Sediment characteristics of a fjord transect across the Southern Andes at 53°S

(1)

0 100 200 km

54°

Antarctic Plate

Scotia- Plate

50°

triple- point 46°

Palaeozoic Basement Patagonian Batholithe

Rocas verdes Folded Orogen Patagonian Basalts

Recently active Volcanoes

100200 300

437

100 100

200

300

300 400

200

200 m

400 627

607

200 500 m

Villa Tehuelches

Rio Verde

Kon Aiken

SENO

OTW AY

SENO SKYRING

ISLA RIESCO

Mte Olvidado 1189

Co Castillo 1236

695

386 Mte Alto

Mte Chaigneu 1040

Mte Toro 994 Ladrillero

1665 1250 Pico Sur

Aguirre 1140

Huidobro 912

Rio Ca nelo

Laguna Blanca

0 20 Km

31

73 73

64

36

78 35 37 29 91 68

97 57 66 58 80 73 66 68

64 64

117 170 46 73 58

62 Estrecho

de Ma

gallanes

100 100 m

200 m

200 m 200 m

500 m

500 1000 m

2000 m

53°S 52°S

55

Muñoz-Gamero-Halbinsel

Andean clay

Sky1

GRAN C AMPO

NEVA DO

0 - 100 m 100 - 200 m 200 - 500 m 500 - 1000 m 1000 - 2000 m 2000 - 3000 m

>3000 m

fan of glacial clay river

cores mentioned in this poster other core sites of this project e.g. Kilian et al. 2004

Water depths

road

2.0 2.5 3.0

3.0 3.4 3.8 4.2

MgO

10 20 30

clay fraction

SiO₂/Al₂O₃

SiO₂/ Al₂O₃

Mg (wt.%)

Mt. Burney-T. (4254±120 cal. y. B.P.)

Aguilera-T.

(<3596±230*)

Burney-T. 9009±17*

9175±111*

IRD 17460**

18280**

0.25 mm/a

~13500

40%

Andean glacial clay signature

clay 0

1

2

3

4

Reclus-T. 15384±578*

15933 ±476*

Sediment depth (m)

A

Seno Skyring

* calibrated ages

** ages determinated with the sedimentation rates

Sediment characteristics of a fjord transect across the Southern Andes at 53°S

Tatjana Steinke

¹

, Oscar Baeza

¹

, Ruediger Stein

²

and Rolf Kilian

¹

1

University Trier, Universitätsring 15, 54296 Trier, Germany

2

Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, 27568 Bremerhaven, Germany corresponding author: tsteinke@awi-bremerhaven.de

Fig. 1: The area of investigation in the southernmost Andes and its relationsship to the major lithological units (see: Mapa Geologico de Chile 1:10000000).

Introduction

The Southern Andes are characterized by most variable denudation rates which depend on ice coverage, climate, topography and vegetation. Con- trolled by the erosion process and the terrestrial and aquatic bioproductivity, sediments have most variable compositions (e.g. Silva & Prego, 2002).

This study concentrates on a W-E fjord transect across the Andes at 52- 53°S, from the proglacial lake Seno Skyring (Figs. 1,2,3) to the island zone of the west coast. Late Glacial to Holocene sediment cores from these fjord basins together with sediment echo sounding profiles are used to constrain sedimentation rates, sediment flux and denudation rates. Well dated tephra layers from this region (Kilian et. al., 2003) and AMS 14C ages of marine shells and plant marco remnants are used for chronological contrail. In the Late Glacial sediment pathways along the fjord system have been more or less open and led to a significant mass transfer towards the eastern foreland and also the continental margin and deep sea. First results indicate that the sediment transport became more restricted at the Late Glacial to Holocene transition, leaving often nearly closed systems for denudation and sediment deposition in intra-Andean fjord basins.

Fig. 2: Topography of southernmost South America.

Fig. 7:Chemical and physical characteristics of a sediment core taken in an marine environment near to Parlamento Island.

Fig. 6: Chemical and physical properties of a core taken in an marine enviroment near to Tamar Island.

Fig. 4: Chemical pattern and relative clay content of a sediment core. Changes in the contribution Andean chlorite-rich clay since Late the Glacial are evident.

References

Silva, N. & Prego, R. (2002). Carbon and nitrogen spatial segregation and stoichiometry in surface sediments of Southern Chilean Inlets (41- 56°S). Estuarine, Coastal and Shelf Science, 55: 763-775.

Markgraf, V. (1993). Paleoenvironmental and paleoclimates in Tierra del Fuego and southernmost Patagonia, South America. Paleography, Pa leoclimatology, Paleoecology, 102: 53-68.

