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38 Pet.Sci.(2013)10:38-49 DOI 10.1007/s12182-013-0247-8 Geochemical characteristics of the Permian Changxing Formation reef dolomites, northeastern Sichuan Basin, China 1 1 2 1 2 Hu Zuowei , Huang Sijing , Li Zhiming , Zhang Yingying , Xu Ershe and Qi Shichao State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu, Sichuan 610059, China Wuxi Research Institute of Petroleum Geology, SINOPEC Exploration & Production Institute, Wuxi, Jiangsu 214151, China JHUOLQ+HLGHOEHUHUODJ%9&KLQD8QLYHUVLW\RI3HWUROHXP%HLMLQJ DQG6SULQJHU Abstract: The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil & gas exploration in China. Reef dolomites and their origins have been major research topics for sedimentologists and oil & gas geologists. The petrography, trace element and isotope geochemistry of WKHUHHIGRORPLWHVLQGLFDWHGWKDWWKHGRORPLWHVDUHFKDUDFWHUL] HGE\ORZ6UDQG0QFRQWHQWVUHODWLYHO\ 13 18 87 86 ORZ)HFRQWHQWVYHU\VLPLODUį &DQGį O values and very different Sr/ 6UUDWLRV$OWKRXJKWKH VHDZDWHUHHPHGVWREHWKHGRORPLWL]LQJÀXLGVRIWKHUHHIWHVGRORPLWKHORZ0QFRQWHQWVUHODWLYHO\ORZ )HFRQWHQWVKLJKį &YDOXHVDQGKLJKKRPRJHQL]DWLRQWHPSHUDWXUHVRIWKHGRORPLWHV GLGQRWXSSRUWVWKDW 87 86 JHSURSRUWLRQVRIPHWHRULFZDWHULQWKHGRORPLWL]WKHUHZHUHODU DWLRQSURFHVVDQGWKH Sr/ Sr ratios which were close to coeval seawater also did not support the possibility of the mixture of deep-burial circulated ÀXLGVIURPFODVWLFURFNV+LJKWHPSHUDWXUHGHHSEXULDOFLUFXODW HGHDZDWHUVZLWKORZQ0DQG)HFRQWHQWV KLJK6UFRQWHQWDQGKLJKį C values from the dissolution of widely distributed Triassic evaporites during the burial diagenetic processes (including dehydration of water-bearing evaporites) could have been the GRORPLWL]LQJÀXLGVRIWKHUHHIGRORPLWHV Key words: Permian, Changxing Formation, dolomite, reef, geochemistry, northeastern Sichuan Basin GHYHORSHG%UDQGHL]HUDQG9%DQQHUX+ 1 Introduction et al, 2011). The geochemical characteristics, for example, 6LQFHGRORPLWHZDV¿UVWGHVFULEHGLQGHWDLOE\WKH)UHQFK trace elements, C, O and Sr isotopes have been issues in naturalist Dèodat de Dolomieu in 1791 (Dolomieu, 1791), WKHVWXG\RIWKHGRORPLWHJHQHVLV.DW]HWDO+XDQJ dolomites which form important hydrocarbon reservoirs et al, 2006; 2009). Dolomites with different genesis have DQGKRVWURFNVRIEDVHPHWDOGHSRVLWVKDYHDOZD\VEHHQ different geochemical characteristics due to their different 2+ an important research area for geologists (Warren, 2000; sources, hydrological dynamics, depths and times of the 0DFKHO $OWKRXJKDZHDOWKRIEDVLFLQIRUPDWLRQDQG GRORPLWL]DWLRQLHGLIIHUHQWJHRFKHPLFDOFKDUDFWHULVWLFVRI experience has been accumulated, and a number of different GRORPLWHVFRXOGUHÀHFWGLIIHUHQWJHQHVLVRIGRORPLWHV7KXV GRORPLWL]DWLRQPRGHOVKDYHEHHQHVWDEOLVKHGWRH[SODLQWKH the geochemical characteristics of dolomites could play an dolomite genesis, geologists still do not fully understand important role in the research of dolomite genesis. the ‘dolomite problem’ and cannot satisfactorily answer the The discovery of giant or large-scale gas fields, e.g. the problems of the genesis of widely distributed dolomites. 3XJXDQJ/RQJJDQJ/XRMLD]KDLXDQED< 'XNRXKHDQG 7KHUHIRUHLWLVLPSRUWDQWWRUHFRJQL]HDQGXQGHUVWDQG Tieshanpo gas fields, has made the northeastern Sichuan different types of dolomites. The application of trace Basin one of the main centers of hydrocarbon exploration elements and isotopes in carbonate diagenesis have been in China since the mid-1990s with considerable remaining potential. The reef dolomites of the Permian Changxing )RUPDWLRQZKLFKDUHWKHFXUUHQWPDLQUHVHUYRLUURFNVRIWKH JDV¿HOGVKDYHEHHQSDLGFORVHDWWHQWLRQWRE\VHGLPHQWDU\ HPDLOKX]XRZHL#\DKRRFRPFQ &RUUHVSRQGLQJDXWKRU geologists and petroleum geologists for a long period. The Received October 28, 2011 0J ZLWKPHWHRULFZDWHUDQG FDOFXODWHGUHVXOWVRIWKHÀXLGPL[LQJVXJJHVWHGWKDWDPL[WXUH Pet.Sci.(2013)10:38-49 39 GRORPLWHVPD\VWLOOKDYHDERXWSRURVLW\HYHQZKHQ VWUXFWXUDOEHOWRQWKHQRUWKHDVWHUQHGJHRIDQJW]HWKH8SSHU< EXULHGDWRYHUP0DHWDOE&KHQ 6XFK SODWHXH< %HFDXVHWKLV]RQHH[SHULHQFHGPXOWL JRRGUHVHUYRLUTXDOLW\RIGRORPLWHVLQGHHSEXULDOLVTXLWH phase and multi-type intense tectonic extension, compression, rare in global marine carbonate reservoirs, and thus the WKUXVWDQGXSOLIWVLQFHWKH/DWH3DOHR]RLFWKHUHJLRQDO genesis research of reef dolomites in the Permian Changxing tectonic patterns of the northeastern Sichuan Basin are very Formation, northeastern Sichuan Basin has important FRPSOH[$ODUJHQXPEHURI1(WHFWRQLFVWUXFWXUHVIRUPHG SUDFWLFDODQGWKHRUHWLFDOVLJQL¿FDQFH$ORWRIGHWDLOHGZRUN LQWKHODWHDQVKDQ<SHULRGZHUHVXEVHTXHQWO\WUDQVIRUPHG KDVEHHQFDUULHGRXWDQGGLIIHUHQWGRORPLWL]DWLRQPRGHOV E\1:WHFWRQLFVWUXFWXUHVLQWKH+LPDOD\DQSHULRGDQJ7 ZHUHHVWDEOLVKHGIRUWKHVNHOHWDODQGFU\VWDOOLQHGRORPLWHV HWDO ,QVSLWHRIWKHJHQHUDODEVHQFHRI0LGGOH8SSHU which are significant reservoirs, including the mixed-water Silurian, Devonian and Carboniferous sediments after the GRORPLWL]DWLRQPRGHO0RXHWDODQJ:HWDO late Caledonian movement, the other sedimentary