华南早石炭世碳酸盐岩沉积序列中的粗粒叠层石

Coarse-grained carbonate stromatolites, as a special kind of microbialites, appeared late and were rarely recorded in the geological history. The ones still alive in Shark Bay, western Australia, and the Bahamas provide natural laboratories for sedimentologists to investigate their formation mechanisms. However, it is difficult to precisely determine the effect of some extrinsic factors (i.e., climate, marine physical and chemical conditions, etc.) that could influence on the formation of them. We newly found coarse-grained stromatolite buildups in the Lower Carboniferous Du’an Formation in South China. On the basis of systematic comparisons with modern and other deep-time coarse-grained stromatolite records, the primary aims of this project are (1) to establish a genetic model for the stromatolites discovered herein, by means of defining their ages, ambient environmental settings, and processes of accretion and lithification, and (2) to discuss the roles which climate, eustacy, and marine carbonate saturation state might play in the occurrences of such special microbialites. This project will shed new light on the environmental indication significance of coarse-grained stromatolites.

粗粒叠层石在地质历史长河中首现时间最晚，沉积记录最为稀少，是一类非常特殊的微生物岩。西澳沙克湾和巴哈马地区现在仍在生长的粗粒叠层石为沉积学家研究其形成机制提供了天然实验室，但其不能有效地约束气候和海洋物理化学等外生因素对粗粒叠层石形成的影响。项目申请者在华南下石炭统都安组上部新发现了粗粒叠层石建造，期望通过限定其沉积时代、恢复其增生-岩化过程和沉积环境，建立相应的成因模型；然后将其与现代及其他深时粗粒叠层石记录进行系统性对比，深入探讨气候、海平面和海洋化学（如碳酸盐饱和度）等外生因素对这类特殊微生物岩形成的控制作用，为进一步约束其环境指示意义提供新线索和新见解。

粗粒叠层石是一类特殊的微生物岩，在深时沉积序列中较为罕见。西澳沙克湾和巴哈马地区现在仍在生长的粗粒叠层石为研究其形成机制提供了天然实验室，但不能有效地约束气候和海洋物理化学等外部因素对粗粒叠层石形成的影响。本项目以桂西北巴马碳酸盐岩台地下石炭统都安组上部发育的粗粒叠层石为研究对象，通过系统的有孔虫生物地层研究，限定其沉积时代为维宪期末（Climacammina 带）、谢普霍夫期早期（Bradyina cribrostomata带）和谢普霍夫期晚期（Plectostaffella 带）；通过详实的宏观-微观沉积学、矿物学、沉积相研究，认为早石炭世粗粒叠层石形成于海退期受潮汐影响的滩后潮间带—潮下带环境，并恢复了其增生-岩化过程；通过系统对比研究区粗粒叠层石的形成条件与现代及其他深时粗粒叠层石记录，认为粗粒叠层石形成的必要外部条件包括：相对较高的海水碳酸盐饱和度、较高的海水电解质离子浓度和类型、充足的颗粒供应和脉冲式动荡（受潮汐、波浪或风暴浪的影响）的沉积环境。研究成果对于认识微生物与环境相互作用方式及整个地质历史时期叠层石微观组构演变的驱动机制具有重要意义。