Geochemical compositions of Neogene phosphatic brachiopods: Implications for ancient environmental and marine conditions

Abstract

Isotopic and trace element compositions of Miocene and Pliocene phosphatic brachiopods (Lingulidae and Discinidae) from southern North Sea, the Central Paratethys and the Atlantic coast of Europe were investigated in order to trace past environmental conditions and marine connections between the northern boreal and the southern subtropical–tropical marine basins. The North Sea genus Glottidia yielded low εNd and high δ18OPO4 values through the Mio-Pliocene indicating cold habitat temperature where the local seawater was dominated by the Atlantic Ocean. In contrast, the Middle Miocene Lingulidae and Discinidae of the Paratethys inhabited warm subtropical seawater with the possible influence of the Indian Ocean via the Mediterranean, as supported by their average εNd value of −8.3. The combined geochemical data support a thermal and marine separation of the Paratethys from the North Sea with no direct connection or major exchange of water from the Miocene onwards.The temperature in the Paratethys was very similar to that inferred from brachiopods from the Middle Miocene of western France, but the seawater εNd value here is identical to that of contemporaneous Atlantic Ocean. A Late Miocene lingulid brachiopod from southern Portugal has a high δ18OPO4, similar to the specimens investigated from the North Sea, reflecting either a deep water habitat or formation after the onset of major global cooling that resulted in an increased δ18O value of seawater. The εNd value of −8.4 for this site is compatible with an influence of Mediterranean outflow.