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Icy Hott Geology:A suite of Iceland sediments
A literature review compiled by Jon (J. R.) RotzienPresented to
The Stanford Alpine ProjectFebruary 13, 2009
http://www.wdcgc.spri.cam.ac.uk/news/jokulhlaup/
Tour d’Iceland Sedimentology:Factoids, depositional systems, geomorph, implications,
terminology & problems
1. Sandy deserts2. Tephra3. Coccoliths, diatoms
and ocean circulation4. Glacial deposits VS.5. Turbidites, hummocks,
contourites and Father Hollister
Diamictons:Can we distinguish glacial deposits
from turbidites?
Greek for “through” and “mixed” – poorly or non-sorted conglomerate, up to 25% gravel (>2 mm), angular to well-rounded clasts, matrix support (1960, Flint), descriptive term for poorly sorted and laminated rocks. Classically interpreted as glacial deposits.
Quick facts• All sands are volcanic (Arnalds et al., 2001), mostly
basaltic glass.• Jokulhlaup prone territory, glaciers underlain by
magma chambers = melt and massive floods.• Wind blown sands can strip paint off cars.• 20,000 sq. km of Iceland is covered by sandy deserts.
Skeiðarársandur winds strip paint from cars. Wind blown sands in front of Lómagnú.
Sandy deserts of Iceland, after Arnalds et al., 2001.
Sandy lava field
Sandy glacier, Myrdalsjokull
Sand field in central highlands
Sandy Deserts
-EV threat-lost ecosystems-lost water cycling-black surfaces provide positive feedback -need to prioritize conservation
Wastegard et al., 2001
Tephra dating for civilizations and Holocene climate instability research-Human settlement at Tj0rnuvik on Faroe Islands is heavily debated -These data date cultivated crops at 675-861 AD, older than first implied
Diagram showing tephra horizons from the Faroe Islands confirmed by microprobe analyses (Dugmore & Newton, 1998). Dashed lines show rhyolitic to intermediate tephra horizons and solid lines show basaltic horizons. Uncertain ages for the L 3574 and Mjauvtn tephras are indicated by slanted lines.
Jiang et al., 2001
Diatoms prefer specific environments-Diatom type is closely correlated with environmental variables-SST (summer sea-surface temp), WST (winter “”), WD (water depth), WSS (winter sea-surface salinity)
Diatom assemblages: I. Sea-ice assemblage, II.Cold-water, III. Mixing, IV. Coastal, V. Warm-water.
Giraudeau et al., 2000
Coccoliths and ocean currents
Core location and winter surface currents: NAC = North Atlantic Current
bulk coccolith concentration
sortable silt mean size
total CaCO3 wt% and coccolith CO3
Distinct cooling events at 11.2 and 6 ka:Due to onset of NAC in response to solar insulation and waning of Laurentide ice sheet.
Glaciers: some pics and terminology
Everest & Bradwell, 2003
Terminal moraine complex
500 m from clean ice snout
Terminal moraine with pools containing rockflour. Rockflour = finely ground rock produced by glacial abrasion (AKA glacier meal).
More on glaciers, geomorph, how are rocks deformed beneath a glacier?
Benn, 1995
Squeeze ridges, fluted moraines.
Deformation of rocks from glacial flow.
Glacial striae.
Glacial deposits
Kruger & Kjaer, 1999Kotlujokull, south Iceland.
Knudsen, 2002
Glacial Lakes: I
Where is the fluvial unit?
Glacial Lakes: II
Climbing ripple unit at Lindur.
Mass flow unit.
Iceberg dump & drop structures, dropstones. Stick is 3m.
Laminated sand unit drapes over valley sides. Fine couplets of silt and VFS. Proximal? Distal?
Knudsen, 2002
Gorge length reveals headward retreat of waterfall upcanyon.
Glacial Lakes: III
Conceptual model showing the relationship between coarse- and fine-grained sediments of the Jokuldalur infill (rain-out VS. bypass). Controlled by nature and timing of glacier retreat. Diagram not to scale.
Diverse sedimentologic character observed over short distances.
Knudsen, 2002
Glacial outwash plains: sandur
Facies map of distal outwash plain and coast of Skeidarrsandur. Barrier spits and offshore depositional platform widen to the west.
Hine & Boothroyd, 1978
Eolian cross-stratification.
Sandur (pl. sandar) = glacial outwash plain formed from meltwater sediments at glacier terminus.
Maizels, 1989
Western edge of Skeiðarársandur shows the characteristic diffuse drainage channels of a sandur.
Supraglacial Jokulhlaups I: Landscapes &Structures
Russell et al., 2001View down ice-walled channel May 1997, View down ice-walled channel in 1999.
Gravel pillar structures cutting throughfiner-grained sedimentary structures.
Convolute bedding showing synclinal gravel structures
-analogous to bedrock confined river channel -flow structures-loading-water escape-infer style and rate of deposition
Supraglacial Jokulhlaups II: Outcrop
Russell et al., 2001“Deep-water” rain out suspension rhythmites, circular flow.
Scour, erosion, cross-stratification, rip-up clasts.
Russell et al., 2001
Supraglacial Jokulhlaups III: GPR facies, supraglacial deposits
Turbidites
Lacasse et al., 1998
Volcaniclastic sediment gravity flow deposits.
The Iceland Basin bathymetry with the high and low areas which control the flow path of the Iceland–Scotland Overflow Water across the basin and the turbidity currents across the continental rise.
Hummocks: how are they formed here?
Vogt, 1997
-Previously interpreted as bottomcurrent reworking-Sandy clays VS.biosiliceous oozescreates a density inversion
Contourites
McCave et al., 1980
-12 to 23 cm/sec- mixing within upper 30-90 m of sediment-Extensive reworking-Well sorted, winnowed and cross-bedded-Sharp to rounded ripple crests indicate variability in cohesion
Thank you!
NSF GRFP