The Sequence Of Xibiehe Formation In Central Region Of Jilin Province

The geological time of Zhangjiatun Formation, Erdaogou Formation and Xiaosuihe Formation in central region of Jilin province is one of the disputed issues dscussed by many geologists. There is no divergence of opinion for the strata of Zhangjiatun Formation form the records. The geological time of the formation composed of conglomerate, conglomeratic sand, sand and siltstone with nodule limestone is late Ludlow to early Pridoli of Silurian. Since it was divided into the lower"sand-shale member"and upper"limestone member"by the Northeast Institute of Geology (1975), the two different issues about the relationships of this two parts were formed. The core issue is ineversion or not, inversion means that the upper part is"limestone member"and the lower part is"sand-shale member", and vice versa,"limestone member"is lower,"sand-shale member"is upper. It was considered that this section was an inverse strata sequence by Peng Yujing (1990) and Guo Shengzhe (1992), the upper part is"limestone member"and the lower part is"sand-shale member", but they thought only the limestone member in Yaokeng was the Erdaogou Formation and the sand-shale member exposed near the Xiaosui River reservoir was named Xiaosuihe Formation. There was similar opinion but different tectonic explanation from Nan Runshan (1992). Among that the"sand-shale member"is Xiaosuihe formation and the"limestone member"is Erdaogou formantion. It was considered that Zhangjiatun formation and Erdaogou formation was droped to member, belonging to Xibiehe formation in Lithostratigraphy of Jilin province, The lower part of Erdaogou formation is sand-shale (Xiaosuihe formation) and the upper is thick bedded limestone with siltstone (Erdaogou formation). Whether the strata sequence is Zhangjiatun Formation-Xiaosuihe Formation-Erdaogou Formation or Zhangjiatun Formation-Erdaogou Formation-Xiaosuihe Formation is controversial, and this is what we want to illustrate in this thiesis.Erdaogou Member and Xiaosuihe Member in central Jilin are remeasured in field. Firstly, It's the first time to find coral reef from Xiaosuihe Formation during the course of measurement. According to the stratigraphical sign of coral growth direction, we think that the current stratigraphic sequence is normal, rather than the reverse sequence originally identified. Secondly, convolute bedding is also found in Xiaosuihe sedimentary section, sand bed immersed plastic mud seam with water saturated, and sand bed is upper and mud seam is lower illustrating that the sequence of Xiaosuihe Member is normal.A molasse-type strata the geological time of which is Late Silurian to Early Devonian is widely distributed in Darhan Muminggan Joint Banner region, Inner Mongolia,now collectively named the Xibiehe Fromation. There is a widespread basal conglomerate in the bottom of Xibiehe fromation in Inner Mongolia Xibiehe region, and the lower part is various grit with thin layers of limestone lens; the middle part that is variegated sandstone and siltstone is pink, yellow, khaki, brown and gray sandstone and thick folder limestone and reef limestone, the thickness of limestone has a big lateral variation on horizontal; the upper part is fine clastic quartz and feldspar sandstone beded limestone.The lower part of the original Heilonggong Formation in West mountain in Heilonggong region of Heilongjiang province grows complex components conglomerate and pebbled feldspathic polylitharenite, and the bottom vanished because the exposure conditions in the wild is not good. There are purple, gray-green, yellow, white, rose red sandstone and tuff with thick crystalline limestone and living clastic limestone on the top of the lower part, and the upper part is made up with gray sandstone. The top of the formation is not found. The appearance of basal conglomerate in Heilonggong Formation marks that it was still deposited after Caledonian movement. A thick layer of carbonate as well as a set of clastic rock were developed from bottom to top, which is coasta-shallow—sea-half—deep-sea sand and shale-carbonate combination.The original Zhangjiatun formation is on the top of alkaline granodiorites formed in Caledonian with unconformity. The lower part of Zhangjiatun formation is granitic conglomerate, granitic pebbly siltstone, and the upper part is red tuff sandstone with egg cyan siltstone. According to field measured, the east mountain section in Xiaosuihe region is mainly feldspathic polylitharenite, fine grained sandstone, and siltstone with limestone lens. The original Erdaogou Formation is a thick layer of limestone with siltstone. Marked with conglomerate and gravelly grit at the bottom. The original Zhangjiatun Formation was developed after Caledonian movement in the middle part of Jilin region, which means the Zhanjiatun Formation developed due to continuous deposition after the Caledonian orogeny. Carbonate platform in Erdaogou group was developed with the sea level raising. The clastic rock in Xiaosuihe Formation is turbidites sediment in slopes for a deep-water. When the Zhangjiatun Formation, Erdaogou Formation and Xiaosuihe Formation were developed, the seawater was constantly increasing.We compare the original Heilonggong Formation,Xibiehe Fromation in central Jilin and Xibiehe Fromation in Darhan Muminggan Joint Banner region by cyclic correlation. The sequence of the original Heilonggong Formation and Xibiehe Fromation in Darhan Muminggan Joint Banner region is coarse clastic rock-carbonatite-fine clastic rock from bottom to up. According to lithocorrelation, Xibiehe Formation in central Jilin has identical senquence. The senquence of Xibiehe Formation in central Jilin is also coarse clastic rock (Zhangjiatun Formation)—carbonatite (Erdaogou Formation)—fine clastic rock (Xiaosuihe Formation) from bottom to up,which means that the upper part is"sand-shale member"and the lower part is"limestone member",the current sequence is normal.The area which enclosed by Mongolia-Okhotsk suture zone,the Xar Moron River -Yanji suture zone, middle Sikhote subduction zone is a stable Neopaleozoic tectonic unit—Jiamusi-Mongolia Block. Neopaleozoic tectonic marine strata develop greatly in Jiamusi-Mongolia block. the Late Silurian to Early Devonian strata in the southern margin of Jiamusi-Mongolia Block, composed of Xibiehe Fromation in Darhan Muminggan Joint Banner and central Jilin region, the original Heilonggong Formation, and the original Heitai Fromation in Shalan region, distribute discontinuously in a belt extending from east to the west . rock stratigraphic unit is Xibiehe Formation, and the geological time is Late Silurian to Early Devonian. The sequence is coarse clastic rock-carbonatite-fine clastic rock from bottom to up, the lower part is composed of coarse clastic rocks,a molasse-type of sediment,overlying unconformably on the Lower Paleozoic, the middle part is composed of colored beds, the upper part consists of quartz sandstone with limestone, bearing abundant marine invertebrate fossils.Based on Jiamusi-Mongolia Block, we compare the Late Silurian to Early Devonian strata in the southern margin of Jiamusi-Mongolia Block from the lithostratigraphy, and they have the same senquence, which shows that the strata from Late Silurian to Early Devonian in the southern margin of Jiamusi-Mongolia Block is the identical continental margin deposits. No continent,no continental margin deposit, On the contrary, if it is existing continental margin deposits, there is a corresponding block naturally. Xibiehe Formation is continental margin sediment belonging to the southern margin of Jiamusi-Mongolia Block.