沉积学报  2019, Vol. 37 Issue (1): 62−71

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文章信息

赵梦, 杜晓峰, 王清斌, 冯冲, 庞小军, 李欢
ZHAO Meng, DU XiaoFeng, WANG QingBin, FENG Chong, PANG XiaoJun, LI Huan
渤海东部旅大29-1构造沙二段砂砾岩锆石定年及物源示踪
Detrital Zircon U-Pb Geochronology of the Es2 Sandstones of Lvda 29-1 Structure of the Eastern Bohai Sea, and Its Implication for Provenance
沉积学报, 2019, 37(1): 62-71
ACTA SEDIMENTOLOGICA SINCA, 2019, 37(1): 62-71
10.14027/j.issn.1000-0550.2018.149

文章历史

收稿日期:2018-04-23
收修改稿日期: 2018-06-13
渤海东部旅大29-1构造沙二段砂砾岩锆石定年及物源示踪
赵梦 , 杜晓峰 , 王清斌 , 冯冲 , 庞小军 , 李欢     
中海石油(中国)有限公司天津分公司渤海石油研究院, 天津 300459
摘要: 为示踪辽东凹陷LD29-1构造沙二段(Es2)砂岩沉积,对LD29-1-1、LD29-1-1Sa及LD29-1-2等3口井的沙二段砂岩6个岩屑样品进行了碎屑锆石U-Pb定年和锆石阴极发光(CL)图像分析。结果表明:LD29-1-1井样品中白垩纪(K)锆石含量高达41.2%,具有108 Ma峰值年龄,锆石柱状晶形完整,并且棱角明显;而LD29-1-1Sa及LD29-1-2井样品的中元古代(Pt2)锆石含量高达74%~75%,中生代(Mz)锆石含量少,具有~1.5 Ga和~1.8 Ga双峰值特征,锆石晶体明显小于LD29-1-1井沉积物,并且晶形不完整、边缘均被磨圆。因此,认为LD29-1-1井沙二段砂岩为近源沉积,母岩为长兴岛凸起斜坡带中生界碎屑岩,而LD29-1-1Sa及LD29-1-2井沙二段砂体为远源沉积,母岩以辽东半岛西部复州地区广泛分布的中、上元古界沉积岩为主,在搬运至斜坡带时才混入少量中生界碎屑岩。
关键词: 旅大29-1构造    物源示踪    碎屑锆石U-Pb年龄    中元古界    上元古界    
Detrital Zircon U-Pb Geochronology of the Es2 Sandstones of Lvda 29-1 Structure of the Eastern Bohai Sea, and Its Implication for Provenance
ZHAO Meng , DU XiaoFeng , WANG QingBin , FENG Chong , PANG XiaoJun , LI Huan     
Bohai Oilfield Research Institute, China National Offshore Oil Corporation, Tianjin Branch, Tianjin 300459, China
Foundation: National Science and Technology Major Project, No.2016ZX05024003
Abstract: To trace the sedimentary source-to-sink systems of the Lvda 29-1 structure in the eastern Bohai Sea, six sandstone cuttings of the second Member of Shahejie Formation (Es2) were collected from LD29-1-1, LD29-1-1Sa and LD29-1-2 for detrital zircon U-Pb dating and cathodoluminescence (CL) image analysis. The results showed that the sandstones of LD29-1-1 contained 41.2% Cretaceous (K) zircons and featured a 108 Ma peak, and the columnar crystals were characterized by sharp edges. The LD29-1-1Sa and LD29-1-2 sandstones contained 74%-75% Mesoproterozoic (Pt2) zircons with peaks at ~1.5 Ga and ~1.8 Ga, and the broken crystals were well rounded. We concluded that the Es2 sandstones of LD29-1-1 were near-source deposited, and the provenance was the Mesozoic sedimentary rocks along the slope of the Changxingdao Uplift; the Es2 sandstones of LD29-1-1Sa and LD29-1-2 were distal from the source area and were dominated by the widespread Mesoproterozoic and Neoproterozoic sedimentary rocks exposed in Fuzhou on the western Liaodong Peninsula, with only a slight influence of Mesozoic sedimentary rocks from the slope of the Changxingdao Uplift.
Key words: Lvda 29-1 Structure    provenance    detrital zircon U-Pb ages    Mesoproterozoic    Neoproterozoic    
0 引言

