cubanpete that is possible with a bit of configuration however you would need to have Plus Package extension for this.
So, first, you would need to restrict access to all pages and media and allows only those that are created by users. You can define the default access for all Pages and Media by checking EDIT BY OTHERS, LIST TO OTHERS, etc.
The next step is to define specific categories for both pages and media that you, as an administrator, will use to create/upload content to. This way you can overwrite the default access to all the pages and media that belong to those categories by unchecking EDIT BY OTHERS, LIST TO OTHERS, etc.
Note! With Plus Package extension you have the ability to group your pages and media assets with categories by enabling Page Categories and Media Categories options.