کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
4724239 | 1639694 | 2009 | 12 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Oceanic redox conditions in the Late Mesoproterozoic recorded in the upper Vazante Group carbonates of São Francisco Basin, Brazil: Evidence from stable isotopes and REEs
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
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چکیده انگلیسی
The Vazante Group consists of a late Mesoproterozoic (â¼1.0-1.1 Ga) carbonate-dominated marine platform sequence in east-central Brazil. The upper part of the sequence consists of a glaciomarine diamictite unit overlain by a cap carbonate. The δ13C profile of the upper Vazante shows significant negative plunges, one preglacial (drop of â¼5.5â° VPDB) and two postglacial (drops of â¼9 and 5â°VPDB, respectively). The C-isotope plunge in the preglacial carbonates is correlated with low Th/U ratios (0.1-1.4) and a negative Ce/Ce* shift (â¼0.4), suggesting deposition under relative reducing conditions. In contrast, the C-isotope plunges in the postglacial carbonates are associated with high Th/U ratios (>2) and positive Ce/Ce* shifts (up to â¼1.5), thus reflecting oxidizing conditions. Variations in the redox conditions of the late Mesoproterozoic ocean, reflected by changes in the Th/U and Ce/Ce* ratios, are likely attributable to a combination of both global and local climatic and oceanographic changes, similar to what has been inferred for the Neoproterozoic oceans.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Precambrian Research - Volume 168, Issues 3â4, February 2009, Pages 259-270
Journal: Precambrian Research - Volume 168, Issues 3â4, February 2009, Pages 259-270
نویسندگان
Karem Azmy, Paul Sylvester, Tolentino F. de Oliveira,