Formal zones have now been proposed for virtually the entire stratigraphic range of nannoplankton. Those for the Late Cretaceous and Cenozoic, though in various states of standardization, are generally applicable. However, the study of Early Cretaceous nannofossils is just emerging from the descriptive state, taxa are becoming stabilized, and attention is being directed to their stratigraphic and geographic distribution patterns. Recently published zonations, based primarily on coccoliths and related forms, are reviewed and evaluated in terms of their practical utility in the subsurface of the Gulf Coast. A state of flux is indicated by the general lack of agreement among these zonal schemes, either in terms of species ranges or in the choice of species by which zones sho ld be defined. These conflicts suggest, in part, that provincialism and perhaps homotaxis are involved. Most of these zonations have been established outside of the Gulf Coast. The practice of defining zonal boundaries by evolutionary appearances renders them difficult to apply to most subsurface samples. Consequently, none of these zonations are entirely satisfactory.

Nannoconids are an important, and someplaces the only, constituent in Gulf Coast Early Cretaceous nannofossils suites. This group represents a remarkable evolutionary lineage consisting of approximately 12 usable species. They are geographically widespread and their occurrence in varied lithofacies suggests that they were less environmentally restricted than many nannoplankton. They apparently are less susceptible to diagenetic destruction than other calcareous microfossils and consistently are recovered from the deepest wells of the region. Although nannoconids themselves do not provide the desired degree of resolution, they are indispensable as a means of establishing a basic biostratigraphic framework which can be augmented by less common occurrences of coccoliths and related nanno ossils, as well as other microfossil groups. Despite

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shortcomings, which reflect mostly the state of the art, calcareous ynannofossils are increasingly important in Gulf Coast Early Cretaceous exploration.

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