A New Understanding on South China Permian Coal-bearing Strata and Coal Accumulation Regularity

Vol. 74 No. 3ACTA GEOLOGICA SINICA711A New Understanding on South China Permian Coal-bearingStrata and Coal accumulation regularityLI Wenheng and goNg ShaoliJiangxi Bureau of coal Geology, Nanchang 330001, Jiangxithat the lower, The Longtan Formation was originally thought to belong to the Late Permian, but this study revealspart of this formation belongs to the Middle Permian. The study proposes the corresponding chro-stratigraphic boundary and new schemes for the correlation of geological sections. Based on these schemes a newunderstanding on the accumulation regularity of Permian coal measures in South China is reachedKey words: South China, Permian, sequence stratigraphy, coal-bearing strata, coal accumulation regularityIn the lower part or bottom of the Longtan Formationcal conodonts of the Wujiapingian age were found atiangsu, northern Zhejiang, central the bottom of the Dalong Formation, showing thatJiangxi, southern Hunan and northern guangdongAltudoceras is a relict. So, the lower part of the da-fusulinid, ammonoid and brachiopod fossils of thelong Formation in Hunan should be ascribed to theMaokouan age were found one after another thus thWujiapingian age instead of the Maokouan agBecause in Jiangsu-Zhejiang area the 4thLongtan Formation is considered to belong to thelimestone layer contains Late Permian fossils, whileperiod from the late Middle Permian to early Late the 5th limestone layer contains a large number ofPermian, which seems to be a final conclusion( ChenMiddle Permian fossils, the boundary of the Upperet al., 1965; Ding, 1959; Han et al., 1961; Li Shiqiand the middle permian has to be put between these1963: Wang and Dong. 1991: Zhang et al., 1992two limestone members. Therefore the bottom of theZhao et al 1978; Zhou, 1987). However, there isoolitic mudstone under the main workable coal seamstill a divergence of views on the chronostratigraphicnostratigraphic boundary. As to the southeast Chinadivision. To solve this problem, the research group ofand Yangtze stratigraphic subregions, becausethis study, i.e. the South China Research Grouphard to differentiate the exposed eluvium and nmeasured 78 geological sections, collected 6375cised-valley sediments from the overlying transgresfossil samples and put the focal point on the study ofsive sediments, the disconformity under the longtanconodont fusulinids and ammonitesFormation is taken as the chrorMeticulous work was carried out for the Dalongboundary for the sake of convenienceFormation in Xiaoyuanchong and Jiahe, HunanMiddle permian fossils were discovered in thevinceand, finally, Clarkina postbitter andlower part or bottom of the Longtan Formation inHindeodus sp. were obtained in an intercalated me-Xinyu, Anfu and Lianhua of Jiangxi Province, anddium-bedded biomicritic limestone: Clarkina bitterYongxing, Xiangyong and Tandong of Hunan Prov-nd hindeodus minutus obtained at the bottom of theince. Moreover, coal-bearing strata can be correlatedDalong formation in borehole zK5215 of the matianmining area in Yongxing; Clarkina lingshanensi andwith those in the Jiangsu-Zhejiang area. Therefore,C. cf. guangyuagnensis were found along the guarthe initial sea flood-plane (under the B4 coal of theshan section in Lianyuan, forming a symbiotic asso-Laoshan member in Jiangxi, under the 2nd coal seamciation with conodonts and ammonites altudocerasn central and southern hunan undeand Paraceltites. Because of a large number of typi-This project was supported by the National Natural Science Foundation of China中国煤化工CNMHGVol. 