SQL & PL/SQL

I am trying to convert CDT (Central Daylight Time) into a timestamp, then into a date. I can't seem to get Oracle to recognize CDT, even though the documentation seems to reference it as a valid format:

http://download.oracle.com/docs/cd/B14117_01/server.101/b10759/functions082.htm#SQLRF00671

Seems to me like it should be recognized as a synonym to CST (Central Standard Time). Something that I am missing?

SQL> select to_timestamp_tz('Fri Apr 16 08:50:34 CDT 2010','Dy Mon DD HH24:MI:SS TZR YYYY')
  2  from dual;
select to_timestamp_tz('Fri Apr 16 08:50:34 CDT 2010','Dy Mon DD HH24:MI:SS TZR YYYY')
                       *
ERROR at line 1:
ORA-01882: timezone region  not found


SQL> select to_timestamp_tz('Fri Apr 16 08:50:34 CST 2010','Dy Mon DD HH24:MI:SS TZR YYYY')
  2  from dual;

TO_TIMESTAMP_TZ('FRIAPR1608:50:34CST2010','DYMONDDHH24:MI:SSTZRYYYY')
---------------------------------------------------------------------------
16-APR-10 08.50.34.000000000 AM CST

Oracle Version 10.1.0.4
--=Chuck