Transient fluid flow in the Binbei district of the Songliao Basin, China： Evidence from apatite fission track thermochronology

314 11： ： ! ! !兰：DOI l0.1007/s12182-013-0280-7Transient fluid flow in the Binbei district ofthe Songliao Basin，C hina'.Evidence fromapatite fission track thermochronologyXiang Caifu ，貅.Martin Daniik3 and Feng ZihuiState Key Laboratory for Petroleum Resource and Prospecting，China University ofPetroleum，Beijing 102249，ChinaColege ofGeosciences，China University ofPetroleum ，Beijing 102249，ChinaDepartment ofEah&Oceanic Sciences，University ofWaikato，Hamilton 3105，New ZealandProspecting and Exploration Institute ofDaqing Oil Field，Heilongjiang 163458，China◎China University ofPetroleum(Beijing)and Springer-Verlag Berlin Heidelberg 2013Abstract：The Songliao Basin is famous for the Daqing Oilfield.the biggest in China. However，noeconomic hydrocarbon reservoir has been found in the northeastern Binbei district. Its thermal history，which 1s of great importance for hydrocarbon generation and migration， is studied with apatite fissiontrack(AFT)thermochronology.Samples with depositional ages of the late Cretaceous f～1 08-73 Ma1 areanalyzed.The AFT ages of the samples from reservoir rock(depositional age>76.1 Ma1 faU betweenthe late Cretaceous(725 Ma)and the early Eocene(4 1 4-3 Ma)period，indicating their total annealingafter deposition.In contrast，two samples from the main seals of the Qingshankou(depositional age>89.3 Ma)and the Nenjiang Formation fdepositional age>73.0 Ma)are not annealed or partialyannealed(AFT ages of 979 Ma and 704-4 Ma，respectively).Because the maximum burial temperature(<90。C)evidenced by low vitrinite reflectance <0.7)is not high enough to account for the AFT totalannealing(1l 0-1 20。C)，the transient therm a1 effect arising from the syntectonic fluid flow between thelate Cretaceous and the early Eocene is proposed.Transient thermal effects from fluid flow explains theindicated temperature discrepancies between the AFT thermometer and the R thermometer because thetransient thermal effect from the fluid flow with a temperature high enough f 1l 0.1 20。C1 to anneal theAFT thermometer does not last long enough(1 0 .1 0 yrs.)for an enhancement of the R (minimum 1 0 -l 0 yrs.under the same temperature).This indicates that dating thermal efect from fluid flow might bea new means to reconstruct the tectonic history.It also answers why the samples from the main seals arenot an ealed because the seals will prohibit fluid flow and supply good thermalinsulation.The large.scalefluid flow in the Binbei district calls for a new idea to direct the hyrdrocarbon exploration. Key words：Apatite fission track，vitrinite reflectance，transient fluid flow，Binbei district，SongliaoBasin1 Intr0ducti0nThe therm a1 history of sedimentary basins reflects theirtectonic evolution.It controls source rock maturation，hydrocarbon generation，migration and accumulation，and also influences the late.stage variation of trappedhydrocarbons(Lutz and Omar，1991：Hansen et al，2001)。

Apatite fission track rAFT)analysis is a method commonlyused to trace sedimentary provenance and to quantitativelyconstrain the therma1 history of sedimentary basins(Milerand Duddy，l989；Resak et a1 2010：Danigik et al，2010)。

This study is intended to reconstruct the therm al historyCoresponding author.email：xcf###cup.edu.caReceived November 6，20 1 1of the Binbei district of the Songliao Basin.There are severalextraordinary features that make the thermal history aninteresting area to study.The most obvious feature is fromthe hydrocarbon exploration.The Binbei district accounts for1/3 area of the whole Songliao Basin，but the hydrocarbonexploration here has failed to make any signifcant progress inthe past fifty years(Yang et al，l985：Wang et al，2006b；Linet a1.2009).The main source rocks of the Qingshankou andthe Neniiang formations have been discovered in more than1.000 exploration wells and proved to be widely distributedin the whole district(Yang et al，1985；Yang，1985；Wanget a1.2006b；Lu et a1.2009)Their thermal evolution isthe only question to be further specifed.Limited researchusing vitrinite reflectance(R )and clay minerals indicatethat the highest temperature(75 93。C1 occurred at the lateCretaceous f～65 M a1 and then cooled in the Cenozoic due toPet.Sci.(2013)10：314·326 3l5tectonic inversion and denudation(Cai and Fu，2005).Thethermal gradient in the Cretaceous(4.5-5.7。C/100 m)washigher than that in the Cenozoic(3.7.4.5。C/100 m)(Renet a1.2001：Cai and Fu，2005；Su et al，2006).HowevetheBinbei district should be further considered because mostof the thermal data sets are from the north of the centraldepression zone(CDZ)。

