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Quartzite Burrows

30 October 2021

Another link sent in by Gary. See https://phys.org/news/2021-09-geologists-half-century-old-mystery-animal… … the mystery is a geological one. Perforations in an Australian rock section, namely in a quartzite, appear to resemble animal burrows of some kind. They are thought to belong to marine crustaceans – which is even more perplexing. They have been known about for some 50 years, roughly, and until now nobody has come up with a sound explanation. The quartzite is as hard as cement. The rock is very old. How could animals dig burrows in such hard rock.

The problem is that the quartzite is dated 1.7 billion years ago on the geological column, using a dating methodology that is considered to be reliable. This is some one billion years prior to the appearance of the first animals in the fossil record. However, rather than redating the quartzite, scientists have come up with a uniformitarian solution. An Australian, Chinese, American, and Swedish team have come up with an explanation for the riddle. They measured the age of the sand in the burrows and they claim it is dated one billion years after the formation of the quartzite. It is now projected the quartzite deteriorated and became loose enough for animals to dig burrows into it – but at a later stage it became hard quartzite once again. In other words, they spread a window in time to enable burrowing, dating it around 40 million years ago, during the Eocene. The crustaceans, we are told, invaded SW Australia during a short lived marine transgression event. I am supposing this explanation will now enter the textbooks – assuming they had never bothered to inform Joe Public there was a mystery in the first place. Obviously, successive catastrophic events could perchance have caused the quartzite to harden as well as soften – but what part of the quartzite is 1.7 billion years of age. What part of it is 40 million years ago, we might add. The full article, and therefore the answer to my query is at https://doi.org/10.1073/pnas.2105707118 or www.pnas.org/content/118/40/e2105707118

PS .. it is worth pointing out the delayed explanation is not unusual in geology as the initial research may have lingered for a long time before being picked up by another geologist to rethink and take field notes. Years and years can pass. Even stratigraphical uncertainties can be left hanging around for generations until a new geologist homes in on it and does some fresh research. Geology is not like archaeology. People don't dig holes in the ground. They go to railway and road cuttings, quarries and cores, that are already cut out of the landscape. Or to known rock faces and fractures etc. The interesting thing here is that the quartzite rock was surrounded by Miocene rock formations – which provided the means to explain the mystery. Actually, what they do say is that the quartzite over time became weathered and therefore the face crumbled allowing access to the less hard interior once the formation had been swallowed up by the transgression event. It is a perfectly uniformitarian explanation.

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