While I can't speak to the original author (as I'm partial to a proto-Mark per Burkett and see the didactic scene in Mark 13 as potentially being a post-70 CE interpolation providing explanation of a more generic saying in 13:1-2), there's evidence of LXX use in Mark 13:14's "abomination of desolation":
...βδέλυγμα των ερημώσεων...
- Daniel 9:27 in the LXX
...βδέλυγμα τῆς ἐρημώσεως...
- Mark 13:14
Given the ambiguity of the original Hebrew in Daniel 9:27, that the author (or here redactor) of Mark is following the LXX here to arrive at this specific wording seems probable.