The Binbei district underwent tectonic uplifting anddenudation during the inversion stage of the basin.But veryfew studies have discussed its specific tectonic evolutionaryhistory mainly due to the shortage of sedimentary recordsf～500 m1，which makes it impossible to rebuild the longevolutionary history f65.0 Ma)by traditional methods(Luet a1.2000；Yu et a1.2005).Whether or not it has undergonethe same tectonic evolutionary history as the southern partofthe basin is a question to be further answered(Xiang et al，2007).Due to the signifcance arising from both hydrocarbonexploration and tectonic evolution，three boreholes weretargeted and sedimentary samples of late Cretaceous fromthe depth shallower than the present-day partial annealingzone(PAZ)were collected.The samples were analyzed bythe AFT method and the results combined with availableR data were used to quantify its thermal history and thecontrolling factors.The results allowed an identification ofthe theHTlal efect from fluid flow and provided new insightsfor hydrocarbon exploration and tectonic evolution。

2 Geologic settingThe Songliao Basin is one of the biggest lacustrinebasins(an area of 26x 1 04 km 、in the world.Exploration anddevelopment of the Daqing Oilfield in the central depressionof the basin have played an important role in Chinaspetroleum industry and in the advancement of non-marinepetroleum geologic theories(Yang et al，1985；Yang，1985；Zhao et a1.20 1 0).The Binbei district refers to the vast area ofthe Songliao Basin that lies to the north of the northwestwardtrending Binzhou fault along the railway from Harbin toQiqihar rFig.1 1.It is characterized by tectonic units of theuplifting zones and/or slope zones surrounding the northempart of the CDZ(Lu et al，2000).Abundant hydrocarbonshave been found in the south.but only limited hydrocarbonshave been found in this district。

Fig.1 Geological and tectonic characteristics of the Binbei district，SongliaoBasin.1：Boundary of the basin；2：Fault；3：Tectonic boundaries(See Yang et alf1985)for details)；4：Wels that have been sampled；5：The profile shown in Fig.2The flling sequence of the district which is identical withthat of the Songliao Basin.can be classified into Jurassicrifting.early Cretaceous subsidence and late Cretaceous-Cenozoic inversion(Yang et al。1985；Feng et al，2010a).Thefilling sequence and the tectonic feature can be best ilustratedby a typical northeast profile from the central depression zone(CDZ)to the northern plunge zone(NPZ1 fFig.2)。

The synrift sequence(Jurassic.early Cretaceous、consistsmostly of thick coa1.bearing 1acustrine and volcanic rocks thatare controiled by syn.depositional faults(Fig.21.It has beenextensively studied due to the discovery of the big Oingshengas reservoir(Feng，2008；Zhao et al，2008).The post-rifling sequence(1ate Cretaceous)is made up of the upperCretaceous Qingshankou， ，aoia and Nenjiang Formations，all of which are mainly 1acus仃ine.fluvial mudstone.oil shaleand sandstone according to both the numerous exolorationwells and the China Cretaceous Continenta1 ScientificDriling Songke.I borehole(Wu et al 2008；Cheng et a1。

2009；Wang et al，2009).The Qingshankou and the NenjiangFormations provide the most important source rocks andseals in the basin.The Yaojia Formation provides the mostprevailing reservoir rocks for the Daqing Oilfield(Yang et al，3l6 Pet.Sci.(2013)10：314-326OE-2 C ∞工 -4Fig-2 Representative NE-trending cross-section from the CDZ to the NPZ ilustrating the filing sequence and the tectonicframework.The post-Cretaceous sedimentary record is thin(<500 m)which makes it hard to reconstruct the tectonicevolutionary history by traditional methods1985：Hou et al，2004；Feng et a1.2010a)。

