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| Titel |
Organomineral nanocomposite carbon burial during Oceanic Anoxic Event 2 |
| VerfasserIn |
S. C. Löhr, M. J. Kennedy |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 18 ; Nr. 11, no. 18 (2014-09-18), S.4971-4983 |
| Datensatznummer |
250117597
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| Publikation (Nr.) |
 copernicus.org/bg-11-4971-2014.pdf |
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| Zusammenfassung |
| Organic carbon (OC) enrichment in sediments deposited during Oceanic Anoxic
Events (OAEs) is commonly attributed to elevated productivity and marine
anoxia. We find that OC enrichment in the late Cenomanian aged OAE 2 at the
Demerara Rise was controlled by the co-occurrence of anoxic bottom water,
sufficient productivity to saturate available mineral surfaces, and variable
deposition of high surface area detrital smectite clay. Redox indicators show
consistently oxygen-depleted conditions, while a strong correlation between
OC concentration and sediment mineral surface area (R2 = 0.92) occurs
across a range of total organic carbon (TOC) values from 9 to 33%. X-ray
diffraction data indicate the intercalation of OC in smectite interlayers,
while electron, synchrotron infrared and X-ray microscopy show an intimate
association between clay minerals and OC, consistent with preservation of OC
as organomineral nanocomposites and aggregates rather than discrete,
μm-scale pelagic detritus. Since the consistent ratio between TOC
and mineral surface area suggests that excess OC relative to surface area is
lost, we propose that it is the varying supply of smectite that best explains
variable organic enrichment against a backdrop of continuous anoxia, which is
conducive to generally high TOC during OAE 2 at the Demerara Rise. Smectitic
clays are unique in their ability to form stable organomineral nanocomposites
and aggregates that preserve organic matter, and are common weathering
products of continental volcanic deposits. An increased flux of smectite
coinciding with high carbon burial is consistent with evidence for widespread
volcanism during OAE 2, so that organomineral carbon burial may represent a
potential feedback to volcanic degassing of CO2. |
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