Stratigraphy and dating are crucial tools in archaeology. They help us understand the order of events and the age of artifacts found during excavations. By studying layers of soil and using various dating techniques, archaeologists can piece together the story of human activity over time.
These methods are especially important for studying the Age of Exploration. They allow us to date sites and artifacts from this period, helping us understand how European exploration impacted different parts of the world. Stratigraphy and dating give us a timeline for these historical events and changes.
Principles of stratigraphy
- Stratigraphy is the study of rock layers (strata) and layering (stratification) used to understand the sequence of geological events and processes that have occurred over time
- Principles of stratigraphy provide a framework for interpreting the relative ages of rock layers and the relationships between them, which is essential for reconstructing past environments and human activities in archaeology of the Age of Exploration
Law of superposition
- In an undeformed sequence of sedimentary rocks, the oldest layers are at the bottom, and the youngest layers are at the top
- Helps establish the relative ages of archaeological remains found within different stratigraphic layers
- Allows archaeologists to determine the chronological order of past events and cultural phases
Original horizontality
- Sedimentary layers are deposited in a nearly horizontal position
- Any departures from horizontal indicate that the layers have been deformed or tilted after deposition
- Helps identify post-depositional disturbances that may have affected the archaeological record
Lateral continuity
- Sedimentary layers extend laterally in all directions until they thin out or terminate against the edge of the depositional basin
- Allows correlation of stratigraphic units across a site or region
- Helps in understanding the spatial distribution of archaeological remains and past landscapes
Cross-cutting relationships
- A feature or structure that cuts across a stratigraphic layer is younger than the layer it cuts
- Includes intrusions (igneous dikes), faults, and erosional features (channels)
- Provides a way to establish relative ages between stratigraphic units and archaeological features
Relative dating techniques
- Relative dating techniques determine the age of archaeological remains in relation to other remains or geological events, without providing a specific numerical age
- These techniques are based on the principles of stratigraphy and the observation of stylistic changes in artifacts over time
- Relative dating is crucial for establishing chronological sequences and understanding cultural change in archaeology of the Age of Exploration
Seriation
- Arranges artifacts in a chronological sequence based on changes in their style, form, or frequency over time
- Assumes that certain styles or attributes of artifacts gradually increase or decrease in popularity
- Helps establish relative chronologies for sites and regions (ceramic seriation)
Typology
- Classification of artifacts into types based on shared physical characteristics (shape, size, decoration)
- Assumes that artifact types change over time in a predictable manner
- Allows for the creation of chronological sequences and the identification of cultural phases
Fluorine dating
- Measures the amount of fluorine absorbed by bones from the surrounding soil
- Fluorine content increases with the age of the bone, as it is absorbed from groundwater
- Provides a relative age estimate for bones found in similar soil conditions
Nitrogen dating
- Measures the amount of nitrogen in bone collagen
- Nitrogen content decreases with age due to protein degradation
- Can be used to determine the relative age of bones from the same site or region
Absolute dating techniques
- Absolute dating techniques provide a specific numerical age for archaeological remains, expressed in years before present (BP) or calendar years (BCE/CE)
- These techniques are based on the measurement of radioactive decay, chemical changes, or annual growth rings in organic materials
- Absolute dating is essential for anchoring relative chronologies and understanding the timing of past events and processes in archaeology of the Age of Exploration
Radiocarbon dating
- Measures the decay of radioactive carbon-14 in organic materials (wood, charcoal, bone)
- Living organisms absorb carbon-14 from the atmosphere, which begins to decay after death
- Provides ages up to ~50,000 years BP, with decreasing accuracy for older samples
Potassium-argon dating
- Measures the decay of radioactive potassium-40 to argon-40 in volcanic rocks
- Potassium-rich minerals (feldspar, mica) begin to accumulate argon after cooling and crystallization
- Provides ages ranging from thousands to billions of years, depending on the rock type
Uranium-series dating
- Measures the decay of uranium-234 to thorium-230 in calcium carbonate materials (speleothems, corals, shells)
- Uranium is soluble in water, while thorium is not, leading to a predictable accumulation of thorium over time
- Provides ages up to ~500,000 years, with high precision for younger samples
Dendrochronology
- Analyzes the annual growth rings in trees to establish a precise calendar date
- Patterns of wide and narrow rings reflect variations in climate and can be matched across different trees
- Provides exact calendar years for the outermost ring of a tree, which can be used to date associated archaeological remains
Thermoluminescence dating
- Measures the accumulated radiation dose in crystalline minerals (quartz, feldspar) since their last exposure to heat or sunlight
- Minerals emit light (luminescence) when heated, proportional to the absorbed radiation dose
- Provides ages for ceramics, burnt stone, and sediments, ranging from a few hundred to several hundred thousand years
Stratigraphic excavation methods
- Stratigraphic excavation methods are designed to carefully remove and record the layers of an archaeological site in reverse order of deposition
- These methods allow for the detailed documentation of the vertical and horizontal relationships between stratigraphic units and archaeological remains
- Stratigraphic excavation is crucial for understanding site formation processes and reconstructing past human activities and environments in archaeology of the Age of Exploration
Single context recording
- Excavates and records each stratigraphic unit (context) individually, following the natural boundaries of the deposits
- Assigns a unique number to each context and documents its characteristics (soil type, color, inclusions) and relationships to other contexts
