"What Wark avoids, in this discussion at least, is choosing technologies which are marked by considerable historical separation"
could you paraphrase marked by so I can get it
“Marked by” in this sentence has a meaning of : indicated, featured, denoted. Example: The civil movement was marked by many public protests. Meaning that one of the main features, most important aspect of the movement was the protests.
In his discussions, Wark tries to avoid technologies that includes any historical separation.
To be marked by X is to have X as a clearly perceivable distinguishing mark.
The sentence may be paraphrased:
Wark avoids choosing technologies which are obviously distant from each other in time.