Characterization of fossils and typomorphic minerals and its implications for source rocks in the Lower Congo Basin
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ORIGINAL PAPER
Characterization of fossils and typomorphic minerals and its implications for source rocks in the Lower Congo Basin Youran Yang 1,2 & Xianghua Yang 1,2 Linan Pang 3
&
Wanzhong Shi 1,2 & Hongtao Zhu 1,2 & Wei Wang 1,2 & Hongquan Kang 3 &
Received: 14 May 2020 / Accepted: 2 September 2020 # Saudi Society for Geosciences 2020
Abstract The development of source rocks is closely related to palaeoproductivity and preservation conditions. This study examined the developmental characteristics of fossils and typomorphic minerals in different strata in the Lower Congo Basin. This study utilized thin section examination, SEM (scanning electron microscope), cathodoluminescence and chemical element analysis. The results show that there are strata rich in fossils, phosphate and pyrite in the Madingo Formation. The palaeontological record reflects the level of palaeoproductivity. The appearance of phosphate minerals is closely related to upwelling, which can bring nutrients from the subsurface. Pyrite develops in anoxic water environment, so it can be used to identify palaeoredox conditions. The Madingo Formation is rich in organic matter, which results from its high palaeoproductivity and good preservation conditions. The microstructures of sedimentary rocks and typomorphic minerals are examined, and the sedimentary characteristics and preservation conditions of organic matter in shale are comprehensively discussed. This study provides suitable tools to determine the formation mechanism and the complex heterogeneous distribution of source rocks and has great significance for oil exploration in the Lower Congo Basin. Keywords The Lower Congo Basin . Source rock . Madingo Formation . Fossil . Phosphate . Pyrite
Introduction
Highlights • The Madingo Formation is rich in fossils, phosphate and pyrite. Phosphate and pyrite can be used as typomorphic minerals. • The sedimentary environment in the Madingo Formation exhibited high productivity and a reducing environment, which is good for source rock development and preservation. • Source rock heterogeneity is studied. Responsible Editor: Santanu Banerjee * Youran Yang [email protected] * Xianghua Yang [email protected] 1
Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan 430074, China
2
Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China
3
China National Offshore Oil Corporation Research Institute, Beijing 100027, China
Understanding controlling factors of marine source rock development has been one of key questions in sedimentology and petroleum geology. Two models, the “productivity model” and the “conservation model”, have been proposed to explain its development (Demaison and Moore 1980; Pedersen and Calvert 1990). However, recent studies show that these two models are not mutually exclusive and the combined analyses of both models are needed to objectively reflect the enrichment mechanism of organic matter in source rocks (Zhang et al. 2007; Li 2015). Org
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