Permian sequence stratigraphy of shallow water basin in Tarim Basin

Global Geology, 14(4): 221-230(2011)doi;10. 3969/j. issn. 1673-9736. 2011. 04.02Article ID: 1673-9736(2011 )040221-10Permian sequence stratigraphy of shallow water basinin Tarim BasinLIU Chensheng',2，GUO Jianhual!2 and YIN Qiong',2I. Key Laboralory of Nonferrous Meallogentic Prognosis，Ministry of Education, Central Souh University, Changsha 410083, China;2. School of Geosciences and Info-physics , Central South University, Changsha 410083, ChinaAbstract: Based on analysis of drilling, logging and field profile data, six sequence boundaries in Permian areidentified in Bachu and Tazhong regions of Tarim Basin. All sequence boundaries are of type I sequence bound-aries, and are characterized by down cut. According to the six sequence boundaries, the Permian in this areacan be divided into 5 third-order sequences, and all the sequences correspond with classic sequence model ofVail. Sequence Psq4 indicates lake transgressive system tract (TST) and highstand system tract ( HST). Se-quences Psq1，Psq2, Psq3, Psq5 indicate low stand system tract ( LST) , transgressive system tract and high-stand system tract. LST is deposited by incised channel ifilling with features of fluvial facies. TST is depositedby shore shallw lake and semi -deep lake. HST is deposited by semi -deep lake ，shore-shallow lake and delta.In addition, volcanic rocks are present on the top part of HST in sequence Psq3. Incised channel inilling anddeltaice deposits were mainly distributed on westerm slope of Tadong uplift.Key words: Tarim Basin; Permian; sequence stratigraphy ; incised channel in6lling; deltaic depositing and inner framework of sequences.1 IntroductionTarim Basin is a typical shallow basin in PermianThe reasons for formation of shallow basins arewhich is also the most important period for transfor-drought climate and flat lake bottom. Because waterming of Tarim Basin from marine to continental facies.body of shallow basin is shallow , basin sediments areMarine carbonates deposited in west and southwesterndifferent from others in type, mainly including shore-parts of the basin in Early Permian. During later Earlyshallow lake, semi-deep lake and delta, rare deepPermian, regression happened from east to west( He etlake. Due to drought climate , shallw water body andal, 2005), and fllowed by deposition with craton-lttle provenance， lacustrine fan and wedge-shapeinner-depression continental facies. During Middlebody deposited in lowstand system tract don not devel-Permian, lots of volcanic rocks are present in the ba-oped. Major sediment is fine grain sediment, such assin because of close of South Tianshan Ocean and col-mudstone which intercalates with thin lake carbonatelision between Tianshuihai block ( Qaidam block) andin the basin. Coarse grain sediment often distributesTarim block (Fig. 1). Most area of the basin is uplif-around basin margin. Because shallow basin has spe-ted with continental deposition during Late Permiancial sedimentary environment, there are particularities(Ji中国煤化工Ioreland basin onlyin sequence boundaries recognizing, sequence divid-distri!YHC N M H Greas, where devel-Received 22 June 2011, accepted 20 July 2011222liwC.S., GuoJ.H. and Yin Q.oped fluvial and lacustrine facies. Comprehensive re-derstanding of reservoir types and distribution fea-search of Permian sequence is beneficial for better un-UrumchiJunggar PlateNt-haptiashagsag-ntianshan block.PAKS0--KurleHgishichang sction 10wuping， Tazhong areTadong uplft arca"Makeleinkagblock1Qaidam Plate'Hertian\●1312口subduction belt口mainfault CV ieland- are beltactive belt of ancient landthe studied arca国basement rocks of Tarim Plateblock boundaryFig.1 Location of study area2 Sedimentary characteristic3 Sequence boundary recognitionTarim Basin can be divided into four blocks viz:The main evidences for recognizing sequenceSouthwestern block, Keping block , Taklimakan blockboundaries include:①absence of strata; ❷change ofand Nantianshan block. Bachu and Tazhong are theparasequence superimposing styles; ③sharp changesfocused study areas in this paper are located in Takli-of facies;④erosion and infll of fluvial;⑤inner re-makan block, where the Permian strala are divided in-flection features of seismic data. According to thoseto Nanzha Formation, lower clastic-rock member, vol-evidences, six sequence boundaries can be recognizedcanic member and upper clastic-rock member. Thein Permian in this area. 