TY - JOUR
T1 - Out of the oven and into the fire
T2 - Unexpected preservation of the seasonal δ18O cycle following heating experiments on shell carbonate
AU - Moon, Lindsay R.
AU - Judd, Emily J.
AU - Thomas, Jay
AU - Ivany, Linda C.
N1 - Funding Information:
A number of people made this work possible, and we thank them all. Amanda Pattridge, Bruce Wilkinson, and LCI collected the Spisula shell from Atlantic City, NJ. Shiv Das provided the shell of live-collected Spisula. Edward Berry provided access to the X-ray diffractometer at SUNY Upstate Medical University. Karin Ruhlandt provided access to the X-ray diffractometer at Syracuse University. Alex MacKnight and Jacqueline Corbett assisted with the SEM images. Lora Wingate at the University of Michigan and Bruce Barnett at the University of Kansas performed stable isotope analyses. Bruce Wilkinson provided feedback and made many helpful suggestions on the manuscript. Two thorough reviewers, together with Tom Algeo and guest editors Melita Peharda and Bernd Schöne, offered feedback that much improved the final product. This research was supported by NSF PLR-1543031 to Ivany, a Small Equipment Grant from Syracuse University's Office of Research ( SEG-26-2019 ) to Ivany that allowed for the purchase of the SEM, a grant from the Syracuse Office of Undergraduate Research & Creative Engagement (SOURCE) at Syracuse University to Moon, and a graduate student research grant from the Geological Society of America to Judd.
Funding Information:
A number of people made this work possible, and we thank them all. Amanda Pattridge, Bruce Wilkinson, and LCI collected the Spisula shell from Atlantic City, NJ. Shiv Das provided the shell of live-collected Spisula. Edward Berry provided access to the X-ray diffractometer at SUNY Upstate Medical University. Karin Ruhlandt provided access to the X-ray diffractometer at Syracuse University. Alex MacKnight and Jacqueline Corbett assisted with the SEM images. Lora Wingate at the University of Michigan and Bruce Barnett at the University of Kansas performed stable isotope analyses. Bruce Wilkinson provided feedback and made many helpful suggestions on the manuscript. Two thorough reviewers, together with Tom Algeo and guest editors Melita Peharda and Bernd Schöne, offered feedback that much improved the final product. This research was supported by NSFPLR-1543031 to Ivany, a Small Equipment Grant from Syracuse University's Office of Research (SEG-26-2019) to Ivany that allowed for the purchase of the SEM, a grant from the Syracuse Office of Undergraduate Research & Creative Engagement (SOURCE) at Syracuse University to Moon, and a graduate student research grant from the Geological Society of America to Judd.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/1/15
Y1 - 2021/1/15
N2 - Oxygen isotope values of shell carbonate sampled along the growth trajectory of fossil mollusks provide one of the few types of proxy data available for reconstructing seasonal temperature variation in Earth's past. Understanding how diagenesis affects the preservation of seasonal cycles is key to their interpretation in a paleoclimate context. An assumption common in the literature, albeit tenuous, is that the alteration of an aragonite shell to calcite will homogenize intra-shell stable isotope variation, thus attenuating or erasing any seasonal cycle and resetting bulk shell values. Demonstration of regular variation in δ18O values across growth bands in a still-aragonite mollusk is therefore generally interpreted to reflect retention of the primary environmental signal. However, this implied assumption remains untested, and experimental studies have demonstrated that heating can decrease shell δ18O values with negligible mineralogical transformation. Here we investigate how dry heat impacts both the geochemistry and mineralogy of shell aragonite by roasting time-equivalent shell sections of a modern bivalve, Spisula solidissima, at 200 °C for intervals ranging from 2 hours to 2 weeks, and comparing seasonal oxygen isotope variations recovered from the same one-year period of shell accretion with those from untreated shell. Oxygen isotope values from heated shell sections decline by as much as 1.5‰ across all parts of the ~2.5‰ annual cycle, and degree of 18O depletion decreases logarithmically with time heated. Neither Raman spectroscopy nor X-ray diffraction indicate mineralogic change in association with heating. Scanning electron microscopy reveals that heating results in some intra-crystal pitting and subtle smoothing of crystal edges, but heated shell lacks any textural evidence for inversion to calcite, suggesting that fine-scale isotopic exchange may take place with shell-bound water vapor and/or organic matter. The surprising magnitude of this shift in the absence of mineralogic transformation highlights the potential impact of diagenetic processes on the preservation of paleotemperature signals, seasonal or otherwise, in accretionary biogenic carbonates, and suggests a need for more stringent guidelines in assessing the preservation of these materials during the employment of common sclerochronological methodologies.
AB - Oxygen isotope values of shell carbonate sampled along the growth trajectory of fossil mollusks provide one of the few types of proxy data available for reconstructing seasonal temperature variation in Earth's past. Understanding how diagenesis affects the preservation of seasonal cycles is key to their interpretation in a paleoclimate context. An assumption common in the literature, albeit tenuous, is that the alteration of an aragonite shell to calcite will homogenize intra-shell stable isotope variation, thus attenuating or erasing any seasonal cycle and resetting bulk shell values. Demonstration of regular variation in δ18O values across growth bands in a still-aragonite mollusk is therefore generally interpreted to reflect retention of the primary environmental signal. However, this implied assumption remains untested, and experimental studies have demonstrated that heating can decrease shell δ18O values with negligible mineralogical transformation. Here we investigate how dry heat impacts both the geochemistry and mineralogy of shell aragonite by roasting time-equivalent shell sections of a modern bivalve, Spisula solidissima, at 200 °C for intervals ranging from 2 hours to 2 weeks, and comparing seasonal oxygen isotope variations recovered from the same one-year period of shell accretion with those from untreated shell. Oxygen isotope values from heated shell sections decline by as much as 1.5‰ across all parts of the ~2.5‰ annual cycle, and degree of 18O depletion decreases logarithmically with time heated. Neither Raman spectroscopy nor X-ray diffraction indicate mineralogic change in association with heating. Scanning electron microscopy reveals that heating results in some intra-crystal pitting and subtle smoothing of crystal edges, but heated shell lacks any textural evidence for inversion to calcite, suggesting that fine-scale isotopic exchange may take place with shell-bound water vapor and/or organic matter. The surprising magnitude of this shift in the absence of mineralogic transformation highlights the potential impact of diagenetic processes on the preservation of paleotemperature signals, seasonal or otherwise, in accretionary biogenic carbonates, and suggests a need for more stringent guidelines in assessing the preservation of these materials during the employment of common sclerochronological methodologies.
KW - Bivalve
KW - Diagenesis
KW - Sclerochronology
KW - Seasonality
KW - Stable isotope
UR - http://www.scopus.com/inward/record.url?scp=85097475628&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85097475628&partnerID=8YFLogxK
U2 - 10.1016/j.palaeo.2020.110115
DO - 10.1016/j.palaeo.2020.110115
M3 - Article
AN - SCOPUS:85097475628
SN - 0031-0182
VL - 562
JO - Palaeogeography, Palaeoclimatology, Palaeoecology
JF - Palaeogeography, Palaeoclimatology, Palaeoecology
M1 - 110115
ER -