Obtaining rich nannofossil assemblages from 'barren' samples: processing organic-rich rocks in nannofossil investigations.

Abstract

Campanian-Maastrichtian carbonate and marl successions in Israel are rich in organic matter (OM) of marine algal origin. Samples from these sections, which were originally processed for nannofossil study by standard techniques, were found to be almost completely devoid of nannofossils. However, removal of the OM by approximately 10 hours of controlled bleaching with sodium hypochlorite (household bleach) yielded extremely rich and diverse nannofossil assemblages. It is suggested that, by selectively bleaching the OM, calcareous nannofossils which were incorporated within the intricate organic debris were released. The fact that, after bleaching, both abundance and species diversity were clearly increased, and the preservation of the nannofossils had not changed significantly, suggests that the bleaching agent did not 'attack' the nannofloras and did not produce a biased assemblage. The proposed preparation method enables rich and diverse calcareous nannofossil assemblages to be recovered from samples which would have provided poor, or even barren, assemblages with the deployment of standard processing