Coastal response to late-stage transgression and sea-level highstand Christopher J. Hein1,2,†, Duncan M. FitzGerald2, Joao Thadeu de Menezes3, William J. Cleary4, Antonio H.F. Klein5, and Marcio B. Albernaz6 1Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 2Department of Earth and Environment, Boston University, Boston, Massachusetts 02215, USA 3Laboratory of Geological Oceanography, Laboratory of Geoprocessing and Remote Sensing, UNIVALI–CTTMAR, Itajaí, SC 88302-202, Brazil 4Center for Marine Science, University of North Carolina at Wilmington, Wilmington, North Carolina 28403, USA 5Department of Geosciences, Center for Philosophy and Human Sciences, Federal University of Santa Catarina, University Campus– Trindade, Florianópolis, SC 88040-900, Brazil 6Civil Engineering and Geosciences Department, Delft University of Technology, Delft 2628CN, The Netherlands ABSTRACT exposed bedrock coasts (type A), back barrier ner and rates at which coastal zones can respond deposits (type B), transgressive barrier to this transgression and changes in the rate of Coastal morphologic features associated ridges (type C), and barrier-island complexes rSLR is therefore of crucial importance. with past shoreline transgressions and sea- (type D), according to localized conditions Examination of coastal morphologic fea- level highstands can provide insight into the of upland migration potential, wave expo- tures associated with past shoreline transgres- rates and processes associated with coastal sure, and sediment supply. These Brazilian sions can provide such insight. Unfortunately, response to the modern global rise in sea systems present a paradigm for understand- transgressions are commonly fully erosional in level. Along the eastern and southern Bra- ing future coastal response to climate change nature (Kraft, 1971), thus reducing the preser- zilian coasts of South America, 6000 years and accelerated sea-level rise: the recognition vation potential of their sedimentary sequences. of sea-level fall have preserved late-stage of a minimum threshold sea-level-rise rate of Although some examples of complete drowned transgressive and sea-level highstand features ~2 mm yr–1 above which transgression pro- barrier sequences have been identifi ed (e.g., 1–4 m above present mean sea level and sev- ceeded too rapidly for the formation of these Forbes et al., 1991; Hijma et al., 2012; Mellett eral kilome ters landward of modern shore- stable accretionary shoreline features dem- et al., 2012), most nearshore transgressive sedi- lines. GPS with real-time kinematics data, onstrates the nonlinearity of coastal response mentary sequences typically have a simple mor- ground-penetrating radar, stratigraphy, and to sea-level change, and the site specifi city of phological surface and are evidenced primarily radiocarbon dating within a 2–3-km-wide conditions associated with the formation by former lagoonal and backbarrier environ- river-associated strandplain in central Santa of each highstand deposit type, even within ments (Hoyt, 1967; Belknap and Kraft, 1985; Catarina (southern Brazil) uncovered a di- a single small embayment, demonstrates the Reinson, 1992). Thus, at least in much of the verse set of late-stage transgressive and high- non-uniformity of that response. Northern Hemisphere, many of the coastal mor- stand deposits. Here, the highstand took the phologic features associated with rapid post- forms of (1) an exposed bedrock coast in areas INTRODUCTION glacial transgression were removed by contin- of high wave energy and low sediment supply; ued rSLR during the latter half of the Holocene. (2) a 3.8-m-high transgressive barrier ridge Marine transgression is defi ned as a condi- By contrast, the complex Southern Hemi- where landward barrier migration was pro- tion in which shorelines translate in a landward sphere Holocene sea-level history has produced hibited by the presence of shallow bedrock; direction. It occurs when the rate of creation of wide-scale preservation of transgressive and sea- and (3) a complete barrier-island complex space available for potential sediment accumula- level highstand (SLH) deposits. Global eustasy containing a 5.2-m-high barrier ridge, wash- tion (accommodation space) outpaces sediment dominated late Pleistocene and Holocene rel- over deposits, a paleo-inlet, and a backbarrier supply (Curray, 1964; Bokuniewicz, 2005). In ative-sea-level changes in most regions of the lowland, formed in a protected cove with am- its most simplifi ed form, transgression gener- world not directly affected by glacial isostasy. ple sediment supply from small local streams ally results from rising relative sea level (rSL) In non-glaciated regions of the Northern