Only two drill cores are available from the Reykjanes high-temperature field in SW-Iceland, on the Reykjanes Peninsula, which is a direct continuation of the Mid-Atlantic Ridge on land. The coring activity was funded by the International Scientific Continental Drilling Program (ICDP) in conjunction with the Iceland Deep Drilling Project (IDDP). The spot core from RN-19 was drilled at 2245-2248 m (2.97 m) in 2005. The spot core from RN-17 was drilled in a side tracked well (RN-17B) at 35° angle at depth of 2798.5-2807.5 m (9.3 m) in 2008. The true vertical depth from the surface above the RN-17B core is approximately at 2560-2570 m.

This paper describes the depositional environment of these deep drill cores. The RN-19 core is composed of a homogeneous coarse-grained dolerite that is relatively unaltered, and is interpreted to come from a sheeted dyke complex. Only narrow chlorite-acinolite veins are present in that core. On the other hand, the RN-17B core is composed of a shallow marine volcanoclastic/hyaloclastite breccia containing lenses of fine-grained tuffaceous sediment, which appears to contain remnants of shallow marine fossils (shell fragments). However, lower greenschist facies hydrothermal alteration and rock replacement by secondary minerals is almost complete, preventing study of the apparent fossil remains in the core. In spite of the great depth of the core in this well, the abundant vesicles in the volcanoclastic rock, as well as the extent of pillow lava formations suggest a relatively shallow marine depositional environment.

Based on the depth of these shallow marine sedimentary sequences, we estimate that rocks of the Reykjanes geothermal field have been subsiding at a rate of some 6 mm/year over the last 500.000 years, yielding a ratio of 1/3 subsidence/spreading rate on this part of the landward extension of the Mid-Atlantic Ridge.

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