Stratigraphic evidence for Cimmerian events in NW Caucasus (Russia)

Abstract

The Upper Permian and Triassic sequences of the NW Caucasus present a good record of the Cimmerian events, rather undisturbed by the subsequent Alpine deformations. Original field work with new fossil identifications, microfacies analysis, and sandstone petrography were carried out. During the late Permian, active strike-slip basins were filled by continental clastics successions. Marine ingressions during the latest Permian, led to the formation of sponge reefs and skeletal carbonate ramps. During the Triassic, several siliciclastic wedges were intercalated within the marine carbonate succession. Most important is a conglomerate body made up of serpentinite pebbles of Spathian age (early Triassic), recording the exhumation and erosion of schistose antigorite serpentinites. By the late Anisian a severe deformation affected the Peredovoy (= Fore) Range of the NW Caucasus. Lower Triassic to Anisian sediments deformed also in chevron folds were overlaid with angular unconformity by a siliciclastic, and also volcaniclastic, conglomeratic and arenitic body, up to several hundred meters thick. By the late Ladinian-earliest Carnian, marine sedimentation resumed locally, forming a carbonate ramp during part of the Norian. Towards the end of the Norian, the entire area emerged and was again mildly tilted. The subsequent post-Cimmerian transgression occurred largely during the Middle Jurassic. Consequently, the most important Cimmerian deformations appear to be of early and middle Triassic age.

Triassic synthems of southern South America (southwestern Gondwana) and the Western Caucasus (the northern Neotethys), and global tracing of their boundaries

“…Unfortunately, detailed paleotectonic reconstructions have not been attempted for this region yet, and therefore, it is difficult to justify an exact paleoposition for the Western Caucasus. However, we agree with the suggestion of Gaetani et al (2005), who suggested strike-slip movements in this region. They might have been related to the activity of the major shear zone located just to the north of the Western Caucasus (Arthaud and Matte, 1977;Ruban and Yoshioka, 2005;Tawadros et al, 2006).…”

“…They are the Khodzinskaja Group (Norian-Lower Rhaetian), embracing carbonates, including reefal limestones (packstones in the lower part, overlain by wackestones in the upper part), and the Khadzhokhskaja Group (Upper Norian), encompassing shales with sandstone and carbonate interbeds. Rostovtsev et al (1979) established a Norian age for the clastic deposits in the Kamennomostskij area with the typical Monotis assemblage; however, this age was not confirmed by the studies of Gaetani et al (2005). In this paper, we prefer to continue the usage of the Khadzhokhskaja Group following the lithostratigraphic framework of Rostovtsev et al (1979) because of their macrofaunal evidence and our field observations.…”

“…They have been described by D'jakonov et al (1962), Azarjan and Azizbekov (1973), Dagis and Robinson (1973), Slavin (1973), Jaroshenko (1978), Prozorovskaja (1979), Rostovtsev et al (1979), and Zakharov et al (1999). Gaetani et al (2005) have recently presented their most comprehensive overview, which provides detailed information on the Triassic in the studied region. Ruban (2006a) summarized the available data and presented a composite Triassic section for the Western Caucasus.…”

“…The upper Rhaetian-lower Liassic interval corresponds to a major regional hiatus. Triassic deposits are known in four areas of the Western Caucasus: Kamennomostskij area, Tkhatch-Bol'shoj Sakhraj area, Jatyrgvarta-Urushten (Malaja Laba) area, and Guzeripl' area (Rostovtsev et al, 1979;Gaetani et al, 2005) (Fig. 4).…”

“…The regional lithostratigraphic framework summarized by Rostovtsev et al (1979), Jaroshenko (1978), Gaetani et al (2005), and Ruban (2006a) may be chosen as a valid base for identifying synthems. An analysis of this framework coupled with field observations were used to define synthems in the Triassic of the Western Caucasus.…”