Journal
SCIENCE CHINA-EARTH SCIENCES
Volume 60, Issue 6, Pages 1133-1146Publisher
SCIENCE PRESS
DOI: 10.1007/s11430-016-9031-9
Keywords
Lungmachi Formation; Black shales; Graptolite biozone; Graptolite depth zonation; Transgressive distribution stage; Regressive shrinking stage
Categories
Funding
- Chinese Academy of Sciences [XDB10010100]
- National Natural Science Foundation of China [U1562213, 41272042]
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The Lungmachi Formation is widely distributed in Guizhou, Chongqing and the adjacent area. It is important for the study of Silurian biostratigraphy and shale-gas investigation. Based on those biostratigraphically well-studied sections from Guiyang to Huayingshan, we reveal the stage-progressive distribution pattern of the Lungmachi black shales. The distribution of the Lungmachi black shales in the studying area can be subdivided into four geographic belts from the south to the north, reflecting the joint effect of regional and global environmental changes. The graptolite depth zonation model was adopted herein to infer the water depth of major graptolite assemblages from the black shales. The changes in the water depth indicate two major stages. The first stage is named the transgressive distribution stage which ranged from the Persculptograptus persculptus Biozone (LM1, upper Hirnantian) to the Coronograptus cyphus Biozone (LM5, upper Rhuddanian), an interval mostly controlled by global sea-level rise. The second stage, ranging from the Demirastrites triangulatus Biozone (LM6, lower Aeronian) to the Spirograptus guerichi Biozone (LM9, lower Telychian), is named the regressive shrinking stage, during which the black shales were gradually replaced by mixed-facies or carbonate sediments from the south to the north, representing the effects of the persistent uplifting of the Central Guizhou Oldland.
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