Samarium-neodymium isotope stratigraphy of the Lunde and Statfjord Formations of Snorre Oil Field, northern North Sea

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Abstract
Two sequences of fluviatile sediments from Snorre Oil Field are investigated by the Sm-Nd isotopic method. The results illustrate distinctly different source areas for the (Upper Triassic) Upper Member of the Lunde Formation and for the (Lower Jurassic) Statfjord Formation. The Lunde Formation has Sm-Nd provenance ages mainly in the range 1500 to 1700 Ma, which is not diagnostic of a specific source area. The Statfjord Formation has provenance ages in the range 1700 to 2150 Ma. This is old within the context of source areas in the hinterland of the northern North Sea and provenance partly from the Archaean Lewisian shield to the northwest is suggested. Intensive sampling through the Statfjord Formation in one well illustrates that the provenance ages evolve systematically with time. The pattern provides a detailed record of how source areas evolved during deposition of these strata. The possibility is recognized of correlating changes or trends in provenance between wells. The data also suggest that Sm/Nd ratios and isotopic compositions of these rocks are not significantly fractionated between fine- and coarse-grained sediments by mechanical or diagenetic processes.