La-Icp-MS U-Pb Ages of Detrital Zircons From Sedimentary Rocks of the Komsomolskaya Group (Northern Sikhote-Alin)

Abstract

A geochronological study of detrital zircons from sedimentary rocks of the Gorinskaya (91 zircons with concordant ages), Pionerskaya (117 zircons with concordant ages), and Pivanskaya (115 zircons with concordant ages) formations of the Komsomolskaya Group was carried out. Comparison of the 206Pb/238U isotopic age of the youngest zircon populations from these formations with their stratigraphic age revealed that they are consistent only for one of them (Pivanskaya Formation). For the other two formations, the youngest zircons turned out to be significantly younger than the upper limit of their stratigraphic age. New evidence shows that: 1) the age of the «Berriassian-Valanginian» deposits of the Pionerskaya Formation is not older than the Barremian; and 2) the age of the «Titonian-Berriasian» deposits of the Gorinskaya Formation is not older than the Hauterivian. The division of deposits in the Komsomolskaya Group into formations is based primarily on lithological criteria, and since the composition of the formations is very similar, similar deposits in other Lower Cretaceous sections of the region may have been assigned to other stratigraphic units, so the above conclusion is valid only for the sections we studied.