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Depositional environment and apparent age of the Fauske carbonate conglomerate, North Norwegian Caledonides

Melezhik, V.A., Heldal, T., Roberts, D., Gorokhov, I.M., and Fallick, A.E. (2000) Depositional environment and apparent age of the Fauske carbonate conglomerate, North Norwegian Caledonides. Norges Geologiske Undersokelse Bulletin, 436 . pp. 147-168. ISSN 0332-5768

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Abstract

The Fauske conglomerate represents a rather rare case of a monomict carbonate conglomerate in the Late Neoproterozoic to Silurian, lithostratigraphic successionsof the Norwegian Caledonides. Lithological varieties of this conglomerate unit from the Lovgavlen quarry have a highly decorative quality and are well known in both domestic and international markets under trading names such as 'Norwegian Rose', 'Jaune Rose', 'Norwegian Green', 'Antique Fonce' and 'Hermelin'. The Fauske conglomerate is a 60m-thick unit which rests on either dark grey ('blue') calcite marbles or white dolomite marbles. The latter are jointed and fragmented, and also appear as sedimentary collapse-breccia and debris where they are in direct contact with the conglomerate. Although the Fauske conglomerate has been involved in two main pulses of Caledonian tectonic deformation, which produced an early, syn-metamorphic flattening of the clasts and a later folding or rotation of clasts into a spaced cleavage, the overall sedimentary features are still remarkably well preserved. The Fauske conglomerate unit consists of 25 beds (5 cm to 3 metres thick) comprising landslide, carbonate debris and carbonate breccia-conglomero-breccias-greywacke lithofacies. Blocks, fragments, cobbles, pebbles and smaller clasts are mainly of white dolostone and pink, beige, white and 'blue' calcite marbles. The matrix has a granoblastic texture and similar range in lithology with variable amounts of quartz, fuchsite, sericite, muscovite and chlorite. Within the unit, an upward fining of the clasts is followed by the gradual development of calcareous greywacke layers which show both cross bedding and channelling. The depositional model involves: (i) a locally developed, tectonically unstable carbonate shelf-margin, (ii) a temporary lowering o sea level, (iii) formation of a high-relief, shore-to-basin fault scarp followed by (iv) the development of a channel, with (v) subsequent, long-distance transport of clasts of pink carbonates from the continent-basin margin,w hich were (vi) redeposited together with a carbonate debris (white dolomite and 'blue' calcite marbles) on the tectonically fragmenting edge of a carbonate shelf. Both matrix and pebbles show a similar range in isotopic values: -1.9 to +0.6 per mil (vs. PDB) for 13Ccarb and 0.70896 to 0.70946 for 87Sr/86Sr. The least altered 87Sr/86Sr (0.70896) isotopic value plotted on the calibration curve is consistent with a seawater composition corresponding to ages of 470-475, 505-510 and 520, whereas the least altered 13C carb (-0.6 per mil) value matches only 520 Ma.

Item Type:Article
Status:Published
Refereed:Yes
Glasgow Author(s):Fallick, Prof Anthony
Authors: Melezhik, V.A., Heldal, T., Roberts, D., Gorokhov, I.M., and Fallick, A.E.
Subjects:Q Science > QE Geology
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Norges Geologiske Undersokelse Bulletin
Publisher:Norges Geologiske Undersoekelse
ISSN:0332-5768
Copyright Holders:© 2002 NGU
First Published:First published in Norges Geologiske Undersokelse Bulletin 436:147-168
Publisher Policy:Reproduced with the permission of the Publisher.

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