<p> Models suggest that global warming will cause an intensification of the hydrologic cycle, but they are poor at predicting changes in the frequency of short, intense precipitation events at the regional to local scale. High-resolution stable isotope measurements across tree rings have shown potential for resolving precipitation at sub-annual resolution, but identification of single intense precipitation events across multiple tree rings has proven elusive. In this work, I report 218 high-resolution carbon isotope (&delta;¹³C) measurements made across eight growth rings of two Pinus trees cored in southern Louisiana. Tree rings were targeted for the presence and absence of extreme rainfall associated with land-falling tropical cyclones within 100 km of the study site. Comparison of the &delta;¹³C record to meteorological data yields a significant correlation (r = -0.576, p = 0.0004) with monthly precipitation and &delta;¹³C value measured across the rings. Significant, intra-ring declines of >1&permil; are associated with monthly precipitation > 200 mm that cannot be resolved by low-resolution sampling. Comparing the effects of sample resolution on &delta;¹³C patterns suggests that wide-ringed samples are preferred for identifying precipitation events at sub-seasonal resolution. Recent technical and methodological advancements allow for more rapid preparation and analysis of intra-ring &delta;¹³C data and provide opportunity for quantifying sub-seasonal environmental information within high-resolution tree-ring datasets. This work indicates the potential for quantifying changes in the magnitude and frequency of extreme precipitation events at individual sites from long-term intra-ring &delta;¹³C records.</p><p>

<p> The Lower Mississippi River Alluvial Aquifer (LMRAA) is a critical groundwater resource for Arkansas, Mississippi, and Louisiana. It is second only to the Ogallala aquifer in terms of the volume of groundwater pumped for irrigation. High concentrations of salinity, iron (Fe), and arsenic (As) affect several regions of the LMRAA. In this study, long-term geochemical changes in the LMRAA in Louisiana were evaluated to better understand the relationships among salts, Fe, and As. The geochemistry was investigated using historical data collected from the LDEQ and USGS. Data from the LDEQ were collected every three years from approximately 2001 to 2013. Major and some trace element data were available, including concentrations of sodium (Na), chlorine (Cl), magnesium (Mg), calcium (Ca), Fe, and As. These historical data were supplemented with recent (2016/2017) sampling and analysis of the isotopes of oxygen (&delta;¹⁸O) and hydrogen (&delta;²H). Geochemical results show that groundwater in the LMRAA in Louisiana can be characterized by two main groupings. The first group is generally characterized by a Na/Cl ratio close to one and/or higher salinity, while the second group is generally characterized by excess Na (relative to Cl) and tends to be more alkaline and rich in Fe. The highest salinity regions are spatially limited, and their extents appear to have remained stable over time. Areas of elevated salinity in the northeast part of the study area may be attributable to mixing of deeper salt-rich waters with the shallow groundwater system, while the salt-rich areas in the southern part of the study area are thought to be attributable to dissolution of salt domes. The waters potentially influenced by brines in the northeast are additionally characterized by higher Mg/Ca ratios. These waters are also enriched in &delta;¹⁸O relative to other areas of the LMRAA. There was no correlation between the areas of potential brine interaction and the concentrations of Fe or As. Instead, areas of high Fe concentration correlated spatially with areas of high alkalinity and the development of waters with excess Na (i.e., waters where Na is in substantial excess relative to the amount of chloride, and instead counterbalanced by HCO_3^-). Arsenic concentrations varied from below detection to 67.7&micro;g/L at one location sampled by the LDEQ in 2010. Six of the approximately 25 wells historically sampled by the LDEQ as part of the ASSET program consistently had concentrations of As >10 &micro;g/L. These locations generally correspond with the groundwater characterized by higher Fe, alkalinity, and Na-excess, but at the same time appear to be localized and often surrounded by wells with low concentrations of As. The concentrations of Fe and As were not correlated. This rather heterogeneous distribution of As contamination could point to anthropogenic influences or sources. The concentrations and spatial distributions of waters rich in salts, Fe, and As in the LMRAA appear to have remained relatively consistent for the last decade, even though demand for groundwater in the LMRAA of Louisiana has more than doubled over this time to 493 million gallons per day (in 2016). </p><p>

