Precision and Reliability of 40Ar/39Ar Dating of Thin Tephra in Lacustrine Paleoclimate Archives
Abstract
Definitive interpretation of paleolake sediments in terms of climate history strongly depends on the availability of a precise chronostratigraphy. In East Africa, lake sediments often contain intercalated ash and pumice layers, which can usually be dated with the 40Ar/39Ar method. However, dating of tephra will provide valuable age control only if (a) fresh volcanic material was deposited into the paleolake at or near the time of eruption, and (b) multiple volcanic events can be dated. The small amount of material typically available when tephra is obtained from sediment cores constrains the dating precision and accuracy, especially on the <100 ka timescale, due to the limited radiogenic accumulation of 40Ar. Total-fusion experiments on sanidine and anorthoclase phenocrysts from two paleolake records in Kenya (the Soysambu diatomite deposit and the Lake Nakuru sediment core) illustrate that considerable effort must be undertaken to optimize dating results. Valuable age control can be obtained from even limited quantities of tephra if sample preparation is conducted carefully and 36Ar-background abundances are minimized during argon extraction.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.V23B1443B
- Keywords:
-
- 1105 Quaternary geochronology;
- 1115 Radioisotope geochronology;
- 4942 Limnology (0458;
- 1845;
- 4239);
- 4950 Paleoecology