I
Introduction: A Depositional Approach to the Study of Archaeological Excavations

Look at Figure I.1. It shows two photographs from archaeological sites in Greece that we have studied: Figure I.1a is a profile of Middle and Upper Palaeolithic layers from the site of Theopetra and Figure I.1b is from post Late Roman to recent deposits in the southern part of Ancient Corinth. Without knowing anything about the sites and without any geological training, an observer is immediately struck by the complexity of these stratigraphic sequences. How do we make sense of these deposits and how do we incorporate this information into our understanding of the significant archaeological findings from these two important localities? That is the subject of this book.

Figure I.1 Profile photographs from (a) Medieval Corinth and (b) Palaeolithic Theopetra, Greece (from Karkanas and Goldberg, 2017b). Note the complexity in both despite the vastly different ages. Scale in (a)?=?3?m and in (b)?=?1?m.

Theoretical Issues

It is probably the only consensus in archaeology that stratigraphy is 'the jugular vein of archaeological practice' (McAnany and Hodder, 2009a,b). Stratigraphy has many definitions and is defined here as the spatial and temporal arrangement of depositional units. Regardless of the wording, it provides the framework of reconstructing the history of a site. Stratigraphic units, layers, features, cuts, or strata - also called context or locus according to different archaeological schools of thought - are made of sediments that are the product of natural processes and anthropogenic activities, and are deposited on the surface of the earth. Archaeological deposits - those that contain artefacts and anthropogenic products - are thus by their very nature forcibly part of the archaeological record. In order to interpret the archaeology of a site correctly, it is a prerequisite to understand how stratigraphy is built and how the strata are formed. This book is about how we recognize the processes and activities that produce the deposits of a site and how these are organized in time and space to form a stratigraphic sequence.

Our personal understanding of stratigraphy and archaeological deposits is based on a conceptual model, which is described by a few fundamental propositions:

• A site is a three-dimensional arrangement of artefact-bearing deposits, therefore the fundamental unit of a site is the deposit, not the artefact or the pattern of the artefacts.
• The deposits have accumulated by natural or anthropogenic processes or a combination of these.
• The fabrics of the sediment are indicative of the different processes involved in their formation.
• Traditional artefacts (pottery, flints, etc.) are fabric elements within archaeological deposits.
• Architectural features (e.g. walls, mosaics, etc.) may have their own typology and internal stratigraphy but the relationship between construction phases and the surrounding artefacts is mediated by the enclosing deposits.
• Natural deposits in a site may have a cultural meaning (e.g. sediments trapped within aqueducts).
• All elements that form a deposit should be treated as having equal importance with the traditional items of the archaeological record (architecture, pottery, lithics, objects, etc.) in the study of a site.
• Time resolution is essentially determined in the field by how finely we can recognize the vertical and horizontal extent of individual stratigraphic units, which are the proxies for activities and processes. Similarly, such units should be recognized and recorded only during excavation and not after.

For most prehistoric archaeologists, the above principles are known and generally accepted because prehistory traditionally evolved in parallel with geology. But this is not always the case, particularly for those who investigate the archaeology of historical periods, which traditionally treats archaeology as history, with a reliance on texts. Excavating a site by utilizing the above principles is not straightforward, as it demands knowledge of natural and anthropogenic sedimentary processes. However, most archaeology programs in academia do not include basic sedimentology courses. The outcome is that most archaeologists acquire knowledge of stratigraphy through practice in the field and detailed observations of what they see. The question that underlies this reality is therefore can everyone 'see' all stratigraphic boundaries (or interfaces) in an excavation? Is it a matter of experience, knowledge, or talent?

In the following discussion we will show how stratigraphy is produced, and examine the fundamental elements and attributes that create it. At the same time, we will touch on common misconceptions about what constitutes a deposit, issues related to the nomenclature used, and the different approaches to investigating archaeological stratigraphy.

The Formation of Stratigraphy

Human earthen structures and anthropogenic sediments in general (floors, occupational surfaces, middens, fills, pits, mounds, etc.) have a materiality that, at an initial level, can be described and understood by using concepts and methods derived from the natural sciences, such as geology; in fact, no new terminology is required. The deposits of the site consist of materials that are overwhelmingly particles (clasts) of minerals and rocks. It is puzzling to assume that a unit can be described without referring to the fundamental attributes of sediments, mainly grain-size distribution, sorting, roundness, orientation, grading, colour, and ultimately the fabric produced by the organization of the attributes. All these attributes are not neutral and meaningless, or simply geometric features. The mineralogical content and chemistry are also fundamental properties of an archaeological deposit as they provide information about its source and post-depositional alteration.

Knowledge of the fundamental properties of human earthen constructions is a prerequisite for interpreting this aspect of site stratigraphy. On one hand, these properties serve to convey descriptive criteria to interested researchers, but more importantly they transmit information of the processes that produced them. In the realm of natural sedimentary basins, these descriptive terms imply certain depositional environments. For example, rounding is caused by abrasion during transport (e.g. streams) or by reworking by wave action, for example; transport does not fundamentally reduce the size but does selectively sort material (Folk, 1974). Each transporting medium produces certain types of sediments because the dynamics of transport and deposition are different.

In the realm of a site, human processes do not produce such attributes, which even in earthen constructions are mostly inherited from the original material at the natural source, but now organized in a different way through a 'human filter'. Anthropogenic activities admittedly produce new organizations, but the essential building blocks are the same. Human activities are no different in representing the elemental dynamics of transporting and depositing materials through actions such as trampling, digging, dumping, kneading and pugging, sweeping, brushing, discarding, and placing. Therefore, rounding can be produced by continuous trampling and scuffing, and brushing and sweeping may bring about sorting and lamination. Similarly, dumping may cause grading within the deposits, and pugging will produce orientation, whereas discarding may lead to clustering of grains (see Chapter 3). Some activities do produce new materials, such as burning (ashes) and other pyrotechnological activities (ceramics). Nevertheless, their accumulation and final deposition on the earth's surface is the product of the actions described above.

All the aforementioned attributes are the building blocks of every description of what is called a lithostratigraphic unit. These units are bounded by contacts, and contacts are the product of changes in the attributes, whether they be differences in composition or the way that they are organized. Sometimes, the contact itself records a change in the attributes, although they are rarely discerned as such in the field (further discussed in Chapter 4). However, all these attributes cannot be identified without knowing what to look for, and what they might mean. As is so often the case, without understanding how things can form - in this case, units - it is difficult and challenging to discern and describe stratigraphic entities. In addition, all material and earth science studies in an archaeological site use descriptions derived from physical sciences, mainly mineralogy, petrology, sedimentology, and soil science (pedology). During the last two decades geoarchaeological studies have made significant inroads toward archaeological interpretation of urban sites by providing microstratigraphic histories within rooms, and data on the life of buildings and the use of space (e.g. Matthews, 2005; Matthews et al., 1996; Shahack-Gross et al., 2005; Macphail and Crowther, 2007; Macphail et al., 2007; Milek and Roberts, 2013; Karkanas and van de Moortel, 2014). It will be confusing to have a separate and different system of description for archaeological deposits, and another one for geological ones.

Bear in mind that observation is not...