Geology And Geography Of Jordan

Nature create ancient residence .

The geology of Jordan is both its foundation and its building stone. It controls the country's wealth in terms of
 natural habitats and landscapes, as well as the availability of water, building material, economic minerals and trade routes. Jordan's development, from its earliest days, owes much to its geology - with the use of flint and copper by Stone Age man and the use of geological/geomorphological features as ancient trade routes. Natural habitats and wildlife reflect the underlying geology in many ways: for example, certain plants favour limestone soils and particular birds are restricted to specific rock types - as we shall see ...

Jordan's Geological Regions

Jordan can be divided into 5 regions, based on its underlying geology:

1. Limestone with flint in the highlands and interior deserts.
2. Sandstone hills in the Rift Margins and Wadi Rum area.
3. Ancient basement rocks behind Aqaba.
4. Basalt desert in the north-east.
5. The Rift Valley, forming Jordan's western borders.

1. Limestone Country

The majority of the highlands and interior deserts of Jordan, especially in the north, are composed of limestone. Commonly, hard limestone, with or without chert beds, alternates with softer, more easily eroded layers. This forms craggy outcrops in cultivated areas and stepped hill profiles in desert areas, such as we shall see in Wadi al Mujib.

The combination of limestone and a humid climate (as is experienced in the NW Highlands) leads to fertile soils and a rich natural flora. Jordan's best soils are found in these NW Highlands, but an increasing area is being built on by urban expansion.

The limestones span a wide age range from the Triassic to Palaeogene - 248 million to 25 million years old - but most of those around Amman are of Late Cretaceous age. They were deposited in nearshore environments, lagoons and reefs at a time when a warm, shallow sea full of marine life covered the whole of the Middle East region. The beds are often fossiliferous containing shells and echinoids.

In many cases, the limestones contain significant amounts of hard chert (or flint) which is less easily eroded than the limestones. In the highlands, it forms outcrops and ridges, whereas in the desert it often forms a remnant surface layer of shattered pieces on the desert surface. These flint occurrences were discovered by Stone Age man, who fashioned them to make tools. They also occupied the natural caves, which are locally common in the limestone valley sides.

The limestone has a variety of uses, most important being as a common building stone (especially in Amman) and to produce cement (e.g. above Wadi Dana). These strata also contain the mineral phosphate, Jordan's main export, and also contain one of Jordan's principle underground aquifers (see later).

Wadi al Mujib site details

From a view point high on the northern rim of Wadi al Mujib, the deeply-dissected valley cuts through many layers of rocks, mainly limestones and marls. The thick, hard limestones form high crags, whilst the softer marls form low angle slopes and are often landslipped. The valley is 800m (2625 ft) deep.

The geological sequence (from bottom to top) is:

Cambrian sandstones - in the deepest part of the wadi, near the Dead Sea (not visible from here).
---Unconformity---
Kurnub sandstones - in the valley bottom.
Upper Cretaceous limestones and marls - exposed in the valley sides with Na'ur limestone crags etc.
---Unconformity---
Miocene(?) Basalt - with columnar jointing, caps the plateau on both sides of the wadi.

2. Sandstone Country

Sandstones crop out along the Rift Margins and in the Rum Desert, where they produce some of Jordan's most dramatic scenery e.g. at Petra, Dana and Wadi Rum.

The sandstones are mainly of Palaeozoic (Cambrian to Silurian) age - 590 million to 408 million years old. Some younger, Lower Cretaceous, sandstones are 'only' 100-140 million year old.

There are three main types of sandstone in Jordan, each producing its own distinctive desert scenery:

• hard, red sandstones (Cambrian age) forming cliffs,
• white sandstones (Ordovician age) forming domes, and
• soft, pink and white sandstones (Lower Cretaceous) forming gentle slopes.

Wadi Dana site details

Wadi Dana has formed where a line of weakness (a fault at right angles to Wadi Araba) has been exploited by erosion. Rivers, possibly much more vigorous than today's, have cut this deep valley over many thousands of years. Now, springs around the village irrigate fields, but there is only a small, perennial stream. The valley descends from 1700m (5580 ft) to sea-level.

From a view point close to the campsite, we can see the complete cross-section of local geology.

