Dating the sphinx construction
(3) Present on the body of the Sphinx, as well as on other Giza Plateau structures (and essentially forming an overlay on many precipitation-induced and wind-induced megascopic weathering features), are weathering features that are interpreted as resulting from relatively recent (within the last couple of centuries) efflorescing of dissolved and recrystallized minerals (such as halite) on the rock surfaces, which have subsequently flaked off and deteriorated the stone. (4) Weathering due to the dissolution and recrystallization of calcite and other minerals in the rocks is visible within various tombs and other chambers cut into the bedrock of the Giza Plateau.
In order to carve the body of the Sphinx, the ancient Egyptians dug a ditch or moat around it, such that the figure now sits in a hollow or depression, commonly referred to by such names as the "Sphinx ditch", the "Sphinx enclosure" or the "Sphinx quarry." The blocks of limestone removed from the Sphinx enclosure (in order to create the form of the body) were used to construct the so-called Sphinx Temple sifting directly due east of the Sphinx itself (in front of the paws of the sculpture) and the so-called Valley Temple located immediately south of the Sphinx Temple.The floor of the Sphinx enclosure is approximately sixty-five feet (twenty meters) above present-day mean sea level; this is probably near, or only a few meters above, the typical level of Nile flooding during various periods in ancient times.[ I have divided major geological and field evidence bearing on the age of the Great Sphinx into four main categories : (1) Weathering Patterns, (2) Two-Stage Construction of the Sphinx and Valley Temples, (3) Ancient Repair Campaigns to the Body of the Sphinx and (4) Seismic Surveys of the Sphinx Area.The rocks displaying this mode of weathering also often contain prominent vertical crevices and other solution features, as well as cross-cutting diffusion fronts. Many of the vertical and inclined solution features follow joints and faults in the bedrock.(2) Wind-induced weathering and erosional features are seen on structures that are attributed unambiguously to Old Kingdom times.
In this mode of weathering, the original profiles of the carved faces of tombs and other structures are still clearly visible (sometimes containing easily legible hieroglyphic inscriptions); but the softer, less competent layers of rock have been "picked out" by wind and sand abrasion, with the consequent formation of deeply eroded "wind-tunnel" features.
This wind-induced weathering is distinctly different in nature from the precipitation-induced weathering; it is well exemplified on various Old Kingdom tombs and structures south and west of the sphinx, which have been carved from the same sequence of limestones as the body of the great sculpture itself.