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Sand Provenance Analysis on and around Greenland

Christian Knudsen
Geological Survey of Denmark & Greenland, Copenhagen, Denmark.

To facilitate interpretation of sand dispersal systems in sedimentary basins around Greenland, a large number of stream sediment and till samples have been analysed in combination with sandstone samples on- and offshore East and West Greenland, Canada and Faroe Islands. The aim of stream sediment and till analysis is to fingerprint the potential source areas for clastic material in the sedimentary basins.

The techniques used are: A) Computer Controlled Scanning Electron Microscopy (CCSEM), which automatically measures and stores both grain-size and chemical compositional data for heavy minerals (ca. 1200 grains per sample). B)Laser Ablation ICP-MS, where detrital zircon ages are obtained from U/Pb isotope measurements.

The composition of the heavy mineral fraction derived from CCSEM analysis is used to classify the minerals and compute the modal compositions. The mineral chemistry is further used to evaluate systematic changes in garnet composition between regions when regarded as source of sand (stream sediment and till) or in sandstones when the provenance is evaluated. Compositional variations in other heavy minerals are used to evaluate sediment maturity and diagenetic features.

Stream sediments in Central West Greenland show that ca. 85 % of the zircons have an age of ca. 2.8 Ga with minor zircon populations of ca. 3.6 Ga and 1.9 Ga. The provenance signature of the Cretaceous deltaic sandstones onshore in the Disko Bay area broadly mimics that of the entire Central West Greenland area, suggesting that the river systems depositing these sediments were draining a very large area from the interior part of Greenland. In an offshore well in Greenland waters, the pattern is very similar but with two small but distinctive ca. 1 Ga and 1.6 Ga age peaks, suggesting sediment influx from the south. Paleocene sandstones on Svartenhuk Peninsula to the north of Disko Bay, show a change from this zircon distribution in the Cretaceous to a unimodal 1.9 Ga age population, indicating a change to a sediment supply from very local source. Wells in the Labrador Sea show very diverse patterns, where some are very simple with a distinctive Archaean or Paleoproterozoic probably local source, whereas others are very complex and are probably remotely sourced with zircon ages ranging from Early Archaean to Mesozoic.

In South-eastern Greenland the knowledge of the age distribution of detrital material is based on analysis of Cretaceous and Paleogene sandstones from the Kangerlussuaq area. The main zircon populations in this area are Archaean and are characterised by having multiple peaks at ca. 2.7, 3 and 3.2 Ga. Apart from these Archaean zircons, Paleoproterozoic and Mesoproterozoic zircons occur locally in the area, suggesting that the source of these sandstones was changing.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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