Basement: way down, at the bottom of the valley.
---Unconformity---
Burj Limestone: copper-bearing limestones and shales (not discernible from here).
Umm Ishrin Sandstone: main red cliffs in the wadi
Disi Sandstone: white domes around the camp
---Unconformity---
Kurnub Sandstone (Lower Cretaceous): soft slopes above the camp
Upper Cretaceous limestones: up to the highest point; limestone quarries; crags behind village

Depositional environment: these clastic sediments were deposited as sand and mud in a variety of marine and fluvial settings. Fluvial sandstones are most common with thick cross-bedded units. Sand and pebbles from these rocks are now being eroded, and it is possible to find water-rounded pebbles littering the desert floor e.g. in Wadi Rum. These were rounded by water 400-500 million years ago, not by recent floods! Thin interbedded shales can contain fossils, indicating that a brief marine incursion took place. The interbedded marine limestones and shales of the Burj Limestone contain shells and trilobites and represent the most extreme example of this kind of marine incursion onto the alluvial plains that covered Jordan for many millions of years.

In Jordan, the Sinai Rosefinch breeds almost exclusively on the Palaeozoic sandstones.

Petra site details

The ancient city of Petra is located in the heart of mountainous desert, but importantly, adjacent to an ancient route down from the plateau to Wadi Araba . In detail the site occupies an open valley (occupied by the town itself) surrounded by mountains (use for religious ceremony, tomb building and water collection in cisterns). Routes through the mountains follow deep clefts or siqs. Although the formal entrance was through the Siq, general access is also possible from the north. The gorges were formed when the force of desert flash floods exploited lines of weakness in the rocks (faults, joints and fractures) - over many thousands of years, and continuing today. The properties of the rock itself may have persuaded the Nabataeans to site their city here - it was evidently suitable for rock carving and excavating, as well as being aesthetically pleasing to look at. After 2000 years, however, much of the worked and excavated stone is showing signs of erosion, not least by the footsteps of many tourists.

The geological succession is as follows (from bottom to top):

Basement: visible beyond the Monastery only.
---Unconformity---
Salib Sandstone: thin unit resting on the unconformity.
Umm Ishrin Sandstone: most of the monuments are carved in the middle part of this unit; Liesegang banding is abundant.
Disi Sandstone: white domes near Wadi Musa and behind the Resthouse.
---Unconformity---
Kurnub Sandstone: soft sandstones; occupies the graben (valley) in the centre of Petra; also visible behind Wadi Musa.
Upper Cretaceous Limestones: above Wadi Musa; Musa (Moses) spring flows from here.

Liesegang banding.

At Petra the sandstones are spectacularly colour-banded in yellow, orange, red, grey, brown and mauve. These patterns, termed Liesegang banding (or rings) by geologists, were formed deep underground by the rhythmic deposition of various iron and manganese compounds from mineral-rich water that once flowed within the rock. Some examples are fan-shaped, others closely resemble sedimentary cross-bedding (but their orientation can be seen to cut primary, sedimentary features).

Wadi Rum/Wadi Umm Ishrin site details

The dramatic mountain blocks ('mesas' in US terminology) surrounded by flat sandy desert are best developed in Wadi Rum. They were formed when a network of intersecting faults divided the sandstone rock into rectilinear blocks. Exploited by erosion, these fault lines first became gorges and finally formed wide valleys filled with the products of erosion (sand). The mountain tops lie 800 m (2635 ft) above the valley floor.

In Wadi Rum the succession of rock strata is (from bottom to top):

Basement: granites form a 'plinth' on which the mountains rest (buried beneath the sand in Wadi Umm Ishrin).
---Unconformity--- marked by line of springs
Salib sandstone: thin conglomeratic beds at base
Umm Ishrin Sandstone: sheer rock faces, favoured for climbing
Disi sandstone: white domes on the mountain tops
Further east, the overlying Umm Sahm Sandstone forms different-shaped mountains.

3. Basement Country

Jordan's oldest rocks (of Precambrian age, 570 million years old) form the mountains behind Aqaba. They mainly consist of granites, which are criss-crossed with sheets of intruded igneous rock, known as dykes. At the time of dyke formation, the granitic rocks were still deep below the surface. The rocks were affected by great tensional stresses, and the cracks which this created where subsequently filled by molten rock. Today, the dykes form the characteristic dark stripes across the hillsides.

