Kerogen associations and paleoenvironmental interpretation of the Upper Triassic Mungaroo Formation in the Gorgon Area, Northern Carnarvon Basin, Western Australia

Abstract

Summary Kerogen slides were made from 92 core samples selected from the Upper Triassic Mungaroo Formation in four wells in the Gorgon area of the Northern Carnarvon Basin. The slides were examined to investigate relationships between kerogen assemblages and their depositional environments (“depofacies”). Although the assemblages naturally vary and overlap to an extent, each depofacies has a characteristic kerogen assemblage. Moreover, depofacies which are genetically similar tend to have similar assemblages even though they may have been deposited in different parts of the delta. For example, active channels tend to have similar kerogen assemblages (abundant black-opaque particles, few cuticles, sparse palynomorphs) irrespective of whether they are fluvial, crevasse or distributary channels; in this case, it is inferred that the overwhelming factor in the kerogen assemblages is the high energy level of the environment of deposition, and its consequent inhibition of local vegetation and promotion of mechanical degradation of organic particles.