PIPING AND SITE FORMATION AT DMANISI, A 1.85-1.76 MA HOMININ SITE IN THE GEORGIAN CAUCASUS

Piping is an important mechanism in the development of gully systems that occurs in a broad range of settings and in diverse host sediments. This “pseudokarst” process results in construction and enlargement of subsurface tunnels by corrosion. Control factors include seasonal climates and proper slope configuration enabling an outlet. Pipes form in texturally variable sediments and soft sedimentary rocks. Typically pipes collapse within decades, and evolve into gullies. At the Dmanisi site piping occurred during a brief phase in the middle of the site sequence, corresponding with the accumulation and burial of thousands of mammal bones and the remains of hominin fossils including five skulls of earliest Homo erectus. Documented piping stages include: initiation and growth (length and diameter), breaching from the surface, partial collapse and obstruction, and full collapse followed by gullying. These processes were all arrested by a major series of ashfalls that filled pipes and gullies. Pipes influenced site formation processes indirectly by creating dens for carnivores, whose prey remains may have attracted human scavengers. Then pipes and filled gullies entrained dense accumulations of bones and artifacts. Rapid burial resulted in superb bone preservation. Dense accumulation of bones at the ca. 1 Ma open air paleontological site of Akhalkalaki west of Dmanisi are probably the result of carnivore denning in pipes. Thus, pipes may be important factors in site formation in other settings, and may help explain bone concentrations in otherwise unlikely geomorphic contexts.