1.2.1.1.3 Avon Subgroup

The Avon Subgroup (Figure 3 and Figure 4) forms the lower stratigraphic component of the Gloucester Coal Measures and has eight discrete coal members. Of the several coal members recognised in the Avon Subgroup, the Avon Coal Member, which occurs near the top of the Waukivory Creek Formation, is the most consistent recognisable seam, in the formation and in the entire Gloucester Basin (Hughes, 1995, p. 424). The Parkers Road and Avon coal members represent depositional hiatuses (i.e. sedimentation ceased), which were important events as they allowed much of the surface to be covered with coal-forming swamps, leading to the coal seams today (Roberts et al., 1991, p. 177). Hughes (1995, p. 425) recorded an Rv,max for the Parkers Road Coal Member in the Stratford area of 0.71%.

The Avon Coal Member is present along the eastern margin and in the northern and southern areas (refer to Figure 22 of companion product 1.1.3 for the Gloucester subregion (McVicar et al., 2014)). It is a banded coal ranging in thickness from 20 m in the Stratford area to around 5 m in the south, and generally consists of a clean coal ply at the top with interbanded coal and non-coal material as the remainder. According to AGE (AGE, 2013, p. 4–45) the seam consists of five main plies in the Rocky Hill Coal Project area with an average combined net coal thickness of 7 m. Due to reverse faulting the maximum thickness recorded is approximately 60 m in some areas (Hughes, 1995, p. 424).

Roberts et al. (1991, p. 178) recognised the Marker Two and Glenview coal members within the Dog Trap Creek Formation. The Glenview Coal Member is the marker for the top of the formation and occurs as a single coal bed which developed in a back barrier environment, resulting in high but variable sulfur contents ranging from 0.7 to 7.5%. It has a maximum thickness of over 3 m and is mainly developed to the north of the Stratford area, but is also present throughout a large part of the eastern margin of the Gloucester Basin (Hughes, 1995, p. 424).