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| Titel |
Testing the Orbital Hypothesis for Climate Variability in the Lacustrine Green River Formation |
| VerfasserIn |
Kevin Lewis, Adam Maloof |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053526
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| Zusammenfassung |
| The Eocene Green River Formation of the western United States
represents one of the most often cited examples of cyclicity preserved
in a continental sedimentary succession. Up to hundreds of meters of
strata were deposited in a series of large, shallow lacustrine basins.
Preservation of a number of organic-rich intervals has also made the
Green River Formation an economically important oil shale resource.
Several studies have drawn a potential link between repetitive facies
indicating fluctuating lake levels, and orbital Milankovitch
cyclicity. However, few attempts have been made to quantify the
cyclicity, or rigorously demonstrate that orbital climate forcing had
enough of a control on sediment input to imprint a signal above the
noise level of autogenic variability. Among these, Machlus et al. [2008]
used oil yield data from cores as a proxy to evaluate the presence of
significant periodicities in the strata. Although there appears to be
significant sub-Milankovitch variability in the Green River Formation,
spectral peaks identified at longer wavelengths show a promising
correspondence to known orbital frequencies.
We have collected a diverse array of new data sets to evaluate the
presence of spatial periodicity in the Piceance and Bridger basins of
Colorado and Wyoming. These include color, lithology and grain size
records obtained from field work, along with analysis of cores and
high-resolution multi-spectral remote sensing images. Core records
allow us to directly compare physical properties with existing oil
yield records, while providing higher spatial resolution and
depositional context. Due to the fact that organic content controls a
large fraction of the visual variability within the sediments, our
continuous color record has an excellent correspondence to previously
analyzed oil-yield records. Additionally, we have undertaken a wider
characterization of the Green River stratigraphy from remote sensing
data. Using stereographic satellite images, we have derived 2~m scale
Digital Elevation Models of our field sites. From these, we are able
to extract geometrically corrected multi-spectral color and slope
records at meter-scale stratigraphic resolution. These data in
particular allow us to document lateral variability within the
sedimentary basins. Pietras et al. [2006] presented evidence of lateral
impersistence among individual cycles, implying that the
reconstruction of a continuous climate record would be difficult. We
will present the results of our multi-scale characterization of the
Green River formation, assessing both temporal and lateral
variability, and their implications for both astrochronological tuning
and climate cyclicity. |
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