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Chapter 7 Geoarchaeology and Site Formation Processes

Chapter 7 Geoarchaeology and Site Formation Processes

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Page 1: Chapter 7 Geoarchaeology and Site Formation Processes

Chapter 7

Geoarchaeology and Site Formation Processes

Page 2: Chapter 7 Geoarchaeology and Site Formation Processes

Outline

• The Law of Superposition• Reading Gatecliff’s Dirt• Gatecliff’s Stratigraphy• Is Stratigraphy Really that Easy?• Site Formation Processes: How

Good Sites Go Bad• Conclusion

Page 3: Chapter 7 Geoarchaeology and Site Formation Processes

Geoarchaeology

• Applies concepts and methods of the geosciences to archaeological research.

• Objectives:– Place sites and artifacts in a context

through the application of stratigraphic principles and dating techniques.

– Understand the natural processes of site formation.

Page 4: Chapter 7 Geoarchaeology and Site Formation Processes

The Law of Superposition

• In any pile of sedimentary rocks undisturbed by folding or overturning, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on.

• This principle seems simple, but it was a critical observation in the 17th century when formulated by Nicolaus Steno.

Page 5: Chapter 7 Geoarchaeology and Site Formation Processes

Fossil Footprints at Laetoli:Law of Superposition in

Action• For decades, specialists in human

evolution argued that bipedalism must have arisen in response to tool use.

• Based on her knowledge of the region’s geology, Leakey guessed that the age of the footprints at Laetoli was more than a million years older than the oldest known tool use.

Page 6: Chapter 7 Geoarchaeology and Site Formation Processes

How Old Are the Footprints?

• Leakey worked with geologists Robert Drake and Garness Curtis, who processed a series of potassium-argon dates on samples from the major stratified layers recognized in the Laetoli area.

• The fossil hominid footprints are between 3.49 and 3.56 million years old.

• With the dating of the Laetolil footprints, Leakey showed that humans were bipedal long before they made stone tools.

Page 7: Chapter 7 Geoarchaeology and Site Formation Processes

What Happened to the Laetoli Footprints?

• When Leakey completed her work she backfilled the site with 2 feet of soil.

• After a few years, trees grew on the spot.

• In 1995, archaeologist Fiona Marshall unearthed the trees’ roots without disturbing the tracks.

• In 100 years, the footprints will be uncovered again and if possible safely removed to a museum.

Page 8: Chapter 7 Geoarchaeology and Site Formation Processes

Stratigraphic Profile: Laetoli

Page 9: Chapter 7 Geoarchaeology and Site Formation Processes

Reading Gatecliff’s Dirt

• Gatecliff Shelter has a 40-foot stratigraphic profile covering more than 7000 years.

• The Gatecliff sediments, like those of all archaeological sites, resulted from both natural processes and human behavior.

Page 10: Chapter 7 Geoarchaeology and Site Formation Processes

Physical Stratigraphy of Gatecliff Shelter

Stratum

Soil

Nature of sediment

Field designation

Age (C-14 yr bp)

1 S-1 Rubble GU-14 0–1250 BP

2Sand and

siltUpper GU 13

1250 BP

3 S-2 Rubble Part of GU 12 1250–1350 BP

4Sand and

siltGU 13 and GU 12 Silt

1350 BP

5 S-3 Rubble Part of GU 12 1350–3200 BP

6Sand and

siltGU 11 3200 BP

7 RubbleGU 11 and

GU 10R3250–3200 BP

Page 11: Chapter 7 Geoarchaeology and Site Formation Processes

Physical Stratigraphy of Gatecliff Shelter

Stratum

Soil

Nature of sediment

Field designation

Age(C-14 yr bp)

8Sand and

siltGU 10 3250 BP

9 Rubble GU 9R 3300–3250 BP

10Sand and

siltGU 8 A and B 3300 BP

11 Rubble GU 7R 3400–3300 BP

12

Sand and silt

GU 7 3400 BP

13 Rubble 6 Living Floor 4050–3400 BP

Page 12: Chapter 7 Geoarchaeology and Site Formation Processes

Physical Stratigraphy of Gatecliff Shelter

Stratum

Soil

Nature of sediment

Field designatio

n

Age(C-14 yr bp)

