in Jurassic and Cretaceous Stratigraphy

Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321
Evidences of Widespread Wildfires in Laurasia and Gondwana During
the Middle Jurassic
376
L. Marynowski 1 , M. Zatoń 1
1. University of Silesia, Faculty of Earth Sciences, Będzińska 60 Street, PL-41-200 Sosnowiec, Poland
(E-mail: leszek.marynowski@us.edu.pl)
Wildfires play a key role in Recent and ancient
terrestrial ecosystem modeling but their geological
history after higher plants colonization is still not
well-recorded. We used the charcoals (Fig.1) and
pyrolytic polycyclic aromatic hydrocarbons (PAHs)
co-occurrence as proxies of Middle Jurassic wildfires
on both the Laurasia and Gondwana continents. The
Laurasian evidence comes from the Lower Callovian
terrigenous deposits of the eastern part of the Central
European Basin. We have detected the charcoal frag-
ments co-occurring with unsubstituted polycyclic
aromatic hydrocarbons in the Lower Callovian, Papilė
Formation of Lithuania, indicating that forest fires took
place at this time. The sum of concentrations of the
pyrolytic polycyclic aromatic hydrocarbons, including
fluoranthene, pyrene, benzofluoranthenes, benzo[e]
pyrene, benzo[ghi]perylene and coronene (Finkelstein
et al., 2005) ranged from 4.66 and 6.57 μg/g TOC for
charcoal-bearing clay and sand samples, respectively,
while for the rest of the samples, the obtained values are
below 0.5 μg/g TOC. Concentrations of PAHs are
significantly lower than those from the Hettangian
samples of Sołtyków and similar to those from the
Podole and Lower Gromadzice localities in central
Poland (Marynowski and Simoneit, 2009). Besides of
pyrogenic PAHs, the charcoal-bearing horizons are
characterized by the occurrence of oxygen-containing
aromatic compounds. The most common are benzo[b]
naphthofurans, dinaphthofurans, and benzobisben-
zofurans. As far as we know, this is the first evidence of
wildfires during Callovian, as based on multi-proxy
documentation (Marynowski and Zatoń, 2010). The
Gondwanan record of wildfires comes from the
Neuquén province in Argentina, where the Upper
Aalenian/Lower Bajocian to Bathonian terrigenous
sequences are characterized by the occurrence of
charcoal and PAHs, a distribution of which suggests
their pyrolytic origin. This is the first multi-proxy
evidence of Jurassic wildfires from the Gondwana
continent and generally one of a very few records of
wildfires in Gondwana during the Mesozoic.
Fig.1 Scanning electron photomicrographs of: (a) relatively well preserved small charcoal fragment from the Lower Callovian
clays of the Karpenai exposure, Lituania. (b) tangential section of excellently preserved charcoal from the Upper Aalenian-Lower
Bajocian of the Rincón del Águila exposure, Argentina.
Temperature interpretations, derived from iner-
tinite reflectance data, show that in all cases the Middle
Jurassic charcoals formed at low temperature surface
fires that, in the case of Aalenian/Bajocian wildfires,
sporadically reached the higher temperature crown fires.
The occurrence of charcoals in the investigated deposits
of the both continents confirms the recent results that
the atmospheric oxygen level reached at least 15%
during the Middle Jurassic times (Belcher and
McElwain 2008; Berner, 2009).
Acknowledgements: This work has been
supported by the MNISW grant: N N307 2379 33 (for
LM).
Key words: Wildfires; Charcoal; PAHs; Middle
Jurassic
References:
Belcher C.M., McElwain J.C. Limits for combustion in
low O2 redefine paleoatmospheric predictions for