Tephrochronologie

Tephrochronology is a geochronological and stratigraphic method that uses volcanic ash layers, or tephra, as time markers to date and correlate sedimentary sequences and archaeological contexts. By identifying and dating individual tephra horizons, researchers can synchronize records from different places and reconstruct past events with improved temporal precision.

The core principle is that tephra produced by a single eruption has a distinctive geochemical fingerprint. Glass shards and minerals in the ash are analyzed for major and trace element composition, often with electron microprobe or laser ablation techniques, to produce a fingerprint that can be matched across locations. Once a tephra layer is recognized in multiple outcrops, cores, or sites, it serves as a Correlation Horizon, allowing the relative timing of different records to be aligned.

Absolute age control for tephrochronology comes from dating the eruption that produced the tephra (for example, Ar-Ar or K-Ar dating on sanidine or other minerals) or from radiocarbon dating of organic material within or immediately adjacent to the tephra layer. Tephra layers can also be tied to well-dated volcanic events or eruptive catalogs, providing an absolute time framework for a regional to hemispheric scale.

Applications include reconstructing past climate and environmental change, dating sediments, ice cores, and marine cores, and providing chronological anchors for archaeological sites. Limitations include bioturbation or reworking of ash layers, non-preservation of tephra, and potential geochemical similarity among different eruptions, which can complicate correlations.