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1.6 GaU-Pb zircon age for the Chorhat Sandstone, lower Vindhyan, India: Possible implications for early evolution of animals

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Title 1.6 GaU-Pb zircon age for the Chorhat Sandstone, lower Vindhyan, India: Possible implications for early evolution of animals
 
Creator RASMUSSEN, B
BOSE, PK
SARKAR, S
BANERJEE, S
FLETCHER, IR
MCNAUGHTON, NJ
 
Subject small shelly fossils
old animals
son valley
paleontology
brachiopods
discoveries
phyla
vindhyan
geochronology
zircon
semri group
trace fossils
proterozoic
 
Description Bedding-plane markings in the Chorhat Sandstone (lower Vindhyan), central India, were recently interpreted as burrows produced by triploblastic animals. Because the rocks were thought to be older than 1000 Ma, these structures were regarded as the oldest fossil evidence for metazoan life. However, the biological origin of the markings has been questioned, as has their age. Current age estimates are based on K-Ar, Rb-Sr, and fission-track dates, though some contentious evidence suggests that the rocks may be only 540 Ma. Here we provide the first robust age data for the lower Vindhyan by using SHRIMP (sensitive, high-resolution ion microprobe) U-Pb zircon geochronology to date silicified tuffs bounding the Chorhat Sandstone. Our results show that the sediments were deposited between 1628 +/- 8 Ma and 1599 +/- 8 Ma. If the Chorhat markings are burrows left by worm-like animals, then our data suggest that complex metazoans had evolved before 1600 Ma, 1 b.y. before the "Cambrian explosion" when animals rapidly diversified and became ecologically dominant. However, given the doubts expressed about the origin of the bedding-plane structures, as well as (lie surprisingly "old" age of the host rocks, further studies are urgently required to provide supportive evidence.
 
Publisher GEOLOGICAL SOC AMERICA, INC
 
Date 2011-07-29T21:21:47Z
2011-12-26T12:52:38Z
2011-12-27T05:39:12Z
2011-07-29T21:21:47Z
2011-12-26T12:52:38Z
2011-12-27T05:39:12Z
2002
 
Type Article
 
Identifier GEOLOGY, 30(2), 103-106
0091-7613
http://dx.doi.org/10.1130/0091-7613(2002)030<0103:GUPZAF>2.0.CO;2
http://dspace.library.iitb.ac.in/xmlui/handle/10054/7837
http://hdl.handle.net/10054/7837
 
Language en