--> Abstract: Deep Ankerite Cementation of the Aldebaran Sandstone, Denison Trough (Eastern Australia) during Upward, Cross-Formational Porewater Flow, by P. de Caritat and J. C. Baker; #91012 (1992).

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ABSTRACT: Deep Ankerite Cementation of the Aldebaran Sandstone, Denison Trough (Eastern Australia) during Upward, Cross-Formational Porewater Flow

CARITAT, PATRICE de, University of Calgary, Calgary, Alberta, Canada, and JULIAN C. BAKER, University of Queensland, Queensland, Australia

Authigenic ankerite in the gas-bearing mid-Permian Aldebaran Sandstone (Denison Trough, Queensland, Australia) precipitated at temperatures of about 100 to 140 degrees C, when the sequence approached maximum burial during the Late Triassic. The oxygen-isotopic composition of the ankerite (Oxygen 18 SMOW range: +7.6 to +14.4o/oo) indicates that it precipitated from Oxygen 18-depleted porewater (Oxygen 18 = -9 to -5o/oo). The formation of this deep, relatively high temperature ankerite phase is difficult to reconcile with meteoric water ingress at that time, and we interpret the ankerite to have precipitated in contact with porewater expelled upward from the earliest Permian Reids Dome beds. This thick unit, consisting mainly of high latitude continental sandstones, mudrocks, and coals, was initially saturated with very Oxygen 18-depleted meteoric water (Oxygen 18 about or equal to -17o/oo) and is likely to have undergone overpressuring during rapid burial (at rates up to 1 km/Ma). Tectonically induced expulsion of the evolved "connate meteoric" porewater out of the Reids Dome beds took place as the sequence approached maximum burial, and this water was flushed upward through the overlying units, still retaining a strongly meteoric isotopic signature as it progressively mixed with heavier marine porewaters.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)