Tephrochronology, lichenometry and radiocarbon dating at Gulkana Glacier, central Alaska Range, USA

Abstract

Multiple geochronologic techniques, when used in an integrated approach, provide a powerful means of deciphering the stratigraphy of Holocene moraine sequences. The Jarvis Creek Ash, deposited across central Alaska at 3650 ± 125 BP, underlies a mid-Holocene lateral moraine of the Gulkana Glacier. This tephrochronological datum provides new control on long-term Rhizocarpon geographicum growth rates in central Alaska, and suggests that this species grows at approximately 4mm per century in the central Alaska Range. Lichenometry, together with tephrochronology and radiocarbon dates from buried organic horizons, indicate Holocene advances of the Gulkana Glacier occurred c. 5700 ± 260 BP, 4100 ± 800 BP, 3600 ± 700 BP, 800 ± 125 BP and 150-200 years ago.