Applications of Elemental Geochemical Data Triassic/Jurassic Sequences of the Barents Sea

Timothy Pearce

Pearce, T.J. Morgan, T. & Martin, J.H. Triassic to Middle Jurassic, deltaic to shallow marine sequences from the Western Barents Sea basin, are increasingly being targeted for hydrocarbon exploration. Reservoir quality is strongly influenced by provenance, lack of well control, marked lateral facies variations and multiple sediment input points. All these contribute to difficulties in correlation and mapping. A major chemostratigraphical study has been undertaken to improve the correlation of Barent Sea Triassic to Middle Jurassic sequences and to aid in reconstructing the history of sediment input into the basin. This paper highlights how elemental data can be used to calculate mineralogical logs for the entire Triassic/Jurassic, which can be then used to improve the interpretation of petrophysical log responses. The succession has been subdivided into five Chemostratigraphic Megasequences (BMS0-BMS4), which are further divided into Chemostratigraphic Sequences (BCS0 to BCS10). These sequences are further divided and correlated within sub-basins such as the Nordkapp and Hammerfest Basins. The chemostratigraphic zonation is largely based on fluctuations in element concentrations that reflect changes in the abundance of feldspar, clay minerals, heavy minerals and opaque minerals (corroborated by data acquired via mineralogical analyses). These reflect variations in provenance and palaeoclimate. This study shows chemostratigraphy is a reliable tool for the regional correlation of the Triassic - Lower to Middle Jurassic sequences of the Western Barents Sea area. Furthermore, the technique can be used to revise the existing lithostratigraphy, highlighting the potential of chemostratigraphy as a standard tool for correlation of these successions. In addition to chemostratigraphic correlation, the geochemical data and selected mineralogical data are used to assist modelling changes in provenance, palaeoenvironment and facies. By mapping lateral variations in the values of selected element ratios, sediment dispersal patterns can also be developed. When sediment dispersal maps are combined with new isopach data, geochemical/mineralogical provenance indicators and sand:shale ratios, sediment input points along basin margins can be identified and source areas position inferred. Geochemical data has also converted mineral abundances via mineral modelling software, enabling mineralogical logs to be constructed for the entire Triassic / Jurassic succession. XRD mineralogical analyses validate this. In summary, elemental geochemical data not only represents an important interpretative resource for correlation and provenance mapping, but also in modelling petrophysical log responses and rock properities too. This approach could be employed on equivalent sequences from the Eastern Barents area, the Russian Arctic, plus similar Triassic sequences in the Canadian Arctic.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013