ABSTRACT: Short-Lived Radioisotopic Chronology of Lake Pontchartrain Sediments

MAROT, MARCI, and CHARLES W. HOLMES

Seven sediment cores taken throughout Lake Pontchartrain in the Fall of 1995 were analysed for Pb-210 to determine the geochronolgy and sediment accumulation rates. In many portions of the lake, shell dredging has destroyed the sediment record. However, two cores collected from the southern portion of the lake show a disequilibrium profile of Pb-210 activity that indicates the sediments may be dated by this method. In September, 1996, a second set of nine cores were collected immediately adjacent to the New Orleans city storm discharge canals, bayous, and channels where undisturbed sedimentation is expected to have occurred for the last 30-50 years. X-radiographs taken for several of the cores show fine-scale lamination down the entire length of the core, suggesting these cores contain a reliable chronologic record. Several other radioisotopes will be analysed by gamma spectroscopy in addition to Pb-210 in order to construct a more accurate date model.

Once a rate of sedimentation is determined, the concentration of a number of metals will be measured using ICP-MS. At present there is little downcore geochemical data available for the lake. The profiles from this study will help clarify temporal and spatial changes in metal-loading of bottom sediments over the past several decades.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana