Late 2012 iMac graphics issues with Mavricks

Everr since I updated to Mavricks I've been experiencing graphics issues.

When waking from sleep or screen saver, the area outside the active window is black, including the app bar at the bottom. Moving my mouse around those areas sometimes will display my background from black but not always.

Also, when playing CIV 5 on occasion, the computer will restart itself and take me back to the log-in window