---
title: "Sequence Stratigraphy | Intro to Archaeology"
description: "Sequence Stratigraphy in Intro to Archaeology reads sediment layers by changes in sea level, helping you interpret site formation, erosion, and deposition."
canonical: "https://fiveable.me/introduction-archaeology/key-terms/sequence-stratigraphy"
type: "key-term"
subject: "Intro to Archaeology"
unit: "Unit 5"
---

# Sequence Stratigraphy | Intro to Archaeology

## Definition

Sequence stratigraphy is a way of reading stacked sediment layers as a record of changing environments, especially shifts in sea level and sediment supply. In Intro to Archaeology, it helps you interpret how deposits formed around a site and what got preserved or eroded.

## What It Is

Sequence stratigraphy is the study of sediment layers as a changing sequence of deposition and erosion, which makes it useful in Intro to Archaeology when you are trying to figure out how a site formed over time. Instead of treating layers as random dirt, you read them as evidence of flooding, shoreline movement, river shifts, dune buildup, or other environmental changes that affected what got buried.

At the center of the idea is the depositional sequence, a package of layers laid down under similar conditions before the system changed. When sea level rises or falls, or when sediment supply changes, the ground surface and the kinds of deposits left behind change too. That means one archaeological layer might represent a stable occupation surface, while the layer above it could be flood silt, beach sand, or erosion that removed part of the site.

This matters because archaeological deposits are not formed in a vacuum. Coastal sites, river valleys, and wetland settlements are shaped by marine transgressions and regressions, river flooding, and climate shifts. Sequence stratigraphy gives you a framework for asking why a layer looks the way it does, not just what is inside it.

A useful part of this approach is the sequence boundary, the surface that marks a major change between depositional episodes. In an archaeological context, that boundary might show up as an erosion surface, a buried land surface, or a gap in the record where older material was cut away before new sediment arrived. That is a big deal for interpretation, because the absence of artifacts can mean the layer was never occupied, or it can mean the evidence was washed out.

Archaeologists often use sequence stratigraphic thinking alongside site stratigraphy and geoarchaeology. For example, if a shoreline site has shell midden material overlain by marine sand, you can start to ask whether people lived there before sea level changed, whether the coast migrated, and whether the site was later sealed by natural sediment. The point is not just to date the layers, but to reconstruct the environmental story that shaped the archaeological record.

## Why It Matters

Sequence stratigraphy matters in Intro to Archaeology because it helps you separate human activity from natural site formation. A layer full of artifacts might reflect a campsite, but it might also be redeposited material moved by water, wind, or slope wash. When you can read depositional sequences, you are better at deciding what the site actually looked like when people used it.

It also connects directly to preservation. Sea level change can bury a site, expose it, or destroy parts of it. That is why coastal and riverine sites often have complicated profiles, with intact cultural layers sitting above or below sterile sediments, erosion surfaces, or flood deposits. Sequence stratigraphy gives you the language for explaining those patterns in a site report or essay.

This term is also useful for comparing sites across a region. If multiple sites show similar sequence boundaries or sediment shifts, you can connect local archaeology to bigger environmental changes such as climate variation, tectonic uplift, or shoreline movement. In other words, it helps you move from one trench wall to the larger landscape history behind it.

## Connections

### Lithostratigraphy

Lithostratigraphy focuses on rock or sediment layers based on their physical characteristics, like color, grain size, or composition. Sequence stratigraphy uses those layer descriptions too, but it adds the extra idea of changing depositional systems over time. In archaeology, that means you are not only naming layers, you are asking what environmental shift produced them.

### Chronostratigraphy

Chronostratigraphy organizes layers by time, while sequence stratigraphy organizes them by how they formed during changes in relative sea level and sedimentation. The two work together when you want both a time framework and a formation story. In an archaeological site, that helps you connect artifacts to a sequence of environmental events instead of a single moment.

### Facies

Facies are the visible features of a sediment deposit that point to a particular environment, such as a river channel, lagoon, floodplain, or beach. Sequence stratigraphy uses facies patterns to interpret how environments shifted from one depositional phase to another. For archaeology, facies can help explain why a layer is sandy, silty, or full of shell.

### [Stratigraphic Column](/introduction-archaeology/key-terms/stratigraphic-column)

A stratigraphic column is the vertical diagram of layers at a site, and it is one of the easiest places to see sequence stratigraphy in action. The column lets you track changes in sediment type, boundaries, and possible gaps in deposition. When you build or read one, you are basically mapping the sequence of site formation.

## On the AP Exam

A quiz question or short-answer prompt may show you a stratigraphic profile and ask what environmental process explains the shift in layers. You would use sequence stratigraphy to identify changes like sea-level rise, shoreline migration, flooding, or erosion, then connect those changes to preservation at the site. In a lab or field exercise, you might also compare two trench profiles and explain why one layer is missing, truncated, or sealed beneath another deposit.

If the class uses site reports, this term can show up in a discussion of how a coastal settlement was buried or abandoned. The best response usually names the layer change, identifies the likely depositional event, and explains what that means for interpreting artifacts in that layer. Do not just describe the dirt, explain the sequence behind it.

## Sequence Stratigraphy vs Lithostratigraphy

Lithostratigraphy classifies layers by what they are made of, while sequence stratigraphy explains how and why those layers were arranged through time. If you only describe sand, silt, or clay, that is lithostratigraphy. If you explain that the sand marks a marine incursion or erosion surface tied to sea-level change, that is sequence stratigraphy.

## Key Takeaways

- Sequence stratigraphy reads sediment layers as a record of changing depositional environments, not just as a stack of dirt.
- In archaeology, it is especially useful for coastal, river, and wetland sites where sea level, flooding, or erosion can reshape the record.
- Sequence boundaries mark major changes between depositional episodes, and they can reveal erosion surfaces or missing parts of the site.
- The term helps you tell the difference between a layer created by people and a layer created by natural processes after occupation.
- When you explain a site profile, sequence stratigraphy helps you connect local strata to larger environmental change.

## FAQs

### What is Sequence Stratigraphy in Intro to Archaeology?

Sequence stratigraphy is the study of how sediment layers formed through changes in sea level, sediment supply, and erosion. In archaeology, it helps you interpret the environmental history of a site and figure out why certain layers were preserved, buried, or removed.

### How is Sequence Stratigraphy different from Stratigraphy?

Stratigraphy is the broader practice of reading layers in order, which helps you build a relative sequence of events. Sequence stratigraphy is more specific because it focuses on depositional packages, boundaries, and environmental shifts like sea-level change. It adds a stronger explanation for how the layers formed.

### Why would an archaeologist care about sea-level change?

Sea-level change can bury settlements, expose them to erosion, or alter the sediments around them. That means the archaeological record may be incomplete or rearranged. Sequence stratigraphy helps you explain those changes instead of assuming every layer came from one occupation phase.

### What does a sequence boundary look like in a site profile?

It often appears as an erosion surface, a sudden change in sediment type, or a break between deposits that formed under different conditions. In a trench wall, that boundary can help you spot where one depositional episode ended and another began.

## Related Study Guides

- [5.1 Principles of Stratigraphy](/introduction-archaeology/unit-5/principles-stratigraphy/study-guide/QsO6SlFjprur5Awa)

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