<p> Source rock kinetics have become increasingly important when defining kerogen maturity and building basin models. Recent studies have suggested that the activation energies (E_a) needed for these applications can be obtained using one-run open-system pyrolysis with a single heating rate and a fixed frequency factor (A). This method is thought to be faster and cheaper than using multiple heating rates with a varying frequency factor. In this study both methods were used to find the E_a of seven organic-rich samples from the Eagle Ford Shale. Activation energies for the multiple heating rate method were calculated in accordance to the Kissinger method, while E_a values for the single heating rate method were found using the One Run Fixed A (ORFA) kinetic software. The multiple heating rate method implemented heating rates of 5, 10, 20, and 50 &deg;C/min, while the single heating rate method used a standard heating rate of 25 &deg;C/min. Due to the use of a fixed A, the single heating rate method produced larger, more consistent values than the multiple heating rate method. However, these E_a values were not always consistent with previous known values. When the fixed A value used in the single heating rate method was replaced with the A values obtained from the multiple heating rate method, E_a became closer to those found using multiple heating rate method.</p><p>

<p> Several studies have suggested a link between the generation of petroleum and the formation of base metal deposits, primarily Pb, Cu, and Zn deposits, in sedimentary basins. The metals incorporated into basinal brines could be derived from a number of sources, including host rock units. In this study we evaluated hydrocarbon source rocks, specifically organic-rich shales, as a source of trace metals for basinal brines using batch leaching experiments and analyzing the USGS&rsquo; produced waters geochemical database. Batch leaching experiments were performed with powdered source rocks from the Eagle Ford, Marcellus, and Wolfcamp Shales. A subset of the samples was subjected to the destruction of organic matter through the loss-on-ignition method prior to leaching. All samples were subjected to batch leaching by combining approximately 1 g of rock with 10 mL of NaCl, acetate, or NaCl and acetate-electrolyte solution with molarities of 0.01, 0.1, 0.5, or 1. The experimental results showed that more trace (Pb, Zn, and Mo) metals were extracted from the Eagle Ford (EF 28) and Marcellus (Ma) source rocks post destruction of the organic matter prior to leaching using a NaCl and acetate-electrolyte solution. The leaching results also suggested that chloride complexes increased metal solubility in solution more than organic complexes (acetate) for trace metals (Zn and V) and some major elements (Mg). In the produced waters database, trace metal concentrations (Cu, Pb, and Zn) in samples from the Appalachian, Arkla, Gulf Coast, and Williston Basins exhibited a positive correlation with increasing chloride concentration. The produced waters database results hint that there are additional complexities associated with metal sources and loading such as pH and the presence of H₂S.</p><p>

This study involves an examination of geochemical data from the Tatara-San Pedro Volcanic Complex (TSPVC), an approximately 250 km2 Quaternary frontal volcanic arc center located at 36° S, 70.5° W in the Southern Volcanic Zone (SVZ) of the Chilean Andes. Every lava flow in almost thirty, mostly vertical, stratigraphic sections was sampled, and used in conjunction with field observations, K-Ar and 40Ar/39Ar ages, and paleomagnetic data, to construct generalized chemo-stratigraphic columns. These columns not only demonstrate changes in lava composition with time, but were used to reveal the sequence of petrogenetic processes that formed those lavas. Geochemical variation both within a single lava flow and amongst members of an eruptive package of lavas was established, using lava flows which had erupted at different times, and were characterized by different mineralogical and geochemical features. Paleomagnetic and geochemical data were also used to correlate lava flows and packages of flows erupted onto different geographic regions of the complex. Petrogenetic modelling suggests that magma supply rates may be the dominant parameter controlling lava compositions; high rates of supply produce compositionally monotonous sequences of mixed basalt and basaltic andesite, which largely comprise the main volcanic edifices. The final-erupted lavas in many of these sequences are the least contaminated and may represent the best proxies for recharge magma compositions. During periods of intermediate magma supply rates, increased cooling and crystallization produces greater compositional range between mixing endmembers, and mixed andesites are the result. Low supply rates are associated with either single, short-lived flank eruptions of mafic lava, or more evolved compositions derived independently from differentiation of magma within small volume chambers. The relationship between fractionated, erupted, and recharge volumes determines the nature of erupted sequences. The range of lava compositions at TSPVC, as the result of multiple sources, different crustal contaminants, and different petrogenetic processes, is almost as great as that exhibited by all volcanoes from the Southern Volcanic Zone. This suggests that the dominant control on SVZ compositions may not be crust:mantle ratio, but different petrogenetic processes and changing crustal contaminants with time.

