First integrated tephrochronological record for the last ∼190 kyr from the Fucino Quaternary lacustrine succession, central Italy. (15th February 2017) - Giaccio, Biagio
Abstract: We present the first integrated tephrochronological study (major and trace elemental glass composition, Sr and Nd isotope analyses, and 40 Ar/ 39 Ar dating) for the last one tenth (∼82 m) of the ∼900 m-thick Quaternary lacustrine succession of the Fucino Basin, the largest and probably only Central Apennine intermountain tectonic depression that hosts a continuous lacustrine succession documenting the Plio-Quaternary sedimentary history up to historical times. Major element glass compositions, determined using a wavelength-dispersive electron microprobe (WDS-EMPA), yielded the geochemical fingerprinting needed for a reliable identification of most of the 23 stratigraphically ordered tephra layers under investigation. These include tephra from Italian volcanoes such as Campi Flegrei, Etna, Colli Albani, Ischia, Vico, Sabatini, and undefined volcanic sources in the Neapolitan area and Latium region. The recognition of key Mediterranean marker tephra layers (e.g. X-5 and X-6) is supported by trace element data acquired by Laser Ablation Inductively Couple Plasma Mass Spectrometry (LA-ICP-MS). The Sr and Nd isotope compositions of selected layers where also determined for circumscribing the volcanic source of distal tephra and for supporting correlations with individual eruptive units. We also propose a new, more expeditious covariation diagram (CaO/FeOtot vs Cl) for identifying the volcanic source of trachytic to phonolitic and tephrytic to phonolitic tephra, that are the most common compositions of pyroclastic rocks from volcanoes of Campania and Latium regions. Finally, we present five new 40 Ar/ 39 Ar age determinations, including a new, analytically well-supported, and more precise 40 Ar/ 39 Ar age for the widespread Y-7 tephra, and the first 40 Ar/ 39 Ar age determinations for one tephra from the Sabatini volcanic district (∼126 ka) and one tephra from Neapolitan volcanic area (Campi Flegrei?; ∼159 ka). These newly dated tephra are widely dispersed (e.g. Monticchio, southern Italy, Adriatic Sea and Lake Ohrid, Macedonia-Abania) and have thus the potential to become important Mediterranean MIS 5 and MIS 6 tephrochronological markers. Altogether the new geochemical data and 40 Ar/ 39 Ar ages precisely constrain the chronology of the investigated Fucino succession spanning the last ∼190 ka. In light of these results and by considering that this sedimentary succession possibly extends back to ∼2 Ma, Fucino is likely to provide a very long, continuous tephrostratigraphic record for the Mediterranean area and become a key node in the dense network of tephra correlations of this region. Graphical abstract: Highlights: The last 190 kry (84 m) of the ∼2 Ma-long (∼900 m) Fucino record yielded 23 tephra. Tephra originate from Campi Flegrei, Etna, Colli Albani, Ischia, Vico and Sabatini. 19 out 23 tephra were correlated to individual proximal or distal equivalents. 5 tephra, including Y-7 and two MIS 5-6 markers, were directly dated by 40 Ar/ 39 Ar. Fucino Basin is candidate to be a key site for the Mediterranean tephrochronology.