Lithium-to-calcium ratios in Modern, Cenozoic, and Paleozoic articulate brachiopod shells

• Published in: Paleoceanography
• Main Authors: Delaney, M. L., Popp, B. N., Lepzelter, C. G., Anderson, T. F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AGU (American Geophysical Union) 1989
• Subjects: Planktonic foraminifera
• Online Access: https://oceanrep.geomar.de/id/eprint/29490/; https://oceanrep.geomar.de/id/eprint/29490/1/Delaney.pdf; https://doi.org/10.1029/PA004i006p00681

Li/Ca ratios in modern brachiopod shells generally correlate inversely with growth temperature, ranging from ∼20 µmol/mol at 30°C to ∼50 µmol/mol at 0°C with no apparent interspecific offsets. Causes of the temperature effect on Li/Ca ratios are not yet understood. Cenozoic brachiopod Li/Ca ratios average ∼30 µmol/mol, similar to the average observed in modern brachiopods. Relatively constant Li/Ca ratios for Eocene to Pleistocene nonluminescent brachiopod shells, consistent with previous observations of Cenozoic planktonic foraminifera, support the conclusion of little variation in Cenozoic seawater Li/Ca. Nonluminescent portions of Permian and Carboniferous brachiopods have Li/Ca ratios substantially lower (generally <10 µmol/mol) than modern, Cenozoic, or Devonian samples. Mass balance considerations, constrained by δ18O of brachiopods, suggest that low Li concentrations in Permo-Carboniferous seawater could be the result of a lower flux of dissolved Li from the continents and/or a higher flux of Li from seawater to clastic marine sediments. Nonluminescent Devonian brachiopods from a single hand specimen have Li/Ca ratios around 70% of the modern average. These Li/Ca ratios can be explained by either somewhat higher temperature with constant seawater Li/Ca, somewhat lower seawater Li/Ca at constant temperature, or a combination of slightly elevated temperature and slightly lower seawater Li/Ca.