Astrochronology and sedimentary noise modeling of Pliensbachian (Early Jurassic) sea-level changes, Paris Basin, France

A high-precision global time scale for the Early Jurassic is important for understanding the relationship between biotic, climatic and sea-level changes that occurred during this time interval. In this study, we present a cyclostratigraphic analysis of iron (Fe) and titanium (Ti) elemental data from the Pliensbachian marine mudstone succession of the Sancerre-Couy drill core (Paris Basin, France). Timeseries analysis of the data, coupled with existing broad chronological constraints, reveals 405 kyr long-eccentricity, 133-100 kyr short-eccentricity, and 34 kyr obliquity cycles in Ti and Fe abundance. Based on astronomical tuning of the 405 kyr long eccentricity cycles, we construct an astrochronology for the Pliensbachian Stage in the Sancerre-Couy record spanning & SIM;7.9 Myr. Anchored in numerical time, our new Pliensbachian timescale can be correlated with the thicker, likely more complete, astronomically calibrated Pliensbachian record in the Mochras Farm (Llanbedr) borehole. This exercise suggests the presence of significant hiatuses near the base and top of the Sancerre-Couy record. The recently developed sedimentary noise model for inferring sea-level change has also been applied and compared to previous estimates of Pliensbachian sea-level change derived from the Sancerre-Couy record and elsewhere. Analysis of the sedimentary noise modeling results, previously published nannofossil abundance data and our elemental data suggests the presence of million-year scale cycles linked to longperiod astronomical forcing. This work provides new constraints on the chronology of the Pliensbachian and its constituent faunal zones, and the role of long-period astronomical forcing in mediating Early Jurassic paleoclimate and sea-level.

Automated summary

In this study, a cyclostratigraphic analysis of iron and titanium elemental data from the marine mudstone succession of the Sancerre-Couy drill core was conducted. The analysis revealed long-eccentricity, short-eccentricity, and obliquity cycles. Based on astronomical tuning, an astrochronology for the Pliensbachian Stage was constructed. This study provides new constraints on the chronology of the Pliensbachian and its relationship with paleoclimate and sea-level changes.