An Analysis of the organic geochemistry and environmental geochemistry of the Sargelu and Garau formations in the Qalikuh region, Lorestan

Sargelu and Garau formations are significant geological units in the Zagros, which are known for having the most important unconventional hydrocarbon resources in Iran. This study aimed to evaluate the hydrocarbon generation potential of two formations by analyzing 15 oil-shale samples collected from the Gashun-G and Pirbadush sections along the Qolyan River in the Qalikuh area, Lorestan. The analysis method used was Rock-Eval pyrolysis. To determine the scatter pattern of heavy elements, a total of 15 samples of river sediments and water were analyzed using ICP-MS. The average values for total organic carbon (TOC) and most hydrocarbon production indicators in Garau oil shales exceed the values observed in Sargelu oil shales. Based on the findings of the elemental analysis and pollution index calculations conducted on sediments, it can be seen that Sargelu shows a higher presence of heavy elements, a higher contamination factor (CF) and average pollution load index (PLI) compared to Garau samples. This difference can be attributed to the physical and chemical characteristics of the sediments. Conversely, Garau samples show a higher average Contamination Degree (CD) in its water, which may be attributed to environmental factors such as temperature and pH of water. The results of the statistical analysis demonstrate a wide range of heavy element formation factors within the sediments and waterways of the Garau route. As a result, despite the lack of human activity in this area, in addition to the amount of organic matter in the oil-shale, the geo-genic activity causes natural environmental pollution that is influenced by various factors, including oxidation-reduction potential, reactive processes, type of bedrock, clay minerals, sediment texture and environmental conditions.