Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
1840
1844
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Geological Legacy of Storm Erosion along a High-Energy
Indented Coastline: Northern Santa Catarina, Brazil
Ilya V. Buynevich†, Antonio H.F. Klein‡, Duncan M. FitzGerald∞,
William J. Cleary§, Christopher Hein∞, Fernando A. Veiga††,
Rodolfo J. Angulo††, Nils E. Asp§§ and Rafael M. Petermann‡
†
Department of Earth and
Environmental Science
Temple University
Philadelphia, PA 19122, U.S.A.
coast@temple.edu
§
Center for Marine Science
University of North Carolina
Wilmington, NC 28409, U.S.A.
wcleary@charter.net
‡
Department of Earth Sciences
Boston University
Boston, MA 02215, U.S.A.
dunc@bu.edu
hein@bu.edu
††
§§
LAGECO/IECOS
Universidade Federal do Pará
Bragança, PA 68600-000, Brazil
nilsasp@ufpa.br
Departamento de Geociências
Centro de Filosofia e Ciências Humanas
Universidade Federal de Santa Catarina
Florianopolis, SC 88040-970, Brazil
klein@cfh.ufsc.br
LECOST
Universidade Federal do Paraná
Curitiba, PR 81531-970, Brazil
angulo@ufpr.br
∞
ABSTRACT
Buynevich, I.V., Klein, H.F., FitzGerald, D.M., Cleary, W.J., Hein, C., Veiga, F., Angulo, R.J., Asp, N.E., and
Petermann, R.M., 2011. Geological legacy of storm erosion along a high-energy indented coastline: northern
Santa Catarina, Brazil. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal
Symposium), – . Szczecin, Poland, ISSN 0749-0208.
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.
ADDITIONAL INDEX WORDS: Cyclones, Strandplain, Scarp, Heavy Minerals, Ground-Penetrating Radar
INTRODUCTION
Due to limited historical records of extreme events along sandy
coasts (intense storms, floods, and tsunamis), particularly in the
Southern Hemisphere, scientists and coastal managers must rely
on geological records to reconstruct their impact and timing. By
employing a combination of morphological, mineralogical, and
geophysical methods, a number of studies have addressed this
issue in different parts of the world dominated by wide sanddominated barriers and coastal plains (Rao, 1957; Woolsey et al.,
1975; Smith and Jackson, 1990; Meyers et al., 1996; Buynevich et
al., 2004; Dougherty et al., 2004; Moore et al., 2004; Buynevich
Journal of Coastal Research, Special Issue 64, 2011
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Geological Legacy of Storm Erosion, northern Santa Catarina, Brazil
and Donnelly, 2006; Buynevich et al., 2007; Nair et al., 2010).
However, in many instances paleo-indicators of erosion do not
have observable analogs, often due to relatively calm conditions
prevailing during the geological investigations. High-energy
mainland beaches and strandplains of Santa Catarina state,
southern Brazil (Fig. 1), present an ideal opportunity to compare
the recent impact of intense storms with the sedimentary record of
past events. The aim of this paper is: 1) to summarize the
morphological features related to most recent oceanographic
events (2004-2006 period) along Camboriú Peninsula beaches and
the Navegantes coastal plain, and 2) to describe examples of past
erosional indicators preserved within Late Holocene portions of
these coastal accumulation forms.
PHYSICAL SETTING
Fig. 3
Navegantes Coastal Plain
5 km
Brazil
Santa Catarina
Atlantic
Ocean
Balneário
Camboriú
Santa
Catarina
27ºN
portions of CP beaches and Navegantes strandplain. We used a
digital Geophysical Survey Systems Inc. SIR-2000 GPR system
with a 200 MHz monostatic antenna (for technical aspects of GPR
and its use in coastal settings, see van Heteren et al., 1998; Jol and
Bristow, 2003; Buynevich et al., 2009). GPR images were postprocessed using RADAN 5.0 software. No topographic correction
was applied to sections of profiles that had less than 0.3 m
variation in elevation. Geophysical data were groundtruthed using
shallow trenches (0.3-1.0 m), hand augers, and vibracores. Grain
size, sorting, organic content, and bulk mineralogy of surficial and
subsurface
samples
were
analyzed
using
standard
sedimentological techniques, focusing on heavy-mineral content
(especially magnetite). Low-filed magnetic susceptibility (MS)
was used to quantify the relative proportion of heavy minerals,
which include both ferrimagnetic (primarily magnetite) and
paramagnetic minerals (Shankar et al., 1996). Measurements were
obtained on vibracore sub-samples using Bartington MS2 meter
with a high-resolution MS2E surface scanning sensor. To establish
the overall chronological framework of coastal progradation, basal
peat samples from ridge swales at the Navegantes site were dated
using AMS technique at the National Ocean Sciences Accelerator
Mass Spectrometry facility (NOSAMS) at the Woods Hole
Oceanographic Institution.
