1. Geoarchaeology and Site Formation Processes
Chapter 7
Geoarchaeology and Site Formation Processes

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. Stratigraphic Profile: Laetoli

9. 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.

10. 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 2
Sand and silt
Upper GU 13
1250 BP 3
S-2
Part of GU 12
1250–1350 BP 4
GU 13 and GU 12 Silt
1350 BP 5
S-3
1350–3200 BP 6
GU 11
3200 BP 7
GU 11 and GU 10R
3250–3200 BP

11. Physical Stratigraphy of Gatecliff Shelter
Stratum
Soil
Nature of sediment
Field designation
Age (C-14 yr bp) 8
Sand and silt
GU 10
3250 BP 9
Rubble
GU 9R
3300–3250 BP 10
GU 8 A and B
3300 BP 11
GU 7R
3400–3300 BP 12
GU 7
3400 BP 13
6 Living Floor
4050–3400 BP

12. Physical Stratigraphy of Gatecliff Shelter
Stratum
Soil
Nature of sediment
Field designation
Age (C-14 yr bp) 14
Sand and silt
GU 5 Silt
4050 BP 15
Rubble
Part of GU 5
4100–4050 BP 16
4100 BP 17
GU 4
4250–4100 BP 18
Silty Sand
GU 3
4250 BP 19
Sand and rubble
GU 2
5000–4250 BP 20
S-4
Silt and clay
GU 1A
5100–5000 BP 21
GU 1 and GU 7–74
5100BP

13. Physical Stratigraphy of Gatecliff Shelter
Stratum
Soil
Nature of sediment
Field designation
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
GU 4R–74
5350–5250 BP 25
Silt
GU 4-74
5350 BP 26
GU 3R-74
5500–5350 BP
27-29
Silts
GU 3A-74
5500 BP 30
Sand
GU 3B-74

14. Physical Stratigraphy of Gatecliff Shelter
Stratum
Soil
Nature of sediment
Field designation
Age (C-14 yr bp) 31
Rubble
GU 2R-74
5700–5500 BP 32
Fine sand, silt
GU 2-74 33
GU 12–76, GU 1–78, GU 1–74 34
Silt, very fine sand
GU 2–78 35
GU 3R–78 36
Silty medium sand
GU 3–78

15. Hypothetical Rockshelter, Filling with Colluvial and Eolian Sediments, and Rooffall

16. Development of a Hypothetical Archaeological Site

17. Development of a Hypothetical Archaeological Site

18. 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.

19. Formation Processes in the Systemic Context
Four key processes in the systemic context influence the creation of archaeological sites:
Cultural deposition
Reclamation
Disturbance
Reuse

20. Cultural Deposition
Dominant factor in forming the archaeological record.
Discard - Everything eventually breaks or wears out and is discarded.
Loss - Example: An arrow that misses its target or a pot left at a camp.
Caching - Some items are intentionally left behind.
Ritual - Example: grave goods.

21. 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.

22. 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.

23. 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.

24. 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.

25. 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.

26. 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.

27. Effects of Natural Formation Processes on Distribution of Artifacts

28. Effects of Natural Formation Processes on Distribution of Artifacts

29. Effects of Natural Formation Processes on Distribution of Artifacts

30. Effects of Natural Formation Processes on Distribution of Artifacts

31. Effects of Natural Formation Processes on Distribution of Artifacts

32. Site Formation Process Summary
Systemic context
Archaeological Context
Cultural Deposition
Floralturbation (plants)
Discard
Faunalturbation (animals)
Loss
Cryoturbation (freezing)
Caching
Argilliturbation (wet-dry cycles)
Ritual interment
Graviturbation (hill slopes)
Reclamation
Disturbance
Reuse

33. How Artifacts Become Oriented to the Direction of River Flow

34. Quick Quiz

35. 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.

36. 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.

37. 2. When Leakey dated the Laeotolil footprints as between 3. 49 and 3
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.
True
False

38. 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.

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

40. Answer: B. False
Floralturbation is a natural formation process in which trees and plants affect the distribution of artifacts.

41. 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.

42. 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.