First check that you have "Select Track Envelopes with Clips" selected. That is set in the TV menu--->Options.
Select all tracks and the time range you wish to delete.
Select "Delete special" from the Main menu--->Edit. There is an option there to delete track/buss automation along with Tempo changes Mete/key changes etc as well as "Delete hole"
If any of those are unselectable it may mean there aren't any in the selection
Press okay
That should sort it out for you