ABSTRACT: Stratigraphic Sequences in Queensland's Tertiary Oil Shale Deposits

LINDNER, A. W., Consultant, Thornleigh, New South Wales, Australia, L. COSHELL, National Key Centre for Resource Exploitation, Curtin University, R. G. McIVER, Southern Pacific Petroleum NL/Central Pacific Minerals NL, J. H. PATTERSON, CSIRO Division of Coal and Energy Technology, and A. C. HUTTON, Department of Geology, University of Wollongong

A number of tectonically controlled Early Tertiary lacustrine deposits in eastern Queensland contain substantial quantities of oil shale and carbonaceous shale, a significant hydrocarbon resource for Australia.

An eroded Paleozoic backarc accretionary sequence provides the provenance for the predominantly argillaceous, allogenic constituents of the Tertiary lake deposits. Smectite and koalinite are the dominant clays; quartz is locally co-dominant in some units. Carbonates are present in accessory to trace levels. These, and trace feldspars, phosphates and opaline silica (in places co-equal with quartz) are to some degree authigenic. Diagenetic processes generally have played a somewhat subordinate role in mineral development.

Kerogen is intimately disseminated with the clay minerals; on the basis of elemental atomic ratios (H/C and O/C), the dominant kerogen is type I derived from lipid rich material (algal remains) but also with horizons and locations high in type III kerogen, derived from vascular, terrestrial plants.

There is ordered repetition of facies (determined by sedimentary structure, lithology, and organic content) and this is interpreted to indicate cyclic deposition. The complete cycle (not always developed) ranges from swamp to open meromictic lake culminating in subaerial conditions. Thus an interplay of subsidence rate, sediment supply, climate, floral assemblage and preserved organic material influenced the stratigraphic record. Variations have resulted in distinctive sequences; within a given graben, however, individual stratigraphic units display remarkably consistent character on both large and small scale and have recognizable equivalents in other deposits.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)