Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 75 (2011): 657-672, doi:10.1016/j.gca.2010.10.016.
Description:
An integrated study of palynology, Mössbauer spectroscopy, mineralogy and osmium
isotopes has led to the detection of the first K-Pg boundary clay layer in a Southern
Hemisphere terrestrial setting. The K-Pg boundary layer was independently identified at
centimetre resolution by all the above mentioned methods at the marine K-Pg boundary site of
mid-Waipara and the terrestrial site of Compressor Creek (Greymouth coal field), New
Zealand. Mössbauer spectroscopy shows an anomaly of Fe-containing particles in both K-Pg
boundary sections: jarosite at mid-Waipara and goethite at Compressor Creek. This anomaly
coincides with a turnover in vegetation indicated by an interval dominated by fern spores and
extinction of key pollen species in both sections. In addition to the terrestrial floristic changes,
the mid-Waipara section reveals a turnover in the dinoflagellate assemblages and the
appearance of global earliest Danian index species. Geochemical data reveal relatively small
iridium enrichments in the boundary layers of 321 pg/g at mid-Waipara and 176 pg/g at
Compressor Creek. Unradiogenic 187Os/188Os values of the boundary clay reveal the presence
of a significant extraterrestrial component. We interpret the accumulation of Fe nano-phases
at the boundary as originating from both the impactor and the crystalline basement target
rock. The goethite and jarosite are interpreted as secondary phases formed by weathering and
diagenesis. The primary phases were probably controlled by the initial composition of the
vapor plume and condensation kinetics rather than condensation thermodynamics. This
investigation indicates that identification of Fe in nano-phases by Mössbauer spectroscopy is
an accurate and cost-effective method for identifying impact event horizons and it efficiently
complements widely used biostratigraphic and geochemical methods.
Description:
V. Vajda acknowledges the
financial support provided by the Swedish Royal Academy of Sciences through the Knut &
Alice Wallenbergs Foundation and from the Crafoord Foundation. P.S. Willumsen
acknowledges financial support from the Carlsberg Foundation no.2008_01_0404.
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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