RECOVERY OF MICROFOSSILS
A] Recovery of microfossils from ordinary shales, Siltstones, soft calcareous shales, semi consolidated sediments and claystones.
Rock samples are fragmented into pieces of more than 1-2cm and less than 2-4mm. Crushed material is then kept in a metal container containing about 1 litre of distilled water and allowed to soak for 1-2 hours. once the sample is disintegrated the mixture is stirred and allowed to settle. Then it is decanted, process is repeated till water poured off is clear. The wet Residue is then dried on hotplate under observation and then screened through standard sieves of 10-, 35-, 60-, 120-, Mesh content of each sieve is then transferred to separate plastic bottles and numbered each fraction of content is then observed separately under microscope.
B] Recovery of microfossils from siliceous, carbonaceous, fissile shales.
Jones has suggested to boil the rock fragments into solution of photographic hypo. after boiling for some time the mixture is spread in shallow enamel tray till liquid hypo evaporates. Formation of hypo crystals leads to disintegration of rocks. To recover conodonts and other chitinous remains from Fissile, black shales, Jones has suggested to split shales into thin lamellae which can be observed under microscope if fossils are observed, they are circled preferably by a light colour pencil, then with dissecting needles all Matrix around the Fossil is trimmed off making it isolate and removed with pointed, long nosed plier. Then Fossil is placed on slide.
C] Resistant shales.
Modified techniques such as thoroughly drying, heating, dipping in kerosene or gasoline and repeating the above steps to disintegrate such shales and recover the microfossils.
D] shales containing diatoms and dinoflagellates.
Fragments of such shales are boiled in con.HCL for about 15 minutes. then without washing fragments are kept in a con. HNO3 and boiled for another 15 minutes. after thorough washing with water it is again boiled in con H2SO4 .
Material is then washed and boiled with NAOH, for 5 minutes to disintegrate it. To neutralize NAOH, few drops of HCL are added after cooling, remaining samples are pipetted out or taken off by dropper and kept in a water glass to evaporate it. A small drop of pipette sample is kept on clean glass slide and gently spread with the distilled water and allow to evaporate.
E] Dark organic Marine shales.
Dark shales are broken in small pieces of about 0.5cms and kept in a copper beaker containing 52% of N hydrophoric acid and allowed to digest for 16 hours. Residue is then diluted with distilled water, centrifuged, Rewashed and recentrifuged trice. Residue left after centrifuge is mixed with glycerin and if possible stained with light red dyes and observed under microscope for Organic Walled microfossils like pollens, spores, and similar microfossils.
RECOVERY OF MICROFOSSILS FROM THE LIMESTONE :-
The recovery of microfossils from limestones depends upon the chemical composition of the microfossils and the amount of silica and dolomite in the limestone. A preliminary test is done.
A] If the fossils are calcareous, they will be difficult to extract from the limestone. however, if the limestone is crushed to approximately granule size (2-4 mm), washed, and decanted certain percentage of the specimens, including foraminifera and entire ostracods, will break free of the limestone. The remaining Rock fragments may then be examined and fossils cleaned from the matrix with fine dissecting needles. it is advisable to leave the cleaned specimen in the limestone, rather than risk destroying it by removing it from the rock surface, unless the limestone is much soften than the fossil.
B] If the microfossils are arenaceous, siliceous and chitinous in composition as shown by preliminary test then the rock specimen is immersed in a dilute solution of HCL (10%) or Acetic Acid (50%) close and allowed to digest, when effervescence has ceased, the spent acid is poured off, and new acid added. This process is repeated until No effervescence occurs. The Residue in the beaker is washed, filtered, dried and prepared for inspection under the microscope. drying should be done on a hot plate with caution, in order to prevent shattering of the specimens.
MACERATION TECHNIQUE [FOR COAL]:-
To macerate means to soften and hence the process of separation of pollens and spores from the coal is also often called as maceration technique. Coal is broken into small pieces and kept in a beaker containing containing schulxe’s solution (mix one part of saturated aqueous solution of KCL with two parts of cold concentrated HNO3) within few hours, the humic matter is removed by maceration. after the digestion the mixture is washed with water till the liquid attains a normal PH of 7.
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Негізгі бет Recovery of Microfossils
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