Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil
ABSTRACT: Paleoredox indicators were used to assess the depositional environment of the Permian Irati Formation, and discuss the controls on the accumulation of organic-rich sediments. Geochemical data were measured for 43 drill-core samples in southern Paraná Basin. We infer that redox boundary was located at the sediment-water interface during the accumulation of these sediments. Trace-element data demonstrate that Irati shales were similar to average shales, except during deposition of two organic-rich beds in which U and Mo are enriched, suggesting fully anoxic conditions. The variable degree of oxygenation of bottom waters is also attested by DOPT, FeT/Al, and sedimentological indicators of episodic ventilation. DOPT and Fe and S correlation points to an iron-limited environment, where the main sulfur sink is organic matter rather than pyrite. Cu and Cu/Mo ratio suggests bottom-water anoxia driven by increased organic flux. The Irati Formation was probably deposited in a salinity-stratified body of water, with positive water balance. The main control on the accumulation of the organic-rich sediments was the high organic carbon flux resultant from high primary productivity in surface waters. Anoxia arose as a consequence of increased productivity, not as the primary driver in the formation of these organic-rich rocks.
Main Authors: | , |
---|---|
Format: | Digital revista |
Language: | English |
Published: |
Sociedade Brasileira de Geologia
2016
|
Online Access: | http://old.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892016000300377 |
Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
id |
oai:scielo:S2317-48892016000300377 |
---|---|
record_format |
ojs |
spelling |
oai:scielo:S2317-488920160003003772016-11-22Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern BrazilGoldberg,KarinHumayun,Munir black shales paleoredox proxies Irati Formation Permian ABSTRACT: Paleoredox indicators were used to assess the depositional environment of the Permian Irati Formation, and discuss the controls on the accumulation of organic-rich sediments. Geochemical data were measured for 43 drill-core samples in southern Paraná Basin. We infer that redox boundary was located at the sediment-water interface during the accumulation of these sediments. Trace-element data demonstrate that Irati shales were similar to average shales, except during deposition of two organic-rich beds in which U and Mo are enriched, suggesting fully anoxic conditions. The variable degree of oxygenation of bottom waters is also attested by DOPT, FeT/Al, and sedimentological indicators of episodic ventilation. DOPT and Fe and S correlation points to an iron-limited environment, where the main sulfur sink is organic matter rather than pyrite. Cu and Cu/Mo ratio suggests bottom-water anoxia driven by increased organic flux. The Irati Formation was probably deposited in a salinity-stratified body of water, with positive water balance. The main control on the accumulation of the organic-rich sediments was the high organic carbon flux resultant from high primary productivity in surface waters. Anoxia arose as a consequence of increased productivity, not as the primary driver in the formation of these organic-rich rocks.info:eu-repo/semantics/openAccessSociedade Brasileira de GeologiaBrazilian Journal of Geology v.46 n.3 20162016-09-01info:eu-repo/semantics/articletext/htmlhttp://old.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892016000300377en10.1590/2317-4889201620160001 |
institution |
SCIELO |
collection |
OJS |
country |
Brasil |
countrycode |
BR |
component |
Revista |
access |
En linea |
databasecode |
rev-scielo-br |
tag |
revista |
region |
America del Sur |
libraryname |
SciELO |
language |
English |
format |
Digital |
author |
Goldberg,Karin Humayun,Munir |
spellingShingle |
Goldberg,Karin Humayun,Munir Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
author_facet |
Goldberg,Karin Humayun,Munir |
author_sort |
Goldberg,Karin |
title |
Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
title_short |
Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
title_full |
Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
title_fullStr |
Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
title_full_unstemmed |
Geochemical paleoredox indicators in organic-rich shales of the Irati Formation, Permian of the Paraná Basin, southern Brazil |
title_sort |
geochemical paleoredox indicators in organic-rich shales of the irati formation, permian of the paraná basin, southern brazil |
description |
ABSTRACT: Paleoredox indicators were used to assess the depositional environment of the Permian Irati Formation, and discuss the controls on the accumulation of organic-rich sediments. Geochemical data were measured for 43 drill-core samples in southern Paraná Basin. We infer that redox boundary was located at the sediment-water interface during the accumulation of these sediments. Trace-element data demonstrate that Irati shales were similar to average shales, except during deposition of two organic-rich beds in which U and Mo are enriched, suggesting fully anoxic conditions. The variable degree of oxygenation of bottom waters is also attested by DOPT, FeT/Al, and sedimentological indicators of episodic ventilation. DOPT and Fe and S correlation points to an iron-limited environment, where the main sulfur sink is organic matter rather than pyrite. Cu and Cu/Mo ratio suggests bottom-water anoxia driven by increased organic flux. The Irati Formation was probably deposited in a salinity-stratified body of water, with positive water balance. The main control on the accumulation of the organic-rich sediments was the high organic carbon flux resultant from high primary productivity in surface waters. Anoxia arose as a consequence of increased productivity, not as the primary driver in the formation of these organic-rich rocks. |
publisher |
Sociedade Brasileira de Geologia |
publishDate |
2016 |
url |
http://old.scielo.br/scielo.php?script=sci_arttext&pid=S2317-48892016000300377 |
work_keys_str_mv |
AT goldbergkarin geochemicalpaleoredoxindicatorsinorganicrichshalesoftheiratiformationpermianoftheparanabasinsouthernbrazil AT humayunmunir geochemicalpaleoredoxindicatorsinorganicrichshalesoftheiratiformationpermianoftheparanabasinsouthernbrazil |
_version_ |
1756440989481828352 |