Sedimentary records

In this balance SO4 is removed by CaS04 and FeS2 in proportion to their abundance in the sedimentary record (50/50). Ca is removed as CaCOa with enough Mg to correspond to the natural proportions. Chloride is removed as NaCl, and enough H4Si04 is removed to make opal sediments. Some Na is taken up and Ca " ... 

The failure to identify the necessary authigenic silicate phases in sufficient quantities in marine sediments has led oceanographers to consider different approaches. The current models for seawater composition emphasize the dominant role played by the balance between the various inputs and outputs from the ocean. Mass balance calculations have become more important than solubility relationships in explaining oceanic chemistry. The difference between the equilibrium and mass balance points of view is not just a matter of mathematical and chemical formalism. In the equilibrium case, one would expect a very constant composition of the ocean and its sediments over geological time. In the other case, historical variations in the rates of input and removal should be reflected by changes in ocean composition and may be preserved in the sedimentary record. Models that emphasize the role of kinetic and material balance considerations are called kinetic models of seawater. This reasoning was pulled together by Broecker (1971) in a paper called "A kinetic model for the chemical composition of sea water."... 

As shown in Table 11.3, the concentrations of trace elements in the water column is - despite anthropogenic pollution - extremely small (10 11 - 10 7 M) illustrating the remarkable efficiency of the continuous "conveyor belt" of the settling adsorbing and scavenging particles. The sedimentary record reflects the accumulation of trace elements in sediments and a profile of concentration vs sediment-depth (or age) gives a "memory record" on the loading in the past (Fig. 11.9). 

Nriagu, J. O., A. L. W. Kemp, H. K. T. Wong, and N. Harper (1979), "Sedimentary Records of Heavy Metal Pollution in Lake Erie", Geochim. Cosmochim. Acta 43, 247-258. 

Simoneit BRT (1986) In Johns RB (ed) Biological markers in the sedimentary record. Elsevier, New York, p 43... 

Minerals derived from evaporation of saline solutions have not been extensively examined. Evaporitic salts from the western U.S. Great Basin concentrated Li (5 Li = +31.8 to +32.6 Tomascak et al. 2003). Evaporation of thermal waters from Yellowstone yielded travertine with extremely low 5 Li (-4.8 Sturchio and Chan 2003), offset from its coexisting fluid by -ll.l%o. Such evaporites, where preserved in the sedimentary record, could afford an opportunity to examine variations in spring water compositions and hence information on hydrothermal processes over time. 

The unique chemical composition of cosmogenous debris has provided some insight into why approximately 70% of the species of organisms on Earth were driven extinct over a relatively short time interval approximately 66 million years ago. Evidence for this mass extinction has been observed in marine sediments throughout all the ocean basins. In a contemporaneous layer deposited at the end of the Cretaceous period, the hard parts of many species of marine plankton abruptly vanished from the sedimentary record. This sedimentary layer is also characterized by a large enrichment in the rare element iridium. 

Where the waves and currents weaken, resuspended sediment settles back down to the seafloor. Given the small particle sizes of the suspended material (mostly 3 to 10 pm), redeposition can take many years. The resulting redistribution of sediments creates patches of clay, mud, and exposed rock on the continental margins. In other words, resuspension from waves and currents can cause some sediments to become reUct deposits. Hard bottoms can serve as good habitats for some members of the benthos as they promote the formation of coral reefs. For paleoceanographers, relict deposits are problematic because they represent gaps, or imconformities, in the sedimentary record. 

Hoefs J (1970) Kohlenstoff-und Sauerstoff-Isotopenuntersuchungen an Karbonatkonkretionen und umgebendem Gestein. Contrib Miner Petrol 27 66-79 Hoefs J (1992) The stable isotope composition of sedimentary iron oxides with special reference to Banded Iron Formations. In Isotopic signatures and sedimentary records. Lecture Notes in Earth Sci 43 199-213, Springer Verlag, Berlin... 

Simoneit BRT, Cyclic terpenoids of the geosphere, in Johns RB. (ed.), Biological Markers in the Sedimentary Record, Elsevier, Amsterdam, pp. 43—99, 1986. 

Johns RB (ed.) Biological Markers in the Sedimentary Record, Elsevier, Amsterdam, 1986. 

Tosca, N. J., McLennan, S. M., Clark, . C. et al. (2005) Geochemical modeling of evaporation processes on Mars insight from the sedimentary record at Meridiani Planum. Earth and Planetary Science Letters, 240, 122-148. 

Gevao, B., T. Hamer, and K. Jones, Sedimentary record of polychlorinated naphthalene concentrations and deposition fluxes in a dated Lake Core , Environ. Sci. Technol., 34,1, 33-38 (2000). 

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