POST–EARLY CARBONIFEROUS THERMAL HISTORY RECONSTRUCTION FROM WELL DATA IN THE AMADEUS BASIN, CENTRAL AUSTRALIA

Abstract

Apatite Fission Track Analysis (AFTA) combined with maturity data has revealed that four (possibly five) cooling events affected the northern margin of the Amadeus Basin since the Early Carboniferous. A consistent regional thermal history framework is developed, with recognition of cooling events beginning in the Carboniferous/Early Permian (between ~360 and 290 Ma), the Early Jurassic (~200 Ma), Late Cretaceous (between ~80 and 70 Ma) and Tertiary (between ~ 25 and 20 Ma). We suggest the first of these reflects uplift and erosion associated with the Alice Springs Orogeny, while Early Jurassic cooling reflects uplift and erosion associated with the Fitzroy Movement. Uplift and erosion in the Late Cretaceous probably relates to the breakup of Australia and Antarctica (opening of the Tasman Sea) at about this time. Later uplift and erosion in the Miocene may reflect Neogene collision of the Australian and SE Asian Plates in the region of the Banda Arc.

In Tyler–1 (northern Amadeus Basin), maturation modelling using paleotemperature constraints from AFTA and VR equivalent data suggests the main source rock horizon (Ordovician Horn Valley Siltstone), went through the dry gas window during burial associated with the latter stages of the Alice Springs Orogeny. Basinward (south) of this foreland wedge, the influence of Devonian-Carboniferous loading decreases enabling oil expulsion from the Horn Valley Siltstone to have charged the Mereenie Structure. This was later partially displaced by gas.

To date the Neoproterozoic sequences have yielded only dry gas (at Dingo field, Ooraminna–1 and Magee–1) which could be due to original source rock characteristics, but more likely to high maturity levels in the main depocentres. Previous notions that the Ordovician petroleum system was probably only active in the northern portion of the basin appear correct, but gas charged traps at the level of the Neoproterozoic should be ubiquitous.