Geological applications of fossils

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Geological Applications of Fossils Sue Rigby An introduction to palaeontological data Biostratigraphy Palaeobiogeography Palaeoenvironments Taphonomy + practicals and computer assignments Assessment by practical folder and exam An introduction to palaeontological data a Types of fossil b The potential of the fossil record c How good is the fossil record? d Taxonomy and phylogeny e Data from a single fossil f Data from a set of fossils Practical: A crash course in fossil identification Computer assignment: Manipulating data from fossils a Types of fossil Body fossils Trace fossils Biomarkers, eg dinosterane Isotopic signatures eg light C isotopes Rocks - reefs, coal, oil, black shale etc Temporal information in DNA/RNA b The potential of the fossil record Secular changes in organisms Secular changes in Earth system Local changes in environment Local changes in palaeogeography Short term records of events - ontogeny, population dynamics Relative timescales Post-mortem events c Is the fossil record good enough? For some things but not for others Fossil record is of about 250 000 species About million species known today Probably less than half the total number (But most of these are insects and their fossil record is terrible) Fossil record lasts 3.5 billion years Hence a small sample In addition it is a biased sample Bias in the fossil record To skeletonised organisms, and within this group to organisms with robust skeletons To common organisms - this carries ecological implications To organisms living in environments of net deposition, or at times of the year when deposition occurs And in areas of rapid deposition To more recent fossils Towards higher taxonomic groups To particular sea level stands/ systems tracts d Taxonomy and phylogeny Organisms have a name and are assigned a place in a hierarchy - eg Phylum Vertebrata Order Primates Genus Homo Species sapiens This may also reflect an evolutionary succession, but it may not Eg Climacograptus Phylogeny is the study of evolutionary relationships, usually undertaken with cladistic methods Naming a fossil gives it utility and implies the possibility of deducing its family tree e Fossil climate from plants Most useful feature is leaf morphology controlled by temperature and water availability ie local climate Univariate methods mainly entire/nonentire margins Multivariate methods eg CLAMP (climate leaf analysis multivariate program) also factor in things like leaf size and presence of diagnostic features like drip-tips Also wood anatomy - ring porousity, presence of annual growth rings Using leaves to estimate climatic variables Taphonomy a Fossilized materials b How things fossilize c Preservation bias - information loss and gain d Lagerstatten Practical: Fossil identification test Taphonomic assessment of specimens a Fossilized materials DNA - only back to 50K Proteins - perhaps back to 100K ? Ordovician collagen? Lipids - constitute most chemical fossils Bacteria - ubiquitous but impossible to classify Plant tissues - high levels of bias result from original composition Animal cuticles - as above Shells - reflect conditions of postmortem transport and burial Bones - ditto Plant tissues - high levels of bias result from original composition Bones - reflect conditions of postmortem transport and burial Bones - reflect conditions of postmortem transport and burial b How things fossilize Death Decay - usually rapid, especially in presence of oxygen Retarded by aridity and low temperatures Bioerosion - boring, rasping, fungal infestation Highest in shallow, highly productive areas with low rates of sedimentation Informative about these palaeoceanographic parameters (4 Preservation on or under microbial mats) Transport - almost ubiquitous By physical or biological agents But, mostly transport within habitat - studies suggest death assemblages have high spatial fidelity with local living fauna Time averaging - controlled by sedimentation rate and shell destruction rate Burial - and post-depositional chemical and physical effects Bioerosion - boring, rasping, fungal infestation Highest in shallow, highly productive areas with low rates of sedimentation Informative about these palaeoceanographic parameters (4 Preservation on or under microbial mats) Time averaging - controlled by sedimentation rate and shell destruction rate c Preservation bias What is the quality of the fossil record and how does bias occur? See table a Bias due to variety of biological materials Eg For living intertidal macrobenthos off Washington State 100% of robust shelled forms known from fossils 73% of fragile shelled species 0% of shell-less invertebrates b Bias linked to postmortem environment Biggest divide between land and sea More on the detail of this in practical c Secular trends Precambrian/Cambrian boundary Calcite/aragonite seas d Lagerstatten Extraordinary fossil occurrences Konzentrat-lagerstatten Konservat-lagerstatten eg Flies in amber Hunsruck Slate All geological periods, most environments Windows on the past But what degree of bias? [...]... group - big, small, odd? Unique indicator of conditions? Eg Kodonophyllum from Torquay Limestone f Data from a set of fossils Variations within and between sets of fossils Univariate Bivariate Multivariate measures of form data Explored in computer assignment 2 Biostratigraphy a Stratigraphic procedure b Correlating with fossils evolution vs ecology c Calibration of the fossil record d Confidence limits... the period 580-380 Ma Correlation is often imprecise because sections with appropriate lavas may lack good zone fossils The Precambrian/Cambrian boundary is a good example of this By contrast there are around 50 graptolite biozones for the Silurian (443-417 Ma), so many of these, and their relative lengths remain unconstrained d Confidence limits on stratigraphy Fossils disappear in most places before... around the world - dispersal theories and ideas of vicariance b Dispersal Organisms evolve in one place and migrate to others Maps of modern diversity suggest that it remains highest close to the point where organisms originate Migration away from this site is via corridors of dispersal, and is impeded by barriers to dispersal Corridors often take the form of islands Barriers can be permanent, ephemeral... fossil record d Confidence limits on stratigraphy e Sequence stratigraphy and fossils Practical: A crash course in microfossil identification Computer assignment: Producing a functional biostratigraphic solution from outcrop data a Stratigraphic procedure ‘Stratigraphy is the study of the geometry, composition and time relations of stratified rocks.’ Biostratigraphy addresses these questions via fossil... a rock type, eg Speaton Clay Formation Formation boundaries need not by isochronous Definition of formations is the choice of the individual mapper Correlation Primary unit: Biozone (or zone) This is visualised as a bed or set of beds characterized by a particular fossil, not a time period Different types of zone include: Total range zone Partial range (Overlap) zone Assemblage zone Acme zone Should... - that is barriers form This is a plate tectonic scenario, but works on smaller scales as well, for example river dissection of uplands When two areas are separated, evolution will produce new species in each Species evolution therefore mirrors geological evolution of a region Offers a powerful tool for geoscientists ... reasons for this including sea level changes These often interpreted in the light of sequence stratigraphy Sequences are built up from parasequences which are shallowing-upward sedimentary cycles bounded by flooding surfaces These packets can be erosional on on another Apparent extinctions cluster at flooding sequence boundaries, because they represent times of nondeposition Also, sequences reflecting changing... and this can lead to multiple repeats of faunas, and apparent extinctions of the more diverse shallow water forms 3 Palaeobiogeography a Modern biogeography b Moving organisms - dispersal and vicariance models c Identifying fossil provinces d Examples Practical: Fossil identification test Brookes Parsimony analysis a Modern biogeography The modern distribution of organisms is controlled by geographical... Lower Palaeozoic b Correlating with fossils - evolution vs ecology Why it works: Evolution changes morphology Species disperse Why it doesn’t work Morphology may not reflect phylogeny Local variation may not be an evolutionary signal Species don’t completely disperse Bioturbation Good zone fossils Evolve rapidly Have a wide geographic range Are common c Calibration of the fossil record By isotopic dating,... interval for the true end-point of a range and α is given by α = [(1-C)-1/(H-1) -1] where H is the number of fossiliferous horizons that contain the fossil and C is the desired confidence level (say 95%) In other words, real extinction is more likely to be close to the last occurrence in fossiliferous sections (not rocket science but useful) e Sequence stratigraphy and fossils But most sections are not
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