Stable isotope analysis of Dacryoconarid carbonate microfossils: a new tool for Devonian oxygen and carbon isotope stratigraphy

• Published in: Rapid Communications in Mass Spectrometry
• Main Authors: Frappier, Amy Benoit, Lindemann, Richard H., Frappier, Brian R.
• Other Authors: National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Planktonic foraminifera
• Online Access: http://dx.doi.org/10.1002/rcm.7159; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Frcm.7159; https://onlinelibrary.wiley.com/doi/full/10.1002/rcm.7159

Rationale Dacryoconarids are extinct marine zooplankton known from abundant, globally distributed calcite microfossils in the Devonian, but their shell stable isotope composition has not been previously explored. Devonian stable isotope stratigraphy is currently limited to less common invertebrates or bulk rock analyses of uncertain provenance. As with Cenozoic planktonic foraminifera, isotopic analysis of dacryoconarid shells could facilitate higher‐resolution, geographically widespread stable isotope records of paleoenvironmental change, including marine hypoxia events, climate changes, and biocrises. We explored the use of Dacryoconarid isotope stratigraphy as a viable method in interpreting paleoenvironments. Methods We applied an established method for determining stable isotope ratios (δ 13 C, δ 18 O values) of small carbonate microfossils to very well‐preserved dacryoconarid shells. We analyzed individual calcite shells representing five common genera using a Kiel carbonate device coupled to a MAT 253 isotope ratio mass spectrometer. Calcite shell δ 13 C and δ 18 O values were compared by taxonomic group, rock unit, and locality. Results Single dacryoconarid calcite shells are suitable for stable isotope analysis using a Kiel‐IRMS setup. The dacryoconarid shell δ 13 C values (–4.7 to 2.3‰) and δ 18 O values (–10.3 to –4.8‰) were consistent across taxa, independent of shell size or part, but varied systematically through time. Lower fossil δ 18 O values were associated with warmer water temperature and more variable δ 13 C values were associated with major bioevents. Dacryoconarid δ 13 C and δ 18 O values differed from bulk rock carbonate values. Conclusions Dacryoconarid individual microfossil δ 13 C and δ 18 O values are highly sensitive to paleoenvironmental changes, thus providing a promising avenue for stable isotope chemostratigraphy to better resolve regional to global paleoceanographic changes throughout the upper Silurian to the upper Devonian. Our results warrant further exploration of ...