Lecture 5 - Terrrestrial Facies Models

Question 1

Definition of facies

Answer 1

“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.

Question 2

Facies models explanation

Answer 2

Observe moden proccess to refer to the acient records

Question 3

What are the process

Answer 3

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

Question 4

What are the products of these in the same order

Answer 4

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

Question 5

whats key in this

Answer 5

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

Question 6

Why use facies models

Answer 6

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

Question 7

Alluvival fans as an example of a facies model

Answer 7

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

Question 8

example of an allivial fan

Answer 8

Death Valley

Question 9

What is the tectonic setting of an aliuvial fan

Answer 9

Areas undergoing rapid uplift

Question 10

Geometry

Answer 10

Wedge shaped, limited in lateral extend

Question 11

Sedimentology

Answer 11

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

Question 12

Fossils present?

Answer 12

Rare

Question 13

What is the acient example of an alluvial fans

Answer 13

Hornelen basin, Norway

Question 14

Example 2: Braided rivers

Answer 14

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.

Question 15

Braided rivers techtonic setting

Answer 15

upper reaches of allival fans, near uplift

Question 16

Geometry

Answer 16

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

Question 17

Sedimentology

Answer 17

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

Question 18

Fossils?

Answer 18

Rare, possible vegiation

Question 19

Example 3: Mendering rivers

Answer 19

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

Question 20

Tectonic setting

Answer 20

lower reaches of the fulival system

Question 21

Geometerry

Answer 21

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

Question 22

Sedimentology

Answer 22

Gravels to pebbles.

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

Question 23

Fossils

Answer 23

wood on a flood plain, water molcuse

Question 24

Example 4: Lake deposits

Answer 24

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

Question 25

Tectonic sessint

Answer 25

Downward basins

Question 26

Geometerry

Answer 26

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

Question 27

Sedimentology

Answer 27

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

Question 28

Fossils

Answer 28

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