The Most Complete Sequence of Telychian Graptolite Zones in the World

This paper divides the Telychian into 7 graptolite zones, 12 subzones and 4 chitinoans in the Ziyang region, China. The zones and subzones of England are almost totally suitable for the case of Ziyang in China, though they are 10000 km apart. All the above-mentioned biozones are found only in a unitary continuous section in Ziyang. It has been proved that the Ziyang section is the one with the most complete sequence of Telychian graptolite biozones in the world.

Biostratigraphy and reservoir characteristics of the Ordovician Wufeng Formation-Silurian Longmaxi Formation shale in the Sichuan Basin and its surrounding areas,China

Through graptolite identification in profiles,graptolite zone division,contour map compilation,and analysis of mineral composition,TOC content,lamina distribution features of shale samples,the biostratigraphic and reservoir characteristics of Ordovician Wufeng Formation-Silurian Longmaxi Formation in the Sichuan Basin and its peripheral are sorted out.There are 4 graptolite zones(WF1 to WF4)in Wufeng Formation and 9(LM1 to LM9)in Longmaxi Formation,and the different graptolite zones can be calibrated by lithology and electrical property.The shale layers of these graptolite zones have two depocenters in the southwest and northeast,and differ in mineral composition,TOC,and lamina types.Among them,the graptolite zones of lower WF2 and WF4 are organic matter-poor massive hybrid shale,the upper part of WF1-WF2 and WF3 have horizontal bedding hybrid shale with organic matter,the LM1-LM4 mainly consist of organic-rich siliceous shale with horizontal bedding,and the LM5-LM9 graptolite zones consist of organic-lean hybrid shale with horizontal bedding.The mineral composition,TOC and lamina types of shale depend on the paleo-climate,paleo-water oxidation-reduction conditions,and paleo-sedimentation rate during its deposition.Deposited in oxygen-rich warm water,the lower parts of WF1 and WF2 graptolite zones have massive bedding,low TOC and silicon content.Deposited in cooler and oxygen-rich water,the WF4 has massive bedding,high calcium content and low TOC.Deposited in anoxic water with low rate,the upper part of WF2,WF3,and LM1-LM4 are composed of organic rich siliceous shale with horizontal bedding and high proportion of silt laminae.Deposited in oxygen rich water at a high rate,the graptolite zones LM5-LM9 have low contents of organic matter and siliceous content and high proportions of silt lamina.

Dispositional characteristics of Ordovician Wufeng Formation and Silurian Longmaxi Formation in Sichuan Basin and its adjacent areas

According to data of gas wells and typical sections of Wufeng Formation and Longmaxi Formation in Sichuan Basin,shale of various graptolite zones were analyzed to determine depositional environment,lithology and thickness characteristics of the graptolite shale interval of WF2-WF3 in the lower part of Wufeng Formation,the graptolite shale interval of WF4 in Guanyinqiao Member of Wufeng Formation and the graptolite shale interval of LM1-LM4 in the bottom of Longmaxi Formation,and characteristics of shale horizontal distribution were also investigated.During the depositional period of the graptolite shale interval of WF2-WF3,the study area was less affected by the Guangxi movement,the depositional environment was the deep water of open sea,where black shale was mainly deposited;the sedimentation center was developed in northeast Guizhou-northeast Sichuan and south Sichuan,the maximum thickness was from 4 to 6 m in the sedimentation center.During the depositional period of the graptolite shale interval of WF4,the depositional environment in the study area changed greatly due to global sea level fall and enhanced Guangxi movement;the central Sichuan paleouplift,the central Guizhou paleouplift and the Jiangnan-Xuefeng palaeouplift were further expanded,and the area of the sedimentary basin decreased;the depositional environment was mainly carbonate bioclastic shoal of shallow sea,and partially deep sea which only was distributed in the Shizhu-Fuling-Wuxi area in east and northeast Sichuan and the Gongxian-Yongchuan area in south Sichuan;sediments of shallow water were dominated by limestone and argillaceous limestone with abundant Hirnantia,sediments of deep water were dominated by calcareous mudstone and shale with Hirnantia.During the depositional period of the graptolite shale interval of LM1-LM4,due to rise of global sea level and Guangxi movement,the sedimentary area was larger than that in the depositional period of Guanyinqiao Member,and the sedimentary environment mainly was stagnant deepwater;thickness of black shale in the graptolite shale interval of LM1-LM4 was large,and the maximum thickness was over 20 m.Furthermore,control of the central Sichuan paleouplift,the central Guizhou paleouplift and the Jiangnan-Xuefeng paleouplift on black shale was discussed,and control of the Zhiliujing underwater highland/uplift,Huayingshan highland and Dingshan highland as well as western Hubei-Hunan underwater highland/uplift on shale deposition and preservation was also investigated.