BIOLOGICAL RESPONSE TO HIGH FLUX RATES OF PYROCLASTICS IN FLUVIAL AND NEARSHORE SHALLOW MARINE ENVIRONMENTS IN THE PANAMA CANAL BASIN

The Late Miocene Gatun Formation, located in the northern-most section of the Panama Canal Basin, is comprised of thick beds of fossil poor pyroclastic deposits (lapilli tuff and ash) and coarse-grained (conglomeratic) volcaniclastic deposits interbeded with fossiliforous ,shallow marine, muddy sandstones and shales. These sedimentary sequences record periods of intense volcanic activity that drove high fluxes of pyroclastic material (carried both fluvialy and aerially) into the shallow nearshore marine environment, followed by periods of volcanic quiescence and a marked increase in abundance and size of Gatun fauna. We use quantitative stratigraphc data from the field and from cores coupled with estimates of faunal abundances and relative size in order to reconstruct sediment transport mechanisms and flux rates of pyroclastic material into the basin as well as to constrain biological response to these high fluxes.