Reconstructing a sequence
In an undisturbed depositional sequence, an overlying layer usually formed later. Floors, abandonment fills and rebuilding can document successive activities through their relationships.
Formation processes matter too. A later pit can cut below an earlier surface without becoming earlier than it. Recording boundaries, feature form and relationships is therefore more informative than depth alone.
Objects and deposits have different histories
An object can be used long after manufacture and moved again with later fill. An older object within a later deposit need not date the deposit to its manufacture; intrusive material creates a different complication.
Object age, deposition and the target activity must be distinguished. Scientific dating measures samples, whose relationship to the deposit must be supported before constraining its chronology.
Records make interpretation reassessable
Excavation removes deposits, making drawings, photographs, descriptions and sample records essential. Finds retain explanatory value through documented relationships to their locations and features.
Weathering, animals, farming and construction can alter those relationships. Observed boundaries and interpretations require reassessment alongside other evidence. A stratigraphic sequence does not automatically assign exact calendar dates to every phase.