含油气盆地的物源演化影响着盆地储集砂体的发育及分布,因此,在我国的边缘海含油气盆地,在渤海湾盆地、珠江口盆地、琼东南盆地及莺歌海盆地等区域均进行着大量相关研究,通过三维地震资料古地貌分析、沉积岩碎屑组分分析、元素分析、重矿物分析、碎屑锆石U-Pb定年分析等分析手段重建盆地不同地质时期的源汇体系及其演化过程[1-13]。其中,沉积岩中的碎屑锆石U-Pb年龄由于其几乎不受搬运过程及成岩过程的影响,最大限度地保留了母岩的信息,从而成为研究沉积岩物源示踪的有效方法[13-19]。目前,在渤海海域,对沉积岩的碎屑锆石年代学物源示踪分析主要集中在渤海西部地区石臼坨凸起、沙垒田凸起及其围区一带[8-9, 13, 20],在渤海东部仅有部分花岗岩基底锆石U-Pb定年数据发表[21-22],尚无系统的沉积岩碎屑锆石年代学物源示踪研究发表。本研究首次在渤海东部开展了旅大29-1构造沙二段砂体的碎屑锆石年代学分析,发现研究区不同井位沉积物年龄组分和晶体形态差异明显,识别出两组不同的物源体系,并对研究区的潜在陆上物源区展开调研,推测其源区分布范围,为认识、理解旅大29-1构造沙二段沉积期的古物源体系提供了新的证据。

1 地质概况

图 1所示,旅大29-1构造位于渤海东部,地震、钻井资料表明,研究区紧邻长兴岛凸起向西倾没的斜坡带,凸起上发育元古界变质花岗岩基底,在斜坡带底部发育小面积中生界碎屑岩,在斜坡带南段发育中生界碎屑岩和元古界碳酸盐岩。在古近系沙河街组二段沉积时期,斜坡带沟谷体系发育,来自长兴岛凸起的碎屑沉积物,在斜坡带底部堆积形成多个辫状河三角洲扇体,除LD28-1-1井受南段斜坡带物源区影响之外,LD29-1-1、LD29-1-1Sa及LD29-1-2等井位均受到东侧及东北侧斜坡带物源区影响[11]

图 1 辽东凹陷南洼物源区地质图与钻井位置[11] Figure 1 Geological map of the provenance of the southern Liaodong sag and location of wells [11]

钻井资料显示,LD29-1-1、LD29-1-1Sa及LD29-1-2井沙二段岩性差异很大(图 2):LD29-1-2井沙二段砂体最为发育,砂体总厚度约106 m,以砂砾岩为主,局部砂体含灰质,泥岩、页岩及煤层夹层少且薄;LD29-1-1Sa井沙二段砂体总体厚度约50 m,为含砾中砂岩,泥岩发育;LD29-1-1井沙二段整体以泥岩、泥砾岩、灰质泥岩和泥灰岩为主,砂体总体厚度仅为27 m左右,为含砾中砂岩和粉砂岩。其中,LD29-1-1Sa井沙二段砂砾岩储层段DST测试获得629 m3/天的产能,证实了该构造沙二段砂砾岩储层勘探潜力巨大。但该构造沙二段砂砾岩储层纵向分布非均质性强,砂砾岩体的展布规律有待进一步明确,制约了该地区下一步的勘探评价。因此,对该构造沙二段砂岩进行碎屑锆石年代学分析、开展物源示踪研究、并重建其源汇体系对该地区的储层预测和勘探评价具有重要意义。

图 2 各井沙二段岩性剖面 Figure 2 Lithology of the 2nd Member of the Shahejie Formation (Es2) of the wells
2 材料方法

对LD29-1-1、LD29-1-1Sa及LD29-1-2 3口井的沙二段砂岩岩屑取样,共采集6个岩屑样品(取样层位深度如图 2所示),进行碎屑锆石U-Pb定年分析。样品岩性为辫状河三角洲前缘含砾中砂岩、砂砾岩。样品的预处理、阴极发光(CL)图像拍摄和LA-ICP-MS定年均在中国地质大学(武汉)地质过程与矿产资源国家重点实验室(GPMR)完成,激光剥蚀系统为GeoLas 2005,ICP-MS为Agilent 7500a。

