Abstract: After a detailed description of the earliest Triassic thrombolite at the Dawen section, Guizhou Province, South China, four mesostructural categories were distinguished: spotted, layered, dendritic, and reticular mesostructures of thrombolite. The sedimentary characters and the lithologic statistics of the four types of thrombolites indicated that those thrombolites were formed in a subtidal environment, where the spotted and layered thrombolites usually in a lower-energy, deep-subtidal environment, in contrast with the dendritic and meshed thrombolites in a shallow-subtidal environment. The stacking pattern of eighteen shallowing-upward cycles in the microbialitic succession showed that this area experienced a relative fall in sea-level during the Hindeodus parvus Zone, and its minimum appeared during the Isarcicella staeschei Zone and the earliest period of the I. isacica Zone, then the sea-level began to rise. The fall of sea-level in the latest Permian are found at various sections in the world, and the pattern of sea-level changes during the earliest Triassic (the H. parvus, the I. staeschei, and the I. isacica zones) are correlated with some areas in Palaeo-Tethys. Those fluctuation patterns probably indicated the eustatic sea-level changes to a certain extent.

Key words: microbialite, thrombolite, mesostructure, earliest Triassic, sea-level change

摘要： 对华南地区贵州罗甸大文剖面早三叠世早期的凝块石进行了系统的沉积学描述, 区分出斑状、层状、枝状和网状4种中型构造。凝块石所具有的沉积构造特征和岩石学统计数据表明其形成于潮下带沉积环境, 其中, 斑状和层状中型构造的凝块石形成于能量较低的深潮下带, 而枝状和网状中型构造的凝块石形成于能量较高的浅潮下带。18个向上变浅的沉积旋回显示Hindeodus parvus带内部海平面逐渐降低; Isarcicella staeschei带和I. isarcica带早期, 海平面降到最低, 之后海平面开始升高。通过与其他地区二叠?三叠系界线剖面的海平面变化情况对比发现, 全球普遍存在二叠?三叠纪之交的海平面下降, 而大文剖面早三叠世早期的H. parvus带、I. staeschei带和I. isarcica带的海平面变化情况在古特提斯洋范围内可以广泛对比, 可能主要受到全球海平面变化的影响。

关键词: 微生物岩, 凝块石, 中型构造, 早三叠世, 海平面变化