Brazil Highstands Talk

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.