Random reading of an unformatted file?

Hi All,

I have a large file of geographic information created thus:

open(1,file=trim(shapefile),status='replace',form='unformatted',iostat=ios, &
   err=1000,recl=128,recordtype='stream')

I read the whole file and display its information on screen. The user clicks somewhere on screen and from that I know I have to re-sample a small part of the file starting at some byte N. Is there some Fortran way I can get at that byte number immediately without having to start from the beginning of the file?

Many thanks

Mike