U-Pb zircon date from the Neoproterozoic Ghaub Formation, Namibia: Constraints on Marinoan glaciation

被引：444

作者：

Hoffmann, KH

Condon, DJ

Bowring, SA

Crowley, JL

机构：

[1] Geol Survey Namibia, Windhoek, Namibia

[2] MIT, Dept Earth Atmospher & Planetary Sci, Cambridge, MA 02139 USA

来源：

GEOLOGY | 2004年 / 32卷 / 09期

关键词：

Neoproterozoic; glaciation; zircon; geochronology; Marinoan; Ediacaran;

D O I：

10.1130/G20519.1

中图分类号：

P5 [地质学];

学科分类号：

0709 ; 081803 ;

摘要：

Dropstone-bearing glaciomarine sedimentary rocks of the Ghaub Formation within metamorphosed Neoproterozoic basinal strata (Swakop Group) in central Namibia contain interbedded mafic lava flows and thin felsic ash beds. U-Pb zircon geochronology of an ash layer constrains the deposition of the glaciomarine sediments to 635.5 +/- 1.2 Ma, providing an age for what has been described as a "Marinoan-type" glaciation. In addition, this age provides a maximum limit for the proposed lower boundary of the terminal Proterozoic (Ediacaran) system and period. Combined with reliable age constraints from other Neoproterozoic glacial units-the ca. 713 Ma Gubrah Member (Oman) and the 580 Ma Gaskiers Formation (Newfoundland)-these data provide unequivocal evidence for at least three, temporally discrete, glacial episodes during Neoproterozoic time with interglacial periods, characterized by prolonged positive delta(13)C excursions, lasting at most similar to50-80 m.y.

引用

页码：817 / 820

页数：4

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