Constructing tephrochronologies covering periods of landscape instability

2026/04/22 by Nick A. Cutler, Richard Streeter, William Hutchison +1 · 1 voice
Earth and Planetary Sciences · Environmental Science · #Geology and Paleoclimatology Research #Plant Water Relations and Carbon Dynamics #Tree-ring climate responses

paper · doi:10.1016/j.quageo.2026.101745

openalex publication_date 2026/04/22 · openalex created_date 2026/04/23 · openalex updated_date 2026/07/22

Abstract

Tephrochronology is an established technique for dating and correlating sedimentary sequences, but it can be challenging to deploy when tephra layers are mixed, i.e., when they contain tephra from different sources. Mixing of tephra deposits is likely a ubiquitous process in regions with high levels of volcanic activity and dynamic landscapes, but remains understudied: to our knowledge, no one has systematically analysed the frequency and degree of mixing in terrestrial sedimentary sequences, nor assessed the reliability of a mixed, visible tephra layer as a chronostratigraphic horizon. We addressed this knowledge gap by quantifying tephra mixing in sedimentary sections encompassing the Landnám tephra layer (LTL), a key chronostratigraphic horizon in Iceland. We logged nine stratigraphic profiles in three sites associated with the earliest settlement of Iceland and analysed the major element chemistry of 44 tephra layers (957 shards in total). We used a statistical technique (clustering) to identify distinct geochemical populations within each layer and made novel use of Shannon’s diversity (entropy) index ( H ˊ) to estimate the degree of mixing. Our analysis showed that 43% of the tephra layers were mixed to some degree and around a quarter exhibited marked geochemical heterogeneity. We attributed the mixing to human activities associated with Norse colonisation of Iceland, which created a mixture of unstable surfaces (where tephra could be remobilised) and stable surfaces (where tephra layer formation was possible). We propose a model for the formation of mixed tephra layers. Our work has implications for the dating of the earliest phases of human colonisation in Iceland and the use of tephrochronology in areas — both proximal and distal to tephra sources — where conditions promote surface instability.

Citations

• Vegetational response to human colonisation of the coastal and volcanic environments of Ketilsstaðir, southern Iceland
• Katla volcano, Iceland: magma composition, dynamics and eruption frequency as recorded by Holocene tephra layers
• Ash layers from Iceland in the Greenland GRIP ice core correlated with oceanic and land sediments
• The Peopling of Iceland
• Tephrochronology and the late Holocene volcanic and flood history of Eyjafjallajökull, Iceland
• A catalogue of major and trace element data for Icelandic Holocene silicic tephra layers
• Correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods: Review and evaluation
• The onset of the palaeoanthropocene in Iceland: Changes in complex natural systems
• Identification and definition of primary and reworked tephra in Late Glacial and Holocene marine shelf sediments off North Iceland
• 1000 years of environmental change and human impact at Stóra-Mörk, southern Iceland: A multiproxy study of a dynamic and vulnerable landscape
• Geochemistry of historical-age silicic tephras in Iceland

Discussions

• A new paper: "Constructing tephrochronologies covering periods of landscape instability" doi.org/10.1016/j.qu... It turns out that interpreting tephra layers can be complicated when a) volcanic erup [bsky, 0 points, 0 comments]