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1. Packrat Midden Analysis, since late Pleist.
– Sonoran Desert History (veg & climate)
2. Alluvial Stratigraphy, since early Holocene
– Dry-wet and/or warm-cool periods
3. Dendrochronology, since 300- 400 ybp
– Precipitation
– Temperature
Paleo –Vegetation and –Climate of SW
At our starting point, 20,000 years ago…At our starting point, 20,000 years ago…
(40,000 years of vegetation data from…(40,000 years of vegetation data from…packrat middens)packrat middens)
1. Packrat middens- past 20,000 years1. Packrat middens- past 20,000 years
“Sonoran Desert”
22000-11000 ybp, Late Pleistocene
• Vegetation
22,000 11,000 8,000 4,000
“Sonoran Desert”
22000-11000 ybp, Late Pleistocene
• Climate relative to today:
22,000 11,000 8,000 4,000
“Sonoran Desert”
11000-8000 ybp, Early Holocene
Vegetation
22,000 11,000 8,000 4,000
“Sonoran Desert”
11000-8000 ybp, Early Holocene
• Climate
22,000 11,000 8,000 4,000
Sonoran Desert
8000-4000 ybp, Mid Holocene
• Vegetation
22,000 11,000 8,000 4,000
Sonoran Desert
8000-4000 ybp, Mid Holocene
• Climate
22,000 11,000 8,000 4,000
Sonoran Desert
4000 ybp - present, Late Holocene
• Vegetation
22,000 11,000 8,000 4,000 0
Sonoran Desert
4000 ybp - present, Late Holocene
• Climate
22,000 11,000 8,000 4,000 0
Packrat Midden Summary
for
Sonoran Desert:
Packrat Midden Summary
for
Sonoran Desert:
Graphically it looks like this…
SW VegetationSW Vegetation
And this…And this…
• Alluvium: (n)
• Alluvial: (adj)
• Stratigraphy: (n)
• Alluvial stratigraphy:
• Recent geology (Pleistocene-Holocene).
2. Alluvial Stratigraphy of the SW: Definitions…
2. Alluvial Stratigraphy of the SW (Holocene)
Alluvial Stratigraphy sites…
“Filling in”DEPOSITION
“carving out”EROSION
Replication
Why are sediment sites so common in SW?
• It’s like a jig-saw puzzle
• Distinct layers– Color– Texture– Fossils
• Separated by time– Erosion– Soil
In The Field
Layers C-14 dated
Alluvial History: Climatic Interpretation
Summary
3. Dendrochronology (past 300 – 400 years)
• Dendroclimatology
• Subdiscipline of dendrochronology
– Reconstruct past climate
– Heavily replicated
• Within sites
• Within regions
Dendrochronology recap…
We’ve Seen This Before
Summary Paleoenvironments of SW
