Assessing potential for diagenetic overprinting of climatic signals in benthic foraminifera: Preliminary results.
Robert K. Poirier, Reinhard Kozdon, Maureen Raymo, Morgan Schaller
Benthic foraminiferal stable isotope records (δ18O, δ13C) are the most common paleoclimate records produced to date, which capture changes in temperature, ice volume, and the global carbon system on orbital to sub-millennial timescales. General relationships between deep sea δ18O and sea level have long been established, and more recent paired δ18O and Mg/Ca records seek to disentangle the temperature and ice volume components of corresponding sea level records. However, the extent to which diagenesis may potentially alter the original isotopic signature recorded in tests of benthic foraminifera remains relatively undefined. We present preliminary results of a project focused on constraining the extent to which such diagenetic overprinting might alter sea level estimates based on records produced from modern to mid-Pliocene Cibicidoides and Uvigerina specimens. These include advanced imaging techniques (SEM, CL-spectroscopy), single shell stable isotope analyses (δ18O, δ13C), and chamber wall trace metal profiles (LA-ICPMS) paired with in situ δ18O analyses (SIMS). In addition, we present strict specimen screening criteria developed based on a new quantitative assessment of visual preservation in both individual foraminiferal tests and whole assemblages.
http://forams2018.wp.st-andrews.ac.uk
Session II: Advances in Foraminiferal Geochemistry
Conveners: Jelle Bijma, Howard Spero
Session Overview: http://forams2018.wp.st-andrews.ac.uk/program/
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This content will become publicly available on February 1, 2025
Trace element concentrations as proxies for diagenetic alteration in the African archaeofaunal record: Implications for isotope analysis
Isotope ratio analyses of trace elements are applied to tooth enamel, ostrich eggshell, and other archaeological hard tissues to infer mobility and other aspects of hominin and animal paleoecology. It has been assumed that these highly mineralized tissues are resistant to diagenetic alteration, but this is seldom tested and some studies document diagenetic alteration over brief time spans. Here, we build on existing research on Maximum Threshold Concentrations (MTCs) to develop screening tools for diagenesis that can inform heavy isotopic analyses. The premise of the MTC approach is that archaeological tissues are likely contaminated and unsuitable for isotope ratio analysis when they exceed characteristic modern concentration ranges of trace elements. Furthermore, we propose a new metric called the Maximum Threshold Ratio (MTR) of 85Rb/88Sr or whole element Rb/Sr, which can be measured simultaneously with 87Sr/86Sr during laser ablation (LA) MC-ICP-MS or applied during post hoc screening of specimens. We analyzed 56 enamel samples from modern Kenyan mammals and 34 modern ostrich eggshells from South Africa, Namibia, and the United States by solution ICP-MS, as well as a subset of shells using LA-MC-ICP-MS. Our results indicate that thresholds are consistent across taxa at a single location, but likely vary across locations. Therefore, MTCs and MTRs need to be tissue and locality specific, but not necessarily taxon-specific. Other important differences are observed between the inner and outer surfaces of the eggshells and between LA and solution ICP-MS. This exploratory study provides guidelines for building reference thresholds to screen enamel and eggshell for diagenesis potentially impacting biogenic isotope ratios.
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- Award ID(s):
- 2018010
- NSF-PAR ID:
- 10488648
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of Archaeological Science: Reports
- Volume:
- 53
- Issue:
- C
- ISSN:
- 2352-409X
- Page Range / eLocation ID:
- 104403
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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