[tlug] cron+pam syslogs

[Botond Botyanszki <botond@example.com>]

I have been googling around and looked into various docs but haven't yet
found a solution.
I have some cron jobs installed into /etc/cron.d. Some of these run pretty
frequently, and the following syslogs by pam are getting annoying. Is
there a way to disable these? Of course I only want to disable the cron
related ones. 

May 18 23:00:01 localhost cron(pam_unix)[1071]: session opened for user
mail by (uid=0)
May 18 23:00:01 localhost cron(pam_unix)[1072]: session opened for user
root by (uid=0)

TIA.