Astronomical Cycles Controlled the Formation of Late Ediacaran Sedimentary Alternations (~547 Ma): A Drone-Based Cyclostratigraphic Analysis of the Kuibis Subgroup (Nama Group, Namibia)

Abstract

The Ediacaran Period (~635–538 Ma) saw major climatic and biological transitions, including the emergence of early multicellular life. Understanding how astronomical forcing influenced climate and sedimentation during this time is key to reconstructing environmental conditions. However, the relationship between sedimentary patterns and astronomical cycles in the late Ediacaran Kuibis Subgroup (Zaris Subbasin, Namibia) remains unclear. This thesis uses high-resolution drone imagery to analyse sedimentary stacking patterns in the Hoogland and Urikos Members. Visual inspection, steepness analysis, and spectral analysis identified hierarchical stacking of sedimentary alternations. Cycle thicknesses of ~36 m, ~19 m, ~6.5 m, and ~3.5 m were detected, with ratios of these cycle thicknesses suggesting influences from precession (~18 kyr), short eccentricity (~100 kyr), or obliquity (~30 kyr) and its modulation (~173 kyr). Radio-isotopic dating was used to provide age constraints and assess the duration of the alternations. The second radio-isotopic dating scenario, which places the Nudaus ash bed at the top of the Urikos Member, supports these ratios, as the estimated maximum duration of medium-scale alternations (190.9 ± 27.3 kyr) closely matches obliquity modulation (~173 kyr) and short eccentricity (~100 kyr). eCOCO analysis was used to estimate sedimentation rates and interpret shifts in cycle thicknesses. A significant increase in cycle thickness from the Hoogland to Urikos Member suggests either an increase in sedimentation rate or a shift in the dominant astronomical forcing. In the first scenario, both members record precession-forced small-scale (~3.5–6.5 m) alternations, with medium-scale (~19–36 m) alternations linked to eccentricity. In the second scenario, the small-scale alternations in Hoogland are precession-forced, while in Urikos, they are controlled by obliquity. With precession- and eccentricity- or obliquity-driven deposition, these alternations were likely formed by glacio-eustatic sea-level changes.