Improving the temporal resolution of middle Eocene–late Oligocene foraminiferal biomagneto-chronology: Insights from CONOP and chronologic significance of biotic events

Abstract

To understand Earth's history, a comprehensive time scale integrating available stratigraphic information is crucial. The middle Eocene to late Oligocene offers abundant stratigraphic information, including foraminiferal and magnetostratigraphic data. However, traditional biostratigraphy uses only a small fraction (1–10 %) of foraminifera as markers, reducing the time scale's temporal resolution and lacking a quantitative method to assess the chronologic significance of both mearker and non-marker biotic events. This study employs the quantitative stratigraphic method, Constrained Optimization (CONOP), using 11 reference sections to create a high-resolution magneto-foraminiferal time scale for the middle Eocene–late Oligocene. The new composite sequence improves temporal resolution by nearly tenfold over traditional methods, incorporating 409 additional biotic events while aligning closely with established markers. Two evaluation factors, diachrony and centrality, were developed to assess the temporal consistency of events among different locations and geographic ranges. Findings reveal that the chronological significance of small benthic foraminifera, planktonic foraminifera, and foraminiferal zonal species events increases sequentially. Conversely, larger benthic foraminiferal events are affected by endemism, complicating their evaluation. Incorporating magnetostratigraphic data into CONOP enhances the robustness and accuracy of stratigraphic correlation. Our approach offers a way to apply CONOP for high-resolution time scales, allowing for a comprehensive assessment of biotic events beyond the use of zonal fossils.