Kerosene or hydrogen peroxide? Comparison between recovery methods of mineralized microfossils in siliciclastic rocks

Abstract

One of the most important steps in the recovery of mineralized wall microfossils is chemical preparation. However, this process can often be destructive to microfossils if they are not applied extremely carefully. In this way, this research tested two different methods of micropaleontological preparation to compare the rock disaggregation and the amount of recovered microfossils between the two methods. To achieve the objective, the samples were attacked with 20% hydrogen peroxide concentration and pure kerosene in fractions of 200g of each collected sample. Thirteen samples were collected, with different compositions, such as sandstones, shales, heteroliths and siltstones. After preparation, the samples were washed over sieves with a mesh between 420 and 75 μm. The disaggregation rate was calculated based on the initial mass and the mass retained on the 420 μm sieve. These values were plotted in a scatter diagram and the dispersion coefficient r was calculated, which indicated a strong positive linear correlation between the two methods. The strong linear correlation between the disaggregation rate of the samples indicates that probably the parameters that influence the rock disaggregation are intrinsic to its characteristics. Regarding the recovery of microfossils, in the kerosene method the hyaline foraminifera and phytoclasts presented a better preservation, while in the hydrogen peroxide method the agglutinating foraminifera had a better recovery. As a secondary result this research presents new data about the microfauna of the Rio Bonito Formation. The taxa retrieved were the genus Paralingulina, Thuramminoides?, Saccammina and fusiform morphotypes, three phytoclast, an ostracod and unidentified bioclasts.