对每颗锆石进行U-Pb定年,最终获得三组年龄:207Pb/206Pb,207Pb/235U,206Pb/238U。对于封闭体系,U-Pb年龄是谐和的,反映出锆石的结晶年龄。而在实际情况下,由于热液或变质作用的影响,锆石有可能会Pb污染或丢失,导致U-Pb年龄不谐和。在数据处理中,对206Pb/238U年龄小于1 000 Ma的锆石选取206Pb/238U年龄,并以100×(207Pb/235U)/(206Pb/238U)计算谐和度;对206Pb/238U年龄大于1 000 Ma的锆石选取207Pb/206Pb年龄并以100×(207Pb/206Pb)/(206Pb/238U)计算谐和度[23]。结合样品数据情况,选取谐和度大于90%的锆石U-Pb年龄,并根据Kernel Density Estimation(KDE)方法绘制锆石年龄谱图[24-26]

3 碎屑锆石U-Pb年龄及形态特征 3.1 碎屑锆石U-Pb年龄特征

测年数据经过预处理,共计获得205个谐和年龄(谐和度>90%,图 3表 1),其中96%的锆石样品Th/U>0.3,说明样品锆石以岩浆成因为主,不含Th/U < 0.1的变质成因锆石(图 4)。样品碎屑锆石年龄从太古代到新生代都有分布(表 1图 5),最年轻年龄为52.5 Ma(LD29-1-1Sa,2 575~2 580 m,沙二段Es2),最古老年龄为2 758 Ma(LD29-1-2,2 725~2 735 m,沙二段Es2)。

图 3 旅大29-1构造沙二段砂岩碎屑锆石U-Pb年龄谐和图 Figure 3 Detrital zircon U-Pb concordant plots of the Es2 sandstones, LD29-1
表 1 旅大29-1构造沙二段砂岩碎屑锆石U-Pb年龄组成(%)统计表 Table 1 U-Pb ages distribution of detrital zircons of the Es2 sandstone, LD29-1
井名 测年点数 < 65 < 140 < 208 < 250 < 290 < 362 < 409 < 439 < 510 < 570 < 1000 < 1800 < 2500 >2500 Mz Pz Pt
Kz K J T P C D S O Pt3 Pt2 Pt1 Ar
LD29-1-1 51 0.0 41.2 5.9 7.8 3.9 2.0 2.0 0.0 0.0 0.0 9.8 15.7 9.8 2.0 54.9 7.8 35.3
LD29-1-1Sa 96 1.0 6.3 0.0 2.1 1.0 2.1 0.0 0.0 0.0 0.0 3.1 75.0 8.3 1.0 8.3 3.1 86.5
LD29-1-2 58 0.0 6.9 1.7 0.0 1.7 0.0 0.0 0.0 0.0 0.0 5.2 74.1 8.6 1.7 8.6 1.7 87.9
图 4 旅大29-1构造沙二段砂岩碎屑锆石Th/U比值 Figure 4 Th/U ratio of detrital zircons of the Es2 sandstones, LD29-1
图 5 旅大29-1构造沙二段砂岩碎屑锆石U-Pb年龄谱图(n为年龄点个数) Figure 5 U-Pb age spectra for detrital zircons of the Es2 sandstone, LD29-1 (n refers to the number of age measurements)

LD29-1-1井其沙二段含砾中砂岩及砂砾岩样品共测得51个谐和锆石U-Pb年龄点。样品富含大量中生代(Mz)锆石,含量为54.9%,其中白垩纪(K)锆石含量高达41.2%,侏罗纪(J)锆石占5.9%,三叠纪(T)锆石占7.8%。古生代(Pz)锆石含量较少,含量为7.8%,其中二叠纪(P)锆石占3.9%,石炭纪(C)锆石占2.0%,泥盆纪(D)锆石占2.0%,不含志留纪(S)、奥陶纪(O)或寒武纪(∈)锆石。元古代(Pt)锆石含量为35.3%,其中新元古代(Pt3)锆石占9.8%、中元古代(Pt2)锆石占15.7%,古元古代(Pt1)锆石占9.8%。样品中的太古代(Ar)锆石含量为2%(表 1图 5)。其碎屑锆石U-Pb年龄谱以显著的108 Ma峰值为特征,其他峰值均不明显(图 5)。

