Organic geochemistry of the Amiran Formation in the Amiran anticline, SW of Lorestan

Document Type : Research Paper



The Amiran Fm. (Mastrichtian- Paleocene in age) was deposited in the Zagros basin. This Fm. Comprises variegated shale beds in the Lorestan province. As presumably the majority of the formation was deposited in a deep marine environment, it is expected to find organic-rich facies within fine- grained facies of the Amiran. Fm. Hence, attempts were made to evaluate hydrocarbon potential of the Am. Fm. in this region. For this purpose, an outcrop of the Amiran Fm. in northern flank of the Amiran anticline was investigated and 52 samples were collected, of which12 samples, particularly of dark color fine-grained facies were selected for geochemical analysis. These samples were analyzed by Rock-Eval Pyrolysis type III in Research Instituteof Petroleum Industry (RIPI). Geochemical analysis revealed that TOC content of the 55% samples is less than 0.5 Wt %.Other parameters such as S1, S2, S1 + S2 suggest weak hydrocarbon production. Results also revealed that the Amiran Fm. predominatly copmrises kerogen types III and IV. The HI vs. Tmax cross-plot and PI vs. Tmax show that 73% of the samples fall in catagenesis stage. According to Jone’s diagram, the Amiran Fm. represents various organic facies including (BC, CD and D). Various organic facies may imply mixing of land-derived OM with autochthonous OM during turbidity currents, which intermittently occurred within the basin. Hence, we purpose that organic facies of the Amiran Fm. were deposited in oxic to suboxic conditions during relative see- level fall.