Varved sediments

DeMaster D. J. and Turekian K. K. (1987) The radiocarbon record in varved sediments of Carmen Basin, Gulf of California a measure of upwelling intensity variation during... 

Zhao M., Eglinton, Read G. G., and Schimmelmann A. (2(X)0) An alkenone (U37) quasi-annual sea surface temperature record (AD 1440 to 1940) using varved sediments from the Santa Barbara basin. Org. Geochem. 31, 903-917. 

Schimmelmann A. and Kastner M. (1993) Evolutionary changes over the last 1000 years of reduced sulfur phases and organic carbon in varved sediments of the Santa... 

Alonso-Zarza, A.M. (2003) Paleoenvironmental significance of palustrine carbonates and calcretes in the geological record. Earth-Science Reviews 60, 261-298. Anderson, R.Y. (1961) Solar-terrestrial climatic patterns in varved sediments. 

Proceed immediately with step 3, 4 and 5 if images of the fresh sediment surface are desired. In varved sediments, the colour of the fresh sediment is sometimes determined by iron species and the sediment must be oxidised for a couple of days before digitizing (Renberg, 1981a Petterson et al., 1993, 1999). 

Provided that a statistical relationship between grey-seale and sediment composition can be established, image analysis can be used to infer fluxes of sediment components in records containing thousands of years. Ifa varved sediment is used, annual or perhaps even seasonal resolution can be obtained. Petterson et al. (unpublished) have inferred the annnal accumulation rate of minerogenic matter for 6400 years in Kassjon (Sweden). 

Pore water data have been presented by Benoit Hemond (1991) to support redistribution of Pb. Such a finding has not been reported by other researchers. Indeed, studies of2 "Pb in varved sediments have failed to detect migration (e.g., Appleby et al., 1979 Crusius Anderson, 1995). While not being able to explain this discrepancy, Hamilton-Taylor Davison (1995) conclude that an overwhelming body of evidence supports the view that Pb is only minimally mobile in lake sediments. 

Dean, W. E., 1993. Physical properties, mineralogy, and geochemistry of Holocene varved sediments from Elk Lake, Minnesota. In Bradbury, J. P. W. E. Dean (eds.) Elk Lake Minnesota Evidence for Rapid Climate Change in the North-Central United States. Geol. Soc. Amer. Spec. Paper 276 97-113. 

Granar, L., 1958. Magnetic measurements on Swedish varved sediments. Ark. f. Geofys. 3 1-40. 

Calvert, S.E. 1966b. Origin of diatom-rich, varved sediments from the Gulf of California. Journal of... 

Varves suggest themselves as another data base from which to evaluate the history of the climate. These are sequences of sediment layers deriving from fresh water streams, the summer sediment having a different particle size and color than does the spring sediment, so that the deposit for each year becomes visible... 

Varve or rhythmites chronology is another approach based on the examination of geological materials. In this model, the distribution of the laminated sediments formed in the bottom of the beds of dried-out lakes (as a consequence of the seasonal melting of glaciers and the subsequent deposition of coarse particles supplied by streams, followed by finer materials such as sand, silt, and clay) is analyzed and correlated with climate changes [64],... 

Esser and Turekian (1988) estimated an accretion rate of extraterrestrial particles in ocean bottom and in varved glacial lake deposit on the basis of osmium isotope systematics and concluded a maximum accretion rate of between 4.9 x 104 and 5.6 x 104 tons/a. The discrepancy between this estimate and those derived from helium can easily be attributed to the difference in the size of the cosmic dust particles under consideration. Cosmic dusts of greater than a few ten micrometers may not be important in the helium inventory of sediments because the larger grains are likely to lose helium due to atmospheric impact heating (e.g., Brownlee, 1985). Stuart et al. (1999) concluded from studies on Antarctic micrometeorites that 50- to 1 OO-qm micrometeorites may contribute about 5% of the total flux of extraterrestrial 3He to terrestrial sediments. Therefore, the helium-based estimate deals only with these smaller particles. 

The measurements on Fairbanks Barbados corals spurred efforts to find other means of extending the calibration curves back in time. Several tacks were taken. One obvious strategy was to count annual layers (varves) in lake and marine sediments. Smiver, the hero of the calibration effort, had adopted this approach way back in the... 

Nijampurkar V. N., Rao D. K., Oldfield F., and Renberg I. (1998) The half-life of Si a new estimate based on varved lake sediments. Earth Planet. Sci. Lett. 163, 191-196. 

Young D. R., Johnson J. N., Soutar A., and Isaacs J. D. (1973) Mercury concentrations in dated varved marine sediments collected off southern California. Nature 244, 273-275. 

Mammoth Cave provides excellent exposures of slackwater facies (Fig. 4). At the tops of most sediment piles is a layer, seldom more than a few cm thick, of thinly layer clay and very fine silt. Some of these sedimentary layers are varved, apparently representing an annual cycle of flooding with the rise and fall of the ancestral Green... 

Foraminifera from the sediments of the Cariaco Trench (Fig. 7.6) (Hughen et al, 2004). Since the sediments of this anoxic basin are varved, the age filter applied to most sediment cores by bioturbation is not an issue. Calendar ages of the varves in the sediments of this basin were determined by matching the percent reflectance (a measure of the color of the sediments) with 5 0 variations in the ice of a Greenland ice core (described later in Fig. 7.19). Since the latter record is precisely dated back to 40 000 years by actual counting of annual ice layers, and the two records are undeniably correlated, it was possible to determine an accurate calendar age for the Cariaco Trench sediment core by using variations in the percent reflectance record. The results in Fig. 7.6 indicate offsets of up to 5 ky between C age and calendar age at about 30 ky BP and an abrupt shift at 40 calendar kiloyears (cal. ky) BP in which 7000 C years elapsed in only 2000 y. The results have been explained as variations in the source function and the ventilation of the deep sea and are now used to correct C dates back to more than 40 cal. ky BP. 

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