Preservation of organic matter

A comparison of organic matter (OM) components in cores from Dabob Bay (oxic bottom waters) and Saanich Inlet (anoxic bottom waters) indicates that 02 availability ultimately has little or no independent effect on OM preservation in these environments (Cowie Hedges, 1992). Comparative analyses of organic compounds in sediment traps and bottom sediments from Saanich Inlet indicates that the anoxic benthic interface is an important site of diagenesis, and that selective removal takes place at both compound-class and molecular levels (Cowie etal., 1992). Preferential loss of marine organic material is indicated by the calculated delta-C-13 value and biochemical composition of the substrate. 

Framvaren has a well documented history of environmental change from fjord to lake and then back to a fjord. Sediment cores from both oxic and anoxic past environments contain organic carbon contents of 6-18% and reveal complex distributions of lipid compounds, the dominant classes being n-alkanes, n-alcohols, sterols and long-chain alkenones (Ficken Farrimond, 1995). The alkenones, which are predominantly produced by marine prymnesiophyte algae, are most abundant in the fjord facies of both cores, but are also detectable in the lacustrine sediments, albeit in much lower concentrations. The dramatic increase in abundance of these compounds is interpreted to record the change in environment from lake to fjord. 

These studies present great promise that bottom sediments in anoxic fjords may hold important keys to unlocking the past, particularly with regards to global climate change history. 

Anderson, R.F., Lehuray, A.P., Fleisher, M.Q. and Murray, J.W. (1989) Uranium deposition in Saanich Inlet sediments, Vancouver Island. Geochimica et Cosmochimica Acta, S3, 2205-2213. 

Anschutz, P., Sundby, B., Lefran ois, L., Luther III, G.W. and Mucci, A. (2000) Interactions between metal oxides and species of nitrogen and iodine in bioturbated marine sediments. Geochimica et Cosmochimica Acta, 64, 2751-2763. 

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Hare, PE. and von Endt, D. 1990 Variable preservation of organic matter in fossil bone. Annual Report of the Director of the Geophysics Laboratory. Carnegie Institution, Washington. 1989-1990. Washington, D.C., Carnegie Institution ofWashington 115-118. 

Hedges, J.I., J.A. Baldock, Y. Gelinas, C. Lee, M.L. Peterson, and S.G. Wakeham. 2001. Evidence for non-selective preservation of organic matter in sinking marine particles. Nature 409 801-804. 

Pederson, T.F., G.B. Shimmield, and N.B. Price. 1992. Lack of enhanced preservation of organic matter in sediments under the oxygen minimum of the Oman Margin. Geochimica et Cosmochimica Acta 56 545-551... 

Simoneit BRT, Natural hydrous pyrolysis — Petroleum generation in submarine hydrothermal systems, in Whelan JK, Farrington JW (eds.). Productivity, Accumulation and Preservation of Organic Matter in Recent and Ancient Sediments, Columbia University Press, New York, 368-402, 1992. 

Kaiser K. G. Guggenberger (2000) The role of DOM sorption to mineral surfaces in the preservation of organic matter in soils. Org. Geo-chem. 31 711-725... 

The writer believes that there is a direct relationship between these acid distillate compounds and sedimentary environments which favored production and preservation of organic matter. 

Controls on the Preservation of Organic Matter in Estuarine Sediments... 

The preservation of organic matter in coastal and estuarine sediments is believed to be principally controlled by productivity, sedimentation accumulation rate, bottom water and sediment redox conditions, and sorption as a function of specific surface area of sediments (see review, Hedges and Keil, 1995). In this section the focus will be primarily on factors controlling preservation or organic matter in estuarine sediments the use of chemical biomarkers for historical paleo-reconstruction of past estuarine environments is discussed in chapter 15. 

The preservation of organic matter in coastal and estuarine sediments is believed to be principally controlled by productivity, sedimentation accumulation rate, bottom water and sediment redox conditions, and sorption as a function of specific surface area of sediments. 

Sun, M.Y., and Wakeham, S.G. (1994) Molecular evidence for degradation and preservation of organic matter in the anoxic Black Sea Basin. Geochim. Cosmochim. Acta 58, 3395-3406. 

Perel man (1968) points out that in neutral waters true dissolved molecules of undissociated Fe(OH)3 can also occur in predominant amount (compared to Fe " ion). Probably the molecules of Fe(OH)3 are stabilized by organic acids. It is important that transport in the form of true ionic solutions is possible only for divalent iron, while trivalent iron migrates mainly in the form of colloids and organic compounds. However, Castano and Garrels (1950) believe that aerated waters provide conditions adverse to the preservation of organic matter itself. The available data suggest that organic matter decomposes at the same rate at which it arises. 

Keil R. G. and Hedges J. I. (1993) Sorption of organic matter to mineral surfaces and the preservation of organic matter in coastal marine sediments. Chem. Geol 107, 385-388. 

Pratt L. M. (1984) Influence of paleoenvironmental factors on preservation of organic matter in the Middle Cretaceous Green Formation, Pueblo, CO. Am. Assoc. Petrol. Geol. Bull. 68, 1146-1159. 

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