Summary Oil shales, and the less common limestones associated with them, represent freshwater lacustrine phases within the Dinantian Oil Shale Group at the eastern end of the Midland Valley of Scotland. The understanding of the areally extensive Burdiehouse Limestone Formation is fundamental to an appreciation of the palaeolimnology of the lake in which algal oozes (consisting mainly of planktonic algae analogous to the modern form Botryococcus braunii ), later to become oil shales, accumulated. The lake, referred to as Lake Cadell, was shallow (< 100 m) with gently sloping margins. It was meromictic and formed a closed system during deposition of the limestones, draining eastwards to the sea during oil shale deposition. The climate was wet tropical ensuring ideal conditions for a prolific flora of algae and vascular plants both around and within the lake, and providing a regular freshwater input. The lacustrine phase forms part of the cyclical Oil Shale Group succession in which each sedimentary cycle can be resolved into four phases indicating long-term lake expansion and contraction.

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