Pressure-Dissolution and Cementation in an Oligo-Miocene Non-Tropical Limestone (Clifton Formation), Otway Basin, Australia
Published:January 01, 1997
Stelios Nicolaides, Malcolm W. Wallace, 1997. "Pressure-Dissolution and Cementation in an Oligo-Miocene Non-Tropical Limestone (Clifton Formation), Otway Basin, Australia", Cool-Water Carbonates, Noel P. James, Jonathan A. D. Clarke
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The late Oligocene-Miocene subsurface Clifton Formation in the Otway Basin, southeastern Australia, consists predominantly of skeletal carbonate grains of originally calcite mineralogy deposited in a non-tropical shelf environment. Bryozoans are the dominant allochem, with echinoderms, foraminifers and siliciclastics as subordinate grain types. In the area of study, the Clifton Formation had an uncomplicated burial history and was subject to very little uplift (< 100 m). Present burial depths (ranging from 160 m to 670 m below present surface) equate approximately with maximum burial depths. Shallow-buried limestones are weakly cemented by calcite (<5% calcite cement down to 430-m depth) while more deeply buried limestones (>550 m) are almost completely cemented by calcite. Evidence for mechanical compaction (mainly grain breakage) is present throughout the unit. Products of pressure-dissolution in the Clifton Formation, which can only be observed microscopically, are interpenetration of grains (with smooth and sutured contacts), fitted fabrics, dissolution seams and microstylolites. Significantly, no macroscopic stylolites are present (to a maximum depth of 670 m), suggesting that in these limestones, stylolite formation requires burial depths greater than about 700 m.
In grainstone intervals, interpenetration of grains is apparent in the shallowest samples (less than 200 m), whereas fitted fabrics and microstylolites first appear at depths of approximately 550 m. In clay-rich lithologies, dissolution seams occur at depths as shallow as 190 m, although they are better developed at and below 340 m.
In the Clifton Formation, microstylolites appear to develop from an amalgamation of sutured interparticle contacts in grainstones with fitted fabrics. Further dissolution and amplification of these microstylolites could lead to the formation of stylolites. Such a model has implications in the timing of origin of particular diagenetic events such as hydrocarbon emplacement or mineral precipitation from metal-bearing fluids.
The coincidence of a dramatic increase in cementation with an increase in pressure-dissolution features (in the form of fitted fabrics and microstylolites) between 430-m and 550-m depth suggests that much CaC03 cementation was caused by pressure-dissolution. Mechanical compaction, on the other hand, dominates pressure-dissolution in porosity loss.
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This book is a collected series of papers on the sedimentary geology of carbonate sediments deposited on shelves and offshore banks in cool to cold oceans. Contributions come mainly from a workshop organized by Jonathan Clarke held in Geelong, Victoria from January 14 to 19, 1995. Most earth scientists have traditionally viewed carbonate sediments as warm-water deposits and interpreted them as such in most of the geological record. Yet large areas of the modern seafloor are covered with neritic carbonate sediments formed in seawater that is colder than 20ºC. Such environments are not easily studied. Thus, our knowledge of cool-water carbonates has lagged far behind our understanding of their warm-water counterparts. This situation has changed somewhat as more and more investigators have braved the chill waters and rough seas. This book brings together a group of studies that illustrate the present status of our understanding and current research in a field that is in mid-life.