RESULTS
Camboriú Peninsula Beaches
Camboriú Peninsula (CP) Beaches
Fig. 2
Figure 1. Location of study sites along the northern coast of Santa
Catarina state, Brazil: small pocket beaches along the indented
Camboriú Peninsula (CP) and the adjacent Navegantes
strandplain.
The high-energy coastline of southernmost Brazil experiences
occasional cyclones (Barletta and Calliari, 2003), including the
record Santa Catarina storm of March 2004. The moderate-relief
coast of Camboriú Peninsula, northern Santa Catarina, is
characterizedby a series of 0.5-2.0-km-long, headland-segmented,
coarse-grained, reflective beaches (Klein and Menezes, 2001;
Figs. 1 and 2A). In contrast to the CP setting, the Navegantes
coastal plain is a 10-km-long, 1-5-km-wide prograded strandplain
fronted by a fine-grained, dissipative beach (Fig. 1). Similar to
coastal plains to the south (Pinheira and Tijucas), the Navegantes
beach/dune ridge system has experienced progradation during the
Late Holocene (past 2,000-3,000 years), due to an abundant
sediment supply from the Itajaí River and relative sea-level fall
(Buynevich et al. 2005; FitzGerald et al., 2007; Angulo et al.,
2009; Barboza et al., 2009; Hesp et al., 2009). It is this regime of
rapid net accretion (punctuated coastal progradation) that allows
for the preservation of geological indicators of past erosional
episodes.
METHODS
Field observations and measurements of recent erosional
indicators were conducted during March 2004 (just prior to Santa
Catarina Cyclone), November 2004, and March 2006.
Morphological analysis was complemented by high-resolution
ground-penetrating radar (GPR) images of the older (landward)
The most distinct morphological features of beach and dune
erosion are steep dune and berm scarps displaying diagnostic
profiles of variable alongshore continuity (Fig. 2A; Woolsey et al.,
1975; Buynevich et al., 2004). During field observations at
Estaleiro and Estalerinho Beaches, the scarps and low-gradient
beach surfaces were covered by heavy-mineral concentrations
(HMCs). It is this combination of morphological and lithological
attributes that accentuates event horizons in subsurface records.
As shown in Figure 2B, a distinct tangential-oblique near-surface
disconformity truncates the older (landward) seaward-dipping
reflections in a GPR transect across Estaleiro Beach. This feature
coincided with a 15-cm-thick magnetite-rich HMC at 2.6 m depth
in a sediment core (Fig. 2B). In addition to shore-parallel features,
shore-normal surge channels may result from storms and
tsunamis, however their identification is possible only in shoreparallel trenches or geophysical records (Buynevich and Donnelly,
2006). Several weeks prior to the Santa Catarina Cyclone, a
massive rainstorm, combined with high wave energy, produced a
number of shore-perpendicular surge channels. These features
differed from small perennial inlets along the bedrock-framed
extremities of pocked beaches in their larger number and size.
However, they are similar to washouts observed in the
neighboring state of Rio Grande do Sul (Calliari et al., 1998;
Pereira et al., 2003).
Navegantes Strandplain
Several linear kilometers of GPR profiles were collected along
the Navegantes plain, from the Itajaí River in the south to the
headlands in the north. This study focuses on the main geological
transect in the northern portion of the strandplain (Fig. 3A), but
the data are supported by geophysical profiles and excavations in
other parts of the study site. A series of shore-normal GPR
transects reveal offlapping sigmoidal to tangential-oblique
clinoforms, with at least seven distinct truncations (Fig. 3B). Hand
Journal of Coastal Research, Special Issue 64, 2011
1841
Buynevich et al.
augers and vibracores along the main GPR profiles recovered 1030-cm-thick HMCs, which coincide with sharp disconformities.
These horizons are enriched in magnetite (>20% by volume),
which occurs primarily in the finer fraction of the well-sorted,
fine-grained sands (mean grain size: 0.16-0.20 mm). Magnetic
susceptibility measurements on both the background quartzose
sands and HMCs show a dramatic difference in values, ranging
from 0-20 to 900-3,200 (*10-5 SI units), respectively (Fig. 3C).
