PALYNOLOGIC CONTRIBUTIONS TO PETROLEUM EXPLORATION IN THE PERMIAN FORMATIONS OF THE COOPER BASIN, AUSTRALIA

Abstract

From 1959, when Permian spores and pollen were first identified from Delhi-Santos wells in the Cooper basin until 1967, appreciation of the palynologic succession was impeded by problems associated with the severe carbonization of the microfossils. By 1966, sufficient data had been accumulated for the elucidation of the broad palynologic framework. The Merrimelia Formation was identified as early Permian (palynologic unit Plb of Evans), the Lower and Middle Members of the Gidgealpa Formation as Lower Permian (units Plc-P3a) and the Upper Member of the Formation as Upper Permian (units P3b-P4). Breaks in the microfloral succession were noted above the Merrimelia Formation and between the Middle and Upper Members of the Gidgealpa Formation corresponding with observed litho-stratigraphic hiatuses.

Well-preserved microfloras were recovered from four wells in late 1967 and early 1968, and produced a dramatic advance in knowledge of the Permian biostratigraphy. It became possible to relate the microfloral succession to the Permian palynologic stages proposed by Evans (1967), for eastern Australia. The Merrimelia Formation was referred to stage 2, while stages 3, 4 and 5 were recognised within the Gidgealpa Formation. In addition, two units of apparently short duration were recognised in each of stages 4 and 5. A six-fold biostratigraphic subdivision of the entire Permian sequence was thus possible.

Palynology is finding wide application to problems encountered in current drilling and stratigraphic investigations. It has shown particular value when applied to those problems associated with the mid-Gidgealpa Formation disconformity, which is an important feature relative to hydrocarbon accumulation in the Gidgealpa Field.