their sandstone content, and (4) their paleosol-to-sandstone ratio. For each model, results suggest no evidence of statistically significant cyclicity, contradicting the hypothesis that fluvial sedimentation was mainly driven by glacio-eustatic cyclothems. Additionally, a total of 7 lithologies were recognized through 1,655 beds. Evaluation of 8 spherical semivariograms suggests no evidence for cyclicity in the frequency, order, or distribution of the data based on lithologies, although some covariance was found at distances between 550 and 750 m suggesting similar processes controlling sedimentation in the lower and upper Joggins Formation. Our results suggest that Joggins records tectonically induced ponding of a part of the sedimentary basin, allowing more extensive preservation of abundant coal and organic-rich units, as well as still-standing fossil forests exposed along the cliffs. These new results suggest that tectonic subsidence of the Cumberland Basin during the late Paleozoic ice age was a more important driver of fluvial sedimentation than previously thought. This novel application of the TAR methodology provides a mathematical description of the sediment accumulation history of terrestrial basins when applied to conformable sedimentary successions, along with the means of linking paleosol development to climatic processes
Taphonomic and mass-extinction research from an ichnological perspective.
No full textThe assemblage of Pleistocene megafauna at Waco Mammoth National Monument (WMNM) and the terrestrial Cretaceous-Paleogene (K-Pg) boundary at Big Bend National Park are just two examples that demonstrate the peril effects of an extreme environmental perturbation on ancient ecosystems. Ichnology is the study of traces that are generated by organismal behavior; therefore, analyzing major die-offs through an ichnological lens can provide a unique perspective to understand the ethology of the survivors. At WMNM trace-fossil analysis was combined with taphonomy, which revealed that the Columbian mammoth herd was subjected to extensive vertebrate and invertebrate scavenging. These findings necessitated a re-evaluation of the causal mechanisms responsible for the death of the herd, as well as demonstrated that scavenging organisms out-survived, at least for some time, the large herbivores in this case. The application of ichnology to the terrestrial K-Pg boundary revealed new findings about the surviving organisms in response to the end-Cretaceous extinction. Herbivorous, soil-dwelling insects, as evidenced from analogous traces, were significantly reduced in body size (Lilliput effect) following the aftermath of the event. These findings, in conjunction with research on marine-organism responses, provide empirical evidence that the Lilliput effect was a phenomenon that affected surviving organisms across highly disparate trophic levels and ecosystems. Lastly, a hybrid approach of ichnology and zooarchaeology was used to develop morphological criteria for taphonomic analysts to differentiate between carnivore traces and unintentional, preparator air-scribe marks, which can be more similar than one might imagine. Utilization of an ichnological perspective to study survival behaviors from the ancient past may one day help address some of the decisions regarding our current mass extinction
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