Pre-Great Blue Hole Formation:

• Pleistocene Epoch: Limestone island formation, likely with cave systems.
• Glacial and Postglacial Times (up to ~12.5 ka B.P.): Sea level is significantly lower (up to 120 m below modern). Collapse of a cave roof on the limestone island leads to the formation of a subaerial terrestrial sinkhole, or cenote, which will eventually become the Great Blue Hole (GBH).

Unit A: Cenote Phase (12.5 to 7.2 ka B.P.)

• 12.5 ka B.P.: Earliest deposition recorded in the GBH core composite BH8 begins. The environment is a partially inundated subaerial terrestrial sinkhole (cenote).
• Early Holocene: Sea level rises at a rate of 4.0 ± 0.4 m/ka. The water level in the cenote increases from a ...