vivartakalpa (P. vvivaṭṭakappa; T. chags pa'i bskal pa ཆགས་པའི་བསྐལ་པ་; C. chengjie 成劫) is translated as "eon of formation," "eon of creation," etc. It is one of the four periods in the cycle of creation and destruction of a world system, corresponding to the four divisions a great eon (mahākalpa).
Science and Philosophy in the Indian Buddhist Classics (Vol 1) states:
- The eon of formation is posited from the initial development of the wind maṇḍala as the lower foundation up to the birth of the first sentient being in the hells. The formation of external worlds takes one intermediate eon, and the evolution of their inhabitants takes nineteen intermediate eons. Thus it lasts for twenty intermediate eons.