HYPERTHERMAL REVEALED IN THE GREAT SPHINX OF EGYPT

Hyperthermals are transient global warming events produced by the release of huge amounts of CO2 to the atmosphere. First discovered in 1991, a hyperthermal may have been staring us in the face for the past 4,500 years. Carved in situ, like a road cut, I conclude that the limestone of the Sphinx head is likely an exposure of the Middle Eocene Climatic Optimum (MECO) hyperthermal. The MECO is a ~500-kyr long period of global warming ~40 million years ago. The presence of a hyperthermal was identified by what appears to be a carbonate dissolution horizon exposed at the Sphinx chin. Evidence for the MECO itself comes from the occurrence of Nummulites gizehensis within the Sphinx body, indicating Shallow Benthic Zones (SBZ) 14, 15, and 16. The presence of Nummulites striatus in the overlying strata indicates SBZ 18 and 19. Stratigraphically, this brackets deposition of the Sphinx head to the MECO during SBZ 17, making it Bartonian in age. Previously the entire Sphinx sequence had been considered Lutetian in age.

The nummulitic limestone of the Sphinx body is overlain by a marly limestone exposed at the neck, which abruptly transitions to a rather pure erosion resistant limestone at the chin. The absence of N. gizehensis and other fossils within the limestone of the Sphinx neck and head may be indicative of an extinction event driven by ocean acidification associated with the CO2 release. Subsequently uplifted and exposed, the erosion resistant limestone became the caprock of the Giza Plateau. The ancient Egyptians quarried this erosion resistant limestone to construct the Great Pyramid of Khufu and to carve the head portion of the Sphinx. If not for dramatic climate change 40 million years ago the Giza pyramids and the Great Sphinx would not exist.