C412 Coma
The Primordial God Tablet was a Paleogene, a sarcophagus that buried the Heavenly Dao. Most of the energy contained within was from the Heavenly Dao.
It was just that later on, when he absorbed countless Martial Saint, the power of the Martial God evolved into an unknown power. Of course, this unknown power was still hidden within the Primordial God Tablet