The tectonic inversion sequence rlate Cretaceous-Cenozoic)is characterized by the moderate-total inversionand denudation of the NPZ and the northeast uplifted zonefNUZ)and by the subsidence and deposition in the westslope zone(wsz1 and the CDZ(Fig.2 and Fig.31.It isrelated to the westward compression from the east.which ledto a quick shrinkage of the lacustrine basin and a westwardmigration of the subsidence and depositional centers(Yang etal，1985：Feng et al，2010a).The widely distributed inversionstructures，including the Daqing anticline，were formed at thisperiod(Song，1997；Xiang et al。20101.Structures in the NUZand the CDZ are totally or moderately inverted，while thosein the WSZ are only mildly inverted(Song.1 997)。

3 Sampling and methodsSampling targets were selected according to their tectonicfeatures with the intention to reveal the tectonic and therm alevolution.The wels were selected on the basis of the extentof core segment availability in order to maximize the verticalsample distribution.As a result.ten sandstone samples werecollected from three different wels，two of which are fromthe NPZ that is obviously influenced by tectonic uplifting anddenudation.The samples cover the filling sequence from theNeni ang Formation to the Denglouku Formation with thedepositional ages ranging from 73 Ma to 94.3 Ma accordingto biostratigraphic and paleomagnetic study(Feng et al，2010a；Wu et al，2008)f1砒)le 11。

The well temperatures that were determined duringoil testing were used to constrain the burial temperature。

According to the result(Fig.41.the geothermal gradient is～ 4.5。C/100 m.Meteorological data from 10l observationstations over fifty years f1958 to 2007)show that the presentmean annual land surface temperature in the basin rangesfrom-5 to 10。C(Sun et al，2009；Ma et al，2009).Thus thesurface temperature is assumed to be 1 0。C(Zhou and Litke，1 999).The partial annealing zone(PAZ from Wagner et al，l 989)for the AFT thermometer is 60-1 20。C，dependingon mineral chemistry and cooling rate(Laslet et al，l 987；Ketcham et al，1 999)，which corresponds to a buria1 depth of1，300-2，700 m(Fig.4).The samples cover a depth range from～ 200 m to～l，100 m，which falls above the upper boundary ofthe PAZ and fits for the reconstruction of the thermal history(Table 1，Fig.4)。

stratum Dep ： 。 m 髁 Series Formation lSeg age 赘 言重 詈l (Ma)Fal Rise §Quaternary O ) 1 75Pliocene Taikang N2t o o o § 5 3Miocene Daan N d0 23 嚣 Eocene Yian E，y。蠹 - 61 1 盆Mingshui 2 器 65 3茎 Km.1 66 7 l；、 Sifangtai K s 。 -7 ； 68 7 旦5 / ∞ 696旦 Nenjiang 4 ÷ -/ 702H3 ：/ U K.n 70 6卫 2J 731761 SYaojia 23 ； 83 5K2Y 1 口85 0 旦ingshankot 23 89 3 GI<2qn 1～ g 94 3 雪d F § Quantou - - 1 Y 言 量 3。 I(2q 21 L99 6 ；车；： 。

- Denglouku 3o 量吾军 K d 2山 1 110 $Yingcheng 3 oK yc 4- 130jLShahezi 2K.sh Ⅲ 1 OO o 0 J 145Huoshiling J3h百 Carboniferous.Permian C-P圆 1 国 2 目 3 目 4 目 5 目 6Fig.3 Stratigraphic column and elements of the petroleum system inthe Songliao Basin.1：Volcanoclastic rocks；2：Conglomerate；3：Sandyconglomerate；4：Sandstone；5：Sandy shale；6：Shale；Dep.Age：theminimum depositional ages according to Wu et al(2008)and Feng et al(2010a1.Diferent reservoirs of Heidimiao(H)，Saertu(S)，Putaohua(P)，Gaotaizi(G)，Fuyu(F)，Yangdachengzi(Y)were developed and were bestdescribed in Feng et al(2010a)Pet.Sci.(2013)10：314-326 321Fig.7 Distribution of the vitrinite reflectance isolines from the Quantou Formation.a-b.Verticaldistribution of the vitrinite reflectance from the NPZ and the NUZ respectively.c.Horizontaldistribution of the vitrinite reflectance.The low R values of<0.5% from well Tongl and wellBai3 and the R。of～0.7% from well Dongl，which correspond to the highest burial temperature of6O-90。C.indicate that burial heating cannot account for the AFT total annealinggravimetric analyses，and by the thermal evolution ofsaturated/aromatic hydrocarbons and clay minerals(I/S)(Yanget a1.1985)。

