Abstract

Grain fabric and the depositional volume of modern foreshore deposits from the Pacific coast of southern Ibaraki Prefecture, Japan, are influenced by tides. Reversals of imbrication dip were found that may result from predominance of uprush transport during the flood stage and backwash transport during the ebb stage. The thickness of sediment deposited during both rising and falling water stages varies directly with tidal range for that cycle, so that diurnal inequality leads to alternations of thick (3-4 cm) and thin (1-2 cm) layers on the foreshore.

Pleistocene foreshore deposits exposed near the Pacific coast are also characterized by reversals of grain imbrication and may have been controlled by tidally-influenced uprush-backwash processes. The Pleistocene example also possesses alternating thin and thick layers, suggesting a diurnal variability in tidal pattern similar to the modern tidal pattern along the Pacific coast.