And speculations are all you can get since there is no consensus.
Burton Mack in A Myth of Innocence argues Mark was drawing on a sayings collection similar to Q, plus earlier written or oral accounts of the passion already circulating. Helmut Koester did substantial work on pre-Markan sources, arguing the passion account in particular looks like it was assembled from earlier independent units rather than composed fresh.
John Dominic Crossan went further and proposed a "Cross Gospel" embedded in the Gospel of Peter as a source Mark used, though most scholars don't buy it.
For the miracle stories specifically, Paul Achtemeier made an influential argument that Mark inherited two pre-existing collections of miracle stories, each following a similar pattern, and combined them into a single sequence.
The NRSV is the standard scholarly choice; it's what most of the academics I cite use, and the New Oxford Annotated Bible (NRSV) gives you the notes that flag where the text is doing something interesting.
I have been trying to come up with scholarship that has some kind of speculation as to what sources the author of Mark may have used.
And speculations are all you can get since there is no consensus.
Burton Mack in A Myth of Innocence argues Mark was drawing on a sayings collection similar to Q, plus earlier written or oral accounts of the passion already circulating. Helmut Koester did substantial work on pre-Markan sources, arguing the passion account in particular looks like it was assembled from earlier independent units rather than composed fresh.
John Dominic Crossan went further and proposed a "Cross Gospel" embedded in the Gospel of Peter as a source Mark used, though most scholars don't buy it.
For the miracle stories specifically, Paul Achtemeier made an influential argument that Mark inherited two pre-existing collections of miracle stories, each following a similar pattern, and combined them into a single sequence.
What version of Mark do you recommend reading from your sources?
The NRSV is the standard scholarly choice; it's what most of the academics I cite use, and the New Oxford Annotated Bible (NRSV) gives you the notes that flag where the text is doing something interesting.