Climatic precession is the main driver of Early Cretaceous sedimentation in the Vocontian Basin (France): Evidence from the Valanginian Orpierre succession
Résumé
The Valanginian sediments outcropping in the Vocontian Basin (SE France) exhibit striking marl-limestone alternations, which were formed under the influence of orbital forcing and which have served for geochronological and paleoenvironmental studies. Previous studies have suggested an obliquity forcing during the Late Valanginian interval, reflecting specific environmental conditions such as polar ice. Using a cyclostratigraphic correlation of previously studied sections and performing time-series analysis on the most complete Late Valanginian interval we argue that the climatic precession cycle is the primary driver of these marl-limestone alternations. In addition, we highlight the modulation of the precession by the ~ 100 and 405 kyr eccentricity cycles. We suggest that the cyclostratigraphic misinterpretation (i.e., obliquity-forcing hypothesis) results mainly from poorly preserved 405 kyr eccentricity cycles, due to local hiatuses and/or “missed beats”. This study shows the potential of cyclostratigraphic correlations for the detection and quantification of differential hiatuses and/or “missed beats” within intrabasinal sequences, hence providing constraints on cyclostratigraphic interpretations. The recorded 405 kyr eccentricity cycle is of prominent amplitude, and controlled the fourth-order sea-level sequences. These latter are faithfully detected through cyclostratigraphically inferred sedimentation rate. Finally, we show that the well-known, pronounced lithostratigraphic markers/intervals in the basin were orbitally paced by the 405 kyr eccentricity extrema. This is a good argument for the strong impact of this cyclicity on the sedimentary processes, especially during greenhouse periods.
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