柴达木盆地古近纪—新近纪湖相叠层石与藻礁的沉积组合特征与意义

在柴达木盆地发育了各种类型的渐新世—中新世湖相叠层石，其中丘状叠层石具有重要的地质意义，丘状叠层石直接生长在砾岩上，并向上逐渐演化为藻礁，藻礁向上又重新转化为叠层石沉积。通过对内部纹层特征和沉积组分的研究并结合叠层石的同位素、地球化学以及古生物资料分析表明，微生物自身的钙化作用以及微生物引发的沉淀作用形成了这种具有典型内部纹层的丘状叠层石。较高的温度、炎热和干燥的气候条件、坚硬的基底以及较少的藻类干扰作用是叠层石生成的主要因素。总体上，叠层石形成于较为低能的环境中，与高能环境中所形成的藻礁完全不同，而且两者具有明显的相互竞争作用。因此，与气候和水体条件密切相关的后生生物的生长和真核藻类的发育是叠层石在显生宙迅速衰落的主要因素。

Miocene Stromatolites Associated with Lacustrine Algal Reefs:Qaidam Basin,China

Various stromatolites, in form and structure, are developed in the Qaidam Basin, West China. In the sequence, the stroamtolites overlying the conglomerate grade into algal reef which integrates another relatively thin stromatolite bed. Based on the study on the internal lamination and fabrics combined with the analysis of isotopic, geochemical and fossil data, it is apparent that biofilm related calcification and microbial mediated precipitation produced the layered structures in dome form. Formation of these stromatolites in fluctuated lacustrine settings is attributed to higher temperature, hot and dry climate, availability of a hard substrate and reduced competition from algae. The low-energy stroamtolites and high-energy algal reefs are completely different from, and incompatible with each other. Fluctuated lacustrine conditions behave as a key role in stromatolites formation and preservation, and provide an optimal opportunity to study the stromatolites genesis and relation with algal reefs.