Accordingly，the 1ow R values of<0.5% from well Tbn21and well Bai3 indicate a burial temperature<60。C and theR of～0.7% from well Dongl indicates a burial temperatureof 60.90。C.Since the vitrinite reflectance tends to record thepeak temperature fBaker and Goldstein，1 990)，it js clear thatthe above defined burial temperature cannot 1cad to the tota1annealing of the AFT thermometer.We have to rely on sometransient therlna1 efrect to explain the AFT annealing and thetemperature discrepancies between the AFT thermometer andtheRo。

5.2 Thermal annealinfrom fluid flowThermal effects from different scales of fluid flow havea far greater influence on the temperature field than thosefrom the 1ithosphere-scale events and have been widelydocumented(Blackwell and Steele.1 989：Ehlers.2005)。

Al1 the AFT ages from the samples that have been totallyannealed range between the late Cretaceous and the earlyEocene，during which time the Songliao Basin was under itstectonic inversion.Because almost all the tectonic movementsinvolve the movement of fluid.our consideration of thethermal ef.fect from fluid flow is iustified(Sibson.2000；2003；Oliver and Bons，200 1：Stanislavsky and Garven，2003；Barker et al，2006).To seek foundations for our explanation。

questions concerning the source，the driving mechanism andthe pathway systems of the fluid should be first answered。

The questionhow the thermal effects from fluid flow controlthe AFT annealing”is then discussed。

11 Source ofthe hot fluidHigh temperature fluids both from the CDZ and fromthe underlying rifling sequences existed.High temperaturefotination water and hydrocarbon fluid have been documentedby fluid inclusions from the CDZ.The time of their existenceand movement was betw een the late Cretaceous and the earlyEocene.High temperature fluids must have existed at theunderlying rifling sequence of the Binbei district as indicatedby>3 km burial depth(Fig.2、and the high(-45。C/km)geothermal gradient(Fig.4)。

2、DrivinmechanismThermal effects from the fluid account for the AFTannealing。thus the AFT ages record the time of the fluidflow.Because all the samples that have been totally annealedrecord the time from the late Cretaceous(oldest age of 724-5Ma)to the early Eocene r4 14-3 Ma).during which time thebasin underwent extensive inversion from east to west rXianget al，20 1 01，the fluid flow might have been syntectonic.It wastriggered or driven by tectonic faulting or compression andwas oflen advective fluid flow(Sibson，2000；2003；Oliverand Bons，200 1：Stanislavsky and Garven，2003；Barker etal，2006).There exist different mechanisms that could havedriven the fluid flow to the Binbei district during the mainstage of tectonic inversion。

One of the possible driving mechanisms is the fluid flowdriven by the tectonic compression along the faults.Faultsin the Binbei district are obvious as shown in Fig.2.Someof them have cut through the main seals of the QingshankouFormation.As the NW-strike faults tend to open duringthe main stage of the NW tectonic compression at the lateCretaceous(Sibson，2000；2003)，it was easy for the hot fluidto migrate from the underlying formation verticaly along thefaults and enter the reservoir to reset the AFT thermometers。

Thermal effects from the hot fluid along the faults canbe used for an easy explanation of the AFT an ealing of the322 Pet.Sci.(2013)10：314-326samples from well Tong 1 because it is situated on the vicinityof the NW faults.However.it is hard to account for thosesamples from the wel1 Dong 1 and wel Bai3 because there areno obvious faults from the seismic cross section.The othermechanism of large.scale lateral fluid flow is proposed。

0ne of the driving mechanisms for large.scale latera1 fluidflow is the combined efect from the abnormal high pressuresystems that developed in the CDZ and from the tectoniccompression.according to the model that has been well built(Sibson 2000；2003：Stanislavsky and Garven 2003).TheQijia-Gulong Depression is characterized by an abnormalhigh fluid pressure fthe pressure coeficient falls between1.2 and 1.6)，which is controlled by both the rapid burialprocesses and the hydrocarbon generation(Liu et al，2000；Wang et al，2002；Xiang et al 2004).It is quite possible thatthe abnormal，highly pressurized fluid flow from the Qijia-Gulong Depression，triggered by the tectonic compressionduring the inversion of the Songliao Basin.will migrate to theNPZ and lead to the total AFT reseting。

