Abstracts
197
precipitated close to equilibrium with atmospheric CO2. Radiocarbon ages are in sequence and are
believed to be representative. Apparent ages of Cardium are about 2000 years older than expected
from a supply of old carbon through the vertical seepage of the confined aquifer. No correction
is possible from the 13C content of the carbonates, possibly because of biological effects in the
system.
The age discrepancy between carbonate shallow water and interstitial waters of bottom mud cannot
be reconciled by U/Th measurements. Uranium appears to be thoroughly leached, leading to
excesses of 230Th and to ages that are too old. Assuming the age is representative of the inorganic
calcite, we can evaluate the amount of leached uranium in the shallow deposits and its
accumulation in the deeper reduced horizons of the profile.
We also discuss implications for age estimates of continental deposits.
SAPROPEL CHRONOLOGY AND NILE RIVER DISCHARGE
DURING THE HOLOCENE
MICHEL FONTUGNE, MA URICE ARNOLD, LOUIS LABEYRIE and JEAN CLAUDE DUPLESSY
Centre des Faibles Radioactivit6s, CNRS, 91198 Gif sur Yvette Cedex, France
Organic-rich layers (more than 2% organic carbon) occur in deep eastern Mediterranean Sea
sediments. These sapropels were attributed to the stratification of the seawater column due to a
large input of fresh water, mainly associated with a Nile River discharge which inhibited the
thermohaline convection. 14C AMS determinations performed on the base of the sapropel show
the synchroneity of the event at 8600 BP over the whole eastern Mediterranean Sea, recording the
beginning of the major pluvial period during the Holocene. Oxygen isotopic values from core MD
84641 taken in the Nile River fan show that the large input of Nile water was maximum between
8600 and 8000 BP, and decreased drastically after that time.
THE HOLOCENE CLIMATIC RECORD IN THE SALT CAVES OF MOUNT SEDOM,
ISRAEL
AMOS FRUMKIN', ISRAEL CARMI2, MORDECAI MAGARITZ2 and ISRAEL ZAK3
The climatic history of the Dead Sea during the Holocene was reconstructed from data on outflow
levels and geometry of caves in Mount Sedom, and from ages of 33 plant remains found in the
caves. The salt diapir of Mount Sedom emerged from the Dead Sea early in the Holocene. A
small watershed on the top of the mountain accumulated water, which dissolved shafts and,
afterwards, caves in the rock salt, and also swept plant remains into the caves. The widths of the
caves varied between less than 100% and 400% of the width of the presently active cave, due to
variations in the amount and intensity of rains.
The upper and middle Holocene was divided into ten stages of alternating dry and humid climate,
each characterized by the stand of the Dead Sea (high stands at 7000, 4500, 3000 and 1000 BP),
and by the climate of the Dead Sea region and the conditions on the top of Mount Sedom. The
changes in climate are within a period of about 1000 years. Good correlation was found with the
1Israel Cave Research Center, 90906
4fra, Israel
Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, 76100 Rehovot, Israel
3Department of Geology, The Hebrew University of Jerusalem, Jerusalem, Israel