A new methodology for extracting foraminifera from lithified carbonate rocks and fine-grained sediments: Consecutive uses of dilute acid and basic solutions (DAB)

Abstract

Morphologic characters are of primary importance in identifying foraminifera.Within the last few decades, the use of either dilute acidic (acetolysis) or basic solutions has become widespread for extracting microfossils exhibiting less than optimum preservation in strongly lithified rocks, particularly limestones and claystones. Previous studies have involved the use of different acid or basic solutions for micropaleontologic purposes. This study proposes a new method (Dilute acidic and basic solutions; DAB), which is based on the consecutive use of acidic and basic solutions to free benthic and planktic foraminifera from carbonate rocks (argillaceous limestones, marls, phosphatic limestones, chalks) and fine-grained siliciclastics (claystone). It has been successfully employed to prepare micropaleontologic samples from Upper Cretaceous (Maastrichtian) deposits of the Dababiya Quarry Corehole (Upper Nile Valley, Egypt) of which carbonate content varies between 10-80%. The successive use of these solutions yielded good recovery for quantitative analysis but the effects on preservation (i.e. etching) still remain problematic in some cases. Additional heating of solutions provided promising results to reduce the disaggregation time. Processing time may vary depending upon the terrigenous and organic material content for carbonates and claystones. It can be reduced by monitoring the process, or using some other equipment such as a magnetic stirrer.