Intense fluvial erosion of the Aqaba granites has produced extensive alluvial fans which fill the wadis and mantle the lower hill slopes. With the availability of water supplies at depth beneath these fans, acacia savannah woodland has developed in many places.

4. Basalt Desert

The basalts of northern Jordan are the products of volcanic activity which began 25 million years ago and ceased less than one million years ago. There were six major periods of emissions.

The various lava flows radiate from the Jabal ad Druz centre in Syria, but in Jordan there are small cones and fissures many kilometres long.

The weathering of this volcanic rock in the extreme temperatures of the desert climate (hot days and cold nights) has formed the extensive boulder fields found there today. Silt-filled depressions between low basalt hills are common.

Species have evolved a distinctive coloration in response to the geological characteristics of the desert they occupy. Of particular note is the Desert Lark, which has a dark race (A. d. annae) found only on the dark flint and basalt deserts. The black morph of the Mourning Wheatear is also restricted to these basalt outcrops.

The Azraq oasis, and several smaller springs, lie on the margin of the Basalt Desert. The Azraq area is low enough to tap the water table which lies beneath the Basalt Desert, thus forming natural, artesian springs.

5. The Dead Sea Rift Valley

The single most important structural feature in Jordan is the Dead Sea Rift Valley which extends the whole length of the country and defines its western border with Israel.

The Rift Valley is a continuation of the East African Rift Valley and the Red Sea. It owes its existence to a deep-seated, linear, strike-slip (or transcurrent) fault which marks the boundary between the Arabian and African Plates. Movement took place mainly during mid Miocene and Pliocene-Recent phases. It is a left lateral (sinistral) strike-slip fault system leading to an offset of 105 km (66 miles) between similar geological features on either side of the Rift Valley (e.g. the Timna copper deposits of Israel are 105 km south [left, if you are facing the fault] of those at Feinan). This strike-slip movement has also led to the formation of alternating extensional grabens and compressional folds (i.e. deeper and shallower segments) along its length. In the vicinity of Jordan, the major active fault runs near the east side forming dramatic cliffs and threatening occasional earthquakes.

Jordan's youngest rocks are to be found in the Rift Valley. They are typically soft siltstones and mudstones deposited in the extensive lakes which formerly occupied these sites until just a few thousand years ago. In the Jordan Valley these rocks have been easily eroded into a bad-land landscape of gullies and cliffs.

The Dead Sea

• Originally formed over 5 million years ago in the Miocene in the deepest part of the Dead Sea Rift.
• Thousands of years ago it was more extensive, forming a huge lake which geologists call Lake Lisan. This was 320 km (200 miles) from N to S (now 76 km, 47 miles) with its surface 180 m (591 ft) below sea-level (i.e. 229 m [750 ft] above the current Dead Sea level) - but even then it was prevented from flowing out into Red Sea by the highest point in Wadi Araba, which acted as a dam. It completely dried up, depositing huge thicknesses of salt (as found at Mount Sedom in Israel). Soft, lake deposits can now be seen high and dry on the valley sides.
• Maximum depth is 399 m (1309 ft) in NE corner; but it is only 6 m (20 ft) deep south of the Lisan Peninsula.
• Its water is some six times as salty as ocean water. Its salinity at the surface is 22.7-27.5% solids, at 110 m (360 ft) this increases to 32.7% (c.f. 4-6% for ocean water). Composition: MgCl, NaCl (common salt), CaCl, KCl, MgBr, CaSo₄. Because of the density of solids in the water, the human body easily floats on the surface.
• It is land-locked - water flows in from the Jordan River and several minor side wadis, but there is no outflow.
• Surface lies at 409 m (1342 ft) below sea level (in 1995) - the lowest water surface on Earth.
• Changes in level. In Roman/Byzantine times (and possibly the time of Sodom and Gommorah) level was much lower (c.-430 m), but for centuries the level rose due to increased rainfall. Now it is falling due to lack of inflow from Jordan River. In the past, 1200 million m³ flowed from the Jordan River and small amounts from other wadis kept pace with evaporation and Dead Sea level was constant at -392 m (-1286 ft). In 1964, Israel started diverting Jordan River water to irrigate fields, now only a slow, salty trickle flows into Dead Sea (except in periods of flood, e.g. in winter 1991/92). Its level is falling by 0.5 m/year (18 inches/year), so that in 50 years it could be virtually dry.
• Bitumen seepages. The Roman referred to the Dead Sea as Lacus Asphaltitis, and before modern drilling found large quantities of oil, Dead Sea bitumen was a very important substance - for construction and waterproofing. We know from documents that the Romans collected bitumen from the surface of the Dead Sea, and it has been suggested that Sodom and Gommorah (and the other Biblical 'cities of the Plain') had economies based on bitumen some 2000 years previous. Today, the occurrence of bitumen is rare, and it has been suggested that this is due to a higher level of the Dead Sea to that in the historical past. After earthquakes asphalt blocks floated to the lake's surface - escaping from natural oil seeps under water.
• The Dead Sea contains no life, except for two species of bacteria (e.g. Haloarcula marismortui); fish are unable to live in these waters and die if they are washed out of the rivers (see the Madaba map, where fish are shown returning up the Jordan River).
• Potash (potassium salts) has been extracted since 1930. Evaporation and refining produces KCl for agricultural fertiliser. As well as potash, bromine, gypsum and salt are also extracted.

