Tephrochronology of the North Atlantic region: linking marine and ice-core records spanning the last glacial cycle

• Tephrochronology has recently become a key technique for the precise correlation of Late Quaternary records in the North Atlantic region. Recent developments have extended the geographical distribution of significant tephra strata and, as a result, have established important tie-points between diverse palaeoarchives during the last glacial cycle. We will report on the work being undertaken to identify, date and geochemically characterise tephra horizons in marine cores from the Faroe Islands region and the Greenland ice-cores. Four ash zones including the widespread North Atlantic Ash Zone II (NAAZ II; 52-53 ka BP) and three mainly basaltic ash zones here referred to as the Faroe Marine Ash Zones (FMAZ) I (ca 15.4 14C ka BP), II/Fugloyarbanki Tephra (ca 23-24 14C ka BP) and III (ca 33 14C ka BP) occur in several cores from the Faroe Islands margin. Detailed investigations of NAAZ II in high-resolution cores show that two separate layers can be distinguished; a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra, separated by as much as 1500 years. FMAZ III is a thick and relatively scattered basaltic ash zone found in three cores from the Faroe area. It has not been directly dated, but extrapolation of AMS radiocarbon dates from all cores suggest an age of c. 33,000 14C years BP, slightly above Heinrich layer 4, and close to the onset of GIS8. An equivalent tephra was recently identified in NGRIP where it is situated right at the peak of GIS8. The FMAZ II/Fugloyarbanki tephra occurs in all analysed marine cores in the Faroe Islands region and in NGRIP. It is dated to 26,740 ± 390 b2k according to the Greenland Ice Core Chronology (GICC05). This tephra falls right after the warmest peak of GIS3 in both the NGRIP and marine records and provides another important tie-point. Other tephras identified within the ice-core material have revealed the presence of previously unreported tephra horizons of Icelandic origin, thus, adding considerably to our knowledge of Icelandic volcanism during the last glacial cycle.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Quaternary geology

Kvartärgeologi

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