Anglo-Saxon Chronicle

The Anglo-Saxon Chronicle (ASC, for short) is a document tracing the history of the Anglo-Saxon people from 60 BCE (around the time of Julius Caesar's first British campaign) up until 850 CE, though it does mention the arrival of the Scots in Hibernia (Ireland) and of the Picts in Caledonia (Scotland), both of which are generally accepted to have begun earlier than Caesar's invasions of Britain. It was widely copied, and many different versions exist, none of which agree in all particulars as they were each updated in the place where they were stored.

Genealogies
The Anglo-Saxon Chronicle contains genealogies tracing the royal line back to the Norse god Odin whence sprang its claims to legitimacy. In pagan times, the Saxons practiced ancestor veneration, and even into the early Christian period they put such stock by accurate portrayal of one's ancestors that a whole bevy of family sagas were reproduced with the utmost truthfulness to avoid having a band of angry relatives burn the writers' houses down.

This put the monks who were the early Christian chroniclers between a rock and a hard place: Odin had been officially reclassified as a demon at that time, and it was not good to have demons in one's ancestral line. But neither could the chroniclers disavow the old line; Charlemagne had only recently had to kill 4500 recalcitrant pagan Saxons. Christianity was not very popular with the people at that point, as it was imposed from the top down, a process that was greatly aided by the pagan belief that the king was of divine descent. Furthermore, the sort of Christianity being practiced had extremely heavy syncretic influence from the old paganism, not being very recognizable to a Christian of today. See, for example, the Anglo-Saxon poem Dream of the Rood, which describes an event that happened both to Jesus and Balder, and calls the former by some of Balder's epithets.

So, to keep their royal line intact, Odin was reclassified as a man, a dead king, and Noah (yes, the one who is most famous for his large ark) was stuck at the front of the list of kings. To make up for the fact that all but one of the names in the modified list were entirely Saxon, several mythical kings listed as ancestors of Odin were reclassified as descendants of Noah.

The current British royal family claims descent from the sixth century Saxon king, and through Cerdic, from Odin.

The ASC and young-earth creationism
Just naturally the above interpretation of the genealogies led to considerable strains on the Bible, with some extremely unbiblical statements making their way into the chronicle. For example, although Genesis 10:32 has it that Noah had only three sons, who were all adults at the time of the Great Flood, the ASC reclassifies one of the mythical kings, Sceaf, as a fourth son of Noah who was born on the ark.

Of course, the more far-out and implausible something is, the more the young-earth creationists love it. So, instead of correctly dismissing the genealogy as syncretic bullshit, which (unlike most other things) they actually could do without compromising their world-view, they go to great pains to insist that the chronicle is a completely accurate record that entirely proves their point.

The creationist Bill Cooper argues that Sceaf is actually Japheth, the son of Noah who was said to have populated Europe.

That none of the Saxon chroniclers actually said this (and furthermore contradicted it by noting Sceaf's supposed birthplace) does not appear to concern Cooper ("B.A. Hons" ); his reasoning is that since the chroniclers made such blatant mistakes, they were, as a matter of course, right on the mark:

If it really had been a fact that certain unscrupulous Christian monks had fraudulently invented the pre-migration Saxon genealogies, ... is it at all conceivable that they would have used a form of Japheth's name that was utterly unfamiliar to those very readers whom they hoped to convince? And surely, no educated monk would have made such a silly error over Japheth being both in the Ark when every one of his readers would have known that Japheth, far from being born in the Ark, had helped to build it! ... we are not dealing here with any attempted fraud or piece of Christian fiction.

That (despite his own insistence that he would use only pre-Christian documents) he used only the Christian-era ones to support these claims, and quote-mined and misrepresented those, does not appear to concern him either; he was criticized even by other YECs for shoddy scholarship and misrepresenting the Prose Edda.

Not to mention that the chronicle describes all sorts of other outlandish and clearly made up events. For instance: