PALEOENVIRONMENT OF MESOZOIC SEDIMENTS REVEALED BY PALYNOLOGICAL ANALYSIS: IMPLICATION FOR HYDROCARBON POTENTIAL OF THE ORANGE BASIN

The paleogeography of the Southern Hemisphere during the break-up of Gondwanaland and the emergence of the proto-South Atlantic during the Mesozoic has long interested scientists. The realignment of the landmasses and ultimate formation of the Orange Basin in southern Africa had a profound effect on the environment, which is reflected in the fossils preserved in the rocks. Although there are known hydrocarbon accumulations within the Orange Basin, the basin is still largely underexplored and has much future potential. Palynology has proven to an invaluable tool for inferring paleoenvironment and hydrocarbon potential, and is being integrated with foraminifera in this study. Thirty-eight core samples and ditch cuttings from four wells within three blocks in the Orange Basin ranging in depth from 2907.03 m to 4083.10 m were analyzed for their palynomorph and dispersed organic matter (palynofacies) contents. Marine amorphous organic matter comprises the majority of the dispersed organic matter components, which also include variable abundances of structured and degraded phytoclasts, opaque clasts, sporomorphs (spores and pollen), marine palynomorphs, and fungal remains. A diverse Aptian to Albian palynomorph assemblage is present. Nonmarine palynomorphs include various terrestrial and aquatic species, such as Taxodiaceaepollenites sp., Ghoshispora bella, Cyathidites sp. and Cicatricosisporites sp., along with marine palynomorphs such as the dinoflagellate cysts Spiniferites sp. and Exochosphaeridium sp. The inferred paleovegetation indicates a diverse group comprised mainly of gymnosperms, ferns, and algae. Our results suggest that warm temperate to subtropical climate existed during sediment deposition in proximal shelf to distal suboxic-anoxic basin conditions with deltaic influence. Palynofacies analysis is reflective of primarily type II-III kerogen.