摘要： 基于对川北米仓山西部旺苍县鼓城乡唐家河下寒武统仙女洞组露头剖面的观察与镜下分析发现,仙女洞组下段由生物碎屑泥晶灰岩(L)、粉砂质泥岩(M)、似瘤状砾屑灰岩(L′)、角砾灰岩(R)、藻凝块灰岩(A)和含生屑钙质砂岩(S)组合而成,其以角砾灰岩、似瘤状砾屑灰岩和藻凝块灰岩为特征,且发育异地岩块和滑塌变形构造。进一步分析认为:L-M岩石组合为正常的斜坡环境低能沉积;L′-R岩石组合中的角砾灰岩为上斜坡生物灰泥丘崩坍滑动至下部而形成的,似瘤状砾屑灰岩可能是由于L-M岩石组合快速沉积导致沉积物失稳滑动变形、上斜坡生物灰泥丘崩落角砾致使的差异压实和滑动、以及后期物质成分差异引起的压溶作用等共同作用的结果,从而使灰质层发生破碎并被泥质包围形成断续的砾屑状,甚至轻微的位移,进而形成条带特征不明显的杂乱变形构造;微生物岩(Mb)组合为上斜坡的灰泥丘沉积;S-M岩石组合为斜坡上部的浊流沉积。根据上述分析结果建立米仓山西部仙女洞组碳酸盐岩台缘斜坡沉积模式,表明仙女洞组沉积早期米仓山西部存在台缘斜坡相沉积。

关键词: 斜坡灰泥丘, 似瘤状砾屑灰岩, 变形机制, 台缘斜坡, 仙女洞组, 寒武系, 四川盆地

Abstract: In this paper,a case study of the Lower Cambrian Xiannüdong Formation in Tangjiahe,Wangcang County of western Micang Mountain was conducted. On the basis of the observation and analysis with microscope,the bottom of Xiannüdong Formation is composed of six major rock types,such as bioclastic mudstone,silty mudstone,analogous-nodular limestone,rudstone,algal clot limestone and calcareous sandstone with bioclastic,and is characterized by rudstone,analogous-nodular limestone,algal clot limestone,slump deformation structure and slide structure. Further analysis shows that L-M association was mostly deposited in low-energy slope environment. The rudstone,as a part of the L′-R association,deposited by the collapse and slump from the mud mounds in upper slope. The other part,analogous-nodular limestone,deformed from L-M association,was supposed synthetical effects by the collapse and slump from mud mounds,the force of differential compaction and the pressure solution caused by the differences of the components. These effects can be used to break the limestone layer to be rudstone shape,even lead to generate some slightly displacement. As a result,L-M,also be called ribbon rocks,become littery deformation structures. Mb association can be considered a mud mounds environment in upper slope. S-M association was deposited in turbidity environment of upper slope. After establishing the sedimentary model and the four associations of slope,all of the evidences indicate that at least during the Early Cambrian Xiannüdong period,the platform marginal slope was developed in western Micang Mountain.

Key words: slope mud mounds, analogous-nodular limestone, deformation mechanism, platform marginal slope, Xiannüdong Formation, Cambrian, Sichuan Basin

中图分类号: 

• P588.24＋5