塔里木盆地下寒武统台缘带沉积结构特征及其形成过程

目前对于缺乏宏观造礁生物而仅由微生物参与形成的寒武系台缘带沉积结构的沉积学理论研究仍然比较薄弱。塔里木盆地柯坪地区出露下寒武统台缘带地层，对其进行系统的野外调查、剖面分层精细测量和室内薄片镜下分析，刻画了台缘带的沉积结构特征，建立了台缘带的沉积结构模型，阐述了在微生物参与下台缘带的形成过程。研究结果表明，塔里木盆地下寒武统台缘带发育从较深水区向潮间带过渡的水体向上逐渐变浅的沉积演化序列，具有由泥晶沉积、层纹石、微生物丘、颗粒沉积和叠层石等5种沉积类型从下至上分层叠置的沉积结构特征，其中，泥晶沉积、层纹石、颗粒沉积和叠层石在整个台缘带上呈层状展布，而微生物丘在台缘带上的南北向展布宽度仅10 km左右。据此，将台缘带的形成过程划分为泥晶沉积发育阶段、层纹石发育阶段、微生物丘发育阶段、颗粒沉积发育阶段和叠层石发育阶段。微生物丘的发育在台缘带上形成地层局部加厚且向两侧减薄的特点，导致台缘带从微生物丘发育之前具有的沉积厚度从南向北缓慢减薄的缓坡属性转变为从微生物丘发育开始具有的地层局部加厚形成隆起部位的弱镶边属性。上述认识能为确定塔里木盆地下寒武统碳酸盐台地的结构样式和探索台缘带优质碳酸盐岩油气储层的发育规律提供沉积学依据。

Sedimentary Texture and Formation Process of the Lower Cambrian Plat-form Marginal Zone in the Tarim Basin,NW China

The theoretical study on the sedimentary texture of Cambrian platform margin is still rather weak at present, which was formed merely under the participation of microorganism due to the lack of reef-building organism. The platform marginal stratum of Lower Cambrian system in the Kalpin outcrop area of Tarim Basin was investigated and studied in this paper, using systematic field survey, field profile's measurement and indoor thin section analysis,to characterize the sedimentary texture of the platform marginal zone, establish a model of the sedimentary texture, and expound the formation process under the participation of microorganism. All study results above showed that the Lower Cambrian platform marginal sediments of the Tarim Basin had a width of about 30 km from south to north and a thickness of 110-167 m, which were composed of micritic deposition, laminated microbialite, microbial mound, granule deposition and stromatolite bottomup. These features indicated an upward shallowing sedimentary sequence from deep sea to intertidal zone, and hence the forming process of the platform margin could be divided into five stages. Micritic deposition, laminated microbialite, granule deposition and stromatolite showed stratiform feature on the whole platform margin, while the microbial mound only had a width of about 10 km from south to north on the platform margin and a maximal thickness of nearly 30 m. During this period, a upwarping region may occure locally on the platform margin and lead to the change of platform margin property before and after the formation of microbial mound. The platform margin showed some property of gentle slope before the formation of microbial mound but then transferred to a platform margin with slight rim after its formation. Such researches could provide sedimentary foundation to confirm the platform structure style and look for high-quality platform margin reservoirs in the Tarim Basin.