A 50 meter thick unit of Proterozoic cumulate layered wehrlite, lherzolite, and olivine websterite exposed at river mile 91 in the Ninetyone Mile Creek Canyon, a side canyon to the Grand Canyon, Arizona, USA, hosts numerous spheroid to ellipsoidal, dunite enclaves that range in size from 1 to 20 cm in diameter. Major-element geochemical analyses suggest that the dunite enclaves and cumulate peridotites are co-genetic. A harzburgite enclave does not appear to be related by fractionation to either the surrounding cumulate peridotite or the dunite enclaves. The unusual major element composition of the harzburgite enclave is also not a product of reaction with a percolating melt. It is suggested that the harzburgite enclave formed as a residue of partial melting of a less primitive peridotite. The ellipsoid and tear-drop shapes of many of the enclaves suggests that they were emplaced while hot enough for ductile deformation. Diffusion profiles also suggest emplacement while both the enclaves and the surrounding cumulate peridotite were still at high enough temperatures for rapid diffusion. The restitic harzburgite enclave(s) were probably dislodged from their original location by eruptive events, tectonic events, or convective flow followed by gravitational settling and deposition before being subsequently covered by more evolved cumulate peridotite. The dunite enclaves were either dislodged and transported in a similar fashion or moved, transported, and ultimately deposited by a within-pluton mass wasting event before being covered by more evolved cumulate peridotite. Chromite, hercynite, and magnetite grains included in olivine, serpentinized olivine, and pyroxene from the Ninetyone Mile Peridotite. With the exception of a single sample, spinel grains observed in the Ninetyone Mile Peridotite retain very little of their original igneous composition. Subsequent overprinting by post-cumulus, subsolidus, and metamorphic processes dominates the eventual compositions providing some insights into the evolution of the Ninetyone Mile Peridotite. Interaction between spinel grains and trapped intercumulus melt (or liquid) during the later stages of crystallization resulted in a slight increase in Cr/[Cr+Al] and large increases in Fe3+/[Fe 3++Cr3++Al3+] and TiO2. The extent of these changes suggests a large shift in melt composition and a long of time between the crystallization of earlier mineral phases and the remainder of the melt in the Ninetyone Mile Peridotite magma chamber. Sub-solidus re-equilibration of Mg and Fe between spinel grains and surrounding olivine resulted in a substantial decrease in Mg/[Mg+Fe2+] in spinel. Subsolvus unmixing textures (hercynite + magnetite) in some of the better-preserved grains, and re-equilibration of Fe3+ between spinel grains and surrounding clinopyroxene and serpentine suggest slow cooling as well. Hydrothermal metamorphism led to decreases in spinel TiO2 and increases in Cr/[Cr+Al]. Amphibole occurring in both inclusions with spinel and silicate grains in olivine formed as devitrified hydrous melt inclusions. In the most evolved lherzolite samples in the Ninetyone Mile Peridotite, coronas of orthopyroxene and orthopyroxene + amphibole symplectite are ubiquitous in separating cumulate grains of olivine from interstitial amphibole (with minor amounts of magnetite, spinel, and clinopyroxene), and occasional, albitic plagioclase. Compositional (low-Al coronitic orthopyroxene and albitic plagioclase) and textural (cuspate, convex inward olivine-orthopyroxene grain boundaries) evidence suggests that the olivine corona microstructures in the Ninetyone Mile Peridotite formed during a multistage process involving reaction between cumulate olivine and surrounding interstitial volatile-rich liquid. SiO 2 in the liquid reacted with olivine resulting in the inward dissolution of olivine to form orthopyroxene. Simultaneously, O2 from the liquid oxidized the fayalite component in the olivine, producing magnetite and SiO 2. The fayalite consumption resulted in a wide layer (reaction rim) of low-Al orthopyroxene with higher Mg/(Mg+FeTotal) than the original olivine and the production of small amounts of magnetite near the new orthopyroxene grain boundary. A change in the composition of the liquid then resulted in the partial replacement of orthopyroxene by amphibole and the formation of an orthopyroxene + amphibole symplectite layer. Finally, highly fractionated interstitial liquid crystallized to form albitic plagioclase. The availability of H2O was an important factor in the development of these coronas. The reactions depicted in the coronas in the Ninetyone Mile Peridotite occurred at pressures greater than 0.6 GPa and at ∼900-1000°C, which is consistent with regional metamorphic history.

