Pinheira - GSA 2010

Geophysical Examination of a Regressive Barrier: Implications for Mid- to LateHolocene Sea-Level Fall in the Southern Hemisphere

Christopher Hein, Duncan FitzGerald, Marcio Albernaz, William Cleary, Joao Thadeu de Menezes, Antonio Klein GSA Annual Meeting 2 November 2010

Motivation: Effects of Climate and Sea-Level Changes on Strandplain Development

Angulo et al, 2006, QSR

Sea Level in Southern Brazil Paranรก

Parana Florianopolis Santa Catarina Pinheira Rio Grande do Sul

Mid- to Late- Holocene Sea Level Fall: Oscillations?

Angulo & Lessa, 1997, Marine Geology (after Suguio et al., 1985; Villwock and Tomazelli, 1989; Tomazelli, 1990)

Mid- to Late- Holocene Sea Level Fall: Oscillations? vermitid: Petaloconchus varians Mid-Holocene Highstand in Southern Brazil: • 5.8 ka BP • 1 - 3 m above present sea level Gradual, mildly oscillating SL fall

Angulo et al, 2006, QSR

Study Site: Pinheira, Santa Catarina, Brazil

• • • •

15 km post-processed ground-penetrating radar (GPR) 4 wash boring / direct push cores (16 m deep) 13 vibracores (3 – 6 m deep) 9 auger cores (1 – 6 m deep)

5 km

Results: Progradational Sequence muddy swales

Depth (m)

4 0

signal attenuation

-4

modern fill / organics

4

Depth (m)

60 m

Unit III 0

Unit II Unit I

-4

GPR Section

UNIT I: Shoreface - 2.2o – 2.7o; v. f. sand interbedded w/ muddy units UNIT II: Foreshore - 3.75o – 4.75o; seaward dipping w/ few, thin landward-dipping beds; fine sand and > 5% shell hash UNIT III: Beachface and Foredune Complex - dune facies w/ variety of bed orientations; fine aeolian sand

Depth (m)

Results: Paleo-Barrier Sequence 4 0 -4

Depth (m)

50 m 4 0 -4

modern fill / organics Barrier Sequence

Unit III Unit II

Unit I GPR Section

Cores

Results: Paleo-Inlet Sequence Depth (m)

4 0

10 m

-4

Depth (m)

0

aeolian dune complex

road fill

4

upper barrier and foredune

freshwater marsh active inlet fill

-4

GPR Section

Cores

lower barrier and foreshore

Results: Progradational Sequence 5000 – 3600 Years BP

Depth (m)

8 4 0 -4

bedrock 60 m

Depth (m)

Results: Progradational Sequence 3600 Years BP

4 0 -4

50 m

Depth (m)

Results: Progradational Sequence 3600 – 3000 Years BP

4 0 -4

50 m

Depth (m)

Results: Progradational Sequence 3000 – 2800 Years BP

4 0 -4

50 m

Depth (m)

Results: Progradational Sequence ~1000 Years BP

4 0 -4

50 m

Implications: Barrier Island Formation 3 Possible Perturbations: lagoon

(1) sediment supply (2) wave climate

barrier inlet island

highstand strandplain initiation

(3) rate or direction of sea level change

Implications: Change in Sediment Supply Pinheira Strandplain: Thickness: 16 m Volume: 0.5 km3

Implications: Change in Sediment Supply

Itajaí River Ad = 15,500 km2 Qw = 230 m3/sec

Rio de la Plata Ad = 3,100,000 km2 Qw = 22,500 m3/sec

Paraná

Tijucas River Ad = 2420 km2 Qw = 40 m3/sec Massiambu River Ad = 70 km2 Qw = 2 m3/sec

25 km

Madre River Ad = 330 km2 Qw = 7 m3/sec

Santa Catarina

Implications: Change in Sediment Supply Sao Francisco River (631,000 km2) 1000 km

Pinheira

Rio de la Plata (3,100,000 km2)

Implications: Change in Wave Regime Variation in Storminess:

Evidence from Pinheira:

• 2 “large” storms in 100 yr record: Cyclone Catarina (2004) & Tropical Storm Anita (2010)

• Ridge crests: spacing & shape (180o, arcuate)

• Quiescent coastline

• Protection from headlands & Ilha de Santa Catarina

Implications: Change in Wave Regime Substrate Slope:

Wolinsky & Murray, 2009, JGR

• Nearshore slope affects migration rate of transgressive barriers • Shallowing of nearshore during SL fall

Evidence from Pinheira:

• Modern slope: 0.1 – 0.2 % shallows ~5 km offshore • Deep regressive reworking • Transgressive ravinement flat slope

Implications: Sea-Level Fall

active barrier (2800 – 3600 BP)

SST Variations? – 18O: 10s of cm during Holocene (Baker et al, 2001) LIA & Medieval Climatic Optimum – SL ∆ 10 – 100 cm (Mörner, 1973; Nunn, 1998; van de Plassche et al., 1998; Gehrels et al., 2005; Szkornik et al., 2008)

Acknowledgements Field / Lab Assistants: Marcos Berribilli, Thelma Luiza Scolaro, Dominicio Freitas Neto, Guilherme Vieira da Silva, Carolina Brandl, Rafael Sangoi, Diego Bittencourt, Jean Berná Paim, Gustavo Hattenhauer Gomes, Luiz Fernando Borghi, and Vanessa Barbosa Machado, Nick Cohn, Mary Ellison, Akina Chuigyn Funding: American Chemical Society (ACS) - Petroleum Research Fund, ACS Project SEED, Conselho Nacional de Desenvolvimento Científico e Tecnológico, NSF Graduate Research Fellowship Program