On the Canonization of the Gemara

The canonization of the Gemara must have happened in Palestine in the 300’s. Have a look at the English summary at the end of Rory Boid's article “LÁntiquité des Racines du Karaïsme”, where he mentions the same phenomenon in Babylonia later on. The Karaites were not innovators, but rather a group of theologians that rejected the new heresy. I think you have indirectly shown why the Palestinian Talmud was finished before the Babylonian. The new dogma originated in Palestine and took time to take hold in Babylonia. Once the Gemara, whether Palestinian or Babylonian, was canonised and made the HIGHEST authority, it only needed some final editing, but further work on it was by definition unnecessary or even undesirable. It was the turn of the Savora’im to tidy up and then the Ge’onim to expound the new sacred text and ultimate authority.