'These boundaries from lowerNanzha Formation deposited by micrite and grainedto upper strala are BI, B2, B3, B4, B5 and B6.limeslone is only distributed al Bachu and southwest-boundary B1 : under which develops carbonateem Tarim Basin ( Wang et al., 2006). Thickness ofrock deposited in Carboniferous, locates in the bottormNanzha Formation becomes thinning from southwest toof Permian. Paleo-weathering crust, inilling of ero-Bachu area, and the strata are absent in Tazhong areaded channel and tide flat facies are present over the(Ding el al, 1998). light-gray and brown red thicksequence boundary. Facies sharply developed uppermudstone intercalated with sandstone and limestone ,and lower boundary BI change , thus, boundary BI isis the major deposition in the lower clastic-rock mem-ast中国煤化Iygena zone， Trit-ber and upper clastic -rock member. Clastic-rock faci-icites:IHCNMHGare normally pres-es include lacustrine, fluvial and delta (Jiang et al.,ent beuween rerman au Luarouerous are absenl ac-2003) .cording to paleontological data( Xiong, 1997; ZhangPermian sequence stratigraphy of shallow water basin in Tarim Basin223el al, 2006). The reason is that the strata were up-conformity surface in Qimugen-Sangzhuhe section inlifted after Carboniferous deposition and then eroded.Southwesterm block (Xi et al. , 2002). Platform car-Thus, the boundary B1 is a type I sequence bounda-bonate of Keziliqiman Formation ( corresponding tory, it corresponds to T rllecting surface according toNanzha Formation) deposits under boundary B2, butseismic data, and the reflecting surface is a strong re-tide , fluvial and shore facies of Qipan Formation ( orflecting crest in Bachu, Tazhong and basin margin ar-Pusige Formation) deposits upper boundary B2. Flu-eas, and this reflecting surface can be tracked all overvial inilling sediment superimposes on Carboniferousthe basin.strata, thus, the boundary B2 is a type I sequenceThe boundary B2 is located between Nanzha For-boundary (Fig.2).mation and lower clastic-rock member, and is an un-Third orderStrataFacies divisionGR CurvescqucnceLithological20406080section占旁|SP Curve互|兰40506070名|g|4000TST4010Psq2Bank51020.Fuvial LST5|030Riverbed|答4040名|马|夏复喜S|文嚣Mudstone圈Siuysmudstone巨ilstome Noeratre 罾Pobsrorsandstone需SanpySequenceTransgressiveLSTLowerstandErosion臣习Limestone[ B2boundaryTSTsystcm traetTsystem tract surfaceFig.2 Characteristics of sequence boundary B2 of Permian in Well J4The boundary B3 is located in lower clastic -rockpresent in well block J2-J1-J3. In addition， thismember，under which developing fine sandstone de-boundary can also be tracked in Sishichang section inposited in delta and siltstone deposited in lacusrine fa-nort中国煤化The boundary alsocies. At the Upper boundary ifilling of incised chan-show:YHCN M H Ghe bounday B3 isnel is developed. The incised surface is very wella type 1 sequence boundary.224Liu C.s., GuoJ. H. and Yin Q.Third orderStrataFaciessequenceGR CurveLithological重复号:2scction后。TSTPsq41990。|虽雷|点25|519208|1940HST| Psq3|Mudstone国Silty^ Voleanic uff HSTHighstandTr ansgressivemudstonesystem tractL TST Jsystem tractsystem tractFig.3 Characteristics of sequence boundary B4 of Permian in Well J3The boundary B4 is located on the top of volcanierock member, and mudstone deposited in semi-lacus-010 20m> NWtrine present above the boundary (Fig. 3), which in-dicates that lake water invades into study area rapidlyafter volcanic eruption ，and a large scale of transgres-110*∠60°sion had happened in the basin. Erosion and fluvial(Upper clastie.rock Member) L30°∠30 (Volcanie rock Member)deposition don't present inner basin, but the eoded.......凹surface and unconformity contact develops well on theSandstonePebbly sandstone MudstoneVolcanic rkmargin of the basin (Kang et al, 1994)(Fig. 4).Thus the boundary is also a type I sequence boundary.Tig.4 Sequence boundary B4 in Kuche depressionThe boundary B5 is located in upper clastic-rock中国煤化工member. Inflling of incised channel is well present aprMHCNMHGInilling of in-bove the boundary. Sand- mudstone deposited in deltacised cnannel 1s mainly developed in southeast ofor mudstone is deposited in semilake to deep-lakeTazhong area, and this kind of deposition is not presentPermian sequence stratigraphy of shallow water basin in Tarim Basin225'GR CurveFaciesThird