饶阳凹陷蠡县斜坡古近系沙河街组一段物源特征研究

Sedimentary provenance of the first member of the Shahejie Formation,Lixian Slope,Raoyang Sag

物源供应不仅影响了冀中坳陷饶阳凹陷蠡县斜坡地区沙河街组一段展布特征,而且控制了沉积类型和相带分布,进而决定了有利油气储层的发育。为了厘清蠡县斜坡地区的物源特征,从而指导进一步的沉积体系研究和勘探开发工作,本文基于饶阳凹陷蠡县斜坡3D地震资料、古近系沙河街组沙一段岩石学特征、重矿物组合及ZTR指数、碎屑锆石晶型及U-Pb年龄谱图,开展了沙一段沉积物源综合分析。研究结果表明:(1)蠡县斜坡北部、西部、南西部均发育有地震前积结构,且碎屑岩成分成熟度、ZTR指数分别向南东、东、北东方向增加,指示蠡县斜坡北部、西部、南西部各有一组水系携带物源注入。(2)依据岩屑组合和重矿物组合在平面上的展布特征,可以将蠡县斜坡地区划分出A、B、C 3个区域。其中A区地层具有来自基底隆起、切割岛弧环境的组分特征,且发育有一定的再旋回组分。岩屑组合为岩浆岩+沉积岩岩屑,重矿物组合为石榴石+锆石+磁铁矿+赤褐铁矿;B区地层具有来自基底隆起的组分特征,岩屑组合为岩浆岩+沉积岩+少量变质岩岩屑,重矿物组合为石榴石+锆石;C区地层具有来自基底隆起的组分特征,岩屑组合为岩浆岩+沉积岩+变质岩岩屑,重矿物组合为石榴石+锆石+钛铁矿。A、B、C区内沉积地层的发育依次由北部、西部、南西部水系控制,3组物源在西柳地区交汇。(3)锆石颗粒形态与年龄特征显示,工区内各物源对应的母岩区均为太行山隆起。其中注入工区北部的河流主要流经五台—忻州—涞源一带,携带的母岩主要为元古宇岩浆岩和古生界岩浆岩;携带西部物源的河流主要流经繁峙—涞源—阜平地区,对应的母岩主要为古生界岩浆岩;携带南西部物源的河流主要流经五台—阜平—定州一带,对应母岩主要为元古宇岩浆岩和古生界岩浆岩。相比沙二段,沙一段沉积时期西部物源供源能力有显著增强,南西部物源输入能力相对下降。(4)各组水系携带物源注入工区后形成浅水三角洲沉积体系,且距物源越近,物源供给强度越大,砂体发育情况越好。

Source supply not only affected the distribution characteristics of the 1 st Member of Shahejie Formation,Lixian Slope,Raoyang Sag,Jizhong Depression,but also controlled the sedimentary type and facies distribution,which in turn controlled the development of favorable hydrocarbon reservoirs.In order to clarify the sedimentary provenance of the Lixian Slope to support further research on the sedimentary system and oilfield exploration,we carried out a comprehensive analysis of sedimentary provenance based on 3D seismic data,petrological characteristics,heavy mineral compositions as well as the ZTR index,detrital zircon geochronology and morphology of the Paleogene Shahejie Formation.The results are summarized below.(1)Progradational seismic reflections were mapped downlapping in the northern,western and southwestern parts of the slope,and the composition maturity and ZTR indices of clastic rocks increased toward southeast,east and northeast,respectively,indicating water systems carrying material sources were injected,into the northern,western and southwestern parts of the slope,respectively.(2)According to the component characteristics of lithics and heavy minerals,the Lixian Slope can be divided into three regions A,B and C.Strata in region A resemble basement uplift or dissected arc in terms of component characteristics,and contain recycled orogenic elements;the components of lithic and heavy mineral assemblages are igneous and sedimentary rocks and garnet-zircon-magnetite-hematite,respectively.In regions B and C,strata resemble basement uplift.In region B,lithification resulted in magmatic and sedimentary rocks with small amount of metamorphic rock,and heavy minerals are garnet and zircon.Region C featured igneous/sedimentary/metamorphic rock combination in lithic rock fragments,and heavy minerals are garnet,zircon and ilmenite.Sedimentary deposition on the slope was controlled by the water systems injected from the north,west,and southwest and converging in the Xiliu area.(3)The morphology and geochronology of detrital zircons showed that the Taihangshang uplift was the parent rock area corresponding to each provenance in the survey area.The rivers carrying the northern,western and sourthwestern provenances mainly flew through the Wutai Xinzhou Laiyuan,Fanshi Laiyuan Fuping and Wutai Fuping Dingzhou areas,respectively,and the parent rocks they carried were mainly Proterozoic and Paleozoic,Paleozoic and Proterozoic and Paleozoic magmatic rocks,respectively.Compared with the 2 nd Member of the Shahejie Formation,the capacity of the western provenance in the 1 st Member was significantly enhanced while that of the southwestern provenance relatively decreased.(4)The shallow-water delta deposition systems formed after the water system injection,with the tendency of stronger provenance supply thus better sand-body development closer to the source.