Paleo lecture, page




старонка1/13
Дата канвертавання22.04.2016
Памер1.23 Mb.
  1   2   3   4   5   6   7   8   9   ...   13

PALEO LECTURE, PAGE



I. Tales Told by the Dead
A. Paleontology - study of ancient life
Fossil = any evidence of prehistoric life
1. Paleozoology - study of fossil animals
a. Invertebrate paleontology - study of fossil invertebrates (animals without a vertebral column)
b. Vertebrate paleontology - study of fossil vertebrates (animals with a vertebral column)
2. Paleobotany - study of fossil plants
a. Palynology - study of pollen and spores (some also include marine one celled "plants"; i.e. acritarchs, dinoflagellates, tasmanites, silicoflagellates, diatoms, ebridians, calcareous nannoplankton/coccoliths)
3. Micropaleontology - study of small fossils (includes many groups mentioned under palynology and also foraminifera, radiolaria, chitinozoa, graptolites, pteropods (gastropods), ostracods (crustaceans), conodonts
B. Objectives of the paleontologist
1. Identification
2. Determine Form (= Morphology) and Function
3. Association of plants and animals and environmental reconstruction (paleoecology)
4. Evolution in Various Organisms
5. Dispersal and distribution of plants and animals through space and time (including studies of paleozoogeography/paleogeography and biostratigraphy)
6. Correlation and Dating Rocks
7. Studies of Geochemistry - especially changes in ocean chemistry due to actions of organisms
C. Prerequisites/Preferred Conditions for fossilization:
1. Relatively abundant organisms
2. Presence of hard parts
3. Avoid chemical and physical destruction

- rapid burial, typically within a relatively low energy depositional environment

- preservation depends on Eh/pH environment; plants often preserved within acidic and reducing conditions; calcareous shells and bones typically within non-acidic
D. Types of Hard Parts
1. Plants
a. Cellulose - fibrous polysaccharide forming cell walls
b. Lignin - complex polymer binding cellulose fibers
2. Invertebrates
a. Organic Compounds include:
a1. Chitin = nitrogen-containing polysaccharide (carbohydrate) forming fibrous molecules; Ex. = arthropods
a2. Scleroproteins = fibrous proteins such as collagen (Ex. = graptolites) and conchiolin (Ex. = molluscs)
b. Minerals include:
b1. Calcium carbonate = forms intergrowth of crystals in an organic matrix; includes calcite (Ex. = echinoderms) and aragonite (Ex. = some molluscs; aragonite is a chemically-unstable mineral and typically recrystallizes to calcite)
b2. Opaline silica = often occurs as spicules (discrete parts; Ex. = some sponges) or forms coherent network (ex. = radiolarians)
3. Vertebrates
a. Bone = collagen (a scleroprotein) hardened by mineral salts (mostly calcium phosphate); with cellular structure
b. Cartilage = a resilient, partially fibrous protein; usually not preserved
c. Teeth = with dense calcium salts overlain by enamel (almost pure calcium phosphate and carbonate)
E. Types of Fossil Preservation
1. Unaltered
a.Unaltered Soft Parts

- unstable organic compounds such as carbon, hydrogen and oxygen

- rarely preserved; sometimes within permafrost (Ex. = mammoths) or glaciers, mummification in dry caves (ground sloths), tanning by humic acids in peat (Ex. = "bog people"), within anaerobic aqueous environments (such as the "limnic stagnation deposits" in the Eocene German "brown coal" at Messel), within oil seeps, and in amber
b. Unaltered Hard parts (Durapartic Preservation)

- preserve original calcium carbonate or calcium phosphate "hard parts" such as bone (ex. = La Brea tar pits, California), shells, "coralline" algae; relatively rare