Samples of Hawaiian tholeiitic basalt were collected from successive prehistoric flow and intrusive units, exposed on the walls of the summit caldera of Mauna Loa Volcano. Based on major, minor, and trace element analyses, a caldera stratigraphy divided into three separate lava suites is presented. Suite A, the oldest, consists of sparsely to moderately phyric lavas with generally low levels of MgO (6.6 $\pm$ 0.5%) and highly variable incompatible element ratios (K/Y 136 $\pm$ 16) that systematically decrease with time. Suite B is characterized by moderately to highly phyric lavas with highly variable major element chemistry (10.9 $\pm$ 3.2% MgO), predominantly controlled by the addition or subtraction of olivine. Incompatible element ratios are generally low (K/Y 129 $\pm$ 7) and progressively increase with time. The youngest Suite (C) consists of sparsely phyric lavas with low levels of MgO (6.6 $\pm$ 0.2%) and uniformly high levels of incompatible elements (K/Y 158 $\pm$ 5). A tentative correlation with radiocarbon dated flank eruptives constrain the age of the oldest examined lavas to approximately 1,500 yrs, and the youngest to roughly 590 yrs. Sill-like intrusive units were found to be compositionally indistinguishable from Suite B lavas, and probably the result of downward or lateral injection of dense, ponded Suite B lava. Correlations between incompatible element ratios, major element compositions, and flow morphologies indicate that Mauna Loan lava chemistry is linked with eruptive activity and magma supply rate. Periods of high magma supply rates are associated with MgO-rich, incompatible element depleted lavas, whereas infrequent, low-volume activity is linked with moderately evolved, incompatible element enriched eruptives. The observed systematic oscillation of incompatible element ratios with time is consistent with the view that the range of incompatible element abundances observed in Mauna Loan lavas has not significantly change over the last 30,000 years (Rhodes et al., 1982). A change in eruptive behavior probably occurs each time there is a significant shift in incompatible element ratios. This behavioral scenario is consistent with the open-system, shallow (3-5 km depth) magma reservoir model of Rhodes (1987; 1988).

