安徽绩溪新元古代海底扇沉积环境分析

Sedimentary environment analysis of Neoproterozoic submarine fan in Jixi,southern of Anhui Province

研究区位于安徽绩溪县杨溪镇,区内主要发育一套新元古代浅变质碎屑岩系,厚度为639.7 m.碎屑岩以泥岩、泥质粉砂岩、砂岩、含砾砂岩和砾岩为主,发育水平层理,粒序层理,韵律层理等沉积构造,可见鲍马层序Ta、Tc、Td、Te段.碎屑组分以跃移组分为主,含量为35％～58％.地层上段厚为254.8 m,包含粉砂岩、泥质粉砂岩和粉砂质泥岩,水平层理和粒序层理发育,为中扇—外扇扇叶沉积;中段厚为192.5 m,主要为细砂岩、粉砂岩和泥质粉砂岩,砂岩条带广泛发育,属于中扇水道沉积;下段厚为192.4 m,为一套砾岩层,砾石分选较差,砾岩层间夹有粉砂质泥岩,为上扇水道滞留沉积.总体上,形成一套退积的海底扇沉积序列.

The study area located in Yangxi town of Jixi, Anhui Province, is mainly a set of clastic sedimentary rock of Neoproterozoic,which has a thickness of 639.7 m. The strata are mainly comprised of mudstone, argillaceous siltstone, sandstone, pebbly sandstone and conglomerate. Sedimentary structures contain horizontal bedding, graded bedding, bedding and rhythmic bedding. Tb,Tc and Td of Bouma sequences can be recognized. Probability cumulative grain- size curves have a high content of saltation population, ranging from 35%- 58%. The upper segment of the profile, 254. 8 m in thickness, consisting of fine argillaceous siltstone, mudstone, silty mudstone, developing horizontal bedding and graded bedding,is deposited in the lobe of outer fan. The middle segment of the profile, 192.5 m in thickness, is composed of siltstone,fine sandstone, argillaceous siltstone. Sandstone ribbon is widely distributed in the middle segment, which is considered to be deposited in channel of middle fan. The lower segment with 192.4 m thickness is a set of conglomerates interbedded with silty mudstone,and the conglomerates have a poor sorting,which was regarded to be deposited in channel of upper fan. As a whole, a set of submarine fan sedimentary sequence formed during the retrogradation.