LD29-1-1Sa井沙二段含砾中砂岩样品共测得96个谐和锆石U-Pb年龄点。样品测得一颗新生代(Kz)锆石,占样点总数的1%。中生代(Mz)锆石含量较少,为8.3%,其中白垩纪(K)锆石含量为6.3%,三叠纪(T)锆石占2.1%,不含侏罗纪(J)锆石。古生代(Pz)锆石含量仅为3.1%,其中二叠纪(P)锆石占1.0%,石炭纪(C)锆石占2.1%,不含泥盆纪(D)、志留纪(S)、奥陶纪(O)或寒武纪(∈)锆石。样品含有大量的元古代(Pt)锆石,含量为86.5%,其中新元古代(Pt3)锆石仅占3.1%、中元古代(Pt2)锆石占75.0%,古元古代(Pt1)锆石占8.3%。样品中的太古代(Ar)锆石含量为1.0%(表 1图 5)。其碎屑锆石U-Pb年龄谱的主要峰值年龄为1 548 Ma和1 770 Ma,并具有108 Ma次要峰值(图 5)。

LD29-1-2井沙二段砂砾岩样品共测得58个谐和锆石U-Pb年龄点。样品的中生代(Mz)锆石含量较少,为8.6%,其中白垩纪(K)锆石含量为6.9%,侏罗纪(J)锆石占1.7%,不含三叠纪(T)锆石。古生代(Pz)锆石含量仅为1.7%,全部为二叠纪(P)锆石,不含石炭纪(C)、泥盆纪(D)、志留纪(S)、奥陶纪(O)或寒武纪(∈)锆石。样品含有大量的元古代(Pt)锆石,含量为87.9%,其中新元古代(Pt3)锆石含量为5.2%、中元古代(Pt2)锆石占74.1%,古元古代(Pt1)锆石占8.6%。样品中的太古代(Ar)锆石含量为1.7%(表 1图 5)。其碎屑锆石U-Pb年龄谱的主要峰值年龄为1 542 Ma和1 757 Ma,并具有126 Ma次要峰值(图 5)。

可以看出,LD29-1-1、LD29-1-1Sa及LD29-1-2 3口井的沙二段砂砾岩碎屑锆石年龄组分及其U-Pb年龄频谱特征存在差异,总体上,依据其锆石U-Pb年龄特征可以识别出两组不同的物源体系:南部LD29-1-1井单独具有一套物源体系,母岩以108 Ma峰值年龄为特征,富含K锆石,Pt锆石含量很少;而LD29-1-1Sa井的沙二段砂岩特征与北部LD29-1-2相似,二井的沉积物来自另一套物源体系,母岩以中元古代~1.5 Ga和~1.8 Ga双峰值年龄为特征,富含中元古代锆石。

3.2 碎屑锆石形态特征

利用锆石CL图像,对三口井位沙二段砂岩样品进行了锆石形态学分析,受篇幅限制,仅在本文中列出部分样品锆石CL图像以便讨论。分析发现,如图 6所示,LD29-1-1井沙二段含砾中砂岩样品锆石粒度多在100~300 μm之间,以中生代(Mz)锆石为主。中生代锆石颗粒大、柱状特征明显,多数晶形完好,晶体棱角分明,岩浆生长振荡环带明显。元古代(Pt)锆石则一定程度被磨圆,但大部分锆石仍能看出完整晶形。该井砂岩样品中锆石整体上晶形完整,具棱角,因此LD29-1-1井沙二段沉积物搬运距离非常短,为近源沉积(图 1),LD29-1-1井紧邻斜坡带中生界碎屑岩和元古界变质岩,而LD29-1-1井白垩纪(K)锆石含量高达41.2%,不符合元古界变质岩的年龄特征,因此认为LD29-1-1井母岩主要为斜坡带的中生界碎屑岩。

图 6 LD29-1-1井沙二段样品部分锆石CL图像 Figure 6 CL images of the Es2 sandstones, Well LD29-1-1

锆石CL图像分析显示,LD29-1-1Sa井和LD29-1-2井沙二段砂砾岩样品锆石形态特征相似,锆石粒度多在60~200 μm之间,粒度整体小于LD29-1-1井沙二段,且以元古代锆石为主。如图 7所示,LD29-1-1Sa井中生代(Mz)锆石部分晶形完好,岩浆生长振荡环带明显,具有一定棱角,与LD29-1-1井中生代(Mz)锆石形态相似,认为其母岩同样为斜坡带中生界碎屑岩。但LD29-1-1Sa井和LD29-1-2井样品的中生代(Mz)锆石含量很少,分别为8.3%和8.6%,远远少于LD29-1-1井样品中高达54.9%的中生代(Mz)锆石含量(表 1),说明斜坡带中生界母岩对LD29-1-1Sa井和LD29-1-2井的沉积贡献很少。而样品中大量的元古代(Pt)锆石不但多数晶形不完整,且均被磨圆,显示其母岩锆石形成之后被再次破碎、磨圆,经过了长距离的搬运之后最终抵达研究区沉积(图 7)。因此认为LD29-1-1Sa井和LD29-1-2井沙二段沉积物主要受控于一远距离物源区,母岩可能为元古界岩浆岩和沉积岩,沉积物在搬运至斜坡带时,有少量中生界碎屑岩加入。虽然长兴岛凸起基岩为元古界,但凸起紧邻研究区,搬运距离不足以令其锆石晶体完全破碎并磨圆,因此认为凸起上发育的沟谷体系以搬运作用为主,物源区应自凸起再向东侧拓展。