2. Altered - more typical case.
a. Petrification includes:
a1. Cellular Permineralization (Impregnation) = percolating groundwater introduces minerals (ex. = silicates, carbonates, iron compounds, phosphates) into the pore spaces (especially permineralize calcareous shells with calcite; also wood and bone often permineralized)
Coal Balls = permineralize uncompacted peat with calcium carbonate; especially important for Carboniferous plant studies from bituminous coal beds
a2. Recrystallization = change form and/or size of original crystal structure; Ex. = conversion of aragonite to calcite often destroys fossil detail
a3. Replacement = percolating ground water dissolves hard parts and replaces them with different minerals; Minerals involved include carbonates, silicates, iron oxides such as hematite and "limonite", pyrite, and collophane
b. Carbonization - volatile components (hydrogen, oxygen, nitrogen) decrease and the outline of the animals is preserved as a carbon film; scleroprotein, chitin, cellulose and lignin may be carbonized; often combines with petrification
Coalified Compressions - plant cell walls collapse after deposition; cause loss of soluble materials with residues altering to black, coaly deposits
3. Traces of Animals
a. Molds and casts
Mold - impression of skeletal (or skin) remains in an adjoining rock

External mold = impression of outer side

Internal mold (steinkern) = impression shows form or markings of inner surface
Cast - original skeletal material dissolves and cavity (mold) fills with material
Endocast- natural infilling of cranial cavity (may study brain evolution in fossil mammals)
b. Ichnology - study of trace fossils (Ichnofossils = tracks, trails and burrows of organisms)
c. Coprolites - fossil excrement of animals; may contain undigested remains of food
F. Pseudofossils

- many rocks and rock structures look like fossils, but aren't!


- the following represent a few sedimentary features that may be confused for fossils:
1. Differential Weathering

- weathering of rock and mineral surfaces often yield fossil-looking features


2. Nodules

- formed by filling voids in the sediment and incorporation of sedimentary materials within the sedimentary body


a. Chert Nodules

- microcrystalline quartz; typically found along bedding planes in limestone


b. Septaria

- large nodules with radial and concentric cracks in their centers


- Melikaria are boxwork patterns of material filling septarian cracks; may be all that is left after weathering of the septaria
c. Rosettes

- radiating macrocrystalline bodies of discoidal or spherical shape, consisting essentially of one mineral (typically pyrite, marcasite, barite, or gypsum)


3. Concretions

- mineral growth within sediment often forms structures that resemble bones, turtle shells, logs, etc.


4. Dendrites

- precipitation of manganese oxide along bedding planes creates fern-like patterns

II. Rocks, Fossils and Ages
A. Biases of the Fossil Record

- certain environments and processes preferentially preserve fossils; collecting techniques are also biased


1. Hard Parts - soft-bodied organisms rarely fossilize
2. Preferential environments
- those with rapid burial
a. Aquatic environments preferentially preserved; especially shallow waters of continental margins and inland seas, deltas, lagoons, rivers (especially floodplains), coal swamps and lakes

- typically lower-energy (finer grain size) environments with best preservation; Ex. = limestone, shale, siltstone, chert


b. caves and fissure fillings also good for preservation
c. Konservat-Lagerstätten

- fossil localities exhibiting exceptional preservation

- fossilization often takes place under anaerobic conditions and/or within fine-grained sediments

- some examples include the Burgess Shale (Cambrian; British Columbia, Canada), Mazon Creek (Pennsylvanian; Illinois), Solnhofen Limestone (Jurassic; Germany), Messel (Eocene; Germany) and La Brea (Pleistocene; California)


3. Preservational Biases

- most fossils are known from species that were common, widespread and long-lived


4. Collecting Biases
a. best fossil hunting is often in erosional areas such as "badlands" of deserts and semiarid areas (where you can see the fossils)
b. collecting techniques may be biased to large animals, small animals or animals from certain paleoenvironments
B. Geologic Time
1. Relative Dating Techniques

- sequence geologic events


a. Biostratigraphy - see section below
b. Lithostratigraphy - correlation based on rocks
Correlation is often Accomplished by Use of:
b1. Key (Marker) Beds - distinctive bed which is nearly the same age everywhere; Exs. = volcanic ash, tillite
b2. Unconformities - deposits resting on unconformities (erosional surfaces) are of similar age; often "global" unconformities are due to marine regressions [Eustatic (worldwide) lowering of sea level]; unconformities can be located in subsurface by seismic surveys
c. Formal Lithostratigraphic Units - rock-stratigraphic units
c1. Formation - fundamental rock-stratigraphic unit; with mappability and lithologic constancy
c2. Member - subdivision of formation; may be mapped locally
c3. Group - contains several formations united on basis of similar characteristics
c4. Supergroup - composed of several groups
2. Absolute (Actual) Dating Techniques

