The common occurrence of oil and gas in sandstone within stratigraphic sequences composed of interstratified marine and non-marine sediments, formed in environments at or adjacent to a shoreline, is well known to most geologists. Such gross relations are ascertained readily, but the nature and mode of origin of individual sandstone bodies generally have been of little concern. It is probable that these sequences must include sandstone of both marine and non-marine origin. Marine types to be expected include beach, shoal, and shelf sandstone; whereas, non-marine types include deltaic, estuarian, paludal, and lagoonal sandstone. Knowing the mode of origin of sandstone in a petroleum-bearing sequence should be of considerable importance. One type may never contain oil; some andstone types may contain petroleum in predictable, more permeable zones; some types may be long and sinuous and others broad and sheet-like; some may parallel old shorelines whereas others may be at right angles to them.

Positive determination of the genesis of a sandstone, either at the outcrop in the subsurface, is difficult, but can be done with some assurance by using multiple criteria--no one of which is entirely diagnostic and only a few of which may be ascertainable for a particular sandstone body. Parameters of value in determining origin include geometry of the sandstone body, sedimentary structures, log characteristics, composition, nature of boundaries, and composition of surrounding or enclosing sediments.

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