华北高于庄组硅化微体化石组合的古环境

华北中元古代高于庄组 ( 1 4- 1 5亿年 )的硅质叠层石中保存了完好的多种微生物化石。从这些叠层石的微细构造分析 ,成岩早期硅质矿物的交代作用为微体化石的原位保存起了很重要的作用。除部分居住者和浮游的分子外 ,两种丝状蓝藻 ( Siphonophycus inornatum和Eoschizothric composita)和两种球状蓝藻 ( Coccostratusdispergens和 Eoentophysalisbelcherensis)是这些藻席的主要建造者。以球状蓝藻 Eoentophysalis为主的藻席可能发育于潮下高能环境中 ;而以多种丝状蓝藻为主的藻席可能反映了当时的沉积环境为中—高潮间带的局部静止小水体

PALEOENVIRONMENTAL DISTRIBUTION OF SILICIFIED MICROFOSSIL ASSEMBLAGES FROM GAOYUZHUANG FORMATION, NORTH CHINA

Stromatolitic cherts from the Mesoproterozoic Gaoyuzhuang Formation (1.4- 1.5Ga) contain well preserved, paleoecologically diverse microfossils. The cherts also harbor varied synsedimentary precipitates and void filling cements, now replaced by early diagenetic silica minerals, which was an essential condition for fossil preservation. Most microfossils are preserved in their original growth position, and are analyzed by their paleoecological positions. Two filamentous ( Siphonophycus inornatum and Eoschizothric composita ) and two coccoid ( Coccostratus dispergens and Eoentophysalis belcherensis) microfossils are recognized as main mat building taxa, together with several mat dwelling and planktonic components. Eoentophysalis dominated mats with a low species diversity are interpreted to have deposited in a low intertidal zone with high hydrodynamic activity, while filament dominated mat communities with a diversified species composition are likely to reflect a quiescent depositional environment of small pools in the middle to upper intertidal zone.