Research on sedimentary environment and provenance for hydrocarbon source rocks of Upper Carboniferous Batamayineishan Formation in northeastern Junggar Basin: evidences from the geochemistry of mudstones

Abstract

The distribution rules and hydrocarbon potential of source rocks are the major factors which determine oil and gas exploration in the northeastern Junggar Basin. Sedimentary background and environmental changes are the main factors controlling the genesis, distribution, and organic matter types of hydrocarbon source rocks. The main and trace elements and rare earth elements in sedimentary rocks are often influenced by palaeoclimate, paleo water chemical conditions, palaeoenvironment, and palaeosource during sedimentation process. Therefore, a comprehensive analysis of the distribution patterns of elements in sedimentary rocks can help to determine sedimentary environment and evolution process. The geochemical characteristics of major and trace elements and rare earth elements for mudstones of the Upper Carboniferous Batamayineishan Formation from outcrops of the north- eastern Junggar Basin were studied to reveal the sedimentary environment and the tectonic setting of the provenance, which can provide geological constraints for the origin and development conditions of hydrocarbon source rocks. According to a comprehensive analysis on chemical weathering indicators, element contents, and ratios between various major and trace elements, the mudstones of Batamayineishan Formation were deposited in a warm and humid paleoclimate background, and the deposition process was relatively stable in a shallow water with brackish-fresh features under oxidizing environment. Major and trace elements of mudstones indicate that the parent rocks are sedimentary rocks and felsic volcanic rocks and their provenance is derived from the weathering products of acidic igneous rocks of the Karamaili Island Arc, reflecting the tectonic transition from compression to extension during the post collision stage. The depositional environment and tectonic setting controlled the increased input of terrestrial higher plants, resulting in the medium abundance of organic matter with good hydrocarbon generating potential.

Keywords

• hydrocarbon source rock
• geochemical characteristics
• sedimentary environment
• batamayineishan formation
• northeastern junggar basin