Cenomanian-Turonian astronomical calibration and orbital forcing in Central Tunisia

Abstract

The Cenomanian to Turonian (C-T) transition marks a period of significant environmental disturbance characterized by shifts in climate, biogeochemical cycles, and ecosystems. During this time, marine ecosystems struggled to adapt to ocean oxygenation and nutrient availability changes. This study hypothesizes that Oceanic Anoxic Event 2 (OAE2) was driven by orbital influences from the 2.4 and 1.1 million-year g4-g3 eccentricity and obliquity cycles, respectively, during the C-T transition. These orbital factors probably contributed to contrasting climatic conditions, which played a crucial role in the impact on biogeochemical cycles and ecosystems. The astronomical calibration of the Oued Ettalla section reveals a period of 2.15 million years, from 94.73 to 92.58 million years ago. This newly established, astronomically-calibrated timeline, based on previously published data from the same section and samples, includes six calcareous nannoplankton bioevents, ten foraminiferal bioevents, and seven carbon isotope excursions, providing a refined temporal framework for understanding the paleoenvironmental changes. The different phases of OAE2 (a-d), distinguished by chemostratigraphic data occurred during a 0.8 million-year portion of the obliquity antinode modulation. The Lulworth carbon isotope event marks the onset of the Middle Turonian, while two 1.1 million-year obliquity modulations frame the Early Turonian. The Filament Event coincided with an eccentricity and obliquity node, which led to intensified summer insolation and increased ocean temperatures, supported by warm-water nannofossils.