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Carbonate clumped isotope constraints on Silurian ocean temperature and seawater δ^(18)O

Cummins, Renata C. and Finnegan, Seth and Fike, David A. and Eiler, John M. and Fischer, Woodward W. (2014) Carbonate clumped isotope constraints on Silurian ocean temperature and seawater δ^(18)O. Geochimica et Cosmochimica Acta, 140 . pp. 241-258. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20140721-091040266

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Abstract

Much of what we know about the history of Earth’s climate derives from the chemistry of carbonate minerals in the sedimentary record. The oxygen isotopic compositions (δ^(18)O) of calcitic marine fossils and cements have been widely used as a proxy for past seawater temperatures, but application of this proxy to deep geologic time is complicated by diagenetic alteration and uncertainties in the δ^(18)O of seawater in the past. Carbonate clumped isotope thermometry provides an independent estimate of the temperature of the water from which a calcite phase precipitated, and allows direct calculation of the δ^(18)O of the water. The clumped isotope composition of calcites is also highly sensitive to recrystallization and can help diagnose different modes of diagenetic alteration, enabling evaluation of preservation states and identification of the most pristine materials from within a sample set—critical information for assessing the quality of paleoproxy data generated from carbonates. We measured the clumped isotope composition of a large suite of calcitic fossils (primarily brachiopods and corals), sedimentary grains, and cements from Silurian (ca. 433 Ma) stratigraphic sections on the island of Gotland, Sweden. Substantial variability in clumped isotope temperatures suggests differential preservation with alteration largely tied to rock-buffered diagenesis, complicating the generation of a stratigraphically resolved climate history through these sections. Despite the generally high preservation quality of samples from these sections, micro-scale observations of calcite fabric and trace metal composition using electron backscatter diffraction and electron microprobe analysis suggest that only a subset of relatively pristine samples retain primary clumped isotope signatures. These samples indicate that Silurian tropical oceans were likely warm (33 ± 7 °C) and similar in oxygen isotopic composition to that estimated for a “modern” ice-free world (δ^(18)O_(VSMOW) of −1.1 ± 1.3‰). This result joins the growing body of evidence that suggests the δ^(18)O of Earth’s ocean waters has remained broadly constant through time.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.gca.2014.05.024DOIArticle
http://www.sciencedirect.com/science/article/pii/S0016703714003536PublisherArticle
ORCID:
AuthorORCID
Fike, David A.0000-0003-2848-0328
Fischer, Woodward W.0000-0002-8836-3054
Additional Information:© 2014 Elsevier B. V. Received 12 January 2014; accepted in revised form 19 May 2014; available online 2 June 2014. We acknowledge Nami Kitchen, Kristin Bergmann, Daniel Stolper, and the rest of the Eiler lab for help with the clumped isotope measurements and J. Garrecht Metzger for assistance in field collection. We thank Chi Ma for his assistance with the SEM and the E-probe, and Joel Hurowitz for help with trace element geochemistry. We also thank Mark Garcia and David Mann for their help with sample processing, Clint Cummins for help with statistics, and Uno Granquist and Anders Birgesson at Cementa for quarry access. We are also grateful to Karlis Muehlenbachs and one anonymous reviewer whose comments greatly improved the quality of our data analysis and manuscript. This work was supported by NSF grant EAR-1053523 and the Agouron Institute.
Funders:
Funding AgencyGrant Number
NSFEAR-1053523
Agouron InstituteUNSPECIFIED
Record Number:CaltechAUTHORS:20140721-091040266
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140721-091040266
Official Citation:Cummins, R. C., Finnegan, S., Fike, D. A., Eiler, J. M., & Fischer, W. W. (2014). Carbonate clumped isotope constraints on Silurian ocean temperature and seawater δ18O. Geochimica et Cosmochimica Acta, 140(0), 241-258. doi: http://dx.doi.org/10.1016/j.gca.2014.05.024
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:47361
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:21 Jul 2014 17:13
Last Modified:13 Dec 2019 00:44

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