图 7 LD29-1-1Sa井沙二段样品部分锆石CL图像 Figure 7 CL images of the Es2 sandstones, Well LD29-1-1Sa

由此可见,在本研究中,通过样品的碎屑锆石U-Pb年龄特征和形态特征分析,可将研究区物源体系分为两组:LD29-1-1井为近源沉积,沉积物富含白垩纪(K)锆石,具有108 Ma峰值,母岩以斜坡带中生界碎屑岩为主;而LD29-1-1Sa及LD29-1-2井为远源沉积,沉积物锆石年龄组分的中元古代(Pt2)锆石含量高达74%~75%,中生代(Mz)锆石含量少,并具有~1.5 Ga和~1.8 Ga双峰值,其主要母岩类型可能为元古界岩浆岩和沉积岩,分布范围应自长兴岛凸起再往东侧拓展。

4 物源示踪及源区讨论

在前文中,LD29-1-1井样品锆石晶体颗粒大、柱状特征明显,多数晶形完好,晶体棱角分明,具有近源沉积特征,其含量高达54.9%的中生代(Mz)锆石不符合相邻的元古界基底年龄特征,因此认为其母岩主要为邻区斜坡带的中生界碎屑岩。而LD29-1-1Sa及LD29-1-2井的锆石U-Pb年龄特征和CL图像形态学分析表明其主要母岩类型可能为元古界岩浆岩和沉积岩,沉积物历经远距离搬运,物源范围可能拓展至长兴岛凸起以东地区。然而,受矿区范围限制,目前长兴岛凸起及其东侧海域范围内均缺乏钻井样品及分析数据,因此,对辽东半岛陆上部分展开了调查研究,收集、对比了辽东半岛太古界—元古界锆石年龄数据[27-31],以期为研究区的物源分析提供母岩的锆石年龄证据。

辽东半岛属于辽南地块(图 8),以瓦房店为界,辽东半岛东部地区岩性以太古界变质岩及中生界岩浆岩为主,元古界地层具有显著的1.9 Ga主峰值年龄[30],而LD29-1-1Sa及LD29-1-2井的太古代锆石组分极少,其含量分别为1.0%和1.7%(表 1),其年龄谱未见太古代峰值(图 5),故认为辽东半岛东部地区并非研究区的物源区。在辽东半岛西部,元古界沉积岩广泛分布,上元古界地层层序齐全且分布广泛(图 8),在多地角度不整合于太古代混合岩之上或平行不整合于下元古界之上。该地区中、上元古界地层主要包括:青白口系永宁组河流—冲积扇相灰白色、紫红色中厚层砾岩,细河群钓鱼台组灰色中厚层石英砂岩,细河群南芬组灰绿色粉砂质页岩,和震旦系[33-35]

图 8 辽东半岛地质图(据1:100万中国地质图,2013[32]) Figure 8 Geological map of the Liaodong Peninsula (modified after 1:1 000 000 geological map of China, 2013[32])

