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Vol 31, No 1 (2023)
Biostratigraphy of the Devonian–Lower Carboniferous Deposits of the Bambui-Olingda Subzone (South Muya Ridge, Western Transbaikalia)
Abstract
The results of biostratigraphic studies of the Devonian–lower Carboniferous deposits of the Bambui-Olingda subzone of the Vitimkan-Tsipinsk zone of the Baikal-Vitim fold system are presented. These deposits are isolated from the composition of the Riphean and Vendian–Cambrian formations. Their age was revised on the basis of numerous findings of fauna and flora. The carbonate Bambui and terrigenous Chulegma formations and the terrigenous-carbonate Kadalin stratum are assigned to the Devonian. The volcanogenic-terrigenous Yendekt sequence is dated as late Devonian (Famennian)–early Carboniferous (Tournaisian), while the terrigenous Ognenskaya and Amatkanskaya formations are dated as early Carboniferous (Tournaisian and Visean). Significant changes have been made to the Paleozoic stratigraphy scheme of the subzone. Paleolandscape reconstructions for the Bambui-Olingda basin and coastal land areas in the Devonian–early Carboniferous are proposed. The Devonian carbonate complex was formed in calm conditions of a shallow warm shelf sea. A change in the paleolandscape situation occurred at the Devonian–Carboniferous boundary. Sedimentation of significant thicknesses continued under the conditions of a deepening open shelf-slope paleobasin adjacent to the volcanic zone.
3-26
Early Jurassic Flood Basalt Volcanism on the Franz Josef Land Archipelago: Geological and Palynostratigraphical Data
Abstract
Biostratigraphic evidence of the presence of Early Jurassic flood basalts on the Franz Josef Land archipelago is presented. The flood basalts form layered section with two units, which is not discovered for Early Cretaceous basalts. The lower unit is composed by large-columnar basalts (colonnade), and the upper unit by small-columnar (entablature) chaotic-fan basalts. On the Hooker Island, the basalt flow is exposed on the Sedov Plateau, on the Lunacharsky Rock Cape and, possibly, on Al’banov Cape. On the southern slope of the Sedov Plateau, the basalt flow overlaps sands and sandstones, which contain palynoassemblage of the lower Toarcian. In the Lunacharsky Rock Cape outcrop, the underlying basalt sands are of the Pliensbachian to Early Toarcian chronostratigraphic interval. Apart from the Hooker Island, we observed basalts with the “colonnade/entablature” on three other islands: Scott Keltie, May and Leigh-Smith. The most complete section was found in the western part of the Leigh-Smith Island, where basalts are underlain and overlapped by sand units. The underlying sands in contact with basalts have a quenching zone. There is no quenching zone at the contact with the overlapping sands. A palynocomplex from the lower sand unit is early Toarcian in age. The palynocomplex found in the upper sand unit indicates its accumulation in the interval from the lower part of the late Toarcian to the early Aalenian. A palynological study of the underlying and overlying deposits of the basalt flow has shown that the flow is underlain by continental and coastal-marine sediments of the Pliensbachian to the upper part of the early Toarcian age interval. Basalt flow is overlain by the earliest late Toarcian–early Aalenian marine sediments. According to the modern chronostratigraphic scale, the age of the basalt flow can be estimated as approximately 180 million years, which is quite consistent with the earlier obtained 40Ar/39Ar data of 189.1 ± 11.4 million years. These data indicate that the basalt flow was formed during a narrow stratigraphic interval of the uppermost lower–earliest upper Toarcian.
