The Clarence-Moreton Basin is the youngest of a series of Mesozoic basins in south-east Queensland and north-east New South Wales, and is genetically linked to:
- Esk Trough
- The Esk Trough contains sedimentary rocks of Middle Triassic age, which may be possible correlatives of the Nymboida Coal Measures (Ingram and Robinson, 1996). The Esk Trough is not a pure pull-apart basin associated with either two parallel strike-slip faults or a major bend in a single strike-slip fault (Korsch et al., 1989). An unconformity between the Esk Trough and the Clarence-Moreton Basin sedimentary succession represents a break of about 12 million years during which time sediments and volcanics of the Ipswich Basin were deposited further to the east (Korsch et al., 1989). Sedimentary rocks in the Esk Trough wedge-out against the Gatton Arch, and the Clarence-Moreton Basin directly overlies the Esk Trough in this vicinity.
- Ipswich Basin
- the Ipswich Basin is a partly fault-bounded, asymmetric intermontaine basin in south-east Queensland and north-east New South Wales (Chern, 2004). It is interpreted to have formed during a second phase of extension associated with strike-slip faulting.
- Nambour Basin
- The Late Triassic to Early Jurassic Nambour Basin is a small basin north-east of the Clarence-Moreton Basin in south-east Queensland. It includes the Landsborough Sandstone, which overlies the Paleozoic basement and the Middle Triassic rocks of the Ipswich Basin.
- Surat Basin
- The Surat Basin is separated from the Clarence-Moreton Basin at its north-western boundary by the sub-surface pre-Jurassic Kumbarilla Ridge (Johnstone et al., 1985). Sedimentation was continuous from the Lower Jurassic across this ridge, but all units thin significantly across the ridge, and only four stratigraphic units (Woogaroo Subgroup/Precipice Sandstone, Gatton Sandstone/Evergreen Formation, Koukandowie Formation/Hutton Sandstone and Walloon Coal Measures) are common to both the Surat and Clarence-Moreton basins. The Helidon Ridge (Figure 17), a basement ridge running south-west from Helidon is considered to be the groundwater-divide and thus the eastern margin of the Great Artesian Basin in this area (Smerdon and Ransley, 2012).
There is currently a very limited understanding of the hydraulic connectivity between the basal Clarence-Moreton Basin aquifers and the basement rock aquifers. Faults are abundant and fractures are common features throughout the Clarence-Moreton Basin. However, most rocks that form the basement to the Clarence-Moreton Basin sedimentary sequences are part of the New England Orogen, which is dominated by granitic plutons, igneous complexes or metasedimentary rocks. These rock types are commonly considered low-yielding aquifers; however, there are currently insufficient data to determine the degree of hydraulic connectivity between Clarence-Moreton Basin sequences and the underlying basement rocks.
Paleogene and Neogene
Paleogene and Neogene volcanoes and fissure eruptions were widespread throughout the Clarence-Moreton Basin. These features were associated with rifting of the east coast of Australia which began during the Early Cretaceous (Bryan et al., 2012).
Prominent central volcanoes within the Clarence-Moreton Basin include the: Main Range Volcanics, Mount Warning, Focal Point, Tweed and Mount Barney igneous complexes, Lamington Volcanics and Alstonville Plateau (Figure 19). These large igneous complexes in south-east Queensland and north-eastern New South Wales are associated with large-scale volcanic migratory ‘swell and pinch’ volcanic chains developed over intraplate plumes (Sutherland, 2003; Cohen et al., 2013). Two major eruptive centres occur in south-east Queensland (the Tweed and Focal Peak shield volcanoes) in addition to many smaller vents and fissures that have been identified to the north and north-west where lavas and sills of the Main Range Volcanics form the crest of the Great Dividing Range (Donchak et al., 2007). The Main Range Volcanics consist of massive, fine-grained olivine basalt, occurring mainly as flows with minor mudstone and fine-grained sandstone locally interbedded with the flows. The lavas of the Main Range Volcanics are typically less than about 200 m (DNRM, 2013, pers. comm.). However, locally near Toowoomba (Figure 19), they reach thicknesses of approximately 250 m and maximum thicknesses of up to 900 m have been reported from the Southern Main Range near prominent central volcanoes (Cohen et al., 2013). These rocks unconformably overlie the Marburg Subgroup and Walloon Coal Measures and are dated as Late Eocene to earliest Miocene (Cohen et al., 2013). The Alstonville Plateau consists of a sequence of Miocene basaltic flows, interbedded with weathering horizons and sediments (Brodie, 2007; Santos and Eyre, 2011). The flows of the Alstonville Plateau are the southern extent of the Lamington Volcanics (Figure 19), which are associated with the Tweed Shield Volcano which erupted between 23 and 20 Ma (Brodie, 2007).
Alluvial sediments: Extensive alluvial sequences have variably infilled river basins in the Clarence-Moreton Basin in Queensland and New South Wales. The thickness of alluvial sediments typically increases downstream from the headwaters to lower parts of the river basins, associated with the change from v-shaped to broader u-shaped valleys. For example, in the Lockyer Valley (Queensland), the maximum thickness of alluvial sequences is approximately 30 to 35 m, with a distinct fining upwards sequence of gravels and coarse sands at the base, and fine-grained floodplain sediments at the top. In the Bremer river basin and Warrill Creek basin, as well as in the Logan river basin, the alluvial sediment thickness is about 20 to 25 m. Similarly, the thickness of alluvial sediments in the Richmond river basin varies, to a maximum of 25 m. Only limited drillhole control exists in the Clarence river basin, hence the thickness of the alluvial sediments is poorly constrained. The headwaters of the Queensland alluvial systems and the Richmond River alluvial system are deeply incised into the Cenozoic Volcanics. As a result, the composition of alluvial sequences is dominantly volcanic-derived, forming the characteristic black soils of these regions. In contrast, the headwaters of the Clarence river basin are formed by rocks of the New England Orogen, which are dominated by plutonic and metasedimentary rocks, resulting in different alluvial sediment compositions in this river basin.
Quaternary coastal sediments and acid sulfate soils: the floodplains in the eastern Richmond river basin, Clarence river basin and Tweed river basin form large back barrier lagoons infilled with Quaternary sediments. These Quaternary coastal or estuarine sediments are dominated by permeable marine sand and impermeable estuarine clay, which are commonly pyritic and can develop into coastal acid sulfate soils if disturbed (Santos and Eyre, 2011).
Potential connectivity and pathways to the surface
Geological structures, particularly faults, can significantly influence vertical connectivity between aquifers. Depending on the characteristics of the fault zone and the aquifers, faults can form either barriers or conduits to groundwater flow, or they can compartmentalise regional groundwater flow systems by juxtaposing rocks of contrasting hydraulic properties. In the Clarence-Moreton Basin, particularly the Logan sub-basin, significant fault off-sets have been inferred based on seismic data (Figure 20). Such fault displacements occur commonly in the Clarence-Moreton Basin and juxtapose rock units with contrasting hydraulic properties. Many faults may also extend to the surface and potentially form preferential pathways linking deeper and shallower aquifers (Figure 20).
a. The location of this cross-section is shown in Figure 17.
Source:is figure is not covered by a Creative Commons Attribution licence. It has been reproduced with permission from NSW Trade and Investment.
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- 1.1.1 Bioregion
- 1.1.2 Geography
- 1.1.3 Geology
- 1.1.4 Hydrogeology and groundwater quality
- 1.1.5 Surface water hydrology and surface water quality
- 1.1.6 Surface water – groundwater interactions
- 1.1.7 Ecology
- Contributors to the Technical Programme
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