Climatic and Sedimentological Forcing of Strandplain Progradation at Tijucas, Central Santa Catarina, Brazil
Duncan M. FitzGerald1, Christopher J. Hein1,*, William Cleary2, Antonio H.d.F. Klein3, J. Thadeu d. Menezes4, Ilya V. Buynevich5, Steven T. Petsch6 Dept. of Earth Sciences, Boston University Boston, MA, USA (dunc@bu.edu); * - presenter (hein@bu.edu) 2 Center for Marine Science, University of North Carolina, Wilmington, Wilmington, NC, USA (wcleary@charter.net); 3Coastal Oceanography Laboratory, Dept. of Geosciences, Federal University of Santa Catarina, Florianópolis, SC, Brazil (antonio.klein@ufsc.br); 4Laboratory of Geological Oceanography, UNIVALI – CTTMAR, Itajaí - SC, Brazil (thadeu@univali.br); 5Dept. of Earth and Environmental Science, Temple University, Philadelphia, PA, USA (coast@temple.edu); 6 Dept. of Geosciences, University of Massachusetts – Amherst, Amherst, MA, USA (spetsch@geo.umass.edu) 1
1. Abstract
2. Background: Southern Hemisphere Sea-Level Fall
Strandplains along the Atlantic coast of southern Brazil have formed due to an abundant sediment supply and a forced regression associated with a gradually falling sea. Geophysical, sedimentological, and chronological examination of the Tijucas Strandplain has revealed that it abuts a laterally discontinuous 4-m high sand ridge that is tentatively interpreted as the Stage 5e Pleistocene shoreline. Seaward of this feature, the mid-Holocene (5.8 ka) highstand ridge contains landward-dipping strata overlying muddy sequence. These sands are interpreted as overwash deposits building into a lagoon, representing the leading edge of the transgression.
2m
4
6
2
ka
6
North Queensland, Australia
30o
Brazil
Sea Level Elevation (m)
5 4 3 2 1 0 -1
6
2
4 3 Age (x 1000 yrs. BP)
5
0
1
Figure 4. SL curve for Santa Catarina coast (Angulo et al., 2006; based on vermitid records). Highstand: ~5.8 ka at ~2.5 m above modern SL; gradual fall to modern elevations.
90o
6 km
TJD-2
4m
TJD-3
Holocene Highstand
Strandplain
TJD-6
Flood Events
10
8
ka
2
4
6
12 m
8
2
ka
6
Buenos Aires Province, Argentina
Tierra del Fuergo, Argentina
Elevation Above MSL (m)
Bedrock Headland
Flood Events
Flood Events
2
ka 8
Santa Catarina, Brazil
8
TJV-25
0 km
TJD-01 TJV-24
TJV-22
6
Suriname
-4
Landward (West)
0
8m
Basin-Fill Mud
-42
Lake Junin, Peru
-44 -46
0
(c)
0.35
(d) more austral winter precip.
-4
δ18O ‰ VPDB
0.15
Cariaco Basin, Caribbean Sea
% Titanium
0.25
Precipitation
0.05
-5
-6
-7
more austral summer precip.
(e)
Rio Grande do Sul, Brazil
Humid
(f) 5000
Dry
4000
3000 2000 Time (cal yr BP)
1000
0
Relative Precip
relative increased rainfall
Cristal Cave, Santa Catarina, Brazil
B
Continent
Ocean
UPWARPING t1
SUBSIDENCE UPWARPING t2 > t1
SUBSIDENCE
Figure 2. Conceptual models for southern hemisphere Holocene SL fall (Milne et al., 2005)
Present
8m 4m
Meters
400
Post Mid-Holocene Highstand
4m
Seaward (East)
0m
600
Mid-Holocene Highstand
8m 4m 0m
Pre Mid-Holocene Highstand
8m 4m 0m
5e Highstand (120 ka)
8m 4m 0m Basement / Bedrock Pleistocene Barrier Deposits: Dunes Barrier Sands Mid-Holocene Transgressive Barrier / Washover Sands
Explanation Prograding Beach Ridges
Brackish-water Peat Fresh-water Mud
Channel Fill
Fresh-water Peat
Lagoonal Mud
Water
Figure 6. Conceptualized evolution of the highstand Holocene strandplain ridge system, which formed 400 m seaward of the highstand 5e Pleistocene shoreline.
