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
Approach: Transgressive Records Preserved by SL Fall
Angulo et al., 2006, Quaternary Science Reviews
• 5.8 ka BP; 2 - 4 m • Gradual, mildly oscillating SL fall
Hein et al., 2014, GSA Bulletin
Approach: Transgressive Records Preserved by SL Fall Roy et al., 1994, Cambr. U. Press
Pinheira Strandplain, Santa Catarina, Brazil
Caravelas Strandplain, Bahia, Brazil
Study Site: Navegantes Strandplain, Santa Catarina Paranรก Navegantes
Tijucas Santa Catarina Rio Grande do Sul
Florianopolis
Study Site: Navegantes Strandplain • High relief (900 m) Bedrock Headland Navegantes Strandplain
• Relatively narrow coastal plain (10–45 km) • Rugged Precambrian – Cambrian bedrock headlands • Coast smoothed: strandplains formed between headlands
Itajaí Itajaí River Bedrock Headland
Photo: I. Buynevich
Hein et al., 2014, GSA Bulletin
Examples of Diverse Highstand Deposits at Navegantes Exposed Bedrock Coast • Full exposure • No transgressive / HS features • Waves crashing along bedrock cliff at HS
Hein et al., 2014, GSA Bulletin
Examples of Diverse Highstand Deposits at Navegantes Transgressive Barrier Bar • Shore-parallel bar; no lagoonal deposits • Pinned to resistant upland material (bedrock)
Hein et al., 2014, GSA Bulletin
Examples of Diverse Highstand Deposits at Navegantes Barrier Island System • Barrier w/ lagoonal deposits in protected area of plain • Overtops low resistance upland deposits
Hein et al., 2014, GSA Bulletin
2.8
Modern Elevation
5.2
Lowland (paleo-lagoon?)
Pleistocene Upland
Pleistocene Upland
Ridge Gap (paleo-inlet?)
Hein et al., 2014, GSA Bulletin
A Comparison Barrier Island System: Tijucas Strandplain
FitzGerald et al., in prep
N
Classification of Highstand Deposits 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 Hein et al., 2014, GSA Bulletin
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)
Hein et al., 2014, GSA Bulletin
• Barriers stabilized: SLR decel. to <1.5–2.0 mm/yr (5– 6 ka)
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.