orderStratasequence35506580LithologicalsectionSP Curve分引|之20 40 60另品2820TST283028402850Psq5|5|2860 :管8 |LST.2870 ;Fuvial...2880289029002910Delta HSTPsq4占图Mudstone图Silty景A Muddy 国Pebbly 原用Pebbly moderatem udstonesand stonesandstone.1 LowerstandTransgressiveHighstandSequenceJ system tractsystem tractHSTsystem trac|BSboundary四Erosion surfaceFig.5 Sequences boundary features of B5 in well J6 in Tarim basinin Manjiae , Bachu and Southwestern areas. Thus, thewvere widely devel-sequence boundary B5 is also a type I sequenceoped中国煤化工pper clastic-rockboundary.membJYHC N M H G boundary. DeltaB6 boundary is located on the top of upper clas-developed in highstand system tract is mostly absent inLiuC.S., GuoJ. H. and Yin Q.upper part of upper clastic-rock member due to ero-wells J9, J4 and J10 in westem slope of Tadong up-sion. B6 sequence boundary . corresponds with To 5lift. In addition, LST also distributes around the wellssurface in seismic sections, and this surface is aJ11 and J12. TST, which is distributed in all over thestrong-mediate relecting wave crest. In addition, thisstudied area with mean thickness of 58.3 m, whichsurface is also a truncating surface， which can beare the mainly deposits of semi-deep lake and shore-tracked all over the study area.shallow lake. The major facies of HST include of thesemi- -deep lake ，shore-shallow lake , and rarely devel-4 Inner characteristics of sequencesoping delta. The average thickness of HST is 79.5 m.Five third-order sequences can be divided in Per-In addition, thin micrite intercalates in mudstone de-mian strata in Tarim Basin according to above the sixposited in HST. This kind of lake limestone developedsequence boundaries. These sequences are Psq1 ，during flling stage of lake level with dry climate andPsq2, Psq3, Psq4 and Psq5 in ascending order.rare provenance( Sha, 2001; Zhang, 2000; Liang et4.1 Psq1 sequenceal. , 2007). The deposition of lake limestone denotesPsq1 sequence consists of the whole Nanza for-end of the Para-sequence.mation; it is located between BI and B2. The se-4. 3 Psq3 sequencequence comprises lowstand system tract ( LST ),Psq3 sequence comprises the upper part of lowertransgressive system tract ( TST) and high stand sys-clastic-rock member and volcanic rock member, loca-tem tract ( HST). The sequence distributes aroundted between B3 and B4. Psq3 can be divided intoSouthwesterm block and Bachu area. Its biggest thick-LST, TST and HST. Sediment of LST comprises of in-ness is located at the southwest of the basin, and be-flling deposit of incised channel with thickness of 39comes thinner eastward and northward. The sequencem. The facies of TST comprises of semi-deep lake,is absent in Tazhong area. The LST distributes mainlywhich mainly deposit mudstone with thickness of 53.6Bachu and Keping areas. The sediments of LST main-m. HST comprises the upper part of lower clastic- rockly consists of pebbly fine sandstone and siltstone inter-member and volcanic rock member. The volcanicbedded with purplish red mudstone deposited in in-rocks erupted from fracture in a form of efusion( Chencised channel, in wells J3 and J5. The thickness ofetal, 2004; Chen et al, 1998). Effusive facies,LST ranges from 0 to43 m. LST is not developed inwhich has a linear magma source, are different fromthe Southwesterm block. Facies of TST consist of car-central type eruption, and effusive eruption can form abonate platform, platform margin and bioherm inter-volcanic plain rather than a volcanic cone. Statisticalbedded with thin clastic rock deposited in tidal flat.thickness of volcanic rocks indicates that volcanicFacies of HST mainly comprises tidal flat, which de-rocks is dstributed all over Bachu and Tazhong areaposits clastic rock intercalated with thin carbonate.except western Bachu area. The maximum thickness4.2 Psq2 sequenceamounts to 552 m ( Well J12), average thickness ofPsq2 sequence comprises lower part of lower323.2 m.clastic-rock member, and is located between B2 andLots of clastic rocks intercalate between outcropsB3. Psq2 consists of LST, TST and HST. This se-of volcanic rocks. The clastic rocks mainly comprisequence is well present in the studied area exceptof thick pebbly sandstone with poor sorting and largesoutheasterm and northern Tazhong area and the Wellscales of trough cross bedding. This kind of clasticJ7 to well J8 area. The sediments of IST are consis-0C |中国煤化工acumulation duringting mainly of pebble， pebbly sandstone ，moderate:DHCNMHgraually. Thus, thesandstone and fine sandstone, deposited in incisedvoleamue ruck aurt aucaeu 1iw nST in this paper. Irchannel. The LST is mainly distributed around theaddition，the collision between plates not onlyPermian sequence straigraphy of shallow water basin in Tarim Basin227strengthens volcanic activity but also uplifts the basin,Qaidam plate with Tarim plate took place. Thus, theand therefore, the accommodation space further de-Tarim plate was uplifted ，which caused upper strata increases.Carboniferous erosion， and forms the first sequence4.4 Psq4 sequenceboundary in B1. During the Early Permian, transgres-This sequence is located between B4 and B5,sion takes place in Tarim Basin, and Psql sequenceand can be divided into TST and HST. Because of in-s deposited on the top of unconformity surface.flling of gap by previous sediment and volcanicTransgression extent of Psq1 is local, and mainly dis-rocks, the terrain becomes flat during the depositiontributed in southwestern and southern Bachu areaof Upper Permian. After volcanic eruption, a largethrough correlation of wells. After deposition ofscale of transgression took place and a set of mudstoneNanzha Formation, Tarim plate is uplifted again be-deposited in semi-deep lake, shore-shallow lake oncause of tectonic activity, and sea water retreats fromthe top of volcanic rock. TST is distributed all overstudy area rapidly. The strata in basin margin were e-the studied area, and the maximum thickness of 249roded because of exposure, forming an eroded se-m is located in Bachu area ( Well J1)，average thick-quence boundary B2.ness of 110 m. HST is distributed all over the studiedLST of Psq2 sequence is mainly distributed onarea with maximum thickness of 377.5 m ( Wellwesterm slope of Tadong uplift based on correlation ofJ13)，and average thickness of 176m. Sediments ofwells, and TST and HST are mainly distibuted inHST mainly include dark mudstone deposited in semi-west of Tazhong and Bachu areas. Psq2 sequence on-deep lake and shore-shallow lake， and fine sand-lap western slope of Tadong uplift in east of study are-stone, which intercalates with celadon and purplisha, which is shown in seismice section. Extent of Psq3red mudstone，deposited in delta.sequence is wider than that of Psq1 and Psq2, and4.5 Psq5 sequencedistribution of Psq3 sequence is stable in the study ar.This sequence comprises of LST, TST and HST,ea. LST of Psq3 sequence is mainly ditributed onlocated between B5 and B6. Because the sequence iswestermn slope of Tadong uplift. TST and HST are dis-located above B6 boundary, it significantly erodestributed all over the study area except western part ofHST of Psq5. Thus, the upper part of HST of Psq5 iswells J13 - J14 - J12. Psq4 sequence is deposited onpartly or completely absent. The sediments of LSTthe basic of previous sediment flling sag, and the se-consist of variegation and moderate to thick pebblyquence can be divided into LST, TST and HST. TSTcoarse sandstone intercalated with purplish red thin toand HST stably ditributed all over the study area.moderate mudstone with average thickness of 43.6 m,Especially, deltas are significantly present in HST ofwhich deposits in incised channels. Facies of TST in-Psq4 , and mainly distributed on the western slope ofclude shore-shallow lake and semi-deep lake, and av-Tadong uplift and south of Bachu area. LST of Psq5erage thickness of sediment in TST amounts to 80. 1sequence is mainly distributes on westemn slope of Ta-m. Facies of HST comprise semi -deep lake and delta,dong uplift. TST and HST of Psq5 sequence is distribl-and sediments deposited in those facies, with averageuted all over the study area, and on lap the westermthickness 177. 