Petrography, strontium, barium and uranium concentrations, and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies: Soreq Cave, Israel
A. Ayalon et al., Petrography, strontium, barium and uranium concentrations, and strontium and uranium isotope ratios in speleothems as palaeoclimatic proxies: Soreq Cave, Israel, HOLOCENE, 9(6), 1999, pp. 715-722
The reconstruction of the palaeoclimate of the eastern Mediterranean region
for the last 60 ka BP is based on the delta(18)O and delta(13)C variations
of speleothems from Soreq Cave, Israel. Climatic conditions during most of
the rime interval between 60 and 17 ka BP (the period equivalent to the la
st glacial) were relatively cold and dry, while they were warmer and wetter
from 17 ka BP to the present. At similar to 17 ka BP, there was a major cl
imatic change with a sharp increase in annual rainfall and temperature and
a very wet period occurring between 8.5 and 7.0 ka BP. During the colder an
d drier period, large, detritus-free, preferentially oriented calcite cryst
als were deposited from slow-moving water. As a result of a sharp change in
the hydrological regime at similar to 17 ka BP, fast-moving water started
entrainment of the soil and carrying detrital material into the cave, and t
he calcite crystals deposited became small and anhedral. Coinciding with th
e petrographic and isotopic changes, a sharp drop occurred in the concentra
tions of strontium, barium and uranium, and in the ratios Sr-87/Sr-86 and (
U-234/U-238)(0), which reached mini mum values during the wettest period. T
his drop reflects enhanced weathering of the soil dolomite host rock. Durin
g colder and drier periods, higher trace-element concentrations and higher
isotopic ratios reflect an increase in the contribution of salts derived fr
om exogenic sources (sea spray and aeolian dust), and a reduced contributio
n of weathering from the host dolomites.