Spatial aspects of concretionary growth in the Upper Lias of Northeast England

Spatial distribution, size and orientation measurements on 143 concretions from the Jet Rock (Upper Lias) of northeast England are reported. The distribution of concretions conforms to a Poisson or random model at the scale sampled. Approximately 30% of the Jet Rock concretions are sufficiently asymmetrical in bedding plane section for a major axis orientation to be recorded. Orientations cluster in the range 10–30°, possibly indicating a preferred direction of pore water transport in the bedding plane during compactional expulsion.