J1b is what we call nowadays the Iranic branch, because it is predominantly found among Iranic groups and nations who are said to had contact to them (Britain, Iberia, Germany).
J1b nowadays is almost non existent in the Caucasus. And the fact that this Haplogroup is so diverse and frequent on the Iranian Plateau (mostly the Western and Northern parts), I think is another indiciation for the possibility that those CHG people might have started off from the Iranian Platea, possibly in connection with some other Haplogroups (R1b or R1a?), while one wave went to Georgia another went directly through the Caucasus or Central Asia into the Steppes.
Many people speculate that the J1 in the Sarmatian samples was also possibly part of the J1b branch cause the article stated that the J1 in these Sarmatians doesn't belong to any branch of the modern Caucasus but resembles that of people from West Iran and West India.
This should interest the member Ricardo and he can probably also tell us more.