以金州为界,辽东半岛西部可进一步分为北部复州地区和南部大连—金州地区。在复州地区,高林志等[31]在长兴岛西侧上元古界青白口系细河群钓鱼台组中薄层砂岩夹粉砂岩和灰色泥岩露头处取样,发现沉积岩样品锆石年龄谱具有突出的1.6 Ga峰值,以及1.8 Ga、1.3 Ga和1.0 Ga等次要峰值年龄(图 9),中元古代(Pt2)锆石含量高达87.5%。而在本研究中,LD29-1-2和LD29-1-1Sa井沙二段砂岩样品同样具有该系列峰值特征,并且二井样品的中元古代(Pt2)锆石含量高达74%~75%(图 5),十分接近长兴岛样品的锆石年龄特征。此外,长兴岛样品中的锆石晶体呈柱状,晶形完好,锆石粒度多在100~200 μm之间,岩浆生长振荡环带明显[31],而LD29-1-2和LD29-1-1Sa井的沙二段砂岩样品中的元古代(Pt2)锆石虽仍能识别出岩浆生长的振荡环带特征(图 7),Th/U比值也显示其为岩浆成因(图 4),但均已不具备完整的长柱状晶形,晶体破碎,大小多为100 μm,且磨圆度很高,显示其经历了长距离的搬运,而长兴岛与研究区相距60 km,满足远距离搬运条件,因此,可以认为该上元古界钓鱼台组沉积岩是LD29-1-2和LD29-1-1Sa井沙二段砂砾岩的母岩之一。

图 9 长兴岛钓鱼台组砂岩碎屑锆石U-Pb年龄谱图(数据引自高林志等[31]n为年龄点个数) Figure 9 U-Pb age spectra of the detrital zircons for sandstones of the Diaoyutai Formation, Changxing Island (data from Gao et al.[31]; n refers to the number of the age measurements)

在区域地质上,长兴岛属于复州地区,该区域整体主要发育中、上元古界沉积岩(图 8),高林志等[31]所测样品为上元古界钓鱼台组砂岩,该套砂岩底部与中元古界永宁组砂岩整合或平行不整合接触[33-35],二者连续沉积,可以认为钓鱼台组砂岩继承了永宁组砂岩的锆石年龄特征,二者均为研究区母岩地层。此外,钓鱼台组和永宁组又分别是复州地区上元古界和中元古界的代表性地层,因此,认为辽东半岛复州地区的中、上元古界同为研究区的母岩地层,其分布范围即为物源区范围。

图 8所示,在辽东半岛西部,中、上元古界不但覆盖整个复州地区,还在大连—金州地区也广泛出露。研究表明,在大连金州地区,太古代变质基底出露,锆石年龄为2.53~2.46 Ga[36],上元古界钓鱼台组砂岩主峰值年龄为1 484 Ma,不同于长兴岛同层系样品,上元古界兴民村组砂岩具有934 Ma和1 623 Ma双峰值年龄,并含有大量0.9~1.0 Ga锆石[29],上元古界桥头组以潮坪相黄色、白色中厚层石英砂岩为主,被三叠纪辉绿岩侵入,该辉绿岩中含有大量0.9~1.1 Ga锆石[27, 37]。可见大连—金州地区上元古界沉积岩中碎屑锆石的最主要年龄组成是0.9~1.0 Ga,然而,这组年龄不是本研究中旅大29-1构造沙二段砂体的主要锆石年龄组成,故认为辽东半岛大连—金州地区在沙二沉积时期并未处于研究区的源区范围。

综上所述,认为在沙二沉积时期,LD29-1-2和LD29-1-1Sa井沉积物的母岩以广泛出露于辽东半岛西部复州地区的中、上元古界沉积岩为主,母岩被风化剥蚀后历经长距离搬运最终抵达旅大29-1构造再沉积。

5 结论

本研究首次在渤海东部开展了旅大29-1构造沙二段辫状河三角洲前缘砂体的碎屑锆石年代学分析,发现研究区三口钻井沉积物均为岩浆成因锆石,但年龄组分差异明显,研究区受到两组不同的物源体系控制:

(1) LD29-1-1井沙二段砂岩含有高达41.2%的白垩纪(K)锆石,具有108 Ma峰值年龄,多数锆石晶形完整,呈柱状,并且棱角明显,为近源沉积,母岩以斜坡带中生界碎屑岩为主;

(2) LD29-1-1Sa及LD29-1-2井沙二段砂砾岩的中元古代(Pt2)锆石含量高达74%~75%,中生代(Mz)锆石含量少,并具有~1.5 Ga和~1.8 Ga双峰值特征,锆石晶体明显小于LD29-1-1井沉积物,并且晶形不完整、边缘均被磨圆,为远源沉积,母岩为辽东半岛西部复州地区广泛分布的中、上元古界沉积岩。LD29-1-1Sa及LD29-1-2井物源区远离沉积区,其中、上元古界母岩被风化剥蚀后历经长距离搬运最终抵达旅大29-1构造再沉积,在抵达斜坡带时才混入少量中生界碎屑岩。

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