Geoscience Reference
In-Depth Information
Fig. 8. Thickness of climatic cycles (base green through red/purple to base green) plotted against cycle number for the
base Britta Dal Formation in Paralleldal (Broad Ravine) and Gauss Halvø (Nathorst Bjerg). The horizontal bars are
sandstones. The base of the section measured in Paralleldal is at the top of the Wimans Bjerg Formation. On Gauss
Halvø the cycle measurements started in the Wimans Bjerg Formation, hence the higher cycle numbers. The sections are
tied at the top Wimans Bjerg Formation, cycle peaks (e.g. cycle 17 and 51) and troughs (20 and 54) show a clear
correlation together with the position of the sand bodies. This shows the 1174 m locality to be located at a level just
below the midpoint of megacycle 2.
migration of channel bends within a moderate to
high sinuosity system. The fossil vertebrates were
recorded as restricted to the low-angled sets, that
is, the point bar deposits. The interpreted palaeoen-
vironment was therefore an ephemeral meandering
stream of moderate to high sinuosity. This interpret-
ation has proved to be very influential and under-
pinned many environmental reconstructions and
arguments (Coates & Clack 1995; Clack 2002,
2006; Larsen et al. 2008) concerning the habitat of
these early tetrapods.
In 1996 this locality was briefly logged during an
altimeter traverse up the SE ridge of Stensi¨ Bjerg
carried out to place it within the new measured stra-
tigraphical section. The main Britta Dal Formation
log was made on the better exposed section that is
present on Nathorst Bjerg. However, it should
be noted that on Nathorst Bjerg the Stensi¨ Bjerg
Formation is truncated by erosion with the
overlying Obrutschew Formation only being pre-
served on the mountains of Stensi¨ Bjerg and
Wimans Bjerg.
In 2006 the tetrapod locality was restudied
to produce a digital photomontage (Fig. 9). The
Acanthostega-bearing sandstone was seen as
slightly different to most other sand bodies within
the Stensi¨ Bjerg Formation. However, its situation
is entirely typical of the Britta Dal Formation sand
bodies as it occurs just beneath a major sandstone
body that is laterally extensive, flat-based and with
internal scoured surfaces. Figure 9 shows the sand
body on both the western (Fig. 9a) and eastern
(Fig. 9c, tetrapod locality) sides of the ridge together
with the exposure (Fig. 9b) on the ridge crest. There
is now less information available from the exposure
as
the inclined low-angle sets that contained
