Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmpp33b1550v&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #PP33B-1550
Other
1041 Stable Isotope Geochemistry (0454, 4870), 3344 Paleoclimatology (0473, 4900), 4914 Continental Climate Records, 4946 Milankovitch Theory, 9604 Cenozoic
Scientific paper
Part of one of the largest petroleum reserves in the world, the Green River Formation of the Uinta and Piceance Creek basins of Utah and Colorado, formed in a huge Eocene lake system during the warmest, most equable period in recent Earth history. Despite the unit's great potential economic importance and correspondingly large number of geochemical analyses and the preeminent role of these strata in Milankovitch theory (Bradley, 1929), there are surprisingly few systematic studies of the geochemistry of the characteristic permeating cyclicity. Here, we report multiple proxies of lacustrine ecosystem dynamics including oil shale yields, sedimentary facies, carbon and nitrogen isotopes, and molecule-level carbon isotopes from the most oil-rich parts (including the Mahogany oil shale zone) from a series of cores and outcrops in a transect across the Uinta and Piceance Creek basins spanning ~500 m stratigraphically and 3.2 m.y. temporally. Our initial results show covariation in sedimentary facies, oil shale yield, TOC, C/N ratios, and δ13Corg in the expected Milankovitch periodicities, although significant lateral and vertical changes in accumulation make the relative spectral power in the precessional range rather weak. There are, however, differences in the mode of response with oil shale yield, TOC, and sedimentary facies showing more power in the precessional range, while C/N ratios track the 100 ky cycle. C/N ratios tend to be high through multiple precessional cycles dominated by kerogen derived from microbial organic matter suggesting persistent anoxia and a large resulting pool of hypolimnetic ammonium. This pool was eliminated during low lake stands and C/N values then fluctuate through several precession controlled steps. The δ13Corg record, while showing a signal coherent with that of other proxies, has a rather complicated relationship with other proxies, the analysis of which is in its early stages. Molecule-level δ13Corg analysis of n-alkanes suggests mixing of carbon from different sources of varying isotopic composition, and presents a dramatically different pattern from that seen in published studies of the saline facies of the formation. Based on our results, the Milankovitch cyclostratigraphy of these cores in concert with that from the rest of the Uinta and Piceance basin sections, can provide a basis for a time scale for continental environments and pivotal mammalian evolution during the hot-house Eocene.
Eglinton Timothy I.
van Keuren M. A.
Whiteside J. H.
No associations
LandOfFree
Astronomical pacing of ecosystem function in the Green River Formation of Utah and Colorado does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Astronomical pacing of ecosystem function in the Green River Formation of Utah and Colorado, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Astronomical pacing of ecosystem function in the Green River Formation of Utah and Colorado will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1243560