Let's look at the history of sediment deposition now. The limestone formations constituting the Sphinx and its surrounding enclosure are usually subdivided into three members (member, part of the formation), as shown in the diagram below.
The Great Sphinx - Member I.
This member is well exposed in the western parts of the enclosure walls and floor and also forms the lower part of the Sphinx sculpture, (now covered with repair blocks). It is composed mostly of un-stratified dark gray limestone containing fossils and coral fragments, probably deposited in a shallow marine reef environment. After uplift the top of Member I was weathered and eroded, as can be seen in the topography and structure of the top of the layer. This resulted in secondary high porosity and the top formed an unconformity for later sedimentation, visible in the western part of the enclosure wall where Member II is lapping onto Member I.
Refraction seismic acquired on the floor of the enclosure recorded notably higher interval velocities behind the Sphinx compared to the area in front of it. This conforms with the observation that the floor of the enclosure is carved well into the less weathered parts of Member I in the back of the Sphinx, while in the front the lower velocities, caused by the high porosity, were measured along or close to the top of the weathered unconformity of Member I.
The Great Sphinx - Member II.
This member constitutes the entire remaining enclosure walls and the body of the Sphinx up its neck. Member II is composed of stratified layers of very fine-grained light yellow/gray limestone some visible fossils, partly lapping on to Member I. It appears to have been deposited in a shallow marine, low energy, lagoonal environment, where the internal layering reflects variation of water depth, energy level and grain size during deposition.
The Great Sphinx - Member III.
This member is just represented by the head of the Sphinx. It appears to be a more homogeneous yellow/brown limestone in which layering is visible, but repair work using cement and the large distance to the head makes a detailed evaluation difficult. Since the head is small compared to the body, it has been suggested that it was re-sculpted at a much later date and hence appears less eroded. We can assume that this rock member was a topographical high just prior to carving of the Sphinx, but far back in time it was part of a uniform layer covering the entire Giza Plateau.
Further burial history of these members during early Tertiary time (cca 50-30 Ma) was not investigated, but a considerable additional sedimentary section must have been deposited on top of Member III on the Giza Plateau to account for the degree of lithification observed.
Source: GEO Expro