Confirmation of a Late Miocene Subchron C4n.2n-1r From the Eastern Qaidam Basin in the NE Tibetan Plateau

Refining reversal ages and improving reversal patterns for the geomagnetic polarity timescale are a major task for the paleomagnetic community. The Late Miocene is a period during which the geomagnetic field experienced frequent perturbations and which dramatic environmental changes occurred. Thus, improved (sub)chron definition during this period will enable to provide additional age control points for better understanding age of paleoenvironmental changes. A prior study of the Late Miocene C4n.2n magnetic polarity zone at Ocean Drilling Program Site 1092 in the sub-Antarctic South Atlantic Ocean has revealed the potential existence of a subchron (C4n.2n-1r). However, this subchron has not been incorporated into the geomagnetic polarity timescale yet because its existence has not been confirmed. Moreover, the low sediment accumulation rate of 1.32 cm/kyr at Site 1092 hampers a confident estimation of the age and duration of this subchron. Here we present a high-resolution paleomagnetic data set covering C4n.2n from the Huaitoutala section in the eastern Qaidam Basin, Northwest China, with an average sediment accumulation rate of ~22 cm/kyr. Nine reversed declination/inclination data points define a subchron near the top of C4n.2n, similar to age of reported C4n.2n-1r at Ocean Drilling Program Site 1092. Cyclostratigraphy of the magnetic susceptibility record of the Huaitoutala section suggests that the age and duration of the C4n.2n-1r are 7.7612–7.7554 Ma and 5.8 ± 2.1 kyr, respectively. Confirming the existence of C4n.2n-1r from a northern hemisphere terrestrial site suggests that two geomagnetic reversals bounding this subchron have global imprints and that this subchron can potentially serve as marker for stratigraphic correlation.