Geochemical evidence for a Cretaceous oil sand (Bima oil sand) in the Chad Basin, Nigeria

摘要: Paleogeographic studies have shown that Earth was covered with more water during the Cretaceous than it is today, as global sea level significantly higher. The witnessed one of greatest marine transgressions in Earth's history, represented by widespread deposition sands directly on underlying basement. These sand bodies hold much world's heavy oil. Here, we present for first time, geochemical evidence a oil (Bima sand) Chad Basin, Nigeria. Bima similar to other sands, predominantly occurring at shallow depths basin flanks and generally lacking seal cover, making susceptible biodegradation. bulk properties distribution molecular features oils from suggest they are biodegraded. Sterane maturity parameters trisnorhopane thermal indicator maturities consistent generated conventional light oils, which later degraded into oils. also show no 25-norhopane, strongly suggesting biodegradation occurred depths, depth occurrence Formation study locality. Low diasterane/sterane ratios C29H/C30H greater 1 carbonate source rock studied further suggests were sourced rocks. C32 homohopane isomerization 0.59–0.60, implying has surpassed main generation phase, burial Fika Gongila Formations, both possible petroleum rocks basin.