strata since VHHSDJHUHIOX[GRORPLWL]DWLRQPRGHO/L EXULDO WKH6LQLDQZLWKDQDYHUDJHWKLFNQHVVRIPRUHWKDQP GRORPLWL]DWLRQPRGHO=KHQJHWDO DQGDPL[WXUHRI DUHFRPSOHWHLQWKHQRUWKHDVWHUQ6LFKXDQ%DVLQ0DHWDO PXOWLSOHGRORPLWL]DWLRQPRGHOV/LHWDO +RZHYHU 2005a). Five basic sedimentary facies of the Late Permian many problems have still not been satisfactorily resolved in &KDQJ[LQJ)RUPDWLRQKDYHEHHQGH¿QHGSODWIRUPSODWIRUP these studies, especially detailed geochemical studies. We JLQDOPDUUHHIEDQNSODWIRUPJLQDOPDUVORSHVKHOIDQGEDVLQ DQDO\]HGWKHJHRFKHPLFDOFKDUDFWHULVWLFVRIWUDFHHOHPHQWV UHVSHFWLYHO\DQGWKHURFNW\SHVPDLQO\LQFOXGHOLPHVWRQHV )HQ06U DQGLVRWRSHV&2U 6DQGURFNWH[WXUHVRIWKH GRORPLWHVFKHUWVDQGFDUERQDFHRXVVKDOHV0RXHWDO typical Changxing Formation reef dolomites in the Puguang Currently, at least 56 Permian Changhsingian reefs have EHHQIRXQGLQWKHDQJW]H0LGGOH8SSHUUHJLRQ<LQ6RXWKHUQ reef dolomites, to further understand the genetic environment China (in outcrops and drill cores), and most of them are and mechanism of reef dolomites in the Permian Changxing concentrated in the eastern and northeastern Sichuan Basin Formation, northeastern Sichuan Basin. +HDQG/XR 7KH\JUHZDQGPLJUDWHGJUDGXDOO\IURP east to west (Wang et al, 2008). For a long time, these reefs 2 Geological setting have been important objects of hydrocarbon exploration in DQJW]HUHJLRQWKHDQG8SSHU<PDQ\JHODUDQGPHGLXPVL]HG The northeastern Sichuan Basin is located in the northeast JDVILHOGVKDYHEHHQIRXQGLQWKHUHHIVZKHUHKLJKTXDOLW\ RI6LFKXDQ3URYLQFHQRUWKRI&KRQJTLQJ&LW\)LJ DQGLV reservoirs of platform marginal reef facies act as the main gas-producing formations. Examples include the Puguang, tectonic belt and the northeast of eastern Sichuan high-steep Era- System Formation Lithology Thickness, m them Guangyuan Xuanhan Creta- 0-2000 Nanchong ceous Wanzhou Chengdu Xiongjiapo Penglaizhen 650-1400 Chongqing 340-500 Suining Leshan Luzhou Shaximiao 600-2800 Tieshanpo Guandu Ziliujing 200-900 Maoba 250-3000 Xujiahe Maoba3 Zhujiazui Leikoupo Si Puguang1 Jialingjiang 900-1700 Puguang4 Feixianguan Puguang5 Puguang2 Puguang8 Changxing 200-500 Longtan Dukouhe Chuanyue83 Maokou Qixia 200-500 Liangshan Xuanhan 510km Carboni- 0 Huanglong 0-500 ferous Silurian 0-1500 Place Well Fault Trap Gas field Sandstone Mudstone Limestone Marlite Coquina Oolite Evaporite Dolomite Oolite Reef limestone dolomite Fig. 1 PRGL¿HGDIWHU0DHWDOD0DDQG&DL4LQHWDO Mesozoic Paleozoic Permian Triassic Jurassic 6WUXFWXUDOORFDWLRQDQGVWUDWLJUDSKLFIUDPHZRUNFROXPQLQWKHQRUWKHDVWHUQ6LFKXDQ%DVLQ DQRYHUODSUHJLRQRIWKHVRXWKFHQWUDO'DED0RXQWDLQVDUFKHG DQG0DREDJDV¿HOGVDQGGLVFXVVHGWKHGRORPLWL]LQJÀXLGVRI 40 Pet.Sci.(2013)10:38-49 XDQED/RQJJDQJ'DWLDQFKL<DQG-LDQQDQJDV¿HOGV2ZLQJ SRURVLW\LVDOPRVWDEVHQWLQWKH6(0PLFURJUDSKV)LJ WRH[WHQVLYHGRORPLWL]DWLRQRIWKH3HUPLDQ&KDQJ[LQJ F 7KHVHGRORPLWHVDUHFKDUDFWHUL]HGE\WKHH[LVWHQFHRI Formation reefs in northeastern Sichuan Basin, especially the most original textures of the carbonate grains and reef- LQWKHUHHIFRUH0DHWDOE=KHQJHWDO WKHVH EXLOGLQJRUJDQLVPVDIWHUWKHGRORPLWL]DWLRQUHIOHFWLQJWKH reefs are often typical research topics of the Permian VHOHFWLYHGRORPLWL]DWLRQRIWKHHDUO\EXULDOGRORPLWL]LQJ &KDQJKVLQJLDQGRORPLWHVLQWKH8SSHUDQJW]H<UHJLRQ7KH JRRGSHWURSK\VLFDOSURSHUWLHVFRQVLGHUDEOHWKLFNQHVVDQG 2) Crystalline dolomites. These dolomites with poor developed dissolution pores are advantages of the Permian original textures and little residual textures have mainly Changxing Formation reef dolomite reservoirs, and the main crystalline granular textures, but some samples with porosity types include intercrystalline dissolution pores, transitional texture types retain visible bioclastic textures, intergranular dissolution pores, intragranular dissolution such as bivalves, fusulinaceas, and echinoderms (Fig. 2(d)) SRUHVPROGLFSRUHVDQGJHGVROXWLRQHQODUIUDFWXUHV0DHWDO RUUHHIEXLOGLQJVNHOHWDOWH[WXUHVXFKVDVSRQJHV)LJH 2005b; Chen, 2008). &U\VWDOOLQHGRORPLWHVDUHPDLQO\FRPSULVHGRIYHU\¿QHDQG ¿QHFU\VWDOOLQHGRORPLWHDQGVRPHFU\VWDOOLQHGRORPLWHVDUH 3 Texture types of the rocks WUDQVLWLRQDOWH[WXUHW\SHVZLWKUHODWLYHO\QH¿PLFURFU\VWDOOLQH or relatively coarse medium-crystalline dolomite. The %HFDXVHWKHGRORPLWL]DWLRQRIWKHVXUIDFHRXWFURSVRI crystalline dolomites could be further divided into very the Permian Changxing Formation reefs in northeastern fine crystalline dolomites, fine crystalline dolomites and a Sichuan Basin was very limited and mostly confined to small amount of medium crystalline dolomites. The very the parts of the reef cover, the typical reef dolomites were ¿QHFU\VWDOOLQHGRORPLWHVDUHPDLQO\FRPSRVHGRIYHU\¿QH mainly seen in drill cores, especially concentrated in some crystalline subhedral-anhedral dolomite (0.02-0.05 mm). XOWUDGHHSXQGHUJURXQGGULOOFRUHVIURP6,123(&EORFNV The fine crystalline dolomites are mainly composed of fine Therefore our samples were chosen from the drill cores of crystalline subhedral dolomite (0.1-0.2 mm). The pores of WKH3XJXDQJDQG3XJXDQJZHOOVLQWKH3XJXDQJJDV¿HOG