- yields dates in years


a. Radioactivity
a1. Isotopes - forms of an element with same number of protons, different numbers of neutrons
a2. Radioactive Decay - atoms change to another element by releasing subatomic particles and energy; parent isotope decays to daughter isotope at a constant rate
a3. Radiometric Dating - measure amount of parent materials relative to their daughter products

Half Life - time required for isotope to decay to half its original amount

- in paleontology often use potassium-argon (especially on volcanic rocks) and Carbon-14 (for Pleistocene/Holocene deposits)
Notation:

Kiloannum (plural = Kiloanna; kilo an) = Ka = thousands of years in the radioisotopic time scale


Megannum (plural = Meganna; mega an) = Ma = millions of years in the radioisotopic time scale; M.Y. (or m.y) = millions of years, without reference to the radioisotopic time scale
Gigannum (plural = Giganna; giga an) = Ga = billions of years in the radioisotopic time scale
b. Magnetic Stratigraphy
b1. Earth's Magnetic Field due to motions of liquid, iron-rich outer core (behaves like bar magnet with north and south pole)
b2. Magnetic Reversal - reversal of polarity in earth's magnetic field; is recorded in iron-rich igneous and sedimentary rocks (Normal Interval = polarity same as todays; Reversed Polarity = polarity opposite to todays)
b3. have constructed Paleomagnetic Polarity Scale based on magnetic reversals and "tied" with absolute dates (Ex. = Text, p. 34)
Chrons = larger intervals defined by magnetic stratigraphy
3. Chronostratigraphic Units - body of rock representing a particular interval of time
Time Unit Chronostratigraphic Unit

Eon Eonathem

Era Erathem

Period System

Epoch Series

Age Stage


D. Geologic Time Scale
- learn Time Scale (Last Page of Lecture Notes)
E. Biostratigraphy ("Stratigraphic Paleontology")
1. Biostratigraphic distributions are controlled by:
a. Evolution

b. Paleoecology - no organism inhabits all environments

b1. Facies-controlled organisms = restricted to particular sedimentary environments (often with slow evolutionary change)


b2. Biofacies = facies distinguished on the basis of their fossils (Ex. = reef biofacies - may have corals, coralline algae, stromatoporoids, rudist bivalves)
2. Biostratigraphic Units

- body of rocks delimited from adjacent rocks by their fossil content

- often use fossils for Correlation (matching stratigraphic sections of the same age)
a. First appearances of fossils may be due to 1) evolutionary first occurrence 2) immigration

FAD = First appearance datum FOD = First occurrence datum


b. Last appearance of fossils may be due to 1) extinction event 2) emigration

LAD = Last appearance datum LOD = Last occurrence datum


c. Biozone

- basic unit of biostratigraphic classification

- based on the distribution of Index Fossils (fossils characteristic of key formations; should have short time span, wide geographic range, independent as possible of facies, abundant, rapidly changing and with distinctive morphology)
Types of Biozones Include:
c1. Assemblage Zones - strata grouped together on the basis of an assemblage of forms
Oppel Zone - interval of common occurrences of all or a specified portion of the taxa
Mammal age - geochronologic unit based on an association of fossil mammals considered to represent a particular interval of geologic time; important for correlating Cenozoic fossil vertebrate faunas worldwide
c2. Range Zones - plot stratigraphic range of fossil(s)
Teilzone = partial, local range zone
Taxon Range Zone (Acrozone) - total horizontal and vertical range of a taxon
Concurrent range zone - overlapping ranges of specified taxa

- Taxon and Concurrent Range Zones are most important range zones


c3. Acme Zone (Peak Zone, Abundance Zone)

- grouped together because of abundance of certain forms


3. Major Fossils used in Biostratigraphy

- best are pelagic [planktonic (floating) or nektonic (swimming)] forms


a. Macrofossils

- ammonites (Permian and Mesozoic)

- land mammals and plants (Cenozoic)
b. Microfossils

- most important include foraminiferans, radiolarians, palynomorphs (pollen, spores, dinoflagellates, acritarchs, calcareous nannoplankton), conodonts


4. Quantitative Biostratigraphy

- use statistics to compare the degree of similarity between fossil faunas


- use Similarity Coefficients including:
a. Simpson Coefficient = C/(N1+N2)
b. Jaccard Coefficient = C/(N1+N2-C)
c. Dice Coefficient = 2C/(N1+N2)
d. Otsuka Coefficient = C/square root of N1N2

WHERE: C = number of items in common

N1 = number of species in the smaller sample

N2 = number of species in the larger sample


The larger the values of the coefficients calculated from two faunas when compared, the closer in age they are considered to be. But it is difficult to correlate quantitatively without determining the relative value of the index fossils!

