The answer to your question is somewhat related to the answer to the first question. It is believed that the shale beds that are good sources of oil in Iran were deposited in a shallow marine environment offshore along a passive margin. A passive plate margin is one like our Atlantic coast ,where there is no plate collision occurring and there are few earthquakes and associated faults.

The shale beds are Cambrian to Carboniferous in age and were deposited off the coast of Gondwana, a Paleozoic supercontinent composed of land we now know as Australia, India, South America, Africa, and Antarctica. Iran was located at the northern edge of Gondwana along the margin of the Panthalassic Ocean. The Panthalassic Ocean is basically the ancient Pacific Ocean.

Plankton populations depend on ocean circulation patterns because upwelling of deep ocean water supplies the nutrients the plankton need to live. Blooms of plankton are often associated with areas of upwelling. Perhaps during the Cambrian to Carboniferous, the coast along Iran was the site of significant upwelling.