PARQUET-1387 added int64 timestamps with nanosecond precision.
As 64 bits are not enough to represent the whole 1400..9999 range of Impala timestamps, this new new type works with a limited range:
1677-09-21 00:12:43.145224192 .. 2262-04-11 23:47:16.854775807 UTC
The benefit of the reduced range is that no validation is necessary during scanning, as every possible 64 bit value represents a valid timestamp in Impala. This may mean that this has the potential be the fastest way to store timestamps in Impala + Parquet.
Another way NANO differs from MICRO and MILLI is that NANO can be only described with new logical types in Parquet, it has no converted type equivalent.