Gulf of Aqaba

• The Gulf of Aqaba (or Gulf of Eilat, if you are Israeli) is the northernmost arm of the Red Sea sandwiched between Sinai and Saudi Arabia.
• Maximum depth off Jordan is approximately 1000 m (3200 ft).
• Water is very clear, allowing light to penetrate to 70 m (230 ft) - this provides optimum for growth of coral.
• Along the shore, fossil (Pleistocene) reefs are now left high and dry (so-called 'raised reef') at 30 m (100 ft) above current sea-level. They are eroded by modern wadis. This reef contains fossil corals and echinoids. They were deposited before a relative drop in sea-level, this was possibly due to a rise in land level rather than a 30 m (100 ft) drop in sea-level.
• Tidal range is very small (<1 m or 2-3 ft), which is just enough to expose the reef top at low tide.

Hydrothermal (hot) springs

• Hot springs occur at several places along the Rift Margins e.g. at Zerqa Ma'in and Zara (by the Dead Sea) and at Burbayta (in Wadi al Hasa).
• Maximum recorded water temperature is c.60° C (140° F).
• Gases, such as hydrogen sulphide and (radioactive) radon, are also released.

Earthquakes

• Earthquakes are reasonably common along the Rift Valley, but become progressively rarer towards the interior deserts. They owe their origin to the major fault system which forms a plate boundary between modern-day Jordan and Israel.
• 42 major earthquakes have affected the area (i.e. Red Sea to Syria) during the past 2500 years
• Earthquakes have been responsible for repeated destruction of many cultural centres: e.g. an earthquake in c.2100 BC was probably responsible for the destruction of four of the Biblical 'cities of the Plain' (Sodom, Gommorah, Admah and Zeboiim) [Genesis 13-19] which were probably located SE of the Dead Sea. It was accompanied by burning of carbon disulphide, hydrogen sulphide, oil and asphalt. A large area, including Petra was damaged on 19 May 363 AD, and Petra was never built following another earthquake on 9 July 551. Jerash was finally abandoned after an earthquake on 18 January 748 AD. On 23 May 1834, the King Meisha monolith at Dhiban fell to the ground due to an earthquake; it also caused damage at Rabba, Umm ar Rasas and Madaba.
• Earthquakes also cause: tidal waves on the Dead Sea, large blocks of asphalt to float to the surface of the Dead Sea (as in 1834 and 1837), landslides to affect the soft Lisan marl (in the past these have temporarily blocked the flow of the Jordan River near Damiya), and a so-called 'whitening' of the Dead Sea.
• In the Dead Sea area, major seismic activity is confined to its eastern shore; Wadi Araba is the least seismically active segment of the rift.
• Some of the most recent earthquakes occurred on: 11 July 1927 (centred on Damiya), 31 March 1969 (northern Red Sea) and 22 November 1995 (northern Red Sea).

