Paradise (and Herrin) lost: Marginal depositional settings of the Herrin and Paradise coals, Western Kentucky coalfield

This is the fourth installment in a series of papers on the Asturian (Westphalian D) disrupted mire margins, termed the “ragged edge” in previous papers, and limestone distributions in the Herrin–Baker coal interval in the Western Kentucky extension of the Illinois Basin. New data, indicating in-situ peat development and marine influence, collected from the first in-mine exposure of this interval are presented. Borehole data from the region are examined in the context of “ragged edge” exposures and a carbonate platform depositional model for this portion of the Illinois Basin is presented. This shows that deposition of the sequence was influenced both by the underlying sediments and by a marine transgression. The former influence is seen in variations in coal and limestone thickness over sandstone-filled channels versus over shale bayfill deposits. The latter is marked by the progressive upwards loss of coal benches (i.e., the bottom bench of both coals is the most extensive and the Herrin coal is more extensive than the overlying Paradise coal) and by marine partings in both coals. Further, the brecciated margins seen in both coal seams are similar to brecciated peats encountered along the Everglades margins of Southwest Florida. Overall coal distributions are similar to both those along the Everglades margins and those along a transect from the Belize coast to Ambergis Caye.     

Seasonal variability of soil phosphate stable oxygen isotopes in rainfall manipulation experiments

Phosphorus (P) availability limits productivity in many ecosystems worldwide. As a result, improved understanding of P cycling through soil and plants is much desirable. The use of the oxygen isotopes associated to phosphate can be used to study the cycle of P in terrestrial systems. However, changes with time in the oxygen isotopes associated to available P have not yet been evaluated under field conditions. Here we present the variations in available-P oxygen isotopes, based on resin extractions, in a semi-arid site that included plots in which the amount of rainfall reaching the soil was modified. In addition, the oxygen isotopes in the less dynamic fraction which is extractable by HCl, were also measured. The δ¹⁸O of the HCl-extractable phosphate shows no seasonal pattern and corresponds to the average value of the available phosphate of 16.5‰. This value is in the expected range for equilibration with soil water at the prevailing temperatures in the site. The δ¹⁸O values of resin-extractable P showed a range of 14.5-19.1‰ (SMOW), and evidence of seasonal variability, as well as variability induced by rainfall manipulation experiments. We present a framework for analyzing the isotopic ratios in soil phosphate and explain the variability as mainly driven by phosphate equilibration with soil water, and by the isotopic effects associated with extracellular mineralization. Additional isotopic effects result from fractionation in uptake, and the input to the soil of phosphate equilibrated in leaves. These results suggest that the δ¹⁸O of resin-extractable P is an interesting marker for the rate of biological P transformations in soil systems.     

Migmatite-like textures in anthracite: Further evidence for low-grade metamorphic melting and resolidification in high-rank coals

Previous studies demonstrated that melting, initiated by supercritical fluids in the 375–400 °C range, occurred as part of anthracite metamorphism in the Appalachian Basin. Based on the known behavior of vitrinite at high temperatures and, to a lesser extent, at high pressures, it was determined that the duration of the heating, melting, and resolidification event was about 1 h. In the current study, featureless vitrinite within banded maceral assemblages demonstratesthe intimate association of melted and resolidified vitrinite with anthracite-rank macerals. By analogy with metamorphosed inorganic rocks, such associations represent diadysites and embrechites, i.e., cross-cutting and layered migmatites, respectively. Even though the temperature of formation of the anthracite structures is several hundred °C lower than that seen in metamorphosed inorganic rocks, anthracites are metamorphic rocks and the nomenclature for metamorphic rocks may be appropriate for coal.