14Sand and

siltGU 5 Silt 4050 BP

15 Rubble Part of GU 5 4100–4050 BP

16Sand and

siltPart of GU 5 4100 BP

17 Rubble GU 4 4250–4100 BP

18 Silty Sand GU 3 4250 BP

19Sand and

rubbleGU 2 5000–4250 BP

20 S-4 Silt and clay GU 1A 5100–5000 BP

21Sand and

silt GU 1 and GU 7–74

5100BP

Page 13: Chapter 7 Geoarchaeology and Site Formation Processes

Physical Stratigraphy of Gatecliff Shelter

Stratum

SoilNature of sediment

Field designatio

n

Age (C-14 yr bp)

22 Rubble GU 6R–74 5250–5100 BP

23 Gravel,

sand, and silt

GU 6–74 and GU 5–74

5250 BP

24 Rubble GU 4R–74 5350–5250 BP

25 Silt GU 4-74 5350 BP

26 Rubble GU 3R-74 5500–5350 BP

27-29 Silts GU 3A-74 5500 BP

30 Sand GU 3B-74 5500 BP

Page 14: Chapter 7 Geoarchaeology and Site Formation Processes

Physical Stratigraphy of Gatecliff Shelter

Stratum

Soil

Nature of sediment

Field designat

ion

Age (C-14 yr bp)

31 Rubble GU 2R-74 5700–5500 BP

32 Fine sand, silt GU 2-74

33 Fine sand, silt

GU 12–76, GU 1–

78, GU 1–74

34Silt, very fine

sandGU 2–78

35 Rubble GU 3R–78

36Silty medium

sandGU 3–78

Page 15: Chapter 7 Geoarchaeology and Site Formation Processes

Hypothetical Rockshelter, Filling with Colluvial and Eolian Sediments, and

Rooffall

Page 16: Chapter 7 Geoarchaeology and Site Formation Processes

Development of a Hypothetical Archaeological

Site

Page 17: Chapter 7 Geoarchaeology and Site Formation Processes

Development of a Hypothetical Archaeological

Site

Page 18: Chapter 7 Geoarchaeology and Site Formation Processes

Context

• A systemic context is a living behavioral system wherein artifacts are part of the on-going system of manufacture, use, re-use, and discard.

• Once artifacts enter the ground, they are part of the archaeological context, where they can continue to be affected by human action, but where they also are affected by natural processes.

Page 19: Chapter 7 Geoarchaeology and Site Formation Processes

Formation Processes in the Systemic Context

• Four key processes in the systemic context influence the creation of archaeological sites: – Cultural deposition– Reclamation– Disturbance– Reuse

Page 20: Chapter 7 Geoarchaeology and Site Formation Processes

Cultural Deposition

Dominant factor in forming the archaeological record.

1. Discard - Everything eventually breaks or wears out and is discarded.

2. Loss - Example: An arrow that misses its target or a pot left at a camp.

3. Caching - Some items are intentionally left behind.

4. Ritual - Example: grave goods.

Page 21: Chapter 7 Geoarchaeology and Site Formation Processes

Reclamation Processes

• Human behaviors that result in artifacts moving from the archaeological context back to the systemic context.

• Example: scavenging beams from an abandoned structure to use them in a new one.

Page 22: Chapter 7 Geoarchaeology and Site Formation Processes

Cultural Disturbance Processes

• Human behaviors that modify artifacts in their archaeological context.

• Example: dam building; farming; and construction of houses, pits, hearths, and so on.

Page 23: Chapter 7 Geoarchaeology and Site Formation Processes

Reuse Processes

• In this process, an object moves through a series of behavioral settings before it enters the archaeological record.

• This can entail the recycling of some objects:– Potsherds are ground up and used as

temper in manufacturing new vessels. – Broken arrowheads are re-chipped into

drills.

