The Viséan sequence at East Kirkton was deposited in a shallow lake, set within a richly vegetated landscape formed of volcanic cones a few hundred metres high. There was little volcanic activity, however, while the lake existed, and the many tuff horizons within the sequence were washed in during weathering. The lake may have been generally cool, though of unusual water chemistry, as a result of which the spherulitic East Kirkton Limestone precipitated. At times, however, water temperatures may have risen sharply through localised hot-spring activity; both factors deterred ‘normal’ aquatic life.
The bulk of the preserved biota consists of plants (permineralisations and compressions) and dominantly land-living animals, including the oldest terrestrial tetrapods (amphibians and reptiliomorphs), large terrestrial-aquatic eurypterids, the first harvestman and rare millipedes. All these animals lived close to the lake, in a fire-prone forest dominated by gymnosperms and pteridosperms.
At a late stage in the history of the lake, deposition of spherulitic limestones was replaced by black shales, bearing a ‘standard’ Oil-Shale fish fauna, suggesting that the isolated lake had linked with a larger fish-bearing water body. This is coupled with a shift to a lycopod-dominated flora and may indicate a climatic change to wetter conditions. Finally the lake silted up with tuff, ending an existence of only a few tens of thousands of years.