Coop Phase I - Crustal Onshore-Offshore Project
The five-year Crustal Onshore-Offshore Project (Coop) is an integrated data acquisition and interpretation project established to study the onshore-offshore relationships in the northeastern North Sea and Møre-Haltenbanken area. The Coop Phase I Report summarises the results from the Norwegian North Sea and western Norway. New aeromagnetic, gravity and petrophysical data as well as heat flow data have been acquired. All new data were compiled with existing data. Information on mainland basement structures, deep weathering and heat production has been extrapolated to the offshore region. We conclude that the Norwegian strandflat is an exhumed weathered and peneplaned surface of Late Triassic to Early Jurassic age that has been modified and levelled during Pleistocene erosion. This surface was preserved beneath Late Jurassic and Cretaceous strata until the Neogene. Support for this conclusion comes from the AMAGER mapping and the occurrence of a relatively flat and gently westward-dipping top of basement beneath the Jurassic sedimentary rocks close to the coastline. The heat generation of the mainland basement rocks has been calculated from the chemical analyses of the U, Th and K contents in c. 2000 bedrock samples and airborne radiometric measurements along the coast of western Norway. The heat generation varies with almost one order of magnitude. Temperature logging has been carried out in Fyllingsdalen (Bergen) and Ullandhaug (Stavanger). The heat flow was calculated based on temperature logging and thermal conductivity data. The observed thermal gradients are 16.5 °C/km in Fyllingsdalen and 13 °C/km at Ullandhaug. Tentative palaeoclimatic corrections for Fyllingsdalen and Ullandhaug vary from 15 to 30 mW/m² (i.e., 20-40 % of the original heat-flow values). Two different scenarios show corrected heat-flow values which vary from 43 to 51 mW/m² at Ullandhaug and from 59 to 74 mW/m² in Fyllingsdalen. The increased heat flow in Fyllingsdalen is attributed to high values of radiogenic heat production within the Løvstakken granite. Crustal models of the Norwegian North Sea and western Norway have been established from gravity, magnetic, seismic, well log and bedrock mapping data. By attributing thermal properties (e.g., radiogenic heat production and thermal conductivity) to the individual basement bodies we have calculated the heat flow from the basement into the sedimentary basins. The observed and modelled heat flow is strongly controlled by the lithology and structures in the crust. The temperature at a depth of 5 km in the Egersund and Stord basins is, for example, estimated to c. 155 °C and 170 °C, respectively. A map of Quaternary sand channels in the Norwegian North Sea has been produced. Plans for Coop Phase II are summarised at the end of the report.