Fluid flow driven by gravitational energy is the otherpossible contributor.It is best illustrated by Garven et alf1993)and its thermal effect has been recently reviewed byBernet and Garver(2005).The difference of the elevation(-250 m、between the east and the west has been recognizedin the regional profile(Yang et a1.1 985：Zhou and Littke。

1 999；Xiang et al，2007)if the main seal of the OingshankouFormation or the Neniiang Formation is taken as a reference。

Such a difference might have been even greater at the end ofthe Eocene due to the elevation and denudation r 1.200 1。500m)fXiang et al，20101。

31 Pathway systemsThermal effects from fluid flow indicate a lateralor vertical convective heat transfer，either of which ischaracterized by being more efi cient than conductive heattransfer along the main pathway systems of the fluid flow(Ehlers.2005).The pathway systems for the fluid in a basinhave been defined as the permeable rock masses，which arethe permeable sandstones and unconformities or the faultsand fracture systems(Lin et al，2009)(Fig.1，Fig.2)。

Due to the 1ack of pathway systems for the hot fluidflow，the thermal effect may result in the samples failureto be annealed.Sample SBA3 is from the main seals ofthe Qingshankou Formation that deposited during themain subsidence of the Songliao Basin.The fine grainedsandstone in the seals is discrete and cannot form continuouspathway systems for the fluid from the CDZ.At the sametime.the fine grained mudstone is characterized by 1owthermal conductivity.which will shield the vertica1 and1atera1 heat conductivity.The above two factors 1ead to thesamples failure to be annealed(Blackwel and Steele，l 989)。

The latera1 connectivity of the permeable reservoir mightaccount for the different characteristics of vertical AFT agedistribution between the middle reservoirs group and thelower reservoirs group.The lower reservoirs group wasdeposited under a braided fluvialshalow lake environmentand is characterized by discrete fluvial channel sandstonebodies fFeng et al，20 1 0a)，whereas the middle reservoirsgroup is controlled by the large fluvial-delta systems from theBinbei district and the sandstone bodies are overlapped andwel1 laterally connected fFeng et al，20 l Ob).The vertical AFTages of those from the middle segment increased with theburia1 depth.indicating a local thermal effect from fluid flow(Tagami and OSullivan，2005).Driven by the buoyanciesthat arose from their temperature difierences.hot fluid fromthe CDZ tends to ascend to flow beneath the bottom ofthe main seals during its lateral migration.This resulted inyounger ages with shallower burial depths(Fig.6).Thosesamples from the lower segment are different as indicatedby the younger ages with increasing burial depth.This maybe either due to the limited sampling interva1.which focuseson the upper part of the lower group.or indicates a limitedtemperature anomaly，which has no totally overtumed thermaleffect from conductivity due to the lack of 1ateral pathwayconnectivity。

5.3 1rransient fluid flowThermal effects from the fluid flow accounts for thediferent annealing between the reservoir and the seals.Thefollowing discussion will be focused on the temperaturediscrepancy shown by the AFT thermometer and the Rrespectively。

11，I1ransient thermal eflfectResearch results indicate that the fluid flow of a regionalscale，driven by topographic reliefs may result in transientfl0 .10 yrs.according to Ehlers.2005)regional thermalanomaly as has been documented in the basin and provinceof the middle continent and the Paris Basin(Bachu。1 985：Garven et a1.1 993).Local fluid flow in connection with themagmatism，tectonic faulting or seismic activity，and withthe breakthrough of the abnormal high pressure systems。

is instant and transient fSibson 2000；2003：Stanislavskyand Garven。20031.Both regional and localized thermaleffects from fluid flow are transient and may account for thetemperature discrepancy indicated by AFT therm ometer andR。respectively。

Thermal effects from fluid flow are the only possiblechoice that can account for the AFT total annealing but willnOt result in a signmcant enhancement Of .Research resu1tsshow that the maturation Of the organic matters requireslonger time than the resetting of the AFT.A minimum Of 1 0。。

