Taphonomy of tidal marsh foraminifera: implications of surface sample thickness for high-resolution sea-level studies

Previous research has shown that intertidal foraminiferal faunas can be use d to document Holocene relative sea-level change and large prehistoric eart hquakes. Applications like these, however, require an understanding of the impact of infaunal habitat and taphonomic processes on foraminiferal assemb lages. To evaluate these effects, we analyzed surface sediment samples coll ected along a transect across a tidal marsh at Zeballos on Vancouver Island , British Columbia. Samples of the uppermost 10 cm of sediment in the marsh contain foraminiferal assemblages that permit recognition of a greater num ber of elevation-controlled marsh assemblages than samples of the top centi meter, which are generally used in sea-level studies, This is because the u pper 10 cm contain most infaunal foraminifera species, whereas the top cent imeter commonly lacks some of these species. A 10-cm thickness is somewhat arbitrary, but most foraminiferal taphonomic biasing occurs in the top 10 c m of the marsh, (C) 1999 Elsevier Science B.V. All rights reserved.