PILLOW-BEDS - A NEW TYPE OF SEISMITES - AN EXAMPLE FROM AN OLIGOCENE TURBIDITE FAN COMPLEX, ALICANTE, SPAIN

A new type of soft sediment deformed beds, termed 'pillow-beds', originally a packet of calcarenitic turbidites, show sand-in-sand loading with plane lower and upper surfaces. The pillow-beds have some resemblance to ball and pillow structures and they are considered to have formed as a result of dewatering. The pillow-beds are Oligocene in age and are part of turbidite lobes in a submarine fan system, which was fed through a canyon along the southern border of the ancient Iberian continent. Three hypotheses may explain their occurrence: overloading, sliding or seismic shock. A seismic origin is preferrred on the basis of the flat, undeformed lower surface of the pillow-beds, excluding dewatering of-and loading into-the previously deposited beds. Furthermore, the pillow-bed structures are related to grain size and may show repetitions, thus excluding sliding. The scale and nature of the pillow-beds suggest they could be the result of an earthquake with a magnitude of 6-7 on the Richter scale.