Литосфера (Jul 2019)
Fossil coprolites of Meso-Cenozoic animals as a source of mineralogical-geochemical, paleontological and paleoecological information
Abstract
Research subject. In this article, we present the results of comparative mineralogical and geochemical studies of organic remains and coprolites from the Lower Triassic and Paleogene continental deposits of the Northern Urals and East Kazakhstan.Methods. The studies were conducted using a wide range of analytical methods, including optical microscopy; chemical analysis; determination of Corg content; thermal and powder X-ray diffraction analysis; spectroscopy; scanning electron microscopy; X-ray fluorescence analysis; isotopic analysis gas pyrochromatography; inductively coupled plasma mass spectrometry.Results. A significant concentration of fish bones, teeth and scales, as well as coprolites of labyrinthodonts were identified in the Lower Triassic and Paleogene continental-marine terrigenous and carbonate-terrigenous sedimentary rocks of the Northern Urals and East Kazakhstan. In terms of mineral composition, the fossils and coprolites are found to be almost completely composed of B-type carbonate apatite. The phase-heterogeneous impurities in the coprolites are represented by calcite, siderite, barite, polycomponent carbonates of the MnCO3–FeCO3–MgCO3–CaCO3 system and pyrite. It should be noted that pyrite demonstrates octahedral habitus, which is rather rare for this mineral. The ratio of the essential and xenobiotic elemental concentrations differs for the Lower Triassic and Paleogene coprolites, reaching 0.17 and 0.35 on average, respectively. For the first time, information has been given on the content of lithogenic gases in coprolites and the isotopic composition of the impurity carbonaceous material. According to this data, Lower Triassic labyrinthodonts could feed on plants, as well as herbivorous and carnivorous fish.Conclusion. The findings of coprolites in the Northern Urals and East Kazakhstan in a wide Meso-Cenozoic chronological range and in highly different geological settings indicate the probability of a much wider development of coprogenic-phosphate sedimentary rocks in nature than it has been previously considered. Under a high concentration of coprolites, these rocks can serve as a new and extremely valuable type of phosphorite raw materials, the utilization of which would not require any preliminary treatment.
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