Yeah that just looks like flat-out world corruption there. If you have a backup then pull that chunk from your backup. Otherwise MCEdit ‘might’ be able to do it (although honestly I would expect it to not handle this, maybe crash too or just corrupt it). Otherwise you can start binary editing things but that’s a pain and significantly “not easy”. ^.^;
I’d say just take each region from backup and restore it until you find the one that caused it.
And if you don’t have a backup, then your only option then is to delete the chunk and/or region. Remember to always back up, make it part of your launch script or use the AromaBackup mod or whatever it was to automate it!