III. Continents Have Moved and Climates Have Changed


A. Paleobiogeography

- study of the ancient geographic distribution of organisms


1. Differences in distribution are due to
a. Barriers to organism dispersal - include physical barriers (Ex. = land and water barriers) and environmental barriers (i.e. latitudinal and temperature changes)
b. Historical Factors - evolution of different organisms in different regions, etc.
2. Ancient Faunal Provinces

- often classified in modern ecosystems on the basis of the number of endemic species (= organisms confined to one biogeographic unit)


a. Faunal Realm - largest biogeographical unit; over 75% endemic species
b. Faunal Region - between 50% and 75% endemics
c. Faunal Province - between 50% and 25% endemics
d. Faunal Subprovince - less than 25% endemics

- these classifications not typically used for fossil assemblages


3. Influences of Plate Tectonics

- one of major pieces of evidence for the presence of supercontinents was the common distribution of plants (EX.= Glossopteris flora) and animals (the aquatic reptile Mesosaurus) on the "Gondwana continent"


a. Closing Oceans

- convergent plate margins often cause greater similarity of organisms


b. Opening Oceans

- continental fragmentation often leads to fragmentation of ranges of organisms and increasing evolutionary dissimilarity through time


c. Accreted Terrains

- accreted (suspect) terrains are caused where microcontinents suture to other continental plates

- individual accreted terrains are often recognized by their distinctive (exotic) fossil faunas
d. Vicariance Biogeography

- modern distribution of organisms is largely due to "vicariating" (fragmenting) the ranges of organisms (due to plate tectonics, ice ages, etc.)


B. Paleoecology
1. Ecology - study of the factors that govern the distribution and abundance of organisms
2. Paleoecology - the relationships between species represented in the fossil record and the environments in which they inhabited
3. Taphonomy - all aspects of the passage of organisms from the biosphere to the lithosphere
a. Taphonomic Processes
a1. Physical Processes

- examples include mechanical breakdown of organic material by waves and currents, and burial by sediments


a2. Chemical Processes

- examples include alteration of shell mineralogy, and leaching of shells and skeletons by groundwater


a3. Biological Processes

- examples include destruction of hard parts by scavengers, and breakdown of skeletons by the action of organisms (boring algae and sponges, etc.)


b. Taphonomic Biases - certain environments and taphonomic processes preferentially preserve fossils; collecting techniques are also biased
b1. Preferential environments - Aquatic environments preferentially preserve fossils
b2. Preservational Biases - most fossils are known from species that were common, widespread and long-lived
b3. Time Averaging - fossil assemblages will be less similar to the living community the greater the temporal variation of the living community and the longer the time averaged in the fossil assemblage
b4. Collecting Biases - best fossil hunting where rocks and sediments are exposed; can avoid biases by bulk collecting matrix and estimating proportions of fossils by constructing quadrants or line transects
c. Size Distribution - often fossils are size-sorted due to current action; Micromorph Faunas consist of unusually small individuals of species whose size is due to unusual environmental factors
4. Sedimentary Environments - portion of the earth's surface with distinctive physical, chemical and biological characteristics
a. Facies -body of sediment or rocks with distinctive characteristics

Facies Models - summary of specific sedimentary environments


b. Walther's Law - the vertical sequence of rocks may reflect the horizontal succession of environments/facies
5. Biologic Criteria

- must be cautious in environmental interpretations based on fossils

- modern ecosystems are characterized by biocoenoses ("life assemblages"); paleontologists find primarily thanatocoenoses ("death assemblages", or taphocoenoses)
a. Habitats - environments inhabited by life
b. Species relationships

Ecological niche - way in which a species relates to its environment


c. Ecologic Community - populations of several species living together in a habitat