1 0 yrs.of continuous heating(within l 5。C of maximumtemperature)is required to stabmze me therma1 maturationof organic matters(Barker，1 989).Take the temperaturerange of 1 00.1 20。C for example，decarbonxylation reactionswith an Ea of 30.40 kca1/mol fl30.170 l，J/mo1)，which is theactivatiOn energy f0r preferentially e1iminating water andcarbon dioxide during the early maturation stage(Bumhamand Sweene 1989)，require on the order of 10。.10 yrs。

to approach comp1etion(Barker，1 989).According to theevidences bOth frOm exDeriments and f Om the calculationbased on the Am1enius equation(Green et a1，l 985)，howeve r，the time needed for AFT annealing(<1 year)at the sametemDerature(1 0O.1 20。C)is almost instant(Las1et et al，1987：Green et al，l985；Crow1ey et a1，1991)。

The abOve time diflference between t stabilizatiOn Ofthe vitrinite renectance and the tOtal annealing Of the AFTPet.Sci.(2013)10：314-326 323thermometer can help explain the temperature differenceindicated by AFT total annealing f l1 0.1 20。C1 and thevitrinite reflectance f60-90。C with R <0.7%).The durationof the thermal effect from the fluid flow fwhich 1asts typicallyon the order of 1 0 .1 0yrs.according to Ehlers(2005)is notlong enough to affect the R。，although its temperature is highenough to reset the AFT thermometer。

21 Episodes offluid flowTransient fluid flow indicates that fluid flow happened atsome point between the late Cretaceous and the early Eocene。

It should be treated not as the time span over which the fluidflow has lasted.but typically as the time point when one ormore episodes of fluid flow have been driven or triggered bytectonic compression.For a more accurate time table of thefluid flow，and consequently the time table for the tectonicactivitV.special attention should be paid to how the fluid andthe pathway system cool down after the main episode of fluidflow。

The cooling velocity of the fluid flow depends on thetemperature diferences between the fluid flow and the wallrock.Higher temperature differences will result in a highercooling velocity and more accurate time will be recordedby AFT age because the AFT ages record the time when thetemperature passed the upper boundary of the PAZ rGleadowet a1.1 986).Regardless the cooling efect of the fluid duringits migration along the pathway systems，the temperaturediflference between the fluid and wall rock then depends onthe buria1 temperature which is closely linked to the buria1depth.The post.rifting sequence is a depression with theburial depth increasing from the periphery to the basin centeras shown in Fig.2.Higher temperature differences betweenthe fluid flow and the wall rock are found in samples fromwell Tong3 and wel Bai3.both of which are located at themargin of the basin。

Limited samples from well Tong3 and well Bai3 indicatethree episodes of fluid f1ow at late Neniiang(725-704Ma).1ate Cretaceous(654-635 Ma).and late Paleocene(564-513 Ma)periods respectively(Table l，Fig.5).Allof them fall in the standard deviation of the士1 standard errorof the AFT dating and their accuracy is acceptable(Galbraithand Laslett.1 9931.Due to the transient characteristics ofthe therma1 effect from fluid.they should not be treatedas the same episode of fluid flow because the time lastsso long that the maturation of the organic matter will beenhanced.Although limited samples may fail to suppo theabove conclusion.its reliability is supported by the geologicbackground of the Songliao Basin。

The thermal effect from syntectonic fluid flow suggeststhat there must have been some tectonic actvty that can driveor trigger the fluid flow.According to the geologic setting，three episodes of tectonic movement in the Songliao Basinare wel1 established.The first episode appeared before thedeposition of the third member of the Nenjiang Formation，as indicated by the progradation effect of the filling sequencefrom the east(Feng et a1.20 1 0a；20 1 0b).The second episodeof tectonic movement happened at the late Cretaceous(65Ma)，which marked the beginning of tectonic inversion withmore than 750 m of erosion recorded bv AFT dating from thesouth uplifted zone fXiang et al，2007).The third episode oftectonic activity occured in the 1ate Paleocene r56 Ma)andmight have arisen from the combined effect of the subductionof the Pacitic Plate underneath the Eurasian Plate(Patriatand Achache.1 984；Gordon and Jurdy，1 986；Maruyama eta1.1989；Lee and Lawyer，l995：Sharp and Clague，2006)and of the collision between the Indian subcontinent andthe Eurasian Plate(Maruyama and Send.1 986：Lee andLawver.1 995).The third episode of tectonic movement inthe Songliao Basin must have 1asted til the early Eocene assuggested by the AFT dating from the south uplifted zone ofthe basin rXiang et a1.2007)。

