Toward age determination of the termination of the Cretaceous Normal Superchron

Abstract

We present an integrated chronology for the terrestrial Upper Cretaceous in East Asia based on high‐resolution magnetostratigraphic results and detailed SIMS U‐Pb zircon analyses of a continuous continental sedimentary sequence drilled from the Songliao Basin in northeast China. Correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and SIMS U‐Pb zircon geochronologic data, which suggest that the south core of the CCSD‐SK‐I sedimentary sequence spans from upper chron C34n to lower chron C33r. The age of the termination of the Cretaceous Normal Superchron (CNS) was estimated to be ∼83.4 Ma. Intervals of reverse geomagnetic field polarity of early Santonian age could be present during the late CNS. Two black shale layers at the base of Member 1 of the Qingshankou Formation and Member 2 of the Nenjiang Formation, which were previously interpreted as the products of lake anoxic events LAE1 and LAE2, have been well dated at 91.4 Ma and 83.7 Ma, respectively, by SIMS U‐Pb zircon analyses of intercalated bentonite layers. However, the LAE1 and LAE2 identified here are not temporally correlated to the known oceanic anoxic events.