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3.2.9 Hydrogeology
The groundwater hydrogeology of the Oriners/Sefton area of the Holroyd Plain has not been
studied in detail, with limited data to draw any inferences from in terms of groundwater
recharge or discharge, surface connectivity, and wetland, spring, and stream maintenance.
There is a review of the groundwater hydrogeology and aquifers of the Cape York Peninsula
(Horn, Derrington et al. 1995), but there few data directly applicable to the Oriners area.
Previous research (Commonwealth Scientific and Industrial Research Organization (CSIRO)
2009) also reviews the hydrogeology of the Mitchell catchment and provides some
preliminary modelling analysis, but again the level of detail applicable to Oriners is limited.
Most of the groundwater information for the Oriners region is derived from earlier geological
investigations, limited bore hole data, and preliminary field reconnaissance, which will be
reviewed below.
The geologic structure of the sedimentary beds underlying the Holroyd Plain is dominated by
the Tertiary Wyaaba Beds and the Bulimba Formation, which are in turn underlain by the
deeper Wallumbilla Formation, which are all part of the Karumba Basin and Aquifer (Gibson,
Powell et al. 1973; Grimes and Doutch 1978; Grimes 1979)- see section 3.2.3. The units are
covered by layers of Quaternary Alluvium along major creek and river valleys, which contains
shallow groundwater aquifers well connected to stream channels. Beneath the Tertiary
Karumba Basin is the Mesozoic Carpentaria Basin, which is the northern equivalent of the
Great Artesian Basin (Smart, Grimes et al. 1980a)(Smart et al., 1980a). A sandstone aquifer
(the Gilbert River Formation) occurs at the base of the sequence, and is overlain by marine
mudstones (Rolling Downs Group), which confines the groundwater within the sandstone
and produce artesian pressure.
The structure and stratigraphy of the Karumba Basin below Oriners were analysed by limited
bore holes across the Holroyd Plain. Aquifer pump tests were not performed on these bore
holes to determine water availability. However at a 165m deep bore hole 7 km west of
Oriners through the Bulimba Formation into the Wallumbilla, Gibson et al. (1973) observed
artesian water (under pressure) rising up to the surface, but not flowing out of the bore hole
after drilling. At water bore holes into the Bulimba Formation at Dunbar, Rutland Plains, the
Palmer/Mitchell Rivers confluence, and later Kowanyama, artesian water has been found at
100 to 200m depth flowing at 40,000 to > 135,000 litres per hour (Grimes 1972) .
Undoubtedly there are conductive lenses for water movement in the sedimentary rock within
these formations, with at least some of the water under artesian pressure. The past and
current recharge and discharge locations for these aquifers are unknown, as is the water
residence times (age). However, where these units outcrop onto the landscape surface, or
are interrupted by faults, groundwater could emerge onto the surface as springs or as
gaining water to creeks, rivers, or lagoons. Oriners Station and homestead area is situated
on the transition between the Bulimba Formation and Wyaaba Beds on the surface, and
could be an important area for the recharge of these aquifers. However this does not,
discount the local potential for additional groundwater discharge outflow into springs or creek
systems at contact zones.
The small oval wetlands (pans) that are abundant on interfluves of the Balurga land system
of the Holroyd Plain (Figure 51; Figure 52) offer some clues toward the connectivity between
surface water and groundwater systems. Doutch (1976) originally hypothesized that these
shallow wetlands or pans were from wind deflation that eroded surface sediment locally
during the drier Pleistocene. However, Grimes (1979) in contrast hypothesized that these
features were good examples of lateritic karst or pseudokarst in non-carbonate materials
(Grimes 1975; Grimes 1997; Grimes and Spate 2008). The interfluve ridgelines of the
Holroyd Plain can be indurated and cemented by ferricrete (iron oxide) and silcrete (silica
oxide), occasionally forming a hard cap duricrust on the surface. More often the interfluve
ridgelines are dominated by sandy soils (deeply weathered sandstone), possibly with
indurated ferricrete at depth or just exposed at outcrops at erosional scarps. Where these
indurated layers are thin and weak they can subside into sinkholes (pseudokarst), especially
if under pressure from groundwater below or where groundwater flow erodes sediment and
Working Knowledge at Oriners Station, Cape York
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