A single, spatially and stratigraphically bounded deposit, cut, fill, surface, or constructed feature recorded as one context during excavation and treated as the basic unit for stratigraphic description and relative sequencing.

Principle

Each stratigraphic unit represents, for recording purposes, a single depositional, erosive, or intrusive event (or a discrete phase of activity): its position and contacts with other units determine its relative ordering in the site sequence.

Demonstration

Illustrative scenario → During excavation of a trench, a compact occupation surface (SU 101) is recorded as a single unit because it is a continuous, mappable layer with clear upper and lower contacts. Recognizing SU 101 as one unit, excavators remove it after recording its extent and relationships; its position above SU 102 (a sterile natural deposit) and below SU 100 (a later fill) establishes the local relative order used in the Harris Matrix.

Misapplication

Treating an artifactual assemblage or an interpreted phase (e.g., 'occupation phase') as a stratigraphic unit. This conflates recorded contexts with higher-level interpretive aggregates; the error is mixing description (context) with interpretation (phase), which obscures contact relationships needed for sequencing.

Consequence

When units are defined and recorded correctly, they permit construction of an accurate stratigraphic sequence and sample selection tied to clear contacts. Misdefining units causes conflation of non-contemporaneous deposits, loss of contact information, and incorrect relative sequencing.

Reversal

In heavily bioturbated, reworked, or mass-movement contexts a recorded ’unit’ may contain material from multiple events and thus not represent a single depositional/intrusive episode; microstratigraphic analysis, micromorphology, or subdividing the context may be required.

Boundary

Clearly within: a sealed compact occupation surface with continuous horizons and definable boundaries. Boundary case: a large midden lens containing discreet episodes of discard that may require subdivision. Clearly outside: an inventory record of artifacts or a typological phase label that does not specify spatial/stratigraphic limits.

Semantic Tension

Precision of context recording ↔ Interpretive aggregation (many excavators must balance recording every micro-unit against aggregating contexts into interpretable phases).

Synthesis

A stratigraphic unit is an empirical recording device: the smallest, spatially explicit element on which stratigraphic reasoning rests. Distinguishing recorded units from interpretive constructs (phases, occupations) preserves the contact data essential for building reliable relative chronologies.