tivity on the carmel faul

crystal lattice; (5) when detrital Th is known and corrected for (Kaufman et al., 1998); (6)
when analytical and counting errors as well as decay constants are known.
As mentioned above, a U-series radionuclide system should be closed to postdepositional
migration or addition constituent nuclides. Material analysis should be done in
order to avoid working with the following materials: (1) Authigenic material that shows
evidence of weathering. (2) Any sign of recrystallization, such as conversion from aragonite to
calcite, since it is indicative of potential nuclide migration (Bar-Matthews et al., 1997). Denya
Cave speleothems are dense, macrocrystalline calcites, showing no weathering and
recrystallization effects. In addition, the cave was closed to the surface until the construction of
Denya neighborhood. It is therefore assumed that Denya Cave is a closed system.
In this study dating with the 230 Th/U method was conducted on a Multiple Collector
Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS), which produces high
analytical precision and enables work on a small sample (~0.1g) that in turn gives ages at a
high resolution, due to the ability to sample individual laminae. Results may yield ages which
have an error margin of ca. 1% or less.
For reasons which are explained bellow (ch. 3.3- Dating of seismite samples) two sets of
ages are presented in this study;
1. Based on age equation [1] according to Broecker and Kaufman (1965):
[1] [ 230 Th/ 234 U] = [ 238 U/ 234 U]*(1-e -λ230t ) + {1-[ 238 U/ 234 U]}*{λ 230 /(λ 230 -λ 234 )}*[1-e (-λ230-λ234)t ]
The calculation of age is done using the Newton-Raphson iteration in which the final age and
the analytical error (±2σ) is given. This equation was used for dating single samples.
2. Based on age equation [2] according to Broecker (1963):
[2] [ 230 Th/ 238 U] = (1-e -λ230t ) + {[ 238 U/ 234 U] - 1}*{λ 230 /(λ 230 -λ 234 )}*[1-e -(λ230-λ234)t ]
The calculation of age is done using Isoplot3.7 by Ludwig (2008) with a first derivative
estimation for samples of similar ages plotted on isochron lines (sample age clusters). Here too
the analytical error (±2σ) is given.
In both equations the constants are:
λ 230 = 9.195 x 10 -6 y -1 – 230 Th constant
λ 234 = 2.835 x 10 -6 y -1 – 234 U constant
t –years.
All ratios presented here and in the following passages in brackets represent ac<strong>tivity</strong>
ratios. Those equations are based on the assumption that no initial 230 Th is present in the
sample and that all of the U is derived from the water, rather than from detrital material or
other sources. These assumptions hold well for speleothem samples containing negligible
amounts of detrital Th, but a correction must be made for it in all other samples. Initial 230 Th is
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