Palaeogene climate evolution in the Paris Basin from oxygen stable isotope (δ¹⁸O) compositions of marine molluscs

The constraint of temperature evolution in coastal environments is an important factor in deciphering the Earth’s global climatic history. In this study, we reconstruct the evolution of sea-surface palaeotemperatures from the oxygen stable isotope compositions in four marine molluscs families in the Paris Basin during the Palaeogene. The combination of several taxa living in different environments is used to limit uncertainties related to the influence of salinity variations on palaeotemperature estimations. One family of bivalves (oysters) and three families of gastropods (Volutidae, Cerithiidae and Turritellidae) were sampled in the French part of the Paris Basin, in Belgium and in the Isle of Wight (southern England). Maximum seawater temperatures were observed during the Early Eocene (<em>c</em>. 30°C), which correspond to the Early Eocene Climatic Optimum, and temperatures then decreased until the Lutetian (<em>c</em>. 20°C). A transient warming, identified as the Middle Eocene Climatic Optimum, occurred during the Bartonian, when temperatures reached 32°C. Temperatures decreased through the Eocene–Oligocene boundary, the coolest interval of the Palaeogene (<em>c</em>. 12°C). A final warming period occurred throughout the Early Oligocene, with temperatures reaching 24°C. The fossils analysed thus record the global climatic intervals of the Palaeogene.海岸环境温度演化的约束条件，是解析地球全球气候历史的重要依据。本研究基于巴黎盆地古近纪（Palaeogene）4个海洋软体动物科壳体的氧稳定同位素组成，重建了古海水表层温度的演化历程。研究选取栖息于不同环境的多个分类群（taxa）开展分析，以限制盐度变化对古温度估算结果带来的不确定性。研究采样范围涵盖巴黎盆地法国段、比利时以及英格兰南部怀特岛的样品，包含1个双壳类科（牡蛎科）与3个腹足类科：涡螺科（Volutidae）、蟹守螺科（Cerithiidae）及锥螺科（Turritellidae）。始新世早期（约30℃）达到海水温度峰值，该时期对应始新世早期气候最佳期（Early Eocene Climatic Optimum）；随后温度持续下降，至卢台特阶（Lutetian）时期降至约20℃。巴顿阶（Bartonian）时期发生了一次短暂升温事件，即始新世中期气候最佳期（Middle Eocene Climatic Optimum），此时温度达到32℃。温度在始新世-渐新世界线处持续下降，该时段为古近纪最冷期，平均温度约12℃。整个渐新世早期为新一轮升温阶段，温度升至24℃。综上，本次分析的化石完整记录了古近纪的全球气候演化阶段。