0 km
y = 0.0002x + 0.0152x R2 = 0.9314
2 Depth of Sand
4
-2
Beach Ridges (Sand) 6
Mud & Cheniers (Mud)
4 3
50 100
2 1 0 -1
150
Sandy Cheniers 0
50
100
Meters
8. Conclusions
-130
• Tijucas strandplain abuts OIS 5e shoreline ridge located 7 - 8 m above modern SL.
-135 Explanation Muddy Chenier Ave. Chenier Sandy Ridge Ave. Sand 10
Figure 10. Tijucas progradation rates. Note increasing rate with time. Errors are within size of graph points. Inset: aerial view with core locations in blue; cores from which dates were obtained shown in red.
Mud
• Strandplains in southern Brazil formed due to abundant sediment supply & forced regression.
0
Distance from Modern Shoreline (km)
0
-125
-145
0
2
200
150
200
Seaward (East)
Figure 11. Post-processed GPR profile and sediment cores from a chenier section of the plain. See Fig. 3 & 9 for location. TWTT: two-way travel time. Width of units in graphic core logs ≈ grain size; wider, yellow units = sand; narrow, brown units = mud. Upper-most black units are modern organics. Transparent GPR sections: signal attenuation by mud (Tercier et al., 2000).
20 m
-140
4
5
Landward (West) OCEAN
6
Figure 9. 3-D perspective map of sand / mud depth & distribution in the surficial 8 m of the plain. Based on two semi-parallel GPR transects ground-truthed with sediment cores (see Fig. 9 for core locations). There are ~70 sand-mud transitions.
0
-150
0
2
Tijucas Tijucas River River
Elevation Above MSL (m)
Elevation Above MSL (m)
Elevation Above MSL (m)
Laguna Pallcacocha, Ecuador Precipitation
-40
200
Trackline B
0m
δD C24-C30 Fatty Acids (‰)
Mean Grain Size (μm)
Δδ18O ‰
(b)
SUBSIDENCE
TWTT (ns)
100
Red Color Intensity
200
TJD-02
Trackline A
Sea Level
Figure 8. Sample GPR profiles in two locations in the Tijucas plain (see Fig. 3 for locations).
El Niño
t2 > t1
8m
6 km
-4
Vieques, Puerto Rico
(a)
TJA-22 TJV-11 TJA-21
TJV-04 TJV-12 TJA-23
5957 ± 58 cal BP
7. Climatic Forcing of Strandplain Progradation 0
TJV-36
± 820 BP
20 m
50
REBOUND
6. Strandplain Progradation
A
100
SUBSIDENCE
REBOUND
0 34900
1 km
Figure 12. Correlation of sand-mud transitions to paleoclimate proxies. Yellow vertical bars: periods of sandy deposition; brown: muddy deposition. Data from: (a) Donnelly and Woodruff, 2007; (b) Moy et al., 2002; (c) Maslin and Burns, 2000; (d) Haug et al., 2001; (e) S. Burns and B. Taylor, unpublished data (with permission); (f) Martinho et al., 2008.
t1
0m
-2
frequency of intense hurricane landfalls
Angola
2
0
B
ka
TJA-09
2
-6
2
• Oxygen Isotope Stage (OIS) 5e (ca. 120 ka): global eustatic SL ~8 m above modern mean SL (Kopp et al., 2009): deposits sandy ridge and regressive strandplain. • Holocene SL highstand transgressive barrier: evidence of backbarrier lagoon, inlet channel, and multiple washover deposits at ~5.9 ka. • GPR profiles: low-angle landward dipping reflectors → washovers into muddy lagoon. • Landward dipping sets truncated by seaward dipping reflectors → beachface and foreshore accretion. • Forced regression following highstand results in formation of Holocene strandplain.
Fluvial Sand & Fine Gravel
-4
4
TJV-10
GPR section shown in Fig. 11
• Seaward-thickening basin fill mud sequence underlying mud / sand / chenier strandplain. • Thickness of beachface & foreshore units decrease seaward → decrease in accommodation space. • Progradational reflectors shallow & contain more mud in seaward direction → decreasing wave energy in response to basin infilling.
ka
Figure 5. Ground-penetrating radar (GPR) profile and associated auger cores (TJA-xx), vibracores (TJV-xx), and combined wash boring / direct push cores (TJD-xx) across two topographic highs proximal to western boundary of strandplain. See Fig. 3 for GPR profile location.
