Principle of correlation and fossils

PRINCIPLES OF CORRELATION AND FOSSILS GEOLOGY

1. PRINCIPLES OF CORRELATION FOSSILS BY SYED NAWAZ M-TECH 1 ST SEM PETROLEUM EXPLORATION AND PRODUCTION DELTA STUDIES INSTITUTE, ANDHRA UNIVERSITY 11/11/2019 1

2. CONTENT Introduction Principles of C orrelation Principles of Stratigraphy Fossils Uses of Fossils Conclusion 11/11/2019 2

3. Introduction Facies : A set of lithological characteristics of a sedimentary rock, indicates its depositional environment, are called facies. A lateral variation in lithology and fossil assemblage in a formation results a change in the depositional environment, is called facies variation. Index fossil : those fossil forms which have short time ranges of their existence and wide geographical distributions are called index fossils 11/11/2019 3

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6. Principles of stratigraphy 3 major principles for the determination of ages of strata. Law of Superposition : in a series of undisturbed beds, a bed that overlies another bed is always the younger. The youngest bed will be at the top of the sequence Fossil content : each sedimentary beds contain a particular set of fossils by which it can be identified. Lithological character : A sedimentary bed may be identified by the distinct lithological character. But as similar bed are known to occur in formations of widely different geological ages, the lithology is nor of much use for determining relative ages 11/11/2019 6

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8. Principles of Correlation The rock formations of widely separated areas are correlated with the help of the following criteria : Lithology Fossil content Unconformities Metamorphism Igneous intrusion Radiometric dating 11/11/2019 8

9. Lithology Correlation by means of lithology is not reliable because a rock bed when traced laterally may change its character. Further similar rock beds are known to occur in formations of widely different geological ages. 11/11/2019 9

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11. Fossil Content Fossiliferous rocks are characterized by the presence of distinct and definite set of fossils in them. However, just as the beds show lateral variation in the lithology, they may also show lateral variation in the fossil assemblage. Hence only index fossils are used for correlation purposes. 11/11/2019 11

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13. Unconfirmities The unconfirmities are of great significance in classifying and correlating rock formations. The unconfirmities represent breaks in depositional sequence hence they are significant in the interpretation of the geological history. For example, an angular unconfirmity is a surface of erosion that separates 2 sets of beds was formed in the horizontal disposition. This set was deformed and then eroded to a more or less even surface before the upper set was deposited horizontally upon it. 11/11/2019 13

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15. Metamorphism and Igneous I ntrusion Metamorphism In a particular area, the older rocks may show higher grade of metamorphism as compared to the younger rocks. Igneous intrusion The igneous history of a perticular region may be identical to another region In such cases rocks can be correlated 11/11/2019 15

16. RadioMetric D ating The age of intrusive igneous bodies may be determined by the radiometric methods and then the correlation may be done . Parent (Radioactive isotope) and Daughter product (form from decay of parent product) Common methods Potassium-Argon Method Rubidium-Strontium Method Uranium-Lead Method Radio Carbon Dating Age of Rock= 3.323T log(1+( Nd /Np)) T is half life period of radioactive substance Nd is no of atoms of the daughter product Np is no of atoms of parent radioactive substance (present) Eg : 50 gms of Uranium 236 and 25 gm of Lead 206 11/11/2019 16

17. Fossils Fossils are remains or impressions of ancient animals and plants which have been preserved within the sedimentary rocks. Or A fossil is the preserved remains of a once-living organism 11/11/2019 17

18. Conditions of Preservations All the animals and plants are not preserved as fossils. The 2 most important conditions which favors the preservation of fossils are Possession of hard parts Immediate burial 11/11/2019 18

19. Control of Hard Parts After the death of the organisms, the soft parts are generally easily decomposed. Therefore animals like jelly fish and insects which are totally composed of soft parts, are not ordinarily preserved as fossils. The animals which possess hard skeleton have chance of being converted into fossils. 11/11/2019 19

20. Immediate Burial If the animals and plants are not buried quickly after their death. They are likely to be destroyed by chemical decay and other agencies of erosion. 11/11/2019 20

21. Forms of Fossils The fossils are preserved in rocks in a number of different forms which are as follows: Entire organism preserved Petrification of hard parts Molds Casts Carbonization Imprints 11/11/2019 21

22. Entire Organism P reserved The whole body of the organism including its soft parts, may be preserved. Example, the body of mammoth elephants of pleistoncene age are found preserved in the ice in northern siberia . And captain america from avengers 11/11/2019 22

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24. Petrification of Hard P arts Minerals matter like silica, calcium carbonate and iron sulfide may replace the remains of organism particle by particle thereby preserving the structure faithfully. An example of this type of fossil is the silicified wood. 11/11/2019 24

25. Molds An Organism dies and is buried in sediment such as sand, silt or clay The sediment changes to rock and the organism’s body decomposes leaving an imprint or mold in the rock. And molds can be seen if the rock is broken up 11/11/2019 25

26. Casts When an organism dies and is buried in sediment. It’s body decays by leaving a hole in the shape of its body. Water with minerals fills up the hole. When the water evaporates, an image of the original structure of organism is formed as a rock. 11/11/2019 26

27. Mold and Cast? 11/11/2019 27

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29. Carbonization When plants decompose slowly, their organic tissues are transformed into carbon. Such carbonized remains commonly preserve the structure of the original material. Seams of coal are the best examples of carbonized remains of plants. 11/11/2019 29

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31. Imprints Plants and animals which do not have parts may be preserved as imprints in soft sediments such as shales. Distinct impressions of plants leaves are often found preserved in the shales above coal seams 11/11/2019 31

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35. Uses Fossils The fossils are commonly used for correlating the strata and determining their relative ages Fossils indicate whether the rock is a fresh water deposit or a marine deposit Fossils give information about the climate of the times in which they lived The fossils have helped in understanding the evolution of plants and animals 11/11/2019 35

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37. Appearance of questions in end sem 11/11/2019 37

38. References Physical and Engineering Geology by S.K.Garg Principles of Geology by K.M.Bangar https://www.slideshare.net/mlindsay1/fossils-ppt 11/11/2019 38

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