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Ordovician carbonates near the Wisconsin arch represent the type locality in ancient rocks for the Dorag, or mixing-zone, model for dolomitization. Field, petrographic, and geochemical evidence suggests a genetic link between the pervasive dolomite, trace Mississippi Valley–type (MVT) minerals, and potassium (K)-silicate minerals in these rocks, which preserve a regional hydrothermal signature. Constraints were placed on the conditions of water-rock interaction using fluid-inclusion methods, cathodoluminescence and plane-light petrography, stable isotopic analyses, and organic maturity data. Homogenization temperatures of two-phase aqueous fluid inclusions in dolomite, sphalerite, and quartz range between 65 and 120°C. Freezing data suggest a Na-Ca-Mg-Cl-H2O fluid with salinities between 13 and 28 wt.% NaCl equivalent. The pervasive dolomitization of Paleozoic rocks on and adjacent to the Wisconsin arch was the result of water-rock interaction with dense brines at elevated temperatures, and it was coeval with regional trace MVT mineralization and K-silicate diagenesis. A reevaluation of the Dorag (mixing-zone) model for dolomitization, in conjunction with convincing new petrographic and geochemical evidence, has ruled out the Dorag model as the process responsible for pervasive dolomitization along the Wisconsin arch and adds to the abundant body of literature that casts serious doubt about the viability of the Dorag model in general.
John Luczaj is an assistant professor of earth science in the Department of Natural and Applied Sciences at the University of Wisconsin–Green Bay. He earned his B. S. degree in geology from the University of Wisconsin–Oshkosh. This was followed by an M.S. degree in geology from the University of Kansas. He holds a Ph.D. in geology from Johns Hopkins University in Baltimore, Maryland. His recent interests include the investigation of water-rock interaction in Paleozoic sedimentary rocks in the Michigan Basin and eastern Wisconsin. Previous research activities involve mapping subsurface uranium distributions, reflux dolomitization, and U-Pb dating of Permian Chase Group carbonates in southwestern Kansas.
A partial bovid skull, from the karst deposits of Lunnaya Cave (Karabi karst plateau, Crimea) is re-examined. The subfossil find of unknown age, was retrieved by local cavers from Simferopol, and was allocated to the late Pleistocene Eurasian musk-ox: Ovibos moschatus (Zimmermann, 1780). Most recently, a reexamination of the specimen was possible, and a detailed analysis indicates an appurtenance to the water-buffalo (Bubalus bubalis (Kerr, 1792)), with some morphological disorders caused by Hydrocephalus, an inherited malformation sporadically recorded in extant bovids. However the skull was reported from below a thick flowstone crust, the age of the specimen is not older than 7th to 10th century A.D. (or even younger), when the domesticated form appear in SE Europe including the Crimean peninsula. Probably due to its disease, the animal was killed by a sharp axe-like tool and dropped into the cave. In this respect, late Pleistocene musk-ox finds are still missing from the Crimean theriofauna, their Southern range in the area, being limited to Zhytomyr-Kiev-Chernigov regions in Northern Ukraine.