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Schematic representations of contrasting preservational styles for sand-filled open burrows constructed in a muddy/silty sediment. (A) Passive fill of an open burrow in which burrow fill is continuos with source of casting sediment. (B) Passive fill in which there is a distinct break between the burrow fill and overlying sediment (adhering preservation of ref. 17). (C) Passively filled burrow that is surrounded by silty sediment (floating preservation of ref. 17).
