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Origin of iron-rich minerals, ooids and pisoids in the Jurassic ooidal ironstones of the Labino-Malkin region(Caucasus)

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Journal of Palaeogeography 2024年第3期13卷 475-494页

作者： Natalia A.Kalinina Maxim A.Rudmin Mikhail Sherstyukov Prokopiy Maximov Abdul-Gapur Kerimov Division for Geology School of Earth Sciences & Engineering Tomsk Polytechnic University Laboratory of Sedimentology and Paleobiosphere Evolution University of Tyumen Institute of Earth Science North-Caucasus Federal University

This study investigates the Middle Jurassic rocks of the Labino-Malkin zone(Caucasus), represented by ooidal ironstones, biogenic limestones, and nodular phosphorites. All rocks contain ooids/*** on the mineral composition, nine types of ooids and three possible scenarios for their formation have been identified. The mineral composition of ooids indicates the variable conditions of their deposition and repeated changes in physical and chemical conditions of the environment, including fluctuations in theredox regime. The access of oxygen in the bottom environment as a factor of increasing oxic conditions was associated with the regression of the sea and/or the inflow of meteoric waters. The main sources of ooids are the drift of material from the continent and convecting metal-bearing meteoric and/or deep solutions.

关键词： Ooidal ironstones Mineral formation ooids Pisoids Mineral chemistry

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Calcified Biofilms from Cambrian Oolitic Limestones in China

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Acta Geologica Sinica(English Edition) 2015年第1期89卷 70-76页

作者： LIU Wei ZHANG Xingliang State Key Laboratory of Continental Dynamics and Department of Geology Northwest University

Calcified biofiims are preserved as thin micritic coatings in the Cambrian oolitic limestone of two sections in North and South China. Standard petrographic examination revealed that the biofilms were developed during the early diagenetic stage immediately after the freshly deposited ooids, proceeding in the continuous sequence of depositional processes. The biofilm outlines are highly irregular, with steep sides, tower-like structures and overhanging projections; the internal fabric of the biofilms is composed of roughly laminated micrite aggregates with channel-like structures. Biofilms exhibit a strong fluorescent reaction. Detailed SEM examination suggests that the biofilms are biotically dominated by cyanobacteria. Our study demonstrates that microbial colonies, such as biofilms, can develop on ooid cortices and influence the formation and microstructures of those ooids.

关键词： geobiology ooids micrite cyanobacteria Cambrian Hubei and Shaanxi provinces

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