Abstract
Coal and oil shale are two common sedimentary energy sources which are often symbiotically developed in Mesozoic–Cenozoic continental fault basins. However, the mechanisms and characteristics of the symbiotic development are not yet clearly known. In this research study, the typical continental fault basins of eastern China were chosen as examples for the purpose of conducting an examination of the coal and oil shale symbiotic assemblage types, genetic environmental differences, and transformation mechanisms, as well as the development and occurrence characteristics of different assemblage types. Through a large number of investigations, systematic experimental testing, and sequence stratigraphy studies, the following conclusions were obtained: (1) There were five types of coal and oil shale symbiotic assemblages observed in the continental fault basins, (2) The development of coal and oil shale deposits requires a warm and humid climate, stable structure, abundant organic matter supply, a certain water depth, and a lower terrestrial source debris supply. The observed differences were that the water depth conditions were diversified in the study area, as well as the sources, types, and content of the organic matter. (3) The rapid transformations of the coal and oil shale genetic environments were mainly controlled by the tectonic settings and climatic conditions, which were determined to control the changes in the water depths, salinity, redox conditions, and lake productivity of the genetic environments. Also, in the symbiotic assemblages, genetic environment changes had induced the development of oil shale deposits, which gradually evolved into coal genetic environments. (4) In the isochronous sequence stratigraphic framework of the coal and oil shale symbiotic assemblages, the lake expansion system tracts (EST) were determined to be the most beneficial to the growth of all the types of assemblages and were characterized by more assemblage development phases and smaller bed thicknesses. From the early to the late stages of the EST, and from the lakesides to lake centers, the thicknesses of the coal seams in the symbiotic assemblages showed trends of thinning, while the thicknesses of the oil shale deposits exhibited increasing trends. The early stages of high stand system tracts were found to be beneficial to the development of the symbiotic assemblages of coal seams overlying the oil shale. This tract type generally presented large bed thicknesses and distribution ranges. The low stand system tract and the late high stand system tract were determined to be unconducive to the development of the symbiotic assemblages.
Highlights
In geological exploration for energy sources, the symbiotic development phenomenon of coal and oil shale deposits is often seen, such as in China’s Fushun Basin (Meng et al 2012a, b), Huadian Basin (Sun et al 2013), and Songliao Basin (Bechtel et al 2012); Ethiopia’s Delbi-Moye Basin (Ahmed 2004); and Thailand’s Mae Sot Basin (Curiale and Gibling 1994)
(3) The rapid transformations of the coal and oil shale genetic environments were mainly controlled by the tectonic settings and climatic conditions, which were determined to control the changes in the water depths, salinity, redox conditions, and lake productivity of the genetic environments
In order to more deeply analyze the rapid conversion mechanisms of coal and oil shale genetic environments in the Oil 2–Coal 1–Oil 1 symbiotic assem‐ blage (OS–coal–oil shale (C–OS)), the Oligocene Lijiaya Formation of the Beizao Coal Mine of the northwestern Huangxian Basin was selected as the study object
Summary
In geological exploration for energy sources, the symbiotic development phenomenon of coal and oil shale deposits is often seen, such as in China’s Fushun Basin (Meng et al 2012a, b), Huadian Basin (Sun et al 2013), and Songliao Basin (Bechtel et al 2012); Ethiopia’s Delbi-Moye Basin (Ahmed 2004); and Thailand’s Mae Sot Basin (Curiale and Gibling 1994) It can be seen in the Early Carbonifer‐ ous strata in northern Canada (Cameron et al 1994) and is the most prominent in Mesozoic–Cenozoic continental fault basins (Chen 1951; Liu and Liu 2005; Liu et al 2007, 2012a, b; Liu and Liu 2006). This study focused on the development and occurrence regularity of symbiotic assemblages, in order to further enrich the basic theory of energy geology and to provide some guidelines for future multi-energy comprehensive exploration
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