Geochemical and microfaunal studies are carried out on Miocene sediments from the drill core of an off-shore well of the Oil and Natural Gas Corporation Ltd (ONGC) in the Krishna-Godavari (KG) Basin. Core samples (n = 27), a section with a length of ~ 30 m which contains dominantly sandstone-shale layers, were analysed. The geochemical studies include total organic carbon (TOC), total organic matter (TOM), and total phosphorous (TP). The microfaunal studies were performed through foraminifera and pteropod populations. The study observed that the range of values of TOC, TOM and TP are 0.46–2.94%, 0.79–5.07% and 0–0.36% respectively. Phosphorous has a similar trend with organic carbon, indicating a positive correlation. The variations in TOC content were lithology-controlled. In sandstone layers, the TOC is low, while in shales, it was observed to be high. A significant peak in the TOC (2.94%) and TP (0.36%) was observed at 2197 m depth, where carbonaceous shale with sporadic lignite patches prevails. The forams comprise benthic (n = 21) and planktonic (n = 14) populations and pteropod species (n = 7). The dominance of planktic foraminifer, Globegerinella aequilateralis, in most samples suggests that these sediments could belong to the late middle to late Miocene age. The majority of benthic foraminifera indicate shallow water marine deposition. However, the occurrence of Cibicides wuellerstorfi and C. pseudoungerianus in the bottom portion of the section confirms a deeper depositional regime. Planktic foraminifera and pteropods are characteristic of warm waters and indicate a tropical to temperate climate. The presence of heavy minerals like zircon, garnet, tourmaline, ilmenite, spinel, rutile, monazite, and magnetite indicates an Archaean igneous-metamorphic provenance of the Indian subcontinent from the Eastern Ghat Mobile Belt, through terrigenous river fluxes. Increased fluxes of organic carbon and phosphorous were attributed to increased continental weathering and high sedimentation rate. Pyritized nature and less abundance of the faunal populations coupled with high organic carbon values (0.9–2.9%) and calorification of organic matter as evidenced by the presence of lignite suggest anoxic conditions and plausible source rock for hydrocarbon accumulation. The interpretations of this study were consistent with the exploration results, which proved this well to be one of the few productive oil wells in the KG Basin.