Potential Petroleum Source Rocks in Triassic Lacustrine‐delta Sediments of the Gunnedah Basin, Eastern Australia

Abstract

Integration of lithofacies, inferred depositional environments and organic petrology of a lacustrine delta sequence in the Permo‐Triassic Gunnedah Basin of eastern Australia has provided a logical explanation for the patterns of distribution of the dispersed organic matter. The data show that: (i) sedimentary processes, such as size sorting and transportation, control the association of maceral assemblages in the dispersed organic matter with depositional environments; (ii) the extent of oxidation of organic matter increases downstream, from flood‐plain lake to interdistributary bay, delta front, prodelta and off‐shore lake deposits; (iii) coarse, woody material, mostly oxidised to semifusinite, is concentrated in the delta‐front environment; (iv) leaf material is transported preferentially to the prodelta, via the delta front. On the basis of organic matter type, the prodelta was probably the most favourable environment in this depositional system for the accumulation of oil‐prone source beds.

Terrigenous Clastic Depositional Systems

“…Lacustrine shales deposited in these vast foreland and intracratonic basins contain dispersed, gasprone organics (Tankard et al 1982;Smyth et al 1992). Lacustrine shales deposited in these vast foreland and intracratonic basins contain dispersed, gasprone organics (Tankard et al 1982;Smyth et al 1992).…”

“…Some of these lakes are regarded as being closely analogous to major oilproducing provinces, such as Mesozoic rift basins along the South Atlantic margin (McHargue 1990;Abrahao and Warme 1990). Other ancient lake systems are gas prone as a result of abundant dispersed type III organic matter of land-plant origin (Smyth 1979;Smyth et al 1992). Other ancient lake systems are gas prone as a result of abundant dispersed type III organic matter of land-plant origin (Smyth 1979;Smyth et al 1992).…”

Cretaceous (Hauterivian–Cenomanian) palaeoceanographic conditions in southeastern Tethys (Matruh Basin, Egypt): Implications for the Cretaceous climate of northeastern Gondwana

“…As woody tracheids are usually relatively large and dense fragments, they tend to concentrate in coarse silts and very fine sands that are commonly found in proximal fluvio-deltaic facies (e.g., Habib, 1983;Firth, 1993;Tyson, 1993Tyson, , 1995. high energy, coarse-grained proximal facies of fluvial and delta-top systems (e.g., Nagy et al, 1984;Smyth et al, 1992;Williams, 1992), again controlled by particle size/shape (Tyson, 1995).…”