Contribution of terrestrial material in West Sulawesi based on geochemical and biostratigraphy analysis

Abstract

The LYS and KYS exploration wells were drilled in the north and south of the Bdg Block, onshore West Sulawesi, Indonesia. Geochemical analysis, especially gas chromatography and gas chromatography/mass spectrometry, was conducted on cutting samples of LYS and KYS wells. The existing biostratigraphy analysis shows that LYS samples are in the marine environment (outer neritic-upper bathyal) with age of Late Miocene-Pleistocene, while KYS samples are also in the marine environment (inner neritic-batial) with age of Middle Eocene-Early Pliocene. There are few terrestrial materials found, such as oleanane, bicadinane, taraxastane, and gammacerane, that indicates only a small amount of terrestrial material that was moved to the marine environment. The high oleanane/C30hopane ratio in both wells showed the contribution of higher plants. There are variations in the value of the oleanane/C30hopane ratio in KYS samples at Neogene (Middle-Late Miocene). The ternary diagram shows abundance of sterane (C27, C28, and C29) with marine organic material input, followed by contribution from terrestrial material, and deposited in the marine environment. High concentration of higher plant biomarkers in Neogene compared to in Paleogene indicates depositional environment changes from lacustrine and shallow marine to deep water and also affected by greater abundance of angiosperm plants during Neogene.