Exploring the geochemical, petrographic, and palynological signatures: An analysis of the Mungaroo Formation source rock potential in the Exmouth Plateau, Northern Carnarvon Basin, Australia

Abstract

The Late Triassic Mungaroo Formation of the Exmouth Plateau was investigated through an integrated, stratigraphically and geographically extensive study to characterize its source rock potential and depositional controls. Geochemical, petrographic, and palynological analyses reveal highly variable organic richness across the formation, with total organic carbon (TOC) content values ranging from very low in sand-dominated intervals to notably high in coal-bearing mudstones. The Mungaroo Formation exhibits diverse organic composition, with TOC content ranging from 0.63 % to 54.18 %, demonstrating that while certain intervals contain significant organic richness, others are notably lean in organic content. Petrographic analyses reveal the presence of dinoflagellates, liptodetrinite, sporinite, and cutinite, suggesting transitional settings with varying marine influence. Thermal maturity assessments indicate a range of maturity levels, with vitrinite reflectance (R_o) values ranging from 0.45 % to 1.39 %, reflecting thermal maturity of immature to post-mature stage. Rock-Eval pyrolysis parameters support these observations, highlighting varying stages of hydrocarbon generation. Biomarker characteristics further confirm the mixed organic origin and complex paleo-depositional environments within the Mungaroo Formation. The presence of both marine and terrigenous biomarkers underscores the depositional history of the region, with Pristane/Phytane ratios (Pr/Ph) indicating oxidizing environments typically associated with terrigenous plants’ input. Palynological data indicates strong terrigenous influence within both the wells Mercury-1 and Jupiter-1, characterized by proximal delta-plain environments.