40Ar/39Ar dating of latest Pleistocene (41 ka) marine tephra in the Mediterranean Sea: implications for global climate records

Abstract

Abstract Fifty-one 40 Ar/ 39 Ar laser heating analyses of sanidine crystals in the C-13 tephra layer, recovered out of a piston core raised from 3000 m depth in the Tyrrhenian Sea, yielded apparent ages between 25 and 112 ka. Twenty-four of these measurements define an age probability maximum and generate an isochron of 41.1±2.1 ka (2σ) with a 40 Ar/ 36 Ar intercept of 288±21 that is indistinguishable from the modern atmosphere. However, the entire population is skewed toward older apparent ages with smaller peaks at 48 ka, 55 ka, 67 ka, and 110 ka. The composition of glass shards in the C-13 tephra overlaps that of the SiO 2 -rich phase of the 150 km 3 Campanian Ignimbrite which erupted from the Campi Flegrei caldera 130 km northwest of the core site. Although the 41.1±2.1 ka isochron is ∼15% older than K–Ar and 14 C ages for the Campanian Ignimbrite, it is indistinguishable from recent 40 Ar/ 39 Ar age determinations. The Campanian Ignimbrite eruptions were also chemically similar to, and correlated with, the Y-5 ash layer – the most voluminous and widely dispersed late Pleistocene tephra in the Mediterranean region. The age of the Y-5 layer was constrained originally at 38.0±2.5 ka on the basis of astronomical dating of O-isotope stages. The 40 Ar/ 39 Ar ages, astronomical dating, plus chemical similarities permit correlation of the C-13 tephra layer with both the Campanian Ignimbrite and the Y-5 tephra layer. The older ages preserved in the C-13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the Campi Flegrei caldera 41 ka. The C-13 tephra layer is correlated with a 10 Be peak in an adjacent marine core, O-isotope stage 3.12, and immediately preceded a cooling episode corresponding to Heinrich event 4, thus the age of these features is constrained by radioisotope dating. The 41 ka peak in 10 Be deposition is a global phenomenon whose age matches that of the Laschamp geomagnetic excursion. Thus, our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr. Precise age information, independent of radiocarbon dating, can be recovered from latest Pleistocene marine tephra using the 40 Ar/ 39 Ar laser heating method, despite the presence of multiple components that may have been incorporated during or after its deposition.