Mahogany zone

The bulk Ca and S contents of the raw Estonian kukersite oil shale are rather high (Table 5), considerably larger than those of the Green River oil shale in Colorado (Mahogany Zone, cf. Table 8). However, the Green River oil shale is richer in Mg, Na, K, and Al, as well as in most of the trace metals and metalloids. 

Table 8. Elemental concent rations determined in raw (i.e., feedstock). retorted. and after low-temperature ash (LTA) of oil shale from Green River Formation. Mahogany Zone, (GRFMZ). USA...

Saether, O. M., Runnells, D. D., Ristinen, R. A. Smythe, W. 1981. Fluorine its mineralogical residence in oil shales of the Mahogany Zone of the Green River Formation, Piceance Creek Basin, Colorado, USA. Chemical Geology, 31, 169-184. 

The examination of MI fluorescence spectra of the analogous fractions from the LC of a shale-derived oil (from a simulated in situ bum from Mahogany zone of Green River shale) reveals the presence of the same compounds, in the same fractions, as in the Synthoil fractions. The fluorescence spectra of the shale oil and Synthoil fractions have similar overall appearances. Quantitative analyses for pyrene, benz[a] anthracene (BaA), chrysene, and benzo [a] pyrene (BaP) were performed in the shale oil fractions the results are listed in Table I. 

Figure I. Distributions of Fe, Al, S, Ca, and C along length of Mahogany zone shale. Letters on photomicrograph refer to areas described in text.

Figure 2, Scanning electron micrograph (SEM) and S, Fe, Co, Mg, C. Si, Al, Na, and K x- ay intensity distributions in dark band of Mahogany zone shale...

The sediments deposited in this possible oil shale lake began being deposited about the same time as the earliest deposition in Wyoming and in Colorado, elastics from Uinta Mountain activity apparently destroyed the Utah lake, but oil shale deposition returned to Utah when Colorado s Lake Uinta expanded during the time of deposition of the Mahogany zone (8). 

Table I. Average Element Composition of Organic Matter in Mahogany Zone Composites...

A similar set of results were obtained for the elemental composition of ash at 1000°C from these 10 Mahogany zone oil shale composites. The averages of these results is given in Table II with 95 percent confidence limits of the averages. 

Figure 7. x-Ray diffraction of minerals in 10 Mahogany zone composites. 

This mode of deposition over a wide area explains the lateral uniformity observed in element composition of organic matter in Mahogany zone oil shale (16), and the similarity in properties of the oil-shale organic matter over the entire deposit. The paucity of macrofossils in the oil shale, limited largely to an occasional gar scale and the like, illustrates the power of the lake s lower layer to digest organic matter. 

Inorganic Geochemistry of Mahogany Zone Oil Shale in Two Cores from the Green River Formation... 

In northwest Colorado, the Parachute Creek Member of the lacustrine Green River Formation (Eocene) contains thick sequences of rich oil shale that were deposited in ancient lake Uinta. The richest sequence and the richest oil-shale bed within the Parachute Creek Member are called the Mahogany zone... 

Table I. Chemical abundances (x), standard deviation (s.d.), and observed range of major and trace elements in Mahogany-zone samples from oil-shale cores 01-A and CR-2...

Figure 2. Observed ranges and geometric means of elemental abundances in 01-A and CR-2 Mahogany zone core samples. Average shale (16) and average black shale (17) are...

The Mahogany zone of the Green River Formation is rich in carbonate-related elements and poor in most trace elements compared to an average shale or average black shale. The two cores have similar chemistry, although CR-2 samples have more Ca, Cu, La, Ni, Sc, and Zr and 01-A samples have more As and Sr. These differences probably reflect slight differences in depositional conditions, sediment source areas, or diagenesis. 

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