Geoscience Reference
In-Depth Information
The sedimentary environment of the Late Devonian
East Greenland tetrapods
T. R. ASTIN
1
, J. E. A. MARSHALL
2
*, H. BLOM
3
& C. M. BERRY
4
1
School of Human and Environmental Science, The University of Reading, Whiteknights,
PO Box 217, Reading, RG6 6AH, UK
2
School of Ocean and Earth Science, National Oceanography Centre, University of
Southampton, European Way, Southampton, SO14 3ZH, UK
3
Evolutionary Organismal Biology, Department of Physiology and Developmental Biology,
Norbyv ¨gen 18A, SE-752 36 Uppsala, Sweden
4
School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place,
Cardiff CF10 3YE, Wales
*Corresponding author (e-mail: jeam@noc.soton.ac.uk)
Abstract: The Late Devonian early tetrapods in East Greenland occur in the Celsius Bjerg Group.
Key occurrences are located in a detailed stratigraphic section used here to interpret the sedimen-
tary palaeoenvironments. The palaeoenvironment for the Britta Dal Formation (which contains
both Ichthyostega and Acanthostega) is reinterpreted. The Britta Dal Formation channels have
flat bases, are poorly channelized, are of low sinuosity and are part of a very major distributory
system that periodically experienced extreme flooding. The tetrapod fossils were recovered from
an ephemeral system that was not permanently habitable in the immediate area. Plant megafossils
are poorly preserved casts and impressions dominated by lycopsids and fern-like plants. The
overbank siltstones are dominated by arid soil forming processes and comprise a spectacular
sequence of vertisols. The 1174 m in situ Ichthyostega locality in Paralleldal was relocated and
occurs just below the midpoint of the second megacycle in the Britta Dal Formation.
The Late Devonian Celsius Bjerg Group of East
Greenland is internationally famous for the tetrapods
Ichthyostega and Acanthostega. Although these are
no longer the earliest known tetrapods, they still
remain the best understood and the evolutionary
benchmark against which the older discoveries are
compared (Clack 2006; Ahlberg et al. 2008). Impor-
tantly, the East Greenland tetrapods are known from
over 500 specimens (Blom et al. 2005) throughout a
long stratigraphic section. An earlier contribution
(Marshall et al. 1999) clarified the age of these
tetrapods which had been controversial (Westoll
1941; Jarvik 1948; Hartz et al. 1997; Stemmerik
& Bendix-Almgreen 1998) ever since their original
discovery. This contribution provides an integrated
account of the range of sedimentary environments
present throughout the Celsius Bjerg Group. Impor-
tantly, it significantly revises the published environ-
mental
publications. Those of Olsen (1993) and Olsen &
Larsen (1993) documented the sedimentary
environments and their stratigraphy and spatial
distribution within the basin. Subsequently Larsen
et al. (2008) reviewed, updated and integrated
their original publications with an account of the
vertebrate assemblages. In addition, Blom et al.
(2005) provided a detailed review of the tetrapod
localities and their stratigraphical distribution. A
more general account is given by Henriksen
(2008). The most specific account of the in situ
Stensi¨ Bjerg Acanthostega locality is given by
Bendix-Almgreen et al. (1988, 1990).
The sequences studied in this contribution
(Figs 1 & 2) included a complete vertical section
logged in detail through the Celsius Bjerg Group
from the mountains of Wimans Bjerg, Nathorst
Bjerg and Stensi¨ Bjerg on Gauss Halvø. Particular
attention was paid to the in situ Acanthostega
locality from the Britta Dal Formation on Stensi¨
Bjerg (fig. 14 in Blom et al. 2005). The most
famous Ichthyostega locality (Blom et al. 2005) is
at an altitude of 1174 m on Sederholm Bjerg in
Paralleldal. This was relocated in the field and a stra-
tigraphic section measured. This was then correlated
interpretation (Bendix-Almgreen et
al.
1988) for the habitat of Acanthostega.
Geological setting and methods
The general stratigraphy and tetrapod field local-
ities are well described in a number of recent
