Karak Resources Project

Soil Morphology

The unique morphology of soils is the result of the interaction of the five factors of soil formation; these factors include climate, vegetation (biotic), geology, topography, and length of time the interactions have taken place. Climate, and especially rainfall, is particularly important to distinguish soils on the Karak Plateau. Two profiles illustrating this factor are shown in the photos below; profile 1 is about 3 km north of Mutah in a rainfall region of 500 mm/year while profile 2 east of Fajj has an annual rainfall of <100 mm.

With scant rainfall and subsequently little vegetative matter to incorporate into the soil matrix, profile 2 is very light brown while in a region of more abundant rainfall and vegetation, the soils have dark-colored surfaces. Erosion, of course, can result in the dark-colored surface being removed and the soil surface may have the color of the subsoil or geologic material.

The color of the surface soil is an important morphological characteristic to observe at archaeological sites. Another example is shown in profile 3 of a soil in area D at al-Mudaybi’. Note the dark-colored layer at the bottom of the excavation; this was the original surface during the early activity of the fort around 700 years B.C. The location of buried surfaces in archaeological sites is extremely useful in identifying former living surfaces and sources of artifacts.

Other soil horizons can also aid in the interpretation of archaeological sites. Subsoils (B horizons) such as argillic (clay-rich) can provide estimates on length of weathering time a soil has been exposed to the environment. Generally it requires about 4,000 years to develop a minimal argillic horizon in a humid environment and 10,000 years for a well-developed argillic with a thickness of one meter. Thus, the level of subsoil development can be extremely useful in developing site history. At al-Mudaybi’, the argillic horizon underlying the more recent sediments was probably developed toward the end of the Pleistocene and is probably 15,000 years in age. Other subsoils can also provide information on length of weathering time.

Soil morphology not only includes horizon identification and description but also describes other soil characteristics. These include soil texture (particle size distribution), structure of soil units (e.g. blocky, granular, prismatic), consistence, horizon boundary, and presence of other features. Some of the additional features described may include the presence of free carbonates, concretions, clay or organic coatings on peds, presence of coarse fragments, and mineralogy. All of these characteristics and features are combined to provide the information for the interpretation of archaeological sites.

The occurrence of fecal pellets was noted in several profiles at al-Mudaybi’. Horizons with nearly 70-90% fecal pellets occurred commonly at depths around 50 to 60 cm. This may be an indication of more rainfall during the deposition of sediment and subsequently an increase in population of the small mammals that inhabited the site.