Thank you for your reply. I cannot post a link to my website because I'm now only making tests and it works only locally on my PC.
As you said, I used Graphene Options >> General Options >> Footer Options >> "Copyright Text" to enter my text but actually, since I did not want to write a copyright text but some contact section, I replaced in the file footer.php, the word "Copyright" by the word "Contact". I also modified top-margin and min-height in the CSS file (from the "editor") to make the black footer a bit smaller. Then it looked fine, except the fact that some links had appeared as explained in my previous post. So I decided to come back to the default file footer.php to see if the error disappears but actually it is still there. It seems that I introduced a bug with my modifications and now, even if I come back to the default version, the bug remains.
Thanks for your help.