川中东北部须家河组与珍珠冲段地层划分
摘要
通过地震反射终端研究,认为上三叠统须家河组(J2x)与下侏罗统(J1z)的分界面为一层序界面(T3x被界面截削,J1z沿界面上超);因此可依据LUNA法则予以确定。LUNA认为,层序边界不整合可依据可容空间生成速率突变的岩层几何形态来识别,表现在古河道规模和河道砂岩的叠置方式,而拼合砂岩体底面乃是层序界面(SB)之所在,在录井图上,表现为Gr、Rt曲线的转折点——由下伏层序的反韵律向上突变为上复层序的正韵律。此面与底部砾岩底面是一致的。通过测制华蓥山西缘界线上下短剖面以及取芯井岩芯描述,发现J1z与T3x在古生物—生态及沉积方面存在明显差异——反映地质演变的不可逆性。古生物:主要为植物化石,T3x6黑页岩中植物化石十分丰富且保存完好,粗砂岩中常见茎杆印模;J1z化石罕见,可见炭化植物细碎屑或他生的煤"砾"。沉积与成岩特征:除菱铁矿结核分布于界面上下数米深度范围内,在J1z底、T3x6顶皆可见到外,其他特征都是大不相同的。剖面结构——T3x6中下部为大套灰白色中(粗)—细砂岩,厚数米至几十米,上部为浅灰、灰黄细砂—粉砂岩与黑页岩交互;J1z下部为浅灰、灰绿薄层粉砂岩与红色、杂色泥岩交互,上部泥岩变为灰色,砂岩亦变厚。成分——J1z下部粉砂岩石英含量高于T3x6砂岩,而燧石和变质岩屑显著低于后者。结构成熟度——J1z粉砂岩分选程度显著低于T3x6砂岩,J1z中的薄层浊积是T3x中见不到的。沉积构造——T3x中常见双粘土层、鱼骨状交错层、突然相变、透镜状和脉状层理、薄互层,是J1z中所没有的。硅质中砾岩——J1z底部砾岩为可靠分界标志,与T3x6底部者不难区分;风暴流砾石和牛角炭只见于T3x6;植物根系在J1z中常见,T3x中偶见。这些差异源于沉积环境的不同,T3x属浅海河口湾潮汐成因,J1z为陆相湖泊三角洲系统。它们在测井响应上也各有特点,不难区别。本文证明,在钻进过程中,依据岩屑信息,迅速判断钻达层位是可以做到的。
Studies of the corresponding seismic data revealed the division plane is a sequence boundary(SB)(T3x truncated by the boundary and along which J1z onlaps).So it can be dertermined by LUNA principle.LUNA regards sequence boundary unconformity as can be recognized by strata geometry of abrupt change of accomodation generation rate which is marked by the paleo-channel scale and the superimposition of channel sandstones,and base of the almagmated sandstone body is just the situ of the sequence boundary.In well-log,SB is presented by break point of Gr and Rt curves-the reverse rhythm of the underlain sequence turns into positive rhythm of the overlying sequence upwards at the point.This plane coincides well with the base of basal conglomerate.Measuring the trans-boundary short columns along the west edge of Huayingshan and core-section studies have revealed that apparent differences of paleontology-paleoecology and sedimentology exist in between T3x and J1z successions,which reflect the inreversibility of geological evolution.Paleontology:mostly fossil plants,plants are plentiful and well-preserved in T3x6 black shale,and plant stems are considerably common in coarse sandstone of the same member.Fossils are rare in J1z,however,allochthonous small carbonized plant debris or occasionally coal "pebbles" are seen.Sedimentary and diagenetic feafures:most aspects are quite different beween T3x6 and J1z,except that siderite concretions occur in the interval from below to above the boundary by several meters.Lithology-the lower-middle part of T3x6 is represented by thick gray-white median(coarse)-fine sandstone with single bed thickness of several to decades meters,the upper part by interbeds of light gray,yellowish gray fine sandstone to siltstone and black shales;however J1z is characterized by intercalations of light gray,grayish-green thin siltstone and red,stained mudstome at its lower part,the mudstone are grading into gray colour and sandstone are getting thicker at its upper part.Composition——the guartz content in lower J1z is higher than the sandstones of T3x6,but its chert and metamorphic rock debris are apparently lower than the later;Texture maturity——J1z siltstone is much worse-sorted than the T3xv6 sandstone,the thin turbidites in J1z are not seen in T3x successions.Sedimentary sturctures-bi-clay-layers,herringbone structure,abrupt facies change,lenticular and flaser bedding and thin interbedds are common in T3x but not seen in J1z.Siliceous cobble-the J1z basal cobble is a reliable boundary marker which is easily differentiated from the basal ones of T3x6;the storm-induced conglomerate and "ox-horn coal" occur only in T3x;rootlets are common seen in J1zv and occassionaly presented in T3x.Sedimenfary facies:the above-mention differences between T3x and J1z are thought to be derived from original sedimentary environments,the authors attribute T3x to shallow sea and estuarine origin and J1z to lacustrine delta system.The two successions are also different from each other in well-logging responses and can be easily discerned.This paper proved that to judge the reached stratigraphic level during well-drilling swiftly on the basis of cutting information can be achieved.
