DOI: 10.1016/j.palaeo.2015.09.040
论文题名: Middle–Late Ordovician (Darriwilian–Sandbian) decoupling of global sulfur and carbon cycles: Isotopic evidence from eastern and southern Laurentia
作者: Young S.A. ; Gill B.C. ; Edwards C.T. ; Saltzman M.R. ; Leslie S.A.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2016
卷: 458 起始页码: 118
结束页码: 132
语种: 英语
英文关键词: Carbon isotopes
; Ordovician
; Oxygenation
; Pyrite burial
; Sulfur isotopes
; Weathering
英文摘要: Middle–Late Ordovician sequences from the Appalachian Basin and Arbuckle Mountain regions of North America were analyzed for carbonate-associated sulfate (δ34SCAS) and pyrite (δ34Spyr) paired with carbonate (δ13Ccarb) and organic matter (δ13Corg) chemostratigraphy. Two major negative drops in δ34SCAS (12‰ excursions) are recognized: the older decline in δ34SCAS occurs within the Histiodella holodentata–Phragmodus polonicus Conodont Zones and the younger drop is within the Cahabagnathus sweeti–Amorphognathus tvaerensis (Baltoniodus gerdae subzone) Zones. These overall these negative shifts in δ34SCAS have an antithetical relationship with positive shifts in δ34Spyr (~+ 10‰) and δ13Ccarb (~+ 2‰) recorded in the same successions. The older negative δ34SCAS shift is coincident with the widely documented mid-Darriwilian δ13C excursion (MDICE), and the younger negative δ34SCAS shift is coincident with another positive δ13Ccarb shift in the early Sandbian. Geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative δ34SCAS trends. Additionally, a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends. While increased crustal weathering is broadly consistent with a sea-level lowstand, and the seawater 87Sr/86Sr isotope record of change in continental weathering in the late Darriwilian Stage of the Ordovician, geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in δ34SCAS. These antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates. Pulses of oceanic ventilation would have expanded habitable environments for marine organisms, and thus is broadly consistent with major increases in biodiversification during this period of the Ordovician. © 2015 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/68332
Appears in Collections: 过去全球变化的重建
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作者单位: Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, FL, United States; Department of Geosciences, Virginia Polytechnic Institute & University, Blacksburg, VA, United States; Department of Earth and Planetary Sciences, Washington University, Saint Louis, MO, United States; School of Earth Sciences, The Ohio State University, Columbus, OH, United States; Department of Geology and Environmental Science, James Madison University, Harrisonburg, VA, United States
Recommended Citation:
Young S.A.,Gill B.C.,Edwards C.T.,et al. Middle–Late Ordovician (Darriwilian–Sandbian) decoupling of global sulfur and carbon cycles: Isotopic evidence from eastern and southern Laurentia[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2016-01-01,458