crystalline dolomites included intercrystalline pores (Fig. 2(d), DQGWKH0DREDZHOOLQWKH0DREDJDVILHOG7KHVHGULOO (e)) and vugs (Fig. 2(d), (f)), and some of them were locally cores are from typical reef dolomites with good reservoir ILOOHGZLWKRLOGURSOHWOLNHDQGILOPOLNHELWXPHQ)LJI TXDOLW\'HWDLOHGORFDWLRQVRIWKHVDPSOHGJDVZHOOVDUH J 7KHVHGRORPLWHVDUHFKDUDFWHUL]HGE\WKHGLVDSSHDUDQFH shown in Fig. 1. The samples include dolomites, calcitic of the most original textures of the carbonate grains and reef- dolomites and dolomitic limestones. Examination of standard building organisms, reflecting the superimposed influence thin sections, blue resin vacuum impregnated thin sections RIWKHODWHLQKHULWHGEXULDOGRORPLWL]LQJÀXLGVZKLFKIXUWKHU DQGVFDQQLQJHOHFWURQPLFURVFRS\6(0 ZHUHXVHGWRVWXG\ DIIHFWHGWKHHDUO\IRUPHGVNHOHWDOGRORPLWHVE\WKHVWURQJ the composition and fabric characteristics of samples. The GRORPLWL]DWLRQDQGUHFU\VWDOOL]DWLRQDQGWKHQWKHODUJHU Permian Changxing Formation reef dolomites are divided dolomite crystals were formed. into two main end-member types on the basis of original 3) Vug dolomite and vug calcite. Some crystalline WH[WXUHVDQGWKHFU\VWDOVL]HRIWKHGRORPLWH7KHWZRW\SHV GRORPLWHVFRQVLVWLQJRIYHU\¿QHDQG¿QHFU\VWDOOLQHGRORPLWH DUHVNHOHWDOGRORPLWHVDQGFU\VWDOOLQHGRORPLWHV*RRG show a few dolomite and calcite crystals with large volumes RULJLQDOWH[WXUHLVDFKDUDFWHULVWLFRIVNHOHWDOGRORPLWHV DQGTXDQWLWLHV¿OOLQJGLVVROYHGSRUHVYXJVRUIUDFWXUHV)LJ and good crystalline granular texture is a characteristic of crystalline dolomites. Some samples which consist of fabric types: vug dolomite and vug calcite (Fig. 2(f)). The vug PL[WXUHRIGRORPLWHDQGFDOFLWHDUHFODVVL¿HGDVWUDQVLWLRQDO GRORPLWHDQGYXJFDOFLWHDUHFKDUDFWHUL]HGE\WKHRFFXUUHQFH and a few separable dolomite and calcite crystals from the in the early pores of dolomite reservoirs, indicating that their reef dolomites are classified as the individual fabric types: PRVWLPSRUWDQWIOXLGVRXUFHLVWKHODWHEXULDOGRORPLWL]LQJ vug dolomite and vug calcite. The main features of different ÀXLGVDQGFDOFLWHSUHFLSLWDWLRQÀXLGV texture types of reef dolomites are as follows: UDQVLWLRQDO7 URFNW\SH$OWKRXJKWKHFRQWHQWRIWKH 6NHOHWDOGRORPLWHV7KHVHGRORPLWHVZLWKZHOO UHVLGXDOFDOFLWHRUODWHFDOFLWHFHPHQWVLVPRUHWKDQ preserved original textures were mostly formed by WKHVHURFNVVWLOOFRQWDLQRIGRORPLWHVRWKH GRORPLWL]DWLRQRIUHHIOLPHVWRQHVWKHVNHOHWRQVDUHPDLQO\ dolomite could not be ignored when the samples were composed of reef-building sponges) (Fig. 2(a)), and some 7KHWUDQVLWLRQDOURFNW\SHVEHORQJWRWKHURFNW\SHVFODVVL¿HG dolomites still had a small amount of binding textures (mainly with component transition, and are classified as dolomitic blue-green algae binding texture) (Fig. 2(b)). The samples OLPHVWRQHV7KHGRORPLWL]DWLRQRIVDPSOHVZKLFKPDLQO\ consisted mostly of microcrystalline dolomite, and some consisted of residual calcite and retained complete original ZHUHYHU\¿QHGRORPLWHFU\VWDOV(DUO\GRORPLWHRIWHQIRUPV \ anhedral crystals, but late dolomite deposited along the distributed (Fig. 2(h)). The other samples which mainly edge of vugs often forms euhedral crystals (Fig. 2(c)). The consist of late calcite cements are almost crystalline granular LQWUDJUDQXODUSRUHVRIGRORPLWLFVSRQJHVDUH¿OOHGZLWKVSDUU\ textures and are similar to crystalline dolomites. Some parts of samples retain relatively complete original textures (Fig. calcite (Fig. 2(a)), which might be related to the late sparry L +RZHYHUWKHFRQWHQWRIWKHODWHFDOFLWHFHPHQWV¿OOLQJ FDOFLWHFHPHQWV*HQHUDOO\VSHDNLQJWKHSRURVLW\RIVNHOHWDO WKHSRUHVRIGRORPLWHVLVPRUHWKDQ dolomites with rare visible pores is poor and intercrystalline WH[WXUHVLVUHODWLYHO\ZHDNDQGGRORPLWHLVVSRUDGLFRUORFDOO J VRWKHVHFDUERQDWHFHPHQWVZHUHFODVVL¿HGDVLQGLYLGXDO ÀXLGV Pet.Sci.(2013)10:38-49 41 (a) (b) (c) (d) (e) (f) (g) (h) (i) Fig. 2 Photomicrographs of main texture types of the Permian Changxing Formation reef dolomites D 6NHOHWDOWH[WXUHVFRQVLVWHGRIUHHIEXLOGLQJVSRQJHV VSD UU\FDOFLWH¿OOHGWKHLQWUDJUDQXODUSRUHVZLWKLQSRQJHVVPLON ZKLWHSDUWVXFKDVUHGDUURZV 3XJXDQJZHOOPSODQHSRODUL]HGOLJKWVFDOH PP L]HGOLJKWVFDOH PPF /DWHGRORPLWHFHPHQWVLWKZUHODWLYHO\JRRGHXKHGUDOFU\VWDOVKD SHOOHG¿WKHSRUHVXJXDQJ3ZHOOP(06PLFURJUDSKVF DOH 7KHPVDPSOHG PDLQO\FRQVLVWVRIYHU\¿QHGRORPLWH7KHUHVLGXDOWH[WXUHVRIWKHELRFODVWVHJELYDOYHVUHGDUURZ IXVXOLQDFHDJUHHQDU URZ HFKLQRGHUPV\HOORZDUURZ KDGEHHQUHSODFHGE\JUDQXODUGRORPLWHSRUHV,QWHUGDQGGLVVROXWLRQRYHUVL]HSRUHVKDYHEHHQUHODWLYHO\HOOZGHYHORSHG3XJXDQ JZHOOPEOXHUHVLQ YDFXXPLPSUHJQDWHGWKLQVHFWLRQSODQHSRODUL]HGOLJKWVFDOH PPH 7KHDPSOHVPDLQO\FRQVLVWVRI¿QHFU\VWDOOLQHWHGRORPL7KHUHVLGXDOWH[WXUHVRI WKHVSRQJHNHOHWRQVDUHJUDQXODUVLJQL¿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¿OOHGWKHSRUHVEHWZHHQGRORPLWHFU\VWDOV3XJXDQJZHOO Sr contents are not related to the different texture types of 4 Geochemical characteristics dolomites. The Sr content is related to the crystal chemistry of dolomite, and the Sr distribution coefficient in dolomite 4.1 Characteristics of Fe, Mn and Sr trace