A stratigraphic or depositional event in which a later feature, deposit, or material penetrates, cuts, or is introduced into earlier deposits, thereby displacing or mixing earlier contexts and creating secondary associations that are temporally younger than the surrounding matrix.

Principle

Intrusions introduce younger material into older contexts (or displace older material upward) and therefore can create false contemporaneities between intrusive fill and surrounding earlier deposits unless the cut and fill relationships are identified and dated independently.

Demonstration

Illustrative scenario → A modern utility trench cuts through and backfills a Late Neolithic floor, introducing plastic and recent ceramics into underlying contexts. Recognition → Observed cut edges, stratigraphic unconformity and a fill that contains modern artefacts are recorded. Action → Excavators record the cut and exclude intrusive fill from in‑situ context interpretations, and sample pre‑intrusion deposits for secure dating. Consequence → Avoids spurious associations and corrects chronological attributions by separating intrusive material from sealed earlier deposits.

Misapplication

Assuming that all materials found within a stratigraphic unit are contemporaneous with its surrounding matrix. Semantic error: conflating fill contents with the age of the cut or surrounding deposit rather than recognising the intrusion as a later event.

Consequence

Failure to recognize intrusions leads to mistaken functional and chronological associations (for example, dating older features by intrusive artifacts), misdirected conservation or sampling, and flawed reconstructions of occupation history; correct identification preserves stratigraphic integrity and guides targeted dating of cut and fill separately.

Reversal

Intrusions that are completely sealed and exhibit clear cut relationships are easier to identify and therefore less likely to produce misassociation; conversely, small or subtle intrusions, bioturbation‑driven intrusions, or intrusive redeposition that lacks clear cuts can be cryptic and still confound interpretation.

Boundary

Clearly within: a pit or trench that clearly cuts earlier layers and contains fill with younger artifacts. Boundary case: apparent redeposition of older fragments into a later deposit (residuals) where discerning directionality requires dating or refitting. Clearly outside: assemblages mixed by surface scatter without a penetrative cut, or in situ primary deposits undisturbed by later penetration.

Semantic Tension

Integrity versus disturbance: the need to preserve and interpret primary stratigraphic associations conflicts with the reality of post‑depositional actions that create intrusive contexts; resolving this tension depends on careful recording of cuts, fills and relative stratigraphy.

Synthesis

Intrusions must be treated as distinct stratigraphic events: identifying the cut, documenting the fill, and applying independent dating to each component are essential to separate younger intrusive material from older contexts and to avoid false associations.