5.3 Interpretation of Stratigraphic Sequences

Stratigraphy is key to understanding how archaeological sites formed over time. It helps us piece together the order of events and figure out how old things are. By studying layers of soil and artifacts, archaeologists can uncover the story of a site.

Creating diagrams called Harris matrices helps visualize complex relationships between layers. This, combined with dating methods, allows archaeologists to build a timeline of human activity at a site. However, disturbances and incomplete data can make interpretation tricky.

Principles and Interpretation of Stratigraphy

Interpretation of stratigraphic sequences

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• Law of Superposition states that in undisturbed sequences, younger layers are deposited above older layers, establishing relative chronology (Pompeii)
• Stratigraphic units identified by distinct soil composition, color, and texture represent individual depositional events or phases (flood deposits, occupation layers)
• Disturbances and intrusions such as pits, burrows, and later features can disrupt original stratigraphy and complicate interpretation (ancient wells, animal burrows)
• Analyzing sequence and characteristics of stratigraphic units allows inferring natural and cultural processes that formed the site over time (alluvial deposits, midden accumulation)

Creation of Harris matrices

• Harris matrix diagrams depict temporal and spatial relationships between stratigraphic units (Jericho tell)
• Creating a Harris matrix involves:
  1. Identifying individual stratigraphic units and assigning unique numbers
  2. Determining physical relationships between units (above, below, or equal to)
  3. Arranging units in a diagram based on stratigraphic relationships
• Analyzing a Harris matrix helps identify contemporary units, recognize depositional sequences and phases, and determine relative chronology (Neolithic layers, Bronze Age structures)

Dating through stratigraphic principles

• Relative dating determines chronological order of stratigraphic units and associated artifacts based on Law of Superposition and stratigraphic relationships (Oldowan tools below Acheulean handaxes)
• Absolute dating assigns specific dates or ranges to stratigraphic units and artifacts using datable materials ($^{14}$C dating of charcoal, typological dating of pottery)
• Combining relative and absolute dating methods refines site chronology and allows comparisons between sites and regions (Lapita pottery horizon across Oceania)

Limitations in stratigraphic interpretation

• Disturbances and post-depositional processes like erosion, bioturbation, and later human activities can alter or destroy original stratigraphic relationships leading to misinterpretation (agricultural plowing, looting)
• Incomplete or limited exposure during excavations may only reveal a portion of the stratigraphic sequence, making extrapolation challenging (partial house floor, eroded mound)
• Complex stratigraphic relationships with multiple phases of deposition, erosion, and intrusion require careful observation, recording, and interpretation to untangle site formation history (tell sites, urban centers)
• Lack of datable materials or diagnostic artifacts in some stratigraphic units can limit the ability to establish a refined chronology (sterile layers, heavily disturbed deposits)

Applying Stratigraphy in Archaeological Interpretation

Interpretation of stratigraphic sequences

• Distinguishing between natural deposits (alluvial layers, windblown sediments) and cultural deposits (occupation layers, fill) helps identify site formation processes (Nile River floodplain sites, Loess Plateau settlements)
• Analyzing vertical and horizontal relationships between stratigraphic units allows inferring the order and duration of occupation phases, construction events, and abandonment periods (Pompeii volcanic ash layers, Maya city centers)
• Integrating stratigraphic observations with artifact analysis, spatial distribution, and environmental data builds a comprehensive understanding of site formation, function, and change over time (Çatalhöyük room fills and burials, Paleolithic cave sequences)

Creation of Harris matrices

• Harris matrices visualize complex stratigraphic sequences, clarifying temporal and spatial relationships between units, features, and artifacts (Neolithic tell, Roman villa)
• Interpreting Harris matrices helps recognize patterns of deposition, erosion, and intrusion, inferring the sequence and duration of occupation phases and activities (Bronze Age citadel, Medieval castle)
• Comparing Harris matrices from different areas or sites identifies similarities and differences in site formation processes and explores spatial and temporal relationships (regional settlement patterns, urban development)

Dating through stratigraphic principles

• Stratigraphic relationships establish relative chronologies, determining the order of deposition and relative age of artifacts and features (Olduvai Gorge Bed I and II, Mayan stela)
• Integrating absolute dating methods (radiocarbon, thermoluminescence) with stratigraphic data calibrates and refines the relative chronology (Neolithic transition, Roman conquest)
• Interpreting site chronology estimates duration and intensity of occupation phases and identifies periods of abandonment, hiatus, or rapid deposition (tell settlement, floodplain city)

Limitations in stratigraphic interpretation

• Recognizing potential for misinterpretation due to disturbances and post-depositional processes like erosion, bioturbation, and later human activities is crucial for critically evaluating reliability and representativeness of stratigraphic data (plowed fields, looted tombs)
• Addressing limitations of incomplete or limited stratigraphic exposure by acknowledging potential for missing relationships and using multiple lines of evidence to supplement interpretations (partial house foundations, eroded shell middens)
• Dealing with complex or ambiguous stratigraphic relationships requires careful observation, recording, and analysis techniques to untangle sequences and consider alternative interpretations (deeply stratified caves, densely occupied tells)
• Working with limited chronological resolution or lack of datable materials by using relative dating and typological analysis to establish general chronological frameworks and collaborating with specialists to explore new dating methods (lithic typologies, ceramic seriation)