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Interpreting the PastInterpreting the Past
Part 1Part 1
More Chapter 17More Chapter 17plus Chapter 18plus Chapter 18
To interpret the geologic pastTo interpret the geologic past
• History of Earth and its life can be read as a sequence of events
• Geological record events can be interpreted by a study of the present– The principle of uniformitarianism:
• Developed by James Hutton• “the present is the key to the past”• Championed by Charles Lyell in his book
Principles of Geology • Changes can be gradual or sudden
Sometimes, however, catastrophes occur.
Beginnings of relative datingBeginnings of relative datingTo make sense of the data, geologists
constructed the geologic time scale– It records major geologic events– It notes appearances, and disappearances, of
varied forms of life
The sedimentary recordThe sedimentary record
• Formed by familiar surface processes• Sediments 75% of surface-exposed rock• Sediment sequences record environments
where they accumulated• Different sequences represent different
times and places:– Evidence of past mountain belts and
coastlines, seas, rivers, lakes, etc.– Some give information about past climates
Sedimentary FaciesSedimentary Facies• Individual rock types are not specific to just a
single environment of deposition• Example: Sand that eventually becomes
sandstone may be deposited in river channels, sand dunes, beaches, a shallow ocean shelf, or a deep ocean landslide (a turbidite), etc.
Sedimentary Rock InterpretationSedimentary Rock Interpretation
• To identify the depositional environment for a sedimentary rock body, we must consider:
• Sedimentary structures• Fossils & the “niche” of modern
counterparts - define• The relationships to other sedimentary
rock units both above and below and laterally i.e. the sedimentary facies
StratigraphyStratigraphy• The study of sedimentary rock sequences
• Layering of sedimentary rock is the
result of grain size or grain composition changes during deposition
• The changes record:
(a) Tectonic activity
(b) Rising or falling sea level
(c) Climate changes
(d) Variations in sediment type deposited
Division of stratigraphic sequencesDivision of stratigraphic sequences
• We need discrete units to define lateral and vertical rock relationships “lithostratigraphic”
• The most commonly used stratigraphic unit is the FORMATION:– A rock body distinguishable from rocks above and
below it– A rock body large enough to be shown on a map
• It may contain one sedimentary facies over a wide area, for example a widespread limestone
• OR it may contain several time related facies: alluvial fan conglomerate, point bar stream deposits, lake mudstones.
Names of rock formationsNames of rock formations Bloomsburg Formation named for
Bloomsburg, Pennsylvania
• “Formation” as second part of name if rock types are diverse
• Correlated with similar rocks in, for example, the Delaware Water Gap area, there called High Falls Formation.
You will hear me call it “High Falls Bloomsburg”
Names of rock formationsNames of rock formations
• Or, a rock formation may be named for a single rock type
• Navajo Sandstone
• Redwall Limestone
Correlation of strata in southwestern United States
Some are named “Formation”Others sandstone (“Ss”) orLimestone (“Ls”)
Subdivision of formationsSubdivision of formations• A formation may be divided into members
• For example, the red “Passaic Formation*” outside can be divided into members, e.g. the Perkasie member, Graters member, etc.
*Formerly called the Brunswick Formation
Groups of FormationsGroups of FormationsTwo or more vertically adjacent formations can be
combined into a group. For example, the Late Triassic and Early Jurassic rocks around here form the Newark Group.
• Included are the Passaic Formation, the Lockatong Formation, the Stockton Sandstone.
• Related groups can be combined into a Supergroup• These formed in a rift valley, eventually flooded, opening
the Atlantic
Role of Tectonic Forces - 1Role of Tectonic Forces - 1
• Uplift may control distribution of sedimentary facies:
• Uplift increases stream gradients and velocity, rate of erosion of sediments into basin. Streams faster, erosion greater.
• Example: Continent-Continent collision
• Causes thick sedimentary clastic wedges
Clastic wedgesClastic wedgesThick and coarse-grained close to source area, thinner and more fine-grained further from source area
Shallow water deposition in a basinShallow water deposition in a basin
Crust deforms as weight increases. Basin floor stays at about the same depth.
