SEQUENCE STRATIGRAPHY OF THE EASTERN OFFICER AND ARROWIE BASINS: A FRAMEWORK FOR CAMBRIAN OIL SEARCH

Abstract

The Early Cambrian eastern Officer and Arrowie Basins share a common sequence stratigraphic framework despite their contrasting settings. The Arrowie Basin was initially a shallow marine shelf between two land masses with moderate to abrupt shelf-ramp and shelf-slope profiles deepening to the north and south. Tectonic activity subsequently restricted open marine access to the north resulting in evaporite and red bed deposition. In the eastern Officer Basin epeiric sea sediments had open marine access only to the northeast. The palaeoslope was low and surrounding land supplied abundant siliciclastics. Following marine withdrawal alkaline playa lake and evaporitic mudflat deposits spread across the hinterland. Potential source rocks in the Arrowie Basin are thick transgressive and early high-stand deposits of the lowest three sequences. Organic carbon content may be highest (on slender evidence) where marine circulation was restricted. Carbonate reservoir quality on the shelf depends on subaerial exposure during marine lowstands. Prograding highstand sands, carbonate grainstones, and syntectonic channel deposits have untested reservoir potential. In the eastern Officer Basin potential source rocks are thin but widespread. Oil has been generated in the playa lake sediments. Fluvial, aeolian and shoreline sandstones, and those interbedded with carbonates, have excellent reservoir characteristics. The interbedded sands are thin but may be grouped near sequence boundaries. Lowstand carbonate breccias have generally unpredictable reservoir quality. Major differences in source and reservoir bed distribution between these basins, which share the same cycles of relative sea level change, are: palaeoslope, proximity to open marine conditions, duration of subaerial exposure and availability of terrigenous clastics.