BRUCS: a new system for classifying and naming mappable rock units

A new scheme is introduced for classifying and naming mappable rock bodies that lack primary stratification. In recognition of their distinctive geological characteristics, these ‘nonstratiform’ bodies are defined and classified according to their 3D form, spatial distribution and genetic relationships, in two hierarchical (parent-child) chains: one for intrusions and one for tectonometamorphic units. Geologically complex units, encompassing bodies of different genetic classes, are classified in a third chain reserved specifically for ‘mixed-class’ units. The new classification scheme is offered as an alternative to existing recommendations in the International Stratigraphic Guide and North American Stratigraphic Code, in which nonstratiform bodies are recognised and defined primarily by their lithological character. BRUCS (the BGS Rock Unit Classification System) combines the three new parent-child chains for nonstratiform units with the well-established chain for stratiform units (bed-member-formation-group-supergroup) to create a flexible, practical and effective solution for classifying and naming all mappable rock bodies. The taxonomic rigour of BRUCS means the considerable capabilities of modern digital systems for managing and communicating mapping data can be exploited fully.