EXTRACTION OF CALCIFIED RADIOLARIA AND OTHER CALCAREOUS MICROFOSSILS FROM MICRITIC LIMESTONE UTILIZING ACETIC ACID

Until recently it has been impossible to extract calcareous microfossils form micritic limestone. Studies by Lethiers and Crasquin (1988) and Tur et al. (2001) demonstrated that acetic acid could be utilized to extract calcareous microfossils (e.g. planktonic foraminifera) from indurated micrite.

Hitherto, all calcareous microfossils had to be identified in thin section. During the summer of 2002 the senior author independently developed a somewhat different method of acetic acid extraction. This technique was born of the frustration caused by trying to extract calcified radiolarian from micrite nodules occurring in the Lower Cretaceous part of the Great Valley Supergroup (GVS), in California Coast Range (Mohsen Kariminia, research for Ph.D. dissertation in progress). In the past calcified radiolaria could only be extracted from GVS micrites using concentrated hydrofluoric acid ( Pessagno 1977).

Micrite nodules are the only source of Radiolaria within the upper Tithonian to Aptian interval of Great Valley Supergroup of northern California Coast Ranges. While all Radiolaria recovered from GVS micrite nodules are either calcified or pyritized, this paper describes a method for extracting well preserved calcified Radiolaria from micritic limestone utilizing acetic acid.

The same method resulted in the extraction of well preserved Upper Cretaceous planktonic foraminifera from indurated micrite within the Khoy complex of northwestern Iran and Lower Cretaceous Favusellids from micrite in the Albian Duck Creek Formation of Texas. Assumedly the clay content in the rock matrix, the chemical homogeneity of the test and the heterogeneity of the matrix are the main reasons for the differential solution of calcareous microfossils by the acetic acid. These factors resulted in the rapid dissagregation of carbonate matrix and the release of the calcareous tests from matrix. In most cases the preservation of the extracted microfossils is excellent.