Do still waters run deep? Formation processes of natural and anthropogenic deposits in the Neolithic wetland site Zug-Riedmatt (Switzerland)

摘要

Micromorphological analysis is used to improve our understanding of wetland site taphonomy and stratigraphy. Twelve profile columns from the Neolithic lakeshore site of Zug-Riedmatt are macroscopically described here, microscopic analyses are applied to sediment facies, defining 14 sedimentary units (U): The natural basal sediment (U1) is carbonate-rich, U2 a transition phase to the anthropogenic units U3 to U12. Uppermost are the natural carbonate-rich U13 and U14. The creation of a micromorphological database and the application of 27 defined indices allow a better understanding of the natural, anthropogenic and taphonomic processes taking place at the site. Natural sediment input originated from Lake Zug, the nearby river Lorze with its delta, and a local marshy waterbody. Organic rich accumulations and calcitic ash played a major role in pH changes, leading to carbonate and silica dissolution, alongside bone alteration. Signs of degradation processes under aerobic and anaerobic conditions within a single layer points to complex, multiphase processes under changing water levels, a milieu belonging to both land and water, an amphibious environment. Finally, good layer preservation seemingly correlates to low aquatic reworking in a stable depositional context linked to the marshy area.