U–Pb geochronology and Hf isotope systematics of detrital zircon from the late Ediacaran Kalyus Beds (East European Platform): palaeogeographic evolution of southwestern Baltica and constraints on the Ediacaran biota

Abstract

A maximum depositional age (MDA) of 551.2 ± 4.2 Ma for the black argillites of the Kalyus Beds, Nagoryany Formation (East European Platform, northeastern Republic of Moldova) is reported based on the youngest cluster of detrital zircons dated by LA-ICP-MS. Their source can be linked to an arc-related volcanism that fed the tuffite layers interbedded in the basal part of the Kalyus Beds and reasonably support our inference that the reported MDA is consistently compatible with the true depositional age (TDA) of the Kalyus Beds. The volcanic event that led to ash deposition for the tuffites may be related to the active margin processes which developed adjacent to the Baltica palaeocontinent. Hf isotope values of two detrital zircons from the youngest cluster suggest mantle input, and a third detrital zircon was derived from felsic rocks that originated from re-melting of the older crustal rocks. The older detrital zircon clusters correlate well with known published ages of the different lithotectonic units from the East European Platform. The precise geochronological U–Pb ages, including the Kalyus detrital zircon age, offer outstanding data to calibrate the sedimentary and volcanic events, and the evolution of the Ediacaran biota in the Moldova-Podillya Basin, specifically the Miaohe biota biozone, for which a few newly identified taxa significantly increase its taxonomic diversity. The anoxic conditions together with the associated phosphorites that controlled the deposition of the Kalyus argillites represent a major depositional event in this area of the Baltica palaeocontinent, and can be correlated with other worldwide anoxic events during the late Ediacaran.