Coastal bluffs of Baldwin Peninsula, NW Alaska, provide excellent exposures of middle Pleistocene nonglacial marine sediment overlain by prodeltaic glaciomarine sediment, indicating that glaciers reached Kotzebue Sound while the shallow Beringian continental shelf was submerged. Because the thin valley glaciers could not have significantly depressed the crust, this glacial advance must have occurred during a global high sea level, most likely during marine oxygen isotope stages 11, 9, or 7. The glacier limit can be traced through the region based on contrasting surface morphology of drift-covered and driftless areas. Simple numerical modelling of valley glaciers in the Noatak and Kobuk River valleys suggests that glaciers flowed over easily deformable sediments, at least in the lower reaches of the valleys. The extent of epimerization of the amino acid isoleucine in fossils molluscs was utilized to estimate the age of the marine and glaciomarine sediments. The preferred molluscan genera were not abundant, but shells of the genus Astarte were. Laboratory pyrolysis experiments reveal that Astarte and Macoma epimerize at similar rates and both are faster than Mya. Epimerization measured in the free fraction of pyrolyzed shells is surprisingly low compared to fossil shells with similar extents of epimerization measured in the total hydrolysate. The pyrolyzed shells show evidence of lower rates of hydrolysis relative to epimerization compared to fossil shells, suggesting that the energy of activation for hydrolysis and epimerization may not be constant over the wide temperature range separating natural burial conditions and laboratory pyrolysis experiments. Overall, Astarte showed greater potential to lose amino acids by leaching, therefore this genus is less preferred for amino acid geochronology. The extent of glaciers in the Beringian Arctic appears to be controlled primarily by moisture availability. The strength of atmospheric circulation, and therefore moisture transport to high latitudes, is largely controlled by the difference in insolation between low and high latitudes. Periods with both high autumn latitudinal insolation gradients (the difference between 0$\sp\circ$ and 60$\sp\circ$N Sept insolation) and decreasing summer insolation that occur during submergence of the Bering/Chukchi continental shelf appear most conducive to glacier growth in northwestern Alaska.

<p> Despite an increased interest in exploitation of hydrocarbon source rock resource plays, there remains an incomplete understanding of organic and inorganic component interaction within source rocks. Few studies have been conducted concerning the associations between organic and inorganic geochemistry for the purposes of understanding kerogen type, thermal maturity influence, and paleoredox setting. This investigation&rsquo;s goal was evaluating these relationships with samples from the Eagle Ford Formation using organic data, obtained by Rock-Eval pyrolysis and oxidation, and inorganic data, obtained using high-temperature and pressure leaching experiments. The study additionally tested various parameters for whole rock batch leaching, including time, temperature of leaching, and use of acids. The most successful leaching technique was applied to samples that (1) had first been subjected to Rock-Eval pyrolysis, at three different maximum temperatures (450&deg;C, 550&deg;C, and 650&deg;C), as well as (2) samples that had not been subjected to pyrolysis. As different kerogen fractions were destroyed at these different temperatures, variances in elemental concentrations leached from these samples could be attributed, at least partially, to these fractions. Using this approach, the lower molecular weight kerogen fraction contained most of the elements likely attributable to carbonates and sulfides associated with the kerogen (e.g., Ca, Mg, Mn, Mo, P, S, Sr, Zn). The higher molecular weight portion contained more elements probably attributable to clays, quartz, and other clastic minerals (e.g., Al, Fe, K, Si). An evaluation of the overall element chemistry of the rock paired with Rock-Eval parameters showed (1) major/trace elements varied according to amount and type of organic carbon in the Eagle Ford samples, (2) relative abundances of certain major/trace elements were useful proxies for bulk mineralogy and depositional environment, and (3) relationships between certain clay-related major and trace elements and T_max values suggesting clays and trace elements acted to catalyze the cracking of the kerogen.</p>

<p> Two hydrothermal experiments were performed using sandstone core material from the Norwegian North Sea with synthetic brines reacted at approximately 150&deg;C and 450 bars, temperature and pressure calculated to simulate a depth of burial of approximately 4 km. The results of the experiments were analyzed with geochemical modeling and with chemical and petrographic analyses. Geochemical modeling with several computer programs indicated that the experimental fluid was undersaturated with respect to K-feldspar, kaolinite, and illite, but supersaturated with respect to muscovite. Chemical analysis with inductively-coupled plasma mass spectrometry indicated that the fluid reached saturation with respect to K-feldspar. Petrographic analysis with scanning electron microscopy and energy-dispersive scanning indicated that changes took place over the course of the experiments in both the clay and non-clay mineral fractions, and this result was verified by X-ray diffraction analysis that indicated dissolution of both K-feldspar and illite and formation of muscovite. These converging lines of evidence indicate that significant changes took place in the clay mineral fraction of the experimental sandstone core material, reacted at realistic basin temperature, pressure and geochemical conditions, over the course of several weeks.</p>