Geological setting

The geological setting at hominid localities is not only an important source of information about environmental settings and changes through time at a specific locality or an area but is also an indicator of the probability of finding fossilized bones and is therefore an essential aspect influencing survey strategies. Moreover, it is an important aspect of the transfer of knowledge relevant to a broad understanding of human evolution as a Pan-African story.

Sedimentary formations with a high potential for fossilization are the required geological setting. These consist of deposits that are products of weathering and transport, erosion, and deposition. Sediments are a mixture of different minerals and organic materials deposited on the earth's surface, or in caves, in interaction with the atmosphere, hydrosphere, and biosphere. Common examples are clays, silts, sands, gravels, and breccias. Due to subsidence of some hundred meters, up to a few kilometers, deposits are typically transformed into sedimentary rock, like sandstone, claystone, or limestone.

Accumulation areas of sediments are divided into marine and continental depositional space.

Even if some of the fossil sites, like Saldanha or Klasies River Mouth in South Africa, are located closely to the ocean shoreline, the most important hominid fossil sites are located in continental deposits. Potential continental bone accumulation localities are fissures, caves, swamps, tar pits, river channels, flood plains, lagoons, and lakes. Such depositional areas can be described as geomor-phological units characterized by climate, size, and shape of a sedimentary basin. Geometry and composition of sediments, and the relationship between units, provides information about the milieu of deposition. Physical, chemical, and biological parameters (O Table 11.1) inform us about the depositional environment and climatic conditions. These parameters have to be recorded during fieldwork. The sum of all primary characteristics of a sedimentary unit defines the sedimentary facies (Reineck and Singh 1980). The analysis of the facies permits us to understand the sedimentary factors responsible for the appearance of the deposit and the fossils.

Medium, current, wave intensity and velocity, as well as water depth, are relevant physical factors (O Table 11.2); these are the important hydrodynamic conditions for the transport of animal remains. Mineral and groundwater composition, including climate, are understood to be the chemical factors of sedimentation

O Table 11.1

Sedimentary parameters of depositional environments

O Table 11.1

Sedimentary parameters of depositional environments

Physical

Surface features (ripple marks, load casts, shrinking cracks etc.)

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