论文标题:辽西牛营子—郭家店盆地晚侏罗世土城子组同构造沉积研究
Study on Late Jurassic Tuchengzi Formation Syntectonic Deposits in Guojiadian-Nuyingzi Basin in the West Of Liaoning Province
论文作者 孙卫华
论文导师 张长厚；徐德斌,论文学位 硕士,论文专业 构造地质学
论文单位 中国地质大学（北京）,点击次数 204,论文页数 40页File Size2381k
2002-06-01论文网 http://www.lw23.com/lunwen_1328462/ 辽西,同构造沉积,物源区,牛营子－郭家店盆地,土城子组
Liaoning province,Syntectonic sedimentation,Provenance,Niuyingzi-Guojiadian basin,Tuchengzi Formation
同构造沉积记录研究是当前地质学研究的热点和前沿领域之一。在我国，类似的研究工作开展的不多，在燕山造山带的地质研究工作中，这种研究尚属空白。 本文依托于1：250000青龙县幅区调项目，选择了辽宁省西部的牛营子-郭家店侏罗纪盆地中的土城子组砾岩进行同构造沉积研究。通过野外填图、实测地层剖面及室内分析工作，取得了如下主要成果和认识： 1、土城子组主要由一套分选性和磨圆度都很差的碳酸盐质砾岩构成。砾岩的成分和结构成熟度都表明它的形成与剧烈的构造活动紧密相关，是研究区内晚侏罗世时期强烈构造变动的沉积记录。 2、更加准确地填绘出了牛营子—郭家店盆地土城子组现存地层所构成的紧闭向斜形态，为认识盆地原始形态并进而开展沉积学研究奠定了基础。 3、初步厘定了牛营子—郭家店盆地土城子组所构成的向斜两翼砾岩中砾石成分的变化规律。向斜西翼砾岩的砾石成分下部以安山岩砾石为主，沿剖面向上砾岩中安山岩砾石成分减少，而灰岩砾石成分增加，至上部砾石成分变为以灰岩砾石为主；东翼砾岩中的砾石成分下部以含燧石带白云岩、白云岩砾石为主，沿剖面向上砾岩中白云岩质砾石成分减少，而灰岩砾石成分增加，至上部砾石成分变为以灰岩砾石为主。 4、确定了土城子组砾岩中的三种主要砾石成分(安山岩、灰岩和白云岩砾石)的来源。安山岩砾石是中侏罗统髫髻山组火山岩剥蚀的产物，灰岩砾石来自于寒武、奥陶系灰岩，白云岩砾石主要来自于蓟县系白云岩。西翼砾岩在剖面上具明显的倒序岩屑地层特征，反映了物源区正常的层序地层，而东翼砾岩在剖面上仍然是正序的岩屑地层，反映了物源区非正常的层序地层。 5、根据土城子组向斜两翼岩层厚度及砾岩砾石成分的显著差异，推测两翼地层可能来自于不同的物源区。结合盆地周围的地层、构造特征，对牛营子—郭家店盆地土城子组砾岩可能的物源区进行了分析和讨论。指出牛营子—郭家店盆地并不是一个单物源的盆地，西翼砾岩的物源区可能是盆地西侧侏罗纪盆地下伏地层，而东翼的物源区可能是盆地东侧具倒转地层的老爷庙-老厂子逆冲断层上盘逆冲岩席。因此，目前所见到的牛营子—郭家店盆地是一个经历后期强烈构造改造和剥蚀的残余盆地，而不是一个原形盆地。
The study of syntectonic sedimentary deposits is one of the advanced topics in current geological research. In China only few similar studies have been conducted and there is still very little known about syntectonic deposits in the Yanshan erogenic belt.Based on the 1:250,000 Qinglong mapping project, we chose to study Nuyingzi-Goujiadian basin, a small Jurassic basin in western Liaoning province. Within this basin, we place emphasis on the Late Jurassic Tuchengzi Formation, which mainly consists of conglomerate. Sedimentological and provenance data from Tuchengzi Formation in Nuyingzi-Goujiadian basin provide information about the links between erosional unroofing of adjacent thrust sheets and deposition within the basin.Through field mapping, measured sections, and Sedimentological analysis, we arrived at the following conclusions:1. The Tuchengzi Formation mainly consists of carbonate (limestone and dolomite) clast conglomerate characterized by poorly sorted and poorly rounded clasts, which shows that the deposition of the Tuchengzi Formation is closely associated with Late Jurassic tectonism.2. The formation of a tight syncline in the Tuchengzi Formation is depicted accurately.3. There are three main clast types in the conglomerate: andesite, limestone, and dolomite. The andesite clasts were most likely derived from erosion of igneous rock in Middle Jurassic time, and the limestone clasts were derived from Cambrian and Ordovician strata. Dolomite clasts were derived from the Middle Proterozoic Jixian Group.The compositional varieties of clasts at both limbs of the syncline have been investigated. On the west limb, there are andesite clasts at the lower section and limestone clasts at the upper section, which indicates normal stratigraphic sequence in its provenance. On the east limb, there are dolomite clasts at the lower section and limestone clasts at the upper section, which indicates reversed stratigraphic sequence in its provenance.4. The differences of strata thickness and clasts composition between west and east limb suggest different provenances. In this paper the possible provenances of the Tuchengzi Formation conglomerate are discussed in detail. This study indicates that Nuyingzi-Guojiadian basin is an relic of a Jurassic basin and it should be much bigger than what it occupies now. Moreover, the main provenance of Tuchenzi Foumation is probably the overturned strata exposed at the Laoyemiao-Laochangzi thrust sheet.
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