Basin history Paleogeography

The distribution, internal sedimentary structures and thickness of sedimentary facies in the Clarence-Moreton Basin indicate that environmental changes occurred commonly during deposition across the Clarence-Moreton Basin (O’Brien and Wells, 1994). There is no fossil evidence of significant marine incursions during the latest Triassic and Jurassic (Burger, 1994a), and non-marine conditions prevailed without any significant hiatus from deposition of the Raceview Formation to the Grafton Formation. Paleocurrent measurements show that the sediments of the Bundamba Group were supplied by streams flowing northward from the highlands to the west, south and south-east of the Logan sub-basin (Ingram and Robinson, 1996), and draining the basin via the northern margin along the Esk Trough (O’Brien and Wells, 1994; Korsch et al., 1989). The climate during deposition of the Clarence-Moreton Basin strata was probably humid, as indicated by the presence of plant fragments, locally abundant thin coal and coaly mudstone as well as the absence of typical markers of arid or semi-arid floodplain deposition, such as red oxidised horizons and carbonate nodules (O’Brien and Wells, 1994).

Depositional and tectonic history

The Clarence-Moreton Basin is the youngest of a number of Mesozoic basins in the region that developed on basement rocks of the New England and Yarrol orogens (Korsch and Harrington, 1981; Johnstone et al., 1985; Day et al. 1983).

Burger (1994b) suggested that there is no evidence of basin-wide low-energy deposition during high sea level phases. Rather than complex cyclic depositional processes, Burger suggested that deposition was largely controlled by local tectonics. This theory has also been supported by other authors who indicated that major north-trending transtension-related strike-slip faults are the primary control on deposition (e.g. Korsch et al., 1989: O’Brien et al., 1994a: Ingram and Robinson, 1996). These tectonic processes, which controlled the formation of the Clarence-Moreton Basin and other Mesozoic basins in the region, are linked to large-scale tectonic processes associated with the development of the New England Orogen and the reorganisation of plates initiated in the Late Carboniferous (Korsch et al., 1989). These processes can be summarised as:

  • Cambrian to Carboniferous
    • From the Cambrian onwards, eastern Australia was an active tectonic plate margin. During the Devonian and Carboniferous, the broader region of the Clarence-Moreton Basin was characterised by a west-dipping subduction zone (Rosenbaum, 2012) and a forearc basin (Tamworth and Yarrol belts), bounded to the west by a volcanic arc and to the east by an accretionary wedge (Leitch, 1975).
  • Permian to Middle Triassic
    • Subduction ceased locally at the end of the Carboniferous, and was followed by orogenic deformation and accretion of exotic terranes during the Permian and Triassic when eastern Australia was part of an active Gondwanan convergent plate margin. Seismic reflection data indicates that during the Late Permian, basin formation beneath the Esk Trough was initiated by trans-tension along dextral strike-slip faults (O’Brien et al., 1994a). During the Early Triassic, this trans-tension shifted further eastwards to the position of the present Logan sub-basin, initiating formation of the Esk Trough through thermal relaxation (Korsch et al., 1989). Sedimentation in the various Mesozoic basins then commenced in the Early to Middle Triassic in a back arc setting (Doig and Stanmore, 2012) during an episode of strike-slip faulting associated with dextral trans-tension on the West Ipswich Fault (Korsch et al., 1981). This resulted in the deposition of up to 5000 m of sediments in the Esk Trough through thermal relaxation.
  • Late Triassic to Early Cretaceous
    • A brief compressional phase in the Middle Triassic was followed by a second tensional episode that initiated the intermontane Ipswich Basin, where deposition was restricted to the east of the north-trending West Ipswich Fault. This separated the stable basement to the west from the tectonically active region to the east (Korsch et al., 1981).
    • Initial sedimentation in the Clarence-Moreton Basin formed coal measures (Nymboida Coal Measures) during the Middle Triassic (Scheibner and Basden, 1998) in the southern part of the basin (Korsch et al., 1981). The southern extent of deposition was probably limited by the Coffs Harbour oroclinal bend (Harrington and Korsch, 1987). Following uplift, deformation and erosion during the Late Triassic, a final tensional phase initiated the deposition of the Bundamba Group in the Clarence-Moreton Basin (Korsch et al., 1981; Johnstone et al., 1985). From the Late Triassic and probably extending into the Cretaceous, a long period of thermal cooling prevailed with the associated thermal relaxation recognised as the dominant driving force for high rates of subsidence across the region. This enabled deposition of sediments in the Clarence-Moreton Basin over rift sequences and basement highs (Korsch et al., 1981; 1989; O’Brien et al., 1994a). Minor dextral strike-slip movements along the basin-forming faults produced locally enhanced subsidence or uplift (Korsch et al., 1981).
  • Mid Cretaceous to Cenozoic
    • Rifting of the east coast of Australia and formation of the Tasman and Coral sea basins began in the mid Cretaceous and continued for much of the Cenozoic (Doig and Stanmore, 2012). This rifting and sea floor spreading resulted in heating and uplift of the eastern Clarence-Moreton Basin and the end of dextral transpression, and lava-field type volcanism was associated with this extensional phase during the early Cenozoic (Cohen et al., 2013). However, most Cenozoic lavas in the Clarence-Moreton Basin are related to central volcanoes associated with hot-spot activity from the latest Eocene (~35 Ma) until the earliest Miocene (~23 Ma), forming prominent volcanic features such as the Main Range Volcanics, Mount Warning and Mount Barney in the Clarence-Moreton Basin (Figure 18) (Cohen et al., 2013). Doig and Stanmore (2012) suggested that the location of Mount Warning on the faulted margin of the Clarence-Moreton Basin indicates that extensional stressed occurred at the time of eruption and that pre-existing faults formed pathways for the injection of the volcanics magmas to form large shield volcanoes.