The variations in MS values are most likely attributed to
differences in the concentration factor (cf. Komar, 1989) within
each HMC. Based on radiocarbon-dated basal peats from interridge swales, the indicators described above were formed during
the time interval of 950-1880 cal years BP.
DISCUSSION
In contrast to HMC formation through long-term, sea-levelmodulated supply and reworking (e.g., examples of extensive
dune placers in Rio Grande do Sul; Dillenburg et al., 2004), the
present examples represent specific episodes of erosion during
high-energy events (Smith and Jackson, 1990; Hamilton and
Collins, 1998; Buynevich et al., 2004; Dougherty et al., 2004;
Moore et al., 2004; Buynevich et al., 2007). The formation of
enriched horizons typically occurs during the waning stages of
high wave-energy events and is a product of selective sorting by
waves and wind (Rao, 1957; Woolsey et al., 1975; Komar and
Wang, 1984; Komar, 1989). HMCs typically occur at the base of
foredunes and along the flattened lower beach, thereby adding a
distinct morphological component to the erosional indicator and
aiding in its recognition in GPR images (Figs 2 and 3; Meyers et
al., 1996; Dougherty et al., 2004; Moore et al., 2004; Buynevich,
2005; Buynevich et al., 2007). The Navegantes system of
prograding clinoforms contains a series of erosional truncations,
which are characterized by high magnetite content and
correspondingly high magnetic susceptibility values. These
disconformities are interpreted as erosional paleo-beach/dune-base
surfaces, likely formed by intense storms during the past 2,000
years. Similar features have been recently described along the
adjacent prograded Holocene barrier systems of Paraná (Angulo
et al., 2009). Quantitative analysis of sediment textures and heavymineral lag deposits will be used to estimate the magnitude of the
paleo-events, specifically the threshold entrainment stresses
necessary for the formation of specific mineralogical anomalies
(Komar, 1989). Furthermore, the assessment of HMC thickness
and concentration relative to background (pre-event) values will
help place constraints on storm duration.
CONCLUSIONS
Diagnostic morphological, sedimentological, and geophysical
signatures along sandy beaches can be used to reconstruct the
extent of past erosional events. The data presented here include
diagnostic erosional indicators, such as: 1) prominent truncations
of offlapping strata in geophysical images; 2) changes in the
apparent dip angle of the truncating reflection, compared to the
truncated strata, and 3) an increase in magnetic susceptibility by
several orders of magnitude for the magnetite-enriched sands
compared to background quartzose sediment. Further refinement
of geochronological techniques for in situ dating of clastic
sediments (OSL, IRSL, etc.) will provide a means of
reconstructing the long-term chronology of high-magnitude
erosional events, especially along prograding sandy coasts. As
Late Holocene sea-level fall is replaced by sea-level rise along this
paleoscarp
HMC
GPR profile
Figure 2. Erosional indicators, past and present, along Estaleiro
Beach (CP): A) Steep erosional scarp produced by a moderate
storm in November 2004; B) Residential area immediately
landward of location A, with a shore-normal GPR profile
below. The steep disconformity accentuated by a magnetite-rich
heavy-mineral concentration (HMC) represents a buried paleoscarp. Note the lack of morphological expression of this feature.
section of the coast, the most recent paleo-scarps may again
become exposed to the agents of erosion.
Journal of Coastal Research, Special Issue 64, 2011
1842
Geological Legacy of Storm Erosion, northern Santa Catarina, Brazil
A
bedrock
C
N
main GPR transect
NVV-03
NVV-02
1.0 m
1.2
15
m
1,672
2.4
1.7 m
95
3,249
m
Atlantic
Ocean
1.4
4
2.7
3.0 m
vibracores (Fig. 3C)
958
road surface
B
beachface/shoreface accretionary surfaces
aeolian sands
progradation
erosional truncation
1m
10 m
Figure 3. Evidence of erosion at the Navegantes strandplain: A) Location of the main transect and vibracores along the northern portion of
the plain; B) Segment of a GPR profile through the younger portion of the plain; C) Photographs of vibracores showing thick HMCs.
Numbers on the right are MS values of three HMCs and adjacent quartz-rich horizons (*10-5 SI units).
ACKNOWLEDGMENTS
The project was funded by the CNPq (UNIVALI, UFPR) and the
Coastal Research Institute and NOSAMS (WHOI). We thank
E. Siegle, G. Vintém, J. T. Menezes, M.R. Lamour, and
M.C. Souza for their assistance in the field and two anonymous
reviewers for their help in improving the manuscript.
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