Stratigraphic Characteristic Devon System Of Mountain Kuldzhuktau (South Tian-Shan)

This article presents the results of long-term stratigraphic studies on the territory of the Kuldzhuktau mountains. Schemes for the division and correlation of Devonian deposits have been created based on complete biostratigraphic data that most effectively reflect the geological age of local stratigraphic units and their reliable correlation with geological age. The tier units of the International Devonian Stratigraphic Scale are substantiated at the present stage of research. Due to the widespread use of conodonts, it was possible to clarify the physical and age volumes, as well as the sequence of Devonian deposits in the territory of Kuldzhuktau, and almost completely reconstruct the Devonian section.


INTRODUCTION
The relevance of the research substantiated the creation of a scheme of dissection and correlation of Devonian deposits in the Kuldzhuktau mountains in the Southern Tien Shan. and only a part are steeply dipping thrusts (Biske, 1996 [8]).
Several formations in the age range from Ordovician to Carboniferous take part in the geological structure of the Kuldzhuktau mountains, which are grouped into two tectonic plates linearly elongated in the latitudinal direction: autochthon (northern block) and allochthon (southern block). These plates have a similar structure with slight differences in the base and upper parts of the section (Mirkamalov et al., 2020 [23]).
The aim of the research is to correlate the Devonian deposits of the Kuldzhuktau Mountains on more complete biostratigraphic data that most effectively reflect the geological age of local strata and their reliable correlation with the longline units of the International Devonian Stratigraphic Scale at the present stage of research.

METHODOLOGY
Stratigraphic studies for the study of Devonian deposits in the territory of the Kuldzhuktau mountains, field research was carried out during 2015-2017. by employees of the Stratigraphic Party, the State Unitary Enterprise "Regional Geological Survey Expedition" under the Committee of the Republic of Uzbekistan on Geology and Mineral Resources.

Sultanbibin Formation -D1-2 sl
The Sultanbibin Formation is exposed in the form of elongated sections of latitudinal and sublatitudinal strike at the western end of the Beltau Mountains, west and east of the Dzhangeldy village, west of the Tozbulak intrusion, in the areas of the Uchkuduk, Aktosta, Sultanbibi, Izakuduk wells, in the basin and eastern parts of the Arapkaz mountains of Gujumda. The formation has stratigraphically normal contacts with the underlying deposits of the Turkmentau Formation west of the Tozbulak intrusion. The top contact is not known. South of the count. The Izakuduk Sultanbibin Formation adjoins the upper part of the Arapkazgan Formation by tectonic contact. The section of the Sultanbibin Formation is characterized by a complex tectonic structure with widespread folding and numerous faults (  The upper part of the Sultanbibin Formation is exposed in the form of tectonic blocks of sublatitudinal strike east of the Dzhangeldy village, north of the Uchkuduk well, southwest and south of the Izakuduk well, and in the eastern part of the Guzhumdy mountains. It is represented by gray micritesparite limestones, silicified, stratified, platy, with an admixture of clay-dolomite material and brown clay smears along the bedding planes. Siliceous rocks are developed in the form of lenticular interlayers and nodules. According to the conodonts, the age of the Sultanbibin Formation is dated to the extent of the Ems-Eifel-Givetian centuries. The thickness is 400-500 m. Contact with overlying sediments is tectonic everywhere.

Arapkazgan Formation -D1-3 ak
The Arapkazgan Formation is exposed in the form of separate sections and narrow strips of During biostratigraphic studies of the Kuldzhuktau mountains, thanks to the use of conodonts, a new group of fauna for this region, from separate outcrops, blocks of the Arapkazgan Formation, it was possible to reconstruct a consistent, faunistically substantiated stratigraphic section, clarify the lithological-material composition, establish the physical and age volumes, and determine the genesis of the formation's deposits. Transgressive occurrence was not confirmed. It has been established that the lower Arapkazgan Formation is an age analogue of the lower part of the Sultanbibin Formation. In general terms, the reconstructed section consists of carbonate-siliceous rocks, with an insignificant amount of terrigene. Formed in deep areas of a remote shelf or continental slope at the end of the Early -Late Devonian.
The lower part of the formation is traced from the Arapkazgan Say basin in the west to the Izakuduk well in the east as separate isolated blocks in the Arapkazgan Formation distribution. The greatest thickness of the sediments is found in the area of the Arapkazgan say and is approximately 180m. It is represented by quartz-siliceous-jasper rocks, thin-medium-bedded, platy, light gray, whitish, lumpy with single interlayers of hiddengrained thin-bedded, platy, light-gray limestones and calcareous crimson-gray siltstones. This part of the formation has a peculiar appearance and is easily recognizable by its light gray, whitish color and texture and structural features.  The above conodont assemblages, which characterize the sediments of the formation, make it possible to determine its age in the volume of the Late Emsian -Zhivite -Frana-Famen. The formation is 300 -330 m thick. Contacts with the surrounding formations of the Sultanbiba and Taushan formations are tectonic. The interrelationships between members within the formation are often tectonic as well, which are most likely the result of thrust-thrust movements in the post-Hercynian time.

