A vexed question – what causes extinction events? The problem has disturbed scientists for a long time, eager to keep their distance from the idea of catastrophism. Most of the problems, it could be argued, rise out of geochronology and the inordinately long time scales assigned to sediments laid down at extinction events. This sounds like me repeating the same mantra, over and over again, but some kind of rationalisation is required in order to differentiate sediment layers formed quickly, as a result of catastrophism, from those sediments that really are formed over a long period of time – such as sea bed or lake cores, or ice cores. Geologists need to seriously consider recognising that sediments can be laid down quickly, within the course of a single day, for example, rather than treating all sediment layers as uniformitarian and long winded. Some were. Some were not. Geologists in the field do date some sediments as formed quickly – but this does not always apply to textbooks that continue to treat them all as lasting thousands of years, or longer.
A piece of research published by PNAS is a prime example – see https://phys.org/news/2018-05-scientists-widespread-ocean-anoxia-mass.html … discusses how scientists, over the years, figured out the real cause of an extinction event. These are usually attributed to climate change, volcanoes and super volcanoes, acidic oceans, and just the one asteroid strike. Other factors are methane eruptions and marine anoxic events. The problem here is that all these, in a parallel looking glass, could be attributed as side effects of a cosmic event [asteroid or meteor encounters] and no doubt many other things as well, as a vector is required to produce, for example, anoxic oceans, or sudden climate change, or event setting off a chain of volcanoes. Why would they exist all by themselves? They do, as far as geochronology goes, as the sediments with their evidence are dated prior to or after the actual date of the extinction – in this case, the end of Ordovician. A mass extinction event known from animal and plant fossils, is dated by uniformitarian methodology and can be separated from the evidence of other causes, even the actual boundary event itself. Do fossils in rocks represent a uniformitarian laying down or were they all killed together, and left in a single heap that was buried and fossilised in situ. In this instance, the event was accompanied by climate change – a switch from greenhouse temperatures, very warm, to an ice house. The extinction, it is now being suggested, looking at limestone sediments, was caused by a period of global cooling that create a global marine anoxic event. My question would be – what caused the cooling? See www.pnas.org/cgi/doi/10.1073/pnas.1802438115
The Ordovician pops up in black shales at the next link – https://phys.org/news/2021-07-longest-paleozoic-yukon-wilderness.html … in the Yukon. We are back to a world brimming with trilobites, brachipods, and creatures resembling squids. These are found in what is now dry land and the black shale sediment represents a nice marine ecosystem – on the face of it. Either the Yukon, at the time, was under the sea – or a huge tidal wave swept across the top of North America [or at least, one part of it]. It left behind a treasure trove of fossils – and the black shale rocks. The research indicates oxygen changes on the sea floor, spread across 120 million years, have been preserved at the locale – somewhat miraculously. This is another prime example of geochronological dating. The black shale has been defined as being laid down over a long period of time when the opposite might be true. If it was laid down quickly the researchers efforts may have been different. This site appears to be tied up in the hypothesis of a low oxygen world, including the oceans, switching to a more oxygenated one. The date for the event is irrelevant. It could have been 400 million years ago – and is not necessarily what is in error. It is the laying down of the sediments which is used to create a safe uniformitarian world, a sort of comfy bedtime teddy bear, designed to erase violent catastrophes from the geological past. A geological record that is punctuated by catastrophic events, with an indeterminate period separating them from each other, would be a more honest application of the geological process. However, if one would wish to control the narrative, the recognition of long periods of time when fossils were not being formed, on a global basis, would weaken their position, now and in the past. Regional catastrophes, ssuch as volcanoes, floods, and earthquakes, or even land slides, cannot be used to create a universal geochronology. One cannot help but recognise this view of the past is not going to change – or at least, as long as the West is in ascendancy. There is too much history involved – and long ago battles with those opposed to the idea of uniformitarianism.
One interesting point the researchers make is that the Ordovician extinction led to an oxygenation of the oceans – which allowed big fish to develop. From that we have to accept that no big fish were swept up in the tidal wave, if that was the caused of the deposit – although chert and lime mudstone were also part of the formation.
At https://phys.org/news/2020-04-bad-alive-links-ocean-deoxygenation.html … which is an older piece of research on deoxygenation – all from the same field site in the Yukon, and also concerns the Ordovician extinction event. This was published by Nature Communications with an older theme on oxygenation – a variant on the same tale of woe. See also https://doi.org/10.1038/s41467-020-15400-y