桂林地区早石炭世沉积环境研究——通过对黄金期古生物群落进行复原

A Study of the Early Carboniferous Depositional Environment in the Guilin Area—Through the Recovery of a Golden Age Palaeontological Community

摘要: 广西桂林地区早石炭世黄金组富含丰富的珊瑚、腕足类等化石，对于揭示华南早石炭世沉积古地理、古生态环境都具有重要意义。在现有研究工作的基础上，本文开展了大圩钓鱼山、磨盘山以及兴安南源村剖面的早石炭世黄金组进行了实测勘查并采集化石样品工作，从而揭示早石炭世古生物群落及古地理特征。地层学研究表明，黄金组主要为灰白色泥晶灰岩、深灰色亮晶灰岩及泥质灰岩，夹少量泥灰岩，或深灰色–灰色微晶灰岩，夹泥质灰岩。在兴安地区可见灰黑色灰岩及灰黑色页岩且部分含硅质、钙质结核。灰岩和泥质灰岩多呈韵律出现。古生物学研究表明，黄金组以珊瑚化石居多，以Kwangsiphyllum (广西珊瑚)，Thysanophyllum (泡沫柱珊瑚)，Caninia (犬齿珊瑚)和Kueichouphyllum (贵州珊瑚)为主，腕足类化石中以Productus (长身贝)和Gigantoproductus (大长身贝)为主；少量层孔虫、海百合茎及菊石等，反映了黄金组形成于浅海相环境。野外考察发现，原地埋藏和异地埋藏化石均有出现。早期生长的Thysanophyllum (泡沫柱珊瑚)受水体动荡影响导致大量异地埋藏形成化石层，且岩层中含泥质较多，再次经历水体动荡后腕足类和珊瑚的生长逐渐稳定，且岩性也从较多灰岩与泥质灰岩韵律产出转变为微晶灰岩。这表明黄金期早期和中期水体动荡，晚期水体逐渐稳定。

Abstract: The Early Carboniferous Huangjin Formation in Guilin city in northern Guangxi have preserved numerous fossil corals and brachiopods, which are of great importance to reveal the sedimentary palaeogeography and palaeoecology of the Early Carboniferous in South China. On the basis of previous research, this study carried out palaeontological analyses of fossils collected from the Early Carboniferous Huangjin Formation in the Diaoyushan and Mopanshan sections in the Daxu town, and in the Nanyuan section in the Xing’an County, aiming to reveal palaeobiological community and palaeogeographic characteristics. Stratigraphic studies show that the Huangjin Formation is mainly composed of gray-white marble limestone, dark-gray sparkling limestone and argillaceous limestone, with a small amount of marl, or deep-gray-gray microcrystalline limestone and argillaceous limestone. Gray-black limestones and gray-black shales with siliceous and calcareous nodules are present in the Nanyuan section in the Xing’an area. Limestones and argillaceous limestones appear rhythmically. Fossil corals of Thysanophyllum, Kueichouphyllum, Kwangsiphyllum and Caninia, and brachiopods of Gigantoproductus and Productus are dominant in the studied sections, along with a minor number of foraminifera, sea lily stems and ammonites, reflecting that the Huangjin Formation was formed in shallow marine environment. Field investigation shows that both in-situ and in-situ buried fossils occur. Thysanophyllum, which grew in the early stage, was affected by water turbulence, resulting in a large number of fossil beds buried in different places, and there were more muddy rocks in the beds. After water turbulence, the growth of brachiopods and corals gradually stabilized, and the lithology changed from more limestone and muddy limes-tone rhythm to microcrystalline limestone. This indicates that the water was turbulent in the early and middle stages during the sedimentation of the Huangjin Formation, and gradually stabilized in the late stage.