Foraminifera as sea-level indicators

Abstract

There are over 1000 foraminiferal species presently living in marine environments, but relatively few of these can be used as direct indicators of sea level. We detail here certain assemblages occupying marsh environments that can be used for that purpose. Marsh foraminiferal assemblages have been shown to occur worldwide within narrowly defined vertical zones some of which extend less than 10 cm in total vertical range. These assemblage zones, once known, can be relocated in paleo-marsh deposits and accurately related to paleo-sea level. The key to success of these organisms as sea-level indicators is that their primary controlling factor appears to be elevation above mean sea level.

Other foraminiferal assemblages are controlled by a series of parameters (eg. salinity, temperature, dissolved O₂, etc.) which often have no direct relationship with actual water depth. Under appropriate circumstances, some information concerning sea level can be derived from other foraminiferal assemblages using indirect means. For instance areas which have undergone substantial emergence often contain small basins which, prior to emergence, were marine. The marine sediments at the bottom can be identified using foraminifera and the sill elevation of the basin can then be related to some prior sea-level stand.

Both these methods have imperfections, but in areas where both emergence and submergence have taken place they can be combined to obtain a relatively complete sea-level history.