Kilian, R. et al. (2003). Holocene peat and lake sediment tephra record from the southernmost Chilean Andes (53°-55°S). Rev.Geol. de Chile, 30: 23-37.

PARLAMENTO SEPTEMBER 2004

SEPTEMBER 2004

TAMAR

BAHIA AREVALO ^{MARCH 2004}

-30 m

-35 m

-40 m acoustical

basement

Parker

52°40.03 S

74°11.01 W 52°39.48 S

74°10.54 W

SW NE

Parker

Parlamento

Bahia Arevalo

Tamar

Water depth

100 m distance 200 m

PARKER SEPTEMBER 2004

Fig. 3: Research area in an transect across the southernmost Andes.

Fig. 5b: Chemical and physical properties of a core, taken in the Bahia Arevalo bay near to Gran Campo Nevado Ice Cap.

-10 m

-20 m

Bahia Arevalo

52°41.3‘S

73°23.4‘W 52°41.7‘S

73°24.1‘W

N S

acoustical Basement

100 m distance 150 m

Water depth

Fig. 8b: Chemical and physical characteristics of a sediment core taken in an marine environment near to Parker Island.

Fig. 5a: Bahia Arevalo core position in an echosounding profile.

Fig. 8a: Parker core position in an echosounding profile.

Lithology

Structure

silty clay

sandy silty clay sandy clay

siltclayey silt sandy silt

sandsand with gravel

lamination bioturbation drop stones bivalves

plant remains gravel

sandsilt clay

Results

The chemical pattern of a five meter long sediment core from eastern Seno Sky- ring indicate a systematically decreasing transport of chlorite-rich sediment components (decreasing Mg and increasing SiO₂/Al₂O₃ ratios; (Fig.4) from mafic rock bodies of the central and glaciated part of the mountain range (Fig. 3) during the last 18.000 cal years B.P. (Kilian et al. in press). The sediment core sections has been recovered also from the western Island zone (Tamar and Parker ) which are characterized by very low contents of biogenic material (TOC < 0.5 wt.% and CaCO3 < 0.5 wt%; Figs. 5-8, basal sections). Further age determinations and chemical analysis, which are in progress, should help to determine the sediment path ways from the glaciated Gran Campo Nevado towards the west and also to calculate the Late Glacial sediment accumulation rates. Outside of the recent gla- cier derived debris-fan (Fig. 3), Holocene sediments from small basins in-between the western island zone and fjord inlets show very high contents of organic carbon (5-15 wt %, in the upper part of Parlamento, Tamar, Parker cores, Fig. 6,7,8). As- sociated with increasing salinity, the sediments recovered near to the western en- trance of the Strait of Magellanes show a strong increase in biogenic carbonate (up to 25% CaCO₃, Parker, Fig. 8), indicating high marine bioproductivity and also low Holocene sedimentation rates of terrigeneous components.

Mt. Burney 4254 cal.years B.P.

CaCO3wt. % TOC wt. % C/N Sulfur wt. % Susceptibility

(10-5 SI) Gravel+Sand +Silt+Clay %

Lithology Texture _{0 200} _{600 0} ₄₀ _{80 0} ₂₀ 40 0 5 10 15 0 10 20 0 1 2 3

Water depth: 15 m Recovery: 0-490 cm 52°47.358’ S

73°40.254’W

0

100

200

300

400

490

Depth (cm)

Atlantic Ocean Pacific Ocean

52°41.589’S 73°23.600’W

0 100

200 300

400

500 600

700 800

900 990

Depth (cm)

Lithology Texture Susceptibility CaCO3wt. % TOC wt. % C/N Sulfur wt. % (10-5 SI) Gravel+Sand

+Silt+Clay %

0 200 6000 40 80 0 1 2 0 1 2 0 200 400 0 1 2 3

Water depth: 5 m Recovery: 0-990 cm

Mt. Burney 4254 cal. years B.P.

(10-5 SI) Gravel+Sand +Silt+Clay % Lithology Texture

0

100

200

300

Depth (cm) 400

Water content wt.%

0 500 1500 0 40 80 0 20 60 0 20 40 0 5 10 15 0 20 40 0 2 6 10

73°46.930’W

500

600

716

(10-5 SI) Gravel+Sand +Silt+Clay %

Lithology Texture ₀ ₄₀ _{80 0} ₄₀ ₈₀ ₀ ₁₀ ₂₀ ₀ ₁₀ ₀ ₁₀ ₂₀ ₀ ₂ ₄

74°10.695’W

0

100

200

300

412

Depth (cm)

Late Glacial to Holocene Transition