Verificações de data válidas no Oracle

create function test_date(d varchar2) return varchar2
is
  v_date date;
begin
  select to_date(d,'yyyy-mon-dd hh24:mi:ss') into v_date from dual;
  return 'Valid';
  exception when others then return 'Invalid';
end;

select your_date_col, test_date(your_date_col)
from your_table;