NANKOWEAP FORMATION

---

Fig. 8

Within the Nankoweap Formation a structure was found and identified in 1937 as a trace fossil impression of a strand jellyfish. In 1960, the same type of impression was found, but this time it was identified as an inorganic sedimentary structure, formed by the compaction of fine sands deposited over a compressible, but unidentifiable structure, quite possibly a small gas blister. In 1969 comparisions were drawn with a Mesozoic stellate trace fossil, ASTEROSOMA, and the conclusion was that the organic originator was a sediment feeder that was able to burrow into the sediment, most likely an annelid. Reexamination of the speciemens revealed that the structures were actually quite similar to "sand-volcanoes" formed by the expulsion of gas or fluid from sands deposited in shallow water,turbidite conditions.