皖南晚震旦世中、浅海沉积环境——以滑塌砾岩层、硅质风暴岩为例证.pdf

支利赓,曹祖章,吴德根等.15万旌德县幅、岛石坞幅、绩溪县幅、顺溪幅区域地质调查报告.1989;支利赓,左延龙,汪隆武等.15万七都幅、歙县幅、大阜幅、王阜幅区域地质调查报告.1996;余心起,王德恩,杨荷金等.15万兰田幅、休宁县幅、屯溪幅区域地质调查报告.1998.收稿日期:2002204215 收修改稿日期:2002206212文章编号:100020550(2003)0320398206皖南晚震旦世中、浅海沉积环境 以滑塌砾岩层、硅质风暴岩为例证余心起1 舒良树1 邓 平1,2 王德恩3 支利赓31(南京大学地球科学系 南京 210093)2(核工业二九研究所 广东韶光 512026)3(安徽省地质矿产局332队 安徽黄山 245000)摘 要 皖南歙县、休宁一带晚震旦世下部兰田组上段钙硅质岩中发现碎屑流引起的滑塌砾岩层,上部皮园村组硅质岩中发现浊积岩夹层及风暴流沉积层,表明皖南地区晚震旦世应为半深海 浅海环境,而非通常所说的深海环境。关键词 滑塌砾岩层 硅质风暴岩 皮园村组 兰田组 晚震旦世 皖南地区第一作者简介 余心起 男 1962年出生 博士研究生 高级工程师 区域地质调查及沉积大地构造中图分类号 P512.2 文献标识码 A1 引言硅质岩在化学沉积和生物沉积的岩类中,其数量仅次于碳酸盐岩。它不仅是许多重要矿种的赋存层位和含矿岩系的重要岩类,而且由于它形成于特定的地球化学条件,能够反映出某些沉积相带特殊的地质背景,所以硅质岩的研究具有十分重要的理论意义和实用价值。近年来,国内许多沉积学家125对扬子地台不同层位的硅质岩做了大量的工作。其中朱洪发等6、伊海生等1415、周永章1、唐朝晖等24从不同角度作了很好的研究,不论从广度或深度,使硅质岩的研究程度都大大地向前推进了一步。硅质岩沉积 构造环境可分为三类:大陆边缘、远洋和扩张洋脊附近。弧后盆地、边缘海、陆表海和开放陆架均归属大陆边缘环境。一般认为,硅质岩是深水沉积物,也有人认为形成于半深海环境。近年来,在硅质岩中发现大量风暴岩,而风暴岩发育在浅海陆棚的不同沉积带中2635,这使人们相信,硅质岩也可以是浅水 半深水沉积物。此前,作者等在皖南及相邻地区15万区域地质调查工作中,发现临溪向斜、休宁兰田残留向斜晚震旦世上部皮园村组硅质岩中多处发育浊积岩夹层和风暴沉积岩夹层;其下伏晚震旦世兰田组上部钙硅质岩层中有一层厚20 cm的滑塌砾岩36。表明皖南地区晚震旦世中期可能为半深海 浅海环境,而非通常所说的深海环境3743。2 上震旦统岩性组合皖南的震旦纪 寒武纪以上地层围绕江南古陆东段南北两侧及东(南)部分布(图1)。其中晚震旦世上部皮园村组硅质岩以坚硬的岩性、突出的地貌特征而成为良好的标志层及倍受瞩目的研究目标层。本文仅涉及江南古陆东段北缘的两个残留盆地。东部由震旦纪 奥陶纪地层构成北东走向的临溪向斜盆地,北西翼底界震旦纪休宁组高角度不整合于中元古代牛屋组浊积岩及青白口纪许村岩体花岗闪长岩之上。西部休宁兰田残留向斜近东西 北西西走向。新发现的歙县黄村地区兰田组滑塌砾岩层36位于临溪向斜西翼(图1中 处),产出于兰田组四段薄层含硅钙质板岩中(图2),距离上部皮园村组与兰田组界线约10 m。砾石成分以条纹状硅泥质岩为主,极少量含泥的灰岩,最大近20 cm(水平方向),宽8 cm;最小 1 cm。砾石磨圆度好,分选极差,略具定向。胶结物为灰泥质,少量砂质。砾岩层上、下均为薄层含硅钙质板岩,层面平整,偶夹薄层泥灰岩,单层厚度0.51.5 cm。地层产状为:123 40。皮园村组硅质风暴岩沿临溪向斜西翼往北东(东)延伸,其间夹有具粒序层理的薄层浊积岩。休宁兰田残留向斜内皮园村组风暴沉积层(如图1中 处)多处见及。第21卷 第3期2003年9月沉 积 学 报ACTA SEDIMENTOLOGICA SINICAVol.21 No.3Sep.2003 1995-2006 Tsinghua Tongfang Optical Disc Co.,Ltd.All rights reserved.K 白垩系;寒武系;Z 震旦系;Pt3 新元古界;Pt2 中元古界;J3 燕山期花岗闪长斑岩;Pt2 晋宁期花岗闪长岩;风暴岩观察位置;砾岩层产出位置;兰田残留向斜;临溪向斜图1 皖南地区地质简图Fig.1Sketch geological map of the southern part of Anhui Province左 素描图;右 图象;1 含硅钙质板岩;2 砾岩层图2 兰田组滑塌砾岩层素描图Fig.2Sketch map of the olistostrome of the Lantian Formation 综合150,000七都幅、歙县幅区调报告、兰田等三幅区调报告以及近年来的科研成果等资料,黄村、兰田一带晚震旦世地层岩性(从上至下)为:2.1 皮园村组上段(Z2p2):厚度24209 m。