Mapping of volcanic facies variations onshore West Greenland Asger Ken Pedersen Geological Museum University of Copenhagen

The Nuussuaq Basin in central West Greenland Sediments: Mid Cretaceous to Palaeogene Volcanic Formations: Main stage in Paleocene Late stage in Eocene

Plateau basalt lava stage. Lavas progress far beyond basin margin into graiss hinterland Lava-infilling of lakes, subaqueatic lava flows and invasive lavas (sills) Lava plateau expands. Formation of large Lake complexes, infilling by hyaloclastites, Abundant eruption sites on land and in the Lakes. Lava plateau expands, narrowing of marine basin, large scale infilling by hyaloclastites Volcanism starts in marine basin. Volcanic island stage: Lavas, hyaloclastites, mass flows

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Five sections through the Nuussuaq Basin Nuussuaq north coast 2006 Five sections through the Nuussuaq Basin constructed 1993 and 2001 to 2006 Central Nuussuaq 2002 Nuussuaq south coast 1993 Central Disko 2005 Disko south coast 2003

Photos taken from helicopter, boat and fixed-wing plane. Construct multi-stereo panels Combine with aerial photographs Product: Geological maps Large sections Detailed sections Structural measurements The sections compile Information from Field work Petrology Geochemistry Palaeomagnetism Palaeontology Sedimentology Multi-model photogrammetry: Photos takes with stereo-overlap using calibrated small-frame cameras.

W E Section 1: South coast of Nuussuaq, 1.20 000, 80 km profile length.

W E Section 2: Aaffarsuaq valley in central Nuussuaq, 1:20 000, 110 km profile length

W E Section 3: The south and south-west coast of Disko, 1:20 000, 130 km profile length

W E Section 4: Across central Disko, 1:20 000, ca. 110 km profile length

Topics to be presented Subaerial lava flows Infilling of marine basins Basin subsidence and early volcanic aggradation Large plateau lavas and their interaction with sediments The early volcanic island stage, mass flows and conglomerates Significance of the volcanic feeder systems

Picrite lavas on gneiss in central Nuussuaq

The transition between the Vaigat Formation (picritic pahoehoe flows) and the Maligât Formation (thick plateau basalts) on Nuussuaq

Vaigat Formation: Lavas and hyaloclastites cover Cretaceous and Palaeogene sediments

W E

Pahoehoe lava flows enter the sea at the south coast of Hawaii Hawaii,USGS

Facies transition at Nuuk Killeq, Nuussuaq Lava Hyaloclastite Facies transition at Nuuk Killeq, Nuussuaq

Nuussap Qaqqarsua

Magnetic transition zone ca 5000 y Chron 26R Magnetic transition zone ca 5000 y Nuussap Qaqqarsua

Large plateau basalts from the Maligât Formation at Giesecke Monument, Nuussuaq

Skarvefjeld east of Qeqertarsuaq, Godhavn. 3 3 2 1 1 1 1 Skarvefjeld east of Qeqertarsuaq, Godhavn. 1.Subaqueous lavas 2: hyaloclastites 3: Subaerial lavas

3 2 1

Subaqueous lava flow who has started to burrow into Paleocene mudstone, Maligât Formation, Disko

On top subaerial lava flows, below lava flows who have continued eastwards as ”sills” (invasive lavas), eastern part of the sediment basin

Drill cores and profiles in Anaanaa Member Heavy colours: lava series, light colours: hyaloclastites Max duration of A Mb ca 300 000 y, chron 27n

Lipman et al. 2006

Early picritic eruption site on the sea floor. It is a pillow cone Anaanaa Member in the Vaigat Formation on Nuussuaq

Clast supported conglomerate formed by erosion of lava flows at the coast of small lava island. The conglomerate is now oil-saturated. Early Vaigat Formation at Sikillingi on Nuussuaq

Large mass flow at Nuusaq, Early Vaigat Formation Large fragment with several subaerial lava flows Mass flow A more than 20 m sized fragment with several lava flows, who has slided to a palaeodepth of more than 200 m from the old shore zone. Large mass flow at Nuusaq, Early Vaigat Formation

Eruption sites Subaerial on the lava plain On the sea or lake floor Eruptions channeled into older fault structures Phreatic craters

Eruption site in central Nuussuaq Picrite crater Feeder dyke Eruption site in central Nuussuaq

Two picrite crater sites within the upper part of the Vaigat Formation on Nuussuaq

Thin subaerial picritic lava flows Hyaloclastite with numerous thin picritic feeder dykes Subaqueous eruption site within a large lake

Subaqueous eruption site Thin picritic lava flows Thin feeder dykes Subaqueous eruption site

Picritic lava flows Hy Subaqueous Eruption site Several hundred metres deep lake being filled by hyaloclastites derived from lava flows and by subqueous eruption sites

Large fault at basin margin in central Nuussuaq Gneiss

Central Nuussuaq just west of a large marginal fault zone. Foreset-bedded picritic hyaloclastites from the Vaigat Formation covered by lava flows Central Nuussuaq just west of a large marginal fault zone.

Southern part of the Ilugissoq graphite andesite volcano Erosion on top of cone Southern cone Subaerial graphite andesite tuff Pi Lava Pi Hy Submarine graphite andesite tuff Pi Hy Southern part of the Ilugissoq graphite andesite volcano

What can you learn by studying the Nuussuaq Basin in West Greenland A wide range of subaerial basalt lava features Volcanic infilling patterns in passive and dynamically active marine and lacustrine basins. The morphology and distribution of basaltic eruption sites. Well exposed examples of interaction between basalts and unconsolidated sediments. Invasive lavas. Large and coherent exposures of a sedimentary and volcanic basin and its margin.