| Term: | Marker horizon |
| Definition: | A distinctive, datable layer in ice, firn or snow; see isochrone. Ice-core stratigraphy relies on an uninterrupted series of Annual marker horizons. Volcanic eruptions and nuclear tests (see bomb horizon) yield marker horizons which allow the measurement of average accumulation rates. Marker horizons with relative dielectric constants that contrast strongly enough allow the mapping of accumulation with ground-penetrating radar. |