为深灰、灰黑色薄层含炭硅质板岩、硅质岩、炭质板岩夹钙质板岩,底部有一薄层含锰白云质灰岩。下段(Z2p1)(图34):厚度4649 m。下部灰黑色薄层含炭硅质板岩、条纹状硅质板岩,中部灰 灰黑色中层黑白相间条纹状硅质岩夹炭硅质页岩,上部灰黑色薄层硅质板岩。层中夹有燧石条带、白云岩透镜体。硅质风暴岩总厚58 m,单层860 cm不等,其间为发育水平纹层的硅质岩,也夹有发育粒序层理的薄层浊积岩;局部地区如黄柏山一带(图4),硅质风暴岩连续发育。2.2 兰田组四段(Z2l4):厚度23 m。为极薄层的含硅钙质板岩、炭硅质板岩、硅质板岩夹泥灰岩,发育水平纹层及重荷模等,新发现的滑塌砾岩层即产出于近顶部的含硅钙质板岩中。该段岩性划分有不同意见,唐天福、薛993第3期 余心起等:皖南晚震旦世中、浅海沉积环境 余心起,王德恩,杨荷金等资料.兰田幅、休宁县幅、屯溪幅150000区域地质调查报告.1998支利赓,左延龙,汪隆武等.七都幅、歙县幅、大阜幅、王阜幅150000区域地质调查报告.1995-2006 Tsinghua Tongfang Optical Disc Co.,Ltd.All rights reserved.图3 皮园村组风暴岩素描图Fig.3Sketch map of the tempestite of the PiyuancunFormation sediments耀松等4142将其划入皮园村组底部。本文暂按原方案。三段(Z2l3):厚度49 m。为中层条纹状白云质泥质灰岩、薄互层的泥晶灰岩与泥灰岩(肋骨状灰岩)。二段(Z2l2):厚度30 m。为一套灰黑色厚层粉砂岩、炭硅质板岩、极薄层含炭钙质板岩及炭质岩夹灰岩。一段(Z2l1):厚度3 m,与下伏南沱组呈锯齿状接触。底部为60 cm之饼状白云岩,其上为褐黄色中薄层白云岩,上部为含砂白云岩,具水平纹层。从兰田组滑塌砾岩层到皮园村组硅质风暴岩总厚不足20 m,位于上震旦统中部,占岩性厚度的1/101/15。其上、下均属较深海沉积。3 滑塌砾岩层的地质意义滑塌砾岩层是由杂乱无序的不同类型物质(如岩块和泥质)所组成的一种沉积体,这种沉积体是由水下重力滑动或塌落的松散沉积物堆积而成的。其岩块是崩塌、滑动中打碎的,并且主要来自陡坡处的岩石。它是一个地层单元,以层状或透镜状产出,层序正常,厚度不太大,上、下都是正常沉积物,彼此为正常接触。滑塌堆积象沉积层一样,只需很短一段地质时间,可在不同的构造环境中,只要有陡坡或地震活动就可形成,其分布范围受古地理格架的控制。王剑等43研究表明,在华南新元古代裂谷盆地中,从南沱沉积期开始,以南沱冰碛岩为代表的裂谷盖覆盖了华南盆地的大部分地区,至晚震旦世,碳酸盐台地沉积和炭硅质岩沉积几乎覆盖了整个华南地区,扬子东南区和西缘区连成一片,临溪向斜所处的位置是比较稳定的浅海台地。可见,皖南兰田组形成于较为稳定的陆棚环境3740。考虑到上覆皮园村组下部发育硅质风暴岩,因此,兰田组近顶部砾岩层的形成可能由于风暴引起的盆地边缘塌落所致。至少表明,兰田组四段沉积时水体深度在浪基面之下不会太深,沉积盆地开始变浅,使得上覆皮园村组沉积时受到多次风暴作用的影响。4 硅质风暴岩的成因及形成条件大规模层状硅质岩的形成,是在一定的地史发展阶段,特定的大地构造背景下,属于特殊的沉积环境的左 歙县木石里;右 歙县黄柏山图4 皮园村组下段基本层序Fig.4Basic sequences of the lower member of the Piyuancun Formation004 沉 积 学 报 第21卷 1995-2006 Tsinghua Tongfang Optical Disc Co.,Ltd.All rights reserved.图5 皮园村组风暴流沉积示意图Fig.5Sketch map showing the storm2surgesedimentation of the Piyuancun Formation产物。既要有丰富的物质来源、合适的聚集方式,又要具备饱和沉积的介质条件;同时,风暴事件沉积通常分布在次稳定大陆边缘的浅海陆棚与被动边缘浅海台地及其斜坡带和陆内断陷盆地的构造斜坡带29。在漫长的地质发展历史中,这些综合因素的形成是相当复杂的19,1216。扬子地台晚元古代原生沉积的层状硅质岩的形成同样是复杂的,用同一种观点、同一种模式是无法概括的。如湘西上震旦统层状硅质岩的沉积 构造环境为扬子板块的东南被动大陆边缘,岩石形成于水体宁静、还原 强还原的大洋盆地的深海环境至大陆边缘斜坡的半深海环境。而皖南的上震旦统层状硅质岩则是半深海(或半深海 浅海)环境,主要产于缺氧的暗色岩系3840中。在皮园村组沉积时,风暴作用显著,形成风暴流沉积(图34),其层序下部具有丘状交错层理。