N.O. Jannik, Winona State University

F.M. Phillips, New Mexico Tech

G.I. Smith, USGS, Menlo Park, California

Geological Society of America Bulletin 103 (1991) 1146-1159

10Be concentration. total carbon and grain-size were measured in cores collected in undisturbed estuarine sediments of three tributaries of the Chesapeake Bay. These cores were previously studied by Davis [1] and Brush [2.3] for pollen content. age and sedimentation rate. In this work. we compare the results obtained for these various analyses. In the cores. we observed two increases in 10Be concentration concomitant with two major changes in the pollen composition of the sediments. These two pollen changes each correspond to well-dated agricultural horizons reflecting different stages in the introduction of European farming techniques [2]. In the Chesapeake Bay area. the agricultural development. associated with forest clearing. appears to have triggered the erosion. transport. and sedimentation into the river mouths of large quantities of 10Be-rich soils. This phenomenon explains the observed rise in the sedimentation rate associated with increases in agricultural land-use.