Hydrological differences between the Lutetian Paris and Hampshire basins revealed by stable isotopes of conid gastropods

Alexander J Clark,Johan Vellekoop,Robert P Speijer

doi:10.1051/bsgf/2022002

Abstract

During the Eocene greenhouse (56.0–33.9 Ma), northwest Europe was dominated by a semi-arid para-tropical climate but the paleohydrological conditions are poorly known. To gain more insight into seasonal hydrological conditions in the region, we compare Lutetian (middle Eocene, ∼ 44–45 Ma) mollusk δ18O records from two shallow marine basins on either side of the English Channel,i.e., the Paris and Hampshire Basins. The semi-circular Paris Basin was open to the Atlantic Ocean, while the Hampshire Basin was more enclosed and influenced by the draining of several rivers. The proximity of the basins and the similarity of their faunal assemblages suggest that they experienced roughly similar seawater temperatures but the seasonal hydrology is expected to have been different between these basins. Among the numerous mollusks present in both basins are several members of Conidae, a gastropod family that is particularly well-suited for paleoseasonality reconstructions. To assess the paleohydrological differences between these basins we analyzed the stable oxygen isotopic composition of three specimens ofEoconus deperditusfrom the Banc à Verrains in the middle part of the Calcaire Grossier Formation of the Paris Basin (France), and three specimens ofEoconus edwardsifrom the Shepherd’s Gutter Bed in the upper part of the Selsey Formation of the Hampshire Basin (United Kingdom). While the seasonal variability appears to have been similar between these basins, the δ18O values of the Hampshire Basin specimens are consistently lower than those in the Paris Basin, suggesting a regional difference in δ18Oswof 1–2‰ between the basins. This difference in δ18Oswwas likely related to the greater influence of fluvial discharge within the Hampshire basin, compared to the Paris Basin.

Highlights

The Lutetian age (48.07-41.03 Ma; Speijer et al, 2020) was one of the last times the world experienced high temperatures and CO2 levels (Zachos et al, 2008; Rae et al, 2021).the Lutetian climate could serve as a potential analogue for future climate states (Tierney et al, 2020; Westerhold et al, 2020)
When mollusk δ18O records from nearby regions that experienced similar seawater temperatures are compared, one can assume that any differences in mollusk δ18O values or patterns between the regions would be mostly related to regional differences in seawater δ 18O, rather than temperature (Latal et al, 2006)
We show that further studies to fully constrain the Lutetian paleotemperature and δ18O of the surrounding seawater (δ18Osw) are pivotal

Summary

Introduction

The Lutetian age (48.07-41.03 Ma; Speijer et al, 2020) was one of the last times the world experienced high temperatures and CO2 levels (Zachos et al, 2008; Rae et al, 2021).the Lutetian climate could serve as a potential analogue for future climate states (Tierney et al, 2020; Westerhold et al, 2020). Local seawater δ18O values are controlled by regional and local patterns in precipitation, discharge, evaporation and connections with other water masses (Keith et al, 1964; Swart et al, 1989; Zachos et al, 1994; Schmitz and Andreasson, 2001; Gat, 2010). This approach could provide valuable insights in regional differences in seasonal paleohydrological conditions in the Eocene greenhouse world

Methods

Results

Discussion

Conclusion