When do you consider this split to have occured?
Maybe during the Last Glacial Maximum(LGM), 18-23,000 years ago. There is one skeleton found near Lake Baikal that some argue is Mongoloid (21,000 YO), but, most disagree.
DNA tests show that the Northern Mongoloids (peculiar eye cover, flat-face, lighter skinned) descended from the Southern Mongoloid. The Southern Mongoloids do not have some of the traits of the Northern Mongoloids, they seem to be cold adapted.