Sedimentary record variation

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."... 

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. 

Sinninghe Damste J.S., Keeley B.J., Betts S.E., Baas M., MaxwellJ.R., de LeeuwJ.W. (1993b)Variations in abundances and distributions of isoprenoid chromans and long-chain alkylbenzenes in sediments of the Mulhouse Basin a molecular sedimentary record of palaeosalinity. Org. Geochem. 20, 1201—15. 

The concept for a marine paleoredox proxy based on variations in the U isotope ratio in sediments is very similar to the Mo isotope paleoredox proxy described earlier in this chapter. Since incorporation of U in oxidizing sediments such as ferromanganese crusts results in preferential removal of isotopically light U, and incorporation of U in reducing sediments results in preferential removal of isotopically heavy U, changes in the relative proportions of these two sinks over time should drive systematic shifts in the isotopic composition of U in seawater. In turn, these temporal shifts in the isotopic composition of seawater should be manifested as vertical fluctuations in in the sedimentary record. Excursions in the sedimentary record towards lighter values of (in any of these... 

Tsunamis as Paleoseismic Indicators, Fig. 4 Sedimentary record after tsunami landfall and variation of deposits along sandy shores, with respect to tsunami wave trains, run up and depositional environments. Different colors reflect deposits of differing ages and thickness. Note also the varying topographic height of deposits... 

The advent of new techniques to collect undisturbed sediment cores, with well preserved sediment - water interface has brought into sharper focus the various deep sea sedimentary processes, their rates and their effects on the preserved records. As mentioned earlier, recent studies have shown that the record contained in sediments is not a direct reflection of the delivery pattern of a substance to the ocean floor as has so far been assumed the record is modified as a result of several complex physical, chemical and biological processes. Therefore, information on the temporal variations in the tracer input to oceans, if sought, has to be deciphered from the sediment-residuum. In the following we consider one specific example of retrieval of information from the sediment pile the application of deep sea sediments to obtain historical records of cosmic ray intensity variations. 

Review of the isotope geochemistry of the transition metals is continued by Albarede (2004) in Chapter 11, where isotopic variations in Cu and Zn are discussed. The significant changes in bonding environments of Cu(I) and Cu(II) produce significant differences in 5 Cu values for oxidized and reduced Cu compounds, and isotopic variations of up to 9%o are observed in nature. Isotopic variations of Zn are significantly more restricted, where 5 Zn values vary by less than 2%o, but systematic variations are recorded in Fe-Mn nodules from the ocean floor. Measurable isotopic variations are found for Cu and Zn in sedimentary rocks, as well as ore deposits, and this remains a promising aspect of future Cu and Zn isotope studies. 

Freeman KH, Hayes JM (1992) Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochem Cycles 6 185-198 Freeman KH, Hayes JM, Trendel JM, Albrecht P (1990) Evidence from carbon isotope measurements for diverse origins of sedimentary hydrocarbons. Nature 343 254-256 Freyer HD (1979) On the C-record in tree rings, I, C variations in northern hemisphere trees during the last 150 years, TeUus 31 124-137... 

---