Transgression and RegressionTransgression and Regression• Changing sea level greatly influences distribution of depositional facies
• The process of transgression ( rising sea level): the ocean rises and covers the continental margin
• Shoreline moves towards continental interior
Regression: The process of regression produces lowering of sea levelShoreline migrates away from the continental interiorVery useful for correlation – widespread erosion causes unconformities – Sequence Stratigraphy
•Global sea level changes are called eustatic
Eustatic sea-level changes for the Eustatic sea-level changes for the Phanerozoic EonPhanerozoic Eon
Note how often period boundaries correspond to regressions
These same boundaries often correspond to extinctionsREGRESSION exposes shelf
K\T >Regression at boundary
Pm\TR largest >
extinction, no regression, definite
ash layer
Sauk
Tippecanoe
Kaskasia
Absaroka
Long-term sea level changeLong-term sea level change
• They last tens of millions of years
• Controlled by size of MORs
• Warm, active, buoyant ridges displace ocean waters onto continental margins
(transgression)
• Cold, inactive, dense ridges are smaller and basins have more room for water.
(regression)
Rapid sea-floor spreadingRapid sea-floor spreading
Growing MOR takes up basin volume, sea level rises - transgression
Cessation of sea-floor Cessation of sea-floor spreadingspreading
MOR cools and shrinks, sea level drops - regression
Very short Sea-level CyclesVery short Sea-level Cycles
• Associated with growth and shrinkage of ice sheets
• Last hundreds of thousands of years• Result from removal of water by storage
as glacial ice• Exposed much of continental shelf
surrounding North America• Sea level as much as 140 meters lower
than present
Recall Lowered Sea-level –PleistoceneRecall Lowered Sea-level –Pleistocene
Caused exposed shelfLand Bridge
Recall Sediments controlled by EnergyRecall Sediments controlled by Energy
• Sand deposited at shoreline and in adjacent shallow waterHigh Kinetic Energy – surf, longshore drift
• Mud deposited in calm, deeper water
Low Kinetic Energy lakes in winter, lagoons, bays, very deep ocean beneath the surface
Some time-equivalent sedimentsSome time-equivalent sediments
Differ in energy and distance from source
Facies changes with TransgressionFacies changes with Transgression
• Rising sea level = shoreward migration of sedimentary facies
• Deeper water sediment over shallower• Mud facies is superimposed over sandy
beach facies
• Carbonate Ooze facies is superimposed over Mud facies
• “FINE-ING” UPWARD
Effect of transgression on Effect of transgression on sedimentary faciessedimentary facies
Deeper water sediment over shallower (see center block)Mud facies is superimposed over sandy beach faciesCarbonate Ooze facies is superimposed over Mud facies
Note the wedge
RegressionRegression
• Falling sea level causes landward facies to be superimposed on the seaward facies
• Sandy beach facies is superimposed over muddy lagoon facies
• Shallower water sediment (coarse) over deeper (fine)
• COARSENING UPWARD sequence OR a DISCONFORMITY due to “subaerial exposure” i.e. shelf or inland sea sediments were exposed to erosion when sea-level dropped
Coarsening upward sequenceCoarsening upward sequence
Regression: from deepwater to shallow water over any spot
Fine Muds of Mancos Shale
Coarse Sands of Mesa Verde Group
Regression
Walther’s LawWalther’s Law
• Vertical sequences of sedimentary facies result from superposition of laterally adjacent depositional environments.
• Used to recognize changes in sea-level t-r
• Used to recognize neighboring facies
Walther’s LawWalther’s Law
Vertical sequences of sedimentary facies result from superposition of laterally adjacent depositional environments
Transgression fining (deeper) upward
PaleogeographyPaleogeography
• Reconstruction of past landscapesReconstruction of past landscapes
• Example: Asymmetrical stream ripples Example: Asymmetrical stream ripples indicate flow directions of riversindicate flow directions of rivers
• Gives location of high topographyGives location of high topography
• Paleocurrent indicators in delta deposits:Paleocurrent indicators in delta deposits:
Size of ripples and their formSize of ripples and their form
• Continent positions from PaleomagneticsContinent positions from Paleomagnetics
PaleoecologyPaleoecology
• The reconstruction of past ecosystemsThe reconstruction of past ecosystems
• Example:Example:
• Type and thickness of vegetation near Type and thickness of vegetation near pond, oxbow, lake, or floodplain can be pond, oxbow, lake, or floodplain can be determined from fossil leaves and pollen, determined from fossil leaves and pollen, and fossil soil layersand fossil soil layers
• Niche of modern animals can be related to Niche of modern animals can be related to fossil animals similar in skeleton, teeth.fossil animals similar in skeleton, teeth.
