Organic Matter Assessment of the Jurassic Bazeh-Howz Formation of the Binalud Basin, Iran: Insights from Organic Petrography and Geochemistry

The Bazeh-Howz Formation represents Jurassic siliciclastic strata in the Binalud Basin, northeastern Iran, composed of fluvio-deltaic deposits, that consist of three major types of facies, conglomerate (monomict and polymict orthoconglomerates), sandstone (quartzarenites, sublitharenites, feldspathic litharenites or phyllarenites), and shale. The formation has an underlying fault contact and is overlain by Cretaceous carbonates. Fine-grained deposits (shale) with organic material represent more than 65% of the strata (>1000 m), and commonly alternate rhythmically with siltstone and very fine-grained sandstone. Pyrolysis of 17 samples indicates 0.18 to 26.3 wt. % of total organic carbon (TOC), with an average of 3.09 wt. %. The amount of free hydrocarbon and the residual potential are generally low, which indicates a poor potential to generate hydrocarbon. The organic matter is residual carbon, with no indication of pyrolysis carbon (PC). Based on oxygen and hydrogen (OI, HI) indices, the organic matter is reworked and migratory, and the samples do not contain primary and free organic matter (kerogen). Petrological studies show that the organic material is solid bitumen and pyrobitumen, filling intergranular pores and fractures and following lamination in places. Reflectance of organic fragments varies from 1.12 to 1.77, indicative of the varied genesis and formation time of solid bitumen.