Distribution of sedimentary rock types through time in a back-arc basin: A case study from the Jurassic of the Greater Caucasus (Northern Neotethys)

Abstract The evolution of sedimentary basins can be explored by analyzing the changes in their lithologies and lithofacies (i.e. predominant lithologies). The Greater Caucasus Basin, which was located at the northern margin of the Neotethys Ocean, represents a complete Sinemurian-Tithonian succession. A quantitative analysis of compiled datasets suggests that principal lithologies and lithofacies are represented by siliciclastics, shale and carbonates. The relative abundance of siliciclastics and shale decreased throughout the Jurassic, whereas that of carbonates increased. Evaporites are known from the Upper Jurassic, while volcaniclastics and volcanics, as well as coals, are known only in the Lower to Middle Jurassic. Siliceous rocks are extremely rare. Lithology and lithofacies proportions change accordingly. The Sinemurian-Bathonian sedimentary complex is siliciclastic-and-shale-dominated, whereas the Callovian-Tithonian sedimentary complex is carbonate-dominated. A major change in the character of sedimentation occurred during the Aalenian-Callovian time interval. Regional transgressions and regressions were more important controls of changes in the sedimentary rock proportions than average basin depth. Landward shoreline shifts were especially favorable for carbonate accumulation, whereas siliciclastics and shale were deposited preferentially in regressive settings. An extended area of the marine basin, its lower average depth, and a sharp bathymetric gradient favored a higher diversity of sedimentation. An orogeny at the Triassic-Jurassic transition was responsible for a large proportion of siliciclastics and extensive conglomerate deposition. An arcarc collision in the Middle Jurassic also enhanced the siliciclastic deposition. Both phases of tectonic activity were linked with an increase in volcanics and volcaniclastics. Volcanism itself might have been an important control on sedimentation. A transition to carbonate-dominated sedimentation occurred in the Late Jurassic, reflecting a tectonically calm period

Kimmeridgian-Tithonian sea-level fluctuations in the Uljanovsk-Saratov Basin (Russian Platform)

Abstract The Uljanovsk-Saratov Basin, located in the southeast of the Russian Platform, presents an intriguing record of the Kimmeridgian-Tithonian sea-level fluctuations. In the Late Jurassic, this basin was a trough within the Interior Russian Sea. The data available from both outcrops and boreholes have permitted outlining a number of lithostratigraphic units and regional hiatuses in the northeastern segment of the Uljanovsk-Saratov Basin, thus permitting a precise reconstruction of transgressions/regressions and deepenings/shallowings. In total, three transgressive-regressive cycles and two deepening pulses have been established. These regionally documented changes were both related in part to global eustatic changes, and they also corresponded in part to the regional sea-level changes in some basins of Western Europe and Northern Africa, but not to those of the Arabian Platform. Differences observed between the global and regional curves as well as rapid Tithonian sea-level oscillations are explained by the influences of tectonic activity. It is hypothesized that the regional Tithonian oxygen depletion might have been a consequence from the rapid flooding of a densely vegetated land