The origin and classification of bedding planes

The purpose of this paper is to clarify the meaning of the term bedding plane by discussion of the origin, classification, and modification of bedding planes, and discussion of certain features of sedimentary rocks which may be mistaken for bedding surfaces.

The literature on the subject was found to be meager, most references consisting of subjects related to bedding planes and with only incidental treatment of the latter.

A bedding plane is defined as a surface representing a contact between a deposit and the depositing medium during a time of change. They are primary features of sedimentary rocks formed usually by the depositing media water, and atmosphere. Changes occur in the depositing medium and these are reflected in a difference in texture or composition with a bedding plane representing the change. Many bedding planes represent a time interval of considerable length.

Bedding planes are classified according to extent, orientation and importance of the change which produced them. Ordinary bedding planes are those which were formed essentially horizontally, lie roughly parallel to others above or below, and are always intraformational. Interim bedding planes are formed with at least a part of the surface having considerable inclination to the horizontal or to ordinary bedding planes. These are small in extent and formed by currents. Formational bedding planes are ordinary bedding surfaces of such extent that they limit formation and indicate changes of considerable importance.

Surfaces likely to be misidentified as bedding planes are faults, joints, and solution surfaces.