往上为具包卷层理的硅质岩,最上部为具小型交错层理和水平纹层的硅质岩、含炭硅质板岩,底面见侵蚀现象,另见有硅质成分的团块、球粒和核形石,表明为低能环境的风暴流沉积。显然,皮园村组下段的基本层序就是由浊流旋回与他旋回共同作用的结果(图5)。5 结论从上述讨论中可以清楚地反映出,控制硅质岩形成的因素是极其复杂的,其形成的大地构造环境也是多样的。皖南歙县、休宁一带上震旦统中部浊积岩夹层、滑塌砾岩层及风暴流沉积层的发现,表明皖南地区晚震旦世中期为半深海 浅海环境,并非整个晚震旦世均为深海环境。参考文献(References)1 周永章,涂光枳,Edward H Chown等.粤西古水剖面震旦系顶部层状硅质岩的热水成因属性:岩石学和地球化学证据J.沉积学报,1994,12(3):111 Zhou Yongzhang,Tu Guangzhi,Edward H.Choen,et al.Hydrothermal origin of Top Sinian chert formation atGushui,Western Guangdong,China:Petrologic and Geochemical Evi2denceJ.Acta Sedimentologica Sinica,1994,12(3):1112冯彩霞,刘家军.硅质岩的研究现状及其成矿意义J.世界地质,2001,20(2):119123 Feng Caixia,Liu Jiajun.Current research sit2uation 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M.北京:地质出版社,2000,108128 Wang Jian.Neoproterozoic rifting history of SouthChina:Siginificance to rodinia breakupM.Beijing:Geological Pub2lishing House,2000.108128The Middle2shallow Water Sedimentary Environmentof the Late Sinian of South Anhui Based on the olistotrome and the siliceous storm sedimentsYU Xin2qi1SHU Liang2shu1DENG Ping1,2WANG De2en3ZHI Li2geng31(Department of Earth Sciences of Nanjing University,Nanjing210093)2(Research Institute No.290,CNNC,Shaoguan Guangdong512026)3(332 Team of Anhui Bureau of G eology and Mineral Resources,Huangshan Anhui245000)AbstractWe have found in Shexian and Xiuning Counties of South Anhui that there are some turbidite interlay2ers and a debris flow caused olistostrome near the top of the Lantian Formation of the lower member of the UpperSinian,and there are some siliceous storm sediments in the Piyuangcun Formation of the top member of the UpperSinian.These discoveries indicate that the area of South Anhui belongs to a hemipelagic or shallow environmentwhen sedimentation occurs during the late Sinian,not a pelagic environment as being usually believed,at least thesedimentary surface was not lower than the wave base of the storm.Key wordsolistostrome,storm sediments,Piyuancun and Lantian Formations,Late Sinian,South Anhui304第3期 余心起等:皖南晚震旦世中、浅海沉积环境 1995-2006 Tsinghua Tongfang Optical D