TY - JOUR
T1 - Barium-isotopic constraints on the origin of post-Marinoan barites
AU - Crockford, Peter W.
AU - Wing, Boswell A.
AU - Paytan, Adina
AU - Hodgskiss, Malcolm S.W.
AU - Mayfield, Kimberley K.
AU - Hayles, Justin A.
AU - Middleton, Julia E.
AU - Ahm, Anne Sofie C.
AU - Johnston, David T.
AU - Caxito, Fabricio
AU - Uhlein, Gabriel
AU - Halverson, Galen P.
AU - Eickmann, Benjamin
AU - Torres, Marta
AU - Horner, Tristan J.
N1 - Publisher Copyright:
© 2019 Elsevier B.V.
PY - 2019/8/1
Y1 - 2019/8/1
N2 - Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or ‘marine’), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO4-poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record.
AB - Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or ‘marine’), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO4-poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record.
KW - barite
KW - barium cycle
KW - barium isotopes
KW - cryogenian
KW - Marinoan
KW - Snowball Earth
UR - http://www.scopus.com/inward/record.url?scp=85067921773&partnerID=8YFLogxK
U2 - 10.1016/j.epsl.2019.05.018
DO - 10.1016/j.epsl.2019.05.018
M3 - Article
AN - SCOPUS:85067921773
SN - 0012-821X
VL - 519
SP - 234
EP - 244
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
ER -