Parallelism: sequence of actions vs. cause and effect

Dear GMAT expert,

I am very confused as to how I can differentiate between when something is a cause and effect (no parallelism -->normally use , -ing) and a sequence of actions (use parallelism).

For example:

Scientists have found signs that moving water changed the chemical makeup of the surface of Mars in recent eras, therefore concluding that its crust is harboring up to three times as much water than was previously thought.

NOTE: (in the question the underlined part goes form 'therefore' until 'than' (incl. than).

So, here the structure was changed to parallel because the conclusion they took was a sequence of actions, but is it also not an effect (cause = found water moving) so why is it not: , -ing (not parallel). This is only an example i just want to know how i differentiate between sequences of actions and cause & effect.

Thank you!