The turnaround from transgression to regression of Holocene barrier systems in south‐eastern Australia: Geomorphology, geological framework and geochronology

Abstract

Holocene regressive strandplains that preserve a series of former shorelines are extensive on coasts that were remote from major Pleistocene ice sheets (for example, Australia and Brazil), whereas transgressive barrier islands are typical in glacial forebulge regions (for example, North America and Europe). In strandplains, the regressive phase of strandline development was preceded by a transgressive phase during the final stages of postglacial sea-level rise. This study examines the turnaround from transgression to regression through chronostratigraphic description of three barrier systems in southeastern Australia: Seven Mile Beach, Bengello Beach and Pedro Beach. The authors reconstruct geomorphic and depositional histories using ground-penetrating radar and vibracores along transects across the landwardmost ridges, and optically-stimulated luminescence and radiocarbon dating. At the Seven Mile Beach barrier system, extensive washover deposits are preserved that include distinctive, landward-directed, flame-shaped washover fans along the bayside shoreline of the landwardmost ridge. Landward-dipping ground-penetrating radar reflections in radargrams provide evidence of the culmination of the transgressive phase and transition into the regressive phase dominated by progradation, evidenced by the change to seaward-dipping reflections. A similar progradational plain formed at the Bengello Beach barrier system, but transgressive deposits are largely absent at the site investigated, where an 943

Morphological evolution of a complex drift‐aligned prograded barrier

“…The Holocene history of SSP probably started when the sea rose to present level about 7500 years ago and marine sediments were transported across the shelf and deposited to the shores to the east of Somers. This suggested time for initial barrier development is within the uncertainties of dated ridges in barriers located in South Australia (Oliver, Murray-Wallace, & Woodroffe, 2020) and New South Wales (McBride et al, 2020), despite the existence of barriers formed much later in Victoria (Kennedy et al, 2020) and New South Wales (Oliver, Tamura, et al, 2020). The rapid rise partially drowned the relic topography formed by the basalt reefs and bluff further back.…”

“…Adopting the age of 7500 years ago as the time in the mid‐Holocene when sea level reached present level used in recent studies of barrier evolution (e.g. McBride et al, 2020), and assuming an age of 2600 years for the innermost dated ridge, the chronology indicates that 40% of the barrier (1.44 km 2 ) was formed during this initial 4900‐year period, an average progradation rate of 0.09 m year −1 , considering a mean barrier width of 440 m. A much faster progradation of 0.2 m year −1 occurred in the past 2600 years, considering an average barrier progradation of 520 m.…”

“…Advances in remote sensing technology such as airborne LiDAR, improved our ability to determine detailed ground surface morphology underneath thick canopy of forests that cover some prograded barriers. Optically stimulated luminescence (OSL) dating of sand grains has enabled a more comprehensive understanding of formative processes and evolution of prograded barriers around the globe, including their detailed paleoenvironmental reconstruction (Costas et al, 2016; Dougherty et al, 2018; McBride et al, 2020).…”

Contrasting beach‐ridge systems in different types of coastal settings

“…Asymmetrical growth of strandplains is typically controlled by differences in the progradation rates caused. by changes in the gradient of longshore transport and related to: (1) physical barriers (bedrock) (McBride et al, 2021), (2) distance to source areas, and (3) interference of other depositional features (e.g., river mouth bar).…”

Holocene estuary infill leads to coastal barrier initiation from fluvial sand supply in southeastern Australia

“…A resurgence of coastal barrier studies in Australia, and especially utilising coastal barriers as archives of palaeoenvironmental data in the last 20 years, has been supported by advances in chronology such as Optically Stimulated Luminescence (OSL) dating and geophysics such as Ground Penetrating Radar (GPR) (Brooke et al, 2008a(Brooke et al, , 2008b(Brooke et al, , 2019Dillenburg et al, 2020;Forsyth et al, 2010Forsyth et al, , 2012Kennedy et al, 2020;Murray-Wallace et al 2002;Nott et al (2009Nott et al ( , 2015; Oliver et al (2017aOliver et al ( , 2018Oliver et al ( , 2020aOliver et al ( , 2022; Tamura et al, 2018Tamura et al, , 2019. Coastal barrier research New South Wales (NSW) coast in recent years has focused on revising the depositional history of prograded barriers and understanding sediment sources for barrier deposition (Carvalho et al, 2019;Goodwin et al, 2006;McBride et al, 2021;Oliver and Woodroffe, 2016;Oliver et al, 2015Oliver et al, , 2017bOliver et al, , 2019Oliver et al, , 2020b. New insights on beach and foredune morphodynamics and contemporary shoreline change supplementing local beach surveying efforts (Harley et al, 2017;McLean and Shen, 2006) have emerged utilising remote sensing methodologies and datasets such as airborne Lidar (Doyle et al, 2019), photogrammetry and structure from motion from drones (e.g.…”