Geological legacy of storm erosion along a high-energy indented coastline: northern Santa Catarina, Brazil

TitleGeological legacy of storm erosion along a high-energy indented coastline: northern Santa Catarina, Brazil
Publication TypeJournal Article
Year of Publication2011
AuthorsBuynevich, IV, Klein, AHF, FitzGerald, DM, Cleary, WJ, Hein, C, Veiga, FA, Angulo, RJ, Asp, NE, Petermann, R
JournalJournal of Coastal Research
IssueSI 64

Along moderate to high-energy sandy coasts of the world, periods of accretion are often punctuated by episodes of erosion and retreat. However documenting the legacy of such events in sand-dominated sequences remains a challenge. The present-day moderate-relief coastlines of Camboriú Peninsula (CP) and the adjacent Navegantes coastal plain in Santa Catarina, Brazil, exhibit a variety of geological features related to recent intense storms, such as the Santa Catarina cyclone of record (March 2004) and subsequent events. These systems offer an opportunity to assess the use of modern indicators of storm erosion as a guide to reconstructing their counterparts from the sedimentary record. The 0.5-2.0-km-long, headland-segmented, coarse-grained, reflective beaches of the Camboriú Peninsula contrast with a 10-km-long, fine-grained, dissipative beach of the Navegantes plain. Morphological indicators of erosion include steep dune and berm scarps, as well as ephemeral washout channels produced by rainfall-induced runoff. Where modified by subsequent deposition, these features can still be identified by their diagnostic reflection geometries and variable-angle truncations (disconformities) in highresolution ground-penetrating radar (GPR) images. In addition to morphological indicators of erosion, coastal sedimentary sequences contain distinct lithological anomalies. Heavy-mineral concentrations (HMCs) are easily identifiable in sediment cores and trenches and produce strong reflections on GPR images. Along Estaleiro Beach (CP), a buried disconformity was identified in GPR images beneath a road, approximately 25 m landward of the November 2004 storm scarp. Its geometry is similar to the recent scarp and its strong geophysical signal return is due to a magnetite-enriched horizon at a depth of 2.6 m. At the Navegantes strandplain, patchy thin layers enriched in fine-grained heavy minerals are common on a gently sloping intertidal beach and near the base of foredunes. Moreover, in the landward portion of the plain that developed during the past 2,000 years, the presence of truncated tangential-oblique reflections in GPR records and HMCs reaching 10-30 cm in thickness indicates past reworking of beach and dune sediments by a series of intense erosional episodes. Low-field magnetic susceptibility measurements of vibracores indicate values from thick HMC layers exceeding 1,000 (*10-5 SI) in contrast to 0−15 (*10-5 SI) for background quartz-rich sands. Given the relatively constant background fraction of heavy minerals in beach sands, the thickness and degree of concentration in HMCs can be used as proxies for the relative impact of high-energy events, including their duration and magnitude. Despite the apparent low preservation potential of these features on high-energy coasts, post-storm accretion and rapid progradation increase their chances of being removed from wave action.