Shallow Bedrock 28 m Figure 7. Deep drill core transect across the Tijucas strandplain showing the gross stratigraphy.
150
2
4
-6
20 m
200
4
2m
Far-Field Ocean
Near-Field Ocean
4. Multiple Highstands at Tijucas
-2
Tijucas River
TJD-7
4
2m
Figure 1. SL curves for southern hemisphere coasts (Angulo and Lessa, 1997); note: highstands (+2 - 4 m above modern mean SL) at 4 - 6 ka
16 m
24 m
4
6
2
Continent
}
Flood Events
2m
2
Flood Events
4m 8m
4m
Motivation: 1) Advance understanding of strandplain development 2) Provide a new depositional model for sedimentary systems formed in regimes of falling SL 3) Relate coastal geomorphic response to climate forcings.
TJD-5
0o
4m
Modern Coast
TJD-4
• Sea-level (SL) fall in southern oceans: due to global isostasy. • Glacial forebulge collapse → new accommodation space → siphon water from far-field regions (i.e., South Atlantic; Mitrovica and Milne, 2002; Fig. 2a). • Ocean loading → additional accomodation → additional 40% of SL fall in far field regions (Milne et al., 2005; Fig. 2b). • Model test for east coast of South America: strong correspondence between established SL histories and predicted SL curves (Milne et al., 2005).
ka
2
Tuamotu Islands, French Polynesia
90o
5 km
1 km
2 km
4
A
Age (cal kyr BP)
0m
3 km
4 km
5 km
ka
Society Islands, French Polynesia
Fiji Islands, Fiji
180o
Bedrock Headland
5. Basin Infilling
2
60o
Santa Catarina State
Tijucas
4
Pacific Ocean
Sample Locations (Fig. 13)
GPR Section (Fig. 8b)
ka
2
4
Tropic of Capricorn
Tijucas Bay GPR Section (Fig. 8a)
2m
Atlantic Ocean
TIJUCAS STRANDPLAIN
GPR Section (Fig. 5)
ka
2
Port Hacking, New South Wales, Australia
3. Study Area and Motivation
• Protected by low relief headlands - low wave energy • Formation: forced regression + abundant sediment supply from Tijucas River (catchment: 2420 km2; average discharge: 40 m3/sec → increases 100x during floods). • Saprolite (10s m thick): large quantities of fine-grained sediment as well as sand & fine gravel during floods.
4
0o
Imprinted on this longer-term trend are a series of nearly 70 abrupt transitions between shore-parallel sand- and mud-dominated facies. Preliminary lipid D/H analyses of these various units, combined with correlations with published paleoclimate proxy records, reveals that these decadal- to centennial- scale transitions likely resulted from changes in the fluvial bedload/suspended load ratio. Such changes are related to climate change, which in turn produced modifications in vegetation patterns, bedrock weathering and soil formation processes, and ultimately sediment contribution in the drainage basin.
Approximate location of mid-Holocene highstand GPR Section (Fig. 11)
2m
Tahiti
Tupuai
Following the mid-Holocene sea-level highstand, the Tijucas plain prograded approximately 6 km, during which time the overall trend in sediment deposition shifted from sand-dominated facies (tightly-spaced beach ridges), to alternating sand ridges and muddy cheniers in the mid-plain, to mud-dominated facies with widely spaced sand cheniers in the past few centuries. Seven deep (17 - 25 m) cores through the plain indicate a seaward thickening wedge of marine mud underlying the surface ridges, which suggests that decreasing accommodation space controls sedimentation patterns. In this scenario, basinal filling would have gradually attenuated wave energy leading to less sediment reworking and a change from sand to mud dominance.
Figure 3. Study Area: Tijucas Strandplain, central Santa Catarina State, Brazil
2m
2m
20
30
40
50
% Long-Chain Fatty Acids
60
Figure 13. Analysis of fatty acids from sandand mud-dominated sediments (see Fig. 1 for locations). Note differences in both average δD values of C24-C30 fatty acids (y-axis) & % contributions of C24-C30 fatty acids to total fatty acid concentrations.