Economic geology

Phosphate

• Phosphate is Jordan's number one export. It is transported by rail to Aqaba port. The old Hejaz railway (Damascus to Mecca) was partly upgraded and a branch line to Aqaba added.
• Jordan is the third most important producer and exporter in the world, after the USA and Morocco.
• Annual production (late 1980s) was 5.7 million tonnes. Reserves are estimated to be 1100 million tonnes.
• Two very large open cast mines are in the interior desert (Al Hasa and Ash Shidiya); the original mine at Rusayfa (near Az Zarqa) is now closed (it is within an urban area).
• Main use: agricultural fertiliser.

Potash

• Potassium chloride is extracted from Dead Sea water by evaporation at the Dead Sea Works (and in Israel). It is exported by truck along the Wadi Araba road to Aqaba.
• Annual production (late 1980s) was 1.2 million tonnes
• Main use: agricultural fertiliser.

Copper at Feinan

• Feinan, at base of Wadi Dana, is one of the most important ancient copper mining and smelting centres in the Middle East. It was also mined at nearby Timna in Israel, where there is an operational mine today.
• 200 ancient mines, many furnaces and huge slag heaps date back to 4500 BC.
• Occupied 4500-1500 BC (Chalcolithic to Middle Bronze Age), Iron Age and Persian Period (800-332 BC) and Roman era.
• Only sporadic mining since then. Recent plans to reopen the mines commercially have not materialised.
• Different mines and smelting technologies evolved over 5000 years. Oldest miners exploited rich surface ores, whilst Romans had to dig immense galleries in obtain leaner ore, rework older slag and import manganese for flux.
  

Oil and gas

• Jordan is unfortunately not rich in oil and gas reserves, unlike most of its neighbours.
• There is one very small oil field (Hamzeh, near Azraq) which produced just 95 barrels/day in 1994.
• A moderately-large gas field (Risha, near the Iraqi border) produced 35 million ft³/day in 1994 - enough gas to generate c.30% of Jordan's electricity (note the pylons along the Amman-Azraq-Iraq road) .
• Oil is imported with UN agreement from Iraq (by tanker, not pipeline).
• Two major oil pipelines were built through Jordan in the 1940s, both planned to export oil through Haifa (then Palestine, now Israel). The TAPLINE (TransArabian PipeLINE) runs from the Arabian Gulf, and the Iraq Petroleum Company (IPC) pipeline runs from Iraq. Both were never used due to the formation of Israel in 1948, but lead to the building of the desert towns of Ar Ruwayshid and As Safawi at the H4 and H5 pumping stations.

Water

• Until 1967, the Jordan River was Jordan's lifeblood. Now, its water is mostly taken by Israel.
• Jordan has few other rivers, and lacks funds to build dams.
• Jordan now pumps water from natural underground reservoirs (aquifers). Much of this water percolated underground centuries ago (in wetter times) and is not being replaced in today's drier climate (i.e. it is 'fossil' water).
• There are three main aquifers: under Amman (70 million m³/year extracted), under Azraq (40 million m³/year) and under Disi (potential to yield 100 million m³/year).
• Amman aquifer: rain not recharging (refilling) aquifer - it will be empty in c.25 years.
• Azraq aquifer: rain water not recharging aquifer. As well as supplying Amman, much water is also taken for local agriculture (there is no control over this).
• Disi aquifer: some used for agriculture. Pipeline to Amman would be very expensive.
• Wastage: at Azraq 30% of water pumped is wasted by overwatering and leaks. In Amman, 56% of urban supply is unaccounted for - half of this is through leaks. Water is too cheap - there is no incentive to conserve.

Azraq springs and water extraction
- the death of an oasis

In its original state (pre 1970s) the Azraq oasis was a unique habitat - a classic oasis in the heart of the Jordanian desert. The springs fed an extensive marshland with pools, reedbeds and lush vegetation supporting a varied, and in many ways unique, flora and fauna. It also acted as a focus for human settlement since the Stone Age, man being attracted by the abundant water and rich game.

