The hidden agglutinated foraminifera of the mid-Cretaceous hemipelagic carbonate deposits: A method–derived bias?

Abstract

Five different micropaleontological methods (H2O2, Glauber's salt, liquid nitrogen, acetic acid + Copper(ll) sulfate, and formic acid) were applied to study the differences of obtained agglutinated foraminiferal faunas of typical hemipelagic carbonate deposits of the mid-Cretaceous of Europe, and to prove whether there is a method–derived bias of knowledge about agglutinated foraminiferal faunas in these sedimentological settings. Split samples of the same weight were treated with each method to compare overall (calcareous + agglutinated) numbers of foraminifers per gram, numbers of agglutinated foraminifers per gram, and numbers of agglutinated foraminiferal genera per sample.

The results show that the number of agglutinated foraminifers per gram strongly vary between 0.1 and 7.8 with use of standard micropaleontological methods. With application of formic acid, more agglutinated foraminifers per gram are obtained than with any other tested method. The number of agglutinated foraminifers per gram is 1.5 to 211.0 times higher in formic acid treated residues. Furthermore, with use of standard micropaleontological methods at least 2/3 of agglutinated foraminiferal genera and species are completely missing in these sedimentological settings. Consequently, standard micropaleontological methods are not applicable to study the whole agglutinated foraminiferal fauna, and a bias of knowledge and utility of agglutinated foraminifers in these sedimentological settings is obvious. A separate application of both acetic acid + Copper(II) sulfate and formic acid on samples is suggested for studies on the whole foraminiferal fauna, and a precise description of the applied method in studies is suggested.