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ABSTRACT At Hengistbury Head, Dorset, the Boscombe Sands (Middle Eocene, Bracklesham Formation) are of estuarine channel facies. A mud-filled channel is exposed, the banks and eastern flank of which have a black carbonaceous stain, the degraded remains of a bitumen. At the time of deposition, the bitumen rendered the sediment firm and it was extensively burrowed by a Thalassinoides-forming organism (crustacean). The bituminous sand on the eastern channel bank suffered brecciation and dilation as a result of liquefaction and flowage of the underlying sediments. This is thought to have been due to rapid expulsion of pore water, possibly as a result of seismic shock. The layers of bituminous sand below the surface were ruptured during water-escape, resulting in localized zones of rapid flow causing fluidization and the development of dewatering pipes up to 1.2 m long. The estuarine sediments were subsequently transgressed during which the bituminous sand was exposed on the seafloor, when it was eroded into a hummocky topography and heavily burrowed. Blocks of bituminous sand were reworked into the marine basal conglomerate, composed mainly of flints, demonstrating the remarkable strength of the bituminous cement.