Gen 12:1 -4a is J

This assignment can be made on the basis of linguistic criteria including the use of the phrases Cursed those who curse you and blessed those who bless you (12:3) , v'nivr'chu v'chu (12:3), adamah (12:3).

Also, this section uses the divine name of J (12:1)

The separation of this set of verses from the immediately preceding and following verses is based on factual contradictions.