Mineralogical, KAr and 87Sr/ 86Sr isotope studies of Holocene and Late Glacial sediments in a deep-sea core from the northeast Atlantic Ocean

Abstract

Fine-grained silicate fractions (<2 μm and 2–16 μm of Holocene and Late Glacial sediments in a deep-sea core from the northeast Atlantic Ocean (47°30′N–19°30′W) have been analysed by X-ray diffraction, KAr and Sr isotopic methods. During the Holocene, the KAr apparent ages and the 87Sr/ 86Sr ratios of the clay size minerals averaged 436 −22 +13 Ma and 0.72638 ± 0.00051, respectively. The KAr values essentially reflect the high 40Ar contribution from the detrital mica in binary smectite-mica mixtures, where smectite is a low potassium and Tertiary-Quaternary component. Higher KAr age value, up to 569 −124 +112 Ma are determined for the coarser 2–16 μm fractions which contain, in addition to mica, other detrital K-bearing phases (amphibole, K-feldspar and plagioclase). An important change in the mineralogical composition and the KAr ages is displayed by the silicate fractions of a thin layer of ice-rafted detritus, located at the termination of the last glaciation. Their KAr apparent ages increase to 773–933 Ma and correspond to an increase of the detrital supply (amphibole, mica and feldspar) from the Precambrian terrains of North America or Greenland and a dilution or a decrease of the input of basaltic material (smectite, oligoclase) from the region of Iceland.