Part I

The established geological principle "transgression" and "regression" of epi-continental seas, the resultant sediments, together with their fauna and flora, is applied to coral-reef or bioherm-forming organisms. Bioherms which develop during a transgression are differentiated from those of a retreating sea by the associated sediments. A "transgressive" bioherm is surrounded and overlain by marine clastics deposited during submergence, while the "regressive" type of bioherm is associated with evaporites and/or other types of sediments deposited during withdrawal of the sea.

Part II

It is suggested that hydrocarbons found within coral-reef or bioherm reservoirs are in most instances indigenous, because of the obvious concentration and accumulation of organisms within

FOOTNOTE 2. Name not adopted by the United States Geological Survey.

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them. The porosity and permeability of coral-reef or bioherm reservoirs are attributed not only to the hollow corallites etc., but also to the helter skelter accumulation of them so that, in many instances, such porosity is greater, more effective and more continuous. Partial or entire obliteration of porosity is, in part, due to infiltration of evaporites associated with the regressive type of bioherm.

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