The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals – at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ13C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE.
The West Greenland continental margin has been the subject of petroleum exploration by companies and research projects since the 1970s and many data have been acquired since. Licensing rounds issued by the Greenland authorities in 2002 and 2004 offshore southern West Greenland resulted in company licenses which led to data acquisition and three exploration wells. The extensive new data form a basis for updated mapping by means of data, new analyses of the subsurface geology and improved understanding of the stratigraphy and the geological development. The Geological Survey of Denmark and Greenland (GEUS) has recently completed a comprehensive mapping project of the subsurface in an area covering 116 000 km2 offshore southern West Greenland (Fig. 1). The results include maps displaying large structural highs and faults, Cretaceous sedimentary basins and volcanic areas, illustrated by cross-sections through the area. A new seismic stratigraphy with eight mega-units from the seabed to the basement was also defined. In addition, studies from wells of biostratigraphy and petrology were carried out that provide important new information. The new data include extensive 2D seismic data and eight wells including the three exploration wells AT2-1, AT7-1 and LF7-1 drilled in 2011 by Cairn Energy (Fig. 1). Key results of the work are summarised below.
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