SedimentologySedimentology• Interpret sediments deposited in past by
comparison to sediments in modern environments
• Energy decreases with depth• Fine-grained sediment indicates deep water• So: Fining-upward sequence of sediments
indicates decreasing energy (deeper water - Transgression)
• And: Coarsening-upward sequence of sediments indicates increasing energy (shallower water - Regression)
PaleoclimatologyPaleoclimatology
• Certain types of sedimentary rocks are Certain types of sedimentary rocks are good indicators of paleoclimategood indicators of paleoclimate
• Evaporites indicate dry regionsEvaporites indicate dry regions
• Coals indicate swamp conditionsCoals indicate swamp conditions
• Dunes and desert pavement semi-arid Dunes and desert pavement semi-arid to arid regionsto arid regions
• Tillites, striated rock surfaces, loess Tillites, striated rock surfaces, loess etc. record very cold glacial conditionsetc. record very cold glacial conditions
End of Part 1End of Part 1
Importance of FossilsImportance of Fossils
• Many early philosophers (including Aristotle) Many early philosophers (including Aristotle) recognized fossils are remains of ancient liferecognized fossils are remains of ancient life
• Importance of fossils to geology realized Importance of fossils to geology realized laterlater
• Wm. Smith – Mapping in Wales and England Wm. Smith – Mapping in Wales and England developed Principle of faunal successiondeveloped Principle of faunal succession– Different-aged rock layers contained different Different-aged rock layers contained different
fossilsfossils– Allowed formulation of the geologic time scaleAllowed formulation of the geologic time scale
Fossil Wooly MammothPleistocene and Cold
Part 2Part 2
• Mostly Chapter 18
Index fossils vs. Long RangingIndex fossils vs. Long Ranging
Wm. Smith: used fossils to correlate rocks far apart and establish relative age
Short range“index fossil”
Long range useless for correlation
Domains of lifeDomains of lifeJohn Ray (1680) Grouped organisms according to similarity
Carl von Linne’ ,1760, called LinnaeusCarl von Linne’ ,1760, called Linnaeus Binomial Nomenclature Binomial Nomenclature (Genus and species)(Genus and species)
Species based hierarchy of relationships
Similar species grouped together in a Genus (capitalized) each with a unique species name (lower case). Example lion Felis leo, African wild cat Felis silvestris
Note plural of species is species. Plural of genus is genera. Similar genera grouped into families, families into orders, orders into classes, etc. Mnemonic
• Knew of similarities among diverse organisms, Naturalist on Beagle 1831-1836, saw changes in fossils through time.
• Knew of Artificial Selection by farmers
• Was aware of Malthus (1798) essays on population, “more individuals are born than
food supply can support.”
• Read Lyell’s Principles of Geology- supports Hutton’s uniformitarianism/gradual change
• Suggested Natural Selection
Darwin’s RoleDarwin’s Role
http://www.aboutdarwin.com/voyage/voyage01.html
Evidence: Homologous structuresEvidence: Homologous structures
Homology: Same anatomy to make different structures. Why, if not related?
Darwin’s Idea: Natural SelectionDarwin’s Idea: Natural Selection
• Organisms produce more young than 2
• There is competition for food and mates
• There is variation in characteristics (types) essential to survival and reproduction
• Some individuals (types) survive to reproductive age, mate and have progeny more frequently than others. This is “success”.
• “Successful” individuals pass on their characteristics to the next generation
InheritanceInheritanceIndividuals vary, but we look like our parentsHow does variation get passed on?• Jean Baptiste de Lamarck (pub.1801)
– Acquired Traits are inherited - WRONG– Giraffe strains to reach high leaves, offspring
have longer necks – failed idea
• Johann Gregor Mendel (pub.1866) Established rules of inheritance in peas. – Traits controlled by genes – Genetic traits are inherited - RIGHT
http://anthro.palomar.edu/mendel/mendel_1.htm
http://www.ucmp.berkeley.edu/history/lamarck.html
Mendel 1865 -1866Mendel 1865 -1866
Prevailing idea was that the characteristics of an Prevailing idea was that the characteristics of an organism were due to the blending of the traits from organism were due to the blending of the traits from each parent (blending inheritance). each parent (blending inheritance).
