TY - JOUR
T1 - Low and seasonally variable salinity in the Pennsylvanian equatorial Appalachian Basin
AU - Jimenez, Marie Y.
AU - Ivany, Linda C.
AU - Judd, Emily J.
AU - Henkes, Gregory
N1 - Funding Information:
Funding for this research comes from student research grants to MYJ from the Paleontological Society and the Geological Society of America and from the John J. Prucha Field Research Fund at Syracuse University. Thanks to Lindsay Moon for assistance in the field and with micromilling. Additional specimens were graciously provided by Gordon Baird, Joseph Carter, and the Carnegie Museum of Natural History, and Gordon Baird is especially thanked for making us aware of these deposits. Bruce Barnett at the Keck-NSF Paleoenvironmental and Environmental Laboratory at the University of Kansas provided stable isotope analyses, Edward Berry at SUNY Upstate Medical University helped with XRD, Christopher McRoberts at SUNY Cortland helped with SEM, and Deb Driscoll at SUNY-ESF provided elemental analyses. Bruce Wilkinson, Scott Samson, and Chris Junium read the manuscript and it is stronger for their insights. Isabel Montañez, Ethan Grossman, and an anonymous reviewer provided substantive and helpful feedback that much improved the final paper. Louis Derry handled the manuscript for EPSL, and we thank him for his insights.
Funding Information:
Funding for this research comes from student research grants to MYJ from the Paleontological Society and the Geological Society of America and from the John J. Prucha Field Research Fund at Syracuse University . Thanks to Lindsay Moon for assistance in the field and with micromilling. Additional specimens were graciously provided by Gordon Baird, Joseph Carter, and the Carnegie Museum of Natural History, and Gordon Baird is especially thanked for making us aware of these deposits. Bruce Barnett at the Keck-NSF Paleoenvironmental and Environmental Laboratory at the University of Kansas provided stable isotope analyses, Edward Berry at SUNY Upstate Medical University helped with XRD, Christopher McRoberts at SUNY Cortland helped with SEM, and Deb Driscoll at SUNY-ESF provided elemental analyses. Bruce Wilkinson, Scott Samson, and Chris Junium read the manuscript and it is stronger for their insights. Isabel Montañez, Ethan Grossman, and an anonymous reviewer provided substantive and helpful feedback that much improved the final paper. Louis Derry handled the manuscript for EPSL, and we thank him for his insights.
Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/8/1
Y1 - 2019/8/1
N2 - 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 tend to be low and increasingly depleted with age. Demonstrating the preservation of original chemistry and thus eliminating diagenesis as a factor is a primary hurdle in reconstructing climatic conditions in deep time. Here, we report stable isotope data from serially sampled, Middle Pennsylvanian mollusks from the tropical Appalachian Basin of Kentucky, USA. X-ray diffraction and scanning electron microscopy indicate an aragonite mineralogy with retention of primary microtextures, elemental chemistry is consistent with the shells of living mollusks, and δ18O data reveal regular cyclic variation over ontogeny, together suggesting that original shell carbonate is preserved and records environmental 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‰, calling for significant summertime runoff of fresh water to the basin in which the shell-producing organisms grew. Our data extend a documented trend toward more depleted carbonate values eastward across the midcontinent sea with increasing distance from Panthalassa, reflecting a salinity gradient driven largely by isotopically depleted and seasonal runoff from the Central Pangaean Mountains. Mollusk data support the primary nature of low δ18O values from brachiopod shells in the midcontinent, but they also highlight the problems with calculating paleotemperatures from δ18O values of carbonates precipitated in epicontinental seas by assuming a marine seawater composition. While carbonate clumped isotope paleothermometry is a potential solution to this seawater δ18O ‘problem’, we demonstrate that such data from these aragonitic samples are related to burial diagenesis and not the Pennsylvanian paleoenvironment. The bias toward samples from such settings in the Paleozoic, because continental margins are more likely to be deformed, suggests that postulated regional and global temperature histories should be treated with caution until epeiric oxygen isotope seawater values can be better constrained.
AB - 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 tend to be low and increasingly depleted with age. Demonstrating the preservation of original chemistry and thus eliminating diagenesis as a factor is a primary hurdle in reconstructing climatic conditions in deep time. Here, we report stable isotope data from serially sampled, Middle Pennsylvanian mollusks from the tropical Appalachian Basin of Kentucky, USA. X-ray diffraction and scanning electron microscopy indicate an aragonite mineralogy with retention of primary microtextures, elemental chemistry is consistent with the shells of living mollusks, and δ18O data reveal regular cyclic variation over ontogeny, together suggesting that original shell carbonate is preserved and records environmental 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‰, calling for significant summertime runoff of fresh water to the basin in which the shell-producing organisms grew. Our data extend a documented trend toward more depleted carbonate values eastward across the midcontinent sea with increasing distance from Panthalassa, reflecting a salinity gradient driven largely by isotopically depleted and seasonal runoff from the Central Pangaean Mountains. Mollusk data support the primary nature of low δ18O values from brachiopod shells in the midcontinent, but they also highlight the problems with calculating paleotemperatures from δ18O values of carbonates precipitated in epicontinental seas by assuming a marine seawater composition. While carbonate clumped isotope paleothermometry is a potential solution to this seawater δ18O ‘problem’, we demonstrate that such data from these aragonitic samples are related to burial diagenesis and not the Pennsylvanian paleoenvironment. The bias toward samples from such settings in the Paleozoic, because continental margins are more likely to be deformed, suggests that postulated regional and global temperature histories should be treated with caution until epeiric oxygen isotope seawater values can be better constrained.
KW - Appalachian Basin
KW - Pennsylvanian
KW - mollusk
KW - oxygen isotope
KW - salinity
KW - seasonality
UR - http://www.scopus.com/inward/record.url?scp=85065901908&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85065901908&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2019.04.051
DO - 10.1016/j.epsl.2019.04.051
M3 - Article
AN - SCOPUS:85065901908
SN - 0012-821X
VL - 519
SP - 182
EP - 191
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -