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

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.

Pleistocene climate variability in eastern Africa influenced hominin evolution

“…The longterm trends in the K/Zr record show an anticorrelation with eccentricity (~125 and 400 kyr cyclicity) and a correlation with pre cession (~21 kyr and ~11 kyr halfprecessional cyclicity) 15,17,18 , while the influence of obliquity (~40 kyr cyclicity) is weak or absent 19 (Fig. 2 and Extended Data Fig.…”

“…Facies 1 is a bluegreen or grey clayey silt, reflecting anoxic conditions at the sediment/water interface and/or higher levels of organic matter. This is associated with poorly ventilated bottom water of the lake during episodes of high water level and a wetter climate 15 . Facies 2 is light brown and reddishbrown silt.…”

“…Facies 2 is light brown and reddishbrown silt. The brown colour results from the formation of an abundance of oxidized iron at the oxygenated sediment surface associated with episodes of lower lake levels or exposed lake floor dur ing drier climate conditions 15 . Intercalation and mixing of sediment types occur at transitions reflecting changes in the hydrology of the lake and its catchment (see Methods for details of sediment colour data).…”

“…Several pronounced wet phases at CHB during episodes 7-9 align with humid pulses in northeastern Africa 13,25 and the Mediterranean 26 , perhaps opening favourable migration routes out of Africa on a roughly north-south axis along the East African Rift System and into the Levant 11,45 . One possibility is that early dispersals involved populations dispersing in line with expansions or shifts of suitable habitat 15 . As cultural inno vations accumulated during episodes 7-9, however, they provided H. sapiens populations with the means to expand beyond their native habitat 14,37,44 , with this expansion ultimately leading to the global dispersal of modern humans 11 .…”

Exploring the Past Biosphere of Chew Bahir/Southern Ethiopia: Cross-Species Hybridization Capture of Ancient Sedimentary DNA from a Deep Drill Core

“…The duplicate cores were retrieved in close proximity to each other, core HSPDP-CHB12-2A at 4.7612°N, 36.7668°E and core HSPDP-CHB14-2B at 4.7613°N, 36.7670°E (Cohen et al, 2016;Campisano et al, 2017). They are 278.58 mbs ( meters below surface) (core HSPDP-CHB14-2A) and 266.38 mbs (core HSPDP-CHB14-2B) long and were merged into a composite core, ∼292.76 mcd ( meters composite depth, hereinafter written as ∼292.76 m for simplicity) long, after correlating the physical properties and imagery of the cores 2A and 2B (Arnold et al, 2021;Duesing et al, 2021;Roberts et al, 2021;Schaebitz et al, 2021;Trauth et al, 2021). Together they replenish missing data in each other and the composite core with ∼90% continuity will be referred to as one core in the following.…”