CAN THE CONFINEMENT INDEX (CALCULATED ON THE BASIS OF FORAMINIFERAL POPULATIONS) BE USED IN THE STUDY OF COASTAL EVOLUTION DURING THE QUATERNARY

One of the major present preoccupations of ecologists is to foresee th e effect of the predicted sea level change on the coastline, and there fore on the biosphere. Prospective studies first require a thorough kn owledge of present conditions and of past evolution. Paralic environme nts are very sensitive to coastline variations, and provide one of the most sensitive tools for studying sea level change. One of their main characteristics is the degree of marine influence, named confinement, that depends on climatic conditions and on the coastline morphology a nd evolution. However, these environments are under the influence of c omplex interacting parameters, and their study requires a set of compl ementary tools. A confinement index (Ic), calculated on the basis of t he main species of foraminifers, has been worked out in the paralic en vironments of west Africa. It provides a numerical value that can be c alculated rapidly, and gives an immediate objective indication of slig ht changes in the environment, with a tendency toward more restricted (Ic increases) or less restricted (Ic decreases) conditions. This tend ency might be in relation with sea level change. Thus, Ic is proposed as a preliminary tool for quantifying changes in the paralic ecosystem s. Used together with a set of complementary indicators (sedimentology , geochemistry, and so on) it can be used for the detection of sea lev el change.