Browne formation The most notable formations in the Officer basin, in terms of thickness and hydrocarbon potential are the Browne, Hussar and Kanpa. The Browne formation, much like the other formations within the Officer, is deepest in the central portion of the basin, up to several kilometers. This is typical of the Officer basin, as it is deepest in the central portion in the east, and generally shallows westward. The Browne formation constitutes the most identifiable and thickest basal unit of the Officer, and shows remarkable lateral continuity, with limited change in
facies across the basin. The
lithology of the Browne is largely shale and
mudstone, but can vary from
dolomite to
dolomitic limestone, to thick evaporitic sequences. Based on this, it is likely that the Browne formation's provenance was an
intertidal to lagoonal environment. Due to the prevalence of evaporites within the Browne, diapir formation is common and there are many instances of
brecciated or contorted strata proximal to diapirs. The Browne has little potential as a hydrocarbon reservoir or source, as it likely reached maximum hydrocarbon production early in the basin’s history. Thus, much of the hydrocarbon production was exhausted during the Neoproterozoic.
Hussar formation The Hussar is the next youngest layer above the Browne, albeit a much thinner layer in comparison. The Hussar’s evaporitic content is almost nonexistent; instead this formation is predominantly
sandstone and shale, sometimes
interbedded with dolomite. The lack of evaporites in the Hussar contrasts sharply with the
halite-rich underlying Browne formation. In addition, the basal unit of the Hussar is a very distinct, near 100 m-thick mudstone unit that has been traced in
seismic logs, making it a significant
marker horizon. Several
progradational sequences have been identified within the Hussar, suggesting that its
depositional environment was a transitional one, ranging from shelf and
shoreline to
tidal flat and
fluvial.
Kanpa formation The Kanpa formation overlies the Hussar, and again the trend of younger formations being less thick than the previous formation continues. The Kanpa formation is unique because it contains a very compact sequence of basaltic flows, called the Kenne Basalt, which has minimal interbedded sediments. Generally, the Kanpa is a mixed siliciclastic-carbonate sequence of interbedded dolomite, with shale, evaporites, and
chert.
Detrital zircons within the uppermost sandstone layer of the Kanpa were dated using
U-Pb dating, and provide a maximum age constraint of 725 Ma. The prevalence of
stromatolites within the Kanpa suggest that its depositional setting was a carbonate-dominated shallow marine to tidal flat setting.
Steptoe formation The Steptoe formation overlies the Kanpa, and constitutes the final member of Supersequence 1. Its thickness is not well constrained, as it has only been observed in 2 cores to date, but can be up to ~500 m thick. The lithology of the Steptoe is largely sandstone and dolomite, which typically grade into siltstone. The age of this formation is also unconstrained, but it must be younger than 725 Ma, the age of the top of the Kanpa. Due to the lithologic similarities between the Kanpa and the Steptoe, it is likely that their depositional settings were similar, although the Steptoe’s was likely more restricted. More in-shore coastal settings are hypothesized for the depositional environment of the Steptoe. == Hydrocarbon potential ==