Abstract
A method for the relatively fast, inexpensive, and safe dissolution of rock gypsum and rock anhydrite for the recovery of palynomorphs is described. Rock gypsum and rock anhydrite deposits are widely distributed geographically and throughout the geologic column. They represent deposition under environmental conditions unlike those of most other rock types. Consequently, palynomorphs and other microfossils recovered from these rocks may present unique paleontological and biostratigraphic insights not provided by other strata. Despite their relatively high solubility, rock gypsum and rock anhydrite tend to be difficult to process and do not yield to typical palynological methods. Consequently, potentially important sequences of sulfate rocks may be largely neglected in palynological investigations. The method described herein utilizes gently boiling dilute (10%) hydrochloric acid (HCl) and will completely dissolve 25 grams of rock gypsum in approximately 1.5 hours. Rock anhydrite can be similarly treated but takes substantially longer than gypsum to completely dissolve. Important aspects of the process include boiling HCl at or near 102 °C, a beaker without a pouring spout but with a loose-fitting cover to reduce evaporation, and quenching of the hot solution in cool, filtered water to prevent reprecipitation of the dissolved calcium sulfate. The size of the rock fragments treated by this process also appears to be of importance with larger pieces of gypsum but smaller pieces of anhydrite producing the best results. Palynomorphs recovered by this method show no apparent deterioration of the exines. In addition to palynomorphs (spores, pollen, dinoflagellates, etc.), the method also resulted in the recovery of other acid insoluble fossils such as foraminiferal test linings, scolecodonts, arthropod fragments and diatoms as well as amorphous inorganic material and acid insoluble minerals. The method is also safe as long as appropriate precautions are taken.
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