Significant quantities of petroleum occur in algal buildups of Pennsylvanian age in the Paradox basin. Isopach and lithofacies mapping by others suggest that low-relief paleostructures appear to have controlled Pennsylvanian sea-floor topography and thus the distribution of the buildups. Several workers have reported that these paleostructures trend northwest and northeast. Therefore, the basin can be visualized as a

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mosaic of fault blocks that were differentially active through geologic time. The buildups are elongate northwest, and their distribution and overall shape appear to be controlled by northwest-trending paleostructures. Some larger buildups (i.e., Ismay) show local northeast-trending thicks within an overall northwest-trending buildup.

Examination of Landsat imagery revealed an extensive network of northwest-and northeast-trending lineaments that parallel linear patterns apparent from aeromagnetic, gravity, and subsurface isopach data. Additionally, outcrops along selected lineaments contain fractures that parallel these lineaments, suggesting that the lineaments are related to fundamental (i.e., basement) fracture zones along which algal buildups may have developed. Comparison of the fracture network to the distribution of algal thickening reveals these buildups occur predominantly along northwest-trending lineaments. Local disruptions within and apparent terminations of the buildups correspond to cross-cutting northeast-trending lineaments. This relationship provides guidance to locating prospective algal buildups Integration of these data with detailed subsurface mapping can refine some leads into prospects. Several of these features have been successfully drilled.

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