Abstract: The Lower Cambrian solid bitumen, with high organic content, high hydrogen index and low asphaltene maturity, was collected from the Kuangshanliang area in the northwestern Sichuan Basin to study the evolution of calcium speciation during TSR and pyrolysis of solid bitumen.. The generation and expulsion simulation experiments were carried out in a high temperature and pressure simulator, and the calcium speciation was determined using a direct, non-destructive synchrotron-based calcium K-edge X-ray Absorption Near Edge Structure (XANES). Calcium carbonate was the major calcium compound in the asphalt pyrolysis simulation experiments (series 1). However, in the asphalt TSR simulation experiment (series 2), with the increases of temperature and pressure, the yield of H₂S and sulfate increased, indicating that both oxidation and reduction reactions occurred. The generation and enrichment of calcium sulfate in the simulation experiments of series 2 indicated that the acidic fluid from the TSR process could produce significant dissolution in dolomite reservoirs.