New radiocarbon age constraints for the 120 km-long Toomba flow, north Queensland, Australia. Issue 1 (2nd January 2019)

• Record Type: Journal Article
• Authors: Mishra, A. K.; Placzek, C.; Wurster, C.; Whitehead, P. W.
• Is Part Of: Australian journal of earth sciences. Volume 66:Issue 1(2019)
• Page Start: 71
• Page End: 79
• Publication Date: 2019-01-02
• Subjects: Toomba -- 14C -- hydrogen pyrolysis -- radiocarbon dating -- young basalts -- Queensland; Earth sciences -- Australia -- Periodicals; Earth sciences -- Periodicals; Geology -- Australia -- Periodicals; Geology -- Periodicals; 559.405
• DOI: 10.1080/08120099.2019.1523227
• Languages: English
• ISSNs: 0812-0099

Abstract

Abstract: The Toomba flow is the youngest flow of the Nulla volcanic province, located in north Queensland. This 120 km-long flow has yielded a published 40 Ar/ 39 Ar age of 21, 000 ± 3000 years. In contrast, seven published conventional radiocarbon ( 14 C) analyses of carbon-bearing material beneath the flow yielded radiocarbon ages of 16, 000 to <2500 BP. These radiocarbon ages are younger than the 40 Ar/ 39 Ar age, potentially due to contamination of the charcoal by younger carbon that was not removed by the acid–base pre-treatment. We have re-examined the radiocarbon age of Toomba flow using newly sampled charcoal buried beneath the Toomba flow in combination with hydrogen pyrolysis pre-treatment and accelerated mass spectrometer (AMS) measurements. We determined a calibrated radiocarbon age of 20, 815–19, 726 cal BP (2σ) for the material beneath the Toomba flow. Our radiocarbon age, therefore: (1) is older than previous radiocarbon ages for the Toomba flow, (2) provides the most precise age yet available for the Toomba flow, (3) is in agreement with the 40 Ar/ 39 Ar age, and (4) validates that hydrogen pyrolysis is a robust and effective pre-treatment method, for subtropical conditions where samples are susceptible to contamination by younger carbon. The Toomba flow erupted during the Last Glacial Maximum, but the preserved surface suggests that the rate of weathering and soil formation has been almost negligible in this region, despite being situated in a subtropical climate that experiences highly variable often intense rainfall.