Sedimentary architecture and depositional controls of a Holocene wave‐dominated barrier‐island system

Abstract

Barrier‐island system evolution is controlled by internal and external forcing mechanisms, and temporal changes in these mechanisms may be recorded in the sedimentary architecture. However, the precise role of individual forcing mechanisms is rarely well understood due to limited chronological control. This study investigates the relative role of forcing conditions, such as antecedent topography, sea‐level rise, sediment supply, storms and climate changes, on the evolution of a Holocene wave‐dominated barrier‐island system. This article presents temporal reconstruction of the depositional history of the barrier‐island system of Rømø in the Wadden Sea in unprecedented detail, based on ground‐penetrating radar profiles, sediment cores, high‐resolution dating and palynological investigations, and shows that ca 8000 years ago the barrier island formed on a Pleistocene topographic high. During the initial phase of barrier evolution, the long‐term sea‐level rise was relatively rapid (ca 9 mm year−1) and the barrier was narrow and frequently overwashed. Sediment supply kept pace with sea‐level rise, and the barrier‐island system mainly aggraded through the deposition of a ca 7 m thick stack of overwash fans. Aggradation continued for ca 1700 years until sea‐level rise had decreased to <2 mm year−1. In the last ca 6000 years, the barrier prograded 4 to 5 km through deposition of a 10 to 15 m thick beach and shoreface unit, despite a long‐term sea‐level rise of 1 to 2 mm year−1. The long‐term progradation was, however, interrupted by a transgression between 4000 years and 1700 years ago. These results demonstrate that the large‐scale morphology of the Danish Wadden Sea shoreline influences the longshore sediment transport flux and the millennial‐scale dispersal of sediment along the shoreline. On decadal to centennial timescales, major storms induced intense beach and shoreface erosion followed by rapid recovery and progradation which resulted in a highly punctuated beach and shoreface record. Major storms contributed towards a positive sediment budget, and the sustained surplus of sediment was, and still is, instrumental in maintaining the aggradational–progradational state of the barrier island.

Depositional controls on a hypertidal barrier‐spit system architecture and evolution, Pointe du Banc spit, north‐western France

“…Hence, changes in controlling mechanisms of sediment supply can have largescale implications for coastal evolution (e.g. Hampson & Storms, 2003;Fruergaard et al, 2018;Raff et al, 2018). Given the fact that the depositional mode of the PDB spit system changed from transgression to regression ca 1000 years ago during a period of constant RSL rise (Lambeck, 1997;Goslin et al, 2015), sediment supply to the coast must have increased, resulting in a positive sediment budget.…”

“…Understanding barrier spit formation and evolution is increasingly important in order to assess how these soft-sediment coastal systems will respond and adapt to expected future changes in storm intensity and sea level (von Storch & Woth, 2008;Seneviratne et al, 2012;Church et al, 2013;Grinsted et al, 2013). The evolution of barrier spits is the result of complex interactions between wave and tide dynamics (Evans, 1942;Hine, 1979;Allard et al, 2008;Lindhorst et al, 2008;Dalrymple et al, 2012;Poirier et al, 2017), fluctuations in sea level (Kraft, 1971;Colman & Mixon, 1988;Van Heteren & Van De Plassche, 1997;Fruergaard et al, 2015a;Sander et al, 2016), the impact of storms (Sexton & Hayes, 1991;Morton & Sallenger, 2003;Dougherty et al, 2004;Fruergaard et al, 2013;, sediment supply (Aagaard et al, 2004a;Timmons et al, 2010;Fruergaard et al, 2015b;Oliver et al, 2017;Fruergaard et al, 2018), and geological and morphological inheritance (Belknap & Kraft, 1985;Riggs et al, 1995;Dillenburg et al, 2000;Cooper et al, 2012;Sander et al, 2015;Cooper et al, 2018). To predict barrier spit evolution, it is a prerequisite to have detailed knowledge about their geomorphology, sedimentary architecture and depositional history.…”

Mapping the Shoreface of Coastal Sediment Compartments to Improve Shoreline Change Forecasts in New South Wales, Australia

“…However, inherited morphodynamic processes may also oppose such losses. The shoreface provides a steady long-term sand supply to beaches via wave action in some settings (Cowell et al 2003b;Schwab et al 2013;Kinsela et al 2016), for example, which might counter shoreline retreat for slow rates of sea level rise or even maintain shoreline progradation where the rate of supply exceeds the effect of sea level rise (Fruergaard et al 2018).…”

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

“…This transition was revisited in a recent study of another barrier system in southern Brazil (Lima & Parise, 2020). Other studies of the transition from transgressive to regressive Holocene coastal deposits investigated the Dutch North Sea coast (Hijma & Cohen, 2011), the Danish Wadden Sea coast (Fruergaard et al, 2018) and the Virginia barrier islands along the US Atlantic coast (Raff et al, 2018).…”