Page 24: Chapter 7 Geoarchaeology and Site Formation Processes

Formation Processes in the Archaeological

Context• Once an object enters an

archaeological context, a host of natural as well as cultural formation processes takes place.

• These natural processes determine whether organic material will be preserved and where objects will be found.

Page 25: Chapter 7 Geoarchaeology and Site Formation Processes

Natural Formation Processes

• Floralturbation - Process in which trees and plants affect the distribution of artifacts.

• Faunalturbation - Process in which animals, from large game to earthworms, affect the distribution of material.

• Cryoturbation - Process in which freeze/thaw activity in a soil pushes larger artifacts to the surface of a site.

Page 26: Chapter 7 Geoarchaeology and Site Formation Processes

Natural Formation Processes

• Argilliturbation - Process in which wet/dry cycles in clay-rich soils push artifacts upward as the sediment swells and then moves them down as cracks form during dry cycles.

• Graviturbation - Process in which artifacts are moved downslope through gravity, sometimes assisted by precipitation runoff.

Page 27: Chapter 7 Geoarchaeology and Site Formation Processes

Effects of Natural Formation Processes on Distribution of

Artifacts

Page 28: Chapter 7 Geoarchaeology and Site Formation Processes

Effects of Natural Formation Processes on Distribution of

Artifacts

Page 29: Chapter 7 Geoarchaeology and Site Formation Processes

Effects of Natural Formation Processes on Distribution of

Artifacts

Page 30: Chapter 7 Geoarchaeology and Site Formation Processes

Effects of Natural Formation Processes on Distribution of

Artifacts

Page 31: Chapter 7 Geoarchaeology and Site Formation Processes

Effects of Natural Formation Processes on Distribution of

Artifacts

Page 32: Chapter 7 Geoarchaeology and Site Formation Processes

Site Formation Process Summary

Systemic context Archaeological Context

Cultural Deposition Floralturbation (plants)

•Discard Faunalturbation (animals)

•Loss Cryoturbation (freezing)

•CachingArgilliturbation (wet-dry cycles)

•Ritual interment Graviturbation (hill slopes)

Reclamation

Disturbance

Reuse

Page 33: Chapter 7 Geoarchaeology and Site Formation Processes

How Artifacts Become Oriented to the Direction of

River Flow

Page 34: Chapter 7 Geoarchaeology and Site Formation Processes

Quick Quiz

Page 35: Chapter 7 Geoarchaeology and Site Formation Processes

1. The _____ ______ ________ states that in any pile of undisturbed sedimentary rocks, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on.

Page 36: Chapter 7 Geoarchaeology and Site Formation Processes

Answer: Law of Superposition

• The Law of Superposition states that in any pile of undisturbed sedimentary rocks, the strata on the bottom were deposited first, those above them were deposited second, those above them third, and so on.

Page 37: Chapter 7 Geoarchaeology and Site Formation Processes

2. When Leakey dated the Laeotolil footprints as between 3.49 and 3.56 million years old, she showed that humans made stone tools long before they were bipedal.

A. TrueB. False

Page 38: Chapter 7 Geoarchaeology and Site Formation Processes

Answer: B. False

2. When Leakey dated the Laeotolil footprints as between 3.49 and 3.56 million years old, she showed that humans were bipedal long before they made stone tools.

Page 39: Chapter 7 Geoarchaeology and Site Formation Processes

3. Floralturbation is a systemic site formation process caused by cultural deposition.

A. TrueB. False

Page 40: Chapter 7 Geoarchaeology and Site Formation Processes

Answer: B. False

• Floralturbation is a natural formation process in which trees and plants affect the distribution of artifacts.

Page 41: Chapter 7 Geoarchaeology and Site Formation Processes

4. Scavenging beams from an abandoned structure to use them in a new one is an example of a _____ ______, human behaviors that result in artifacts moving from the archaeological context back to the systemic context.

Page 42: Chapter 7 Geoarchaeology and Site Formation Processes

Answer: reclamation processes

• Scavenging beams from an abandoned structure to use them in a new one is an example of a reclamation process, human behaviors that result in artifacts moving from the archaeological context back to the systemic context.