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Sulfur isotope geochemistry of the A...

Kakegawa, Takeshi.

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Sulfur isotope geochemistry of the Archean sedimentary rocks.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Sulfur isotope geochemistry of the Archean sedimentary rocks./
作者:	Kakegawa, Takeshi.
面頁冊數:	163 p.
附註:	Source: Dissertation Abstracts International, Volume: 58-12, Section: B, page: 6443.
Contained By:	Dissertation Abstracts International58-12B.
標題:	Geochemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9817504
ISBN:	0591688417

Sulfur isotope geochemistry of the Archean sedimentary rocks.
Kakegawa, Takeshi.

Sulfur isotope geochemistry of the Archean sedimentary rocks. - 163 p.

Source: Dissertation Abstracts International, Volume: 58-12, Section: B, page: 6443.

Thesis (Ph.D.)--The Pennsylvania State University, 1997.

Sulfate-reducing bacteria are considered to be one of the earliest biota in the Earth's history. However, there has been uncertainty as to when sulfate-reducing bacteria became active, and when sulfate accumulated in the oceans. In order to examine if: (1) Archean oceans were sulfate-rich; and (2) sulfate-reducing bacteria were active in the Archean oceans, micro-analyses of sulfur isotopes have been performed using the Nd-YAG laser ablation technique on pyrite crystals in carbonaceous shales and black cherts. Samples were collected from the 2.7 to 2.5 Ga Hamersley Range, Australia (Chapters 2 and 3), the 2.7 Ga Abitibi greenstone belt, Canada (Chapter 4) and the 3.4 to 3.1 Ga Barberton greenstone belt, South Africa (Chasulfate). All sample suites have variable

ISBN: 0591688417Subjects--Topical Terms:

539092
Geochemistry.

Sulfur isotope geochemistry of the Archean sedimentary rocks.
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100 1 $a Kakegawa, Takeshi. $3 1904975
245 1 0 $a Sulfur isotope geochemistry of the Archean sedimentary rocks.
300 $a 163 p.
500 $a Source: Dissertation Abstracts International, Volume: 58-12, Section: B, page: 6443.
500 $a Adviser: Hiroshi Ohmoto.
502 $a Thesis (Ph.D.)--The Pennsylvania State University, 1997.
520 $a Sulfate-reducing bacteria are considered to be one of the earliest biota in the Earth's history. However, there has been uncertainty as to when sulfate-reducing bacteria became active, and when sulfate accumulated in the oceans. In order to examine if: (1) Archean oceans were sulfate-rich; and (2) sulfate-reducing bacteria were active in the Archean oceans, micro-analyses of sulfur isotopes have been performed using the Nd-YAG laser ablation technique on pyrite crystals in carbonaceous shales and black cherts. Samples were collected from the 2.7 to 2.5 Ga Hamersley Range, Australia (Chapters 2 and 3), the 2.7 Ga Abitibi greenstone belt, Canada (Chapter 4) and the 3.4 to 3.1 Ga Barberton greenstone belt, South Africa (Chasulfate). All sample suites have variable $\ delta\sp{34} ${ -}2.9\perthous $ to +7.7 $\ perthous $ for Abitibi ( $\ sim $6 0 analyses), ${ -}5.3\perthous $ to +12.7 $\ perthous $ for Hamersley ( $\ sim $9 0 analyses), and ${ -}2.5\perthous $ to +8.4 $\ perthous $ for Barberton samples ( $\ sim $2 00 analyses). Remarkable features of the analytical results are large $\ rm\delta\sp{34}S $ variations (up to 10 $\ perthous) $ within a sedimentary bed ( $\ sim $2 mm $\ sp2) $ and a rock chip (volume $\ rm{\sim}5\ cm\sp3) $ of the Barberton and Hamersley samples, and systematic zoning of $\ rm\delta\sp{34}S $ values in pyrite nodules in the Abitibi samples. This new data set of $\ rm\delta\sp{34}S $ variations on micro-scale clearly indicates that Archean oceans were sulfate-rich, and that organic or inorganic sulfate reduction was responsible for pyrite formation in Archean sedimentary rocks. These results are in contrast to the previously popular model with Archean oceans that were H $\ sb2 $\ sb4\sp{2-} $- rich.
520 $a $\ rm\delta\sp{34}S $ frequency patterns and variations of sedimentary pyrites in the examined samples suggest that: (1) most pyrites in the Archean shales ( $> $3 .4 Ga) were formed by microbial reduction of seawater sulfate in sediments (i.e., a closed system) rather than syngenetic or hydrothermal processes; and (2) deviation of $\ rm\delta\sp{34}S $ of seawater sulfate from 0 $\ perthous $ had already begun 3.4 Ga, due to the preferential fractionation of $\ sp{32}
520 $a $\ rm\delta\sp{34}S $ values of seawater sulfate were previously estimated from the $\ rm\delta\sp{34}S $ values of evaporite sulfate. This study demonstrates that $\ rm\delta\sp{34}S $ values of seawater sulfate can also be estimated from an examination of frequency patterns of $\ rm\delta\sp{34}S\sb{(pyrite)} $ determined by micro-analytical techniques. The results of this study suggest that the $\ rm\delta\sp{34}S $ values of seawater sulfate increased from +2 $\ perthous $ at 3.4 Ga to +5 $\ perthous $ at 2.7 Ga and to +10 $\ perthous $ at 2.5 Ga. The kinetic isotope effects $( \Delta) $ associated with the microbial sulfate reduction also appear to have changed during the Archean; the maximum $\ Delta $ values increased from 6 $\ perthous $ at 3.4 Ga to 12 $\ perthous $ at 2.7 Ga and then to 20 $\ perthous $ at 2.5 Ga. The increase in the $\ Delta $ value with time may have been related to the cooling history of the lithosphere, hydrosphere and atmosphere of the early Earth.
590 $a School code: 0176.
650 4 $a Geochemistry. $3 539092
650 4 $a Paleoecology. $3 608789
650 4 $a Biogeochemistry. $3 545717
690 $a 0996
690 $a 0426
690 $a 0425
710 2 0 $a The Pennsylvania State University. $3 699896
773 0 $t Dissertation Abstracts International $g 58-12B.
790 1 0 $a Ohmoto, Hiroshi, $e advisor
790 $a 0176
791 $a Ph.D.
792 $a 1997
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9817504