INCONSISTENCIES IN ACCUMULATION RATES OF BLACK SEA SEDIMENTS INFERRED FROM RECORDS OF LAMINAE AND Pb-210

Recently-published estimates for the age of the unit 1-unit 2 contact in Black Sea sediments based on accelerator mass spectrometry (AMS) C-14 measurements (Jones, 1990; Calvert et al., 1991] appear to be older than those based on the previously published chronology based on lamina couplets [Degens et al., 1980; Hay, 1988] by a factor of 2 to 3. To help reconcile the differences, we compare sediment accumulation rates based on the Pb-210 method with estimates based on lamina counts for two cores from the Black Sea abyssal plain. Accumulation rates estimated using the Pb-210 technique have varied little over the last 150 years from the averages of 55 and 50 g m(-2) yr(-1) at stations in the western and eastern basins, respectively. These values are about a factor of 2 lower than accumulation rates derived by counting lamina couplets over the dated intervals. Close examination of the laminae suggests that the descrepancy exists both because it is difficult to count the very fine laminae and because a complete couplet is not deposited every year. In order to provide a useful stratigraphic horizon for future investigators studying sedimentary records of the Black Sea, we estimate the age of a distinct black marker horizon which can be easily identified across the entire abyssal plain to be 150+/-8 years (deposited in 1838+/-8 A.D.).