一个最古老的肾形藻泥丘相的首次发现及其地质意义——以滇东北地区震旦系灯影组为例

FIRST DISCOVERY OF AN OLDEST RENALCIS MOUND FACIES AND ITS GEOLOGICAL SIGNIFICANCE——AN EXAMPLE FROM THE UPPER SINIAN DENGYING FORMATION IN NORTHEASTERN YUNNAN

摘要:

迄今为至,国内外对肾形藻的研究还很少,而且研究多集中在寒武纪泥丘相(Pratt,1984;James＆Klappa,1983;王剑等,1990)和泥盆纪泥丘相(Mountjoy＆Jull,1978;高健,1991)中,还未涉及到前寒武纪。近年来,通过对滇东北地区震旦纪灯影期中大比例尺岩相古地理研究,作者首次发现表附-肾形藻不仅发育于古生代,而且更发育于震旦纪灯影期(距今约为650Ma)。这是全球范围内发现的最古老的肾形藻生长层位。灯影期肾形藻的发育程度,包括肾形藻的含量及其功能、空间展布和分布于相剖面上的纵向厚度等,均远超过古生代的任何一个时期。

Abstract:

The Dengyingian(Late Sinian)sedimentary environment in northeastern Yunnan is a rimmed peritidal epeiric platform. From SW through NE to SE, four sedimentary facies belts have been distinguished, including tidal flat, shallow subtidal flat, platform-margin shoal and basin facies belts.
For several years, numerous studies have been conducted on the Dengyingian sedimentary facies and palaeogeography in the study area, and for the first time Renalcis and Eiphyton, some of which have developed into the mound faeies, have been recognized in large amounts in the Dengying Formation, especially in the second member of the formation. So far, these Renalcis have been the oldest and their growth horizons are the lowest. The environments of Renalcis and Epiphyton consist mainly of tidal flat lagoon and low-energy shallow subtidal flat.
The original mineral compositions of Renalcis dolostones are high-Mg catcite(cell wall)aragonite(cell centre). These minerals have undergone a series of diagenesis, including neomorphism, dolomitization, silicification and recrystallization. The irregular and stratoid fenestral and stromatactoid structures are common in Renalcis dolostones and mound facies in the Dengying Formation, which are bound up with the Pb-Zn sulfide ore deposits and oil-gas reservoir traps. Therefore, the discovery of Renalcis dolostones and mound facies may provide one useful approach to prospecting for the concealed Pb-Zn deposits and oil-gas resources in the study area.