East Australian marine abrasion surface

Abstract

Almost one-third of the seabed off the coastline north and south of Sydney comprises a planated bedrock surface, evident from sidescan surveys over the inner continental shelf. In seismic records, this rock surface extends up to 23 km offshore from the sea cliffs along 300 km of the coast. The rock surface dips offshore to as much as 180 m below sea level, where it merges with a major unconformity in the shelf sediment wedge. The surface is eroded into Mesozoic and Palaeozic rocks and is heavily dissected by sediment-filled, palaeo-valley incision and structural jointing. The sediment-fills comprise sand wedges that thicken landwards to form beaches and estuarine flood-tide deltas, respectively, in smaller and larger palaeo-valleys incised to below present sea level. At the base of the cliffs, the planated surface is buried by shelf sand bodies up to 30 m thick in places. The seaward edge of the surface is everywhere buried by the onlapping continental-shelf sediment wedge. The contiguity of the abrasion surface with the unconformity in the shelf sediment wedge suggests that marine planation began in the Mid-Oligocene, indicating time-average rates of gross cliff retreat at about 1 mm a−1.

Second-Pass Assessment of Potential Exposure to Shoreline Change in New South Wales, Australia, Using a Sediment Compartments Framework

“…Representative secondary sediment compartments [33,34] Sediment cover across the inner shelf is relatively thin, except where relict coastal barriers and shelf sand bodies accumulated during lower sea levels, prior to erosional reworking during the late Holocene post-glacial marine transgression and subsequent sea-level highstand [45,46]. A marine abrasion surface extends along 300 km of the central to southern coast, frequently outcropping across the submerged inner-shelf seabed [46]. The abrasion surface is related to the prominent coastal escarpment that is evident on steeper sectors of the coast, and is thought to have formed by cyclic erosion and planation of the Palaeozoic to Mesozoic bedrock by coastal processes, as the shoreline migrated in and out across the margin during late Quaternary sea level fluctuations [46].…”

“…The small red dots indicate identified erosion hot spots [44]. Representative secondary sediment compartments [33,34] Sediment cover across the inner shelf is relatively thin, except where relict coastal barriers and shelf sand bodies accumulated during lower sea levels, prior to erosional reworking during the late Holocene post-glacial marine transgression and subsequent sea-level highstand [45,46]. A marine abrasion surface extends along 300 km of the central to southern coast, frequently outcropping across the submerged inner-shelf seabed [46].…”

“…A marine abrasion surface extends along 300 km of the central to southern coast, frequently outcropping across the submerged inner-shelf seabed [46]. The abrasion surface is related to the prominent coastal escarpment that is evident on steeper sectors of the coast, and is thought to have formed by cyclic erosion and planation of the Palaeozoic to Mesozoic bedrock by coastal processes, as the shoreline migrated in and out across the margin during late Quaternary sea level fluctuations [46]. The extent of the marine abrasion surface captured in detailed seabed mapping off the Sydney coastline [47] suggests that many central and southern compartments may be sediment deficient offshore.…”

Automated Sensing of Wave Inundation across a Rocky Shore Platform Using a Low-Cost Camera System

“…The seabed substrate is sandy, with sedimentological properties consistent with an inner-shelf sand body (Figure 1b) that was mapped and sampled to the north along this coastal sector [19]. The escarpment, cliffs, and rock platform form part of the East Australian marine abrasion surface formed of Mesozoic-Paleozoic sedimentary rocks cut and planed by cyclic marine erosion that extends 300 km along the coast north and south of Sydney, and up to 23 km offshore beneath the shelf sediments [20].…”

A preliminary OSL chronology for coastal dunes on Moreton island, Queensland, Australia – Marginal deposits of A large-scale quaternary shelf sediment system

“…It seems unlikely that sand on the coast and nearshore of southern NSW is transported northwards (Fig. 5) during highstands due to the interruption of longshore transport by bedrock headlands and rock reefs that extend offshore from many areas of rocky coast (Roy and Thom, 1981;Sloss et al, 2007;Jordan et al, 2010;Thom et al, 2010). However, during periods of intermediate sea levels, up to a few tens of metres below interglacial highstands but well above glacial lowstands (e.g.…”