Yoredale Cyclothems of Northumberland

Abstract

IN discussion of Yoredale cyclothems insufficient attention has been paid to the degree of change between successive environments of deposition in thinly bedded sequences. There is general agreement that the study of cyclothemic and cyclical sedimentation is primarily an investigation of the sequence of the environmental changes that take place. If it is accepted that this is so regardless of how long a new environment may persist or how widespread it may be, then the full implications of such a statement must be appreciated. For example, in the case of a sandstone–limestone junction the change from a sandstone to a limestone two feet thick is exactly equivalent to the change from an identical sandstone to an identical limestone thirty feet in thickness. That is to say, the change in environment is of the same degree in both cases and that this change occurred in a distinct period of time. The duration for which the new conditions were maintained is of no consequence in this context since this indicates the history of the rock after the all-important event had taken place.