A detailed description and interpretation of the carbonate lithologies present in drill cores recovered from two recently completed SADME stratigraphic wells have revealed that the Observatory Hill Beds in the Marla area were deposited in a shallow lagoon which developed on a broad marine platform. The lithologies are mainly fine-grained and dolomitic, with interbeds of packstone, algal boundstones and sandstones. Inferred sedimentary depositional environments were peri-sabkha to open lagoon, deemed to be favourable for the development of Mississippi Valley - type mineralisation throughout the 300 m of section penetrated by this drilling. No indications of petroleum were noted.