In a sequence of undisturbed, stratified deposits, each depositional layer (stratum) is younger than the one it overlies and older than the one that overlies it; the law provides a relative chronological ordering of strata but not absolute ages.

Principle

Relative temporal ordering: vertical position in an undisturbed stratigraphic sequence corresponds to relative age, with lower units deposited earlier than higher units.

Demonstration

Illustrative scenario → During excavation of a hypothetical tell, stratigraphic units are recorded: an intact layer of occupation debris lies above a layer of sterile flood silt. Applying the law, archaeologists infer the flood deposit predates the overlying occupation layer and use that order to build a site chronology before any radiometric dating.

Misapplication

Applying the law to deposits that have been disturbed (e.g., by burials, pits, bioturbation, or human reworking) and treating vertical position as equivalent to primary deposition; the error is assuming stratigraphic integrity where post-depositional processes have altered original order.

Consequence

The law enables reconstruction of event sequences and relative chronologies essential for stratigraphic interpretation and for determining which contexts should be sampled or dated first; misapplication can invert or scramble inferred sequences.

Reversal

The law does not hold when layers have been overturned, folded, truncated or re-deposited; tectonic deformation, slumping, cryoturbation, intrusive features and later backfilling can violate the assumption of undisturbed superposition.

Boundary

Applies to layered depositional contexts (archaeological strata, sedimentary beds) that retain primary superpositional relationships. It does not apply to non-stratified deposits (isolated features, scatters) or to vertical sequences altered by intrusive or post-depositional processes.

Semantic Tension

Relative stratigraphic ordering ↔ Absolute dating methods (chronometric techniques) that provide calendar ages; both are complementary but answer different questions.

Synthesis

The Law of Superposition is a foundational heuristic for ordering depositional events; it functions as a first-order test of relative chronology that must be corroborated by assessment of disturbance and, when available, absolute dating.