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2. BiostratigraphyPresented By:Muhammad Asif AbbasMuhammad Zubair Idrees2 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 Correlation3 4. Biostratigraphy Biostratigraphy is the branch of stratigraphy which focuseson correlating and assigning relative ages of rock strata byusing the fossil assemblages contained within them. It is based on the principle that organisms haveundergone successive changes throughoutgeological time (evolution).4 5. Introduction The occurrence of fossils in beds of sedimentary rocksprovided the basis for correlation of strata and theconcept of a stratigraphic column. Highly useful method for subdividing sedimentary rocks.5 6. The main objectives of biostratigraphy are:Differentiation of StrataCorrelationInterpertation of earth history6 7. Fossils and Stratigraphy Fossils are indicators of processes and environments ofdeposition, as well as provide the Fundamentalinformation of evolution of Life on Earth. The concept of biostratigraphy is based on the principlethat organisms have undergone successive changesthroughout 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 determinableorder. Was applied to Tertiary rocks only. 9 10. Name of subdivisionExtant species in the rocks ( % ) Pliocene (more recent) Newer Pliocene 90 Older Pliocene 33-50 Miocene (less recent)18 Eocene (dawn of recent)3.5 Table 1: Lyells subdivision of the tertiary.10 11. Concept of Stage Alice dOrbigny Stages groups of strata containing the same major fossilassemblages. Applied to Jurassic and cretaceous rocks. The boundaries of stages were defined at intervals marked bythe last appearance, or disappearance, of distinctiveassemblages of life forms and their replacement in the rockrecord by other assemblages11 12. Concept of Zone Albert Oppel introduced the concept of zone. He conceived the idea of small scale units defined by thestratigraphic ranges of fossil irrespective of lithology. Oppel noted that the assemblages of fossils that characterizedthe strata were made up of overlapping ranges of fossils. Oppel noted that the assemblages of fossils that characterizedthe 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 stratigraphic13 record and their age ranges. 14. Three Principlal kinds Interval ZoneAssemblage ZoneAbundance Zone14 15. Interval Zone: It is a body of strata between two specific, documented lowest or highest occurrences of single taxa. It has three types1. Taxon range zone.2. Concurrent range zone.3. Lineage zone.15 16. Taxon range zone: based on a range of a single taxon. Concurrent range zone: based on the concurrence of two taxa. Lineagezone: successive related taxa forming a zonal sequence. Assemblage zone: 3 or more together. Acme zone: zone of maximum abundance.Diagram illustrating the principal kinds of biozones as defined in North American StratigraphicCommission 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 American16Stratigraphic Code: AAPG Bull., v. 85, Figures 4 and 5, p. 373.] 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 relatedabundance of one or more taxa . 18 19. 19 Zonation schemes used in biostratigraphic correlation. (Adapted from North American Commission on Strati-graphic Nomenclature 1983.) 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, includinghabitat (planktonic nektonic, benthonic) and environmentaldistribution (littoral, neritic, bathyal etc.) Taxonomic classification based on morphological anddevelopmental similarities and presumed genetic relationshipsis most pertinent to recognizing evolution and biostratigraphiczonation.21 22. Classification of Organisms22 23. Species species is one of the basic units of biological classification and a taxonomic rank. Paleontologists are more concerened with the species for the detailed analysis23 24. Ranks in Taxonomy Subspecies and races are distinct sets which show commoncharacteristics that set them apart from others, but which canstill be considered to be part of the same species. A genus (plural genera) is a group of species that are closelyrelated, and when an organism is named it is given a genus aswell as a species: for example Homo sapien is the Linnaeanclassification 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 thePhanerozoic and it is possible to compare fossils to modernrepresentatives of these subsets of the main kingdoms (animaland plant).24 25. 25 Fig.Taxonomy of Human 26. Depositional environment controls The adaptations required to live in a desert compared with aswamp, or a sandy coastline compared with a deep ocean,demand that the organisms that live in these environments aredifferent. The nature of the environment strongly influenced thedistribution of fossil groups. Correlation problem between continental and marineenvironments because very few animals or plants are found inboth settings. The rates of sedimentation in different depositionalenvironments are also a factor in the preservation anddistribution of stratigraphically useful fossils.26 27. Dispersal of organisms27 28. 28 Classification of marine organisms by habitat. 