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Determining the Diagenetic Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using Clumped Isotopes

Loyd, Sean J. and Corsetti, Frank A. and Eiler, John M. and Tripati, Aradhna K. (2012) Determining the Diagenetic Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using Clumped Isotopes. Journal of Sedimentary Research, 82 (12). pp. 1006-1016. ISSN 1527-1404. doi:10.2110/jsr.2012.85.

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Carbonate-δ^(18)O paleothermometry is used in many diagenetic studies to unravel the thermal history of basins. However, this approach generally requires an assumed pore-water δ^(18)O (δ^(18)O_(pw)) value, a parameter that is difficult to quantify in past regimes. In addition, many processes can change the original isotopic composition of pore water, which further complicates the assignment of an initial δ^(18)O_(pw) and can lead to erroneous temperature estimates. Here, we use clumped-isotope thermometry, a proxy based on the ^(13)C–^(18)O bond abundance in carbonate minerals, to evaluate the temperatures of concretion formation in the Miocene Monterey Formation and the Cretaceous Holz Shale, California. These temperatures are combined with established carbonate–water fractionation factors to calculate the associated δ^(18)O_(pw). Results demonstrate that diagenetic processes can modify the δ^(18)O of ancient pore water, confounding attempts to estimate diagenetic temperatures using standard approaches. Clumped-isotope-based temperature estimates for Monterey Formation concretions range from ∼ 17 to 35°C, up to ∼ 12°C higher than traditional δ^(18)O carbonate–water paleothermometry when δ^(18)O_(pw) values are assumed to equal Miocene seawater values. Calculated δ^(18)O_(pw) values range from +0.3 to +2.5‰ (VSMOW)—higher than coeval Miocene seawater, likely due to δ^(18)O_(pw) modification accompanying diagenesis of sedimentary siliceous phases. Clumped-isotope temperatures for the Holz Shale concretions range from ∼ 33 to 44°C, about 15 to 30°C lower than temperatures derived using the traditional method. Calculated δ^(18)O_(pw) values range from −5.0 to −2.9‰ and likely reflect the influx of meteoric fluids. We conclude that the use of clumped isotopes both improves the accuracy of temperature reconstructions and provides insight into the evolution of δ^(18)O_(pw) during diagenesis, addressing a longstanding conundrum in basin-evolution research.

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Additional Information:© 2012 Society for Sedimentary Geology. Received 18 May 2012; accepted 26 September 2012. Published Online: December 2012. The authors would like to thank Rob Eagle, David Bottjer, Will Berelson, and Jon Schwalbach for insightful scientific discussion. Reviews and input by Cedric John, Associate Editor Peter Mozley, and Editor Gene Rankey helped significantly strengthen the final manuscript. This research was supported by the Agouron Institute, the American Chemical Society’s Petroleum Research Fund (grant # 51182-DNI2) and the National Science Foundation (EAR grant # 0949191) through awards to A.T. and S.L.
Funding AgencyGrant Number
Agouron InstituteUNSPECIFIED
American Chemical Society Petroleum Research Fund51182-DNI2
NSFEAR 0949191
Issue or Number:12
Record Number:CaltechAUTHORS:20130301-144025702
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Official Citation: Sean J. Loyd, Frank A. Corsetti, John M. Eiler, and Aradhna K. Tripati Determining the Diagenetic Conditions of Concretion Formation: Assessing Temperatures and Pore Waters Using Clumped Isotopes Journal of Sedimentary Research December 2012 82:1006-1016; published online December 17, 2012, doi:10.2110/jsr.2012.85
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37255
Deposited By: Ruth Sustaita
Deposited On:01 Mar 2013 23:10
Last Modified:09 Nov 2021 23:27

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