In the southern Paradox basin many of the oil and gas fields produce front bioherms. Extensive coring operations in the Ismay-Flodine Park field have permitted a detailed inspection of a typical bioherm in the lower Ismay zone of the Pennsylvanian Paradox Formation. The four basic depositional environments that have been differentiated are shoal, bioherm, basin, and channel environments. Variations of chemical composition, particle size, allochems, degree of winnowing, biological remains, color, and terrigenous clastics are used to differentiate the environments. Distribution of environments in relation to tectonic features leads to a reconstruction of the ecologic conditions that produced the bioberms. The bioherms are not considered to be reefs, but remains of algal for sts.

Diagnostic parameters for identifying the major environments are: (1) shoal--light-colored calcareous muds and disturbed calcareous muds interbedded with poorly winnowed intraclasts, pellets, and Foraminifera (Glomospira); (2) bioherm--light-colored, slightly winnowed to well winnowed algal remains (Ivanovia); (3) basin--dark, argillaceous, calcareous muds near the biohermal front, with anhydrite followed by halite farther basinward; and (4) channel--light gray brown calcareous muds with siliceous sponge remains, in places overlain by relatively thick quartzose sands.

The depositional history begins with a transgressive sea, during which the green algae Ivanovia found favorable growth conditions on the slopes of calcareous shoals. The algae grew upward and shoreward as the sea rose. Near shore, the very gentle waves formed intraclasts and pellets from calcareous muds. These particles, together with fine fossil debris, then were loosely cemented in a matrix of contemporaneous calcareous mud. In the channels between the masses of algae, siliceous sponges were nourished by circulatory waters. During maximum transgression, calcareous

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muds covered the bioherms. Upon regression of the sea, the shoal environment moved basinward over the bioherms, terrigenous quartz sands were washed into the channels, and finally, evaporites were precipitated from the waters trapped in the basin.

By considering the Paradox basin as a vast lagoon, marginal to the open waters of the Cordilleran mio-geosyncline, we may visualize the Ivanovia bioherms as algal masses or banks growing on lagoonal shoals comparable with the current habitat of the green algae Halimeda.

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