Seeps give tantalizing tease
Dead Sea Geology Promise Unmet
As one approaches the Dead Sea, it is seen to be in a deep valley with an elongated body of water. Soon after starting on the road down, a sign says “sea level,” which tells one that the valley is indeed deep.
Indeed, it is the deepest non-ocean place on earth at 1,378 feet below sea level.
The valley is stark, barren and forbidding, with steep walls around a lake completely devoid of vegetation except for one anomalous occurrence – the oasis around a fresh water stream at En Gedi, where tucked close to the wall are palm trees, oranges and other tropical fruit and vegetables.
By definition, the Dead Sea is a lake, as there are no outlets.
This lake/sea basin is a segment of a rift system that extends from the Red Sea through the Gulf of Elat, through the Dead Sea, Galilee and on to eastern Asia Minor where it merges into the Tarus Mountains.
This rifting is a result of the abrasion between the African tectonic plate on the west and the Asian or Arabian tectonic plate on the east. The rifting began in mid-Miocene, 15 million years ago, and has continued through the Pliocene, Pleistocene and on into historical time.
The eastern plate has moved northward 65 miles along a strike-slip fault system, with 18.6 miles of those having been in the last five million years.
The Red Sea is in a pull-apart graben, but the branch that extends to Elat has narrowed to a rift about 11 miles wide. While the principal movement was strike-slip, there was a significant downward movement. The western wall of the rift is primarily downward with a series of left-stepping fault segments.
The African plate is tending to rotate in a counterclockwise direction, so when there is northward movement, the segment is shifted slightly eastward creating this left-stepping configuration. The west side being essentially normal faulting, the fault planes and segments form a ragged wall of irregular “flat irons” of Cretaceous limestones and marls and Miocene gravel and sandstones.
The downward components of the east and west faults form a deep graben in which the Dead Sea is located.
Steeply dipping faulted strata, west wall Dead Sea graben.
The eastern boundary is a “running-through” fault not like a single saber slash, but a system of closely spaced, sub-parallel faults where movements were transferred from one fault to another.
The north end of the west fault, within a few miles of Jericho, makes an odd turn eastward and rejoins the eastern border fault. The Dead Sea graben is more complex compared to the textbook-like diagram showing fault blocks stepping down from two parallel faults to a central deep.
With all this faulting the region is infamous for its many earthquakes. There are records of earthquakes from very ancient times continuing to present day.
In the Jericho area, toward the end of 2003 and extending into mid-2004, there was an earthquake “swarm” in the Dead Sea fault system of 4.9 magnitude that was felt as far away as Syria, Egypt and the northern part of Saudi Arabia. This was the largest earthquake in the last two decades.
In the present era five destructive earthquakes have occurred in the Dead Sea rift zone. Some of the biblical accounts of damages and disappearances can, in several cases, be related to earthquakes.
When the rifting started, the stratigraphic column of this general area was granitic basement, a series of Paleozoic rocks, Triassic, Jurassic, Cretaceous and early Tertiary of the Oligocene-Miocene. The African plate seems to be the passive one and those strata still exist on the west side. Those that covered the zone of the rift are now at great depths.
The Dead Sea’s east wall graben is of different geology than the west wall. The edge of the Arabial plate has moved northward 65 miles. The trough-going fault system is at a base of the wall. Extending from the eastern shore is the hook-shaped Lissan Peninsula.
The scene on the rift’s eastern side has changed slowly as the Asian plate has moved northward. So they are now quite different from the strata on the westward side.
After the rifting began, the Miocene, Pliocene and Pleistocene continued to be deposited particularly within the rift zone, but also in the widespread Lake Lisan. These strata have been thoroughly studied by David Neev of the Geological Survey of Israel and K.O. Emery of Woods Hole Oceanographic Institution, Mass.
The results of their studies are extensively described in their book The Destruction of Sodom, Gomorrah and Jericho.
The look-alike nature of the younger tertiary strata was separated with the help of palynology (study of pollen and spores). The nature of the sediments indicates, through time, that there were dry, barren periods as well as wet ones in which plants grew. These were not seasonal periods but periods of millions of years in duration.
