We will apply the 11129 I system to the study of the origin and migration history of brines in the Louisiana Gulf Coast Basin. This basin consists of a sequence of sedimentary layers ranging in age from Jurassic to recent. Generally, there exist three different flow regimes in this basin, a shallow fresh-water system, and two deeper systems, one hydropressured, one geopressured, which are characterized by fluids with higher concentrations of solutes. Although the depositional sequence of the sedimentary formations in this basin is well undeerstood, the relation of the brines to their host formations is often not clear. The geochemical characteristics of iodine combined with the half-life of 129 I (15.7 Ma) make this isotope system potentially useful for the determination of source ages for fluids and orgainic material in this basin and, in conjunction with determination of 36 Cl, for the estimate of residence times of waters in their respective host formaiton. The results of this study will give information on the age relation between the fluids and their host rocks, on the relation between fluids in the different parts of the basin and on communication between different reservoirs. Because the presence of iodine is related to that of organic material the result will given information on the origin and the age relation of hydrocarbons in this basin. Since this project represents the first time that this isotope system is to be used on a regional scale in a sedimentary basin, the study will also indicate to what extent the 129 I system is useful for the investigation of fluid movement in basins containing organic material. This has very strong implication for understanding basin evolution, oil accomulation and formation of sedimentary ores.//
