Petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in Late Permian coal measures, Bowen Basin (Queensland), Australia

• Published in: Sedimentary geology 2000-11, Vol.136 (3-4), p.189-206
• Main Authors: Uysal, I.T., Golding, S.D., Glikson, M.
• Format: Article
• Language: English
• ISSN: 0037-0738
• DOI: 10.1016/S0037-0738(00)00097-X

Authigenic carbonate minerals are ubiquitous throughout the Late Permian coal measures of the Bowen Basin, Queensland, Australia. In the northern Bowen Basin, carbonates include the following assemblages: siderite I ( delta super(18) O sub( SMOW )=+11.4 to +17%, delta super(13) C sub( PDB )=-5.3 to +120), Fe-Mg calcite-ankerite-siderite II mineral association ( delta super(18) O sub( SMOW )=+7.2 to +10.20, delta super(13) C sub( PDB )=10.9 to -1.80 for ankerite) and a later calcite ( delta super(18) O sub( SMOW )=+5.9 to +14.60, delta super(13) C sub( PDB )=-11.4 to +4.40). In the southern Bowen Basin, the carbonate phase consists only of calcite ( delta super(18) O sub( SMOW )=+12.5 to +14.80, delta super(13) C sub( PDB )=-19.4 to +0.80), where it occurs extensively throughout all stratigraphic levels. Siderite I occurs in mudrocks and sandstones and predates all other carbonate minerals. This carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions. Fe-Mg calcite-ankerite-siderite II occur in sandstones as replacement of volcanic rock fragments. Clay minerals (illite-smectite, chlorite and kaolinite) postdate Ca-Fe-Mg carbonates, and precipitation of the later calcite is associated with clay mineral formation. The Ca-Fe-Mg carbonates and later calcite of the northern Bowen Basin are regarded as having formed as a result of hydrothermal activity during the latest Triassic extensional tectonic event which affected this part of the basin, rather than deep burial diagenesis during the Middle to Late Triassic as previously reported. This hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta super(18)O values of ankerite and calcite, together with radiometric dating of illitic clays and recently published regional geological evidence. Following the precipitation of the Ca-Fe-Mg carbonates from strongly super(18)O-depleted meteoric-hydrothermal fluids, continuing fluid circulation and water-rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks. Subsequently, the later calcite and clay minerals precipitated from relatively evolved ( super(18)O-enriched) fluids. The nearly uniform delta super(18)O values of the southern Bowen Basin calcite have been attributed to very low water/rock ratio in the system, where the fluid isotopic composition was buffered by the delta super(1