Black screen after login and frozen loading wheel
the part you want to pay attention to is the 


  CoreStorageGroup::completeIORequest - error 0xe000002ca detected for
  LVG "Macintosh HD" (...) disk2: I/O error.


I Googled that error code and found a few reports online of people with that issue.  It looks to me like your hard-drive is failing (but that may not be true - it's just a guess).. any time I see the "I/O error", I typically assume the data is in jeopardy even if there's a chance it might not be.  You want to be as safe as possible.  I hope you have backups .. if you don't, you'll want to treat this situation as though you could lose all your data.

Hire a professional to make backups of your hard-drive and advise you on your best next steps.  It never hurts to talk to Apple, if it's under warranty they may be able to help.  If not, you'll want to decide if you want to get a new hard-drive put in (depending on the year your iMac was manufactured, it could be very easy or very difficult) or just buy a new iMac.