Techniques of study of fossils and Applied aspects of palaeobotany
Techniques of study of fossils:-
1. Ground Thin Section Technique:-
> The specimen to be studied is cut into small-sized sections. Its surfaces are smoothed with 400-carborundum. The smooth surface of the section of the specimen is mounted on a glass slide. It is warmed and coated with melted resin.
> The latter hardens upon cooling. The fastened specimens are cut to form very thin slices which are ground on revolving 100-carborundum lap. Liquid resin-mounting medium is used for mounting the sections.
2. Peel Technique:-
> The first step of this technique involves the etching of the fossil surface with the help of some mineral acids (e.g., hydrofluoric acid) and the final step involves transfer of the exact fossil structure.
> Another mixture usually used for etching is prepared by mixing butyl acetate (1000ml), nitrocellulose (115gm), toluol (10ml), amyl alcohol (200ml) and dehydrated castor oil (5ml). Before using for etching purposes, this mixture is aged for at least two weeks.
> After etching the specimen surface is washed with water, dried and covered with nitrocellulose. Wait for a few hours. The so formed film will dry during this period. It is peeled off from the specimen and studied.
3. Transfer Technique:- Delicate fossil materials are studied by this technique. Several methods are used in the form of transfer technique In the Ash by cellulose film transfer method, peel solution is coated on the delicate fossil material adjoining the rock surface. When the solution dries, the portion of the rock having fossil material is removed. 25% hydrofluoric acid is then used for dissolving the rock material.
4. Maceration Technique:- In the usual method of maceration technique, the fossil material is immersed in a mixture of 5% KOH and Cone. HNO3 for one week. The material is then washed thoroughly with water so that the acid is completely removed. It is then incubated with the solution of NaOH. Hydrofluoric acid is used for cleaning the thus separated cuticularized parts of the fossil material.
5. X-ray Technique:- Highly sensitive celluloid films are used to obtain X-ray photographs of the fossil specimens.
6. Microtomy Technique:- Fossil specimens, specially their macerated tissues, are embedded in celloidin or wax before microtomy. Sectioning of the embedded material is done by usual process of microtomy. The sectioned materials are stained and studied.
Applied Aspect of Studying Fossil Plants:- To provide useful information in the exploration of fossil fuel like coal and oil.
> The plant inhabitants of Palaeozoic- Mesozoic swamps served as a source of coal and formed coal seams. Accumulation of plant materials with a variety of minerals coupled with mud, silt and other organic materials constitute a coal bed. Many plant parts get beautifully preserved as fossils in the stratified sedimentary layers which are closely adjacent to coal layers.
> A stratified scale based on fossils can be made to establish the age of coal deposits and their position in the succession of rocks. Palaeobotanical studies have served as a tool to ascertain age of coal layers, their lateral extent and quality of coal deposits. Such information are required to specify the suitability of a particular coal for energy production. In India, the palaeobotanical study has helped to demarcate the nature and quality of Raniganj coal (Permian Age) from that of Rajmahal coal (Jurassic Age).
> The assemblage of fossil pollen grains and spores has contributed significantly in the field of oil exploration. The problem of oil exploration begins with search of oil reservoirs.
> Exploration of oil is done by:
i. Determining the Thermal Alteration Index:-
- The sporopollenin present in the walls of pollen and spores undergo post depositional thermal changes in course of the geological ages. These thermal changes brought about carbonisation resulting in changes in exine colour of fossil pollen and spores in transmitted light.
- The basic idea involved is the usage of the variation in the exine colour as an indicator of the degree of carbonisation in the rocks to predict their changes of bearing reservoir. Pearson’s colour chart directly relates exine colour to a numerical index called Thermal Alteration Index (TAI) which is a measure of the degree of carbonisation. TAI having a range of 2+-3+ and exinite flourescence colour white-yellow, dark yellow-brown indicates the possibility of exinite containing rock to possess liquid petroleum and even natural gas.
ii. Palynostratigraphy:- To avoid unnecessary and costly drilling the determination of oil zone is made by comparing the biostratigraphic data of one to those of the others.
iii. Defining of Ancient Shorelines:- The sediments parallel to sea shore are rich in oil. The density of pollen and spores decreases in the seaward direction. Sedimentary environment with pollen assemblages are limited to near shore marine or lacustrine waters. Thus by the study of microfossils along with marine microfossils if presents, one can determine the distance and direction of ancient shore lines, possibly bearing oil deposits.