滇东南中三叠世拉丁期沉积体系与层序地层格架下的聚锰特征

Research on Manganese-accumulation Features in Middle Triassic Ladinian Sedimentary System and Sequence Stratigraphic Framework,Southeastern Yunnan

为了研究海平面变化对含锰岩系的影响,找到沉积型锰矿层的分布规律。本文综合利用地层剖面岩相组合、沉积构造序列、生物化石标志等分析了滇东南地区中三叠世拉丁期含锰岩系的沉积体系与其空间配置格局。在此基础上,通过对不同古地理背景下层序界面及体系域界面的识别,建立了研究区中三叠世拉丁期的层序地层格架。总结了锰矿层位的空间叠置关系及其形成机制,指出海平面快速上升过程中的低速率沉积期最有利于锰矿沉积成矿,并提出研究区锰矿成矿模式:由于海平面区域性下降,由构造活动或风化淋滤带来的锰矿物质,在凹陷或者低洼部位聚集,伴随新一轮海平面快速上升,促使凹陷或者低洼部位更加封闭缺氧,达到锰矿进一步富集,最终在蓝绿藻类生物化学作用下成矿。

The aim of this paper is to study sea level changes on the impact of manganese ore and its distribution. The depositional systems and spatial distribution as well as temporal evolution of the manganese-bearing intervals in Ladinian stage of Middle Triassic in Southeast Yunnan are analyzed based on the lithofacies associations,sedimentary structures and biological fossils from stratigraphic sections. Ladinian sequence stratigraphic frameworks is established according to identification of sequence and system tracts surfaces under different paleogeographical backgrounds. The writers summarize spatial superimposed relationships and formation mechanism of manganese deposits,and preliminary analyse the manganese ore formation model. It is suggested that low deposition rates period of rapid sea-level rising is most conducive to manganese precipitations,and manganese ore-forming model is established in the study area：regional sea-level fall,manganese material from tectonic activity or leaching weathering,enrich in the depression or low-lying land,with next rapid sea-level rise,promote these position more closed and poor oxygen,further enrichment of manganese,finally mineralized under the biochemical process of bluegreen algae.