74 No. 3ACTA GEOLOGICA SINICASept, 2000712the 7th coal seam in Quren, Guangdong Province)istaken as the bottom boundary of the WujiapingianBased on the above new understanding, the foStageowing coal accumulation regularity is concluded inThe Tongziyan Formation and Longtan Formationterms of the sequence stratigraphic methoddiffer greatly and can be hardly correlated. At present1. From the land-source area towards the basinthe tendentious opinion is to correlate the formercentre, the coal-bearing strata are getting thinner,Ith the Longtan Formation guanshan member Itsgains getting finer, continental strata getting fewermedium- to coarse-grained arkose indicates that it isand marine strata getting more. On the west side ofsediments of new land-source area so contradictionsCathaysia, the thickness of the Tongziyan and Cuipmay occur if correlation is made between this straingshan Formations is 1100 m and 450 m and 370 mtum and paralic Longtan Formation. The authorsfor the Shangrao and Xinfeng Formations respeccorrelated the second Member of the Tongziyantively. The thickness is 200-500 m in Jiangsu,Formation with the upper part of the Gufeng FormaJiangxi and Hunan. In the northwestern part of thetion. The sandstone of the Longtan Formation wasplift, the thickness of coal measuresdeposited in a fault depression zone when both of itsranges from metres to tens of meters, being 300 m tosides were eroded because of crustal uplift. Thus it isthe west of Guiyang and 150 m toreasonable to make a stratigraphic correlation from aXikang-Yunnan old land. The coal measures are ofviewpoint of sequence stratigraphy, sedimentarycontinental facies near the land-source area andfacies and palaeogeography and coal accumulationchange gradually into marine deposits towards theregularity(Fig. 1)(Huang and Chen, 1987)basin centre with paralic facies in betweenSince a sedimentation hiatus exists between the2. Coal-bearing property is getting betterCuipingshan Formation and Tongziyan FormatIon inthe land-source area, but gettingFujian, they should be two different formations andbouring areas, that is Type Ill is the worst, Type II isthe best and Type I is poor. In other words, paralictheir names should be retained. Coal measures overfacies strata with a medium thickness have the bestlying the Maokou Formation (or Gufeng and Dangcoal-bearing property, such as Wuxi, Changxingchong Formations) in other places should be calledDongping, Fengcheng, Lianyuan, Chenzhou, Qujiangthe Longtan Formation without exception. Thus itand Renhua in southeastern China and the liupanshui coalfield in southwestern Chinacan be seen that the longtan formation is a diachro3. Different coal measures have different coal-richnous lithostratigraphic unit. This formation belongszones and coal-rich centers Middle and late middleto ages from the Late Maokouan to Wujiapingian agePermian Tongziyain the southern Jiangsu-northern guangdong areabearing strata of the southeastern part of South China,(e.g. Anfu), to ages from the Late Maokouan to Midwhich have good coal-bearing property and numerdle wujiapingian age in areas from central Hunan toous coal seams, forming a relatively wide coal-richzone with the coal-rich center located at the TianShanggao of Jiangxi(e.g. Shaoyang), and to thehushan-Longyan area of Fujian. The western coalEarly Wujiaping Age in northern Jiangxi, southernrich zone of the Longtan formation is distributed inHubei northwestern Hunan, central Guizhou andChongqing, Panxian of Guizhou and Shizong ofcentral Sichuan(e.g. Guiyang), to ages from theYunnan while the eastern coal-rich zone distributedaround Suzhou and Yixing of southern jiangsuWujiaping to Early Changxing Age in southern $-Changxing of Zhejiang, Guangde of Anhui, Lepingchuan. western Guizhou and GIof Jiangxi, Fenyi of Jiangxi, Leiyang of Hunan andpanshui)( Jin et al., 1994; Mei et aL., 1994), and toShaoguan of Guangdong. The distribution directionages from the Middle Wujiaping to Changxing Ageof the coal-rich zone coincides with the strike of thein the east Xikang-Yunnan old land(e. g. Zhijin). Thebasingeneral trend is that the age of coal measures is get-4. Coal-bearing horizons migrate regularly toards a certain directionting newer from east to west.中国煤化工CNMHGNew Understanding on Permian Coal-bearing StrataLi Wenheng et al713turD .IppwuonBuuoJuonouuo ueArzauolBurxaueyq ueys8utdIn.ⅢlquaI squaWunHQ-田囗s5酣囚nens Suurag-1eo0 dol nens auuew eens 8uco3 JoMo uonspues es 8uueaq-tcouonEuuOHuoneuuo Buonouetuu. IodinFig. 