Introduction

The geological formations of Ramallah District range in age from Lower Cretaceous to Quaternary. Lithological composition of these formations consists mainly of limestone, dolomite, marl, chalk, cherts and alluvium (Figure 4.1).

Figure 4.1

Geological Formations

The detailed geology of Ramallah area, as outlined in Table 4.1 shows the following formations:

1. Lower Cretaceous Rocks

   They are regarded as equivalent to the Pre-Aptian stage. Their main composition consists of limestone, marl, shale and clay.

    

2. Upper and Middle Cretaceous Rocks

   They are divided into the following formations:

    

   • Kobar Formation: It ranges in age from Aptian to Albian. Outcrops exist in the west of Ramallah. The formation consists mainly of brown ferruginous limestone, marl and sometimes of interbedded limestone. The Albian rocks deposited with unconformity over the Aptian rocks. Total thickness of this formation is approximately 180 m.

      

   • Lower Beit Kahil Formation: It forms the lower part of the lower Cenomanian. It is composed mainly of thin bedded dolomitic limestone at the bottom which become massive towards the top. The total thickness is about 216 m.

      

   • Upper Beit Kahil Formation: It forms the upper part of the lower Cenomanian. The lower part of the formation consists of marly limestone with marly partings and of bedded limestone, somewhat dolomitic at the top. The total thickness is around 180-205 m.

      

   • Yatta Formation: It is the lower part of the middle Cenomanian. The main composition of this formation consists of marl, limestone and chalk. It has a thickness of about 110 m.

      

   • Hebron Formation: It corresponds approximately to the upper part of the middle Cenomanian. The lower part of the formation consists of hard dolomitic limestone and dolomite. While the upper part consists of dolomitic limestone. The total thickness is about 170 m.

      

   • Bethlehem Formation: It forms the upper Cenomanian. It has the following lithological succession: well bedded cream-gray chalky limestone at the bottom, and recrystallized chalky limestone at the top. It has a thickness of about 90-150 m.

      

   • Jerusalem Formation: It ranges from the upper Cenomanian to Turonian. The lower part of the formation consists of massive limestone which is becoming more thinly bedded upwards. The total thickness is about 75-130 m.

      

   • Abu Dis Formation: It is composed mainly of chalk and cherts of Senonian age. The chalk is usually white and in some parts of the formation takes the dark color due to the presence of bituminous materials. The formation has a thickness of about 60-220 m.

      

   • Khan el Ahmar Formation: It extends from Maestrichtian to Danian stage. Lithology and thickness vary greatly because of erosion. Lithology changes from bituminous and phosphatic marl to variegated marl and soft limestone. Total thickness is approximately 115 m.

    

3. Quaternary Rocks

   They are divided into the following formations:

    

   • Lisan Formation: It consists mainly of thinly laminated marl with occasional limestone, marginally of gravel and poorly stored pebble beds. The pebbles are sometimes siliceous or calcareous.

      

   • Nari Formation: It is well developed in the high rainfall areas. Limestone forms the main composition of the formation. It forms a thin coating over the limestone with a thickness of about 10-15 m.

Structural Pattern

Ramallah District was affected by several tectonic movements which determined the general structure of the area. First, the compressive forces from northwest and southeast dominated, producing the main folds. Second, the minor folds were formed, and finally, forces of shear dominated, producing the main faults.

Folding

There are many folds in the Ramallah area. The most important one is the E'in Qinya anticline, which was formed by compressive forces from southeast and northwest. It trends north-south. The general structure of the anticline is symmetrical, but near Biddu it becomes less or more symmetrical. Between Beit Leqia and Beit U'r Al-Tihta, the western limb is steep, about 35^o slope. The western side of the anticline forms two minor folds trend northeast and southwest. The eastern side also forms two pairs of syniclines trend northeast with the first begins north of Al-Bireh and dies near Deir Dibwan and the second passes through E'in Samia (Figure 4.1).

Faults

Most of the faults trend north-south and east-west. The northern part of the area, where the main faults exist, is more faulted than the southern part. Majority of the faults extended for 5-6 km and have throws less than 50 m. Large faults have throws of about (50-150)m, however, they are rarely in the area and die out over 1-2 km. Figure 4.1 shows the distribution of faults and their directions.

