MODE OF INTERNAL DEFORMATION IN SAND WEDGES

Sequential sections of a sand box model are used to quantify displacem ent along imbricate surfaces and their rotation and volume loss histor y within an accreting sand wedge. Model results show that both displac ement along the imbricate surfaces and compaction of the imbricate she ets decrease with sequential accretion of the wedge. The model wedge p ropagates episodically along a basal decollement when displacement alo ng the imbricate surfaces decreases dramatically due to their back rot ation and steepening. During their back rotation, the model imbricate sheets undergo compaction which resulted in an area loss of 12-13%, wh ile the entire model shows 17% area loss. Back rotation of model imbri cate sheets takes place in a domino-type style that is accommodated by ductile deformation of sand layers at deeper levels. Deeply located s and layers undergo 40-50% layer parallel shortening compared to no lay er parallel shortening of the shallow located layers within the same i mbricate sheet. Model sand wedge does not grow self similarly but rath er its length/height ratio increases episodically with deformation.