The planform of epeirogeny: vertical motions of Australia during the Cretaceous

Estimates of dynamic motion of Australia since the end of the Jurassic have been made by modeling marine flooding and comparing it with palaeogeographical reconstructions of marine inundation. First, sediment isopachs were back stripped from present-day topography. Dynamic motion was determined by the displacement needed to approximate observed flooding when allowance is made for changes in eustatic sea-level. The reconstructed inundation patterns suggest that during the Cretaceous, Australia remained a relatively stable platform, and flooding in the eastern interior during the Early Cretaceous was primarily the result of the regional tectonic motion. Vertical motion during the Cretaceous was much smaller than the movement since the end of the Cretaceous. Subsidence and marine flooding in the Eromanga and Surat Basins, and the subsequent 500 m of uplift of the eastern portion of the basin, may have been driven by changes in plate dynamics during the Mesozoic. Convergence along the north-east edge of Australia between 200 and 100 Ma coincides with platform sedimentation and subsidence within the Eromanga and Surat Basins. A major shift in the position of subduction at 140 Ma was coeval with the marine incursion into the Eromanga. When subduction ended at 95 Ma, marine inundation of the Eromanga also ended. Subsidence and uplift of the eastern interior is consistent with dynamic models of subduction in which subsidence is generated when the dip angle of the slab decreases and uplift is generated when subduction terminates (i.e. the dynamic load vanishes). Since the end of the Cretaceous, Australia has uniformly subsided by about 250 m with little apparent tilting. This vertical subsidence may have resulted from the northward migration of the continent from a dynamic topography high and geoid low toward lower dynamic topography and a higher geoid.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71983/1/j.1365-2117.1994.tb00076.x.pd

Quaternary development of resilient reefs on the subsiding kimberley continental margin, Northwest Australia

The Kimberley region in remote northwest Australia has poorly known reef systems of two types; coastal fringing reefs and atoll-like shelf-edge reefs. As a major geomorphic feature (from 12ºS to 18ºS) situated along a subsiding continental margin, the shelf edge reefs are in a tropical realm with warm temperatures, relatively low salinity, clear low nutrient waters lacking sediment input, and Indo-West Pacific corals of moderate diversity. Seismic architecture of the Rowley Shoals reveals that differential pre-Holocene subsidence and relative elevation of the pre-Holocene substrate have controlled lagoon sediment infill and reef morphology, forming an evolutionary series reflecting differential accommodation in three otherwise similar reef systems.The Holocene core described for North Scott Reef confirms previous seismic interpretations, and provides a rare ocean-facing reef record. It demonstrates that the Indo-Pacific reef growth phase (RG111) developed during moderate rates of sea level rise of 10 mm/year from 11 to about 7-6.5 ka BP until sea level stabilization, filling the available 27 m of pre-Holocene accommodation. Despite the medium to high hydrodynamic energy imposed by the 4m tides, swell waves and cyclones the reef-building communities represent relatively low-wave energy settings due to their southeast facing and protection afforded by the proximity of the South Reef platform. This study demonstrates the resilience of reefs on the subsiding margin whilst linking Holocene reef morphology to the relative amount of pre-Holocene subsidence