Pillow‐beds: a new type of seismites? An example from an Oligocene turbidite fan complex, Alicante, Spain

Abstract

ABSTRACTA 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.