It is hard to provide more evidence to prove the above-mentioned three episodes of fluid now.However.we cansuppose all samples from well Dong 1 as tests and get furtherinformation。

Three samples from well Dong 1 that have been totallyannealed record AFT age of 594 Ma.524 Ma and 413 Marespectively.The first two ages fal1 within the late Paleocene。

The limited data from well Dong 1 have proved at least thelast episode of fluid flow，but failed to prove the tw o episodesof fluid flow that happened at the late Nenjiang and lateCretaceous periods.At the same time，one sample recordsanother age of the early Eocene r413 Ma).Whether they arereliable or not iS worth discussion。

5.4 Thermal overprintingTherm al effects from fluid flow left only their foptic)rintson the pathway systems.This 1eads to the following tworesults.Syntectonic fluid flow tends to change its pathwaysystems f0liver and Bons 200 1：Baker et a1.2006)that causesome of their thermal effects to fai1 to be recorded.Thus1arge-scale fluid flow wil1 1eave its thermal efect jn a broadrange and smal1.scale fluid flow will only leave its foptprinton limited reservoir rocks.On the other hand.the unchangedpathway systems wil1 only preserve the thermal ef-fect ofthe latest episode of fluid flow due to its overlapping on thethermal eflfect of the early.stage them al event.The abovetwo characteristics can explain the AFT ages that rec0rd thethennal efrect frOm nuid flow。

The second characteristic of the them al eflfect行om fluidflow gives us a direct clue to explain the AFT data frOm thewel1 Dong 1 which is nearer to the CDZ.The CDZ has a highpressurized nuid now with a high temperature and can beeasi1y triggered or driven by the tectOnic movement.Thus，thermal eflfects丘om the late Paleocene fluid flow must havetotaUy over1apped those f om the late Neniiang and the lateCretaceous periOds and caused their lack Of preservatiOn asAFT ages。

The nrst characteristic of the nuid now gives us moreinfonnatiOn as follOws.First.real large.scale fluid flOw willleave its f0otprint in a wide range of pathway sVstems，whichin tum makes it easier to be samDled and recorded.The latePa1eOcene large.sca1e nuid nOw can be ascertained becauseit has been recorded by samples from the three wells that arescatered in a vast area and verticallv from ～50 - 1.100 m。

The late NeI1jiang nuid now and late Cretaceous nuid nowshould be more obvious than the ear1v Eocene nuid now324 Pet.Sci.(2013)10：314-326because they were recorded by samples from well Bai3 andwell Tong 1.both of which are located in farther north thanwell Dong1.The early Eocene fluid flow is only recorded atgood reservoirs of the first member of the Ylaoiia Formationnear CDZ which in turn indicates its limited thermal effectand distribution。

The above two assumptions may have wide applicationsin dating the tectonic movements if they have been furtherproved.Tectonic reconstruction relies heavily on the rockframework.the 1ack of which will cause big chalenges.Thelate-stage tectonic movement in the Songliao Basin.startingfrom the late Cretaceous r～65 Ma)with<500 m sedimentaryrecord.is one of such challenges.Our analysis defines at leastthree episodes of tectonic movement with the time muchmore accurately defined than anticipated.W hat is more.iftectonic movements can be dated by their syntectonic fluidflow，al the methods that date the fluid flow and the thermalevents can be used to quantify the timetable of the tectonicmovements.Thus，dating the time of the tectonic activityby dating the syntectonic fluid flow and its thermal effectshould evolve into a new method.Thermal overprinting bythe fluid flow may also account for the shortened AFT MTLdistribution(Fig.6).The MTL distribution mav be attributedtO the sluggish annealing kinetics for the samples long timer30-65 Ma)of location in the low temperature range of<70。C(Spiegel et al，2007).According to the above discussion。

transient therlna1 effects from fluid flow with the temperaturebetw een 60。C and 1 20。C can easily lead to partia1 annealingof the AF T.as indicated by the shortening of the MTL。

