Stratigraphy

Question 1

What is the difference between chronostratigraphy and geochronology?

Answer 1

Chronostratigraphy = material stratigraphic unit
- Anything I can touch
- Physical
- “This rock is cretaceous”

Geochronology = geological time unit
- Time
- Non-physical
- “This rock was formed during the cretaceous”

Question 2

What does the law of superposition say?

Answer 2

… at the time when any given stratum was being formed, all the matter resting upon it was fluid, and, therefore, at the time when the lower stratum was being formed, none of the upper strata existed

Question 3

What does the principle of original horizontality say?

Answer 3

Strata - either perpendicular to the horizon or inclined to the horizon - were at one time parallel to the horizon

Question 4

What does the principle of lateral continuity say?

Answer 4

Material forming any stratum were continuous over the surface of the Earth unless some other solid bodies stood in the way

Question 5

What does the principle of cross-cutting relationships say?

Answer 5

If a body or discontinuity cuts across a stratum, it must have formed after that stratum (ie. an intrusion disturbs older layers).

Question 6

What is an angular unconformity (vinkeldiskordans)?

Answer 6

En tydelig vinkel mellem den nedre lagserie og den øvre

Question 7

What is a disconformity (diskonformitet)?

Answer 7

Exists where the layers above and below an erosional boundary have the same orientation.

Question 8

What is a nonconformity?

Answer 8

Develops where sediments are deposited on top of an eroded surface of igneous or metamorphic rocks

Question 9

What is a paraconformity?

Answer 9

Strata on either side of the unconformity are parallel, there is little apparent erosion

Question 10

What is an unconformity (inkonformitet)?

Answer 10

A surface of contact between two groups of unconformable strata.

Et lagplan, hvor der mangler lag fra et tidsrum

Question 11

Hvordan indtegnes en inkonformitet i et stratigrafisk kort?

Answer 11

Som en hiatus; lodret skravering

Et tegn på tidsrum, hvorfra der mangler lag

Question 12

Hvad er litostratigrafi?

Answer 12

The smallest lithostratigraphic unit is a bed (“lag”).

Beds are grouped into a Member (”led”).

Member are forming a Formation.

Formations can be packed into a Group (“gruppe”).

Question 13

Hvad kan være et eksempel på formationer?

Answer 13

Formationsgrænser ved litologiske skift:

Formation A: vekslende ler og sand men overvejende sand
Formation B: vekslende ler og sand, men overvejende ler
Formation C: vekslende kalk og ler, men overvejende kalk

Question 14

Hvad er progradation og retrogradation?

Answer 14

Progradation (= regression): “sea level fall”

Retrogradation (= transgression): “sea level rise”

Question 15

What is biostratigraphy?

Answer 15

Branch of stratigraphy

Focuses on correlating ans assigning relative ages of rock strata by using fossils

Question 16

Hvad erkendte George Cuvier?

Answer 16

At dyr opstår, lever og uddør i en irreversibel proces

= fossiler (makro og mikro) kan bruges til aldersbestemmelse fordi de repræsenterer et unikt tidsrum

-> grundlæggelse af biosøratigrafi

Question 17

Hvad erkendte William Smith?

Answer 17

At lag der litologisk ligner hinanden kan skelnes ud fra deres fossilindhold.

Question 18

Hvad gælder om biostratigrafiske enheder?

Answer 18

• Benævnes biozoner (biostratigrafiske zoner)
• Består af bjergarter
• Defineres ved deres indhold af fossiler
  – makrofossiler (ammonitter, muslinger, m. fl.)
  – mikrofossiler (foraminiferer, kokkolitter, dinoflagellater, m. fl.)
• Kan strække sig på tværs af litostratigrafiske grænser
• Kan korreleres fra én geografisk lokalitet til en anden
  – samtidighed men ikke nødvendigvis samme alder overalt –> IKKE = kronostratigrafisk korrelation
• Er lokale til regionale (evt. globale)

Question 19

Hvad er taxon-range biozone?

Answer 19

Udbredelseszone

Karakteriseret ved den total horisontale og vertikale udbredelse

(range, ultimative opståen til ultimative uddøen) af et element i et fossilt selskab (typisk en art – kunne også være en slægt eller familie)

Question 20

Hvad er interval biozone?

Answer 20

Intervalzone

Fossilførende interval mellem to definerede biostratigrafiske grænser.

Zonen er defineret ved de biostratigrafiske ændringer ved zonens grænser – dvs. fossilindholdet indeni zonen er ikke afgørende.

Question 21

Hvad er assemblage biozone?

Answer 21

Selskabszone

Zone defineret ud fra en bestemt samling/sammensætning af fossiler.

Alle fossiler behøver ikke at være tilstede overalt i zonen og nogle kan også forekomme udenfor zonen.

Tæt forbundet med aflejringsmiljø.

Question 22

Hvad er abundance/acme biozone?

Answer 22

Hyppighedszone

Zone karakteriseret ved den maksimale hyppighed af en art, men ikke dens totale udbredelse.

God kronostratigrafisk indikator.

