Sedimentary Characteristics Of Salt-bearing Sequence In The Oligocene Yaxicuo Formation Formation In Hoh Xil Area, Qinghai-Tibet Plateau

In the period of Oligocene, there are a lot of evaporite and rock salt deposit in thestratum of Oligocene which was called Yaxicuo Formation in Hoh Xil. These rocksare multi-layer and large thickness. Cuorendejia basin and Tuotuohe basin are twoCenozoic sedimentary basins in Hoh Xil area in which the deposition of YaxicuoFormation is very thick. The environment of the two basins are belong to inland playadeposition system in the period of Oligocene， sedimentary environment,paleogeographic and climate condition conducive to potash deposit.Based on the study of Sedimentary characteristics of the typical sections,combining the identification and statistics of the indoor thin-section, we discuss thesandstone composition of Yaxicuo formation in the two basins. With sedimentarycharacteristics study of contrast, summarize the law, Conclusions are as follows:(1) The salt-bearing sequence in Cuorendejia basin mainly distribute in theCuorendejia Lake-Xiushui river area, the rock salt is concentration distribution in inthe upper Mauve Pink sandy mudstone of Yaxicuo Formation and its outcrop is bestmainly in Junmaorimatama, Nuorijiayu, Bayindunriama, Charijiana andGongmaorima to the northern. There are several salt points have been found, they areNuorijiana salt point in the northeast of Cuorendejia lake，Junmaorimatama salt pointand Charijiana salt mine which are both at the west of Maanshan salt lake. Thesalt-bearing formation in Tuotuohe Basin mainly distribute in the East Yaxicuo Lakearea and the southeastern Buchahu Lake-Gaibaxiega(Tongtian River)-Zhaimariahuoarea. All of the salt points develop in the variegated salt-bearing sequence, by the endof2012，the salt points which have been found are Buchahu Lake，Bayinchaergen，Caibaijiayinyong，Biangenchengaqu，Eguoyamajia. All of the salt distribute in the central position of the ancient lake basin deposition.（2）The mass-tone of the salt-bearing sequence in Cuorendejia basin is Purplered with the lithology combination of mudstone, siltstone, fine sandstone sandwichedbetween a large number of gypsum layer. The mass-tone of salt-bearing sequence inTuotuohe basin is variegated, consists of mainly yellow-green, sandwiched betweenthe purple, black, gray and green，and so on. The lithology combination includesmudstone, siltstone, carbonate sandwiched between a lot of gypsum layer.(3) The salt-bearing sequence in Cuorendejia basin main distributed in theCuorendejia Lake-Xiushui river line, salt concentration and development in upperMauve Pink sandy mudstone of Yaxicuo formation, in Junmaorimatama, Nuorijiayu,Bayindunriama, Charijiana and Gongmaorima to the northern outcrop is best. Thereare several salt points have been found,they are Nuorijiana salt point in the northeastof Cuorendejia lake，Junmaorimatama salt point and Charijiana salt mine whichareboth at the west of Maanshan salt lake. Alternative Title salt-bearing Tuotuo RiverBasin are mainly distributed in the East Iasi Lake area. The salt-bearing sequence inTuotuohe basin main distributed in the Yaxicuo lake at the east ofTanggulashanvillage and the southeastern Buchahu Lake-guy Ba Xiega (Tongtian River)-Zhaimariahuo, all of the salt point produced in the variegated salt-bearing sequence,by the end of2012，the salt points which have been found are Buchahu Lake，Bayinchaergen，Caibaijiayinyong，Biangenchengaqu，Eguoyamajia. All of the saltoccurrences are in the central position of the ancient lake basin deposition.（3）Based on the study of the typical sections of the salt-bearing sequence, thelake sedimentary facies of the sections can be identified three sedimentary subfacies，they are Binhu facies, Shallow Lake subfacies and dry Saline Lake facies. From thevertical perspective, both of the two salt basins have obvious periodicity" dry-wet"change, can be identified three sedimentary cycles. but in Cuorendejia basin，duringthe stem Saline Lake sedimentary period，in which the thickness of gypsum layer islarge，there are substantial clastic sediments which formed during the relatively humidperiod, and High frequency " dry-wet" cycle changed obviously, while the TuotuoheBasin does not have these feature.（4）According to the study of detrital composition of sandstones, in Cuorendejiabasin，the rock types of the Yaxicuo Formation are feldspathic lithic sandstone,followed by lithic quartz sandstone. Debris mainly include sedimentary rock debrisand Metamorphic rocks debris，and a small number of volcano rock debris. So, wemay infer from its source mainly comes from the Tanggula orogenic belt and the Bairizhajia orogenic belt, erosion formation is mainly The Permian-The TriassicPeriod stratum. In Tuotuohe basin，the rock types of the Yaxicuo Formation are lithicquartz sandstone, Debris mainly include sedimentary rock debris and Metamorphicrocks debris，but volcano rock debris also occupies a certain proportion. Inferred fromits source mainly comes from the northern Kaixinling mountain uplift, denudationformation is mainly the Permian stratum.（5）During the period of the Yaxicuo Formation deposited，the salt lake centralof Cuorendejia basin appears in now Xiushui River area，in the distribution of neareast-west and the long approximately200km range，with the largest depositionthickness（the maximum of400m）. the salt lake central of Tuotuohe basin is locatedin the Yaxicuo Lake-Tongtian River area，especially the Buchahu Lake nearby.Thedistribution of basin sedimentary center and its salt known points are agreement.