- Allows for the creation of a detailed stratigraphic sequence and the identification of complex features and events
Harris matrix
- A diagram that represents the stratigraphic relationships between contexts using lines and boxes
- Shows the sequence of deposition and the relative ages of contexts, with earlier contexts at the bottom and later contexts at the top
- Helps visualize the site's stratigraphy and identify contemporaneous contexts and phases of activity
Wheeler box-grid system
- Divides the site into a grid of square boxes, typically 5x5 meters, separated by narrow baulks (unexcavated strips)
- Excavates each box in stratigraphic layers, leaving the baulks intact to provide a vertical profile of the site's stratigraphy
- Allows for the correlation of stratigraphic units across the site and the identification of horizontal relationships between features
Interpreting stratigraphic sequences
- Interpreting stratigraphic sequences involves understanding the processes that formed and modified the layers of an archaeological site over time
- This requires considering the nature of the deposits, the agents responsible for their formation, and any post-depositional disturbances that may have affected them
- Interpreting stratigraphic sequences is essential for reconstructing past human activities, environments, and site formation processes in archaeology of the Age of Exploration
Site formation processes
- The natural and cultural processes that create, modify, and preserve the archaeological record
- Includes deposition (accumulation of sediments and artifacts), erosion (removal of material), and post-depositional disturbances (bioturbation, weathering)
- Understanding site formation processes helps distinguish between primary (in situ) and secondary (disturbed or redeposited) contexts
Depositional vs post-depositional events
- Depositional events are the processes that initially create an archaeological deposit (occupation, abandonment, burial)
- Post-depositional events are the processes that modify or disturb the deposit after its initial formation (erosion, bioturbation, human disturbance)
- Distinguishing between depositional and post-depositional events is crucial for interpreting the integrity and meaning of archaeological remains
Anthropogenic vs natural deposits
- Anthropogenic deposits are the result of human activities (occupation layers, middens, construction fills)
- Natural deposits are formed by environmental processes (alluvial sediments, windblown sand, volcanic ash)
- Identifying the origin of deposits helps reconstruct past human behaviors and environmental conditions
Challenges in stratigraphic analysis
- Stratigraphic analysis can be complicated by various factors that disturb or obscure the original layering of an archaeological site
- These challenges can make it difficult to establish a reliable stratigraphic sequence or interpret the meaning of archaeological remains
- Recognizing and addressing these challenges is essential for accurate stratigraphic analysis in archaeology of the Age of Exploration
Bioturbation and disturbance
- Bioturbation is the mixing of sediments and artifacts by the activity of organisms (roots, burrowing animals, insects)
- Human disturbance includes trampling, digging, and the reuse of older materials in later contexts
- Bioturbation and disturbance can blur the boundaries between stratigraphic units and create apparent inversions in the sequence
Erosion and weathering
- Erosion is the removal of sediments and artifacts by wind, water, or gravity
- Weathering is the physical and chemical breakdown of materials exposed to the elements
- Erosion and weathering can truncate or remove entire stratigraphic units, leading to gaps in the archaeological record
Reworked deposits
- Reworked deposits are sediments and artifacts that have been eroded from their original context and redeposited elsewhere
- Reworked deposits can create misleading stratigraphic relationships and mix materials of different ages
- Identifying reworked deposits requires careful attention to the condition and context of archaeological remains
Inversions and reversals
- Stratigraphic inversions occur when younger deposits appear beneath older deposits, contradicting the law of superposition
- Reversals are when artifacts or features appear to be in the wrong chronological order based on their known age or style
- Inversions and reversals can result from post-depositional disturbances, reworking, or the misinterpretation of stratigraphic relationships
Integrating stratigraphic data
- Integrating stratigraphic data involves combining information from multiple sources to create a comprehensive understanding of an archaeological site or region
- This requires correlating stratigraphic units across different areas, constructing site-wide chronologies, and comparing stratigraphic sequences at a regional scale
- Integrating stratigraphic data is essential for understanding the broader patterns of human activity, environmental change, and cultural interaction in archaeology of the Age of Exploration
Correlating stratigraphic units
- Identifying stratigraphic units that are equivalent in age and depositional environment across different parts of a site
- Uses physical characteristics (soil type, color, inclusions), artifact content, and stratigraphic position to establish correlations
- Allows for the creation of a site-wide stratigraphic framework and the identification of contemporaneous activities and features
Constructing site chronologies
- Building a timeline of events and phases for an archaeological site based on the stratigraphic sequence and absolute dating results
- Combines relative and absolute dating methods to anchor the stratigraphic sequence in calendar years
- Provides a framework for understanding the timing and duration of past human activities and environmental changes
Regional stratigraphic comparisons
- Comparing the stratigraphic sequences of multiple sites within a region to identify shared patterns and events
- Uses marker horizons (volcanic ash layers, distinctive soil types) and diagnostic artifacts to correlate stratigraphic units across sites
- Helps reconstruct regional-scale environmental changes, cultural interactions, and population movements
Multidisciplinary approaches
- Integrating data from various disciplines (geomorphology, paleoclimatology, archaeobotany, zooarchaeology) to enhance stratigraphic interpretations
- Provides independent lines of evidence for reconstructing past environments, subsistence practices, and human-environment interactions
- Offers a more comprehensive and robust understanding of the archaeological record and its context