Sedimentary processes involved in mud brick degradation in temperate environments: A micromorphological approach in an ethnoarchaeological context in northern Greece

Sun dried mud bricks are a common building material across the globe, found in many archaeological sites in the Old World since ca. 11,000 years ago. This material is known to disintegrate due to exposure to the elements, mostly affected by rain. Yet, the geomorphic and sedimentological characteristics of this disintegration process have never been studied in detail until recently. Here we report on mud brick degradation processes observed in an abandoned mud brick village in northern Greece. We demonstrate that mud bricks have unique micromorphological characteristics that differentiate them from natural soils. Upon degradation some of these characteristics are lost (e.g., planar voids after fibrous vegetal temper). Rain initiates brick degradation at the upper parts of walls where from brick material is washed down walls and deposited at their feet, forming a conical talus. The talus deposits show micromorphological features indicative of a variety of flows, including wet and dry grain flows, debris, hyperconcentrated and water flows. These flows seem to operate simultaneously across small distances. These talus deposits are different micromorphologically from natural soils thus their characteristics can be used to identify degraded mud brick material in archaeological sites. This, in turn, may help identify the location of long degraded mud brick walls (in the absence of stone foundations) and identify the relationship between house floors and degraded infill that accumulated on floors following wall degradation. A comparison between the current observations with a previous study we conducted in an abandoned mud brick house in arid southern Israel, illustrates the generality of these low energy slope processes in mud brick degradation, which emphasizes the worldwide applicability of the processes identified in this study.