Multiband Wavelet Age Modeling for a ∼293 m (∼600 kyr) Sediment Core From Chew Bahir Basin, Southern Ethiopian Rift

Walter Duesing,K Hauke Kraemer,Martin H Trauth,Nadine Berner,Norbert Marwan,Alan L Deino,Verena Foerster

doi:10.3389/feart.2021.594047

Abstract

The use of cyclostratigraphy to reconstruct the timing of deposition of lacustrine deposits requires sophisticated tuning techniques that can accommodate continuous long-term changes in sedimentation rates. However, most tuning methods use stationary filters that are unable to take into account such long-term variations in accumulation rates. To overcome this problem we present herein a new multiband wavelet age modeling (MUBAWA) technique that is particularly suitable for such situations and demonstrate its use on a 293 m composite core from the Chew Bahir basin, southern Ethiopian rift. In contrast to traditional tuning methods, which use a single, defined bandpass filter, the new method uses an adaptive bandpass filter that adapts to changes in continuous spatial frequency evolution paths in a wavelet power spectrum, within which the wavelength varies considerably along the length of the core due to continuous changes in long-term sedimentation rates. We first applied the MUBAWA technique to a synthetic data set before then using it to establish an age model for the approximately 293 m long composite core from the Chew Bahir basin. For this we used the 2nd principal component of color reflectance values from the sediment, which showed distinct cycles with wavelengths of 10–15 and of ∼40 m that were probably a result of the influence of orbital cycles. We used six independent 40Ar/39Ar ages from volcanic ash layers within the core to determine an approximate spatial frequency range for the orbital signal. Our results demonstrate that the new wavelet-based age modeling technique can significantly increase the accuracy of tuned age models.

Highlights

When investigating paleoclimate records derived from lake cores, the reliability of the age model used is crucial
The MUBAWA approach is based on the application of a continuous wavelet transformation (CWT) to a depth series, with the aim of generating a tuned age model
Step 2: spatial frequency range approximation (SFRA), which is an optional step that uses the available age control to approximate the spatial frequency range of the targeted orbital component, Step 3: spatial frequency path mapping, which involves determining spatial frequencies using a CWT and applying a weighting function to prevent the inclusion of unrealistic sedimentation rates, and Step 4: identification of the best continuous spatial frequency path, adaptive filtering by the consecutive application of Taner filters along this spatial frequency path, and identification of the best age model solution

Summary

Introduction

When investigating paleoclimate records derived from lake cores, the reliability of the age model used is crucial This reliability depends largely on the density of independent age-control points, which should ideally be evenly distributed along the entire length of the core. Cyclostratigraphy can be used in such cases to add additional age control points, evenly distributed in time This method has been applied since the mid1970s to marine records that extend beyond the range of the radiocarbon dating technique (e.g., Hays et al, 1976; Imbrie and Imbrie, 1980; Pisias et al, 1984; Martinson et al, 1987; Tiedemann et al, 1994; Grant et al, 2017). Orbital tuning has often been used to increase the temporal resolution between radiometric age control points, more commonly in paleoceanography than in paleolimnology (e.g., Grant et al, 2017)

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Conclusion