elements is significantly less than (theoretically only half) the Sr The average Sr contents of different types of Permian GLVWULEXWLRQFRHIILFLHQWLQFDOFLWHDKUHQNDPS9DQG6ZDUW Changxing Formation reef dolomites are similar, and they 1990), so there are not very high Sr contents in dolomites DUHDOOOHVVWKDQSSP7KHDYHUDJH6UFRQWHQWVRIVNHOHWDO $]P\HWDO+XDQJHWDO+DUWLJHW dolomites and crystalline dolomites are very close to 140 ppm al, 2011). Only one crystalline dolomites sample had an (Table 1, Fig. 3(a)). The average Sr content of vug calcite can exceptionally high Sr content (1,768 ppm), which might be reach 608 ppm and the maximum Sr content of vug calcite related to the late calcite cements which filled the pores of LVDVKLJKDVSSPDEOH7)LJD +RZHYHUWKH dolomites (Table 1). WOLNHDQG¿OPOLNHELWXPHQUHG ORSHGLQGLVVROYHGSRUHV6RPHSRUHVZHUH¿OOHGZLWKRLOGURSOH J ,QWHUJUDQXODUSRUHVEHWZHHQHXKHGUDOGRORPLWHFU\VWDOVGHYH HGWKHLQWHUJUDQXODUSRUHVEHWZHHQWKHGRORPLWHFU\VWDOV3XJXD RQWKHHGJHRIGLVVROXWLRQSRUHVHJUHGDUURZV %LWXPHQ¿OO E $OJDHELQGLQJWH[WXUHV3XJXDQJZHOOPSODQHSRODU 42 Pet.Sci.(2013)10:38-49 Table 1 Geochemical data of the Permian Changxing Formation reef dolomites 13 18 Depth Dolomite* Sr Fe į C (PDB) į O (PDB) 87 86 Well 5RFNW\SH Sr/ Sr m ppm ppm ppm ‰ ‰ Puguang5 5292.38 6NHOHWDOGRORPLWHV 97.4 21.1 30 121 100 3.26 -5.03 0.708208 Puguang8 5640 6NHOHWDOGRORPLWHV 95.2 20.4 40 140 200 4.23 -4.2 Puguang8 5568.7 6NHOHWDOGRORPLWHV 96.1 21.2 91 165 414 2.38 -5.31 Puguang8 5656.36 6NHOHWDOGRORPLWHV 95.6 20.5 91 131 314 2.48 -4.99 0DRED 4331.29 Crystalline dolomites 89.5 19.3 114 217 2614 1.81 -3.77 0DRED 4339.25 Crystalline dolomites 83.9 19 85 1768 442 0.83 -5.25 0DRED 4348.96 Crystalline dolomites 89.6 20.5 88 143 1105 2.83 -5.41 0DRED 4355.01 Crystalline dolomites 99.2 21.3 50 223 200 3.37 -4.58 0.707534 0DRED 4365.62 Crystalline dolomites 87.4 20.3 73 205 544 2.49 -5.75 0DRED 4382.52 Crystalline dolomites 87.8 17.6 50 248 100 2.8 -4.4 0.707591 0DRED 4393.29 Crystalline dolomites 93.1 20.7 64 139 450 3.2 -5.1 0DRED 4406.66 Crystalline dolomites 87.5 19.9 80 168 394 2.48 -5.28 0DRED 4425.7 Crystalline dolomites 94.4 20.5 50 363 100 2.69 -6.11 Puguang5 5166.3 Crystalline dolomites 85.8 18.6 30 97 500 1.54 -6.49 Puguang8 5528.6 Crystalline dolomites 96.8 21 60 142 300 2.37 -5.2 Puguang8 5555.2 Crystalline dolomites 95 19.5 60 153 600 1.02 -3.55 Puguang8 5586.1 Crystalline dolomites 97.2 21 40 103 100 1.84 -4.9 Puguang8 5618.34 Crystalline dolomites 96.6 21 40 154 100 3.54 -4.54 Puguang5 5146.7 Crystalline dolomites 93 20.9 66 75 537 2.69 -4.79 0.707696 Puguang5 5164.27 Crystalline dolomites 93.5 20.7 75 80 635 2.8 -5.24 0.707705 Puguang8 5508 Crystalline dolomites 94.2 20.1 266 124 1552 1.84 -5.19 0.707747 Puguang5 5157.7 Crystalline dolomites 90.4 20.3 76 100 559 2.52 -5.06 Puguang5 5158.8 Crystalline dolomites 92.9 20.8 67 84 488 2.26 -5.31 Puguang5 5169.8 Crystalline dolomites 94.1 21.3 71 70 293 2.52 -5.06 Puguang8 5510 Crystalline dolomites 93.6 20.1 261 110 1333 2.14 -3.83 Puguang8 5512.1 Crystalline dolomites 91.2 19.3 152 127 2936 2.1 -5.38 Puguang8 5525.7 Crystalline dolomites 95.8 20.8 125 134 1221 2.17 -5.18 Puguang8 5531.5 Crystalline dolomites 93.2 19.8 197 133 2073 2.41 -4.53 Puguang8 5538.5 Crystalline dolomites 87.5 18 260 165 3823 2.21 -3.63 Puguang8 5545.3 Crystalline dolomites 94 19.4 129 117 3898 2.14 -5.39 Puguang8 5563 Crystalline dolomites 98.3 21.5 85 73 303 1.7 -5.16 Puguang8 5572.3 Crystalline dolomites 96.4 20.8 90 128 393 2.5 -4.12 Puguang8 5577.8 Crystalline dolomites 96 20.7 98 124 1178 2.42 -5.62 Puguang8 5604.5 Crystalline dolomites 96.6 20.6 99 176 912 3.02 -5.32 Puguang8 5634.5 Crystalline dolomites 95.9 20.8 69 112 418 2.76 -5.14 Puguang5 5164.27 Vug dolomite 89.3 19.3 40 142 200 2.87 -4.8 0.708278 Puguang5 5292.38 Vug dolomite 92 18.8 40 301 1300 2.63 -6.05 0.707710 Puguang5 5351 Vug dolomite 90 18.3 30 197 50 2.86 -7.75 Puguang8 5508 Vug dolomite 95.2 20.4 20 174 100 1.91 -4.76 0.707591 (To be continued) 0Q 0J2 Pet.Sci.(2013)10:38-49 43 (Continued) 13 18 Depth Dolomite* Sr Fe į C (PDB) į O (PDB) 87 86 Well 5RFNW\SH Sr/ Sr m ppm ppm ppm ‰ ‰ Puguang8 5568.7 Vug dolomite 95.8 20.8 40 123 100 2.81 -4.76 Puguang8 5572.3 Vug dolomite 95.7 20.8 50 168 100 3.06 -3.67 Puguang8 5577.8 Vug dolomite 95.8 20.9 40 165 100 2.95 -5.23 Puguang8 5604.5 Vug dolomite 96.1 20.7 50 244 100 3.7 -3.62 0DRED 4415.54 Vug calcite 3.5 0.8 5 1407 100 -9.36 -5.67 0.707468 Puguang5 5166.3 Vug calcite 1.3 0.3 5 219 50 -0.64 -8.84 0.707746 Puguang5 5288.25 Vug calcite 1 0.2 5 199 200 3.47 -6.6 0.707591 0DRED 4440.06 UDQVLWLRQDOURFNW\SH7 38.9 9.3 53 390 592 2.53 -5.7 Puguang5 5288.25 UDQVLWLRQDOURFNW\SH7 11.9 2.8 45 160 184 3.26 -6.38 0.707293 Puguang5 5285.2 UDQVLWLRQDOURFNW\SH7 20.2 4.8 27 158 171 2.99 -6.42 Puguang5 5290 UDQVLWLRQDOURFNW\SH7 39.5 9.2 64 160 591 3.23 -6.17 Puguang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ÅU6LVRWRSH