Abstract:
Sandstone pillars in the Lower Jurassic eolian strata of the
Clarens Formation are concentrated in clusters, with up to
four pillars within 25 m2 in two localities in the Tuli Basin
of northern South Africa and southern Zimbabwe. The pillars
are generally vertical, have a preserved height of up to
3.3 m, and are elliptical in plan view. Pillars are grouped
into two styles of architecture: those with oriented elliptical
shapes and side buttresses, and those less well oriented
with a smooth outer wall, internal open spaces, and vertical
shafts cutting the pillar. The long axes of the elliptical pillars
are generally oriented to the north.Northwards-oriented
side buttresses also are associated with some of the pillars.
The internal architecture of the pillars is characterized
by intense bioturbation with two different burrowing
styles. Type 1 burrows are composed of a network of randomly
oriented, anastomosing sandstone-filled tubes, 0.3 to
0.8 cm in diameter. Type 2 burrows are rare, north-south
oriented, and have a smaller diameter. Other associated
features are back-filled tubes, open, vertical shafts, and
open spaces between the interior and exterior of the pillars.
The pillars are interpreted as fossilized termite nests.
Type 1 burrows are interpreted as termite passageways
within the nest. Type 2 burrows may be related to invading
ants. Back-filled burrows may be a result of either beetle
predation on resident termites or backfilling by termites
themselves. The strong north-south orientations are comparable
with modern-day nest architecture of magnetic termites
in northern Australia, where nest-orientation is related
to cooling. The orientations and features reported here
are interpreted to be modified for the high latitudes proposed
for the Lower Jurassic Clarens desert. Complex nest
architecture preserved in the Clarens Formation suggests
that advanced eusocial behavior and ability to construct
large nests had appeared in African termites by the Early
Jurassic.