Hemi- and the erosion of upland sediments. Similar and/or net local erosion (Curray, 1964). Recent sphere, sea level has generally risen since the late signatures of the mid-Holocene highstand can Holocene sea-level reconstructions (e.g., Kemp Pleistocene, rapidly at fi rst, slowing in the early be traced across all coastal Brazilian states. et al., 2011; Engelhart et al., 2011), combined and mid-Holocene, and reaching near-modern This study presents the fi rst complete com- with future projections for eustatic sea-level rise elevations around 4000 calibrated yr B.P. (4 ka). pilation of the diversity of these sedimentary (SLR; Schaeffer et al., 2012), predict that coastal However, infl uenced by inter-hemispheric redis- sequences. They are broadly classifi ed here as zones throughout the world may be on the verge tribution of water in the world’s oceans driven of transitioning to a phase of rapid marine trans- by glacio-hydroisostatic processes, sea level in †Present address: Virginia Institute of Marine Sci- ence, College of William and Mary, P.O. Box 1346, gression, driven by relative SLR (rSLR) on an the Southern Hemisphere and some equatorial Gloucester Point, Virginia 23062, USA; E-mail: order not seen since the early Holocene in most regions reached a post-glacial sea-level maxi- hein@ vims .edu. locations. A detailed understanding of the man- mum (highstand) at 5–7 ka and has since fallen GSA Bulletin; March/April 2014; v. 126; no. 3/4; p. 459–480; doi:10.1130/B30836.1; 10 fi gures; 2 tables; Published online 7 January 2014. For permission to copy, contact [email protected] 459 © 2014 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/126/3-4/459/420816/459.pdf by guest on 24 September 2021 Hein et al. 1–8 m (Isla, 1989; Roy et al., 1994; Angulo and 50° W 40° W Lessa, 1997; Angulo et al., 2006). This complex history is a consequence of global hydroisostasy Amapá ATLANTIC during the middle Holocene along previously 1 2 OCEAN glaciated continental margins forced by the col- Equator lapse of glacial forebulges and hydroisostatic loading of continental margins (Mitrovica and Milne, 2002; Milne et al., 2005). In the pres- Pará 3 4 ence of abundant sediment supplies, relative Maranhão sea-level fall (rSLF) along the Brazilian coast Piauí Ceará of South America resulted in the formation of 5 extensive strandplains (broad accumulations of Rio Grande do Norte Paraíba mainland-connected parallel or semi-parallel 6 Pernambuco 7 ridges of sand separated by shallow swales; Brazil 10° S Angulo, 1999). Deposition of these strand- Alagoas 8 plains seaward of SLH shorelines has resulted 9 in excellent preservation of SLH deposits, thus Sergipe providing an ideal location to investigate the Bahia nature of late-stage transgressive and highstand Area of 10 sedimentology. Detail Signatures of the mid-Holocene SLH can be Espirito 11 traced across all coastal Brazilian states, aban- Santo doned several meters above modern sea level, Rio de 12 Janeiro 20° S and often several kilometers landward of the São modern shoreline (Fig. 1; Table 1). These fea- Paulo 13 tures have been the subject of investigation by 14 15 researchers for decades, though generally as Paraná 16 17 ATLANTIC part of broader studies of the development of 18 entire transgressive/regressive barrier-strand- Fig. 3 inset 19 OCEAN 20 (Navegantes) plain systems in individual coastal compart- Santa 21 Catarina ments; these studies are reviewed according 23 22 Rio 24 to their geographic location by Dillenburg and Grande 25 N 30° S Hesp (2009). Although some researchers have do Sul 26 27 1000 km sought to compare Holocene coastal evolution 28 across swaths of the Brazilian coast, these stud- 50° W 40° W ies generally focus on a broader comparison of sites based on some commonality (e.g., fed by Figure 1. Locations of mid-Holocene highstand deposits identifi ed rivers [Dominguez et al., 1981, 1987] or fronted along the Brazilian coast. Numbers 1–28 indicate the locations of by strandplains [FitzGerald et al., 2007]). By mid-Holocene highstand transgressive deposits, and correspond to contrast, we focus here on the highstand fea- location identifi ers listed in Table 1. New data are presented here for tures themselves, comparing and contrasting location 20 (Navegantes), located in central Santa Catarina State in them across the entire Brazilian coastline. southern Brazil. The goals of this paper are to provide new, integrated geophysical, morphological, and sedi- mentological signatures of the multiple forms of REGIONAL VARIABILITY IN tions (Isla, 1989; Peltier, 1998; Milne et al., the mid-Holocene transgression and SLH at one SOUTHERN HEMISPHERE SEA-LEVEL 2005). Regional differences are attributed to such site