ABSTRACT

Inorganic and organic structures of both primary and post-depositional origin are described from siltstone surfaces in the Bembridge Marls. The siltstones occur within an interbedded silt-clay horizon which is approximately 1 foot (30 cm) thick and which occurs about 48 feet (15 m) above the base of the succession on the northeastern side of the Island in Whitecliff and Howgate Bays. A number of the structures to be described occur only on the siltstone soles, while others are also found on upper surfaces. The primary inorganic structures comprise scour and tool markings. Those of post-depositional origin resulted predominantly from the slipping and cracking of the sediment. The most common organic structures are burrowing traces, although resting traces are also found. Deposition occ rred in very shallow water. periodically subjected to drying out. Evidence from structure orientation indicates an approximately northwest-southeast trending movement of water. A current from the northwest is suggested by the author. An upward transition into dominantly clayey sediments, poor in primary structures, indicates the oncoming of quieter and probably deeper water.