You can share any page on the site by using the social icons to the left of the search box (top right below the main menu). Direct shortcuts to share via Twitter, via Facebook, or via mail are provided. This button allows you to share on any of these, as well as other, platforms.
Note: If you share a restricted page (ex. only accessible by AAPG Members) users will be asked to login when they click the link. If they do not have the proper credentials they will then see an Access Denied message.