• Observation: strandplain transitions roughly correlate to periods of precipitation variability • Hypothesis: Δ seasonality → Δ vegetation patterns → Δ soil → Δ basin sediment contributions sediment transitions • Preliminary Data: sand reflects periods of less monsoon variability?
• Mid-Holocene (5.8 ka) highstand transgressive barrier: 400 m seaward of 5e ridge; composed of a 3-m high ridge, backbarrier lagoon, channel fill, & washover deposits. • Seaward-thickening wedge of marine mud underlies the strandplain sequence → decreasing accommodation space controls sedimentation patterns. • Overall deposition trend: beach ridge sanddominated facies (inland) → alternating sand ridges and muddy cheniers (mid-plain) → mud-dominated facies with widely spaced sand cheniers (seaward). • ~70 abrupt transitions between shore-parallel sand- and mud-dominated facies → likely result from changes in the fluvial bedload / suspended load ratio → related to decadal- to centennial- scale climate change.
9. References
Angulo, R. J., Giannini, P. C. F., Suguio, K., and Pessenda, L. C. R., 1999, Relative sea-level changes in the last 5500 years in southern Brazil (Laguna-Imbituba region, Santa Catarina State) based on vermetid C-14 ages. Marine Geology, 59 (1-4): 323-339. Angulo, R.J., Lessa, G.C., de Souza, M.C., 2006, A critical review of mid- to late-Holocene sea-level fluctuations on the eastern Brazilian coastline. Quaternary Science Reviews, 25: 486-506. Donnelly, J. P., Woodruff, J. D., 2007, Intense hurricane activity over the past 5,000 years controlled by El Niño and the West African monsoon. Nature, 447: 465- 468 Huag, G.H., Hughen, K.A., Sigman, D.M., Peterson, L.C., Röhl, U., 201, Southward Migration of the Intertropical Convergence Zone Through the Holocene. Science, 293(5533): 1304-1308. Kopp, R.E., Simons, F.J., Mitrovica, J.X., Maloof,A.C., and Oppenheimer, M., 2009, Probabilistic assessment of sea level during the last interglacial stage: Nature, v. 462, p. 863–867. Martinho, C. T., Dillenburg, S. R., and Hesp, P. A., 2008, Mid to late Holocene evolution of transgressive dunefields from Rio Grande do Sul coast, southern Brazil. Marine Geology, 256: 49-64. Maslin, M.A., Burns, S.E., 2000, Reconstruction of the Amazon Basin effective moisture availability over the last 14,000 yr. Science, 290: 2285-2287. Milne, G.A., Long, A.J., Bassett, S.E., 2005, Modeling Holocene relative sea-level observations from the Caribbean and South America. Quaternary Science Reviews, 24: 1183-1202. Mitrovica, J.X., Milne, G.A., 2002, On the origin of late Holocene sea-level highstands within equatorial ocean basins. Quaternary Science Reviews, 21 (20-22): 2179-2190. Moy, C.M., Seltzer, G.O., Rodbell, D.T., Anderson, D.M., 2002, Variability of El Niño/Southern Oscillation activity at millennial timescales during the Holocene epoch. Nature, 420: 162-165. Tercier, P., Knight, R., Jol, H., 2000, A comparison of the correlation structure in GPR images of deltaic and barrier-spit depositional environment. Geophysics, 65: 1142-1153.
10. Acknowledgments
We acknowledge the National Science Foundation Graduate Research Fellowship Program and the donors of the American Chemical Society Petroleum Research Fund for partial support of this research. Additional funding was provided by FAPESC/ Prof. Number 16247/2007-7, CNPQ Proc. Number 575008/2008-3, UNIVALI Res. Fellowship PQ-2, Proc. Numb.300153/2009-0. We also acknowledge the contributions of Steve Burns (UMass Amherst, USA), Rodolfo Angulo (University Federal do Paraná, Brazil), and Nils Asp (University Federal do Pará, Brazil), as well as CTTMAR / PROPEC / UNIVALI for institutional support and the following students and staff at UNIVALI for their assistance with data collection: Marcos Berribilli, Thelma Luiza Scolaro, Marcio Albernaz, Dominicio Freitas Neto, Guilherme Vieira da Silva, Carolina Brandl, Rafael Sangoi, Diego Bittencourt, Jean Berná Paim, Gustavo Hattenhauer Gomes, Luiz Fernando Borghi.