Unusual biomarker maturation ratio changes through the oil window, a consequence of varied thermal history

Saturated and aromatic biomarker ratios continue to change systematically through the oil window and into the gas-condensate window to high vitrinite reflectances (Ro=1.16%) in mature marine and lacustrine Mesozoic clastic samples from a South African basin. Two of the ratios reverse above Ro=0.9%. These unusual maturation effects result from isolated periods of high rates of maturation increase. The basin cooled regionally after the break-up of Gondwana but high heating rates prevailed during the late Cretaceous–early Tertiary, as Africa moved across a hotspot, and again in the late Tertiary as a result of a possible hotspot and hydrothermal event.