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The Marsh Underground
Published in Robert H. Kadlec, Treatment Marshes for Runoff and Polishing, 2019
Marker methodology is simple in concept: place a recognizable material on the soil surface, and come back later to see how much new material has been deposited on top. But care must be taken in measurement. One method is the use of cryogenic sampling, in which the soil is frozen so as to not disturb the profile. Cryogenic cores are obtained using a straight copper tube with a sharp, closed tip pushed into the sediment far enough to extend through the feldspar marker horizon, and then filled with liquid nitrogen to freeze the sediment adjacent to the tube. The frozen cores were then pulled out and the distance from the sediment surface to the feldspar marker is measured in several places around the circumference of the core. The top is determined by simply observing the interface between brown ice and white ice.
Accretion
Published in Lisamarie Windham-Myers, Stephen Crooks, Tiffany G. Troxler, A Blue Carbon Primer, 2018
This isotope is the result of nuclear fission, and it was spread throughout the northern hemisphere in the 1950s and early 1960s as a result of atmospheric testing of nuclear bombs. The maximum abundance of 137Cs in an undisturbed sediment column reflects the sediment surface in 1963, when testing was at a maximum and just prior to the international agreement that lead to the abolition of atmospheric nuclear bomb testing (Ritchie and McHenry 1990; Reide Corbett and Walsh 2015). The peak of 137Cs activity is directly analogous to a marker horizon that was laid down at that time, and the location of peak within the sediment column provides an average rate of sediment accretion or mass-based accumulation since 1963 (DeLaune et al. 1978; Milan et al. 1995). With a half-life of 30.2 years, 137Cs peaks from 1963 are likely to be found in undisturbed soils for many decades into the future, although they will continue to decline in activity over time (Ritchie and McHenry 1990; Nolte et al. 2013). There also can be more local signals that may provide secondary peaks and additional dating opportunities. For example, the Chernobyl nuclear accident in April 1986 resulted in a plume of 137Cs that has been used to date sediments in northern Europe (Callaway et al. 1996). Spills from power plants or other accidents could also be used to date sediments with local sources (Tsompanoglou et al. 2011). Activity of 137Cs is measured using gamma spectroscopy.
U–Pb geochronology and palynology from Lopingian (upper Permian) coal measure strata of the Galilee Basin, Queensland, Australia
Published in Australian Journal of Earth Sciences, 2018
L. J. Phillips, J. L. Crowley, D. J. Mantle, J. S. Esterle, R. S. Nicoll, J. L. McKellar, A. Wheeler
The Yarrabee Tuff is a prominent regional marker horizon that lies stratigraphically between the underlying Fort Cooper Coal Measures and the overlying Bandanna–Rangal–Baralaba coal measures in the Bowen Basin. Several studies of this ash have yielded ages of 252.54 ± 0.04 Ma (Metcalfe et al., 2015), 252.69 ± 0.16 to 253.07 ± 0.22 Ma (Ayaz et al., 2016) and 252.85 ± 0.07 to 252.92 ± 0.07 Ma (Esterle et al., 2017) (Figure 2b). Given the proximity of the Bowen and Galilee basins (Figure 1), it is reasonable to suggest that the Yarrabee Tuff would also be present in the Galilee Basin; however, it has yet to be identified there.