Studies of the corresponding seismic data revealed the division plane is a sequence boundary(SB)(T3x truncated by the boundary and along which J1z onlaps).So it can be dertermined by LUNA principle.LUNA regards sequence boundary unconformity as can be recognized by strata geometry of abrupt change of accomodation generation rate which is marked by the paleo-channel scale and the superimposition of channel sandstones,and base of the almagmated sandstone body is just the situ of the sequence boundary.In well-log,SB is presented by break point of Gr and Rt curves-the reverse rhythm of the underlain sequence turns into positive rhythm of the overlying sequence upwards at the point.This plane coincides well with the base of basal conglomerate.Measuring the trans-boundary short columns along the west edge of Huayingshan and core-section studies have revealed that apparent differences of paleontology-paleoecology and sedimentology exist in between T3x and J1z successions,which reflect the inreversibility of geological evolution.Paleontology:mostly fossil plants,plants are plentiful and well-preserved in T3x6 black shale,and plant stems are considerably common in coarse sandstone of the same member.Fossils are rare in J1z,however,allochthonous small carbonized plant debris or occasionally coal "pebbles" are seen.Sedimentary and diagenetic feafures:most aspects are quite different beween T3x6 and J1z,except that siderite concretions occur in the interval from below to above the boundary by several meters.Lithology-the lower-middle part of T3x6 is represented by thick gray-white median(coarse)-fine sandstone with single bed thickness of several to decades meters,the upper part by interbeds of light gray,yellowish gray fine sandstone to siltstone and black shales;however J1z is characterized by intercalations of light gray,grayish-green thin siltstone and red,stained mudstome at its lower part,the mudstone are grading into gray colour and sandstone are getting thicker at its upper part.Composition——the guartz content in lower J1z is higher than the sandstones of T3x6,but its chert and metamorphic rock debris are apparently lower than the later;Texture maturity——J1z siltstone is much worse-sorted than the T3xv6 sandstone,the thin turbidites in J1z are not seen in T3x successions.Sedimentary sturctures-bi-clay-layers,herringbone structure,abrupt facies change,lenticular and flaser bedding and thin interbedds are common in T3x but not seen in J1z.Siliceous cobble-the J1z basal cobble is a reliable boundary marker which is easily differentiated from the basal ones of T3x6;the storm-induced conglomerate and "ox-horn coal" occur only in T3x;rootlets are common seen in J1zv and occassionaly presented in T3x.Sedimenfary facies:the above-mention differences between T3x and J1z are thought to be derived from original sedimentary environments,the authors attribute T3x to shallow sea and estuarine origin and J1z to lacustrine delta system.The two successions are also different from each other in well-logging responses and can be easily discerned.This paper proved that to judge the reached stratigraphic level during well-drilling swiftly on the basis of cutting information can be achieved.