Joints

Joints are well developed in the dolomite and limestone especially in Lower Beit Kahil, Hebron and Bethlehem formations. Joints are often up to one meter wide at the surface. Chalky and marly rocks are less affected with joints and solution channels than limestone and dolomite. The presence of joints and karst caves make the formations good aquifers.

Soils

The soil classifications and references to major vegetation were adopted from the document entitled, The Soil of Israel, 1976. The major soil associations found in the Ramallah District are as follows (Figure 4.2):

Grumusols

This type of soil association covers approximately 817 hectares of the district. It is found in areas with smooth to gently sloping topography. The soil is originally formed from fine textured alluvial or aeolien sediments. Primary natural vegetation was destroyed. Today, what appears is segetal vegetation of the Prosopis farcata - Scolymus maculatus association. The use of this soil type for agricultural production purposes is currently limited to cultivating wheat. The American great classification that represents this soil is Xererts.

Terra Rossa, Brown Rendzinas and Pale Rendzinas

These types of soil associations occupy a total area of approximately 58,504 hectares, nearly 70% of the Ramallah District. Around 30­50% of these soils are outcropped with rocks. The major native vegetation cover are Quercus calliprinos, Pistacia palaestina, Pistacia lentiscus, Pistacia atlantica, and Amygdalus korschinskii. Particularly on valley shoulders, these soils are used to cultivate field crops, mainly wheat and barley, vineyards, olive and fruit trees. The American great group classifications that represent these soil associations are Xerochrepts and Haploxerolls.

Brown Rendzinas and Pale Rendzinas

These types of soil associations dominate the area of Deir A'mmar, Jammala, Al-Nabi Saleh, Beit Rima, Kafr Ni'ma, Beit U'r Al-Tihta, Beit Sira, Beit Leqia and Beit Nuba. These soils cover an area of about 15,870 hectares. Similar to the previous soil types, 30-50% of these soils are outcropped with rocks. Major vegetation is Pinus halepensis, Pistacia lentiscus, Pistacia palaestina, Quercus ithaburensis, Ceratonia siliqua and Ballotetalia undulatae. On such areas, cultivation of grapes and olives, field crops (wheat and barley), and grazing is the main land use, especially in shallow and steep sloping areas. The American great group classifications that represent these soil association are Xerorthents, and Haploxerolls.

Brown Lithosols and Loessial Arid Brown Soils

These types of soil associations cover an area of about 6,866 hectares of the Ramallah District. These soils characterize the eastern slopes of the district and are mainly found on steep to moderate rocky and eroded slopes. Brown lithosols are found in the pockets among the rocks. Loessial arid brown soils are found on flat hilltops, plateau and foot­slopes. The parent rocks of this soil association are chalk, marl, limestone and conglomerates. Major vegetation is Ballotetalia undulatae and Artemisietea herbae­albae. The American great classifications group that represent these soils are Haploxeralfs Torriorthents and Xerochrepts.

Loessial Arid Brown Soil

This type of soil association is found at the eastern border of the Ramallah District, covering an area of about 440 hectares. The soil is formed originally from conglomerate and/or chalk and mainly found on gently sloping plateau as well as dissected plateau with locally hilly topography. The major vegetation type found in this region is Achilleetum santolinae. The dominant land use is cultivation of various field crops such as wheat, barely and sorghum which are grown as dry-farming crops and cultivation of some irrigated crops. The American great group classifications that represent this soil association are Palexeralfs, Haploxeralfs and Xerochrepts.

Alluvial Arid Brown Soil

This type of soil association is also located at the eastern border of the district. It covers an area of about 178 hectares. It exists as alluvial fans and plains formed as a result of erosion of calcareous silty and clayey materials. This soil type supports Herbaceous vegetation of desert annual halophytes and glycophytes and responds well to irrigation, producing various crops, mainly subtropical and tropical fruits such as citrus, bananas, and dates, as well as winter vegetables. The American great group classifications that represent this soil association are Haplargids and Camborthids.