Re–Os age for the Lower–Middle Pennsylvanian Boundary and comparison with associated palynoflora

AbstractThe Betsie Shale Member is a relatively thick and continuous unit that serves as a marker bed across the central Appalachian basin, in part because it includes an organic-rich shale unit at its base that is observable in drill logs. Deposited during a marine transgression, the Betsie Shale Member has been correlated to units in both Wales and Germany and has been proposed to mark the boundary between the Lower and Middle Pennsylvanian Series within North America. This investigation assigns a new Re–Os date to the base of the Betsie and examines the palynoflora and maceral composition of the underlying Matewan coal bed in the context of that date. The Matewan coal bed contains abundant lycopsid tree spores along its base with assemblage diversity and inertinite content increasing upsection, as sulfur content and ash yield decrease. Taken together, these palynologic and organic petrographic results suggest a submerged paleomire that transitioned to an exposed peat surface. Notably, separating the lower and upper benches of the Matewan is a parting with very high sulfur content (28wt.%), perhaps representing an early marine pulse prior to the full on transgression responsible for depositing the Betsie. Results from Re–Os geochronology date the base of the Betsie at 323±7.8Ma, consistent with previously determined age constraints as well as the palynoflora assemblage presented herein. The Betsie Shale Member is also highly enriched in Re (ranging from 319.7 to 1213ng/g), with high 187Re/188Os values ranging from 3644 to 5737 likely resultant from varying redox conditions between the pore water and overlying water column during deposition and early condensing of the section

Source apportionment of atmospheric trace gases and particulate matter: comparison of log-ratio and traditional approaches

In this paper we compare multivariate methods using both traditional approaches, which ignore issues of closure and provide relatively simple methods to deal with censored or missing data, and log-ratio methods to determine the sources of trace constituents in the atmosphere. The data set examined was collected from April to July 2008 at a sampling site near Woods Hole, Massachusetts, along the northeastern United States Atlantic coastline. The data set consists of trace gas mixing ratios (O3, SO2, NOx, elemental mercury [Hgo], and reactive gaseous mercury [RGM]), and concentrations of trace elements in fine (<2.5 μm) particulate matter (Al, As, Ba, Ca, Cd, Ce, Co, Cs, Fe, Ga, Hg, K, La, Mg, Mn, Na, P, Pb, Rb, Sb, Sr, Th, Ti, V, Y, and Zn) with varying percentages of censored values for each species. The data were separated into two subcompositions: s1, which is comprised by RGM and particulate Hg (HgP), which are both highly censored; and s2 which includes all of the trace elements associated with particulate matter except Hg, and the trace gases O3, SO2, NOx, and Hgo. Principal factor analysis (PFA) was successful in determining the primary sources for constituents in s2 using both traditional and log-ratio approaches. Using the traditional approach, regression between factor scores and RGM and particulate Hg concentrations suggested that none of the sources identified during PFA led to positive contributions of either reactive mercury compound. This finding is counter to most conventional thinking and is likely specious, resulting from removal of censored data (up to >80% of the entire dataset) during the analysis. Log-ratio approaches to find relationships between constituents comprising s2 with RGM and HgP (i.e., s1) focused on log-ratio correlation and regression analyses of alr-transformed data, using Al as the divisor. Regression models accounted for large fractions of the variance in concentrations of the two reactive mercury species and generally agreed with conceptualizations about the formation and behavior of these species. An analysis of independence between the subcompositions demonstrated that the behavior of the two constituents comprising s1 (i.e., RGM and HgP) is dependent on changes in s2. Our findings suggest that although problems related to closure are largely unknown or ignored in the atmospheric sciences, much insight can be gleaned from the application of log-ratio methods to atmospheric chemistry data

Subsurface drip irrigation application of coalbed methane produced waters: a three-way analysis of the impacts to shallow groundwater composition and storage

Since 1987, coalbed methane (CBM) production in the Wyoming portion of the Powder River Basin has generated 1.2 x 1011 m3 (4,240 bcf) of natural gas and 1.0 x 109 m3 (35.3 bcf) of co-produced water. Year-round introduction of the produced waters with potentially soil-damaging Na-rich composition into infiltration impoundments and ephemeral hydrologic systems have led to serious concerns related to the handling of the water. An alluvial aquifer site where treated Na-HCO3- to Na-SO4-type CBM water is added into the unsaturated zone (~0.9m depth) through the use of a subsurface drip irrigation (SDI) system has been studied to assess the impact to groundwater levels and composition. The SDI system is designed to provide water for alfalfa, which has roots that can reach the depth of the SDI emitters, whereas the Na-rich solutes are stored below the more Na-sensitive upper layers of the soil column.\ud In the first two years of SDI operation, little net change in groundwater levels in wells outside of the SDI areas was observed, whereas groundwater levels have increased in some SDI areas of the site by more than 0.6 m. Changes in groundwater specific conductance, an indicator of solute load, have varied substantially, with both increasing and decreasing trends observed within SDI and non-SDI wells. To better understand the nature of these changes, concentration data (Ba, Cl, Fe, HCO3, H2O, Mg, Na, Si, SO4, and Sr) for water samples collected from 14 monitoring wells during eight rounds of quarterly groundwater sampling were arranged in a three-way array (wells x constituents x sampling events). Because the focus of this study is the chemical composition of groundwater samples, analyses focused on the molar proportions of the chemical constituents, rather than the raw molar concentration data. In attempt to find underlying multivariate structure and to identify processes controlling the data, the three-way array was examined using the recently developed Tucker models for compositional data. Results from this investigation show the potential controls and impacts of SDI application of CBM waters on a shallow groundwater system