Funnel-shaped, breccia-filled clastic dykes in the Late Cambrian Chaomidian Formation (Shandong Province, China)

Abstract

Some examples of a funnel-shaped structure filled with both angular and rounded clasts occur in a peloidal grainstone bed of the Chaomidian Formation (Late Cambrian) in the Jiulongshan area (Shandong Province, China). The clasts consist of peloidal grainstone which is the same as that of the walls of the funnels. The structures are interpreted as dykes formed by upward escape of pore water and/or fluidized sediment through a narrow conduit which was gradually widened by the force of the intruding fluid/sediment. The erosional capacity of the pressurized fluid/sediment mixture consequently diminished upwards, which explains the gradual decrease in intensity of fragmentation from the adjoining walls in this direction.