The Sandstone reservoir in the Cambay basin is primarily associated with the Cambay Shale Formation. This formation is Eocene in age, meaning it formed approximately 56 to 34 million years ago.

However, it's important to note that:

* Age variation exists: The exact age of the Sandstone reservoir within the Cambay Shale Formation might vary slightly depending on the specific location within the basin.

* Multiple reservoirs: The Cambay basin contains other formations with Sandstone reservoirs, some of which may have different ages.

Therefore, while the Eocene age is a good general indicator, further information about the specific reservoir in question would be necessary to determine its precise age.