In southwest Louisiana a relationship is found between the salinity of connate waters and the facies changes of the sediments from which they are derived.

The geological setting of the area is discussed. Facies changes are important in determining the character and relative amounts of sand, shale, or limestone deposited.

Seventy-two salinity determinations were made on waters from sixty-nine wells in twenty-nine oil or gas fields. From these data it appears that the salinity of formation waters from sand bodies is a function of the quantity and degree of compaction of adjacent shales.

The important considerations and results of this reconnaissance study may be summarized as follows.

1. Cenozoic sediments in southwest Louisiana reflect, with lateral variations in their character and quantity, the rapid facies changes in their cyclic depositional history.

2. The saline content of the connate waters obtained for this study appears to be correlative with the relative percentages of sand and shale found in these sediments.

3. High salinities (up to 4½ times that of normal sea water) are found in younger sediments (Miocene-Pliocene) where the relative quantity of shale is small and its degree of compaction slight. Lower salinities (down to ½ that of sea water) are found in older sediments (Eocene-Oligocene) where the relative quantity of shale is large and its degree of compaction great.

4. In sediments of the same age, highest salinities mark the updip non-marine part, lower salinities the downdip marine equivalent. The transition between them is gradual.