The Carribuddy Group and Worral Formation, Canning Basin, Western Australia: reassessment of stratigraphy and petroleum potential

Abstract

Reassessment of stratigraphic relationships and biostratigraphic data pertaining to the Carribuddy Group and Worral Formation in all relevant petroleum wells and many mineral drill holes across the southern Canning Basin has led to the following important results. The Carribuddy Group is restricted to the Late Ordovician to earliest Silurian. The overlying Worral Formation is mostly of Silurian age and does not intertongue with the Middle Devonian Tandalgoo Formation, as previously thought. A thin basin-wide chronostratigraphic marker—the Pegasus Dolomite Member (previously referred to as dolomite spike or dolomite marker) of the Sahara Formation—allows improved correlation between salt-bearing sub-basins and adjacent condensed Carribuddy Group successions. The Mallowa Salt is not as extensive as previously thought; rather the Minjoo Salt thickens to become the only salt seal in the eastern and southern Kidson Sub-basin.

The Carribuddy Group forms the regional seal to the prospective Larapintine 2 petroleum system, but also contains local source and reservoir facies. The Bongabinni Formation contains extremely rich oil-prone source rocks in local lagoonal facies along the Admiral Bay Fault Zone; these rocks have been linked by other studies to migrated oil in that area. The distribution of the source facies is poorly known, but it may extend down-dip into more mature parts of the Willara Sub-basin, and west into offshore areas. Other local source units may be present in the Mallowa Salt, and possibly the Nibil Formation, but are not well documented. Aeolian sandstone with excellent reservoir potential is locally present in the Nibil Formation, but is more extensive in the lower Worral Formation, particularly the Elsa Sandstone Member.