Sequence stratigraphy influenced by tectonics and implications for reservoir development, latest Devonian–Early Carboniferous ramp, Canning Basin, Australia

Abstract

Abstract The interpretation of geologic observations utilizing sequence stratigraphic approach provides a better understanding of controlling mechanisms, i.e. tectonics, eustasy and sediment supply. However, assessing the role of each individual mechanism may be complicated because of the interplay between accommodation, influenced by tectonics and eustasy, and sediment supply. In this study, the sequence stratigraphic framework of the mixed carbonate–siliciclastic Fairfield Group was re-evaluated in association with the extensional tectonic activity to understand the effect of tectonics in controlling depositional facies and sequences. The main phase of extensional tectonic activity in the mid-Devonian led to normal faulting and fault block rotation and tilting, and created the Fitzroy Trough depocentre in the northern margin of the Canning Basin. During the Fairfield Group deposition in the latest Devonian–Early Carboniferous, the Fitzroy Trough underwent at least two pulses of extension. The subsurface data reveal that the extensional pulses resulted in the development of accommodation, suggested by the formation of depositional facies associations and systems tracts that are indicative of an increased accommodation and rapid sedimentation, i.e. transgressive systems tracts. The fault-related antecedent topography also exerted an important control on accommodation and led to an increased thickness of strata in the hanging wall of major normal faults in the Fitzroy Trough. The review of the distribution of known conventional and unconventional reservoirs in the Fairfield Group using the tectonically-influenced sequence stratigraphic framework shows that tectonic setting significantly controlled the distribution of the reservoirs. The conventional reservoirs developed in porous, permeable inner-ramp carbonates of the highstand systems tracts (HST). These are developed on shallow-water, platform tops that were formed on the tilted fault blocks in an extensional setting. The unconventional reservoir was encountered in tight (low porosity, low permeability) mid-outer ramp siliciclastic of transgressive (TST) and lowstand systems tracts (LST) of siliciclastic-dominated sequences that were deposited during extensional pulses in the basin.