DQDO\VHVZHUHPHDVXUHGRQ7D)LQQLJDQPDVV0$VSHFWURPHWHULQWKH,QVWLWXWHRI*HRORJ\DQG*HRSK\VLFV&KLQHVH$FDGHP\RI 6FLHQFHVWKH 10 10 PHDQDQDO\WLFDOUHVXOWVRI1%6LV n EODQNYDOXHVRIDOOSURFHGXUHVDUHDSSUR[LPDWHO\î Jî g. WKHEDVLVRIWKHFRPSRVLWLRQRILGHDOGRORPLWH 7KHFRQWHQWVRIGRORPLWHZHUHFDOFXODWHGIURP0J2FRQWHQWVRQ 7KHDYHUDJH0QFRQWHQWVRIWKH3HUPLDQ&KDQJ[LQJ SSPSSPUHVSHFWLYHO\DEOH7 7KH0QDQG)H Formation reef dolomites are all less than 100 ppm (Table 1, contents of different texture types of the reef dolomites are Fig. 3(b)), and their average Fe contents are less than 1,000 significantly lower than many other reported dolomites in SSPDEOH7)LJF 7KHDYHUDJH0QDQG)HFRQWHQWV WKHZRUOGIRUH[DPSOH+DUWLJHWDO UHSRUWHGWKDWWKH of vug calcite are as low as 5 ppm and 117 ppm respectively 0QDQG)HFRQWHQWVRI3HUPLDQFRDUVHFORXGGRORPLWHLQ (Table 1, Fig. 3(b), (c)). The average and maximum values of Bravo Dome CO JDV¿HOGV86$DUHYHU\KLJKDQGWKHLU 0QDQG)HFRQWHQWVRIFU\VWDOOLQHGRORPLWHVDUHWKHKLJKHVW average contents can reach up to 5,200 ppm and 41,400 ppm, in all the texture types of samples, 99 ppm, 971 ppm and respectively. 700 120 1200 100 1000 80 800 60 600 40 400 20 200 0 0 0 (a) (b) (c) Fig. 30QDQG)HFRQWHQWV7KHKLVWRJUDPVRIWKHDYHUDJHYDOXHVRI6U IURPWKH3HUPLDQ&KDQJ[LQJ)RUPDWLRQUHHIGRORPLWHV negative, because it is affected by one sample with very 4.2 Characteristics of C and O isotopes 13 13 13 7KHDYHUDJHį C values of the reef dolomites are very QHJDWLYHį &YDOXHÅ DQGWKHRWKHUWZRį C values similar, and mainly range from 2.5‰ to 3‰ (Table 1, Fig. DUHÅDQGÅDEOH7 7KHį &YDOXHVRIVNHOHWDO D 7KHDYHUDJHį C value of vug calcite (-2.2‰) is dolomites with original textures are consistent with those of Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type Sr, ppm Mn, ppm Fe, ppm 0Q 0J2 44 Pet.Sci.(2013)10:38-49 WKHWUDQVLWLRQDOURFNW\SHVLWKZWKHDYHUDJHYDOXHVRIÅ around the value of -5‰ (Table 1, Fig. 4(b)). Therefore, $OWKRXJKWKHDYHUDJHį C value of crystalline dolomites is the three texture types of dolomites may have the same or the most negative in the reef dolomites (including transitional VLPLODUIRUPDWLRQHQYLURQPHQWVDQGGRORPLWL]LQJÀXLGV7KH 13 18 URFNW\SHV RQO\ÅWKHUDQJHRIį C value of crystalline DYHUDJHį 2YDOXHVRIYXJFDOFLWHDQGWUDQVLWLRQDOURFNW\SHV GRORPLWHVLVVWLOOVLPLODUWRWKHRWKHUį C values of dolomites. are negative: -7.04‰ and -6.2‰ respectively (Table 1), and 2QO\DIHZį C values are less than 2‰, and these values these values are commonly 2‰ less than the reef dolomites. might be affected by the late sparry calcite with strongly Because of the different oxygen isotope fractionation between 13 13 QHJDWLYHį &YDOXHVDEOH7 7KHUDQJHRIį C values of GRORPLWHRUFDOFLWHDQGSUHFLSLWDWLRQÀXLGVIHUHWKHUHLVDGLI QW the reef dolomites is still consistent with that of the Permian į O value of the coexisting calcite and dolomite from the Changhsingian seawater (1.5‰-3.5‰) (Korte et al, 2004; same precipitation fluid with the oxygen isotope exchange .RUWHDQG.R]XU HTXLOLEULXPLHµǻSUREOHPV¶/DQG 7KHGLIIHUHQW 18 18 7KHDYHUDJHį O values of the Permian Changxing į 2YDOXHRIDERXWÅGRHVQRWLPSO\VHTXDOWRIHUHQWWKHGLI į O value of their corresponding precipitation fluids. The dolomites), -5.0‰ (crystalline dolomites) and -5.1‰ (vug į O values of calcite and dolomite of the reef dolomites GRORPLWH UHVSHFWLYHO\DQGWKHVHį O values all concentrate PLJKWEHVWLOOUHODWHGWRWKHVLPLODUGLDJHQHWLFÀXLGV 0 0.7084 -1 0.7082 -2 0.7080 -3 0.7078 -4 0.7076 -5 0.7074 į į -1 -6 0.7072 -2 -7 0.7070 -8 0.7068 -3 (a) (b) (c) The histograms of the average values of C, O and Sr isotopes from the Permian Changxing Formation reef dolomites Fig. 4 JHQHVLV:KHQZHNQRZWKHVRXUFHRIGRORPLWL]LQJIOXLGV 4.3 Characteristics of Sr isotopic ratio (it is largely the source of magnesium), we can use the 87 86 The average Sr/ Sr ratios of the reef dolomites NQRZQVRXUFHRIGRORPLWL]LQJIOXLGVWRIXUWKHUGLVFXVVWKH DUHVLJQLILFDQWO\GLIIHUHQWVNHOHWDOGRORPLWHV GRORPLWL]DWLRQPHFKDQLVPDQGGRORPLWHJHQHVLV&XUUHQWO\ 0.70765 (crystalline dolomites) and 0.70786 (vug dolomite) DQLPSRUWDQWUHDVRQIRUWKHH[LVWLQJFRQWURYHUV\LVWKHODFNRI 87 86 respectively (Table 1, Fig. 4(c)), i.e. the average Sr/ Sr ratio DGHTXDWHNQRZOHGJHDQGXQGHUVWDQGLQJRIWKHGRORPLWL]LQJ 87 86 RIVNHOHWDOGRORPLWHVLVWKHKLJKHVWDQGWKHDYHUDJH Sr/ Sr IOXLGVRIWKHUHHIGRORPLWHVDQGZHGRQRWUHDOO\NQRZ 87 86 ratio of vug dolomite is moderate, and the average Sr/ Sr ratio of crystalline dolomites is the lowest (Fig. 4(c)). These RUDPL[WXUH,IWKHGRORPLWL]LQJÀXLGVFRXOGEHGHWHUPLQHG 87 86 average Sr/ Sr ratios are higher than that of the vug calcite 87 86 (Table 1). The average Sr/ Sr ratios of dolomites and vug mechanism of the reef dolomites would be solved, including 87 86 FDOFLWHDUHVLJQL¿FDQWO\KLJKHUWKDQWKHDYHUDJH Sr/ Sr ratios the formation environment and genetic mechanism. of the Permian Changhsingian seawater (0.7070-0.7073) 7KH0QDQG)HFRQWHQWVRIWKH3HUPLDQ&KDQJ[LQJ 87 86 Sr/ Sr Formation reef dolomites (except the vug calcite) are higher UDWLRRIWKHWUDQVLWLRQDOURFNW\SH LVFRQVLVWHQW WKDQWKHDYHUDJHQ0DQGULDVVLF)HFRQWHQWVRIWKH7RYHUO\LQJ with that of the Permian Changhsingian seawater (Fig. 5). Feixianguan crystalline dolomites, 19.6 ppm and 353.3 ppm Therefore the dolomites and vug calcite are mixed with UHVSHFWLYHO\+XDQJHWDOSRVLWLYH$ FRUUHODWLRQ high concentrations of radiogenic strontium from external EHWZHHQQ0FRQWHQWVDQG)HFRQWHQWVLQGLFDWHGWKDW0QDQG )HHOHPHQWVKDGDVLPLODUVRXUFH)LJD 0RUHRYHUWKH DQGWKHWUDQVLWLRQDOURFNW\SHDPSOHVVJHO\ODUUHWDLQHGWKHU6 differences of the textural characteristics and the average isotope composition of the coeval seawater. YDOXHVRI0QDQG)HFRQWHQWVDPRQJGLIIHUHQWW\SHVRIWKH reef dolomites reflect the differences in the timing of their FHRIWKHGRORPLWL]LQJÀXLGV6RXU GRORPLWL]DWLRQ7KHVNHOHWDOGRORPLWHVZHUHSUREDEO\UHODWHG 7KHVRXUFHRIGRORPLWL]LQJÀXLGVLVWKHVWDUWLQJSRLQWRI WRWKHHDUO\GRORPLWL]LQJÀXLGVDQGWKHFU\VWDOOLQHGRORPLWHV UHVHDUFKLQWRWKHGRORPLWL]DWLRQPHFKDQLVPDQGGRORPLWH PLJKWVKRZWKHVXSHULPSRVHGLQÀXHQFHRIWKHODWHLQKHULWHG Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type Skeletal dolomites Crystalline dolomites Vug dolomite Vug calcite Transitional rock type C, ‰(PDB) O, ‰(PDB) 87 86 Sr/ Sr ratio GLDJHQHWLFÀXLGVZKLFKZHUHQRWFRHYDOPDULQHGHULYHGÀXLGV 9HL]HUHWDO.RUWHHWDO 2QO\WKH PDQ\SUREOHPVDERXWWKHGRORPLWHJHQHVLVDQGGRORPLWL]DWLRQ ZKHWKHUWKHGRORPLWL]LQJÀXLGVZHUHVHDZDWHUPHWHRULFZDWHU )RUPDWLRQUHHIGRORPLWHVDUHDOVRYHU\VLPLODUÅVNHOHWDO 46 Pet.Sci.(2013)10:38-49 §· Sr ¨¸ was 0.70715, i.e. 86 = 0.70715. The Sr content of the Skeletal dolomites Sr 0.7083 ©¹ ssw Crystalline dolomites Permian Changhsingian seawater was 0.097 mmole/L (the Vug dolomite average Sr content of modern seawater; Stein et al, 2000). 0.7081 Vug calcite 87 86 The average Sr/ Sr ratio of the modern river water (0.7119; Palmer and Edmond, 1989) was substituted for the Sr isotope §· 0.7079 Sr composition of meteoric water, i.e. = 0.7119. The Sr ¨¸ Sr ©¹ Initial value of seawater 0.7077 content of meteoric water was 0.001 mmole/L (the average Sr 0.7073 §· Sr content of modern river water; Livingstone, 1963). ¨¸ Sr ©¹ L 0.7075 87 86 are corresponding to the Sr/ Sr ratios of the reef dolomites. $VDUHVXOWWKHSURSRUWLRQVRIVHDZDWHUDQGPHWHRULFZDWHU 0.7073 LQWKHPL[WXUHVZHUHILQDOO\NQRZQDQGWKHQZHFDQNQRZ Initial value of seawater ZKHWKHURUQRWWKHGRORPLWL]LQJIOXLGVZHUHDIIHFWHGE\ 0.70715 mixtures. 0.7071 7KHFDOFXODWHGUHVXOWVIURPWKHHTXDWLRQVDERYHDUH 70 75 80 85 90 95 100 VKRZQLQ)LJ$YHU\ODUJHSURSRUWLRQRIPHWHRULFZDWHU Sr mole percent from meteoric water Fig. 7 The calculated proportions of different Sr sources in PDLQO\IURPWRDQGHYHQWKHSURSRUWLRQVRI GRORPLWL]LQJIOXLGVZKLFKDUHPL[WXUHVRI3HUPLDQ&KDQJKVLQJLDQ PHWHRULFZDWHULQWZRVDPSOHVZHUHIURPWR VHDZDWHUDQGPHWHRULFZDWHUGHULYHGIURPWKHHTXDWLRQVDERYH 87 86 ,QRWKHUZRUGVWKHGRORPLWL]LQJIOXLGVZHUHPL[WXUHVRI The value of 0.70715 as an average Sr/ Sr ratio of the Permian PHWHRULFZDWHUDQGVHDZDWHU)LJ Changhsingian seawater, and the value of 0.7073 as a maximum 87 86 $FFRUGLQJWRWKHW\SLFDO'RUDJGRORPLWL]DWLRQPRGHOZKLFK Sr/ Sr ratio of the Permian Changhsingian seawater were used ZDVSURSRVHGE\%DGLR]DPDQL WKHGRORPLWL]DWLRQ FRXOGRFFXULQPL[WXUHVRIPHWHRULFZDWHUDQG VHDZDWHUVRWKHGRORPLWL]LQJÀXLGVRIWKH3HUPLDQ (Fig. 8), indicating the precipitation of dolomite and calcite Changxing Formation reef dolomites might be mixtures is related to the diagenesis fluids under high temperature RIPHWHRULFZDWHUDQGVHDZDWHU)LJ (YHQLIZHWRRN FRQGLWLRQV7KHÀXLGVZLWKVXFKDKLJKWHPSHUDWXUHFDQQRW 87 86 the maximum Sr/ Sr ratio of the Permian Changhsingian be the near-surface meteoric water or mixtures. For these 87 86 reasons, there were not large proportions of meteoric water in seawater (0.7073) as the Sr/ Sr ratio of initial seawater WKHGRORPLWL]DWLRQSURFHVVLHPHWHRULFZDWHUZDVQRWDPDLQ §· Sr VRXUFHRIWKHGRORPLWL]LQJÀXLGV,QDGGLWLRQWKHPL[WXUHRI LQWKHFDOFXODWHGHTXDWLRQVLH = 0.7073, the ¨¸ Sr ©¹ PLJUDWLQJÀXLGVDQGSRUHXLGVÀIURPWKHGHHSO\EXULHGFODVWLF ssw URFNVLWKLQZWKHEDVLQFDQDOVROHDGWRPRUHUDGLRJHQLF6ULQ FDOFXODWHGSURSRUWLRQVRIPHWHRULFZDWHULQWKHGRORPLWL]LQJ WKHGRORPLWL]LQJÀXLGV7KHPL[WXUHVZRXOGLQHYLWDEO\UHVXOW IOXLGVZHUHVWLOOPDLQO\FRQFHQWUDWHGIURPWR LQKLJK0QDQG)HFRQWHQWVIURPFODVWLFURFNV)RUH[DPSOH (Fig. 7), so the calculated results seemed to support that WKH0QDQG)HFRQWHQWVRIWKHODWHVWGRORPLWHFHPHQWVIURP GRORPLWL]LQJÀXLGVRIWKHUHHIGRORPLWHVPLJKWEHUHODWHGWR deep-burial diagenetic fluids that had circulated through near-surface mixtures. FODVWLFURFNVLQWKHD]DQWH0HVRSURWHUR]RLF)RUPDWLRQ96mR ,IWKHGRORPLWL]LQJIOXLGVZHUHYHU\ODUJHO\FRPSRVHG )UDQFLVFR%DVLQ%UD]LODUHYHU\KLJKZLWKPD[LPXP0Q of meteoric water as derived in the above calculation, the and Fe contents of 2,090 ppm and 22,010 ppm, and average PHWHRULFZDWHUSOD\HGDQLPSRUWDQWUROHLQWKHGRORPLWL]DWLRQ 0QDQG)HFRQWHQWVRISSPDQGSSPUHVSHFWLYHO\ SURFHVVRZHYHU+VXFKDJHODUSURSRUWLRQRIPHWHRULFZDWHU $]P\HWDO 7KHDYHUDJH0QDQG)HFRQWHQWVRIWKH LJ) UHVXOWHGLQDFRQVLGHUDEOHLQFUHDVHRI0Q 12 16 reef dolomites are low and relatively low, respectively (Table Fe, C and O. In fact, the hypothesis of mixtures is very 1). If there