DOI: 10.1016/j.palaeo.2017.06.009
论文题名: Brachiopod geochemical records from across the Carboniferous seas of North America: Evidence for salinity gradients, stratification, and circulation patterns
作者: Roark A. ; Flake R. ; Grossman E.L. ; Olszewski T. ; Lebold J. ; Thomas D. ; Marcantonio F. ; Miller B. ; Raymond A. ; Yancey T.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2017
语种: 英语
英文关键词: Carbon isotopes
; Epicontinental sea
; Mg/Ca thermometer
; Oxygen isotopes
; Superestuarine circulation
; Upwelling
英文摘要: Stable isotopic analyses of >100 well-preserved Carboniferous brachiopod shells, representing two time slices from across North America, reveal systematic regional changes in environmental conditions. For both of the time slices studied, the Chesterian (latest Mississippian) and the Virgilian (latest Pennsylvanian), δ18O and δ13C show a stepwise decrease moving across the continent from modern-day west to east. Higher δ18O in the west reflects greater water depths, less freshwater input, and more direct upwelling influence from cool, open-marine waters than in the east. Modelling based on these regional isotopic data indicates salinity reductions on the order of ~1-4psu in the Appalachian Basin relative to the Midcontinent Basin for the Virgilian time interval over a range of reasonable thermal gradient and δ18Ofw assumptions. The magnitude of this gradient is similar to those of modern-day Hudson Bay and the Panama Bight, which exhibit permanent haloclines driven by freshwater discharge. Considering existing paleoecological evidence for freshening, the lack of more dramatic benthic freshening suggests that the depth of a regional halocline was shallower than the depths inhabited by thick-shelled stenotopic brachiopods, although other lines of evidence are necessary to verify the strength of the halocline. Estimated δ18O temperatures for Appalachian Basin brachiopods are ~3-5°C cooler than those of coeval conodonts, due to either slightly warmer, fresher surface waters or uncertainty in the phosphate 18O paleothermometer. Despite discrepancies in calculated temperatures, the magnitude of the regional isotopic gradient derived from brachiopod and conodont proxies is similar after making appropriate glacioisotopic and water depth corrections. A decreasing δ13C trend toward the east (southern paleolatitude) likely reflects greater restriction and terrestrial influence near the sea's tropical shoreline. Trace element trends are less consistent and are affected by species and metabolism. Erratic variations in Mg/Ca concentrations, even among pristine samples of the same genera with similar δ18O values, and unrealistic Mg/Ca-derived temperatures justify continued caution in applying existing Mg/Ca thermometer equations to Paleozoic brachiopods. © 2017. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/68143
Appears in Collections: 过去全球变化的重建
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作者单位: Department of Geology and Geophysics, Texas A and M University, College Station, TX 77843, United States; Department of Geology and Geography, West Virginia University, 330 Brooks Hall, 98 Beechurst Av., Morgantown, WV 26506, United States; Department of Oceanography, Texas A and M University, College Station, TX, 77843, United States
Recommended Citation:
Roark A.,Flake R.,Grossman E.L.,et al. Brachiopod geochemical records from across the Carboniferous seas of North America: Evidence for salinity gradients, stratification, and circulation patterns[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2017-01-01