Fig 1.
Geological setting of the Dave Green palaeosurface.
A) Simplified geological map of the main Karoo Basin. Position of the study area is indicated. B) Aerial photo of the palaeosurface (taken by AK). C) Stratigraphic log measured along the Rensburgspruit.
Fig 2.
Orthophoto of the palaeosurface with the positions of the seven large impressions and paths followed for the high-resolution scans indicated.
Numbers used for the impressions are the same throughout the text.
Fig 3.
Features of the upper Waterford and lower Balfour formations in the study area.
A) Large calcareous nodules. B) Rounded/ Smoothed symmetrical ripples on the top of the thick sandstone unit. C) Dark grey, laminated mudstones. D) Iron oxide haloes in sandstone unit. E) Soft sediment deformation. Note how the laminations follow the deformation bed. F) Sequence of rhythmites, comprising alternating mudstone and sandstone units. G) Large symmetrical ripples with sharp, straight crests and Skolithos burrows. H) Yellow-green mudstones typical of this facies association. I) Sandstone lens showing lateral/ downstream accretion. J) Calcareous concretions within a sandstone. K) Slickenside surfaces and nodules in mudstones. L) Fossilised wood weathering out of the mudstones. M) Horsetail impressions. N) Glossopteris leaf impressions. O) Large, unidentified bone c.f. dicynodont.
Table 1.
Descriptions and interpretations of lithofacies types [modified after Miall [60]; * denotes newly erected lithofacies types from Groenewald et al. [37]] from the studied stratigraphic interval.
Fig 4.
Sedimentary structures preserved on the palaeosurface.
A and B) Well preserved asymmetrical ripples indicate a westerly current direction. C) Current-modified ripples, with tongues of sand on the lee side of the ripples, in the northwestern part of the surface. D) Rill marks on smoothed ripple marks in the northwestern part of the surface. E) Depressions with interference ripples F) Smooth, unrippled section in the foreground with rippled surface in the background and a ‘corridor’ of subcircular to blob-shaped depressions (tracks) between the two. G) Aerial view of the portion of the ‘corridor’ passing between impressions 2 and 3. H) Closer view of smooth areas surrounded by ripple marked depressions which could indicate the presence of a microbial mat on the surface, as seen in modern environments (I and J). I) Modern example of smooth areas surrounded by ripple marked depressions at the Mbotyi River Mouth, South Africa. J) Modern example of an algal mat and ripple patches from Mellum Island tidal flats, Germany (modified from [61]).
Fig 5.
Sketch map of the palaeosurface showing the location of the seven large impressions, smooth areas with subcircular depressions, and linear traces.
The palaeocurrent as indicated by the asymmetrical ripples is 258°. The six large impressions are numbered 1–7 and this scheme is followed in the text and subsequent figures. The linear traces are labeled LT1 –LT3.
Fig 6.
Oblique field photographs of the six best preserved large impressions from the Dave Green palaeosurface and simplified sketch of an impression showing the characteristic “body”, “tail”, and intermediate expanded sections.
Numbering of the impressions corresponds with the rest of the figures and text. In parts 1–6: scale bars equal 30 cm.
Table 2.
Dimensions of the better-preserved large impressions and selected smooth traces.
Fig 7.
Textured scan (Left) with the outline of the impressions [2A (yellow) and 2B (white)] and footprints compared to the false-colour depth model (Right). Depth scale is in mm.
Fig 8.
Groupings of subcircular depressions interpreted as footprints on the Dave Green palaeosurface.
A) Aerial oblique photograph of the western portion of the “corridor” of footprints between Impression 2 and 3. B) Overhead photograph of the ‘corridor’ between Impressions 2 and 3 with the false-colour depth model (C). D) Overhead view of the eastern portion of the ‘corridor’ with an oblique view of the footprints between points ‘a’ and ‘b’ (E). F) Overhead view of the concentration of depressions just north of the present-day ‘island’. G) Overhead view of the depressions in the northwestern part of the surface. Large impressions are numbered in A-C and G. Scale bars equal 30 cm (A, D-F) and 50 cm (B and C).
Fig 9.
Linear traces preserved on the palaeosurface.
A-E) A large, paired trace (LT1) can be followed southwards from the northwestern edge of the surface, overprinting (or overprinted by) Impression 1 (A and B). The trace makes a sharp turn (C and D) and heads eastwards (E). The trace is mostly straight except for a small sinuous section (F). The box outlined in E is the area shown in F. G) Paired trace (LT2) cutting through ripple crests only. The trace crosses the smoothed swim trail in the Southwestern corner of the surface. H) Long linear trace (LT3) on northern part of the surface. I) Undichna trace in north-western part of the surface (Off mapped area). Arrows show unidentified invertebrate traces. J) Linear paired trace cutting ripple crests in north-western part of the surface (Off mapped area). Hammer (~30 cm) for scale (A, C, D, F, H and J). Scale card in B = 8 cm and numbers on scale card in I = cm.
Fig 10.
Comparison of Impression 2 from the palaeosurface (A) with a present-day body impression and trail of Alligator mississippiensis on the foreshore at St. Catherines Island, Georgia, United States (B). Photograph courtesy of St. Catherines Island Sea Turtle Program, Gale A. Bishop and modified with permission from [93]. C) A rhinesuchid temnospondyl such as Laccosaurus or Uranocentrodon is probably the tracemaker. Scale bar = 30 cm (A and B).