引文
1四川人民出版社编.四川盆地陆相中生代地层古生物[M].成都:四川人民出版社,1982[Sichuan People’s Press.Stratigraphy andPaleontology of the Continental Mesozoic in Sichuan Basin[M].Chengdu:Sichuan People’s Press,1982]
2刘笛笛,杨子荣,杨彦东,等.四川盆地珍珠冲组植物群特点及侏罗系与三叠界线的厘定[J].地球科学与环境学报,2009,9:31(3):254-259[Liu Didi,Yang Zirong,Yang Yandong,et al.Charac-teristics of the Zhenzhuchong plant assemblage and definition of theboundary between Jurassic and Triassic in Sichuan Basin[J].Journalof Geoscience and Environmental Science,2009,9,31(3):254-259]
3罗启后.水进河床砂体充填在古代沉积中的发现——四川盆地中西部上三叠统某些砂体的成因探讨并试论水进型三角洲[J].沉积学报,1983,1(3):59-68[Luo Qihou.Discovery of water-trans-gressive channel infilling sandstone bodies in ancient sediments:An ap-proach to the genesis of certain Upper-Triassic sandstone-bodies in themiddle-west part of Sichuan Basin and discussion on water-transgressiondelta[J].Acta Sedimentologica Sinica,1983,1(3):59-68]
4侯方浩,蒋裕强,方少仙,等.四川盆地上三叠统香溪组二段和四段砂岩沉积模式[J].石油学报,2005,3,26(2):30-37[HouFanghao,Jiang Yuqiang,Fang Shaoxian,et al.Sedimentary model ofsandstone in the Second and Fourth members of Xiangxi Formation inthe Upper Triassic of Sichuan Basin[J].Acta Petrolei Sinica,2005,3,26(2):30-37]
5郑荣才,戴朝成,朱如凯,等.四川类前陆盆地须家河组层序—岩性古地理特征[J].地质评论,2009,55(4):484-495[Zheng Rong-cai,Dai Chaocheng,Zhu Rukai,et al.Sequence-based lithofacies andpaleogeographic characteristics of Upper Triassic Xujiahe Foarmation inSichuan Basin[J].Geological Review,2009,7,55(4):484-495]
6赵霞飞,吕宗刚,张闻林,等.四川盆地安岳地区须家河组—近海潮汐沉积[J].天然气工业,2008,4:14-18[Zhao Xiafei,LüZong-gang,Zhang Wenlin,et al.The Xujiahe Formation in Anyue area ofSichuan Basin—Littoral tidel deposits[J].Natural Gas Industry,2008,4:14-18]
7 Wendt J,Xichuan Wu,Reinhardt J W.Deep-water hexactinellidsponge mounds from the upper Triassic of northern Sichuan(China)[J].Palaeogeography,Palaeoclimatogy,Palaeoecology,1989,76:17-29
8张闻林,徐丽媛,赵霞飞,等.四川盆地上三叠统须家河组和侏罗系的沉积差异及勘探方式[J].天然气工业,2010,30(增刊):5-10[Zhang Wenlin,Xu Liyuan,Zhao Xiafei,et al.Sedimentary differ-ence and exploration style between the Upper Triassic Xujiahe Forma-tion and Jurassic in Sichuan Basin[J].Natural Gas Industry,2010,30(Suppl.):5-10]
9 Rahmani R A.Estuarine tidal channel and nearshore sedimentation of aLate Cretaceous epicontinental sea,Drumheller,Alberta,Canada[M]∥De Boer P L,Gelder A V,Nio S D,eds.Tide-Influenced Sedimen-tary Environments and Facies.Reidel D Publishing Company,1988:433-471
10 Shanley R W,McCabe P J.Perspectives on the sequence stratigraphyof continental strata[J].AAPG Bulletin,1994,78(4):
11 Vial P R,Andemard F,Bowman S A,et al.The stratigraphic signa-tures of tectonics,eustasy and sedimentology-an overview[C]∥Ein-sele et al.,(Eds),Cycles and Events in Stratigraphy,Springer-Ver-lag,Berlin,1991:617-661
12 Van Wagoner J C.Sequence stratigraphy and marine to nonmarine fa-cies architecture of foreland basin strata,book cliff,Utah,U.S.A.[C]∥Van Wagoner J C,Bertram G T.eds.Sequence Stratigraphy ofForeland Basin Deposits(AAPG Memoir 64),1995,Tulsa,Oklaho-ma,U.S.A.
