Dissolution Tirrawarra Sandstone

Fig. 4. Petrographic, BSE and colour image characteristics of Tirrawarra Sandstone siderites. (A) Plane-polarized view of the main siderite cement generations that can be distinguished under the optical microscope in this case, which is the exception rather than the rule. SI has a brownish colour, whereas S2 and S3 are clear and colourless. SI is typically engulfed by S2. Note the concentration of fluid inclusions in S2, and the irregular serrated boundary between S2 and S3 (arrow), implying some dissolution of S2 prior to precipitation of S3. Sample Ml-9598, Moorari 1, 2925.5 m.

Fig. 5. BSE image of the view shown in Fig. 4(A). SI displays a light colour, whereas the surrounding S2 (medium grey) is characterized by a variable internal composition and complex zoning. S3 is a relatively homogeneous, late-generation pore-filling cement. Note the irregular dissolution boundary between S1 and S2, and between S2 and S3 (arrows). These cement relationships are typical of Tirrawarra Sandstones. Sample Ml-9598, Moorari 1, 2925.5 m.

Tirrawarra Sandstone (Fig. 15). The conclusion is supported by the presence of a dissolution boundary between each major cement generation (Figs 4A and 5). 

Fig. 17. Generalized paragenetic sequence for the Tirrawarra Sandstone in the Fly Lake-Moorari area. Cooper basin. The interpretation is based on the integration of petrographic, isotope and fluid inclusions results. The estimated timing of oil generation and migration is indicated (shaded zone). S1, early generation of siderite cement S2, middle generation of siderite cement S3, late generation of siderite cement D1 and D2, first and second phases of siderite dissolution, respectively.

Tirrawarra Sandstone, either meteoric invasion or source-rock maturation probably accounts for the association of authigenic kaolinite patches with siderite spar displaying dissolution (Fig. 4B). 

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