The oil horizons in the world's greatest productive basin range in age from Miocene to Jurassic. With additional prospecting, older producing horizons can confidently be expected. The younger Tertiary horizons produce on the mobile or mountainward side of the basin. Older horizons thus far have their major accumulations on the low foreland shelf of the basin with the older horizons being productive higher on the shelf than the younger horizons.
Generally speaking, all the oils are relatively high in sulfur and there is a tendency for the oil gravities to become lighter with depth and toward the center of the basin. There is an indication of a tar belt on the northwest side of the basin, as exemplified by the famous tar seepages of Hit. Through Syria, prospecting has thus far been negative in spite of a satisfactory stratigraphic section being present. Three types of structures are present—1. strongly folded and commonly long anticlinal structures paralleling the front of the mobile mountains; 2. long, broad, gentle, uniform structures of the shelf; and 3. a large number of salt domes. A unique feature of this basin is the repeated occurrence of evaporites from the Cambrian up to the Miocene. Apparently, these evaporite beds act as an excellent sealing agent to retain the oil in place.
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Habitat of Oil
The history of oil exploration in a large basin is very much like the history of research in most fields of investigation. In the history of research into the subject of oil occurrence, however, the rate of increase of knowledge has fluctuated greatly. Sourced from the 1955 AAPG Annual Meeting, this publication contains many of the papers presented at that meeting, which discuss the habitat of most of the oil found in the world prior to 1955.