Rocks of the Pliocene and Pleistocene Systems of the Louisiana outer continental shelf are divisible into three rock facies--massive sand, alternating-sand-shale, and massive shale. Similar to older Tertiary rocks of the inner shelf and coastal plain, these facies are related genetically to delta depositional systems. A description of the facies distribution for a discrete time interval can indicate the location of deltaic progradations and the approximate shape and seaward extent of their delta plains. The mapping technique requires a working definition of the individual rock facies to facilitate division of log-correlative time intervals into component facies. Separate isofacies contour maps are drawn simultaneously for each time interval, recognizing that deltaic progr dations are shown by the massive sand isofacies map. The final lithofacies display map shows data relating to all three rock facies and thickness contours showing the distribution of massive sand and alternating-sand-shale facies.

An important interrelation exists between rock facies, structure, abnormal pore-fluid pressure, and the presence of hydrocarbons. Seismic techniques reliably can predict structure and abnormal pressure, and this knowledge can be integrated qualitatively into facies mapping where well control is lacking. Optimum sites for hydrocarbon accumulation can be localized by the recognition of deltas, the locale of their stillstands, and favorable structural and hydrodynamic trapping mechanisms.

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