Coastal response to late-stage transgression and sea-level highstand

Abstract

Coastal morphologic features associated with past shoreline transgressions and sealevel highstands can provide insight into the rates and processes associated with coastal response to the modern global rise in sea level. Along the eastern and southern Brazilian coasts of South America, 6000 years of sea-level fall have preserved late-stage transgressive and sea-level highstand features 1-4 m above present mean sea level and several kilome ters landward of modern shorelines. GPS with real-time kinematics data, ground-penetrating radar, stratigraphy, and radiocarbon dating within a 2-3-km-wide river-associated strandplain in central Santa Catarina (southern Brazil) uncovered a diverse set of late-stage transgressive and highstand deposits. Here, the highstand took the forms of (1) an exposed bedrock coast in areas of high wave energy and low sediment supply;(2) a 3.8-m-high transgressive barrier ridge where landward barrier migration was prohibited by the presence of shallow bedrock; and (3) a complete barrier-island complex containing a 5.2-m-high barrier ridge, washover deposits, a paleo-inlet, and a backbarrier lowland, formed in a protected cove with ample sediment supply from small local streams and the erosion of upland sediments. Similar signatures of the mid-Holocene highstand can be traced across all coastal Brazilian states. This study presents the fi rst complete compilation of the diversity of these sedimentary sequences. They are broadly classifi ed here as exposed bedrock coasts (type A), back barrier deposits (type B), transgressive barrier ridges (type C), and barrier-island complexes (type D), according to localized conditions of upland migration potential, wave exposure, and sediment supply. These Brazilian systems present a paradigm for understanding future coastal response to climate change and accelerated sea-level rise: the recognition of a minimum threshold sea-level-rise rate of ~2 mm yr -1 above which transgression proceeded too rapidly for the formation of these stable accretionary shoreline features demonstrates the nonlinearity of coastal response to sea-level change, and the site specifi city of conditions associated with the formation of each highstand deposit type, even within a single small embayment, demonstrates the non-uniformity of that response.

Insight into the late Holocene sea-level changes in the NW Atlantic from a paraglacial beach-ridge plain south of Newfoundland

“…However, this change in shoreline trend and initiation of barrier progradation clearly occurred when RSL rise slowed to 1.3 mm/yr. This rate is in line with that reported by Hein et al (2014b), who investigated coastal response to RSL for Holocene highstand barrier systems in Brazil and found that, despite great regional and local variability, stabilization of the transgressive barriers occurred when RSL rise decelerated to < 2 mm/yr, while higher rates led to retrogradational barriers. Moreover, the rate of RSL rise at Saint-Pierre-etMiquelon over the period of barrier formation is similar to rates reported during the period for development of similar systems (barriers or beach ridge plains) in the northwest Atlantic.…”

Formation and evolution of back‐barrier perched lakes in rocky coasts: An example of a Holocene system in north‐west Spain

“…Differences in prevailing wind directions, sediment supply, or the sizes of bays and catchments may have contributed to differences in the evolution of these transgressive coastal systems. However, several studies performed on barrier island and non‐rocky coastal plain systems have concluded that bedrock topography plays the most significant role (Buynevich & Fitzgerald, ; Locker et al ., ; Tessier et al ., ; Cooper et al ., ; Traini et al ., ; Hein et al ., ). All of the studied systems herein have significant differences in the elevations of the pre‐Holocene bedrock over which the coastal sediments accumulated, which led to differences in the timing of flooding during the Holocene.…”

“…Niedoroda et al, 1985;Boyd et al, 1992;Roy et al, 1994;Carrasco et al, 2016). Models of post-glacial coastal systems incorporating data about the antecedent pre-Holocene topography of the bedrock and detailed Holocene stratigraphies are less common Hein et al, 2014;Fruergaard et al, 2015a,b). Among these, only a few have dealt with rocky coastal systems that included freshwater perched lakes separated from the open sea by extensive sand barriers (Devoy et al, 1996;Bao et al, 2007;Massey & Taylor, 2007;Cooper et al, 2012), but they did not investigate the parameters and mechanisms involved in their formation from a sequential stratigraphy perspective.…”

Shallow gas seismic structures: forms and distribution on Santa Catarina Island, Southern Brazil

“…More recently, the eustatic sea-level rise following the last glacial maximum resulted in a highstand approximately 5.8 ka ago, encroaching in some locations upon Pleistocene highstand barriers (HORN FILHO et al, 1997;CARUSO JR et al, 2000, DOMINGUEZ, 2009). Since then the sea level has fallen 2 to 4 m (SUGUIU et al, 1985;LESSA, 1997;ANGULO et al, 2006;HESP et al, 2009;MCBRIDE et al, 2013;HEIN et al, 2013HEIN et al, , 2014 as a consequence of global isostasy, as demonstrated by MITROVICA and MILNE (2002).…”

“…This part of the coast is characterized by the high relief of the nearby Serra do Mar range, with a series of grabens and horsts parallel to the current coastline that were created by the Tertiary collapse (58 M yr BP) of a large Cretaceous plateau (ZALÁN; OLIVEIRA, 2005), giving rise, over the course of 30 million years, to Large-scale sea-level fluctuations throughout the Quaternary resulted in the deposition of a series of transgressive barriers and regressive barrier-strandplain systems, thus straightening the bedrock-dominated shoreline (DOMINGUEZ, 2009;KLEIN et al, 2010;MCBRIDE et al, 2013;HEIN et al 2013HEIN et al , 2014. Two Quaternary barriers, dating from the Oxygen Isotopic Stage (OIS) 5e and mid-Holocene highstands (SUGUIO et al, 1985;VILLWOCK et al, 1986;MARTINS et al, 1988) have been identified on the central coast of Santa Catarina where the Serra do Mar mountain range abuts the modern coast (HORN FILHO et al, 1997;CARUSO JR et al, 2000;MCBRIDE et al, 2013;HESP et al, 2009;HEIN et al, 2013HEIN et al, , 2014.…”