Lotte Melchior Larsen
in collaboration with Asger Ken Pedersen and Gunver Krarup Pedersen (Univ. Copenhagen) and Keld S. Dueholm (Techn. Univ. Copenhagen), as well as with several departments within GEUS.
Geology of the Nuussuaq Basin.
: Cretaceous sediments,
: Paleocene sediments,
The south coast of the Nuussuaq peninsula, showing Cretaceous - Paleocene sediments overlain by 300 m of foreset-bedded hyaloclastites followed by c. 500 m of subaerial picritic lava flows. The mountain peak is c. 1400 m high.
The Nuussuaq Basin extends onshore from Disko to Svartenhuk Halvø and is part of a series of linked basins extending offshore along the west coast of Greenland. The Nuussuaq basin was a depositional area for clastic sediments from at least the mid-Cretaceous to the Paleocene. Volcanism started in the Paleocene. Most of the voluminous onshore volcanics were deposited in a short period at c. 61-59 Ma. Younger volcanics occur sparingly onshore and are probably more extensive offshore.
The volcanic rocks erupted into a marine embayment that was gradualy filled out laterally by progradation from west to east. The net result is a very complex facies architecture of the lavas, hyaloclastites and contemporaneous sediments. Excellent exposures in>
1000 m high cliffs are onshore analogues to seismic sections on the NW European shelf, sharing many features with these.
The oldest volcanics are voluminous picrites that formed from very Mg-rich and very hot magmas. Some of the magmas reacted with coal-bearing sediments and became so reduced that they precipitated native iron. The reactions also led to formation of Cu- and Ni-depleted lavas, and accumulations of these elements and PGEs are inferred to be present at depth. Further, oil seeps in the volcanics are widespread.
Recent work is centred in the Disko-Nuussuaq area which is covered by 7 geological maps at scale 1: 100 000 of which 6 are published and one is being mapped. In addition, five 80-120 km long vertical W-E sections through the basin have been compiled photogrammetrically at scale 1: 20 000. Three of these sections are published as 'geological sheets' equivalent to map sheets, while two are in production.
Present studies are concerned with stratigraphic and structural relations, and geochemical and petrological analysis and interpretation. The work is focussed on production of a synthesis of the volcanic development in the Disko-Nuussuaq area, to be published in the GEUS Bulletin Series.
Larsen, L.M. & Pedersen, A.K. 2000. Processes in high-Mg, high-T magmas: evidence from olivine, chromite and glass in Palaeogene picrites from West Greenland. Journal of Petrology 41, 1071-1098.
Pedersen, A. K., Larsen, L. M., Riisager, P. & Dueholm, K. S. 2002. Rates of volcanic deposition, facies changes and movements in a dynamic basin: the Nuussuaq Basin, West Greenland, around the C27n-C26r transition. In: Jolley, D. W. & Bell, B. R. (eds), The North Atlantic Igneous Province: stratigraphy, tectonics, volcanic and magmatic processes. Geological Society (London) Special Publication 197, 157-181.
Larsen, L. M., Pedersen, A. K., Sundvoll, B. & Frei, R. 2003. Alkali picrites formed by melting of old metasomatised lithospheric mantle: Manîtdlat Member, Paleocene of West Greenland. Journal of Petrology 44, 3-38.
Pedersen, A. K., Larsen, L. M., Pedersen, G. K., Heinesen, M. V. & Dueholm, K. S. 2003. Geological section along the south and south-west coast of Disko, central West Greenland. 1:20 000 coloured geological sheet. Copenhagen: The Geological Survey of Denmark and Greenland.
Pedersen, A. K., Larsen, L. M., Pedersen, G. K. & Dueholm, K. S. 2005. Geological section across north central Disko from Nordfjord to Pingu, central West Greenland. 1:20 000 coloured geological sheet. Copenhagen: The Geological Survey of Denmark and Greenland.
Larsen, L. M., Pedersen, A. K. & Pedersen, G. K. in press. A subaqueous rootless cone field at Niuluut, Disko, Paleocene of West Greenland. Lithos.
For maps and other geological sections, see pp 36 (69-70 deg. N) and 41 in