were the mixture of throughflows or pore fluids different from the geochemical characteristics of the Permian enriched in radiogenic Sr from the deeply buried clastic &KDQJ[LQJ)RUPDWLRQUHHIGRORPLWHVEHFDXVHRIWKHORZ0Q URFNVZLWKLQWKHEDVLQWKHGRORPLWL]LQJIOXLGVDIWHUPL[LQJ FRQWHQWVUHODWLYHO\ORZ)HFRQWHQWVDQGKLJKį C values in 87 86 should have much higher Sr/ Sr ratios than that of coeval the most reef dolomites, and very high Sr contents of some 87 86 VHDZDWHU+XHWDO WKH+RZHYHU Sr/ Sr ratios of the sparry calcite cements formed in the late diagenetic fluids reef dolomites were still close to those of coeval seawater DEOH7 0RUHRYHUWKHKRPRJHQL]DWLRQWHPSHUDWXUHVRI )LJ VRWKHSRVVLELOLW\WKDWWKHGRORPLWL]LQJÀXLGVRIWKH WKHVDOLQHÀXLGLQFOXVLRQVIURPWKHUHHIGRORPLWHVDUHPRUH UHHIGRORPLWHVZHUHPL[HGZLWKWKURXJKÀRZVRUSRUHÀXLGV than 100 °C, and the main temperature ranges of the saline IURPWKHGHHSO\EXULHGFODVWLFURFNVZLWKLQWKHEDVLQLVQRW fluid inclusions from the dolomite and calcite are in good supported. agreement, mainly concentrated between 120 °C and 160 °C 87 86 Sr/ Sr ratio of mixing fluid ZDVFRQWDLQHGLQWKHGRORPLWL]LQJÀXLGVRIWKHUHHIGRORPLWHV Pet.Sci.(2013)10:38-49 47 Triassic evaporites during burial diagenetic processes Dolomite (n=22) 30 (including dehydration of water-bearing evaporites) could be Calcite (n=138) WKHGRORPLWL]LQJIOXLGVRIWKHUHHIGRORPLWHV1HYHUWKHOHVV PDQ\TXHVWLRQVUHPDLQWREHVDWLVIDFWRULO\DQVZHUHGVXFK as what were the specific causes of the deep-burial marine- derived brines related to the evaporites, how did the marine- derived brines distribute and migrate in the deeply buried strata, and how did the marine-derived brines participate in 0 WKHGRORPLWL]DWLRQRIWKH3HUPLDQ&KDQJ[LQJ)RUPDWLRQUHHI 90 100 110 120 130 140 150 160 170 180 190 200 210 220 limestones. Homogenization temperature, °C 6 Conclusions 7KHKLVWRJUDPRIWKHKRPRJHQL]DWLRQWHPSHUDWXUHVRIWKHXLGÀVDOLQH Fig. 8 inclusions from the Permian Changxing Formation reef dolomites 1) The average Sr contents of the reef dolomites are similar and relatively low, but the Sr contents of vug calcite %HFDXVHWKHGRORPLWL]LQJIOXLGVRIWKHUHHIGRORPLWHV DUHYHU\KLJK7KHDYHUDJH0QDQG)HFRQWHQWVRIWKHUHHI were not related to the near-surface meteoric water and dolomites are also low and relatively low, respectively. throughflows or pore fluids from the deeply buried clastic 7KHį C values of the reef dolomites are very similar, URFNVLWKLQZWKHEDVLQWKHGRORPLWL]LQJÀXLGVFRXOGEHKLJK PDLQO\UDQJLQJIURPÅWRÅDQGWKHį C values are WHPSHUDWXUHGHHSEXULDOFLUFXODWHGHDZDWHUVLWKZORZQ0DQG consistent with the range of the Permian Changhsingian )HFRQWHQWVKLJK6UFRQWHQWVDQGKLJKį C values. If this is VHDZDWHUEXWWKHį C values of vug calcite can be negative. 7KHDYHUDJHį O values of the reef dolomites are also very RUPDULQHIRUPDWLRQIOXLGV"%HFDXVHWKHDJHVRIWKHUHHIV VLPLODUDQGWKHį O values all concentrate around the value DUH/DWH3HUPLDQWKHGHHSEXULDOGLDJHQHWLFÀXLGVIURPWKH of -5‰. underlying Permian strata and overlying Triassic strata were 87 86 87 86 3) The average Sr/ Sr ratios of the reef dolomites are PRVWOLNHO\WREHWKHGRORPLWL]LQJÀXLGV,IWKH Sr/ Sr ratios 87 86 VLJQL¿FDQWO\IHUHQWGLIDQGWKH Sr/ 6UUDWLRVDUHVLJQL¿FDQWO\ RIWKHUHHIGRORPLWHVZHUHWDNHQDVWKHWUDFHURIGRORPLWL]LQJ 87 86 87 86 higher than the range of the Sr/ Sr ratios of the Permian fluids, the time intervals with the Sr/ Sr ratio more than Changhsingian seawater. The reef dolomites are mixed with the maximum value of the Permian Changhsingian seawater high concentrations of radiogenic strontium from external (0.7073) included the Early Permian and the Triassic based GLDJHQHWLFÀXLGV on the Sr isotope curve of the Permian-Triassic seawater 87 86 $OWKRXJKWKHFDOFXODWHGUHVXOWVRIWKHIOXLGPL[LQJ HL]HU9HWDO LHRQO\WKH Sr/ Sr ratios of Early PRGHOLQGLFDWHWKDWWKHGRORPLWL]LQJIOXLGVRIWKHUHHI Permian and Triassic seawater or marine-derived fluids 87 86 GRORPLWHVFRXOGEHPHWHRULFZDWHUDQG were consistent with the main range of Sr/ Sr ratios of VHDZDWHUWKHORZ0QFRQWHQWVUHODWLYHO\ORZ)HFRQWHQWV the Permian Changxing Formation reef dolomites (0.7075- )LJ +RZHYHUWKHORZHUSDUWRIWKH/RZHU dolomites did not support that there were large proportions of Permian strata is almost completely eroded, and the Lower 87 86 PHWHRULFZDWHULQWKHGRORPLWL]DWLRQSURFHVVDQGWKH Sr/ Sr 3HUPLDQ/LDQJVKDQ)RUPDWLRQ8SSHU7ULDVVLF;XMLDKH ratios which were close to those of coeval seawater also )RUPDWLRQDQGRWKHURYHUO\LQJVWUDWDDUHDOOFODVWLFURFNV did not support the possibility of the mixture of deep-burial ZLWKLQWKHEDVLQ2QO\WKH/RZHUHUPLDQ3L[LD4DQG0DRNRX FLUFXODWHGÀXLGVIURPFODVWLFURFNV IRUPDWLRQVDQG/RZHU0LGGOHU7LDVVLFVWUDWDDUHPDLQO\ +LJKWHPSHUDWXUHGHHSEXULDOFLUFXODWHGHDZDWHUVLWKZ ORZ0QDQG)HFRQWHQWVKLJK6UFRQWHQWVDQGKLJKį C Bureau of Sichuan Province, 1997), so the middle-late Early values from the dissolution of widely distributed Triassic 3HUPLDQDQG(DUO\0LGGOHULDVVLF7VHDZDWHURUWKHLUGHHSO\ evaporites during burial diagenetic processes (including EXULHGPDULQHGHULYHGIOXLGVFRXOGEHWKHGRORPLWL]LQJ dehydration of water-bearing evaporites) could have been the fluids of the reef dolomites. Large-scale potassium-rich GRORPLWL]LQJÀXLGVRIWKHUHHIGRORPLWHV and boron-rich subsurface brines have been found in the /RZHUULDVVLF7-LDOLQJMLDQJ)RUPDWLRQDQG0LGGOHULDVVLF7 Acknowledgements /HLNRXSR)RUPDWLRQZLWKLQWKHEDVLQZLWKWKHFKDUDFWHULVWLFV RIOHDFKLQJDQGPL[LQJDQGVLJQL¿FDQWPDULQHGHULYHGVRXUFH This study was supported by the National Natural (Lin et al, 2004), and the upper part of the underlying Lower Science Foundation (41172099, 40839908), Research Fund ULDVVLF)HL[LDQJXDQ7)RUPDWLRQZLWKLGHO\ZGLVWULEXWHGWKLFN IRUWKH'RFWRUDO3URJUDPRI+LJKHU(GXFDWLRQRI&KLQD evaporites (mainly consisting of gypsums) also provided 7KHDXWKRUVLVKZWRWKDQN)DQ0LQJ=KDQJ favorable conditions for a large amount of brine being HQWDRDQG/LX+DRQLDQIRUWKHLUKHOSLQWKH¿HOGZRUNV: enriched in the neighboring strata (Chen, 2005; Zheng et al, 2011). Therefore, the high temperature deep-burial circulated References VHDZDWHUZLWKORZQ0DQG)HFRQWHQWVKLJK6UFRQWHQWVDQG HL]HU$-HW0LVLDORORPLWL]DWLRQ'\DQG.9LVRWRSHUDWLJUDSK\WV$]P KLJKį C values from the dissolution of widely distributed Frequency, % PDULQHFDUERQDWHURFNVDQGHYDSRULWHV*HRORJLFDO 0LQHUDO &YDOXHVDQGKLJKKRPRJHQL]DWLRQWHPSHUDWXUHVRIWKH KLJKį WUXHZHUHWKHGRORPLWL]LQJÀXLGVFORVHWRWKHFRHYDOVHDZDWHU 48 Pet.Sci.(2013)10:38-49 WH&RU..R]XU+:DQG0RKWDW$JKDL3']KXOILDQWRORZHUPRVW Research. 2001. 112(3-4): 303-329 ULDVVLF7 į C record at the Permian/Triassic boundary section at LR]DPDQL.D%G7KH'RUDJGRORPLWL]DWLRQPRGHO²$SSOLFDWLRQWRW KH 6KDKUH]D&HQWUDO,UDQ+DOOHVFKHV-DKUEXFKIU*HRZLVVHQVFKDIW HQ 0LGGOH2UGRYLFLDQLVFRQVLQRI:-RXUQDORI6HGLPHQWDU\3HWURORJ B Beiheft. 2004. 18: 73-78 1973. 43(4): 965-984 HWDOWURQWLXPLVRWRSH6HYR%UXFNVFKHQ3WH&:.R]XU+.RU OXWLRQRI Late Permian and Triassic seawater. Geochimica et Cosmochimica strontium to studies of carbonate diagenesis. 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Earth Science Frontiers. 2005b. 12(3): 179-185 (in Chinese) &RQWULEXWLRQVWR*HRORJ\DQG0LQHUDO5HVRXUFHV5HVHDUFK <6D00RX&/DQ74<HWDO5HHIEDQNIHDWXUHVRI3HUPLDQ 24(2): 160-165 (in Chinese) Changxing Formation and Triassic Feixianguan Formation in the :::: 7 $UHD6LFKXDQ3URYLQFH6RXWK&KLQDDQGFRQVWUDLQW'D[LDQ;XDQKDQ PDULQHURFNW\SHVIRUSUHVHUYDWLRQRIFRHYDOVHDZDWHULQIRUPDWL RQ for the reservoirs of natural gas. Earth Science Frontiers. 2007b. LQWKH+XD\LQJ0RXQWDLQRI(DVWHUQ6LFKXDQ$FWD3HWURORJLFDHW 14(1): 182-192 (in Chinese) LQ&KLQHVH 0LQHUDORJLFD KHOD0F+*&RQFHSWVDQGPRGHOVRIGRORPLWL]DWLRQ$FULWLFDO QJ6-+XD4LQJ+53HL&5HWDO6WURQWLXPFRQFHQWUDWLRQ LVRWRSH UHDSSUDLVDO,Q%UDLWKZDLWH&-55L]]L*DQG'DUNH*7KH FRPSRVLWLRQDQGGRORPLWL]DWLRQÀXLGVLQWKHHL[LDQJXDQ))RUPDWL RQ geometry and petrogenesis of dolomite hydrocarbon reservoirs. $FWD3HWURORJLFD6LQLFDULDVVLF(DVWHUQ6LFKXDQRI&KLQD7RI London: Geological Society of London Special Publication 235. 22(8): 2123-2132 (in Chinese) 2004. 7-63 QJ6-XD+RQJ7+3/LX/+HWDO3HWURJUDSK\JHRFKHPLVWU\ DQG &/0RX0D<DQJ6:5+HWDO'LDJHQHVLVRIWKH8SSHU3HUPLDQ GRORPLWL]DWLRQPHFKDQLVPVRI)HL[LDQJXDQGRORPLWHVLQULDVVLF7 Panlongdong organic reefs in Northeastern Sichuan. Sedimentary 1(6LFKXDQ&KLQD$FWD3HWURORJLFD6LQLFD Geology and Tethyan Geology. 2005. 25(1-2): 198-202 (in Chinese) 2372 (in Chinese) &/XR0DQJ:5+DQ74<HWDO7KHOLWKRIDFLHVSDOHRJUDSK\ RI ]'DW.$(EHUOL*36ZDUW3.HWDOHFWRQLFK\GURWKHUPDO 7 WKHQRUWKHUQJLQPDUDQJW]HRI%ORFN<LQ&KDQJ[LQJ3KDVHRI/DWH brecciation associated with calcite precipitation and permeability Permian. Earth Science Frontiers. 2011. 18(4): 1-8 (in Chinese) GHVWUXFWLRQLQ0LVVLVVLSSLDQFDUERQDWHUHVHUYRLUV0RQWDQDDQG PHU0DO35DQG(GPRQG-07KHVWURQWLXPLVRWRSHEXGJHWRIWKH $$3*%XOOHWLQ\RPLQJ: modern ocean. Earth and Planetary Science Letters. 1989. 92(1): 11- WH&UR.DQG.R]XU+:&DUERQLVRWRSHVWUDWLJUDSK\DFURVVWKH 3HUPLDQ7ULDVVLFERXQGDU\$UHYLHZ-RXUQDORI$VLDQ(DUWK -=LQ40HQJ44DQG)X;'7KUHHK\GURFDUERQJHQHUDWLRQDQG Sciences. 2010. 39(4): 215-235 DFFXPXODWLRQSURFHVVHVRIPDULQHFDUERQDWHURFNVLQ1RUWKHDVWHU Q 87 86 :7 Sr/ Sr record of Permian seawater. Sichuan Basin, China. Petroleum Exploration and Development. 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Geology. 1990. 18(5): 387-391 system for dolostone in Feixianguan Formation of Northeast Sichuan. 87 86 13 18 ]HU-HL$OD9'$]P\.HWDO Sr/ 6Uį &DQGį O evolution of Earth Science—Journal of China University of Geosciences. 2011. &KHPLFDO*HRORJ\3KDQHUR]RLFVHDZDWHU 36(4): 659-669 (in Chinese) J5DQ:+0RX&/DQ74<HWDO'LDJHQHWLFSURFHVVHVDQG QJ5&=KH+X=*)HQJ4HW3DO*HQHVLVRIGRORPLWHUHVHUY RLURI environments of the reef shoal dolostones from the Changxing the Changxing Formation of Upper Permian, Northeast Sichuan )RUPDWLRQLQWKH'D[LDQ;XDQKDQUHJLRQ1RUWKHDVWHUQ6LFKXDQ %DVLQ-RXUQDORI0LQHUDORJ\DQG3HWURORJ\ LQ Sedimentary Geology and Tethyan Geology. 2006. 26(1): 30-36 (in Chinese) Chinese) J<*DQ+:RQJ+7;LD0/HWDO([SORUDWLRQRIUHHIEDQNJDV (Edited by Hao Jie)
Petroleum Science – Springer Journals
Published: Feb 7, 2013
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