Virtual micromorphology: The application of micro-CT scanning for the identification of termite mounds in archaeological sediments

X-ray micro-computed tomography (micro-CT) scans were conducted on impregnated sediment blocks from the early Holocene rockshelter site of Lapa do Santo, East-Central Brazil. The analysis was designed to investigate the presence of termite mound fragments in the archaeological sediments and test the value of complementary techniques in micromorphological studies. Soil feeding termites have been common in the tropical soils of Central Brazil since the Paleogene/Neogene and exist in high concentrations in the surroundings of Lapa do Santo. The micro-CT scans revealed a distinctive spongy microstructure inside some of the clay aggregates in the sediments that are not visible in thin section, matching the spongy microstructure inside termite mound fragments. The microstructure consists of a mix of clay and organic material (feces, saliva and other body fluids) produced by termites to cement the mounds' matrix. The cements are undistinguishable from the matrix under the microscope, but clearly visible in the micro-CT scans given the low attenuation coefficient of organo-mineral matter. The termite mound fragments appear dispersed within the ashy matrix (made of intact and reworked combustion features), suggesting their possible use in earth ovens. The combination of combustion features and reworked earth ovens attests to the complex input of anthropogenic sediments in the formation of Lapa do Santo. This study demonstrates that micro-CT can potentially disclose materials not visible in thin section and can be utilized as a complementary technique to micromorphology.