Provenance of quartzite clasts in the EoceneOligocene Sespe Formation: Paleogeographic implications

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Provenance of quartzite clasts in the
Eocene-Oligocene Sespe Formation
Paleogeographic implications for southern
California and the ancestral Colorado River
Jeffrey L. Howard, Wayne State University
GSA Bulletin, November 2000, v. 112, no. 111
Presented by David McAlpin, 11 November 2006
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Eocene-Oligocene time frame
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Concept of Eocene-Oligocene North America
http//jan.ucc.nau.edu (Ron Blakey)
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Sespe Formation
http//www.csun.edu/geology/SMM_Hike/smmhikeday3.h
tm14
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Provenance of quartzite clasts in the
Eocene-Oligocene Sespe Formation
Paleogeographic implications for southern
California and the ancestral Colorado River
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Los Angeles Basin and major geologic provinces of
the SW United States
Modified from Howard, 1995
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Sespe Formation Stratigraphy
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Petrographic composition of orthoquarzite clasts
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Petrographic composition of orthoquarzite source
rocks
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Precision based on Confidence intervals versus
standard deviation
CI tSK ½
From Howard, 1994
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Paleographic ReconstructionEocene-Oligocene
Southern California
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Conclusions

• Sespe provenance is consistent with Mojave and
  Sonora Desert provenance
• Dextral displacement of San Andreas fault implies
  a spatial coincidence between the Colorado-Gila
  and Sespe paleodelta
• A westward flowing Colorado paleoriver would be
  at least 18 million years older than previously
  thought (huge)
• But not conclusive yet...

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More work

• Trace element analysis on (non-Poway) Sespe-type
  metavolcanics
• Biogeography of modern and fossil faunas of
  Colorado River affinity
• Seismic surveys -- to identify paleochannels on
  subsurface bedrock
• Cores from the lowest overlying strata for
  provenance analysis.

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David B. McAlpin david.mcalpin_at_asu.edu