Paleoclimate and Geologic History of the Mojave Desert

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Paleoclimate and Geologic History of the
Mojave Desert

• A presentation by Crystal Yates-White

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The Mojave Desert
The Mojave is bordered by the Garlock to the
North and the San Andreas to the south and west
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Late Pleistocene Climate
A Period Of Glacial and INterGlacial Epochs

• Glaciers in Canada split jet stream, redirecting
  it over Southwestern US, where storms increased.
• Milankovich cycles lead to periods of increased
  insolation, warming Earth, increasing monsoons,
  and melting glaciers.
• Over the past 2 million years, Southwestern US
  climates have thus cycled between cooler, drier,
  warmer and wetter.

How Do we Know This? Aluvial Fans Evidence of
Pluvial Lakes Afton Canyon
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The life of an Alluvial Fan

• Storm water deposits form fans on mountain slopes

2) Abandoned fans accrue a layer of windblown
sediments
3) Dark-reddish varnish covers the pavements.
4) Calcite evaporites clog pavement pores water
dissects pavement.
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Alluvial Fans of Death Valley
Geologists Use Pavement Dissection As a Clue
to the Relative Ages of alluvial Fans
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What Can Fans tell us about PaleoClimates?

• When hillsides are vegetated, flows of sediment
  are blocked.
• In arid conditions, vegetation will grow sparse.
• Thus, fans must be indicators of periods between
  glacial and interglacial epochs.

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Pleistocene River Basins

• A series of connected basins extending from San
  Bernadino Mountains to Sierra Nevada
• Formed a pluvial lake system, indicating periods
  of increased rainfall and low evaporation.
• Pluvial lakes indicate periods of glaciation to
  the north
• Increased Precipitation due to split jet stream
• Decreased Evaporation due to lower temperatures

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lake Manix and Afton Canyon

• Dating of Anodonta californiensis indicates Manix
  drained within the last 14,500 years.
• Mojave River Basin depths indicate water from
  Lake Manix may have reached Death Valley
• Geological indications of catastrophe
• Lack of recessional shorelines
• Lack of river terraces
• Steep, narrow, verticle-walled tributaries
• Boulders at the base of fan deposits

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Death Valley
Death Valley is a Pull-Apart Basin Resulting from
The convergence Of Two Right-Lateral Faults
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• The Geology of the Mojave gives us clues about
  its Climate History

Pluvial Lake Ranges indicate periods of high
precipitation and low evaporation
Alluvial Fans and Desert Pavement indicate
cycling of glacial epocs over thousands of years
The formation of Afton Canyon shows the extent of
this precipitation and connectedness of lakes