You can only get shadowbanned for breaking the big rules of reddit, and only a Reddit Staff Admin can perform a ban, not a Mod. Here are the reddit-wide rules that you can be shadowbanned for: http://www.reddit.com/rules
Also if you have never read the reddiquette for the site, these are all the expected behaviors of redditors. They will not necessarily get you punished for not following them, but it's a good guide nonetheless.
If you are concerned about your account and want more information as to why you were shadowbanned, you can contact the Reddit Admins here: http://www.reddit.com/contact
Specifically this link will send you to the form to contact the admins directly. If you think the shadowban was a mistake this would probably be the best course of action.
