Reconstructing the Micrometeoritic Flux and Its Link to Cyclostratigraphic Variations During the Late Devonian and Early Carboniferous at Drewer, Germany

Introduction: The extraterrestrial flux to Earth is strongly influenced by disruptions in the main asteroid belt and the inward migration of cometary bodies. These processes not only generate large impact craters and widespread ejecta, but also lead to an increased delivery of extraterrestrial material, including meteorites and micrometeorites (MMs) [1, 2]. Today, most extraterrestrial particles reaching Earth’s surface are MMs, typically smaller than 2 mm. For a long time, it was thought that such fine particles could not be preserved over geological timescales, limiting reconstructions of the long-term dust flux to indirect proxies such as iridium concentrations, helium-3 isotope ratios, or relict spinel minerals. Recently, MMs flux data have shown potential to investigate and reconstruct the extraterrestrial flux on Earth. A possible relationship has been suggested between cosmic dust flux and changes in the orbital eccentricity of the Earth throughout the Phanerozoic, offering a new application for cyclostratigraphy beyond its traditional role in age-depth modeling and paleoclimate reconstruction. Numerical models suggest that Earth’s cosmic dust influx varies on ~100,000-year timescales and inversely correlates with orbital eccentricity. However, reconstructing these long-term variations remains challenging due to the limitations of available geochemical and physical proxies. As part of the SCATTER project—Investigating a potential systematic link between the flux of Cosmic material and Earth’s orbital eccentricity throughout the Phanerozoic—samples from the Late Devonian to Early Carboniferous interval were collected in the Drewer Quarry, Germany, to reconstruct the fossil micrometeorite flux during this interval. The Drewer outcrop is located in an abandoned and partly filled quarry (“Provinzialsteinbruch”), approximately 1 km southwest of Drewer and 2 km north of Belecke, in the northeastern Sauerland, Germany [3]. This section was selected for the present investigation due to the presence of the Devonian–Carboniferous boundary, well-described stratigraphy, and low sedimentation rate [3]. The studied interval at Drewer includes exposures of different lithologies, such as the Wocklum Limestone, Hangenberg Black Shale and Sandstone, Hangenberg Limestone, and Lower Alum Shale [3].

Material and Methods: The recovery and characterization of fossil micrometeorites (MMs) remain challenging due to inconsistent dissolution protocols and the labor-intensive extraction from sedimentary rocks [4–5]. In this project, we applied the effective dissolution method established by [6]. Thirteen limestone samples, each weighing approximately 5 kg, were collected from the Wocklum and Hangenberg limestones in the Drewer quarry. Each of the samples spans an interval of ~40 cm, covering the transition from the Devonian to the Carboniferous. Limestone intervals were dissolved in hydrochloric acid and wet-sieved into size fractions ranging from <2 mm to 63 µm. Magnetic separation was performed on the sieved residues, and the magnetic fractions were examined under a binocular microscope. Spherules suspected to be MMs were hand-picked and initially screened using microX-ray fluorescence (µXRF). Particles confirmed to be MMs were further analyzed by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) to determine their textures and elemental compositions. Additional chemical and isotopic characterization is planned for the upcoming months. Classification follows the criteria outlined by [7].

Results and Discussion: This project aims to compare the Devonian MM data with the results from other well-characterized sections in southern Belgium, such as Spontin and Royseux, as well as provide the first insights in the MM flux during the Carboniferous. It additionally considers potential variations in flux and explores possible links between MM variations and changes in terrestrial orbital eccentricity. By identifying periodic enhancements in the flux, the project aims to isolate longer-term trends, reduce short-term variability, and test for a terrestrial eccentricity-driven extraterrestrial signal in the sedimentary record.

References: [1] Schmitz B. et al. (2019) Sci. Adv. 5: eaax4184. [2] Marsset M. et al. (2024) Nature 634: 561–565. [3] Becker T. R. et al. (2021) Palaeobiodiversity and Palaeoenvironments 101:357–420. [4] Suttle M. D. and Genge M. J. (2017) Earth Planet. Sci. Lett. 476: 132–142. [5] Tomkins A. G. et al. (2016) Nature 533: 235–238. [6] Krämer Ruggiu L. et al. (2025) Geochim. Cosmochim. Acta, in press. [7] Genge M.G. et al (2008) Meteoritics & Planetary Science 43, Nr 3, 497–515.