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The oxic degradation of sedimentary organic matter 1400 Ma constrains atmospheric oxygen levels

Zhang, Shuichang; Wang, Xiaomei; Wang, Huajian; Hammarlund, Emma U. LU ; Su, Jin; Wang, Yu and Canfield, Donald E (2017) In Biogeosciences 14(8). p.2133-2149
Abstract

We studied sediments from the ca. 1400 million-year-old Xiamaling Formation from the North China block. The upper unit of this formation (unit 1) deposited mostly below storm wave base and contains alternating black and green-gray shales with very distinct geochemical characteristics. The black shales are enriched in redox-sensitive trace metals, have high concentrations of total organic carbon (TOC), high hydrogen index (HI) and iron speciation indicating deposition under anoxic conditions. In contrast, the green-gray shales show no trace metal enrichments, have low TOC, low HI and iron speciation consistent with an oxygenated depositional setting. Altogether, unit 1 displays alternations between oxic and anoxic depositional... (More)

We studied sediments from the ca. 1400 million-year-old Xiamaling Formation from the North China block. The upper unit of this formation (unit 1) deposited mostly below storm wave base and contains alternating black and green-gray shales with very distinct geochemical characteristics. The black shales are enriched in redox-sensitive trace metals, have high concentrations of total organic carbon (TOC), high hydrogen index (HI) and iron speciation indicating deposition under anoxic conditions. In contrast, the green-gray shales show no trace metal enrichments, have low TOC, low HI and iron speciation consistent with an oxygenated depositional setting. Altogether, unit 1 displays alternations between oxic and anoxic depositional environments, driving differences in carbon preservation consistent with observations from the modern ocean. We combined our TOC and HI results to calculate the differences in carbon mineralization and carbon preservation by comparing the oxygenated and anoxic depositional environments. Through comparisons of these results with modern sedimentary environments, and by use of a simple diagenetic model, we conclude that the enhanced carbon mineralization under oxygenated conditions in unit 1 of the Xiamaling Formation required a minimum of 4 to 8ĝ€% of present-day atmospheric levels (PAL) of oxygen. These oxygen levels are higher than estimates based on chromium isotopes and reinforce the idea that the environment contained enough oxygen for animals long before their evolution.

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author
publishing date
type
Contribution to journal
publication status
published
in
Biogeosciences
volume
14
issue
8
pages
17 pages
publisher
Copernicus Publications
external identifiers
  • scopus:85018180947
ISSN
1726-4170
DOI
10.5194/bg-14-2133-2017
language
English
LU publication?
no
id
9c7ed26b-d76d-4ca7-938d-09a57054cce7
date added to LUP
2017-05-17 11:23:47
date last changed
2017-05-17 14:51:13
@article{9c7ed26b-d76d-4ca7-938d-09a57054cce7,
  abstract     = {<p>We studied sediments from the ca. 1400 million-year-old Xiamaling Formation from the North China block. The upper unit of this formation (unit 1) deposited mostly below storm wave base and contains alternating black and green-gray shales with very distinct geochemical characteristics. The black shales are enriched in redox-sensitive trace metals, have high concentrations of total organic carbon (TOC), high hydrogen index (HI) and iron speciation indicating deposition under anoxic conditions. In contrast, the green-gray shales show no trace metal enrichments, have low TOC, low HI and iron speciation consistent with an oxygenated depositional setting. Altogether, unit 1 displays alternations between oxic and anoxic depositional environments, driving differences in carbon preservation consistent with observations from the modern ocean. We combined our TOC and HI results to calculate the differences in carbon mineralization and carbon preservation by comparing the oxygenated and anoxic depositional environments. Through comparisons of these results with modern sedimentary environments, and by use of a simple diagenetic model, we conclude that the enhanced carbon mineralization under oxygenated conditions in unit 1 of the Xiamaling Formation required a minimum of 4 to 8ĝ€% of present-day atmospheric levels (PAL) of oxygen. These oxygen levels are higher than estimates based on chromium isotopes and reinforce the idea that the environment contained enough oxygen for animals long before their evolution.</p>},
  author       = {Zhang, Shuichang and Wang, Xiaomei and Wang, Huajian and Hammarlund, Emma U. and Su, Jin and Wang, Yu and Canfield, Donald E},
  issn         = {1726-4170},
  language     = {eng},
  month        = {04},
  number       = {8},
  pages        = {2133--2149},
  publisher    = {Copernicus Publications},
  series       = {Biogeosciences},
  title        = {The oxic degradation of sedimentary organic matter 1400 Ma constrains atmospheric oxygen levels},
  url          = {http://dx.doi.org/10.5194/bg-14-2133-2017},
  volume       = {14},
  year         = {2017},
}