|
The availability of accurate and reliable age control is a crucial prerequisite for palaeoclimate studies, particularly when different archives are to be compared. Here we present a detailed depth-to-time transformation for the lacustrine sediments of a∼940-m-long drill core (SG-1) from the western Qaidam Basin (NE Tibetan Plateau). To establish a more precise age model than the one previously available, which was based solely on magnetostratigraphic dating using polarity boundaries as tie points, we applied time-series analysis on magnetic susceptibility (χ) variation. The χ data are available in high resolution and are considered to be closely linked to orbital forcing. Since the sediment accumulation rate (SAR) varies strongly throughout the succession of core SG-1, conventional cyclostratigraphy by bandpass filtering cannot be applied. We present two alternative age models based on spectral characteristics and orbital tuning.The first age model (TPspec) is based on the assumption that changes in SAR occurred when the frequency spectra revealed obviously different characteristics in the spectral pattern. For the second age model (SARA), SAR was adjusted every 2 m by comparing observed with expected orbital cycles in accordance with the age of magnetic reversals. This age model appears more robust and shows the most convincing spectral results in the frequency and wavelet power spectrum of χ. According to the SARA age model, SAR varies between 14 and 73 cm kyr–1, and the bottom of SG-1 has an age of 2.69 Ma. Our results show that orbital tuning can be successfully applied for sequences with strongly variable SAR. The age model SARA can be used for a more detailed analysis of the existing multiproxy data set in terms of palaeoclimate evolution. The most prominent feature of χ spectra using the SARA age model is the identification of the middle Pleistocene transition.
|
Kembali