Search Results (3)

Studying carbonate breccias enhances our understanding of various geological processes. Fieldwork in the vicinity of the Sakhray Massif in the Western Caucasus (western edge of the Caucasus Mountains) allowed us to discover a peculiar layer of carbonate breccia in the monotonous succession of Lower Triassic platy limestones. The lithological peculiarities of this breccia and the hosting rocks were examined in the field, as well as in polished slabs and thin sections. The results show that the breccia consists of a chaotic mass of chiefly angular clasts of entirely different limestones with abundant fossil debris and a micritic matrix similar to the hosting rocks but bearing siliciclastic debris. The age of the carbonate breccia is the same as that of the hosting rocks, i.e., it is late Induan–early Olenekian (Early Triassic), but the clasts are attributed to upper Changhsingian (Upper Permian) limestones (also reefal). It is proposed that these clasts were created by erosion in a subaerial environment, after which they were transported from a land mass to a deep sea. Apparently, extraordinary geological events (e.g., severe storms, earthquakes, or tsunamis) triggered submarine debris flows on a steep slope. From a practical point of view, the reported discovery extends the vision of the geological heritage of this part of the Western Caucasus. Full article

Framing geoheritage thematically is important to reveal its diversity. Field investigations in the western part of the Greater Caucasus orogen have allowed for the characterization of three localities representing palaeoislands of the Caucasian Sea, which evolved as a semi-enclosed, marginal palaeosea during the Mesozoic. The Gosh locality represents coarse siliciclastics formed on the cliffed shore of the early Induan (Early Triassic) island. The Lipovy locality exhibits conglomerates accumulated on the shore of the early Toarcian (Early Jurassic) island due to erosion of the uplifted crystalline rocks. The Shakhan locality boasts a representative section of cross-bedded sandstones deposited on the alluvial plain of the Hauterivian (Early Cretaceous) island. All these localities are interpreted as geoheritage points, which are parts of larger geosites. Taken together, these points constitute thematic geoheritage sites reflecting the existence of palaeoislands in all Mesozoic periods, which is essential for the understanding of the evolution of the Caucasian Sea during this era. These localities are perfectly accessible, but visiting them requires professional interpretation. The importance of the thematic geoheritage makes its adequate management urgent (particularly, maintenance of geoheritage points, the installation of interpretive panels, and promotion). A geoexcursion route is proposed to facilitate geotouristic exploitation of the characterized geoheritage sites. Full article

Sedimentary rocks from the Himalayas are well-preserved archives of the Neo-Tethys oceanic conditions. In this contribution, Re–Os isotopic systematics of black shales from the Gungri Formation, Spiti valley and siltstones from the Khunamuh Formation, Guryul Ravine have been investigated to constrain their depositional ages. The Re–Os isochron for the Gungri shales yields a depositional age of 255 ± 22 Ma (2σ; n = 8; MSWD (Mean Square Weighted Deviation) = 5.7), consistent with available biostratigraphic information. The initial ¹⁸⁷Os/¹⁸⁸Os ratio (0.60 ± 0.13) is similar to that reported for the Late Permian shales, indicating the connection of the Neo-Tethys with the global ocean. In contrast, the Re–Os systematic is found to be non-isochronous for the Guryul Ravine section, a proximal site with a strong influence of seismic/Tsunami events. Global compilation of ¹⁸⁷Re/¹⁸⁸Os ratios in Late Permian shales and bathymetric distribution of the Re/Os ratios point to strong role of Re/Os uptake by macroalgae, in addition to oceanic pH and redox state, in regulating the Re–Os systematic in shales. The ⁸⁷Sr/⁸⁶Sr ratios for the Induan carbonates from the Spiti (0.71551–0.71837) are higher than to that expected for the Lower Triassic ocean (~0.707). Co-variations of Sr and ⁸⁷Sr/⁸⁶Sr with Mn concentrations establish the diagenetic alteration of these carbonates. Full article