Geochronology in the Gulf of Mexico. Part I

The geochronology of the Pleistocene sediments in the Gulf of Mexico is currently being investigated. A modification of the Pa ²³¹/Th ²³⁰ dating method is proposed. It consists of the determination of Po ²¹⁵, a daughter of Th ²²⁷, by alpha spectrometry. This method is feasible if all the Th ²³⁰ and Pa ²³¹ in the sediments is derived from the uranium dissolved in sea water. It is also possible to date sediments by this method if additional land derived Th ²³⁰ and Pa ²³¹ are present, provided they are in the same ratio as they are produced in sea water. It has been found that low Th ²³⁰/Th ²³² ratios exist in the Gulf of Mexico indicating that land derived Th ²³² is present in the sediments. This suggests that some Th ²³⁰ and Pa ²³¹ might have been added to the Gulf sediments by this mechanism. A comprehensive study is therefore under way to determine the Th ²³⁰, Th ²³² and Pa ²³¹ content of the Mississippi River water and sediments. If the Th ²³⁰/Pa ²³¹ ratio is the same the fresh water sediment as the ratio of their parent uranium isotopes or if the land contribution is determinable, the Th ²³⁰/Pa ²³¹ dating method may be valid for the Gulf of Mexico.