Week 9: How to build a planet; The Mesozoic Earth

Question 1

What is weathering? What is the difference between chemical and mechanical weathering?

Answer 1

water can break rocks and minerals down chemically and mechanically

Mechanical breaks down rocks (into smaller fragments) without changing composition while chemical changes composition (forms new minerals)

Question 2

What are three major chemical weathering processes? How do simple solution and hydrolysis differ?

Answer 2

Carbonation, oxidation and hydrolysis

1. Simple solution (congruent dissolution)= minerals dissolve liberating alkali and alkali earth elements as soluble products (congruent)
2. Hydrolysis (incongruent dissolution)= dissolution is incomplete, H+ can replace metal ion in some silicate minerals.

Question 3

What is the relationship between a mineral’s stability to chemical weathering and the order in which it
crystallises? Which minerals are most and least stable?

Answer 3

minerals that form at higher temperatures and pressures tend to be less resistant to chemical weathering

quartz and olivine>olivine
(more resistant than)

Question 4

What is the relationship between climate and weathering rates? How do rates of erosion vary with latitude?

Answer 4

atmospheric composition and weather types, higher temperature and greater rainfall increases the rate of chemical weathering.

generally, the lower the latitude the higher the temperature and greater the rainfall so this increases weathering/erosion

Question 5

Where do the residual products of weathering end up?

Answer 5

rivers/oceans

Question 6

What are the general trends in the climate and sea level through the Mesozoic? What are the names of the major Mesozoic continental masses and oceans and the approximate ages of their formation and break up?

Answer 6

Continental masses:
Oceans:
-pacific
-indian
-north atlantic
south atlantic

66Ma

Question 7

Have all Large Igneous Province LIP eruptions resulted in mass extinctions? What controls their impact/severity on biota?

Answer 7

no not all LIP eruptions resulted in mass extinctions, greenhouse gas emissions are generally responsible for the impact on biota

Question 8

How do LIPs cause mass extinctions?

Answer 8

LIPs are massive eruptions of basaltic magma that have environmental effects:
-release of greenhouse gases + global warming
-ocean acidification
-acid rain
-anoxia
-devestationo of vegetation due to altered pH
-drought and extreme heat reduces habitable regions

Question 9

How does increased levels of CO2 affect environmental feedback
relationships?

Answer 9

-release of greenhouse gases + global warming

-ocean acidification

-acid rain

-anoxia

-devestationo of vegetation due to altered pH

-drought and extreme heat reduces habitable regions

Question 10

What is the name of the volcanic units that were erupted at the time of the Permo/Triassic mass extinction event?

Answer 10

Siberian Traps (LIP)

Question 11

What were the climatic conditions at the start of the Triassic? What is the evidence in the rock record of the
severity of the climatic conditions?

Answer 11

• hypothermals, rapid and extreme global warming events driven by LIP volcanism

-very poor environmental conditions 6myr into the triassic caused by pulses of Siberian Trap eruptions

Question 12

What is the name of the intensely humid interval within the Triassic (Carnian)? What was its cause?

Answer 12

carnian pluvial episode
period of increased humidity that occured 234-232ma
during carnian stage of late triassic

Question 13

How long did Pangaea last?

Answer 13

335-175ma (160 million years)

Question 14

When and in what order did Pangaea breakup? When did ocean floor spreading begin in the Central Atlantic? What land masses were created?

Answer 14

-mid jurassic rifting resulted in the seperation of Laurasia and Gondwana and created the central atlatnic sea way

• during the Cretaceous the central atlantic continued to widen, Gondana broke apart - India began to seperate from Australia and Antartica

-Laurasia and Gondwana formed in the Jurassic, continents resembling modern assembly formed in the cretaceous

Question 15

What was the name of the ocean between the two halves of Pangaea that existed during the Jurassic and
Cretaceous? What was the Tethyan trench and where was it located?

Answer 15

central atlantic seaway

Question 16

What was the cause of the end-Triassic mass extinction event?

Answer 16

Central Atlantic Magmatic Provence (CAMP) was the most aerially extensive and LIP on earth, it erupted in 4 bursts between 202-220ma

Question 17

What does OAE refer to, and what deposits are characteristic of these times? What is the relationship between OAE and LIPs?

Answer 17

Ocean Anoxic Event…

marine mass exctinction through anoxia, caused by increased sediment input lead to reduced oxygenation and increased acidity

Question 18

How did Pangaea effect global climate in the Late Triassic/Early Jurassic?

Answer 18

-distribution of landmass and the equatorial tethys ocean led to mega-monsoonal climate, distinct wet and dry seasons associated with the reversal of winds

-vegetated polar regions and ice limited to seasonal

Question 19

How did the break up of Pangaea affect the Cretaceous climate and sea levels?

Answer 19

SEA LEVEL
-increasing sea levels throughout the jurassic and cretaceous
-flooding of lowland (transgression) to form warm and vast inland seas

CLIMATE
-no polar ice
-atmospheric CO2 higher
-increased volcanism causing CO2 and SO2 release

Question 20

What type of sedimentary rock is typical of the Cretaceous?

Answer 20

chalk

Question 21

What is chalk? What is the depositional setting of chalk? Why can there be no chalk deposits that are older than Triassic in age? When did calcareous nannoplankton first appear?

Answer 21

Deposition of cretaceous chalk is caused by coccolithophores
-when they die the sphere breaks apart and coccoliths accumulate on ocean floor
-coccolith ooze on the ocean lithifies to chalk, a limestone

coccolithopores (nannoplankton) first appear after carnian pluvial episode (late triassi) in epicontinental seas

Question 22

What is chert? What is the difference between primary and secondary chert? What is the depositional setting of primary chert? What organism would not have been a constituent of the chert layers that are associated with Banded Iron Formations?

Answer 22

Chert is a hard, fine-grained sedimentary rock primarily composed of silica (silicon dioxide).

Primary chert: forms directly from the deposition of silica from solution or the accumulation of silica-rich remains of organisms in marine environments. therefore the depositional setting is typically deep sea environments on the sea floor

Secondary chert forms from the alteration or replacement of pre-existing materials by silica

Question 23

What is the Calcite Compensation Depth and how does it control the deposition of chalk and chert?

Answer 23

the depth in the oceans where the rate of calcium carbonate material forming and sinking is equal with the rate the material is dissolving. Below the CCD no calcium carbonate is preserved

Question 24

What two events have been invoked as the principal cause of the end-Cretaceous mass extinction event (make sure you know their names and locations)? What is the evidence for each?

Answer 24

-meteorite impact which generated an 11 magnitude earthquake and a tsunami

-wildfires caused by impact

-rifting and flood volcanism

-acid rain