Biostratigraphy

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2. Presented By: Muhammad Asif Abbas Muhammad Zubair Idrees Biostratigraphy 2

3. Table of Content Introduction Fossils and Stratigraphy Principal of Faunal succession Concept of Stage Concept of Zone Rank of biostratigraphic units Classification of Organisms Ranks in Taxonomy Dispersal of Organisms Dispersal Barriers Preservation Potential Marine Macrofossils Biostratigraphic Correlation 3

4. Biostratigraphy Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them. It is based on the principle that organisms have undergone successive changes throughout geological time (evolution). 4

5. Introduction The occurrence of fossils in beds of sedimentary rocks provided the basis for correlation of strata and the concept of a stratigraphic column. H ighly useful method for subdividing sedimentary rocks. 5

6. 6 The main objectives of biostratigraphy are: Differentiation of Strata Correlation Interpertation of earth history

7. Fossils and Stratigraphy Fossils are indicators of processes and environments of deposition, as well as provide the Fundamental information of evolution of Life on Earth. The concept of biostratigraphy is based on the principle that organisms have undergone successive changes throughout geologic time. 7

8. Historical background Law of faunal succession. Concept of Stage. Concept of Zone. 8

9. Principle of Faunal Succession William Smith; 1796 Similarity with superposition of lithostratigraphic units. Fossil bearing strata occur in a definite and determinable order. Was applied to Tertiary rocks only. 9

10. Table 1: Lyell’s subdivision of the tertiary. Name of subdivision Extant species in the rocks ( % ) Pliocene (more recent) Newer Pliocene 90 Older Pliocene 33-50 Miocene (less recent) 18 Eocene (dawn of recent) 3.5 10

11. Concept of Stage Alice d’Orbigny Stages groups of strata containing the same major fossil assemblages. Applied to Jurassic and cretaceous rocks. The boundaries of stages were defined at intervals marked by the last appearance, or disappearance, of distinctive assemblages of life forms and their replacement in the rock record by other assemblages 11

12. Concept of Zone Albert Oppel introduced the concept of zone. He conceived the idea of small scale units defined by the stratigraphic ranges of fossil irrespective of lithology . Oppel noted that the assemblages of fossils that characterized the strata were made up of overlapping ranges of fossils. Oppel noted that the assemblages of fossils that characterized the strata were made up of overlapping ranges of fossils. Main focus was on vertical range of each separate species. 12

13. Major groups of organisms preserved as macrofossils in the stratigraphic record and their age ranges. 13

14. Three Principlal kinds Interval Zone Assemblage Zone Abundance Zone 14

15. Interval Zone: It is a body of strata between two specific, documented lowest or highest occurrences of single taxa . It has three types T axon range zone. C oncurrent range zone. L ineage zone. 15

16. Diagram illustrating the principal kinds of biozones as defined in North American Stratigraphic Commission Note 64, a revision to the 1983 North American Stratigraphic Code. [After Lenz et al., 2001, Note 64-Application for revision of articles 48-54, biostratigraphic units, of the North American Stratigraphic Code: AAPG Bull., v. 85, Figures 4 and 5, p. 373.] Taxon range zone: based on a range of a single taxon . Concurrent range zone : based on the concurrence of two taxa . Lineage zone: successive related taxa forming a zonal sequence. Assemblage zone : 3 or more together. Acme zone: zone of maximum abundance. 16

17. Assemblage Zone : It is defined as a biozone characterized by the association of three or more taxa . It may consist of geographical or stratigraphic restriction. 17

18. Abundance Zone: It is characterized by quantitatively distinctive maxima of related abundance of one or more taxa . 18

19. Zonation schemes used in biostratigraphic correlation. (Adapted from North American Commission on Strati -graphic Nomenclature 1983.) 19