13 Olsen T,Steel R,Hogseth K,et al.Sequential architecture in a flu-vial succession:sequence strigraphy in the upper Cretaceous Mesav-erde Group,Price Canyon,Vtah[J].Journal of Sedimentary Re-search,1995,65(2):265-280
2刘笛笛,杨子荣,杨彦东,等.四川盆地珍珠冲组植物群特点及侏罗系与三叠界线的厘定[J].地球科学与环境学报,2009,9:31(3):254-259[Liu Didi,Yang Zirong,Yang Yandong,et al.Charac-teristics of the Zhenzhuchong plant assemblage and definition of theboundary between Jurassic and Triassic in Sichuan Basin[J].Journalof Geoscience and Environmental Science,2009,9,31(3):254-259]
3罗启后.水进河床砂体充填在古代沉积中的发现——四川盆地中西部上三叠统某些砂体的成因探讨并试论水进型三角洲[J].沉积学报,1983,1(3):59-68[Luo Qihou.Discovery of water-trans-gressive channel infilling sandstone bodies in ancient sediments:An ap-proach to the genesis of certain Upper-Triassic sandstone-bodies in themiddle-west part of Sichuan Basin and discussion on water-transgressiondelta[J].Acta Sedimentologica Sinica,1983,1(3):59-68]
4侯方浩,蒋裕强,方少仙,等.四川盆地上三叠统香溪组二段和四段砂岩沉积模式[J].石油学报,2005,3,26(2):30-37[HouFanghao,Jiang Yuqiang,Fang Shaoxian,et al.Sedimentary model ofsandstone in the Second and Fourth members of Xiangxi Formation inthe Upper Triassic of Sichuan Basin[J].Acta Petrolei Sinica,2005,3,26(2):30-37]
5郑荣才,戴朝成,朱如凯,等.四川类前陆盆地须家河组层序—岩性古地理特征[J].地质评论,2009,55(4):484-495[Zheng Rong-cai,Dai Chaocheng,Zhu Rukai,et al.Sequence-based lithofacies andpaleogeographic characteristics of Upper Triassic Xujiahe Foarmation inSichuan Basin[J].Geological Review,2009,7,55(4):484-495]
6赵霞飞,吕宗刚,张闻林,等.四川盆地安岳地区须家河组—近海潮汐沉积[J].天然气工业,2008,4:14-18[Zhao Xiafei,LüZong-gang,Zhang Wenlin,et al.The Xujiahe Formation in Anyue area ofSichuan Basin—Littoral tidel deposits[J].Natural Gas Industry,2008,4:14-18]
7 Wendt J,Xichuan Wu,Reinhardt J W.Deep-water hexactinellidsponge mounds from the upper Triassic of northern Sichuan(China)[J].Palaeogeography,Palaeoclimatogy,Palaeoecology,1989,76:17-29
8张闻林,徐丽媛,赵霞飞,等.四川盆地上三叠统须家河组和侏罗系的沉积差异及勘探方式[J].天然气工业,2010,30(增刊):5-10[Zhang Wenlin,Xu Liyuan,Zhao Xiafei,et al.Sedimentary differ-ence and exploration style between the Upper Triassic Xujiahe Forma-tion and Jurassic in Sichuan Basin[J].Natural Gas Industry,2010,30(Suppl.):5-10]
9 Rahmani R A.Estuarine tidal channel and nearshore sedimentation of aLate Cretaceous epicontinental sea,Drumheller,Alberta,Canada[M]∥De Boer P L,Gelder A V,Nio S D,eds.Tide-Influenced Sedimen-tary Environments and Facies.Reidel D Publishing Company,1988:433-471
10 Shanley R W,McCabe P J.Perspectives on the sequence stratigraphyof continental strata[J].AAPG Bulletin,1994,78(4):
11 Vial P R,Andemard F,Bowman S A,et al.The stratigraphic signa-tures of tectonics,eustasy and sedimentology-an overview[C]∥Ein-sele et al.,(Eds),Cycles and Events in Stratigraphy,Springer-Ver-lag,Berlin,1991:617-661
12 Van Wagoner J C.Sequence stratigraphy and marine to nonmarine fa-cies architecture of foreland basin strata,book cliff,Utah,U.S.A.[C]∥Van Wagoner J C,Bertram G T.eds.Sequence Stratigraphy ofForeland Basin Deposits(AAPG Memoir 64),1995,Tulsa,Oklaho-ma,U.S.A.
13 Olsen T,Steel R,Hogseth K,et al.Sequential architecture in a flu-vial succession:sequence strigraphy in the upper Cretaceous Mesav-erde Group,Price Canyon,Vtah[J].Journal of Sedimentary Re-search,1995,65(2):265-280
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