Trace and rare earth element compositions of Silurian conodonts from the Vesiku Bone Bed: Histological and palaeoenvironmental implications

Abstract

In-situ minor, trace and rare earth element (REE) compositions have been measured in conodonts from the lower Silurian Vesiku Bone Bed (Estonia), with the aim to visualize and to quantify conodont apatite elemental geochemistry, to evaluate compositional differences between conodont histologies, and to evaluate the use of conodont chemistry as a palaeobiological or palaeoenvironmental proxy. Tissue-selective analyses of minor, trace and rare earth element compositions of albid, hyaline, and basal tissues demonstrated significant chemical offsets among these histologies. The albid tissue had the lowest REE and trace element concentrations, suggesting crystallinity-determined better resilience to diagenetic alteration as documented in previous studies. Conversely, the basal tissue had highest concentrations of REEs and many trace elements, except for Sr that showed an opposite trend. The higher concentrations in albid and hyaline tissues supports the in-vivo Sr incorporation by conodont crown. Nonetheless, the obtained SN-normalized REE patterns were uniform through all the analyzed conodont taxa and different tissues, implying common diagenetic history. Absence of a Ce anomaly, and defined negative Eu anomaly indicate reducing conditions during early burial. These results validate current interpretations of the palaeoenvironmental conditions during the deposition of Vesiku Bone Bed and bolsters the use of REEs in Palaeozoic marine vertebrates as an important palaeoenvironmental proxy.