“Doomed pioneers” – my favorite turbidite ichnofacies!
And, no I am not talking about the Donner Party (hooray, wikipedia links are back!). I am talking about a 1990 Geology paper by Follmi and Grimm called “Doomed pioneers: Gravity-flow deposition and bioturbation in marine oxygen-deficient environments.” The doomed pioneers in this case are shrimp burrows of the ichnofacies Thalassinoides and Gyrolithes that were brought from shallow water into the deep ocean by turbidity currents. A novel idea by the authors – I am not sure of the reception the idea got in the ichnology community, but for what its worth, I think it is a plausible idea. As far as I understand (maybe the ichnologists reading this can clarify for me), these ichnofacies (i.e. shrimp) are not restricted to shallow-marine environments, but in this particular case, the deep ocean was oxygen depleted and hosted little or no life. So, the only way to get the critters into the deep ocean was to bring them in with a turbidity current. Here is a nice image of the process by which the unwilling pioneers become doomed.
The only potential problem I see with keeping the bugs alive on the way downslope is the EXTREME turbulence generated during ‘gravity flow events’. It seems that every time scientists try to measure a turbidity current, the only thing they are sure of is that their instrumentation is destroyed and usually swept away into oblivion. However, with all the torture tests that cockroaches are put through, it seems that relatives of theirs like shrimp may be alright in a turbidity current.
Besides being a great idea, the paper also has beautiful prose. For example, from the abstract:
oxygen-depleted conditions limited the survival time and ecological complexity of the transported infaunal dwellers and rendered them doomed pioneers.
There is also a heading in the paper called “Stratigraphic record of allochthonous burrowers” – beautiful!
Maybe I will continue this ichnology series with a great photo of an echinoderm escape burrow (here is an example), another sad (for the animal) but interesting turbidite related trace fossils. Happy Friday!