Oracle does a special form of block split in this case. Only the new key goes into the new leaf block, and all the existing keys remain in the existing block. Technically it is correct to still call this a block split, but the terminology is a little confusing at this point.

Will an index based on Oracle sequence number ever result in "block split"? The documents I've read from Oracle suggest it will, however, a tuning book by Guy Harisson suggests otherwise.