ABSTRACT

Clay pebble occurrences have been found along a stretch of about 10 km along the China Sea coast of northeastern Johore (Federation of Malaya).

They are derived from clay sheets, which alternate with sand layers in tidal flat deposits. The upper clay sheets lie between the high tide and low tide marks. At low tide the clay, if exposed, dries and forms cracks; wave action at the next high tide loosens flakes and rolls them while washing them ashore. Breakwater develops in a series of low rollers due to the flatness and shallowness of the sea floor. The clay pebbles are left behind at the high tide mark. Another deposit is found higher up the beach at a storm tide mark mainly as the result of monsoon storms.

The size of the clay pebbles ranges between 0.5 and over 30 cm, depending on the thickness of the clay sheet from which they are derived. Their roundness depends on the distance between the exposed clay sheet nip and the high tide mark. In this zone, a third migrating deposit of clay pebbles is usually present. After deposition, some pebbles may sink rapidly into the underlying wet sand, or sand may be blown over them. The clay is mainly provided by the rivers debouching in this area; the sand may be of marine origin, derived from rock capes in the neighbourhood.