Revisiting the "reefs" of Black Reef Cave, Ribblehead, North Yorkshire, UK with some observations on cave divers "chert"

A re-study of black materials encountered in Black Reef Cave as sheets cutting across the main passage has shown that they have influenced the passage morphology. Upstream of the reefs the passages have a typical phreatic tube-like cross-section, whereas downstream the passage cross-section is that of a vadose canyon, suggesting that the reefs have ponded water, resulting in the development of small, perched, phreatic loops. The reefs consist of a core of crystalline calcite surrounded by black manganese/iron material. It is proposed that calcite vein-mineralization along joints caused the ponding of water and the manganese/iron material is secondary, and either deposited preferentially on, or preserved on, the calcite veins. Other similar occurrences and possible occurrences in the region are discussed.