The Characteristics And Sedimentary Environment Analysis Of Thrombolite Of Cambrian In Luxi Block, China

This study focuses on description and interpretation of the origins and sedimentary environment of the Cambrian thrombolite in West Shandong Province, and further analyzes their geological implication. In recent years, the microbialite is always the study hotspot, which Precambrian microbialite is studyed more, but relatively little research on the Cambrian, especially the research of thrombolite is much less. Therefore, the study of the thrombolite is still lack of systematicness and integrity, in many hot problem there is no definite answer, mainly including:the origins of thrombolite, the sedimentary environment of thrombolite, the classification of thrombolite, the microbe character of thrombolite and the significance of different thrombolite in geological study etc, so the research of thrombolite has high theoretical significance.Based on a large proportion of the field measuring the Cambrian sections of Caishi, Jinan; Jiulongshan, Laiwu; Yaowangshan, Qingzhou; Mazhan, Yishui; Taoxu, Mengying etc (1:10 or 1:50), The author found that the Cambrian thrombolite of the West Shandong Province mainly developed in Zhangxia formation and Chaomidian formation. Its symbiotic lithofacies separately are:thin-bedded lime mudstone facies, limstone and shale coulet facies, parallel stratified oolite facies, biohermal microbialite facies, and limestone-marl stone couplet facies, wedge/trough cross-stratified grainstone facies, bioturbated wackestone facies, columnar stromatolite facies, flat-pebble conglomerate facies.Through microscopic analysis of the laboratory, the Cambrian thrombolite of the West Shandong Province mainly form by the Epiphyton bonding and capturing carbonate particles, followed by Girvanella, Renalcis, Actinophycus. Based on the size of branches,the existence of cell-like segments, and the degree of crystallization, Epiphyton can be divided into five types:micrite bifurcating rodlike branches(75～80μm), micrite segmented branches (～80μm), micrite bifurcating fine branches (～40μm), crystallite tubular branches (<40μm), sparry bifurcating rodlike branches (～75μm). Which correspond with the formation of thallus can be divided into four types:micrite bush shaped, single chambered, cluster chambered, sparry bush shaped. And the bush shaped thallus are generally located on the interior of thrombolite bioherms, but the single chambered and cluster chambered thallus are mostly located outside of bioherms, which is mainly affected by the hydrodynamic conditions of the sedimentary environment.According to the auctorial research and analysis of the Cambrian thrombolite in West Shandong Province, the process of its formation can be divided into four stages:the capture and bonding of cyanobacteria, calcification of cyanobacteria itself, carbonate deposition in situ, and postdeposition. For the classification of thrombolite, according to its origins, most of thrombolites are calcified microbial thrombolites, and a small part of thrombolites are post-depositional thrombolites.Based on their fungi, we can be divied into:Epiphyton thrombolites, Girvanella thrombolites, Renalcis thrombolites, Actinophycus thrombolites. And according to the shape of clot can be divided into:clotted thrombolites and meshed thrombolites. Among which the clotted thrombolites are formed by Epiphyton, Girvanella, Actinophycus, and the meshed thrombolites are formed by Epiphyton, Girvanella, Renalcis.The sedimentary environment of Cambrian thrombolite is sublittoral low-energy zone. Its water power is weak, but the only local has certain wave power, and there are rich nutritive materials, sufficient light in the two regions. These are helpful for the multiplication and calcification of Epiphyton, which can form many thrombolite bioherms and biostromes. The depositional mordels of thrombolite are divided into two depositional mordels:one is the depositional mordel of the Zhangxia formation thrombolite in the Caishi area, Jinan, another is the depositional mordel of the Chanmidian formation thrombolite in the Jiulongshan, Laiwu. The former is the thrombolite depositional mordel of Zhangxia formation Cambrian in Luxi block, the latter is the thrombolite depositional mordel of Chaomidian formation Cambrian in Luxi block.The detailed study of the Cambrian thrombolite in West Shandong Province, not only further complement and perfect the research of the sedimentary characters and formation mechanism of microbolite, but also have a new understanding the microbe,which can form thrombolite. Especially for the sedimentary environment analysis of microbial carbonate and its application in biostratigraphy has important theoretical significance.