sentences:  The depositional environment of the Kaili formation is not entirely known, and there are two hypotheses for its formation.It may have been a nearshore marine environment with 'normal' levels of oxygenation; or it may have been a deeper water environment further from the shore, on the open continental shelf; in this setting oxygen would not be available below the surface layers of the deposited sediment.The trace fossil assemblages in the formation suggest that it was below the wave base and was reasonably well-oxygenated.