Someone has to dig through this, here are some references to date Sphinx to 10,000BC
BRADLEY, Raymond S. "Paleoclimatology (International Geophysics Series)." Academic Press Ltd, 1999. Order Paleoclimatology from amazon.com. -- Covers paleoclimatic reconstruction, climate and climatic variation, dating methods, ice cores, marine sediments and corals, non-marine geological and biological evidence, pollen analysis, dendroclimatology, documentary data, and paleoclimate models. CHOWDHURY, A.N.; Punuru, A.R.; and Gauri, K.L. "Weathering of Limestone Beds at the Great Sphinx." ENVIRONMENTAL GEOLOGY AND WATER SCIENCE. Vol. 15, No. 3 (1990), pp. 217-225.
GRIEVE, et al. "The Record of Terrestrial Impact Cratering," GSA TODAY. Vol. 5 No. 10 (1995), pp. 194-196 [Lists about 150 impact sites including the Chixalub crater].
GUARI, K.L.; Chowdhury, A.N.; Kulshreshtha, N.P.; and Punuru, A.R. "Geologic Features and Durability of Limestones at the Sphinx." ENVIRONMENTAL GEOLOGY AND WATER SCIENCE. Vol. 16, No. 1 (1990), pp. 57-62.
GUARI, K.L.; Sinai, J.J.; and Bandyopadhyay, J.K. "Geologic Weathering and its Implications on the Age of the Sphinx." GEOARCHAEOLOGY. Vol. 10, No. 2 (1995), pp. 119-133.
HARRELL, J.A. "The Sphinx Controversy: Another Look at the Geologic Evidence." KMT. Vol. 5 (1994), pp. 70-74.
HILDEBRAND, et al. SCIENCE. Vol. 248 (1990), pp. 843-847 [Chixalub crater].
HILDEBRAND, et al. GEOLOGY. Vol. 19 (1991), pp. 867-871 [Chixalub crater].
IMBRIE, John and Imbrie, Katherine P. "Ice Ages: Solving the Mystery." Harvard University Press, 1986. Order Ice Ages from amazon.com. -- Discusses Milankovich cycles. Provides an excellent overview of theorized mechanics of Earth's ice ages.
KENNETT, J.P.; Hodell, D.A. "Stability or Instability of Antarctic Ice Sheets during Warm Climates of the Pliocene." GSA TODAY. Vol. 5, No. 1 (1995), pp. 1, 10-13, 22.
MEYEROFF, et al. GEOLOGY. Vol. 22, No. 1 (1994), pp. 3-4 [Chixalub crater].
POWELL, James Lawrence. "Night Comes to the Cretaceous: Dinosaur Extinction and the Transformation of Modern Geology." W.H. Freeman and Co., 1998. Order Night Comes to the Cretaceous from amazon.com. -- Was the extinction of the dinosaurs caused by the impact on Earth of an asteroid the size of Mount Everest? Powell describes the whole debate in a highly-readable text.
PUNURU, A.R.; Chowdhury, A.N.; Kulshreshtha, N.P.; and Gauri, K.L. "Control of Porosity on Durability of Limestones at the Great Sphinx, Egypt." ENVIRONMENTAL GEOLOGY AND WATER SCIENCE. Vol. 15, No. 3 (1990), pp. 225-232.
RUDDIMAN, W.F. and Wright, H.E. "North America and Adjacent Atlantic Ocean during the Last Deglaciation," GEOLOGY OF NORTH AMERICA. Vol. K3 (1987), pp. 509.
SAID, Rushdie, editor. "The Geology of Egypt." Rotterdam: Balkema Publishers, 1989. Order Geology of Egypt from amazon.com. -- The holocene climate history of Egypt (pp. 487-507).
SCHOCH, R.M.; West, J.A. "Redating the Great Sphinx of Giza, Egypt," GEOLOGICAL SOCIETY OF AMERICA ANNUAL MEETING, San Diego, CA, 1991. -- Abstracts with programs.
SCHOCH, Robert M. and McNally, Robert Aquinas. "Voices of the Rocks: A Scientist Looks at Catastrophes and Ancient Civilizations." NY: Crown Publishers, 1999. Order Voices of the Rocks from amazon.com. -- For those who follow the work of Robert Schoch, geologist who worked with John Anthony West on "The Mystery of the Sphinx" video.
STANLEY, Steven M. "Children of the Ice Age: How a Global Catastrophe Allowed Humans to Evolve." W.H. Freeman and Co., 1998. Order Children of the Ice Age from amazon.com. -- Intriguing investigation into the effect on early humankind of the movement of land masses millions of years ago between the Atlantic and Pacific Oceans that triggered an ice age that fragmented African forests.
VOGT, Peter R.; Tucholke, Brian E., editors. "The Western North Atlantic Region with Plates (The Geology of North America, Vol. M)." Geological Society of America, 1986. Order The Western North Atlantic Region from amazon.com. -- See pp. 720.
WICANDER, Reed and Monroe, James S. "Historical Geology." International Thomson Publishing, 1993. Order Historical Geology from amazon.com.
Once the soft limestone was exposed, the rain and atmosphere began to erode it. R.M. Schoch, a Boston University geologist, studying the weathering patterns on the Sphinx, found signs of water action up to 8 feet deep in the front and sides of the colossal statue. Other structures in the vicinity, made from the same limestone, supposedly at the same time (about 2500 BC), do not display such deep erosion. Based upon the depth of the weathering, Schoch dates the Sphinx at 5000-7000 BC--- much older than the mainstream date of 2500 BC. In fact, Schoch opines that work on the Sphinx could have begun as early as 10,000 BC.