SYRIA - The Mesozoic.

An era of major tectonic movements, the Mesozoic in Syria began with a rich Triassic sequence of carbonates, mainly limestone and dolomite. Shales and evaporites developed in a succession called "Mulussa" or "Dolaa". There were also migrations from sands of the Late Permian age (close to the terminal Paleozoic). Good anhydrite seals developed, holding fairly large hydrocarbon accumulations.

Major hydrocarbon traps are found within the Triassic sequence. They consist of interbedded Mulussa carbonates, shales, and evaporites. They include the gas and condensate discoveries made by Marathon of the US in a block and adjacent areas of the Palmyrid Belt (the gas fields of Al Shaer, Cheriffe, Soukhne, etc.), as well as SPC's fields of heavy oil at the edge of the Palmyrid Basin.

It is thought that the gas and condensate accumulations in the deeper part of the Palmyrid Basin are due to a greater maturity in the same source rock. The Triassic hydrocarbon occurrences of north-eastern Syria, north-western Iraq and south-eastern Turkey are sourced from interbedded shales in the Mesopotamian Foredeep.

Charge into many of the Triassic hydrocarbon occurrences is said to be a late event. Many of the traps in those Mesopotamian Foredeep areas were developed in the Late Neogene.

There are good evaporite seals under Syria's Triassic carbonates (reservoirs), in the Palmyrid area and in the north-east. Oil discoveries have been made from Triassic sandstones in the east, said to be sourced from Late Permian sands.

As a result of slab-pull forces moving northwards at the beginning of the Upper Cretaceous, rifting took place in the Palmyra region and adjacent areas in Syria as well as in western Iraq. At the end of the Cretaceous, this led to collision between the Arabian Plate margin and the Bitlis-Poturge Massif in the west, and an Iranian arc in the east.

A great deal of sedimentation occurred and a number of fairly large oil reservoirs developed during that age. Most of the Syrian oil discoveries made in 1956-1979 were from these reservoirs.

The Cenozoic: The post-Cretaceous Paleocene of Syria, a Fm known as Aaliji, developed in a thick marly-to-chalky facies outcropping in the Damascene-Palmyrid fold belts, the north-west of the Aleppo area and into south-eastern Turkey. It is transgressive similar to the facies characterising the Maestrichtian (Shiranish) and Campanian (Soukhne) Fms of the Palmyrids. There the facies extends upwards embracing the whole Eocene and includes Upper Eocene.

The sequence is known as the "Palmyra Marl Group", with the Jaddala Fm making up the Eocene portion. Extensive development of chert occurs in parts of the Lower-Middle Eocene portions of the group, such as the Araq flint.

Lower Eocene volcanics were developed in the Aleppo area. The Eocene in other parts of Syria is in a neritic, partly reefoid and partly argillaceous, facies reaching maximum development in Lebanon's Beqa' valley. The Upper Eocene extends from the Palmyrid area into north-western Iraq, across the Jebel Sinjar trough.

The Oligocene is missing from much of Syria, restricted to the north-west and across the Palmyrid Basin and close to Damascus. It is mainly in a limestone facies. In the east Palmyrids, at Jebel Bishri, it is developed in a sandy facies, which includes conglomerate layers, sourced from the Rutbah High.

The Upper Eocene and Oligocene were the times of uplift of the coastal mountains of Lebanon and Syria, as well as much of anti-Lebanon and the Syrian interior. Later cut off were the Tethyan seaway along northern Syria and southern Turkey, into north-western Iraq, with arms extending into the Palmyrids of central Syria.

A renewed transgression in the Late Oligocene and Early Miocene across the northern region left behind some pelagics and limestones. The Miocene, mainly a time of shallow and often restricted deposition, deposited the Lower Fars Fm over northern Syria. This included widespread anhydrites.

By the Upper Miocene, the northern seaway had filled up with Upper Fars clastics, dumped from the rising land as Arabia drifted northwards and partly closed the intervening sea area. During the Pliocene, molasse was deposited all the way from north-western Syria into northern Iraq.

The link between the Mediterranean and the Indian Ocean through the Tethyan seaway and the Persian Gulf was severed. A Messinian salinity crisis in the Mediterranean and Red Sea areas restricted marine Neogene deposits to limited ingressions into the edge of the mountain range, with Lower Miocene carbonates transgressing onto older deposits.

Messinian evaporites are now found in the Lattakia area and in the subsurface of the Lebanese-Syrian littoral border area.

A limited Pliocene marine ingression followed, which quickly turned into continental facies inter-fingering with basalts in the Tripoli-Homs area and parts of coastal Syria. In the interior, along the Levant Fracture System, lacustrine and continental deposits marked the Neogene.

Conclusion: Provided the government in Damascus improves its E&P terms, more widespread exploration in Syria should bear good results, with both the onshore and offshore prospects to be pursued. There could be interesting discoveries resulting from re-exploration in drilled areas.

A concentrated look into pre-Cenozoic horizons can be rewarding in view of Syria's tectonic background, although the costs would be high.

So far, foreign companies have concentrated on areas known to have high possibilities. Because terms under exploration and production sharing agreements (EPSAs) still are not attractive enough for big international oil companies (IOCs) to bear high risks, the pattern in exploration is not likely to change in the near future. The signature bonus which the oil ministry usually demands for exploration permits still has to be lowered.