Missionary Bay, north Queensland, is an example of a tropical modern depositional environment dominated by mangrove swamps. Several major sedimentary facies are represented: coastal sands, brackish-water peats, intertidal organic muds (on which the mangroves are developed), low-tide muds, channel deposits, inshore muds, sandy bay-bottom muds, inshore sands, inshore carbonate sands, and deltaic sands. Large amounts of mangrove litter are carried in nearly anoxic creeks to the bay. Bay-bottom sediments have only a shallow upper oxidized layer, and are strongly reducing at depth. Organic carbon values for most of the inshore sediments range from 1 to 2%.

Total lipid content of the bay-bottom sediments is very high. Sediments average 0.15% by weight total lipids, or about 6% of the total organic carbon. These high values are attributed to the lipid-rich mangrove litter.

Sedimentation rates for the bay-bottom sediments are high, about 1 cm/year. Progradation rates are also high, about 1 m/year. Including offshore fringing reefs and inshore sands, the total area of the system is several hundred square kilometers. Anoxic conditions of transport and deposition, plus the high sedimentation rates, suggest that the low-tide muds and bay-bottom muds are excellent source rock analogs. Progradation and accumulation could result in a section about 50 m thick, with lipid-rich sediments interfingering with barrier sands, fringing reefs, channel sands, and deltaic sands. The section will be capped and sealed by brackish-water peats with a mud matrix. This system is of potential value as a conceptual model for hydrocarbon accumulations on ancient tropical coastline .