29. Barriers to Dispersal Temperature Geographic Barriers Sea-level Changes Plate Movements Other Barriers29 30. Temperature: Temperature barriers are most important latitudinally,although seasonal and even diurnal temperature changes arealso important. Warm water taxa are restricted primarily to the equatorialzone of the ocean Cold-water taxa, on the other hand, can extend their rangecloser to the equatorial region by migrating down thebathymetric gradient into deeper and colder water.30 31. Geographic Barriers These geographic barriers arise out of the distribution patternof landmasses and oceans and variations in water depths ofthe oceans. All organisms have limited water depths at whichthey can survive. water that is either too deep or too shallow can constitute abarrier to a particular species of organism.31 32. Sea-level Changes During a major drop in sea level, water is withdrawn from thecontinental shelves, exposing much of the inner shelf. rises in sea level, water depths on the outer continental shelfare increased, and the total area of shallow water alongcontinental margins 32 33. Plate Movements Tectonism is the major factor controlling the distribution oflandmasses and ocean basins. Plate movements can greatly affect topographic barriers byproducing changes in oceanic widths and depths. Plate movements can also alter latitudinal temperaturegradients by shifting the geographic position of continents,and they can even affect the distribution patterns of majorocean currents.33 34. Other Barriers Salinity differences etc.34 35. Abundance and size of fossils smaller organisms are more numerous and hence the fossils ofsmall 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 sedimentaryrocks deposited in marine environments throughout thePhanerozoic. 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 39. 39 40. Graptolites They appear to have had a planktonic habit and are widespread inOrdovician and Silurian mudrocks. Preservation is normally as a thin film of flattened organicmaterial on the bedding planes of fine-grained sedimentary rocks. The main drawback in the use of graptolites is the poorpreservation 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 goniatitesfrom Palaeozoic rocks as well as themore familiar ammonites of theMesozoic. Fossils are widespread, found in manyfully marine environments. Goniatites have been used in correlationof Devonian and Carboniferous rocks,whereasammonites andotherammonoids are the main zone fossils inMesozoic rocks. Ammonoids becameextinct at the end of the Cretaceous.42 43. Gastropods These also belong to the Mollusca andas marine snails they are abundant asfossils in Cenozoic rocks. They are very common in the depositsof almost all shallow marineenvironments.43 44. Echinoderms This phylum includes crinoids (sea lilies) and echinoids (seaurchins). Most crinoids probably lived attached to substrate and thissessile characteristic makes them rather poor zone fossils,despite their abundance in some Palaeozoic limestones Echinoids are benthic, living on or in soft sediment44 45. Corals The extensive outcrops of shallowmarine limestones in Devonian andLower Carboniferous rocks insome parts of the world containabundant corals. This group is therefore used forzonation and correlation withinthese strata.45 46. Marine Microfossils Microfossils are taxa that leave fossil remains that are toosmall to be clearly seen with the naked eye or handlens. They are normally examined using an optical microscopealthough some forms can be analysed in detail only using ascanning electron microscope.46 47. Foraminifera Forams (the common abbreviation of foraminifers)are single celled marine organisms that belong to theProtozoa Sub kingdom. Calcareous forams generally became more abundantthrough the Phanerozoic and are abundant in manyMesozoic and Cenozoic marne strata.47 48. Radiolaria Subclass ofplanktonicprotozoans and are found asfossils in deep marine stratathroughout the Phanerozoic. Radiolaria commonly havesilica skeletons and are roughlyspherical, often spiny organismsless 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 thedivision of strata. Hence a means of correlating between different successions. 50 51. Illustrating graphically the principle of correlation by fossilassemblages 51 52. Correlating different environments Fossils that have biostratigraphic value, but do not containrepresentatives of the taxa used in the worldwide. Differences in fossil content due to provincialism are notrelated to the environment. The strata containing the fauna or flora of the local schememust then be correlated with the global scheme by finding asuccession elsewhere in which taxa from both the local andglobal schemes are preserved. Organisms that are tolerant of different conditions have thewidest application and most value as zone fossils.52 53. BIOSTRATIGRAPHY IN RELATION TOOTHER STRATIGRAPHIC TECHNIQUES Correlation of strata on the basis of lithology. Biostratigraphy is therefore largely independent oflithostratigraphy, although because depositional environmentcontrols the facies of the sediment and also influences thetypes 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 abundance54 biozones 55. 55