27-51
Taxonomy and Biostratigraphical Significance of the Toarcian Bivalves of the Genus Meleagrinella Whitfield, 1885
Abstract
The morphology of the ligament block and outer parts of the shells of Toarcian bivalves of the genus Meleagrinella (family Oxytomidae Ichikawa, 1958) were studied. The phylogeny of Meleagrinella and Arctotis in the Toarcian was reconstructed on the basis of the conclusions on the evolution of the ontogeny of the ligament pit, made as a result of studying extensive material from Eastern Siberia and Germany, and taking into account the data on the microsculpture of the ostracum. A revision of the species “Monotis” substriata (Münster, 1831), which is widespread in the Toarcian deposits of Europe, Asia, and North America, was carried out. By comparing specimens from different stratigraphic levels of the Lower Toarcian of Eastern Siberia, North-East Russia, and Germany, three species were substantiated: Meleagrinella (Praemeleagrinella?) golberti sp. nov., M. (Clathrolima) substriata (Münster) and M. (Meleagrinella) prima sp. nov. Figures of the ammonite Tiltoniceras sp. ind., Upper Plinsbachian-Toarcian bivalves of the genus Meleagrinella and Upper Toarcian bivalves of the genus Arctotis are given. For the first time, a microsculpture of an ostracum of the Toarcian representatives of the genera Arctotis and Meleagrinella is depicted. In the Upper Pliensbachian–Lower Toarcian, a sequence of oxytomid taxa was established and, based on the Boreal ammonite scale, an assessment of their biostratigraphic significance was given. The sequence is represented by four species: (1) Meleagrinella (Praemeleagrinella) deleta (Upper Pliensbachian), (2) M. (Praemeleagrinella ?) golberti (Tiltoniceras antiquum, Harpoceras falcifer zones), (3) M. (Clathrolima) substriata (Dactylioceras commune Zone), (4) M. (Meleagrinella) prima (Zugodactylites braunianus, Pseudolioceras compactile zones).
52-84
Main Events of the Geological History of Cyprus in the Late Cretaceous
Abstract
The Upper Cretaceous biostratigraphy (radiolarians and planktonic foraminifers) of Cyprus and stratigraphic position of several formations and units are detalized after long-time studies. Main geologic events are dated more precisely, main stages of Late Cretaceous geological history of Cyprus are proposed: (1) early Turonian: completing of sedimentation and formation of the Mamonia Complex; (2) middle Turonian–early Campanian: collision of Troodos and Mamonia complexes, metamorphism of Mamonia units and hydrothermal activity of Troodos Complex, after it – formation of the Mamonia Mélange and beginning of development of Mamonia nappes; (3) middle to late Campanian: formation of Kyrenian volcanic arc, deposition of pyroclastic sediments of the Kannaviou Formation, and in the end of stage – completing of Mamonia nappes and deposition of the Moni Formation (olistostrome); (4) latest Campanian–middle part of Maastrichtian: deposition of the Kathikas Formation (debris flows) during erosion of underwater relief, formed by the development of Mamonia nappe system; (5) late Maastrichtian: domination of deep-water carbonate deposition (the Lefkara Formation).
85-103
Авторский указатель тома 30, 2022
118-120
Discussions
In Addition to Discussion on the Correlation of the Bajocian–Bathonian Sections in the Izhma River Basin, European North of Russia
Abstract
In the Izhma River basin, the Upper Bajocian–Lower Bathonian sections crop out at several localities along the Dreshchanka River. The recently published views (Ippolitov A.P., Kiselev D.N. “Geological Features of the Bajocian–Bathonian in the Reference Section of the Izhma River Basin (European North of Russia) and the Succession of Ammonites of the Subfamily Arctocephalitinae Meledina”, Stratigraphy and Geological Correlation, 2021, vol. 29, pp. 742–755) on the correlation of these sections, as well as the comments made in the same article on the results of our research, are critically reviewed. The correlation model based on the stratohypses of the top of the Arcticoceras-bearing sandstone horizon, constructed by the opponents relative to four marks of the water’s edge, turned out to be factually unfounded and methodologically unjustified. Arguments against this model are as follows: the low efficiency of the interpolation method on a small sample size when constructing the riverbed dip profile under conditions of intensive meandering of the Dreshchanka River on the floodplain terrace; ignoring the geomorphological situation as a whole; the irrelevance of the topographic map of the 1999 edition; the underestimation of the variability of the low-water position of the water’s edge in different years due to changes in the amount of precipitation.
104-117