Brazil Strandplains Coastal Sediments 2015 Presentation

Wave energy, sediment supply, and sea-level fall: Late Holocene basin infilling in southern Brazil Christopher Hein, Ioannis Georgiou, Duncan FitzGerald, Luiz Polido de Souza, Antonio Klein, & Joao Thadeu de Menezes Coastal Sediments 2015 13 May 2015

Approach: Basin Infilling During SL Fall

Angulo et al., 2006, QSR

Paranรก

Study Site: The Strandplains of Central Santa Catarina

Navegantes Tijucas Santa Catarina Rio Grande do Sul

Pinheira

Navegantes Strandplain • A: 45 km2 • Fed by Itajaí River Bedrock • Narrow, exposed plain Headland • Fine-grained, dissipative beach Navegantes o nearshore • 0.11 Strandplain Itajaí Itajaí River Bedrock Headland

Pinheira Strandplain 5 km

Massiambu River

Ilha de Santa Catarina N

Dune fields

Bedrock

Bedrock headlands

Bedrock headlands

Madre River

Dune field

• A: 60 km2 • Offshore sediment source; highly protected embayment • 0.18o nearshore

Tijucas Strandplain • A: 90 km2 • Fed by Tijucas River • Muddy beach • 0.06o nearshore N

Tijucas River mud coarse sand beach

liquid mud

Tijucas Basin Infill: Changing Depositional Setting

Seaward Direction: basin-fill mud sequence thickens; beachface & foreshore units thin

Tijucas Basin Infill: Changing Depositional Setting

Tijucas Basin Infill: Changing Depositional Setting

0m 8m

Tijucas Basin Infill: Changing Depositional Setting

Seaward Direction: progradational reflections shallow; mud % increases

Tijucas Basin Infill: Changing Depositional Setting

Seaward Direction: shoreline becomes more “protected�

modified from Wiegel, 1964, Oceanographical Engineering

5800 BP

2500 BP

Autogenic Change: Decreasing Wave Energy 96

1000 BP

Modern

72 48 24 0

Wave Energy Transport (KW/m)

120

Bay Infilling at Pinheira

modified from Hein et al., 2013, Sedimentology

• Nearly constant progradation rate • Sand-dominated • 9-10 m thick

Bay Infilling at Navegantes

• Progradation rate poorly constrained (0.5-1.0 m/yr time averaged) • Sand-dominated, with thin mud unit at base • 8-16 m thick Holocene sequence

Sediment Sources: Local & Distal ItajaĂ­ River Ad = 15,500 km2 Qw = 230 m3/sec

Massiambu River Ad = 70 km2 Qw = 2 m3/sec

Tijucas River Ad = 2420 km2 Qw = 40 m3/sec

25 km

Sao Francisco River

S.C. Coast

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

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

Tijucas: Vt: 14.8x108 m3 Vs: 6% Vs/Qw: 0.67x108 m3/km3

Pinheira: Vt: 9.1x108 m3 Vs: ~100% Vs/Qw: 34.7x108 m3/km3

Navegantes: Vt: 5.8x108 m3 Vs: ~75% Vs/Qw: 0.62x108 m3/km3

Insights Through Inter-site Comparisons

Summary & Conclusions Allogenic controls on basin infilling in southern Brazil: • Sea-level fall dominant; fluvial & shelf sediment source • Differences in wave energy (& geology?) responsible for inter-site differences in infill sequences Autogenic controls on basin infilling in southern Brazil (Tijucas): • Mud infilling in deeply embayed compartment causes bay shoaling • Produce thick, muddy sequences dampens wave energy & produces rare muddy beach • Spatial variability in sediment texture: implications for future transgression

Upcoming Coastal Geology Technical Session!

Field and Modeling Approaches to Understanding the Response of Coupled Barrier-Backbarrier Systems to Coastal Change Conveners: Christopher Hein (VIMS) & Jorge Lorenzo-Trueba (MSU) Geological Society of America Annual Meeting 1–4 November 2015 Baltimore, MD Abstracts Due: 11 August 2015 Questions?: hein@vims.edu

Autogenic Change: Decreasing Wave Energy