The Geological Proof, part 2.
Geological Knowledge of the Pyramid Plateau, hard limestone and soft limestone
The Figure displays a simplified cross-section of the Giza Pyramids Plateau. The Giza Plateau is an outcrop of the Middle Eocene Mokkatam Formation. A second outcrop of the Upper Eocene Maadi Formation borders the Pyramids Plateau on the South-South West. A large sandy wadi separates the Mokkatam Formation from the Maadi Formation, created by the South-East dip of the Mokkatam Formation. The North side of the wadi, or the southern line of the Mokkatam Formation outcrop, and the South side of the wadi, or the northern line of the Maadi Formation outcrop, where both Formations dip into the wadi, were extensively quarried during the erection of the Giza pyramids.
Simplified NNW-SSE cross-section of the Giza Plateau. The soft-marly nummulite limestone bed (in yellow) that was extensively quarried (Wadi quarries, Sphinx trench) is sandwiched between two hard-gray nummulite limestone beds (pyramids basement and Sphinx head).
According to geologist Thomas Aigner and egyptologist Mark Lehner, the original ground surface of the Mokkatam Formation that constitutes the basement of the pyramids, is made of a very hard and massive limestone bank of the nummulite type (gray limestone banks on the Figure). On the opposite, the outcrop that dips into the wadi, where the quarries are located and also the trench around the Sphinx and the Sphinx body, consist of softer thickly bedded marly nummulite limestone layers with a relative high amount of clay (yellow bank in the Figure). Concurring to the traditional carving theory, Mark Lehner states “… the builders took advantage of the thickly bedded softer limestones of the south part of the Mokkatam Formation, while founding the pyramids on the hard nummulite bank to the north.”
Lehner postulates that the builders did not use the nearby hard limestone but favored the softer material.
Kheops quarry as designated by geologists. The quarry face shows the soft limestone layer that cannot be used for carving stones.
Disaggregation of soft limestone with water
In October 1991, during the shooting of the TV production “This Old Pyramid” by NOVA, aired on the American PBS network on September 1992, Prof. Davidovits had the opportunity to present this unique property of the Giza limestone. A chunk of limestone taken in the quarry was very easily disaggregated within 24 hours, leaving the nummulites and the clay gently separated from each other, whereas a chunk of the hard Mokkatam limestone did not disintegrate at all.
Joseph Davidovits and Mark Lehner in the TV film “This Old Pyramid”, WGBH, Boston, 1992 (NOVA, PBS)
After 24 hour soaking in a plastic bag with water, the limestone chunk separated into clay and mummulites. In the presence of an excess of water, the heavier clay settles down leaving the nummulites separated from each other. “This Old Pyramid”, WGBH, Boston, 1992 (NOVA, PBS)
This topic has been extensively outlined and discussed in the Session F: Applications to Archaeology of Geopolymer Conferences and published; see details in Archaeology applications in geopolymer proceedings.
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