DOI: 10.1016/j.palaeo.2015.09.014
论文题名: Redox conditions across the Cambrian-Ordovician boundary: Elemental and isotopic signatures retained in the GSSP carbonates
作者: Azmy K. ; Kendall B. ; Brand U. ; Stouge S. ; Gordon G.W.
刊名: Palaeogeography, Palaeoclimatology, Palaeoecology
ISSN: 0031-0182
出版年: 2015
卷: 440 起始页码: 440
结束页码: 454
语种: 英语
英文关键词: Cambrian-Ordovician GSSP
; Organic C- and N-isotopes
; Redox conditions
; REE
; U-isotopes
; Western Newfoundland (Canada)
英文摘要: Lime mudstone samples (rhythmites) were collected at high resolution from outcrops of the Cambrian-Ordovician GSSP boundary section at Green Point (western Newfoundland, Canada). The sequence (~45m-thick) consists of slope carbonates with alternating shale and siltstone interbeds, and it spans the boundary located between the Martin Point and Broom Point members of the Green Point Formation (Cow Head Group). Samples were extracted from micritic rhythmites by microdrilling and subsequently screened using petrographic and geochemical criteria to evaluate their degree of preservation. Although the δ13Corg profile (-29.7 to -25.6‰ VPDB) shows insignificant variations, the TOC values (0.1 to 4.1%) exhibit a generally upward decreasing trend. A negative δ13Ccarb excursion, reflecting a sealevel rise, marks a geochemical anomaly that correlates with an increase in the N contents (0 to 2.9%) of organic matter and the δ15Norg values (-0.6 to +6.0‰), which suggests a change to more reducing oceanic conditions. The U contents vary from 0.1 to 3.0ppm and the δ238U values (-0.97 to -0.18‰) generally decrease with the negative δ13Ccarb excursion. The U isotopic variations suggest a widespread increase in reducing conditions associated with sealevel rise during this interval. The investigated sedimentary rocks were slope carbonates where dysoxic conditions likely dominated throughout the entire section. Therefore, the changes in the TOC, N, δ15Norg, and δ238U profiles across the boundary are not as sharp as would be expected by a local change from oxic shallow-water to dysoxic/anoxic deep-water settings. © 2015 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/68726
Appears in Collections: 过去全球变化的重建
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作者单位: Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL, Canada; Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, Canada; Department of Earth Sciences, Brock University, St. Catharines, ON, Canada; Geological Museum, University of Copenhagen, Øster Voldgade 5, Copenhagen K, Denmark; School of Earth and Space Exploration, Arizona State University, Tempe, AZ, United States
Recommended Citation:
Azmy K.,Kendall B.,Brand U.,et al. Redox conditions across the Cambrian-Ordovician boundary: Elemental and isotopic signatures retained in the GSSP carbonates[J]. Palaeogeography, Palaeoclimatology, Palaeoecology,2015-01-01,440