Paleoenvironmental Reconstruction by Identification of Glacial Cave Deposits, Helderberg Plateau, Schoharie County, New York

Eight dissolution caves from the Helderberg Plateau in Schoharie County, New York were studied to investigate unusual sediment packages previously interpreted to be deposits laid down during stagnant ice-cover conditions of the Wisconsin glaciation. The sediment package, consisting of white finely laminated silts and clays are overlain by coarse gravels, in turn overlain by dark silts and clays. Analysis of 63 sediment samples was inconclusive in terms of organic content, but indicated a higher degree of fine-grained calcite material in the white clays than in the overlying units. The caves with the white clays exist only within the footprint of Glacial Lake Schoharie, with lower elevation caves containing a thicker white clay sequence, a measure of the duration of lake cover. The sediment sequence represents glacial rock flour formed under stagnant lake conditions, overlain by outwash deposits emplaced during lake termination, and more recent sediment from soil-loss deposition

Environmental and Growth Rate Effects on Trace Element Incorporation to Calcite and Aragonite: An Experimental Study

The subsumed work of this dissertation is comprised of three independent but interrelated studies which seek to further the understanding of processes which govern the coprecipitation of trace elements with calcite and aragonite minerals. These studies investigate the effects of: 1) pressure on crystal morphology and trace element incorporation to aragonite; 2) growth rate on uranium partitioning between calcite and fluid; 3) aqueous Mg/Ca on the magnesium partitioning to low-magnesium calcite. The importance of this work is to determine how the environment of formation and growth rate influences the geochemistry of CaCO3 in order to improve existing paleoproxies and develop new ones. In the first study a series of experiments were conducted at 1, 25, 75, 100, and 345 bars of nitrogen – this range covers pressures at the oceanic floor. Aragonite precipitation was induced by the one-time addition of a Na2CO3 solution to an artificial seawater. Results suggest that oceanic floor pressures could affect the crystallization of CaCO3 by altering mineralogical composition and aragonite crystal size. In the second study calcite crystallized from NH4Cl-CaCl2-U solution by diffusion of CO2. The calcite growth rate was monitored by sequential spiking of the calcite-precipitating fluids with REE dopants. The resulting crystals were analyzed using Secondary Ion Mass Spectrometry (SIMS). Results showed that the partitioning of uranium increases with increasing growth rate. Growth entrapment model (GEM) and unified uptake kinetics model (UUKM) explain the obtained data.In the third study CaCO3 precipitated in NaCl solution by continuous addition of CaCl2, MgCl2, and either Na2CO3 or NaHCO3. The Mg/Ca of the fluid was adjusted in an attempt to produce calcite where Mg/Ca would match Mg/Ca in foraminifera shells. It was observed that multiple CaCO3 polymorphs precipitated from fluids at high pH (Na2CO3 doping experiments). This result underscores the potential control of pH and/or supersaturation state on CaCO3 polymorph precipitated from low Mg/Ca solutions. Calcite was the only mineral crystallized at low pH (NaHCO3 doping experiments). It was determined that Mg partition coefficient between calcite and fluid (KMg) negatively correlates with Mg/Ca(Fluid) when it exceeds 0.5 mol/mol; no systematic correlation was observed when 0.05\u3c Mg/Ca(Fluid)\u3c0.5 mol/mol

An Obstructed Cave Passage in the Cobleskill Plateau: A Gravimetric Study

The Cobleskill Plateau of central New York, part of the greater Helderberg Plateau, is comprised of Silurian and Devonian limestone. This area displays caves and karst landforms subsequently altered by glaciation. The glacially mantled and in-filled pre-existing karst topography of the area was caused by hydrologic changes that determined current karst flow paths. Determining the nature of the antecedent topography, and the location of cave passages, is critical to a complete hydrologic analysis of the Cobleskill Plateau. Two gravity traverses were conducted along traverses near Cobleskill, New York using a Worden Gravity Meter with the intent to validate the subsurface location of an occluded abandoned trunk passage connecting Howe Caverns and McFails Cave. To clarify, the term ‘abandoned’ is meant as an identifier that the passage is no longer utilized as the primary flow path and is only utilized by flowing water during periods of moderate to high discharge. The importance of the existence or absence of the abandoned trunk passage is to increase the understanding of subsurface geology, potential hazards, and controls on pre-glacial groundwater flow in the region. The findings of this study conclude that subsurface anomaly sources do exist at anticipated locations which were believed to contain the passage in question. The study demonstrates that it is possible to identify this passage through the use of gravity surveys. However, the exact shape and size of the anomaly cannot be definitively determined by this study, as the true depth to bedrock could not be determined. Though it is possible to roughly estimate passage dimensions based on a knowledge of the traversable, upstream and downstream passages. The data collected in this study can be fit to various models which can be interpreted to support the existence of a void beneath the two traverses. Further exploration of the subsurface karst systems in the region is needed to determine the exact nature of the anomaly sources