20. Rank of Biostratigraphic Units The biozone is the fundamental unit of biostratigraphic classification. Other biostratigraphic units are formed by either grouping or subdividing biozones . The International Stratigraphic Guide (Salvador, 1994) suggests that some kinds of biozones may be subdivided into subbiozones (subzones) and/or grouped into superbiozones ( superzones ). The North American Stratigraphic Code provides that a biozone may be completely or partly divided into subbiozones . 20

21. Taxonomy is the  science  of identifying and naming species, and arranging them into a classification. Organisms can be classified in a variety of ways, including habitat ( planktonic nektonic, benthonic) and environmental distribution (littoral, neritic , bathyal etc .) T axonomic classification based on morphological and developmental similarities and presumed genetic relationships is most pertinent to recognizing evolution and biostratigraphic zonation . 21

22. Classification of Organisms 22

23. Species s pecies is one of the basic units of biological classification and a taxonomic rank. Paleontologists are more concerened with the species for the detailed analysis 23

24. Ranks in Taxonomy Subspecies and races are distinct sets which show common characteristics that set them apart from others, but which can still be considered to be part of the same species. A genus (plural genera) is a group of species that are closely related, and when an organism is named it is given a genus as well as a species: for example Homo sapien is the Linnaean classification name for the human species. The higher ranks in the hierarchy are family, order, class, phylum and kingdom in order of scale. The major phyla ( Mollusca , Arthropoda , etc.: Fig.) have existed through the Phanerozoic and it is possible to compare fossils to modern representatives of these subsets of the main kingdoms (animal and plant). 24

25. Fig.Taxonomy of Human 25

26. Depositional environment controls The adaptations required to live in a desert compared with a swamp, or a sandy coastline compared with a deep ocean, demand that the organisms that live in these environments are different. The nature of the environment strongly influenced the distribution of fossil groups. Correlation problem between continental and marine environments because very few animals or plants are found in both settings. The rates of sedimentation in different depositional environments are also a factor in the preservation and distribution of stratigraphically useful fossils. 26

27. Dispersal of organisms 27

28. Classification of marine organisms by habitat. 28

29. Barriers to Dispersal Temperature Geographic Barriers Sea-level Changes Plate Movements Other Barriers 29

30. Temperature: Temperature barriers are most important latitudinally , although seasonal and even diurnal temperature changes are also important. Warm water taxa are restricted primarily to the equatorial zone of the ocean Cold-water taxa , on the other hand, can extend their range closer to the equatorial region by migrating down the bathymetric gradient into deeper and colder water. 30

31. Geographic Barriers These geographic barriers arise out of the distribution pattern of landmasses and oceans and variations in water depths of the oceans. All organisms have limited water depths at which they can survive. water that is either too deep or too shallow can constitute a barrier to a particular species of organism. 31

32. Sea-level Changes During a major drop in sea level, water is withdrawn from the continental shelves, exposing much of the inner shelf. rises in sea level, water depths on the outer continental shelf are increased, and the total area of shallow water along continental margins 32

33. Plate Movements Tectonism is the major factor controlling the distribution of landmasses and ocean basins. Plate movements can greatly affect topographic barriers by producing changes in oceanic widths and depths. Plate movements can also alter latitudinal temperature gradients by shifting the geographic position of continents, and they can even affect the distribution patterns of major ocean currents. 33

34. Other Barriers Salinity differences etc. 34

35. Abundance and size of fossils smaller organisms are more numerous and hence the fossils of small organisms tend to be the most abundant. 35

36. Preservation potential Some organisms do not possess the hard parts that can survive burial in sediments The depositional environment may not be favourable to the preservation of remains All organisms are part of a food chain and this means that their bodies are normally consumed, The stratigraphic record is very incomplete, with only a fraction of the environmental niches that have existed preserved in sedimentary rocks. 36

37. Marine Macrofossils The hard parts of invertebrates are common in sedimentary rocks deposited in marine environments throughout the Phanerozoic . The fossils of organisms such as molluscs , arthropods, echinoderms, etc 37

