[OS X Emacs] <enter> key in fortran mode

[Dany Page]

I just got a new mac in installed Aquamacs.
It does something weird in fortran mode:
when hitting the <enter> key it opens a new line
AND introduce some tabs, both in the new lines and in the previous line.

How do I get rid of this so that <enter> ONLY opens a new line and moves the cursor
at the beginning of this line ?

Thanx, Dany