Supposed Precambrian trace fossils from Jersey, Channel Islands

Squire (1973) described and figured fossil burrows, ascribed to Sabellarites, from the Upper Proterozoic Brioverian Jersey Shale Formation of Jersey, Channel Islands. The meander-like structures are from calcisiltite beds within a turbiditic sequence and were collected from low intertidal reefs. Re-examination by all of us of one of Squire's specimens (Jersey Museum, La Hougue Bie, SJM C 2026; Squire, 1973, plate 1 a) and more decisive material (SJM C 1002, 5 specimens), collected later from the same reefs by Stéphane Rault, confirms that the structures are attributable to modern polychaetous annelids, almost certainly to Polydora sp., an attribution with which Dr J. D. George (Head, Polychaeta Section, British Museum (Natural History)) concurs. Polydora is associated with a wide range of substrate preference, constructing borings in hard calcareous substrates, pseudoborings on the inside of shells and true burrows in loose sediment. In the Jersey material the irregular, but quite typical, U-form tubes have been formed along open joint planes with slight dissolution of the rock, or along thin calcite-filled veins, also with dissolution of the rock. The joints occur at all angles to the bedding. Very pertinent is the attitude of the tubes, which is principally normal to the rock surface rather than to the bedding. No tubes have been seen on freshly broken surfaces and in no instance has a tube been seen to enter the rock, though there are numerous moulds of pyritic concretions which happen to be of about the same diameter as the width of the tubes. Lithothamnium sp. is patchily distributed over the rock surface and locally penetrates into the joints, showing that they were open.