Comparison of organic and inorganic carbon isotope patterns across the Frasnian/Famennian boundary.

Joachimski M (1997)

Publication Type: Journal article, Original article

Publication year: 1997

Journal

Palaeogeography, Palaeoclimatology, Palaeoecology Elsevier

Publisher: Elsevier

Pages Range: 133-146

Journal Issue: 132

DOI: 10.1016/S0031-0182(97)00051-5

Abstract

The carbon isotopic composition of organic matter is reported for two Frasnian-Famennian boundary sections from the Rheinische Schiefergebirge (Germany). During the late Frasnian δ¹³C(org) values commonly range from -27.5‰ to -26‰. Highest δ¹³C(org) values around -24‰ are encountered immediately above and below the Kellwasser horizons. All samples from the Kellwasser horizons are depleted in δ¹³C(org) by -2.5‰ to -4.7‰. This depletion is explained by a higher proportion of biomass derived from isotopically depleted chemoautotrophic bacteria. A comparison of the positive δ¹³C excursions shows that the δ¹³C(org) shifts precede the ¹³C(carb) shifts by some 10⁵ years. Consequently, Δδ¹³C values document a shift towards lower values below the Upper Kellwasser horizon. A contribution of terrestrial organic matter, as well as a thermal alteration of the δ¹³C(org) signals, do not provide compelling explanations for the earlier δ¹³C(org) shift. Increases in primary productivity or carbon burial rate will change the CO2(aq) content of surface waters, affect the carbon isotope fractionation during photosynthetic carbon uptake and thus enrich organic carbon in ¹³C. However, both processes cannot account for the earlier onset of the δ¹³C(org) shift, because the δ¹³C(carb) record should document the resulting ¹³C enrichment in surface waters as well. A reduction in the calcium carbonate precipitation rate, due to the global extinction of the reef ecosystem, may have played an important role in reducing the CO2(aq) content of surface waters without changing the isotopic composition of surface waters. Whether this process or other factors, such as a rise in sea-surface temperature or a change in the phytoplankton association, account for the earlier onset of the positive shift in the δ¹³C(org) curve must be determined by further studies that may be able to confirm the global significance of the reported δ¹³C(org) pattern in Frasnian-Famennian boundary sections from other parts of the globe.

Authors with CRIS profile

Michael Joachimski Lehrstuhl für Geologie (Exogene Dynamik)

How to cite

APA:

Joachimski, M. (1997). Comparison of organic and inorganic carbon isotope patterns across the Frasnian/Famennian boundary. Palaeogeography, Palaeoclimatology, Palaeoecology, 132, 133-146. https://dx.doi.org/10.1016/S0031-0182(97)00051-5

MLA:

Joachimski, Michael. "Comparison of organic and inorganic carbon isotope patterns across the Frasnian/Famennian boundary." Palaeogeography, Palaeoclimatology, Palaeoecology 132 (1997): 133-146.

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