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