There are two formations buried in the graben that are of particular importance to the present day surface appearance and activity:
- One of those is the very thick rock salt of the Sedom formation of Late Miocene/Pliocene age described in the next section Halokinesis (salt tectonics).
- The other is the Upper Cretaceous (Cenomanian) bituminous limestone that is responsible for the oil exploration described in the section by that name.
The Sedom is encountered at depths from 4,500 to 8,100 feet in the Dead Sea south basin area. Research in the United States has shown that rock salt becomes plastic at an overburden pressure of depths of about 5,000 feet.
Mt. Sedom, prominent salt diapir, southwest part of the graben.
The Sedom is the “mother salt” for salt domes and pillars. Because of the difference in specific gravity between salt and sediments, upward flowage will be triggered commonly by faulting. Mt. Sedom is the most spectacular salt figure, being a diapir or a piercemont dome that has risen to a height of over 20 feet.
There are two well known domes that reached equilibrium before piercing the surface: En Gedi and the Lisan Peninsula.
A number of years ago, Neev conducted a “sparker” survey of the Dead Sea and showed that there were many incipient domes or small pimples lying under much of the water of the south basin. From the Pleistocene to the Holocene in most of the south basin there are upward concave Listric faults that emanate from salt swells that have developed from normal gravity sliding into areas of salt withdrawal.
In the shallows of the southern Dead Sea, there are interesting “patches” of salt figures that are not due to tectonics, but to the hyper-salinity of the water and the extreme dryness of the air. With the breaking of little wavelets, the dry air will immediately cause little crusts to form and build a small toadstool or other odd forms.
Waters of the Dead Sea
An arm of the Mediterranean existed in the area before the rifting started. As the land rose, the waters drained off, both eastward through the Haifi Channel to the Mediterranean, and southward into the Gulf of Elat.
The rifting started in the early Miocene, crossed this residual arm of the sea isolating a portion of it, which became the Dead Sea segment. The area grew in size, as it was in a wet period and became known as Lake Lisan. Varying levels of Lake Lisan came and went as recorded on the sediment on the walls of the rift.
(Emery and Neev have studied the stratigraphy of the Dead Sea graben and identified these varying levels.)
With time, the sinking of the graben and evaporation reduced Lake Lisan to a smaller area, which became known as the Dead Sea.
Inwash of waters from the surrounding hills brought minerals so that the residual sea water along with evaporation continuously increased the salinity to point where vegetation and aquatic life could not exist.
Though, this body of water was a lake, by ancient references it became known as a sea – a dead sea because of a lack of life.
The waters of the Dead Sea may be devoid of plant and animal life, but they have commercial importance.
In the 1920s, for example, a plant was built on the north end of the Dead Sea to extract potash from the waters. In 1934, it was the largest industrial site in the Middle East. During a structural evolution a sill had formed, which divided the Dead Sea into a deep, north basin and a shallower south basin.
Later, a second extraction plant known as the Dead Sea Works was built on the shore of the south basin. This plant supplied half of Britain’s potash during World War II.
An array of chemical compounds and metals are extracted from these waters. Evaporating ponds are isolated by a system of dikes that, it is said, can be seen from space.
In 2001, Israel produced from Dead Sea brine tons of elemental bromine, caustic soda, magnesium metal and sodium chloride.
Except for a rare rain, the principal supply of water to the Dead Sea is from the Jordan River that flows from the fresh water of Galilee 50 miles into the north end of the north basin of the Dead Sea. In recent years, settlements along the Jordan River Valley have diverted significant quantities of the water for irrigation and other domestic uses.
Consequently, the level of the Dead Sea is of great concern.
A project has been considered to bring waters from the Mediterranean to the Dead Sea, but as yet nothing has been started. The specific gravity of the high salinity waters is such that a person cannot drown in it, but will strangle before drowning. Salt water gargle that is too strong suggests how one may strangle on salt water.
On the Dead Sea’s southwest area there are several hotels and spas that provide therapeutic treatments from the Dead Sea salt and mud for skin diseases and rheumatic conditions. There are at least two American companies that import the raw materials directly from Israel for body and skin care.