- paleontologists do not observe fossil communities ("paleocommunities"); what they observe are assemblages of fossils (fossils that occur together repeatedly define fossils assemblages)


c1. Ecosystem - organisms and their physical environments
Fauna - animals of an ecosystem
Flora - plants of an ecosystem
Biota = flora + fauna
c2. Diversity

- number of species that live together in a community; tropical climates contain more diverse plant and animal communities

Diversity = number of species/number of specimens
c3. Food chains - sequence of nutritional steps in an ecosystem
Trophic Level - position in food chain; organisms from lower trophic levels have more potential for fossilization than those from higher trophic levels (because organisms from lower trophic levels are more numerous)
c4. Food webs - nutritional structure of ecosystem in which more than one species occupies each level
Competition - two species vie for limited environmental resources
Autotrophs (Producers) = manufacture their own food; "plants"; form lowest trophic level and constitute the base of the biomass "pyramid"

Heterotrophs (Consumers) = feed on other organisms; consist of "animals" (much energy is lost cycling through higher trophic levels, and therefore with fewer organisms)


Herbivores = feed on producers
Predation = effect of a predator on a prey species
Carnivores = feed on other consumers by predation
Parasites = derive nutrition from other organisms without killing them
Scavengers = feed on dead organisms
Commensalism = biological association beneficial to one but does not hurt the host
Symbiosis = mutual benefit to both participants
c5. Succession = changes due to modification of the environment by organisms
Stages of Succession Include:
Pioneer Stage: with abundant, rapid-growing, short-lived species with abundant offspring (r-strategists)
Mature Stage: with the most diversity
Climax Stage: slower-growing, larger, longer-lived species with fewer offspring (K-strategists) replace organisms of earlier stages
6. Limiting factors

- environmental factors controlling species distribution

- includes chemical, physical and biological factors
Organism Distribution (Especially Marine) Depends Upon the Following:

a. Seawater Properties - Density and Viscosity

Density of aquatic organisms typically equals water density

Viscosity - influences shape and feeding (there are many "filter feeders" in aquatic environments, due to the viscosity of water allowing food to be held in suspension)


b. Salinity

- usually measured in parts per thousand (0/00); average seawater salinity is 35 0/00 but varies from 0 to 270 0/00

- in Geochemical Studies of Paleosalinity use boron (greater in saltwater); other trace elements; type of organic matter; carbon and oxygen isotopes [freshwaters depleted in heavy carbon (C-13) and heavy oxygen (0-18)]

- in Biological Studies use stenohaline (restricted by salinity; organisms internal "salinities" equals surrounding water salinity; if rapid change cells may not function) versus euryhaline (salinity tolerant) organisms


c. Temperature

- water moderates temperature

- in cold-blooded organisms, an increase in temperature of 10°C often causes metabolic activity to double

- in warm-blooded organisms there is little metabolic change with temperature change

- temperature influences reproductive cycles

- in Geochemical Studies of Paleotemperature use 18O/16O (less with greater temperature; most important for determining paleotemperatures); boron and bromine greater if greater temperature; Calcium/Magnesium and Calcium/Strontium ratios are less if the temperature is increased

- in Biological studies of paleotemperature use stenothermal (temperature intolerant) versus eurythermal (temperature tolerant) organisms; also may look at species diversity (greater in warmer environments) or morphology (body form reflects environmental factors)


d. Dissolved Gases

- concentrations depend on atmospheric concentration; solubility of gas; water temperature and salinity


d1. Nitrogen (N) - most abundant dissolved gas; required by plants in ionic form
d2. Oxygen (O) - enters sea by photosynthesis, river water, atmosphere; all organisms use oxygen during respiration; oxygen at maximum near surface, minimum at about 700-1,000m Oxygen; approximately 6 to 10 ppm; warmer, saltier or organic debris-rich water with less oxygen
d3. Carbon Dioxide (CO2) - enters sea from organism respiration, atmosphere and rivers; removed by plants for photosynthesis and used by organisms to make shells; increases to approximately 1,000m; increased CO2 leads to Greenhouse Effect (increase temperature)
  1   2   3   4   5   6   7   8   9   ...   13


База данных защищена авторским правом ©shkola.of.by 2016
звярнуцца да адміністрацыі

    Галоўная старонка