Depositional models and consequent stratigraphic "standards" are among the most valuable tools in scientific hydrocarbon exploration. Such models have been established for barrier-island systems based on extensive study of modern coastal areas. However, concepts of genetic stratigraphy have been developed only for the end members of the barrier-island spectrum, i.e., transgressive barriers (U.S. east coast type) and progradational barriers (Texas Gulf Coast type). Stratigraphic models for these pure types may be inadequate when exploration deals with ancient systems that fall towards the middle of the spectrum. Therefore, a different model must be developed for these intermediate types.

One such intermediate type of barrier-island system along the peninsular Florida west coast has been recognized and modeled by the author. Caladesi and Honeymoon Islands (just north of Clearwater Beach, Florida) formed at the end of the rapid Holocene sea-level rise by upward aggradation of an offshore bar. Subsequent development of the system has been episodic and complex in response to fluctuations in relative rates of sea-level rise and sedimentation. The resulting stratigraphy reflects alternating shoreline progradation (slow sea-level rise) and recession (fast sea-level rise). Laterally adjacent mud and sand environments are repeatedly superimposed on each other, producing an attractive sequence of source and reservoir lithology different from that of previously studied systems.

This stratigraphic framework can be recognized in subsurface cores and electric logs. This model can be used to identify position in a subsurface barrier-island system and to lead to hydrocarbon discovery.

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