Lecture 5 - Terrrestrial Facies Models Flashcards Preview

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Flashcards in Lecture 5 - Terrrestrial Facies Models Deck (28)
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1
Q

Definition of facies

A

“the sum total features such as sedimentary rock type, mineral content, sedimentary stuctures, bedding characteristics, fossil content etc. Which characterise a sediment being deposited in a certain enviroment.

2
Q

Facies models explanation

A

Observe moden proccess to refer to the acient records

3
Q

What are the process

A

1) wave and current actvity
2) Debris flow
3) sea level cjhange
4) biochemical precipiation
5) bioturbidation

4
Q

What are the products of these in the same order

A

1) Ripples
2) graded bedding
3) grain size
4) mineralogy
5) trace fossils

5
Q

whats key in this

A

No two depositional settings are identical, therefore we can predict the old setting but looking at the modern day processes.

6
Q

Why use facies models

A

These can be used to predict the setting of these rocks, and thereofre can be used for obvious advantages in economic and engineering geology.

7
Q

Alluvival fans as an example of a facies model

A

allival fans form when a narrow canyon stream enters a flat valley. Cone shaped despoists of coarse stream sediments, sheet flood deposits and debris flow. it requires constant uplift

8
Q

example of an allivial fan

A

Death Valley

9
Q

What is the tectonic setting of an aliuvial fan

A

Areas undergoing rapid uplift

10
Q

Geometry

A

Wedge shaped, limited in lateral extend

11
Q

Sedimentology

A

Clay to boulders, particle size decreases towards to edge of the fan. Debris flow is unsorted and reverse grading.

12
Q

Fossils present?

A

Rare

13
Q

What is the acient example of an alluvial fans

A

Hornelen basin, Norway

14
Q

Example 2: Braided rivers

A

Network of small braching channels often seperated by islands. occour where there is not enough engery to carry sediment load. Found near the source of a system.

15
Q

Braided rivers techtonic setting

A

upper reaches of allival fans, near uplift

16
Q

Geometry

A

Elongated, straight or sheet like sand bodies with cross cutting channels. Grade laterally into finer desposits.

17
Q

Sedimentology

A
Sand dominant
Gravel commment in longtitudal bars
Very little silt
Abudent tabular and cross cut stratification
High verlocity plans in longtitdual bars
Ripples and dune formation common
18
Q

Fossils?

A

Rare, possible vegiation

19
Q

Example 3: Mendering rivers

A

Lower reaches of the fluvial system, erosion on the outside and depoisition on the inside. This leads to lateral accretion of point bars.

20
Q

Tectonic setting

A

lower reaches of the fulival system

21
Q

Geometerry

A

long ribbon like bodies with sand scattered randomly in a thick sequence

22
Q

Sedimentology

A

Gravels to pebbles.

Laterally increasing point bar sand (oldest on the oustide of the depoistion side)

23
Q

Fossils

A

wood on a flood plain, water molcuse

24
Q

Example 4: Lake deposits

A

Landlocked body of standing water, with small tide and small waves. Found in regions of tectonic depression, ie volcanic crators. to be preserved thick sequences must develop before evaporation

25
Q

Tectonic sessint

A

Downward basins

26
Q

Geometerry

A

Lenticular in cross section and circule or long in birds eye view

27
Q

Sedimentology

A

Laminated mudstones on the lake bed. MARLS carbon rich mud. Fresh water limestones. Hypersaline lakes: evaporuites and mud

28
Q

Fossils

A

frequent. Fish and insects, absense of marine fossils is a good indicator of thses lakes.