The Stormberg Group is the name given to the sedimentary geological formations of the Late Triassic Period and the Jurassic Period, found in Karoo Basin region of Southern Africa
They are of the Karoo Supergroup, immediately above the Beaufort Group, and consist mainly of sandstones and mudstones. They preserve a record of gradual desertification.
The Stormberg Group is subdivided into three formations:
Sandstone of the oldest, the Molteno Formation, was formed from river sands in the Upper Triassic. This is now exposed as cliffs in the Drakensberg and can be easily recognised by its sparkling appearance. This is due to minute quartz crystals that coat and bind together the sand grains.The
Molteno Formation consists of two major coarsening-upward sequences, the basal sequence is made up by the
Bamboesberg and Indwe Sandstone and the upper sequence by the Transitional Member. Tabular sheets of horizontally and cross stratified medium- to coarse grained
sandstone dominate the formation. The sandstones were deposited by braided streams on a vast braidplain.
The Molteno Formation is in turn overlain by red mudstone of the Elliot Formation which contains dinosaur fossils such as the 12 metre long Melanorosaurus.The
Elliot Formation is dominated by red floodplain mudstones with subordinate channel and crevasse splay deposits. These were interpreted as a mixed load dominated meandering system in an increasingly arid setting. Towards the top of the formation aeolian sediments occur as metre-scale intercalations in the fluvial deposits of the Elliot Formation.
The white cliffs of the middle Drakensberg are composed of Clarens Formation sandstone. These sandstones were deposited as large dunes in a desert environment. Worm burrows and dinosaur footprints can also be found in these rocks.The Clarens Formation consists of yellow fine-grained sandstones, sandy siltstones and mudstones. This indicates strong aridification of the climate. Wind blown dunes suggest deposition in a desert environment with shallow playa lake and river deposits in the wetter parts of the basin, producing a complex interaction of aeolian and aqueous sedimentation.
