Postdepositional History of the Permian Sequence in the Denison Trough, Eastern Australia (1)

Abstract

The diagenesis of Permian siliciclastic sedimentary rocks of the Denison trough is interpreted in terms of evolving pore-water composition related to the burial history of the basin. In the sandstones, early precipitation of pyrite, siderite, and grain-rimming illite-smectite was followed by development of quartz overgrowths that incorporated silica released by pressure solution, recrystallization of lithics, and smectite/illite reaction. Later, as the sequence reached maximum burial during the Late Triassic, strongly {18}O-depleted siderite and ankerite, which incorporated iron and magnesium liberated by leaching of detrital mafic minerals and continuing smectite/illite reaction, precipitated from connate pore water expelled upward from the underlying, overpre sured continental Reids Dome beds. This implies the existence of significant cross-formational pore-water flow prior to and during attainment of maximum burial. Regional Late Triassic to earliest Jurassic compression resulted in major uplift and exposure of the Permian sequence. Attendant strata-concordant invasion of meteoric water led to labile grain and ferroan carbonate dissolution, and to the formation of strongly {18}O-depleted kaolinite and a second generation of quartz overgrowths. Later postdepositional events, which occurred during a second cycle of burial and uplift, include the precipitation of {18}O-depleted calcite and dawsonite, and hydrocarbon entrapment.