Accurate Jurassic-Cretaceous Ammonite Age Assessment in the North-East Greenland Frontier Exploration Area
Department of Stratigraphy, The Geological Survey of Denmark and Greenland (GEUS), Copenhagen K, Denmark
The recent assessment of the petroleum potential of NE Greenland in 2007 (by USGS) suggests a large exploration potential on the NE Greenland Shelf. Accordingly, the region experiences a marked increase in interest from the industry. The offshore geology is, however, poorly known due to difficult data acquisition condition. The onshore geology is thus an important analogue for improved prediction based on the offshore, very limited seismic data set. A major petroleum-industry sponsored study, launched in 2007/2008 provides data that updates and expands the present understanding of the petroleum geology of NE Greenland Shelf.
The geology of E and N Greenland is mapped to some detail, but though many studies on sedimentology and stratigraphy have focussed on the Upper Palaeozoic - Palaeogene succession, the interval is not fully elucidated and basic information as lithostratigraphy and biostratigraphic dating can be improved.
Ammonites are of major importance in the Mesozoic stratigraphy of E and NE Greenland, and provide high resolution dating, among the best obtainable from fossils. A Jurassic-Cretaceous ammonite zonation has been established over the last half century and has developed into a highly powerful biostratigraphic tool closely correlated with palynostratigraphy, which is more applicable in conventional drillings. Especially in the Jurassic - Lower Cretaceous, the ammonites provide an excellent stratigraphic resolution, and the zonation forms a firm chronostratigraphic framework for detailed sequence stratigraphic interpretations. In contrast, much work remains in the Upper Cretaceous succession.
In outcrops, ammonites are mostly recovered from sandstones and concretions because weathering shale may disintegrate completely. Conventional drilling destroys ammonites but in cores they may be abundant. Finds of more than forty ammonites in a recently drilled shallow core through the Katedralen Member (Upper Jurassic Kimmeridge Clay analogue) in E Greenland, accurately date the best interval of potential source-rocks and provide a solid stratigraphic frame for lateral correlation of the most promising succession throughout the onshore basins. The ammonites are flattened imprints and/or pyritised in the compressed black shale but morphological characters for identification are excellently preserved. Thus, the ammonites provide the best basis for the interpretation of the geochemical data (e.g. TOC, Rval and GCMS), petrophysic logs and sedimentology.
AAPG Search and Discover Article #90096©2009 AAPG 3-P Arctic Conference and Exhibition, Moscow, Russia