An AMS radiocarbon method to determine the emplacement time of recent deep-sea turbidites

Abstract

This paper reports the evaluation of a novel method based on accelerator mass spectrometer (AMS) radiocarbon dating of planktonic foraminifera to evaluate the times of emplacement of recent deep-sea turbidites. It assumes that the standing stock of relatively large ( > 150 μm) planktonic foraminifera in the bioturbated surface mixed layer of box cores represents an integration of the flux from the water column since the turbidite was emplaced, and exploits the potential of the AMS method to analyse the resultant small samples which can be readily separated. The method is evaluated by application to three Atlantic turbidites which form the present-day sediment surfaces on the Horseshoe, Madeira and Tagus Abyssal Plains. The time of emplacement of Madeira Abyssal Plain turbidite α is estimated at 1120, 730 and 870 years before present (each ±120–140 years) in three different cores. The resultant weighted mean emplacement time, 930 ± 76 years before present, is somewhat older than previous estimates by geochemical methods. The times of emplacement for the Horseshoe (240 and 140 years before present, each ± 120 years and Tagus (300 ± 120 years before present) Abyssal Plains are both consistent with initiation by the Lisbon earthquake of 1755.