米仓山前缘早志留世软沉积物变形构造及其触发机制

A Discussion on Deformation Structures of Early Silurian Soft Sediment and Its Trigger Mechanism in the front of Micangshan Mountain

地质历史时期软沉积物变形构造在不同时空沉积岩中均有分布,然而学术界对其变形过程、作用力及触发机制等仍存在许多争议。通过对米仓山前缘野外露头观测,早志留世砂岩、粉砂岩、页岩地层中,发育有多套软沉积物变形构造,其层位分布稳定,但不同层位的形态特征差异较大,包括波浪状变形层构造、包卷层理、枕状(椭球状)构造、火焰构造等,多与丘状交错层理相伴生,可分为三种组合类型,均发育于中陆棚沉积环境中。基于该区软沉积物变形构造特征,结合碳同位素分析、古气候、古板块资料,并与现代飓风研究成果对比,认为研究区早志留世时大体上处于风暴频繁的炎热环境,区内软沉积物变形构造多为风暴作用的结果,较强的风暴触及海底,使未固结成岩的沉积物的孔隙压力增加,切变强度降低,使之液化,进而发生变形。米仓山前缘早志留世软沉积物变形构造的发现及其触发机制的探讨对区内古地理、古气候的恢复,以及古扬子板块的演化具有重要的意义。

As we know,soft sediment deformation structures in the geological history can be found in different spacetime sedimentary rocks,however,its deformation process,active force and trigger mechanism are still in dispute in academia. Through the observation on the field outcrops in the front of Micangshan,there develop multiple sets of soft sediment deformation structures in the sandstone,siltstone and shale strata in Early Silurian. The distribution of the layer is stable,and each stratum has different morphological characters. According to its morphological characteristics and stratigraphic distribution,it can be divided into wavy deformation structure,convolute bedding,pillow structure and flamy structure. What＇s more,they always accompany with hummocky cross-beddings. On the basis of the lithologic character and profile structure combination of the soft sediment deformation structures,they can be divided into three types,which all belong to the continental shelf sedimentary environments. Based on the characteristics of the soft sediment deformation structures and combined with the paleoclimate and paleo-plate materials,carbon isotope data,and modern hurricane research results,the study area is located in the north of the equator. There is hot and arid,and the storm occurs frequently. The soft sediment deformation structures of the research area are mainly the consequence of the storm. Unconsolidated sediments are oscillated and liquefied when the strong storm hit the bottom of the sea.The discovery and the trigger mechanism of the soft sediment deformation structures in the front of Micangshan has a great significance for studying the recovery of the paleoclimate and paleo-plate,and the evolution of ancient Yangtze plate.