The reason you are "unable to get the accurate meaning" is that there is no "accurate" meaning—just a fuzzy blob of meanings from which an experienced reader like jwpat7 extracts what the author intended by disregarding much of what the author actually said.
There are three distinct ideas in the sentence:
- Any day in Syria is like every other day.
- Some days in Syria are notably worse than the others.
- The conflict in Syria is becoming worse.
Proposition 1 is contradicted by propositions 2 and 3; and confusion is exacerbated by:
- "Elegant variation" (the term is Fowler's): bloody, stark horror and gruesome lead you to look for subtle distinctions which are not intended—all are characterizations of the same violence.
- Inappropriate idiom: the author confuses mark in the sense of "a physical sign of distinction" with mark in the sense of "a grade awarded in a class"—it is the latter which is earned.
- Confusing metaphor: How does one either "earn a mark in" or attach a "mark" to a trajectory?
A little attention to coordinating his thoughts might have led the author to say something like this:
In Syria's increasingly gruesome conflict, one bloody day follows another, each bloodier than the one before, none distinct except when everyday bloodiness rises to stark horror.