Erosional events

Numerous erosional events have re-shaped the thickness and distribution of sedimentary rocks in the Clarence-Moreton Basin. Russell (1994) noted that additional sediments of up to 3 km in the east and 1.5 km in the west would have been deposited throughout the basin, but were later removed by erosion. Willis (1985) estimated that about 1.5 km of eroded Cretaceous sediments are required to model the thermal maturity profiles below 1 km in the Clarence-Moreton Basin. Gleadow and O’Brien (1994) used the inflection point in apatite fission track apparent age/temperature curves for well Kyogle 1 to calculate an original overburden thickness of 2 to 3 km.

Evidence of erosional events has been reported for many of the stratigraphic units within the Clarence-Moreton Basin. Ingram and Robinson (1996) noted that the deposition of the Nymboida and Ipswich coal measures was interrupted by several mild periods of folding and erosion. Following uplift, deformation and erosion during the Late Triassic, a new cycle of deposition formed the Bundamba Group, overlying older units and separated by a regional unconformity (Stewart and Adler, 1995). Depositional gaps in the Ripley Road Sandstone sedimentation record were linked to a period of erosion/non-deposition associated with a significant eustatic sea level fall at the base of the Sinemurian (Burger, 1994a). Similarly, an originally larger extent has been inferred for the Koukandowie Formation and the Walloon Coal Measures, with both units now reduced to their current limits by uplift and erosion (Ingram and Robinson, 1996). Doig and Stanmore (2012) suggested that the restriction of the Kangaroo Creek Sandstone and Grafton Formation to the central parts of the Clarence-Moreton Basin in New South Wales is the result of widespread erosion, and that they originally extended over a wider area. The entire Cenozoic was marked by erosion, or unroofing, of the sedimentary sequences in the Clarence-Moreton Basin accompanied by widespread volcanism and deposition of alluvial sequences. Higher exhumation rates in south-eastern Queensland than in central Queensland may also explain the absence of Cretaceous successions in this part of the basin (Bryan et al., 2012; Cook et al., 2013).

Last updated:
8 January 2018
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