The Chinese paper on a comet involvement in the C14 spike at 775AD, as recorded in Tang astronomical records (Liu et al, Nature Science Report 4:3728, 2014) has lasted just a few days before news of another paper debunking a comet connection (Ilyan Ususkin and Gennady Kovaltsov, 'A comet could not produce the C14 spike in the 8th century' which has been released as a pre-publication paper at arXiv). They appear to actually ignore what the Chinese are actually saying, picking up on the news blurb rather than the actual paper itself. As I understood it, it was the coma that had accumulated the C14 and it was the coma lashing against the atmosphere that injected the spike. It seems that Kovaltsov and Ususkin favour a giant solar flare – but lots of others have discounted this idea as there are no records of unusual aurorae at the time. Steve Mitchell has been researching this event and his findings will no doubt be duly published by SIS. The Chinese actually address the issue of a solar flare. I did wonder if the new paper was hastily cobbled together without fully absorbing what Liu and his fellow researchers had to say.
Their argument is based on a comet impact – and lack of geology for an impact at this time. It never occurred to me when reading the Chinese paper that they had proposed an impact – only that a comet came close to the Earth, close enough for its coma to inject a burst of C14 into the atmosphere. You would not expect a geological discovery to go hand in hand with such a situation. The only effect they were proposing was the injection of material from the comet and coma – nothing else. If a comet did come close its trail of dust and debris could have continued to impact with the Earth for some time afterwards and may even explain the downturns and meteoric fireballs that are associated with the 9th and 10th centuries (leading up to 930/940AD) as outlined in a paper by Palmer and Palmer in SIS C&C Review 2002:1. For the new paper see http://arxiv.org/abs/1401.5945 (or arXiv:1401.5945v).
See also www.sciencenews.org/blog/science-ticker/eighth-century-carbon-spike-not-… … where the date of the Chinese paper is given as Jan 16th whereas news of the new paper appeared on Jan 27th – just ten days.