【作者】 刘林玉；

【导师】 曲志浩；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2003， 博士

【摘要】 焉耆盆地在中生界地层发现油气以来，目前已进入开发阶段。焉耆中生代古盆地沉积特征与古盆地边界的确定对于该区油气勘探与开发是一项非常重要的科研任务。本文通过大量的野外调查、钻井岩心观察分析并通过分析已有的钻井地质、测井地质和地震剖面资料，详细研究了焉耆中生代古盆地的沉积特征，首次探索性地采用了一系列新方法恢复了焉耆中生代古盆地边界。 焉耆盆地的中生代地层比较发育且主要分布于博湖坳陷。中生代地层自下而上包括中上三叠统小泉沟群，下侏罗统八道湾组和三工河组，中侏罗统西山窑组和头屯河组。 碎屑岩是焉耆盆地的主要沉积岩石类型之一，碎屑岩的碎屑重矿物组合、粗碎屑组分和矿物成熟度随着搬运距离的不同而变化，它们是本区沉积相分析和确定原型盆地沉积边界的重要依据。为此我们采用了碎屑重矿物稳定系数、含砾碎屑隔岩百分比与矿物成熟度指数三个参数： 碎屑重矿物稳定系数=稳定碎屑重矿物的相对含量(％)／不稳定碎屑重矿物的相对含量(％)=(锆石+电气石+石榴石+磁铁矿+榍石+金红石+锡石+板钛矿+刚玉+萤石+锐钛矿)／(云母+绿帘石+绿泥石+黝帘石+角闪石+透闪石+钠闪石) 含砾碎屑岩百分比=(砾岩厚度+砂砾岩厚度+砾状砂岩厚度+含砾砂岩厚度)／地层厚度×100％ 碎屑岩矿物成熟度指数=石英含量/(长石含量+岩屑含量) 通过对三个参数在盆地内的变化特征以及碎屑重矿物组合、粗碎屑组合和矿物成熟度分析，可以得到以下几方面信息： (1)重矿物和岩屑分区反映原型盆地至少存在两大物源区及相应的两大古水流体系：①存在北部和西北部物源区，古水流方向以东南流向为主，兼有由北向南的古水流方向；②存在南部和西南部物源区，古水流方向以东北流向为主，兼有由南向北的古水流方向。 (2)在盆地北沉积区，侏罗纪由八道湾期至三工河期，重矿物稳定系数由小逐渐变大，含砾碎屑岩百分比由大逐渐变小，说明其古沉积边界随时代变新由近变远，沉积范围在南北方向上扩展而不是萎缩，暗示当时原型盆地主体处于(近)南北向伸展扩张为主的背景之中。在侏罗纪西山窑期，盆地南沉积区碎屑重矿物稳定系数由大变小，显示南部物源区在西山窑期出现北移的趋势。 (3)主体方向南东东的古流向与近乎南北方向的伸展说明古水流主体沿拉张断陷的轴向(或夹角很小)流动为主，且盆地中东部有可能构成当时的稳定沉积区。盆地西-西北部物源提供碎屑物质的幅度和水动力强度逐渐增大的特征与盆地北部不同，这更进一步表明了这一点。 (4)碎屑重矿物稳定系数、含砾碎屑岩石百分比和碎屑岩矿物成熟度指数三个定量参数的计算结果和变化规律非常一致，这进一步说明了上述分析的可靠性。 依据岩石组合、地层颜色、粒度特征、定量参数和沉积构造等沉积相标志，通过编制单井相剖面图、连井相剖面和沉积相平面图，对焉耆盆地中生界沉积相综合分析说明： (1)焉耆中生代盆地发育陆相冲积扇、河流(潮湿扇)、河流、湖泊和三角洲沉积体系，不同沉积体系与含砾碎屑岩百分比、碎屑重矿物稳定系数和矿物成熟度指数之间存在规律性的对应关系，即盆地边缘相带沉积物具有高的含砾碎屑百分比和低的碎屑重矿物稳定系数、矿物成熟度指数：盆地中心相带沉积物具有低的含砾碎屑岩百分比和高的碎屑重矿物稳定系数、矿物成熟度指数。 (2)小泉沟群以辫御可滨浅湖沉积为主体，/曝聘组以河流(潮湿扇卜河流撰豁狮角J曲澎可)沉积为主体，三1芳可组以河流(辫状河和曲流娜一滨浅湖沉积为主体，西山窑组以河流(辫书如沐!曲澎动沉积为主体，头屯河组以辫御可冗积为主体。冲积扇沉积仅分布于翻创匕豆栩七部及西部和南区的南部。 (3)由盆心怨籽U盗也中心形成冲积扇或河流(潮湿扇)-辫状洞一曲流可滨钱糊阮积的相模式。 ④在焉省中生代翻独瞬靡洲创程中，侏罗系地层自下而上形成两个沉积旋何，在夕键踏早期和三口玲可与溯由河流(潮湿扇)或冲积扇一河流(潮湿扇)沉积刀渗台;之后翻救族脑撰腼开始逐渐升高，在产键聘晚期和三工河中晚期出现滨浅湖沉积;从西山窑期开始湖盆萎缩，形成河流沉积。显示焉省盆地在侏罗乡改圣历了断陷一拗陷一断陷-拗阵犷衰退的演化过程。 (5)中侏罗旬咙黔蚜口西山窑期是焉者盆地沼泽环境的主要成煤期，由盆心撰籍嵘她中心形成扇沼一河沼一湖沼的沉积模式。 (6)在焉省中生f锐挑以’J、泉沟至头心可期的茹例刻石断呈中，盔沙也北区七里铺凹陷和南区的沉降中，臼存在着由西向东迁移的铡幸，显示焉誉中生代盆地具有剑刊肠功性质抓孟拙助课又中心存在着由北向南迁移、南部断露斑娇有在着由北向南扩展的规律，显示焉省中生代盆她良于拉张构造环境。由此可以看出，焉奢中封锰脚注体上属于具有右行扭动性质的弓侧性断陷盆地。 (7)焉誉中生于锰她在向新封弋卜香盆地演化过程中，衫翻识中心由南部发生大恻剿七移，说明盆地的构造性质发生明显的变化。 本文根据碎屑重矿物稳定系数、含砾碎屑岩百分比与矿物成熟渡荞幽与搬运距离之间的关系式对盗出引七部中生代古边界州了更多还原

