Paleoclimatic and paleogeographic implications of a lower Tertiary laterite (latosol) on the Iceland—Faeroe Ridge, North Atlantic region

Abstract

SummaryA lower Tertiary lateritic paleosol resting on a plateau basalt was penetrated by drilling at DSDP Site 336 on the NE flank of the Iceland—Faeroe Ridge. The sea floor at the site is about 800 m below sea level and about 400 m below the generally smooth, flat and largely sediment-free top of the ridge. The paleosol is approximately 30 m thick and can be divided into four subunits, in ascending order, basaltic rubble, red clay with altered basaltic clasts, interlayered red and pale-orange clay, and red clay. The paleosol is overlain by about 300 m of marine mudstone of medial Eocene to medial late Oligocene age that was deposited in progressively deeper water through time. About 170 m of Pliocene and Pleistocene glacio-marine sediments unconformably overlie the Paleogene deposits.In the lowest subunit of the paleosol, feldspar, pyroxene, magnetite and chlorite decrease in abundance abruptly upward and are replaced by montmorillonite and small amounts of hematite and goethite. At the contact between the second and third subunits of the paleosol, kaolinite becomes an important constituent and increases greatly in abundance upward. In the uppermost red clay subunit, kaolinite has completely replaced montmorillonite and the amount of hematite and goethite increases markedly. Within the paleosol subunits, the relative amounts of silicon, ferrous iron, magnesium, calcium, sodium, and potassium decrease upward, whereas the amounts of aluminum, ferric iron, and titanium increase upward. The red and pale-orange clay subunit contains layers characterized by veinlet-like structures alternating with more massive layers. The veinlet network is thought to have developed by segregation of ferric iron and alumina as a result of chemical weathering of basalt and possibly thin overlying airfall tuffs.The paleosol indicates a humid, warm climate and demonstrates that the Iceland-Faeroe Ridge was above sea level during the early Tertiary. The ridge formed the main part of the Thulean land bridge that permitted free migration of land mammals between North America-Greenland and Europe prior to late Eocene time. It developed during the early Tertiary break-up and rifting apart of North America-Greenland and Europe. Formerly situated over an active mantle plume or hot spot, the ridge subsequently subsided in late Eocene and Oligocene time, eventually permittingfree interchange of marine waters between the Norwegian-Greenland Sea and the North Atlantic Ocean. Basalts of the Iceland-Faeroe Ridge are simijar in age and character to other basalts of the North Atlantic early Tertiary igneous province on the Rockall and Voring Plateaus, northern Ireland, Scotland, the Faeroe Islands, East and West Greenland, and Baffin Island. Bauxite, lignite, and laterite associated with some of these basalt sequences, as well as vertebrate, plant, and microfossil remains, suggest a relatively uniform, warm, humid climate in the early Tertiary throughout the North Atlantic area and into the region of the Arctic Ocean.