Since antiquity, and probably in late geologic time, blocks of asphalt have been found floating in the waters of the south basin. These floating blocks are 99.99 percent pure, solid form of hydrocarbons.
Chunk of asphalt found floating near margin of south basin.
The size of the asphalt blocks has ranged from that of a tennis ball to huge blocks. In the 1930s there were pieces the size of an automobile and an occasional piece the size of a small island on which a man could stand.
The appearance of asphalt is sporadic, but none of any great size has appeared in the last 30 years. Pieces of the size shown in the picture on page 50 are fairly commonplace.
The asphalt is chemically pure, except that it is usually associated with sulfur compound. The origin of the asphalt is uncertain and has been the subject of considerable debate:
- One theory is that it is the degradation of “normal” crude oil.
- Another apparently more plausible theory is that it arrived from the Cretaceous bituminous rocks deeply buried with other strata at the time of the formation of the graben. Its appearance seems to be associated with active faulting, i.e. an earthquake. It is reported that a sulfurous smell usually precedes the appearance of asphalt blocks.
From biblical times the asphalt has had a trading value, particularly with the Egyptians who used it for waterproofing their baths, cisterns and later in mummification.
Israel geologist E.L. Kashai is one of the most knowledgeable petroleum geologists in the country – and also one of the most disappointed.
To strain a well-known quotation, in the southern Dead Sea area there are seeps and shows everywhere, but not a barrel to flow.
All the “tools of the trade” have been employed in the search for oil: magnetic, gravitational, seismic (both refraction and reflection), aerial photography, hydrodynamics and detailed surface mapping. The time-honored custom was to drill on or near oil or gas seeps.
Such seeps and leaks abound in the southern Dead Sea area and are referred to in the Book of Genesis in the Bible. Results of these tests were tantalizing shows of liquid hydrocarbon, but always of limited extent.
Chemical studies indicate that all of the hydrocarbon occurrences – light oil as well as immature oil and asphalt – in the southern Dead Sea area originate in the Senonian (upper Cretaceous) bituminous chalk and marl buried deep within the rift. Like a peanut butter and jelly sandwich, the oil from the source is squeezed into the rock layers above and below.
These carrier beds work laterally, and by faulting follow a circuitous route to other porous beds.
The principal crustal pressures are horizontal, brought about by the friction between the moving tectonic plates. This stress would normally develop anticlinal-type structures, but the stress is relieved by east boundary strike-slip fault.
The secondary pressure is vertical, which is manifested in the down faulting on the west boundary. Some of the horizontal stress accounts for the left stepping faults that characterize the western boundary.
As a consequence of this complex tectonic structure, there is a paucity of structural traps.
One disheartening example was drilled on one of the fault blocks of the southern Dead Sea. At a depth of 11,319 feet, the well drilled into the source rock, and oil flowed into the well bore.
When Kashai was describing this test, he remarked that the oil flowing into the bore hole was “being born right there.” Unfortunately, additional tests were unsuccessful.
Kashai said on the basis of its geochemical characteristics, this oil is considered an early product of the oil-generation process. In two wells drilled near Masada, light oil was found, which is evidence that advanced, thermal maturation has occurred in some limited places in the south Dead Sea basin area. Dr. Tannenbaum of Hebrew University has calculated a conservative estimation of distribution in the deep-sunken blocks in the graben at a potential of eight to 10 billion barrels of oil.
This would indeed be a wonderful find. Unfortunately, the deep sunken block probably lies below 20,000 feet – but with the price of oil today, it would perhaps justify drilling if there could be some assurance that a sealed trap existed within the deep sunken block.
In a period soon after World War II, exploration found gas in the Zohar area in three small fields 6.2 miles west of the Dead Sea rift. Later, a small gas field was found in the plains on the west side of the rift south of the Dead Sea Works. This was biogenic gas from the Pleistocene and lignitic formations which developed during one of the wet periods.
Although of low pressure and limited extent, the gas was utilized as an energy source in the Dead Sea Works.
It has been shown that this stark and lifeless Dead Sea rift area has some interesting activities unique to this hyper-saline lake/sea: salt features, mineral extraction from the waters, asphalt occurrences and promising but unfulfilled oil prospecting.