【Abstract】 The Yanqi basin has been developed since oil and gas was found in the stratum of Mesozoic erathem.The determination of semidentary characteristics of theYanqi basin in Mesozoic Era and the boundaries of paleobasin is a very important scientific research task for the exploration and development of oil and gas in this region.This article gives a detailed research of the sedimentary characteristics of the Yanqi PaleoBasin in Mesozoic Era through large amount of field study ,observation and analysis of boring well’ s drilling core and an analysis of the given material which includes geology of boring well ,of logging ,and earthquake section .For the first time,mis article heuristic accept a series of new methods reconstruct the boundaries of paleobasin.Mesozoic Era strata of the Yanqi Basin ’s comparative development is mainly located at the Bo Lake depression , which is consisted of Xiaoquangou Group of upper and middle Triassic Series, Badaowan formation of lower Jurassic Series,Sangonghe formation and Xishanyao Group middle Jurassic period and Toutunhe Group from bottom to top.Detrital rock is a major type of the sedimentary rock of the Yanqi Basin.The asseblage of the fragment heavy mineral of detrital rock ,of coarse fragment ,minerak>gic maturity is changed according to different transport distance,so they are essential foundations for analysis of sedimentary fades in this region and determination of deposit boundary of paleobasin. For this,we adopt three parameters,that is, stability coefficient of fragmental heavy mineral,percentage of pebble-bearing rudite fragmental rockrnineralogic maturity index.The stability coefficient of fragmental heavy mineraHhe relative content of stable fragmental heavy mineral(%ythe relative content of instable fragmental heavy mineral(%) = (zirconite+ tourmaline+ gamet+ magnetite+sphene+rutile+cassiterite+brockite+corundum+fluorite+anatase)/(mica+epidoze+zoisite+hornble nde+tremolite+riebeckite)The percentage of rudite fragmental rock=The thickness of conglomerate +mickness of grit rock +of psephitic sandstone +of pebbly sandstone/thickness of stratum 100%The fragmental mineralogic maturity index=content of quartz/content of (feldspar +debris).Based on the analysis of the changing of above three parameters in the basin,asseblage of fragmental heavy mineral ,of coarse fragment and mineralogic maturity,we can obtain the following information about The Yanqi Basin in Mesozoic Era;1) The partitioning of heavy mineral and debris reflect that ancestral basin has at least two big sources zones and two big corresponding ancient stream current systems.(1) There exists northern and northwestern source zones .The majority of the ancient water flows southeastward ,and the minority of the ancient water flows southward.(2) There exists southern and southwestern source zones,with the majority of the ancient water flowing northeastwanLand the minority of the ancient water flowing northward.2) In the northern sedimentary zone of the basin,from Badaowan period to Sangonghe period inJurassic period,Stability coefficient of the heavy mineral increases, while the percentage of pebble-bearingt clastic rock decreases. This shows its ancient sedimentary boundary becomes farther and farther with the development of times, the sedimentary area extends instead of shrinking from south to north, which implies that the main part of the ancestral basin expands from south to north at that time. In the Xishanyao period of Jurassic period, the stability coefficient of the fragmental heavy mineral in the southern sedimentary area of the basin decreases, which demonstrates the southern source zone had the tendency of moving northward in the Xishanyao period.3)The ancient water flowing mainly in the direction of east by south and the near extension of the basin from south to north shows that the main part of the ancient streams flew along the axis of the pulling-apart fault depression, moreover, the central and eastern part of the basin had the possibilit更多还原