DOI: 10.1016/j.gr.2019.12.011
论文题名: Isotopic evidence for partial geochemical decoupling between a Jurassic epicontinental sea and the open ocean
作者: Danise S. ; Price G.D. ; Alberti M. ; Holland S.M.
刊名: Gondwana Research
ISSN: 1342937X
出版年: 2020
卷: 82 语种: 英语
英文关键词: Belemnite
; Bivalve
; Epicontinental sea
; Paleoclimate
; Tethys
英文摘要: We report stable isotope ratios (δ13C, δ18O), minor and trace elements (Mn, Fe, Sr, Mg) together with Ca concentrations from bivalve shells and belemnites from the Middle-Upper Jurassic Sundance Seaway (western United States), we compare them with coeval open-ocean Tethyan data, and reconstruct the palaeo-circulation of seaway waters. The Sundance Seaway was a 2000 km long epicontinental sea with a single entrance at mid latitudes (55–60°N), which would have fostered substantial evolution of seawater chemistry relative to its open-ocean source. Samples are distributed across the 13-million-year marine history of the seaway, and across a 540 km east-west transect spanning Wyoming. Delta13C values are in the same range as Tethyan data, and this suggests that they might record global changes in the carbon cycle, with one exception in the Oxfordian. Delta18O values from the seaway are in contrast highly depleted compared with Tethyan data (−2 to −6‰), and they indicate unrealistically high palaeotemperatures (20–40 °C), assuming an isotopic composition of seawater of −1‰, as generally used for the Jurassic. Given more realistic temperature estimates from Mg/Ca ratios of bivalve shells (10–25 °C), we explain such negative δ18O values by the southward inflow of normal-salinity, isotopically depleted (−3, −4‰), Arctic water into the seaway. Such water would become progressively more saline and denser as it flowed towards the southernmost portion of the seaway. In the Late Jurassic, characterised by wetter climate conditions, less dense Sundance waters may have instead exhibited a northward flow, reducing the southward surface flow from the Arctic. The observed partial geochemical decoupling of Sundance Seaway water masses from the open ocean strongly recommends caution in interpreting the geochemical record of ancient shallow seas, where local, regional and global drivers of change all need to be considered. © 2020 International Association for Gondwana Research Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/158149
Appears in Collections: 气候变化与战略
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作者单位: School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, United Kingdom; Dipartimento di Sicenze della Terra, Università degli Studi di Firenze, via La Pira 4, Firenze, 50121, Italy; Institut für Geowissenschaften, Christian-Albrechts-Universität zu Kiel, Ludewig-Meyn-Straße 10, Kiel, 24118, Germany; Department of Geology, University of Georgia, Athens, GA 30602-2501, United States
Recommended Citation:
Danise S.,Price G.D.,Alberti M.,et al. Isotopic evidence for partial geochemical decoupling between a Jurassic epicontinental sea and the open ocean[J]. Gondwana Research,2020-01-01,82