Evaluation and combined geophysical interpretations of NURE and related geoscience data in the Van Horn, Pecos, Marfa, Fort Stockton, Presidido, and Emory Peak quadrangles, Texas. Volume 1. Final report

This report (two volumes) is the culmination of a two-year study of the six Trans-Pecos Texas quadrangles (Van Horn, Pecos, Marfa, Fort Stockton, Presidio, and Emory Park) surveyed as part of the National Uranium Resource Evaluation (NURE) program. Volume I contains a discussion of the aeromagnetic, gravity and geochemical data, their processing, and their analysis. The geologic history and setting of the Trans-Pecos are discussed along with the uranium potential of the region. Uranium anomalies and occurrences characteristic of numerous different NURE classes are present in the study area, and information is presented on 33 drill holes into these targets. Volume II is a folio of maps reduced to a scale of 1:500,000. Geologic maps for each of the six quadrangles are included and the geophysical maps have been prepared to be overlays for the goelogic maps. In addition to the geologic maps, residual aeromagnetic anomaly, complete Bouguer gravity anomaly, flight line index, gravity station index, and anomaly interpretative maps were prepared for each quadrangle. A large suite of digitally processed maps of gravity and aeromagnetic data were prepared and are included in Volume II

A lost Tethyan evaporitic basin: Evidence from a Cretaceous hemipelagic meta‐selenite – red chert association in the Eastern Mediterranean realm

Ancient evaporite deposits are geological archives of depositional environments characterized by a long-term negative precipitation balance and bear evidence for global ocean element mass balance calculations. Here, Cretaceous selenite pseudomorphs from western Anatolia ('Rosetta Marble') - characterized by their exceptional morphological preservation - and their 'marine' geochemical signatures are described and interpreted in a process-oriented context. These rocks recorded Late Cretaceous high-pressure/low-temperature, subduction-related metamorphism with peak conditions of 1 center dot 0 to 1 center dot 2 GPa and 300 to 400 degrees C. Metre-scale, rock-forming radiating rods, now present as fibrous calcite marble, clearly point to selenitic gypsum as the precursor mineral. Stratigraphic successions are recorded along a reconstructed proximal to distal transect. The cyclical alternation of selenite beds and radiolarian ribbon-bedded cherts in the distal portions are interpreted as a two type of seawater system. During arid intervals, shallow marine brines cascaded downward into basinal settings and induced precipitation. During more humid times, upwelling-induced radiolarian blooms caused the deposition of radiolarite facies. Interestingly, there is no comparable depositional setting known from the Cenozoic world. Meta-selenite geochemical data (delta C-13, delta O-18 and Sr-87/Sr-86) plot within the range of reconstructed middle Cretaceous seawater signatures. Possible sources for the C-13-enriched (mean 2 center dot 2 parts per thousand) values include methanogenesis, gas hydrates and cold seep fluid exhalation. Spatially resolved component-specific analysis of a rock slab displays isotopic variances between meta-selenite crystals (mean delta C-13 2 center dot 2 parts per thousand) and host matrix (mean delta C-13 1 center dot 3 parts per thousand). The Cretaceous evaporite-pseudomorphs of Anatolia represent a basin wide event coeval with the Aptian evaporites of the Proto-Atlantic and the pseudomorphs share many attributes, including lateral distribution of 600 km and stratigraphic thickness of 1 center dot 5 to 2 center dot 0 km, with the evaporites formed during the younger Messinian salinity crisis. The Rosetta Marble of Anatolia may represent the best-preserved selenite pseudomorphs worldwide and have a clear potential to act as a template for the study of meta-selenite in deep time