International Geologiical Congress - Oslo 2008


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AAA-01 Paleogeographic evolution of the Arctic region during the Phanerozoic - Part 1


Late Neoproterozoic - Cambrian palaeogeography of northern Greenland: Early evolution of the Franklinian basin


Jon Ineson, Geological Survey of Denmark and Greenland (Denmark)
John Peel, Uppsala University (Sweden)
Finn Surlyk, University of Copenhagen (Denmark)


Although the broad framework of Franklinian Basin evolution in northern Greenland was unravelled in the 1980s, the early history of the basin was less well understood. Fieldwork over the last decade, focussed on the upper Neoproterozoic - Cambrian, has better constrained and areally extended our understanding of the early palaeogeographic evolution of the basin. Four discrete stages are recognized.
1. The earliest stage (latest Neoproterozoic - earliest Cambrian), recorded by the Skagen Group and the Portfjeld Formation, defines a geographically restricted elongate depocentre in northernmost North Greenland in which at least 1 km of mixed carbonate-siliciclastic sediments accumulated. These are of marine shelf origin, though the lower levels of this succession are not seen, and are of late synrift to early postrift origin, mainly deposited prior to the differentiation of shelf and deeper-water basin. The youngest strata, however, record the gradual development of a rimmed carbonate shelf, facing a deepening basin, and the initial onlap of marine carbonates cratonwards.
2. A karstic unconformity caps the Portfjeld Formation and is associated with a megabreccia deposit and cyclic siliciclastic intrudites/extrudites in central and eastern North Greenland respectively. This mid-Early Cambrian regional uplift event with accompanying seismicity is considered to represent the break-up unconformity, marking the crustal response to the onset of spreading in the Franklinian rift.
3. The late Early Cambrian was characterised by marked transgression, siliciclastic shelf sediments (Buen Formation and western correlatives) onlapping at least 200 km cratonwards of the early rift deposits. Although including a eustatic component, this transgressive episode also records post-drift thermal subsidence, marked subsidence of the deep-water basin and down-flexing of the outer shelf reflecting increased flexural rigidity with age and cooling after rifting.
4. From the late Early Cambrian to the earliest Ordovician, northern Greenland was influenced both by subsidence of the Franklinian passive continental margin and by an uplift event associated with the Caledonian margin. Carbonate sedimentation dominated on the shelf and a flat-topped platform (Ryder Gletscher, Brønlund Fjord and Tavsens Iskappe Groups) prograded stepwise northwards. Sequence stratigraphic analysis across northern Greenland demonstrates the control on platform evolution of both eustasy and successive northward-stepping, down-to-basin faults - probably the consequence of the competing Franklinian and Caledonian stress regimes. Shelf-basin differentiation was resolved in the latest Cambrian at an important E-W structural feature, the Navarana Fjord lineament, which continued to control the position of the shelf edge throughout the Ordovician and the Early Silurian.


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