Bulldog Shale

The Bulldog Shale is a formation of Early Cretaceous age (Aptian to Albian stages) that forms part of the Marree Subgroup of the Rolling Downs Group, located in the Eromanga Basin of South Australia, Queensland and New South Wales.

Description
It is the lowermost unit in the Marree Subgroup, overlying the Cadna-owie Formation and is overlain by the Coorikiana Sandstone. The formation dates to the Aptian to Albian stages of the Early Cretaceous. The Bulldog Shale is composed of finely laminated carbonaceous and pyritic mudstone and claystone beds. Weathering has caused heavy leaching and bleaching in some regions of the Bulldog Shale, including those around Coober Pedy, so that the rocks are white or multicolored. These horizons contain rich opal deposits. Horizons without this bleaching are primarily composed of organic-rich shale. Gypsum, in addition to carbonate limestone concretions rich in fossils are common in these unbleached shaly horizons.

Fossil content
The Bulldog Shale has yielded fossils of plants, invertebrates, fish, and reptiles. The macroinvertebrate fauna of this formation includes several molluscs, such belemnites, gastropods, and bivalves. Fish are represented by chimaeras and ray-finned fish (these include teleosts) and a lungfish. Sharks are conspicuously absent in the Bulldog Shale. Many plesiosaurs are known from the formation, including leptocleidids, elasmosaurids, pliosaurids, and possible polycotylids. Ichthyosaurs are also present. Archosaur fossils from the Bulldog Shale are rare, and are represented mostly indeterminate specimens, some of which can be assigned to Dinosauria. Due to the coastal location of the Bulldog Shale, large amounts of wood have also been recovered in this formation.