Palynological studies Vacherie and Rayburn's domes North Louisiana salt dome basin

A problem associated with the interpretation of the Quaternary deposits over Vacherie and Rayburn's domes is that, in each instance, known Quaternary sediments characterized by coarse sands and chert gravels are underlain by sediments whose age is uncertain. In the case of Vacherie dome, the sediments consist of fine sands with small amounts of silts and clays (anomalous sands). At Rayburn's, a stratum containing calcite boulders and cobbles overlies anhydrite caprock. An objective of the palynological studies reported here was to generate data that would help in determining the age of these two units. A literature search established diagnostic palynological trends within the Tertiary and Quaternary of the Gulf Coast. Diagnostic trends of known geologic age from the study area were determined. Pollen assemblages were extracted from samples derived from cored and calyx borings above both domes using standard palynological extraction methods with some slight modifications. Results of the examination of pollen suites at Vacherie suggest the anomalous sands can range from Miocene (20 million years) to Quaternary in age. Prior to these studies, the age of these sands could only be postulated as ranging from early Tertiary (65 million years) to Quaternary. Pollen assemblages present in the boulder zone at Rayburn's indicate an age range from Oligocene (30 million years) to late Pliocene. More important, pollen from the known Quaternary at Rayburn's proved useful in differentiating glacial from interglacial deposits. Rates of dissolution of the salt and resultant subsidence of very recent Quaternary deposits, dated by 14C methods, were calculated to be one foot per thousand years during the last 15,000 years. 25 references