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PDF of talk from the 2014 annual meeting of the Geological Society of America. Based on work published in GSA Bulletin in January 2014 (http://gsabulletin.gsapubs.org/content/early/2014/01/07/B30836.1.abstract)
Citation preview
Coastal response to late-stage
transgression and sea-level
highstand in Brazil
Coastal response to late-stage
transgression and sea-level
highstand in Brazil
Christopher Hein, Duncan FitzGerald, Joao Thadeu de Menezes, Antonio Klein, Marcio Albernaz,
William Cleary
Geological Society of America
21 October 2014
Angulo et al., 2006, Quaternary Science Reviews
Approach: Transgressive Records Preserved by SL Fall
Hein et al., 2014,
GSA Bulletin
• 5.8 ka BP; 2 - 4 m
• Gradual, mildly oscillating
SL fall
Approach: Transgressive Records Preserved by SL Fall
Caravelas Strandplain,
Bahia, Brazil
Pinheira Strandplain,
Santa Catarina, Brazil
Roy et al., 1994,
Cambr. U. Press
Study Site: Navegantes Strandplain, Santa Catarina
Rio
Grande do
Sul
Santa
Catarina
Paraná
Florianopolis
Navegantes
Tijucas
Study Site:Navegantes Strandplain
Itajaí River
• High relief (900 m)
• Relatively narrow coastal
plain (10–45 km)
• Rugged Precambrian –
Cambrian bedrock headlands
• Coast smoothed: strandplains
formed between headlands
Navegantes
Strandplain
Itajaí
Bedrock
Headland
Bedrock
HeadlandPhoto: I. Buynevich
Hein et al., 2014,
GSA Bulletin
Examples of Diverse Highstand Deposits at Navegantes
Exposed Bedrock Coast
Hein et al., 2014, GSA Bulletin
• Full exposure
• No transgressive / HS
features
• Waves crashing along
bedrock cliff at HS
Examples of Diverse Highstand Deposits at Navegantes
Transgressive Barrier Bar
Hein et
al., 2014,
GSA
Bulletin
• Shore-parallel bar; no lagoonal deposits
• Pinned to resistant upland material (bedrock)
Examples of Diverse Highstand Deposits at Navegantes
Barrier Island System
Hein et
al., 2014,
GSA
Bulletin
• Barrier w/ lagoonal deposits in protected
area of plain
• Overtops low resistance upland deposits
Hein et al., 2014,
GSA Bulletin
Modern Elevation 5.22.8
Pleistocene
Upland
Pleistocene
Upland
Lowland
(paleo-lagoon?)
Ridge Gap
(paleo-inlet?)
A Comparison Barrier Island System: Tijucas Strandplain
FitzGerald et al., in prep
N
Classification of Highstand Deposits
Hein et al., 2014, GSA Bulletin
Sediment Supply:
• In situ, shelf,
fluvial
• Oceanographic
conditions
• Bedrock
headlands
• Fronting
barrier systems
Upland Migration
Potential (UMP):
• Wave energy
• Erodability of
upland deposits
• Upland slope
Deposits of the Mid-Holocene Highstand in Brazil
• 28 documented highstand
deposits along Brazilian coast
• Elevations: 0 to > 5 m above
modern MSL
• Ages: ~ 4–7 ka
Hein et al., 2014, GSA Bulletin
Deposits of the Mid-Holocene Highstand in Brazil
• Diversity: local geological &
oceanographic controls
• Lagoonal deposits extend to
modern shoreline (&
beyond?)
• Barriers present when modern
SL crossing (6.9–7.7 ka)
• Rapid migration: early
Holocene (SLR: 2–3 mm/yr)
• Barriers stabilized: SLR
decel. to <1.5–2.0 mm/yr (5–
6 ka)Hein et al., 2014, GSA Bulletin
Implications for Transgressive Coastal Systems
Coastal response to SLR is non-linear:
• Threshold SLR rate for stability (slow migration / vertical accretion)
of barrier systems at mid-Holocene: 2.0 mm/yr
Coastal response to SLR is non-uniform:
• Site specificity associated w/ formation of HS deposit types
• Diversity (3 HS deposit types) identified w/in
single embayment (Navegantes)
Associated Manuscript
Hein, C.J., FitzGerald, D.M., Cleary, W.J., Klein,
A.H.F., de Menezes, J.T., Albernaz, M.B., 2014.
Coastal response to late-stage transgression and
sea-level highstand. Geological Society of
America Bulletin, v. 126, no. 3/4, p. 459-480.