I would say these log entries are coming from an external SNMP monitoring tool, I see 'Solarwinds time', do you have Solarwinds running somewhere ? 'Superadmin' is the built in admin account in Solarwinds...
You can actually generate these entries manually:
Router#send log 2 Message from 1(superadmin): ----- Start Of the day Thursday, March 7, 2019 0:09 ------- Mar 7 08:20:51.312
This will generate a syslog similar to the ones you see