1. a diagram showing the correlation of the middle and late permian coal-bearing strata in South China中国煤化工CNMHGVol. 74 NOACTA GEOLOGICA SINICASept. 2000forming period in Fujian and adjacent e-← Regressiongions, the coal-forming period is from theMaokou to Wujiaping Age from southernYongchunJiangsu to northern guangdong but themain workable coal seam was formedduring the Wujiaping Age. There is nothe northwestern side of the Jiangnan upliftand only coal seams of the early WujiapingAge were found. In western Guizhou andsouthern Sichuan, early to late WujiapinAge are both important coal-forming perids. There are also workable coal seams ofthe Changxing Age further westwards tothe east of the Xikang. Yunnan old land(2) Different coal-forming periods havedifferent migration direction of coalThe coal-bearing hezons of Tongziyan coal measures in Fujianand adjacent areas rise from east to westFig. 2. Migration of coal accumulation of the Tongziya Formation in Fujian.(Fig. 2); the coal measures from the Maok-ouan to wingan age in Jiangsu,Jiangxi and hunan rise southeastwards(fiE3)and the coal measure from the Wujiaing to Changxing Age in Sichuan, YunnanFengchengand guizhou rise westward(3) Different systems tracts have different migration directioYouxianhorizons. Taking Jiangxi as an examplecoal seams in 5SE transgressive systemstract rise eastwards(Fig. 4), while those inthe highstand systems tract rise westwards(Fig. 5). Althoughcoal-bearing horizons have changing di-rections, they have the same control factor,namely sea-level changes5. In sequence strata with Type Iboundaries, the lowstand systems tractgenerally has relatively poor coal-formingFig 3. Migration of coal accumulation of the Longtan Formation in theconditions, under which only local work-Northern hunan-Central Jianxi regionable coal seams were formed and the highstand systems tract has better coal-forming(1) The coal-forming period of the South Chinaconditions producing more coal seamsbasin is changing from early to late from east to west. while the early transgressive systems tract has condi-For instance the Maokouan age is the main coal- tions beneficial to coal-formation. In South China the中国煤化工CNMHGNew Understanding on Permian Coal-bearingLi Wenheng et al3-2013202218316081316204kcm9-6CK31501180367-1PsyPs30mf, Maximum marine-fsInitial marine.flooding surfacesystems tractLB4 Coat seamCI Flood-plain depositLagoon tidal deposit EaNeanhore deposit目xaid翻 Barriersand4tFig. 4. Sequence stratigraphic cross section and coal accumulation model diagram in the transgressive systems tractof permian Longtan coal series in Jiangxi province量13-1282156-21031-13cKl3-11603HST Highstand systems tract Fmfs Maximum manneCoal seam睡糖 Barrier bar depositS. coastal plain depositFig. 5. Sequence stratigraphic cross section and coal accumulation model diagram in the highstand systems tract ofPermian Longtan coal series in Jiangxi Provincegenerally developed the 5sE main workable coal because of quick transgression. For example, there areseams belong to the transgressive systems tract. Honot relatively good coal seams found in either of 3SEever, the transgressive systems tract with Type II se- 4SE and 6SE sequences. The highstand systems tractquence boundaries have no coal-forming conditions or generally has coal-forming environment, but the coalhave a rather short -term coal-forming environment seams are rathe中国煤化工cooaCNMHG716Vol. 74 No. 3ACTA GEOLOGICA SINICASept. 