RECONSTRUCTION OF SEDIMENTARY ENVIRONMENTS IN HOLOCENE COASTAL DEPOSITS OF THE SOUTHWEST NETHERLANDS - THE POORTVLIET BORING, A CASE-STUDY OF PALEOENVIRONMENTAL DIATOM RESEARCH

Diatoms are valuable indicators of palaeosedimentary environments in c oastal wetlands. In this paper, the utilization of diatoms in coastal reconstructions will be demonstrated in a case study, the Poortvliet b oring (southwest Netherlands). Diatoms supply valuable information abo ut palaeosalinity gradients and palaeotide levers in addition to the e xisting geological data set, obtained from sediment cores. The ecologi cal data of taxa are usually gathered from diatom studies in recent co astal environments. The study of the Poortvliet boring shows that info rmation can also be obtained from the past (`the past as key to the pa st') by comparing the trends of the relative abundances of species of which the ecology is `well-known' to those of which the ecology is `un known'. It is argued both on recent and fossil data that Cymatosira be lgica and Rhaphoneis minutissima have a tychoplanktonic life form.