Beltau Formation -D3 bl
The Beltau Formation is exposed in the form of scattered narrow strips of sub-latitudinal strike southeast of the Bashguzhumdy well and northwest of the Dzhangeldy village. The relationship with the surrounding formations is tectonic.
Southeast of the Bashguzhumdy well, the section of the formation is represented by micritic, micrite-sparite, organogenic-detrital, light gray and gray limestones, thin and medium bedded. The age of the formation for the microfauna complex was earlier dated to the Tournaisian of the Early Carboniferous (Aisanov et al., 1978). However, due to the fact that the boundary between the Devonian and the Carboniferous was later adopted by the International Stratigraphic Commission at the level of the base of the Siphonodella sulcata conodont zone, everything that previously belonged to the lower Tournaisian stage of the Lower Carboniferous is now accepted to be attributed to the Famennian stage of the Upper Devonian. Based on this, the microfauna complex, which was previously considered Tournaisian, is now interpreted by microfaunal paleontologists as Late Devonian. The validity of this interpretation is confirmed by the findings in these conodont deposits: Palmatolepis hassi Muller et Muller and Pa. punctata (Hinde) Frasnian. 3), where gray, light gray to white limestones are exposed, banded, in places reticular, sometimes spotted, multi-layered, massive, marbleized with conodonts: Palmatolepis cf. proversa Ziegler, Paltodus sp. common in the interval of the falsiovalis-linguiformis zones of the Frasnian stage of Europe, the Urals, and Central Asia. The thickness is 400-500 m. In terms of lithological and textural features, the described deposits are close to the rocks of the Shaydaraz Formation.

Figure: 3. Outcrop in the earth's surface of the Shaydaraz Formation east of Mount Bashguzhumdy
The Shaydaraz Formation also includes deposits that are exposed in the eastern part of the Kuldzhuktau Mountains, east of the Bashguzhumdy Mountain, in the carbonate massif that composes the upland from the EI. 716.0 ( fig. 3) 1000 m) and wide distribution, served as the basis for the identification of a new subdivision of the Turkmenkazgan strata. The name was given from the Turkmenkazgan well located on the southern slope of the middle part of the Kuldzhuktau mountains. The strata is exposed in the form of scattered outcrops of sublatitudinal strike in the regions to the west and east of the village of Dzhangeldy, north of the Uchkuduk and Ayakgujumli wells, west of the Shaydaraz well, south of the Aktosta and Sultanbibi wells, in the Turkmentag and Guzhumdy mountains; the width of the outcrops ranges from 0.7 to 1.2 km and the length from 5 to 10-12 km. In the eastern part of the Kuldzhuktau mountains in the east of the Guzhumdy mountains, in the deposits of the Turkmenkazgan strata, the presence of conodonts -Mesotaxis sp. indet, Polygnathus sp. indet, Tortodus sp.indet, Palmatolepis sp. indet, referring to the forms characteristic of the Givetian and Frasnian boundary layers.
The presented data on conodonts make it possible to interpret the age of the Turkmenkazgan sequence in the volume of the Frasnian and Famennian centuries of the Late Devonian. At the same time, there is no reliable information about the underlying and overlying sediments of the sequence, the nature of the relationships between the coeval formations of the Shaydaraz, Beltau and Upper Devonian parts of the Arapkazgan formations is not entirely clear. In facies terms, the deposits of the Turkmenkazgan strata were most likely formed on the outskirts of the carbonate platform from the side of the open sea basin (Kim, et al., 1978(Kim, et al., -2012; Yolkin et al., [33]).
In the lower part, it consists of thin-bedded black siliceous-quartz jasper rocks with sharp lenses of limestone (80 m thick). The middle part is composed of interbedded limestones, siliceous-quartz jasper rocks and shales (30 m). The upper part (40 m) is formed mainly by thin and medium platy gray and dark gray siliceous-quartz layers with single lenses of black limestones at the base. It is noted that the lithological composition of the section in the area is variable. In the central part of Kuldzhuktau, the section is mainly