8 m, mainly include purplish red mud-slope of Tadong uplift eastward ( Fig.6a).stone intercalated with siltstone and calcareous mud-On the whole which are distributed in east part ofstone.the studied area, on lap the western slope of Tadong5Distribution feature of every se-pli |中国煤化工nces developing inquence:TYHCNMHG(Fig. 6b). Froms of TST and HSTAfter deposition of Carboniferous，the collision ofbecomes thicker ，but the thickness of LST becomes228Liu C.S., GuoJ. H. and Yin Q.13JJ16(a)GR MSFLSP RTToS | ST 20-180 50000-60-120 0.1-50000-4.0-900 0.1-5000-25.50 0.1-100生12001399270t 2800HST130018002800Psq5T400290| TST1500专现2000宝9 300003100170022003200Psq423003300TST240022000Tadong Uplift2100200Psq327005 230Psq2PsqLS2800J8(b)ToS ST| -300-0 0.5-100030-70 0.1-100-150-35 0.1-100-40-90 0 1-500045003400+20046003500发30000孔28004700工270030000Psq4 HST4900客3800里3300400, 32003900330[ ToS]ST][ LSTThird OrderSystemLowerstandTransgressiveHighstandSequenceTractSystem TractDeltaFig.6 Comparison of sequences for east.west cross section (a) and north-south cosection (b)thinner ( Fig.6a). Fluvial facies developed in IST6Controlling factors of sequenceand delta facies developed in HST is mainly distribu-ted on the westerm slope of Tadong uplift. Fluvial andSequence developed in shallow water lacustrinedelta rarely developed in the studied area which wasbasin中国煤化Iactivity, climate,mainly deposited at shore- shallow lake and semi-deepprove|YHCN M H Gand terrain. Be-lake.cause the easterm Nantianshan Ocean uplifted and be-Permian sequence stratigraphy of shallow water basin in Tarim Basin229came terrestrial deposition after Carboniferous , easterndark mudstone. The main facies of HST are shore-Bachu and Tazhong areas were also uplifted and be-shallow lake ，and senmi-deep lake distributes loally.came trrestrial land which was subjected to erosion,Delta or lluvial fans of HST only distribute on basinand formed sequence boundary BI. The Followingmargin, and size of delta is small because of shallowtectonics activities eade the lake level change morewater and small accommodation space( Wang, 2008 ).frequently, which contolled forming of sequences in7 Conclusionsthe studied area. In addition, Tarim Basin is afectedby subduction of Northern Tianshan Ocean during(1) Six sequence boundaries in permian can bemiddle period of Permian, so lots of volcanic rocks arerecognized in Permian， Tarim Basin， and thosedeveloped in the studied area(Chen et al, 1998).boundaries are all type I sequence boundary. Five se-Volcanic rocks can infll sag, and make the studiedquences can be divided according to the six sequencearea flat, so lake break belt is not present in the studyboundaries.area, but only locally distributed on the basin margin(2) Psq4 sequence develops TST and HST ex-and iorning type I sequence boundary.cept LST; while Psql, Psq2, Psq3, Psq5 sequencesClimate was also an important factor that afcteddevelop LST, TST and HST. Fluvial facies depositedsequence forming in Permian. The climate in Permianin LST and delta deposited in HST is distributedbelonged to subtropics drought zone ( Ouyang et al,mainly on the westerm slope of Tadong uplift. Shore-2004)，and drought climate made weathering speedshallow and semi-deep lakes are mainly distributed atand weathering quantity decrease, which limited prov-the inner basin, which rarely develops fluvial and del-enance supply to basin area, and had indirect effecta.on change of lake level. In addition, drought climate(3) Carbonate platforms are mainly developed inalso limited transporting distance of coarse grain, s(HST of Psq1 sequence, and clastic tidal flat facies de-mudstone and thin lake carbonalte rock developed aposits are mainly in HST. LST of Psq2, Psq3, Psq5far distance from source area.sequences is deposited by inilling of incised chan-Tazhong and Bachu areas were distributed mostlynels，and TST， HST are deposited by semi-deepin central part of the basin during deposition of Permi-lake, shore sallw lake and delta.Terrains were mostly present around the basinReferencesthan at the center of the basin, showing the pattermn ofopening in southwestem basin. According to seismicChen Y Q, Li B G.2004. Casfication and correlation of Per-data, there was a break belt developed in mid-east ofmian volcanic rocks in Mid-Tarim area. Joumal of ChinaTazhong area ( that is westerm slope of Tadong uplift) ,University of Petroleum, 28(6): 6-10. ( in Chinese)and this break belt created favorable condition forChenH L, YangS F, Jia CZ, et al. 1998. Confirmation offorming in sequence boundary type I, which explainsPermian intermediate-Acid igneous rock zone and a newthat there existed channels on westerm slope of Tadongunderstanding of tectonic evolution in the northerm part ofthe Tarim Basin. Acta Mineralogica Sinica, 18(3): 370-uplift and fluvial deposition was present.76. ( in Chinese with English abstract)Above all, because lacustrine fan and wedge-DingY P, Yang P.1998. 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