Abstract:

Fibrous calcite veins are of great interest to geologists because of their special characteristics and formation mechanisms, which are important indicators of the organic matter enrichment and paleoenvironmental evolution recovery. Based on lithological, geochemical, and C-O isotope data of the large number of fibrous calcite veins found in Upper Member of the Bayingebi Formation in the Yin’e basin, this paper discusses the differences in the formation mechanisms of different types of fibrous veins and their connection with hydrothermal activities. In the Yin’e basin, there are mainly syntaxial and antiaxial fibrous veins. Antiaxial veins are mainly developed in dolomite, with a middle line in the vein. Fibrous features are mainly found at the edge of the antiaxial vein, which show multi-phase growth characteristics. The syntaxial veins are mainly developed in the oil shale, with larger vein widths, obvious fibrous symmetry, and fewer growth phases. Elemental geochemical results show that the fibrous calcite veins in the study area have been affected by hydrothermal activity to different degrees, with an average δ13C of about 9.06‰ and δ18O of about -7.09‰ for syntaxial veins and average δ13C of about 2.24‰ and δ18O of about -10.62‰ for antiaxial veins. The syntaxial veins developed under moderate hydrothermal activity, and the anomalously high pressures required were derived from the dewatering of clay minerals. While the antiaxial veins mainly developed under intense hydrothermal activity, and the anomalously high pressures required were derived from deep hydrothermal activity. All results show a close relationship between the formation of different types of fibrous calcite veins and the intensity of hydrothermal activity.

Key words: Yin’e basin')">

Yin’e basin, Early Cretaceous, fibrous calcite veins, geochemistry, hot-water deposition, isotopes ,
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