Zooming in REE and Other Trace Elements on Conodonts: Does Taxonomy Guide Diagenesis?

• 作 者: Luca Medici Martina Savioli Annalisa Ferretti Daniele Malferrari
• 机 构: National Research Council of Italy, Institute of Methodologies for Environmental Analysis,C. da S. L
• 出 处: 地球科学学刊（英文版）
• 发表日期: 2021年3期
• 关键词: bioapatite crystallinity index HFSE laser ablation mass spectrometry microdiffra

Conodont elements are calcium phosphate (apatite structure) mineralized remains of the cephalic feeding apparatus of an extinct marine organism. Due to the high affinity of apatite for rare earth elements (REE) and other high field strength elements (HFSE), conodont elements were fre- quently assumed to be a reliable archive of sea-water composition and changes that had occurred dur- ing diagenesis. Likewise, the crystallinity index of bioapatite, i.e., the rate of crystallinity of biologically mediated apatite, should be generally linearly dependent on diagenetic alteration as the greater (and longer) the pressure and temperature to which a crystal is exposed, the greater the resulting crystallin- ity. In this study, we detected the uptake of HFSE in conodont elements recovered from a single strati- graphic horizon in the Upper Ordovician of Normandy (France). Assuming therefore that all the specimens have undergone an identical diagenetic history, we have assessed whether conodont taxon- omy (and morphology) impacts HFSE uptake and crystallinity index. We found that all conodont ele- ments are characterized by a clear diagenetic signature, with minor but significant differences among taxa. These distinctions are evidenced also by the crystallinity index values which show positive correla- tions with some elements and, accordingly, with diagenesis; however, correlations with the crystallinity index strongly depend on the method adopted for its calculation.