Question 23

What is cyclostratigraphy?

Answer 23

A branch of stratigraphy that is concerned by cyclic alternations of rock properties

Cyclostratigraphy older than 55 mio. years is very unprecise

Question 24

Hvad er Milankovitch-cyklicitet?

Answer 24

Langsigtede cykliske ændringer af Jordens årstider og solenergi modtaget på forskellige breddegrader.

Question 25

Nævn de 3 Milankovitch-cykler.

Answer 25

Precession: Jordaksens retning (23.000 år, cirkel)
Effekt på årstiderne ift. polerne

Obliquity: Jordaksens hældning (41.000 år)
Mellem 22.1-24,5 grader (= ændrer modtagelse af solens stråling mere lokalt)

Eccentricity: Jordbanens ellipseform (100.000 år og 400.000 år)
Ændrer sig fra mere cirkulær til mere oval (= effekt på indstråling fra solen over længere perioder)

Question 26

What is perihelion and aphelion in the eccentricity cycle?

Answer 26

Perihelion = planet is going too fast so it moves outward

Aphelion = planet is going too slow so it moves inward

Question 27

Eccentricity summary

Answer 27

Only parameter that affects the annual global insolation received by Earth (just 0.25% change)

Varies between nearly 0 and 0.06 with main periods of 100 000 and 405 000 years

Its main influence is through the climatic precession cycle

Question 28

Precession summary

Answer 28

Describes the precessional motion of Earth’s axis relative to the elliptical orbit and varies in a cyclic way with an average period of ~21 000 years.

Does not influence the annual global insolation received by Earth, but determines the latitudinal and seasonal distribution of solar insolation, with an opposite effect on both hemispheres.

Eccentricity determines the amplitude (strength) of the climatic precession cycle.

Question 29

Obliquity summary

Answer 29

Varies between 22 and 24.5 degrees with dominant periods of ~41 000 years.

Like precession, obliquity affects the latitudinal and seasonal distribution of solar insolation, but in a fundamentally different way having the same effect on both hemispheres.

In contrast with precession, its main influence is on higher latitudes and in winter.

Question 30

The summer monsoon’s effect on circulation

Answer 30

Weak summer monsoon = weak Nile runoff = oxygen-rich deep water = normal deep-ocean sediments

Strong summer monsoon = strong Nile runoff = low-salinity lid (with organic debris) + oxygen-depleted deep water = organic-rich black muds

Question 31

What is magnetostratigraphy?

Answer 31

A branch of stratigraphy that relies on the frequent Earth’s magnetic polarity change to provide a relative dating.

Magnetiske anomalier viser et symmetrisk mønster på hver side af riften, der stemmer overens med polvendinger.

Normal configuration => Mag N = Geo N

Reverse configuration => Mag N = Geo S

Question 32

Hvad betyder magnetisk deklination og inklination?

Answer 32

Deklination: Lokal afvigelse mellem magnetisk nordpol og geografisk nordpol. Varierer med tiden.

Inklination: Vinklen mellem Jordens magnetfelt og det vandrette plan. Ved magnetisk ækvator: 0 graders inklination.

Question 33

Hvordan opstår marin-magnetiske anomalier omkring spredningszoner?

Answer 33

Når basalt langsomt størkner, og når det er så mafisk (og dermed indeholder meget Fe (ferromagnetisk) og Mg), vil det naturligt antage en størkningsposition i den retning, Jordens magnetfelt peger på det tidspunkt.

Derved kan vi se, når spredningsryggen spreder sig, at der dannes stribede, magnetiske bånd på hver side af ryggen. Striberne kommer af polvendinger tilbage i tid.

De bliver ældre og ældre, jo længere væk fra spredningsryggen, man kommer.

Question 34

Hvad er en kron?

Answer 34

Magnetisk polaritetszone

Question 35

What is chemostratigraphy?

Answer 35

A branch of stratigraphy that relies on chemical properties of rocks as a relative dating technic.

Figure out the chemical composition of the ocean before (difference between Stontium 88 and 86); then compare with e.g. fossils (dated the same way)

Question 36

Hvad er “apparent polar wander”?

Answer 36

En observation, man havde gjort, inden man havde kontinentaldriften på plads. Da mente man, at det var polerne, der vandrede, fordi det var lettere at forestille sig frem for, at det var de kæmpe kontinenter, der bevægede sig.

Question 37

What is chronostratigraphy?

Answer 37

Chronostratigraphy is the application of disciplines such as biostratigraphy, magnetostratigraphy, chemostratigraphy, cyclostratigraphy, sequence stratigraphy, and numerical dating to stratigraphic successions in order to interpret temporal correlations.

Question 38

What is geochronology?

Answer 38

Denotes time relations in all rocks, specifically when they formed, whether stratified or non-stratified. It also denotes the time of processes in which rocks not only formed but also were eroded (unconformities) and deformed (structural and cross-cutting relationships). It is used to denote the timing of events throughout all of Earth’s history that are interpreted from the rock record (e.g., climatic, biotic, tectonic, and oceanographic).