Dissolution of Calcareous Foraminifera in Microfossil Slides

Dissolution of calcareous foraminiferal tests was noted during a recent study of the foraminiferal standing crop in the northern Adriatic Sea. The dissolution took place after the specimens were stored in microfossil slides. Extensive tests have pointed to the interaction between the material used so far to file foraminifera and the calcium carbonate of the shell. Other materials are more suitable for such purposes and their use should be encouraged. INTRODUCTION A study on living benthic foraminifera (Class: Rhizopodea) from a permanent station in the northern Adriatic Sea, was commenced in February 1991 by the CNR Istituto per lo Studio della Dinamica delle Grandi Masse. To identify living foraminifera the samples of bottom sediment, taken every two months, were stained with a solution of ethanol and Rose Bengal (C20H2 05 14 C14 Na2) according to a procedure widely used (e.g., Daniels 1970; Barmawidjaja et al. 1992). Samples were wet sieved using a 63gLm size sieve, and oven dried at 50?C; the foraminiferal fauna was then concentrated using carbon tetrachloride (CC14). During the microscopic work, a number of individuals were stored in microfossil slides and fixed with tragacanth gum. Within a short time the tests began to dissolve and within a few hours the calcareous tests were completely changed into a gelatinous substance, while the arenaceous tests remained intact. The dissolution of benthic foraminifera reported in the literature (Corliss and Emerson 1990; Jonasson and Patterson 1992) attributes the cause to either an inadequate buffering of formalin due to the high amount of organic carbon present in samples or to the anoxic state of the sediment, but neither of these explanations could apply to our case. Firstly, the dissolving occurred 0