湖北松滋地区下奥陶统微生物岩

首次系统性地对湖北松滋地区下奥陶统微生物岩开展研究。根据微生物岩的生长方式，文中将微生物岩划分为原地生长型和非原地生长型两大类别，前者包括叠层石、凝块石，后者主要为核形石。根据几何形态特征，将研究区的叠层石分为层状、波状、柱状和丘状4种类型，新发现并命名了双锥柱状叠层石。将凝块石划分为斑状、网状和条带状3种类型，在豹斑状和网状凝块石中，发现了许多钻孔捕食软体动物Ecculiomphalus化石以及生物扰动的痕迹，文中认为这两种凝块石均属于生物扰动型凝块石。生物扰动型凝块石的发现不仅填补了国内、外奥陶纪该领域的部分空白，而且为凝块石成因的研究提供新的材料。在对各类微生物岩的沉积特征分析基础上，阐述了各类微生物岩的沉积环境，并总结其沉积环境分布模式。对微生物岩发育与中奥陶世后生动物大辐射之间的关系进行了探讨，根据早奥陶世晚期至中奥陶世初期后生动物的阶梯式和快速辐射与微生物岩突然减少的对应关系，结合研究区叠层石、凝块石中发现许多后生底栖钻孔捕食腹足类Ecculiomphalus化石等现象，认为微生物岩随时间推移而逐渐减少、衰退与后生动物丰度的快速增加有一定关系，指出食草动物不仅啃食了形成叠层石的菌藻类微生物，造成叠层石数量的不断减少，而且破坏了叠层石的生长状态，结果形成了研究区独具特征的生物扰动型凝块石。此外，作者认为，中奥陶世开始，海平面的快速上升也是研究区微生物岩减少直至消失的原因之一。

Microbialites of Lower Ordovician in the Songzi area,Hubei Province

The lower Ordovician microbialites in the Songzi area, Hubei Province are studied systematically for the first time. The microbialites are distributed in the Nanjinguan, Fenxiang and Honghuayuan formations of the Lower Ordovician in the study area. In this paper, microbial rocks are divided into two categories: in-situ and non-in-situ growth types. The former includes stromatolite and thrombolites, and the latter is mainly oncolite. According to geometric classification scheme, stromatolites in the study area are characterized as lamellar-, wavy-, columnar- and mound-shaped types; in addition, we discovered and named a new type, the double cone-shaped stromatolite. Likewise, the thrombolites are divided into three types: porphyritic, reticular and striped clotted types. Fossil record of drilling predation on mollusks Ecculiomphalus and traces of bioturbation were found in leopard porphyritic and striped thrombolites, both, we suggest, are bioturbated thrombolites. The discovery of bioturbated thrombolites filled a gap in domestic and international Ordovician research contributing new knowledge towards understanding of thrombolites genesis. Based on analysis of sedimentary characteristics, depositional environments and their distribution patterns are described for various types of microbiological rocks. And the relationship between microbialites evolution and resuscitation and radiation of metazoan during the early to middle Ordovician is discussed. We believe that the Ordovician microbialites are decreasing with time, and certain relationship exists between the decline of microbiological rocks and increase of metazoan abundance. We also believe that grazers not only chewed up the stromatolite-forming bacteria and algae microbes to cause continuing stromatolite reduction, but also destroyed the growth condition for stromatolites, resulting in bioturbation thrombolites with unique characteristics.