Holocene stratigraphy of the Dead Sea: Correlation of high-resolution seismic reflection profiles to sediment cores

The northern basin of the Dead Sea is occupied by a similar to 300-m-deep l ake. A series of cores in the deep-water part of the lake provide informati on about the top 365 cm of the sediments. The cores were correlated with hi gh-resolution 3.5-kHz seismic profiles from this area and provide lithologi c and age constraints for the high-resolution seismic reflection data. Visu al comparison of the two data sets shows that strong surface and shallow su bsurface reflectors (A and B) correlate to the massive salt at the seafloor surface and the indurated salt at the base of the cores, respectively. Cal culations of an average seismic velocity based on the interval between thes e reflectors and the corresponding sedimentary thickness yield an average 3 500 m/s velocity. This agrees closely with velocities determined from direc t measurements of compressional velocities for sediment samples. Ultrasonic wave velocity measurements of salt samples from the cores and dry rock sal t cores from the southern basin of the Dead Sea indicate that wave velociti es are independent of the burial depth at shallow depths; however, velociti es show strong dependence on porosity. At low hydrostatic pressure a reduct ion in porosity as well as closure of microcracks in the crystals cause an increase in the velocities. This increase disappears at higher stress level s. Synthetic seismograms of the upper 3 ms and the entire 25 ms penetrated by the seismic profiles reinforce the lithologic and seismic stratigraphic correlation and confirm that prominent reflectors in the basin represent th e top boundary of halite layers which are separated by laminated sequences of evaporites and clastics. The salt in the upper salt sequence is deposite d at a very fast rate of more than 20 mm/yr. However, at shallow depths, co nsiderable compaction takes place. Variations in appearance and velocities of the upper salt sequence and middle salt sequence indicate that the porou s, granular, and fine-grained precipitates of the surface salts are diagene tically altered to a coarse and compact crystalline aggregate by re-solutio n and crystallization with burial. The sedimentary sequences recovered in t he cores suggest that significant lake level fluctuations took place in the past in response to climatic changes. The detailed correlation of the core s and seismic profiles makes it possible to extrapolate climatic data from earlier periods beneath the maximum core penetration by analyzing the seism ic stratigraphic sequences of the seismic reflection data.