Natural dissolution of modern shallow water benthic foraminifera: taphonomic effects on the palaeoecological record

Abstract

Comparison of the living and dead assemblages of benthic foraminifera from the coastal areas of the Skagerrak–Kattegat reveals that, although there are considerable similarities in terms of the presence/absence of species, there are major differences in relative abundance at species level. Furthermore, the relative abundance of calcareous tests in the living assemblages is considerably higher than that of the dead assemblages (average values of 67 and 30%, respectively). Since the environments are microtidal, there is little transport of foraminiferal tests due to tidal currents so there are no introduced exotic species although there is local transport caused by waves and wave-induced currents. However, the major taphonomic process appears to be dissolution, of calcareous tests. This is manifested through etching and breakage of test walls, leading to complete decalcification which leaves a residue of organic linings of certain taxa (e.g., Ammonia beccarii), and a marked increase in abundance of agglutinated tests in the dead assemblages. Although dissolution is normal in marsh settings throughout the world, the Skagerrak–Kattegat area is unusual in the intensity of dissolution in the subtidal zone. Whereas most of the calcareous species occur throughout the investigated depth range (except marsh), two of the subtidal agglutinate species (Eggerelloides scaber and Ammotium cassis) show upper depth limits. Consequently, the agglutinated foraminifera are better indicators than calcareous foraminifera of upper depth limits in these shallow subtidal environments.