Investigation of deposition rate of terrestrial organic-rich shales in China and its implications for shale oil exploration

The abundance of organic matter and the types of shale laminae are the key in shale oil exploration. The sedimentary facies of terrestrial shales features complex variation and strong heterogeneity, making accurate identification of deposition rate facing more challenges. The deposition rates of organic-rich shales in typical terrestrial basins of China are mostly above 5 cm/kyr, and those of the organic-rich shales in saline lacustrine basins may reach up to 40 cm/kyr. The high-precision chronostratigraphic framework combined with the statistical tuning of cyclostratigraphy can trace the variation of deposition rate with burial depth. The relative deposition rate of shales can be determined by the rare earth element (REE) assemblage pattern, crystal size distribution, and the abundance of typical interstellar dust elements, etc. Comparison of deposition rates of different types or ages of stratigraphic sequences has to take perturbations such as stratigraphic integrity and differential compaction into consideration. Deposition rate is an important factor influencing the enrichment of organic matter in shale, and the critical threshold for organic matter dilution by deposition rate is usually less than 5 cm/kyr. The flocculation of sediment particles is usually under the effect of hydrodynamic conditions and water salinity, and the various deposition rates for different types of fine-grained sediment are conducive to the formation of shale laminae. The study of deposition rate requires an integration of advanced theories and methods, including geochronology, petrology, cyclostratigraphy, geochemistry, and physical simulation of sedimentation, to gain a deeper understanding of the mechanisms of shale deposition and evolution. Revealing the interrelationship between terrestrial shale deposition rate and shale oil accumulation is of certain guiding significance to shale oil exploration.