Mendel proposed instead that an “element” Mendel proposed instead that an “element” determined a particular characteristic of an organism.determined a particular characteristic of an organism.
Called particulate inheritance. The element (now Called particulate inheritance. The element (now called ‘gene’) is the fundamental unit of heredity.called ‘gene’) is the fundamental unit of heredity.
Mendel’s work was not noticed at the time 1865-66Mendel’s work was not noticed at the time 1865-66 Rediscovered by Hugo deVries, Carl Correns, and Rediscovered by Hugo deVries, Carl Correns, and
Erik von Tschermak in the early 1900’s.Erik von Tschermak in the early 1900’s.
Mendel’s (1865 -1866) DiscoveriesMendel’s (1865 -1866) Discoveries Some physical traits are caused by inheritable particles, Some physical traits are caused by inheritable particles,
now called genesnow called genes May occur in two forms: one is dominant (capital letter, May occur in two forms: one is dominant (capital letter,
e.g. R, the other recessive (lower case letter, e.g. r).e.g. R, the other recessive (lower case letter, e.g. r). Every individual gets two copies of each gene, one from Every individual gets two copies of each gene, one from
each parent. Only need one dominant to get normal each parent. Only need one dominant to get normal appearance.appearance.
Ex: Pea flower color, normal is RedEx: Pea flower color, normal is Red Can get RR, Rr, rR, (all red) or rr (white)Can get RR, Rr, rR, (all red) or rr (white) Double recessive rr red gene is broken, no red, flower Double recessive rr red gene is broken, no red, flower
whitewhite
Mendel’s experiments with peasMendel’s experiments with peasFlower color
Some traits (flower color)occur in two forms. One (Red flower R) is dominant.The other (white r) is recessiveFirst generation all Rr
If Red (R) and white (r) parents 3/4 of next generation are Red (dominant)
Parents
1/4 1/4
1/4 + 1/4 = 1/2
Suppose you cross a RR plant with a white plant
Where are the genes?Where are the genes?
• Early 1900s growing suspicion that the inheritance material is in the chromosomes
• Evidence from microscope studies of cell division (Mitosis) versus gamete formation (Meiosis)
Mitosis – cell divisionMitosis – cell division
Two copies of each per cell.One from mother, one from father. Diploid
In Mitosis (cell division) the chromosomes duplicate and separate, then the cell divides, so each daughter cell again has 2 pairs of chrosomes.
But in Meiosis – formation of gametes:But in Meiosis – formation of gametes:
But in Meiosis, gamete formation, an extra division makes cells with one copy of each chromosome, so many possible combinations
Each gamete has, for each chromosome, either version, not both
Sexual reproductionSexual reproduction
One from each parent
How does the genetic material make copies?
Chromosomes contain lots of DNA deoxyribose nucleic acid
Chargaff’’s Rules on DNA components weighed nucleotides
The amount of Guanine (G) equals Cytosine (C) The amount of Adenine (A) equals Thymine (T) Adenine and Guanine are Purines,Thymine and
Cytocine are Pyrimidines
How does the genetic material make copies?
Francis Crick, James Watson (models) Maurice Wilkins, Rosalind Franklin (x-rays) of DNA The Double Helix by James Watson
http://www.pbs.org/wgbh/nova/photo51/
DNA moleculeDNA molecule
Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin
It has not escaped our notice …It has not escaped our notice …
• Chargaff’s Rules make sense immediately
• Cytosine only fits Guanine (3 H bonds)
• Thymine only fits Adenine (2 H bonds)
• They will bond only to each other, making a perfect copy on the opposite strand
• Parents can pass a copy of their DNA in their gametes
Breaking the Genetic CodeBreaking the Genetic Code
• RNA
• The genetic code UUU (Uracils) => Phenylalanine
• One gene, one polypeptide chain, enzymes
Marshall Warren Nirenberg
Speciation – Geographic IsolationSpeciation – Geographic Isolation
Separated – populations eventually unable to interbreed - definition of “distinct species”