Icy Hott Geology: A suite of Iceland sediments A literature review compiled by Jon (J. R.) Rotzien Presented to The Stanford Alpine Project February 13,

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