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Small diameter core samples were taken from outcrops of the Permian Phosphoria Formation and the Cretaceous Pierre Shale of the Western United States to determine the effects of weathering on organic matter in shale outcrops. While the Pierre Shale core showed no evidence of weathering, the Phosphoria Formation showed significant reduction of overall organic content and pronounced changes in organic composition over the near-surface interval of the core. Total organic carbon is lower by as much as 60% over the upper 2 ft of the core. Chloroform-soluble organic matter and total hydrocarbon (C15+) concentrations are 50% lower over this same interval. The ratio of saturated to aromatic hydrocarbons decreases steadily with core depth over the upper 2.6 ft of the core. Aromatic hydrocarbons are enriched in the stable carbon-13 isotope by an average of 1.7%. over this same interval. Shallow core samples also show a loss of n-paraffins relative to branched/cyclic compounds in the saturated C15+ fraction.Although the extent of weathering is variable, certain characteristic effects are recognizable and can be applied to the interpretation of outcrop data in organic geochemical studies. 相似文献
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Harbridge William Pilkey Orrin H. Whaling Patric Swetland Paul 《Environmental Geology》1976,1(4):215-225
The Lake of Tunis in northern Tunisia is a eutrophic marine lagoon covering 45 km2 to an average depth of 1 m. Exchange of water with the Mediterranean Sea is restricted to a few canals. Bottom sediment is
mainly calcareous sandy mud with much organic material. Sand-size grains commonly include quartz, dolomite, gypsum, and pyrite,
as well as calcareous skeletal material dominated by molluscan fragments. Pyrite is the only important authigenic mineral
presently forming. Principal sources of sediment are sewage sludge and fill, calcareous marine organisms, including abundant
worm reefs, and local intermittent streams. The concentrations of Hg, Pb, Cd, Cr, Zn, Cu, and Fe are significantly higher
in Lake of Tunis sediments than in sediments from Bahiret el Bibane, an unpolluted lagoon in the south of Tunisia.
Man has affected the Lake of Tunis in four important ways. (1) Cultivation by early settlers, particularly the Romans, caused
increased regional erosion and probably provided the sediment that encloses the lagoon. (2) In the mid-1800's the French constructed
a ship canal which reduced intralagoonal circulation as well as exchange with the Mediterranean. (3) Nutrient pollution from
sewage has encouraged the growth of circulation-restricting worm reefs, caused eutrophication and fish kills, and produced
H2S odor which permeates the city of Tunis during the summer. (4) Finally, man has significantly reduced the size of the lagoon
by filling the lagoon and operating salt pans. 相似文献
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