Syracuse University SURFACE Theses - ALL August 2018 Seasonally resolved δ18O from Pennsylvanian mollusk aragonite Marie Yerill Jimenez Syracuse University Follow this and additional works at: https://surface.syr.edu/thesis Part of the Physical Sciences and Mathematics Commons Recommended Citation Jimenez, Marie Yerill, "Seasonally resolved δ18O from Pennsylvanian mollusk aragonite" (2018). Theses - ALL. 264. https://surface.syr.edu/thesis/264 This Thesis is brought to you for free and open access by SURFACE. It has been accepted for inclusion in Theses - ALL by an authorized administrator of SURFACE. For more information, please contact [email protected]. Abstract Use of the δ18O thermometer in deep time investigations is complicated by uncertainty in the oxygen isotopic composition of seawater and an increasing potential for diagenetic alteration with age. These concerns are particularly important when considering that δ18O values from Paleozoic marine carbonates are generally low and show a depletion trend with increasing age. Competing explanations for this trend include increasing alteration with age, evolution of seawater δ18O through time, and increasing ocean temperatures with age. Demonstrating the preservation of original mineralogy, thus eliminating diagenesis as a factor, is a primary hurdle in deconvolving potential causes. Here, we report data from serially sampled, Middle Pennsylvanian mollusks from the Appalachian Basin of Kentucky. XRD and SEM analyses indicate an aragonitic mineralogy with retention of primary microtextures, and δ18O data reveal regular cyclic variation over ontogeny, suggesting that original shell carbonate is preserved and records primary environmental (presumably seasonal) conditions over the life history of the animal. However, values are depleted, centering around -4.6‰, and intraannual variation is significant, spanning up to 2.2‰. Recent work on the Carboniferous of the U.S. suggested that negative values reflect a regional salinity trend toward more depleted values with increasing distance from Panthalassa. Our data extend the trend eastward, suggesting significant freshwater input closer to the Allegheny Front. However, the high degree of seasonality differs from published data in the basin, suggesting that mollusks record conditions in nearshore settings that receive seasonally variable contributions of isotopically depleted runoff. Although our data support the primary nature of low δ18O values from brachiopod shells, they also highlight the influence that δ18O values from epicontinental seas may have on the Paleozoic depletion trend. Seasonally resolved δ18O from Pennsylvanian mollusk aragonite By Marie Y. Jimenez B.S. University of Rhode Island, 2016 THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences Syracuse University August 2018 Copyright © Marie Yerill Jimenez 2018 All Rights Reserved Acknowledgements Funding for this research comes from student research grants from Paleontological Society and the Geological Society of America and from the John J. Prucha Field Research Fund at Syracuse University. Part of the specimens for this study were provided by Carnegie Museum of Natural History, Dr. Gordon C. Baird at SUNY Fredonia, and Dr. Joseph G. Carter at UNC Chapel Hill. I would also like to thank Lindsay R. Moon for assistance in field work done the summer of 2017 to collect more specimens. Thanks to Bruce Barnett at the Keck-NSF Paleoenvironmental and Environmental Laboratory at Kansas University for performing the stable isotope analyses and to Dr. Edward Berry at SUNY Upstate Medical University for training and access to XRD. Thanks to Dr. Christopher McRoberts at SUNY Cortland for helping me perform SEM analyses. I want to thank my advisor Dr. Linda Ivany for her continued and unwavering support throughout my two years here. I am extremely grateful for her guidance, feedback, and mentorship which has truly helped me make the best out of my graduate school experience. Thanks also to the Paleo X extended research group, for providing a sense of community and a venue for weekly scientific discussion; I have learned so much from being a part of this group. I also want to thank Emily Judd for her help with lab work but most importantly for her conversation and mentorship. Being her teaching assistant this past semester has been inspiring. Thanks to my committee members Dr. Christopher Junium and Dr. Scott Samson who have provided valuable feedback at various stages of this study. Lastly, thanks to the Department of Earth Sciences (faculty, staff, and graduate students) for helping and encouraging me during my time here. iv Table of Contents Abstract.............................................................................................................................................i Title Page.........................................................................................................................................ii Acknowledgements.........................................................................................................................iv Table of Contents.............................................................................................................................v List of Figures.................................................................................................................................vi List of Tables...................................................................................................................................vi Introduction......................................................................................................................................1 Geologic Setting and Taxa Sampled................................................................................................2 Methodology....................................................................................................................................3 Results..............................................................................................................................................4 Discussion........................................................................................................................................5 Summary........................................................................................................................................12 Figures............................................................................................................................................13 Supplement....................................................................................................................................17 References......................................................................................................................................31 v List of Figures Main Text Figure 1. Paleogeography, stratigraphy, and samples........................................................13 Figure 2. Oxygen Carbon cross-plot...................................................................................14 Figure 3. Oxygen isotope profiles......................................................................................15 Figure 4. Conceptual model of U.S. epicontinental sea.....................................................16 Supplement Figure S1. Trace element cross-plot..................................................................................17 Figure S2. Temperature ranges based on water composition............................................18 List of Tables Supplement Table S1. Trace element data.............................................................................................19 Table S2. Oxygen and carbon isotope data........................................................................20 vi Introduction The oxygen isotope paleotemperature proxy has been essential in identifying small and large scale environmental change during the relatively recent geologic past (e.g., Emiliani, 1955; Zachos et al., 2008). However, its application to investigations of paleoenvironmental conditions farther back in time has resulted in controversy over the oxygen isotopic composition of seawater 18 (δ Ow) and sea surface temperatures (SST) through time. These concerns are wrought, in 18 particular, by the oxygen isotope values of Paleozoic marine carbonates (δ Ocarb), which show a general depletion with increasing age (Jaffres et al., 2007; Veizer et al., 1997). The Paleozoic marine oxygen isotope record is predominantly derived from the calcitic shells of brachiopods (Veizer et al., 1997), favored because of their prevalence in the rock record and their resistance to diagenetic alteration (e.g., Carpenter & Lohmann, 1995; Grossman, 2012a). The wide range of values in any given time slice, however, has raised questions about the reliability of these materials (Grossman, 2012b). Eliminating the potential influence of diagenetic alteration is a necessary but not straightforward prerequisite before any interpretation can be made. Screening procedures have resulted in an attenuation in the range of the values, yet these remain contentious (Grossman, 2012b; Jaffres et al., 2007). Oxygen isotope data from aragonite, alternatively, are more likely to be primary because of aragonite’s propensity for neomorphism to the more stable calcite (Lowenstam, 1961; Brand, 1989). While aragonite is exceedingly rare in the Paleozoic record, its potential to clarify the significance