At https://phys.org/print405675862.html … we learn there was what is thought to be advanced solar activity smack bang in the middle of the Mid Holocene Warm Period. The evidence comes from tree rings in long lived bristlecone pine trees. The researchers suggest it may involve a change in the Sun's magnetic activity (a super flare) or a number of solar flares arriving in a burst, one after the other.
The study is in PNAS (Feb 2017) says the event occurred in 5480BC. It seems scientists have been looking out for anomalous activity on the Sun after discovering the 775 and 994AD anomalies – but they had to go back a long way. This probably indicates such events are rare.
The team have 'attempted' to explain the anomalous solar activity we are told, and the researchers even suggest the opposite may be true and 5480BC marks a brief phase of low activity on the Sun (allowing cosmic rays to enter the solar system in greater amounts). Clark Whelton posted the same story on his email thread – see http://en.nagoya-u.ac.jp/research/activities/news/2017/02/what-happened-… … where we are told, by the Japanese spokesperson Fusa Miyake, 'although our understanding of the mechanism behind unusual solar activity has hampered efforts to explain the team's findings, they ope to find further knowledge by studying flares given off by other stars.
The same story popped up in the New Chronology Yahoo Discussion Group and one member asked if it affected C14 dating, hoping, I suppose, to provide evidence to refute the methodology.