Skip to Main Content
Skip Nav Destination

Abstract:

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.

You do not currently have access to this chapter.

Figures & Tables

Contents

GeoRef

References

Related

Citing Books via

Close Modal

or Create an Account

Close Modal
Close Modal