The Cyclostratigraphy Intercomparison Project (CIP): consistency, merits and pitfalls of cyclostratigraphy

Cyclostratigraphy is an important tool for understanding astronomical climate forcing and reading geological time in sedimentary sequences, provided that an imprint of insolation from Earth’s orbital eccentricity, obliquity and/or precession is preserved (Milankovitch forcing). Numerous stratigraphic and paleoclimate studies have applied cyclostratigraphy, but the robustness of the methodology and dependence on the investigator have not been systematically evaluated. Here, we present an experimental design of three artificial cases with known input parameters. Each case is designed to address specific challenges that are relevant to cyclostratigraphy. Case 1 simulates the situation of a scientist onboard a research vessel: for his/her analysis, nothing more than a drill-core photograph and the approximate position of a stage boundary is available. Case 2 is a proxy record with clear nonlinear cyclical patterns, which interpretation is complicated by the presence of a stratigraphic gap. Case 3 represents a modeled Late Devonian proxy record, with a low signal-to-noise ratio and no specific astronomical solution available for this age. Each case was analyzed by 17 to 20 participants as part of the Cyclostratigraphy Intercomparison Project (CIP). The test group was heterogeneous in terms of experience and dedicated time and self-reflected on the results during a meeting in Brussels, Belgium. The analyses demonstrate that not every participant came to the correct solution. However, the median solution of all submitted analyses accurately approached the correct solution in all three cases and some participants obtained the exact correct answers. This experiment demonstrates that cyclostratigraphy is a powerful tool for deciphering time in sedimentary successions, and importantly, it is a trainable skill. Systematically better performances were obtained for cases that were closer in type and stratigraphic age to the experience of individual participants. Finally, we emphasize the importance of an integrated stratigraphic approach and provide a set of guidelines on what good practices in cyclostratigraphy should include. With the CIP, we cannot provide a quantitative measure of reliability and uncertainty of cyclostratigraphy. Instead, our case studies provide valuable insight in current common practices in cyclostratigraphy, their merits and pitfalls. Therewith, CIP is a starting point for further discussions on how to move this maturing field forward.