PhD defence: Jeppe Joel Larsen

Jeppe Joel Larsen defends his thesis:

Lateglacial and Holocene tephrostratigraphy in Denmark - Volcanic ash in a palaeoenvironmental context

Supervisor

Professor Nanna Noe-Nygaard, IGN

Assessment committee

Professor Flavio Anselmetti, University of Bern
Professor Siwan Davies, Swansea University
Associate Professor Lars Nielsen (chairman), IGN

Abstract

Deposit of volcanic ash (tephra) may be used for precise correlation of sedimentary successions, as it is deposited instantaneously, in a geological perspective. Each tephra horizon has a distinct geochemical composition and deposition of tephra may occur over large areas and in different depositional environments such as in lakes, the ocean or on ice sheets. Thereby it is possible to precisely correlate palaeoenvironmental proxy-data, over large distances. In addition these tephra horizons may also yield additional chronostratigraphical information to investigated sites, if they previously have been precisely dated.
This study is the first comprehensive investigation of Quaternary distal tephra horizons in Denmark. Here sediment cores from several Danish lakes and bogs have been studied for distal tephra horizons and palaeoenvironmental changes, spanning the Lateglacial and Holocene periods. All observed tephra horizons are of Icelandic origin, except for the c. 13,000 yr old Laacher See Tephra, originating from the German Eifel area. A 294±114 yr older and smaller precursor to the Laacher See Tephra, with similar geochemistry, is also observed. If this precursor is genuine, it will have implications for the understanding of the eruption-dynamics of the Laacher See volcano, but it may also add to future investigations of the warm Allerød Interstadial.
Correlation of the Younger Dryas Vedde Ash, from this study, to lake Kråkenes in Norway suggests a timetransgressive climatic change during the mid-Younger Dryas. Correlation of all early Preboreal Hässeldalen Tephra sites in southern Scandinavia and northern Germany also indicates different environmental responses to major climatic changes within the lakes around the Glacial/Interglacial transition c. 11,700 years ago.
Furthermore, the Fosen Tephra (c. 10.2 ka), and the Hekla-3 and -4 Tephras (c. 3.1 and 4.4 ka) have been identified along with several unidentified tephras.

The thesis is available at the PhD administration office 04.1.409