NOTES ON THE GEOLOGY OF LEBANON(See the MOT maps of Lebanon)
Lebanon is divided into three main units;
Less obvious is the very narrow continental shelf which drops to depths of 1-1.5km within lOkm of the shore.
Geologically Lebanon is dominated by pate limestones; this and/or the snow cover may be the origin of the name as L-B-N is 'white' in the Semitic languages. The surface rocks of Lebanon are relatively recent, the oldest being dated as Early Jurassic (around 200 million years ago).
At the risk of oversimplification, the geology can be summed up in five episodes of around 50 million years each.
EPISODE 1: 250-200 MILLION YEARS AGO.
This episode is not represented by any surface rocks in Lebanon but is known from the adjacent areas. During this time a series of rifts probably opened across the region as the supercontinent Gondwana began to break up.
EPISODE 2: 200-150 MILLION YEARS AGO.
This saw the deposition of up to 2km of Jurassic limestone in quiet shallow, warm water conditions. These are the massive, monotonous limestones of the gorges of northern Mount Lebanon and of the mountains of Barouk and Hermon. Offshore Lebanon an oceanic seaway would have opened as the tectonic plates split further apart.
EPISODE 2:150-100 MILLION YEARS AGO.
This was a more varied period that began with uplift with local basaltic volcanic flows. The area was then covered by a series of swamps, rivers and deltas which has given a widespread sequence of sands and shales up to 500m thick. These Early Cretaceous strata are increasingly worked as building materials. They also contain good fossil amber with well preserved insects.*
EPISODE 4:100-50 MILLION YEARS AGO.
The seas then returned to give another thick sequence (over 2 km in places) of pale limestones and chalks of Late Cretaceous and Early Tertiary age. These are common on the coast as well as forming parts of the high mountains of the Lebanon and Anti-Lebanon Range. It is during this time the famous fish beds formed. The general outline of Lebanon started to form at the start of this episode with a time of gentle uplift.
EPISODE 5: 50 MILLION YEARS AGO TO NOW
From the late Early Tertiary onwards, a series of folding and faulting events affected Lebanon. These are due to the forces generated as the Arabian and African Plates collided slowly with Europe and Asia. The first major folding and uplift occurred at the end of the Eocene and a second uplift event associated with movement along the Dead Sea Fault system started some 10 million years ago and is still going on. One characteristic is that the folding is generally confined to narrow zones; over most of north and central Lebanon, whole blocks were pushed up vertically along faults so that even the highest mountains often have rocks that are horizontal. The most recent folding has involved a 'slicing up' of Lebanon by a number of faults linked with the Dead Sea Fault System.
In the last Ice Age the highest peaks probably had glaciers and small glacial moraines can be seen in the area of the Cedars at Bcharre. From 10,000 years ago the area warmed up and reforestation occurred. Human activity however started to negatively affect the environment on a large scale from around 4000 BC onwards; a process that has increased alarmingly in the 20th Century.
Lebanon has only limited natural resources. Iron oxides occur locally in the mountains and were some of the first iron ores to be exploited; by the 7th century BC Lebanese iron was being exported to Babylon. Unfortunately iron smelting requires high temperatures and was a major factor in the deforestation. The limestone has also been used as a building stone and for fertiliser and cement. The last two processes also use wood. There is no oil known but drilling programs have been minimal and it may exist at depth.
The chief natural resource is water. The high mountains gave a high rainfall (widely over a meter a year in Mount Lebanon), and the porous fractured limestone made excellent aquifers which were refilled over summer by slow snow melt. The resulting abundant springs and rivers, unique to the region, gave the country its abundant forests and legendary fertility. However due to the steep slopes and the stony, shallow soils this fertility has proved hard to harness for agriculture and the removal of the forests tended to produce only short lived farming land.
ISSUES OF ENVIRONMENT & GEOLOGY
IMPORTANCE OF GEOLOGY
Geology has profoundly controlled the history of Lebanon.
C. D. Walley, A. U. B. March 1998
* See Fossils from the amber of Lebanon
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