2000forming conditions existed only during the middle and Referenceslate stagesChen Genbao and Wu Quanshen, 1965. On the early permianCoal-bearing strata in South China were formed inoal-bearing formation in eastern Yunnan. Acta geologiclittoral zones. The characteristics are closely linkeSinica, 45(1): 331-344 (in Chinese with English abstract)with the changes of coastlines in different agesHan Shufen, Zheng Lisuan and Wang Sunyen, 1961. The com-1)When the sea level is relatively stable or goesplex correlation of the coal series with their respective coalseams of a coal field. Acta Geologica Sinica, 31(2)down, coal-bearing horizons migrate toward the sea136-153(in Chinese)basin. Tongziyan coal measures were formed in a Huang Jiqing and Chen Bingwei, 1987. The Evolution of Tethysbackground under which the crust gently went up andof China and Adjacent Regions, Beijing: Geological Pubthe sea level went down Thus the coal seams roselishing House(in Chinese)from east to west(towards the sea basin)Jin Yugan, Zhu Zili and Mei Shilong, 1994. The Maokouan-Lopingian Boundary sequences in South China. Nanjing(2) When the sea level rapidly goes down, coalNanjing University Pressaccumulation is limited to the Jiangxi-Hunan-Guangxi Li Shichi, 1963. The stratigraphic demarkation of the Mesozoicfault depression zone. During the late Maokou Age,coal-bearing formations in southeastern hunan with a dis-the sea level rapidly went down, most areas in Souththeir age correlation. Acta Geologica SinicaChina were exposed above the sea level. Coals were43(4): 331-344 (in Chinese with Russian abstract)accumulated only in the fault depression zone. BeMei shilong, Jin Yugang and Bruce R. Wardlaw, 1994. Zonation of conodont from the Maokouan-Wuchiapingiantween the fault depression and central Hunan rift mul-ndary strata, South China. Nanjing: Nanjing Univ presstiple workable coal seams were formedSheng Jinzhang and Jin Yugan, 1994. Correlation of Permian(3)When the sea level rapidly goes up, coal accu-Deposits in China. Nanjing: Nanjing University Pressulation zones migrate toward the old land. during Ting Hsunfan and Chia Shicheng, 1959. On the geologic charthe early Wujiapingan age, when the crust of the southacteristics and depositional conditions of the upper PermianChina area was generally subsided, coal-forming peatcoal fields of eastern and northeastern Yunnan. geologicalReview, 19(1): 22-27 (in Chinese with English abstract)bogs migrated correspondingly toward the Cathaysia Wang Chenyuan and Dong Zhengchang, 1991. Conodont inand Xikang-Yunnan old land because of episodicPermian System, Suoxiyu, Cili, Hunan. Micropaleontologiasingcal Journal, &(1)(in Chinese with English abstract)Palaeostructures during the coal-forming period Zhang Zichao, Claoue-Long, J.C., Ma Guogan and Du Shaohua,serve as a very important factor responsible for coa1992. Age determination of the Permian-Triassic boundaryaccumulationat Meishan, Changxing, Zhejiang Province, Geological Review, 38(4): 372-381 (in Chinese with English abstract)Since the middle-late Maokouan age of the Permian Zhao Jinke, Liangxiluo and Zhen Zhuoguan, 1978. Late PermiPeriod, faulting has become more intense in Southan Cephalopoda of South China. China Bulletin of Paleon-China, leading to notable depositional diftology, volume 154, New B, No 12 (in Chinese with EnglishContinuously active faults had very obvious controlabstract)on the coal-bearing basins, fracture zones not onlZhou Zhuren, 1987. Early Permian Epoch ammonites fauna ofserve as depositional sites, controlling coal accumueastern Hunan. Postgraduates papers of Nanjing Geologicallated depression overall setup, but also determine suchand Paleontological Institute, Academica Sinica, 1. Nanjing:Jiangsu Science and Technology publishing housefactors as the thickness of coal-bearing strata, deposi- about the first authortional features and coal accumulation palaeo- Li Wenheng Born in June 1933; graduated fromgeographic environment, depositional type and coalHuainan Mining University in 1954; now seniorrich zones. And fossil fractures caused large differen-geologist at the Jiangxi Coal Geological Bureau. Itiation of the depositional environment as well as coal has been engaged in the study of coal geology andmeasures and coal seamsexploration of coal fields. He and his colleagues havediscovered a number of coal fields in Jiangxi ProvinceManuscript received Dec. 1999 He has written 56 papers and won several scientificedited by liu Xinzhuprizes for his marked achievements. E-mailjxmte@ public rTH中国煤化工CNMHG