Modest water pumping began c.1963, but extraction rates soared during the 1980s and 1990s. Signs of habitat deterioration date from the 1970s, but by 1990 the marshes were completely desiccated ... vegetation in poor health (dead or moribund) ... aquatic animal and birdlife depleted or absent ... frequent underground fires ... no discharge from springs ... water murky and stagnant with abundant algal growth. Controlled water extraction could possibly have been achieved with minor affects to the spring flow. But, a man-made disaster has been caused by excessive demands from Amman coupled with uncontrolled and unmonitored pumping from private wells on local farms.

During 1993-95, a $3.3 million grant was awarded by UNDP to conserve and rehabilitate the wetland. Has this had any effect at all?

Flow from the springs (dark blue on histogram). Accepted estimates of the natural (pre-abstraction) spring flow rates range from 16-20 million m³/year, i.e. 3-4 from Druz springs, 10-12 from Shishan springs and 3-4 from others springs and seepages (e.g. Lion spring and the 'canal'). However, due to water abstraction, the springs have not flowed as such high rates since c.1960. Indeed, in 1985 flow rates had already decreased to a quarter of their original rate, and by 1990 both springs had totally dried up.

• Supply to Irbid from Druz springs (yellow). Water pumping from the Druz springs to Irbid (and Al Mafraq and Azraq) took place during 1963-86.
• Supply to Amman from Shishan springs (pale blue). For a short period in 1980-82, water was abstracted from a pool at Shishan. However, within a few months the overflow from the springs had virtually stopped and pumping was abandoned in January 1982. The spring outflow soon reverted to previous rates, and only small amounts were abstracted subsequently.
• Supply to Amman from Wellfield (pink). With the failure of the Shishan abstraction project, it was considered preferable to take water from wells some distance back from the springs. In 1981-82, a well field of 15 producing boreholes was constructed, capable of abstracting 15-16 million m³/year. On several occasions pressure from conservationists and government imposed reductions in pumping, but it has always increased again due to pressure for more water to be pumped to Amman. In several recent years 'safe' extraction rates have been exceeded, and water quality (as well as the marshland) is being jeopardised.
• Local Agriculture (green). There has long been extraction from private wells for local irrigation, but during the last ten years the amount of water taken from such wells has increased exponentially: from 1.5 million m³/year in 1983 to 25.0 in 1993. A survey in 1993 found 600 wells in the Azraq area (two-thirds were unlicensed and some were actually in the wetland area).

---

Glossary

Aquifer
A body of permeable rock that is capable of storing significant quantities of water.

Basalt
A dark-coloured, fine-grained, extrusive igneous rock composed of plagioclase feldspar, pyroxene and magnetite, with or without olivine.

Basement
Metamorphic or plutonic rocks often unconformably overlain by sedimentary rocks.

Chert or flint
A form of silica which occurs as nodules and bands in limestones. The silica originates from micro-organisms, but is mobilised and reprecipicated during burial.

Fault
A line of fracture in a rock, caused by brittle failure and along which relative displacement has occurred between adjacent blocks. Faults are commonly classified as being either normal, reverse or strike-slip.

Limestone
Sedimentary type of rock composed mainly of calcite and/or dolomite, which can be of organic, chemical or detrital origin.

Marl
A clay rich in lime (i.e. calcium carbonate).

Phosphate
An important rock type formed mainly of apatite (Ca₅(PO₄)₃(F,Cl,OH). It has many uses including agricultural fertiliser, chemical industry, animal food, tooth paste, photography, medicine, sugar purification and as a cement in plastics. It is also a source of vanadium and uranium. The phosphorous originates in deep water (where a lower pH allows to be dissolve), upwelling currents then bring this water to shallower areas, where some is precipitated as phosphate mud, while at the same time it also allows organisms to flourish. Larger animals feed on these small, planktonic animals and it is thick layers of their faecal pellets that form some of the phosphate beds found today.

Sandstone
Sedimentary rock type formed of lithified sand grains bound together by a mud matrix and/or a mineral cement.

Transcurrent or strike-slip fault
A fault which results from horizontal (rather than vertical) displacement between adjacent blocks.

Unconformity
Surface between two sets of strata which represents a break (or hiatus) in the geological record due to a combination of erosion and cessation of sedimentation.

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