Cyclostratigraphy in the Silurian: Potential, Progress, Pitfalls, and Proposals

Silurian carbon isotope excursions are among the largest in the Phanerozoic, yet the decoupling of isotopic signals and bioevents, as well as their varied expression and preservation, indicate complex processes which remain incompletely understood. In the past decade, cyclostratigraphic analysis has shed light on links between Paleozoic carbon cycle perturbations (including those in the Silurian as well as the Devonian) and astronomical forcing. Particularly long eccentricity (~2.4 Myr) and obliquity (~1.2) appear to have played a role in the pacing of the global carbon cycle, something that is also known from Meso- and Cenozoic records. Details of the climatic pathways underlying these forcing mechanisms remains scarce in the Paleozoic, however. Cyclostratigraphic investigation of Silurian strata could not only help elucidate the climatic mechanisms underlying Silurian carbon isotope excursions but also further refine the Silurian time scale by adding astrochronological constraints. While cyclostratigraphic work in the Silurian is as of yet limited, there have been substantial advances in the past few years, both in the area of analysing climate forcing of the global carbon cycle as well as reading time in the Silurian rock record. At the same time, many rhythmic Silurian strata consist of limestone-marl alternations, which seem promising targets for cyclostratigraphic studies. Nevertheless, there is potential for diagenetic signal distortion and extracting primary environmental signals (such as Milanković cycles) from these types of successions requires special attention to diagenetic alterations. Here, we present a brief review of existing cyclostratigraphic studies in the Silurian, as well as preliminary and future cyclostratigraphic work planned in the Homerian (Wenlock). We invite the Silurian stratigraphic community to discuss how cyclostratigraphy can best be integrated with existing bio- and chemostratigraphy to help improve the Silurian time scale, and to better understand the global perturbations that characterize this period.