Paleoenvironmental reconstruction by identification of glacial cave deposits, Helderberg Plateau, Schoharie County, New York

Eight dissolution caves from the Helderberg Plateau in Schoharie County, New York were studied to investigate unusual sediment packages previously interpreted to be deposits laid down during stagnant ice-cover conditions of the Wisconsin glaciation. The sediment package, consisting of white finely laminated silts and clays are overlain by coarse gravels, in turn overlain by dark silts and clays. Analysis of 63 sediment samples was inconclusive in terms of organic content, but indicated a higher degree of fine-grained calcite material in the white clays than in the overlying units. The caves with the white clays exist only within the footprint of Glacial Lake Schoharie, with lower elevation caves containing a thicker white clay sequence, a measure of the duration of lake cover. The sediment sequence represents glacial rock flour formed under stagnant lake conditions, overlain by outwash deposits emplaced during lake termination, and more recent sediment from soil-loss deposition

Glacial Lake Schoharie: An Investigative Study of Glaciolacustrine Lithofacies in Caves, Helderberg Plateau, Central New York

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Mg/Ca Ratios in Synthetic Low-Magnesium Calcite: An Experimental Investigation

The work presented sought to determine the effects of Mg/Ca ratios in solution have on Mg partitioning (KMg) between precipitated abiotic low-Mg calcite and solution. Experiments were set up so that Mg/Ca in precipitated abiotic calcite would match the Mg/Ca in planktonic foraminifera. This research intended to investigate the effect of Mg/Ca(Fluid) on KMg when the molar value of Mg/Ca(Fluid) was below 0.5, which is below the previously reported Mg/Ca range. The values of pH, salinity, and aqueous Mg/Ca were monitored during calcite precipitation, and Mg/Ca of calcite was determined at the end of experiments. Partition coefficients of Mg were evaluated as a ratio of Mg/Ca in calcite to the averaged ratio of aqueous Mg/Ca for each experiment

Mg/Ca Ratios in Synthetic Low-Magnesium Calcite: An Experimental Investigation

The work presented sought to determine the effects of Mg/Ca ratios in solution have on Mg partitioning (KMg) between precipitated abiotic low-Mg calcite and solution. Experiments were set up so that Mg/Ca in precipitated abiotic calcite would match the Mg/Ca in planktonic foraminifera. This research intended to investigate the effect of Mg/Ca(Fluid) on KMg when the molar value of Mg/Ca(Fluid) was below 0.5, which is below the previously reported Mg/Ca range. The values of pH, salinity, and aqueous Mg/Ca were monitored during calcite precipitation, and Mg/Ca of calcite was determined at the end of experiments. Partition coefficients of Mg were evaluated as a ratio of Mg/Ca in calcite to the averaged ratio of aqueous Mg/Ca for each experiment

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<p>Changes in iron (Fe) bioavailability influence diatom physiology and community composition, and thus have a profound impact on primary productivity and ecosystem dynamics. Iron limitation of diatom growth rates has been demonstrated in both oceanic and coastal waters of the Northeast Pacific Ocean and is predicted to become more pervasive in future oceans. However, it is unclear how the strategies utilized by phytoplankton to cope with low Fe bioavailability and resupply differ across these ocean provinces. We investigated the response of diatom communities to variable Fe conditions through incubation experiments performed in the Fe mosaic of the California Upwelling Zone and along a natural Fe gradient in the Northeast Pacific Ocean. Through coupling gene expression of two dominant diatom taxa (Pseudo-nitzschia and Thalassiosira) with biological rate process measurements, we provide an in-depth examination of the physiological and molecular responses associated with varying Fe status. Following Fe enrichment, oceanic diatoms showed distinct differential expression of gene products involved in nitrogen assimilation, photosynthetic carbon fixation, and vitamin production compared to diatoms from low-Fe coastal sites, possibly driven by the chronic nature of Fe stress at the oceanic site. Genes of interest involved in Fe and N metabolism additionally exhibited divergent expression patterns between the two diatom taxa investigated, demonstrating that diverse diatoms may invoke alternative strategies when dealing with identical changes in their environment. We report here several mechanisms used distinctly by coastal or oceanic diatom communities as well as numerous taxa-specific strategies for coping with Fe stress and rearranging nutrient metabolism following Fe enrichment.</p