--> Abstract: Shallow Burial Dolomitization of Mid-Cenozoic, Cool-Water, Calcitic, Deep-Shelf Limestones, Southern Australia, by N. P. James, Y. Bone, and T. Kurtis Kyser; #91004 (1991)

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Shallow Burial Dolomitization of Mid-Cenozoic, Cool-Water, Calcitic, Deep-Shelf Limestones, Southern Australia

JAMES, NOEL P., Queen's University, Kingston, Ontario, Canada, YVONNE BONE, University of Adelaide, Adelaide, South Australia, and T. KURTIS KYSER, University of Saskatchewan, Saskatchewan, Canada

Oligocene to middle Miocene, deep-shelf, bryozoan-rich limestones across southern Australia are variably replaced by green to orange, Ca-rich, zoned, medium-crystalline, sucrosic dolomite. The degree of replacement varies from scattered rhombs in limestone to complete dolostones a few tens of meters in thickness and a few kilometers in lateral extent. Dolostone texture ranges from dense and well lithified to completely unlithified, resembling a loose sand of dolomite rhombs. Dolomitization is fabric specific; calcite and Mg-calcite bryozoans are either the last components to be replaced or are molds. The timing and locale of dolomitization are tightly constrained; Sr isotopes indicate a middle to late Miocene age while clasts of dolostone in overlying Pliocene limestones above a regio al unconformity confirm a shallow-burial, pre-Pliocene origin. C(13) and O(18) values support a marine source for the carbonate; the influence of meteoric fluids appears to have been negligible. Quaternary exposure has resulted in local dedolomitization and/or subaerial erosion, especially in the Murray basin.

These rocks are excellent analogues for localized, lenticular dolostone bodies in calcite-rich Paleozoic platform carbonates.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)