First, if this is 80 meters in diameter, or 40 meters in radius, and say at a minimum 40 meters deep, that’ s not quite 10^9 kg of soil moved up order 40 meters, requiring (very roughly) the equivalent of 60 tons of TNT, at a minimum, and thus an equivalent magnitude of ~ 3.2 (again, roughly). Such an explosion should be detectable on seismological networks, such as the ones looking for nuclear testing.
Second, there is another mystery crater in Siberia - the Patomskiy crater. This one is in rock, not sediment, is about 160 meters in diameter, and is maybe 300 years old, but I have to wonder if they have a similar cause.
Third, I am interested in quark nuggets and other types of condensed matter, such as Q-Balls, generically called Compact UltraDense Objects (CUDOs) by Jan Rafelski of U. Arizona. If these things exist in the appropriate masses, they could cause holes such as this and the Patomskiy crater. Even better, if this were to be caused by transiting CUDO, it would cause a "linear earthquake, which should be easily recognizable in the seismic record.