More redo generated duing index rebuild with nologging

I see lots of redo file generated during the index rebuild process. All the indexes rebuilt are with "nologging".

Script:

ALTER INDEX VOY.PK_REPORT_DETAILS
   REBUILD
   NOCOMPRESS
   NOPARALLEL
   TABLESPACE IXREP01
   STORAGE (
          INITIAL   1000M
          NEXT   100M
          PCTINCREASE 0
  ) nologging; 

When I look at the contents of the logs using logminer utility, I see the contents as "Unsupported" as mentioned below:

SQL> select username, sql_redo,sql_undo from v$logmnr_contents;

set transaction read write;

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

commit;

set transaction read write;

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

Unsupported
Unsupported

commit;