东昆仑南坡早二叠世灰岩块体的来源与成因探讨

STUDY ON THE GENESIS OF EARLY PERMIAN LIMESTONE BLOCKS IN THE SOUTHERN SLOPE OF EASTERN KUNLUN

论述了对东昆仑南坡早二叠世灰岩块体的成因的新认识。 1在前人所称的三叠纪地层中发现了中薄层生物或生物碎屑灰岩 ,其中产有大量保存完好的早二叠世类化石。所以该区早二叠世灰岩块体与其周围砂板岩及中薄层灰岩之间应属于同期异相沉积。 2该区早二叠世礁灰岩之下常伴生有砾岩及砂砾岩 ,而非礁相灰岩周围则常常缺乏砂砾岩。这种分布特征是礁相体系沉积的必然结果 ,但很难用推覆体来加以解释。 3通过对砂砾岩与灰岩块体之间的地层序列研究 ,发现它们之间属于一种沉积接触关系 ,而非推覆体的关系。由于该地区早二叠世灰岩块体的成因对于该区大地构造的解释至关重要 ,因此这些新的发现将引起人们对该区大地构造的演化历史进行重新思考。

It is regarded as one of the particular scenery in Eastern Kunlun Orogenic Belt that many large or small carbonate blocks of Permian are strewn in sandstone or slate.For a long time,people have different explanations about the genesis of these white carbonate blocks,of which nappe is dominated.However,we have a completely different explanation based on four years' study in the field.First,we found a lot of well preserved fusulinid fossils in the formerly called Chitang Group of Triassic,showing that the limestone blocks and the surrounding sandstone,slate and thin layer limestone belong to different sedimentary facies at the same time.Second,in the study area,there usually exists conglomerate under reef limestone.However,conglomerate is scarcely seen under or around non reef limestone.This kind of distribution is the result of reef system sedimentation and difficult to be interpreted by nappe.What's more,according to the study of stratigraphic sequence between the conglomerate,sandstone and the massive limestone,we found that the relationship between them is a kind of sedimentary conformity rather than a kind of nappe.Because the gensis of Permian limestone in this area is very important to the interpretation of tectonic, the new discoveries will probably provide people with new materials to reconsider the tectonic evolution in the study area.