The Micromorphological Record of Daily Life and Exceptional Situations in Archaeological Sequences: Tell Dj'adé (Syria), Song Terus Cave (Java, Indonesia) and Moche (Peru).
Marie-Agnes Courty, CNRS, Centre Européen de Recherches Préhistoriques. Avenue Léon-Jean Grégory, TAUTAVEL, 66720, France
Understanding effects of climate changes and environmental crisis on past societal dynamics is a major concern for geosciences. Their abrupt initiation and their short duration have incited to investigate their record in high resolution marine, lacustrine or loessic sequences. Discontinuity of archaeological sequences, their weak chronologies and their local particularities explain that tentative correlation between exceptional situations and cultural changes is often controversial. We have proposed to investigate exceptional situations in archaeological sites with the help of micromorphological study to establishing direct linkages with minimised chronological bias. Finely stratified archaeological sequences that recorded the daily life of past humans offer the best potential for high resolution palaeoenvironmental studies. We have elaborated a three-step analytical procedure based on the integration of the field and micromorphological perception: (1) exhaustive inventory of pedo-sedimentary conditions based on sampling across the cultural deposits; (2) identification of distinctive pedo-sedimentary facies that express anomalous conditions; (3) spatial control of their extent for recognising an exceptional situation and for determining its linkage to societal dynamics. Three examples illustrate this innovative approach: (1) Dja'dé, a Pre-Ceramic Neolithic village at (11000-8000 yr BP) on the Euphrates (Syria); (2) Song Terus cave (Holocene to mid Pleistocene) in the calcareous Punung region (Java Island, Indonesia); (3) the monumental town of Moche (1950-1300 yr BP) settled on late Pleistocene sand dunes bordering the Moche river (Peru). At Dja'de, the PPNB sequence displays a regular cyclicity of finely micro-stratified pedo-sedimentary facies that expresses seasonality of occupation within broadly stable environmental conditions. Incorporation within the finely stratified living floors of recystallized gypsum desegregated by trampling, dry desegregation of the earth bricks by insect burrowing, and fine mixing of calcitic aeolian dust attest for maintenance of dry conditions. The final phase of occupation at ca ~8000 yr BP shows a major change of the construction styles and activities that mark the abrupt termination of the PPNB period. The cultural change coincides with a sudden increase of bioturbation, a rainfall increase responsible for earth-brick deterioration, dissolution of the gypsic features and weak depletion of the calcium carbonate. This indicates the rapid establishment of wet and cool conditions that would represent the regional expression of the 8.2 kyr BP abrupt event known as a global cooling. At Song Terus the Keplek sequence formed during the early to mid-Holocene is characterized by weak layering with patchy volcanic lenses, a massive to open excremental assemblage, a well developed channel microstructure and carbonate depletion. This indicates slow sedimentation resulting from gravity fall of materials regularly eroded from subsurface horizons synchronous to intense bioturbation. In contrast, the underlying layers (late Pleistocene) are characterized by a regular fine cyclicity: (1) clay loam with an open excremental fabric, and discontinuous calcitic bands; (2) fine-textured tephra; (3) massive clay loam with strongly cemented calcitic bands. This is interpreted as three successive phases: (1) Low energy runoff reworking subsurface horizons; (2) high energy runoff reworking freshly deposited tephra; (3) high energy mud flow due to sudden erosion of the soil cover contemporaneous to intense dripping within the cave of carbonate-saturated water. Episodes of volcanic activity (phase 2) are suggested to have induced destruction of the vegetation and sudden soil erosion of the soils (phase 3), later followed by regeneration of the soil cover (Phase 1). Scarcity of human traces during this recurrent instability might express maintenance of inhospitable conditions. At the site of Moche, the lower Moche II phase (ca~2000-1800 yr BP) displays a regular microstratification of well maintained living floors. Evidence for seasonal recrystallization of gypsum, carbonate depletion, and microbial activity attest for high humidity and stable environmental conditions. From Moche III phase a sudden invasion by sand dunes indicates a severe destabilisation of the surrounding soil landscapes by violent winds that could correspond to a mega El Niño event. These drastic conditions were followed by a series of exceptional episodes marked by a similar pedo-sedimentary micro-facies. It consists of a few cm-thick massive unit showing the interstratification of densely packed aggregates derived from the earth-bricks with coarse textural features, and aeolian sands. These micromorphological characteristics help to recognize a sudden deterioration of the monumental construction by torrential mudflow followed by high energy winds. These conditions correspond to a series of exceptional El Niño events. Continuity of occupation from Moche III to V shows that the Moche population had the technological know-how for adapting to the recurrent mega El Niño events.