5.5 Source rock maturation and hydrocarbonexplorationThermal history is the key factor that controls source rockmaturation and the successive hydrocarbon migration andaccumulation.There are two families of source rocks thatdeveloped in the Songliao Basin，namely the Qingshankouand the Nenjiang Formations(Yang，1 985：Lu et a1.2009；Feng et a1.20 1 0a).The proposed thermal effects haveimportant implications for hydrocarbon exploration in theBinbei district。

Hydrocarbon exploration under the guide of conventionalhydrocarbon exploration around loca1 pods of active sourcerocks in the Binbei district has never gained a prominentoutcome.This is mainly due to the low matured source rocksthat have been proved both by the low R。(Fig.7)and by theunannealed AFT age(Fig.5、from the main source rock of theQingshankou Formation。

The defined thermal efect from fluid flOW，however，givesa new idea to overcome the above stalemate.Hydrocarbonexploration around the active source rocks should be changedto look for the hydrocarbons that have migrated from themain active source pods in the CDZ.The 1ate Paleocenefluid flow is a large.scale fluid flow that has left its footprintboth on the vicinity of the mature source region(samplesfrom wel1 Dong 1 1 and in those areas farther north of theBinbei district。where R <0.5%.The two sets of source rocksthat have been buried up to the threshold of hydrocarbongeneration(Yang et al，1 985)before the Paleocene justify ourassumption of the large-scale hydrocarbon migration togetherwith the migration of the formation fluid flow.Independentevidence from the composition and the geochemistry of thenatural gas and the crude oils has demonstrated a long rangehydrocarbon migration in the basin(Feng et al，2003；Xianget a1.2004；2005)。

6 ConclusionsAFT dating in the Binbei district further clarifiesits thermal history and has important implications forhvdrocarbOn exp1oration.The following are the mostsignifcant results：1、The AFT ages of samples from the Cretaceous reservoirrocks(youngest deposition age of 76.1 Ma、faU between the1ate Cretaceous rthe oldest AFT age of 724-5 Ma)and theearly Eocene(the youngest age of 4 13 Ma)，indicating AFTthermometer total annealing after deposition.Two samplesfrom the main seals of the Qingshankou(the youngestdepositional age of 89.3 Ma)and Nenjiang(the youngestdepositional age of 70.6 Ma1 Formations yield AFT ages(704Ma and 974-9 Ma respectively)identica1 with or older thanthe depositional ages.indicating partial or no annealing。

21 Thermal effects from syntectonic fluid flow areproposed to account for the AFT total annealing becausethe burial heating is not high enough as evidenced by 1owR (<0.7%).Driven by the tectonic compression and theabnormal pressure systems，the fluid flow from the CDZ orfrom the underlying rifting sequences is proposed to accountfor the AFT total annealing。

31 The characteristics of the transient thermal effectfrom the syntectonic fluid flow help explain the indicatedtemperature discrepancies between the AFT thermometer andthe R .Therm al effects from fluid flow are hot enough(1l0-1 20。C1 to annea1 the AFT therm ometer，but they do not lastlong enough(104-10 yrs.)to enhance R。(minimum 10。-10yrs.under the above temperature).Thus，dating fluid flowmay be a new way to reconstruct the tectonic history and mayhave extensive applications。

41 The late Paleocene f5 14-3-594-4 Ma1 large.scale fluidflow is recognized from al the AFT ages according to thetherm al overprinting effect.The large.scale fluid flow callsf0r a new idea to direct the hydrocarbon exploration。

AcknowledgementsThe authors are grateful to the Daqing 0ilfield Company，CNPC.for supporting the field work and providing theOriginal geOIOgic data.The samples were prepared andana1Vzed under the instructiOn Of PrOf Yluan Wanming frOmChina Universitv Of GeOsciences.Valuable suggesti0ns仃OmO anOnymOus reViewers are great1y印 preciated.This wOrkwas suppOrted bV the NatiOnal Natural Science FOundatiOnof China(Grant Nos.40872097 and 41272161)and theMaior National Science&1'echnology Program(Grant Nos。

201 1ZX05006.005 and 201 1ZX05006.006).The field tripis partly funded by the State Key LabOrat0ry f0r PetrOleumResource and Prospecting(Grant No.KYJJ2012-01-l2)。

ReflerencesBachu S.Innuence of 1ithology and f1uid nOw On the temperature