38. Trilobites These Palaeozoic arthropods are the main group used in the zonation of the Cambrian. Most trilobites are thought to have been benthic forms living on and in the sediment of shallow marine waters. They are only locally abundant as fossils 38

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40. Graptolites They appear to have had a planktonic habit and are widespread in Ordovician and Silurian mudrocks . Preservation is normally as a thin film of flattened organic material on the bedding planes of fine-grained sedimentary rocks. The main drawback in the use of graptolites is the poor preservation in coarser grained rocks such as sandstones. 40

41. Brachiopodes Shelly, sessile organisms such as brachiopods generally make poor zone fossils but in shallow marine, high-energy environments where graptolites were not preserved, brachiopods are used for regional correlation purposes in Silurian rocks and in later Palaeozoic strata. 41

42. Ammonoids This taxonomic group of cephalopods (phylum Mollusca ) includes goniatites from Palaeozoic rocks as well as the more familiar ammonites of the Mesozoic. Fossils are widespread, found in many fully marine environments. Goniatites have been used in correlation of Devonian and Carboniferous rocks, whereas ammonites and other ammonoids are the main zone fossils in Mesozoic rocks. Ammonoids became extinct at the end of the Cretaceous. 42

43. Gastropods These also belong to the Mollusca and as marine ‘snails’ they are abundant as fossils in Cenozoic rocks. They are very common in the deposits of almost all shallow marine environments. 43

44. Echinoderms This phylum includes crinoids (sea lilies) and echinoids (sea urchins). Most crinoids probably lived attached to substrate and this sessile characteristic makes them rather poor zone fossils, despite their abundance in some Palaeozoic limestones Echinoids are benthic, living on or in soft sediment 44

45. Corals The extensive outcrops of shallow marine limestones in Devonian and Lower Carboniferous rocks in some parts of the world contain abundant corals. This group is therefore used for zonation and correlation within these strata. 45

46. Marine Microfossils Microfossils are taxa that leave fossil remains that are too small to be clearly seen with the naked eye or handlens . They are normally examined using an optical microscope although some forms can be analysed in detail only using a scanning electron microscope. 46

47. Foraminifera ‘ Forams ’ (the common abbreviation of foraminifers) are single celled marine organisms that belong to the Protozoa Sub kingdom. Calcareous forams generally became more abundant through the Phanerozoic and are abundant in many Mesozoic and Cenozoic marne strata. 47

48. Radiolaria Subclass of planktonic protozoans and are found as fossils in deep marine strata throughout the Phanerozoic . Radiolaria commonly have silica skeletons and are roughly spherical, often spiny organisms less than a millimetre across. 48

49. Other microfossils Algae Ranikothalia Misscilinia Missaalia . Lockhartia Globotruncana 49

50. BIOSTRATIGRAPHIC CORRELATION Biostratigraphy can provide a high resolution basis for the division of strata. Hence a means of correlating between different successions. 50

51. Illustrating graphically the principle of correlation by fossil assemblages 51

52. Correlating different environments Fossils that have biostratigraphic value, but do not contain representatives of the taxa used in the worldwide. Differences in fossil content due to provincialism are not related to the environment. The strata containing the fauna or flora of the local scheme must then be correlated with the global scheme by finding a succession elsewhere in which taxa from both the local and global schemes are preserved. Organisms that are tolerant of different conditions have the widest application and most value as zone fossils. 52

53. BIOSTRATIGRAPHY IN RELATION TO OTHER STRATIGRAPHIC TECHNIQUES Correlation of strata on the basis of lithology . Biostratigraphy is therefore largely independent of lithostratigraphy , although because depositional environment controls the facies of the sediment and also influences the types of organisms that may be present. Biostratigraphy plays an important role in subsurface analysis, although analysis is almost exclusively based on microfossils. 53

54. Schematic diagram illustrating why correlation by abundance biozones 54

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