Clasts/ Identifying Sedimentary Rocks

Question 1

Sedimentary Rocks Main components

Answer 1

clasts and matrix

Question 2

clasts in sed rocks

Answer 2

rounded segments (rounded fro transport) 
the rounder the longer transported

Question 3

Matrix

Answer 3

holds togetheer the clasts, matrix,clay, lithified
keeps them together

could also be cement

Question 4

in sedimentary rocks

Answer 4

grains

Question 5

in metamorphic rocks

Answer 5

crystals

Question 6

Quartz in clasts

Answer 6

can endure the most weathering so if you find quartzclasst only: very old, much . weathering endured

old rocks have an abundance of quartz

Question 7

Orientations of a sample

Answer 7

an lead to understand transport mechanism because that will lead to a sediment structure
ex. flat, round pebble → river bed

Question 8

clastic rocks

Answer 8

Clastic rocks are classified primarily by grain size, then by mineralogy & percentage of matrix

Question 9

grain shows

Answer 9

grain unlike crystal shows sign of transport or erosion

Question 10

conglomerate

Answer 10

round clasta

2 to 256 mm

Question 11

breccia

Answer 11

angular

63um to 2cm

Question 12

Sandstone

Answer 12

ugs anything grains is sandstone but actually well defined

grains between 2 mm and 63um, very small but can feel grains!

Question 13

Siltstones

Answer 13

even finer

3.9 to 63 um

Question 14

Claystone/ SHale

Answer 14

layering: Shale

< 3.9 um

Question 15

Toblerone chart

Answer 15

used to also measure matrix content

Question 16

Arkose

Answer 16

Rocks that still contain Feldspar ( less weathered)

Question 17

Litharenite

Answer 17

large amount of lithic clasts

Question 18

“Wacke”

Answer 18

extend to matrix measurement, would then be (arkose) wacke

Question 19

matrix more than 50%

Answer 19

mudstone or shale

Question 20

cements not in classification

Answer 20

ehy are daigenetic product, later product, precipitate out of later product

Question 21

Effective Product

Answer 21

very long transport or repeated transport

Question 22

Breccia

Answer 22

can be very large clasts, also samller

angular grains: deposited close to source – very short transport

Question 23

Conglomerate

Answer 23

rounded clasts

rounded grains - long transport

Question 24

Quartz Arenite

Answer 24

typical sandstone
High percentage of stable mineral grains – long transport
really hard

Question 25

Arkose

Answer 25

High percentage of unstable minerals, angular clasts
short transport - deposited close to source
not as hard

Question 26

Wacke

Answer 26

mainly form in active tectonic environment so often subducted, not seen often
commonly called greywacke, but more correctly quartz-, arkosic- & lithic-wacke
unsorted, usually angular, mixed mineralogy clasts in a muddy matrix
variations in clast size & the ratio of clasts to matrix
debris flow deposits
submarine ‘landslides’
dark coloured due to swift burial (no time to oxidise)
other colours possible, but are due to the colour of material involved in the landslide (ie what happened to it before it was remobilised)
usually more matrix than clasts

Question 27

Glacial Till and Tillite

Answer 27

Unsorted, unstratified, very wide range of clast sizes

Question 28

Diamictite

Answer 28

Unsorted unstratified, very wide range of clast sizes
of unknown origin - could be glacial but if other evidence is lacking, it is a diamictite
if glacial will see scratches on rock surface (quartz espescially)
it could be, for instance, a lithified debris flow

Question 29

Shale

Answer 29

Very fine platey clay mineral grains and quartz silt: highly weathered, long transport
overburden pressure has formed planes, the rock is fissile

Question 30

Volcaniclastic sediments: Ash

Answer 30

fine grains cover large areas
Before the main eruption stratovolcanoes produce ash plumes – lapilli & pumice fall out first
lofted ash is commonly carried 10s to 100s of km
where the wind slackens the grains fall out, largest first = graded bedding
certain structures allow reconstruction of wind direction
can use ash for dating

Question 31

Vocaniclastic Sediments: Lahras

Answer 31

Mud (ash, pumice and lapilli) flow out when the summit crater is breached
Transport by flowing water sedimentary structures
graded bedding
cross-bedding
water escape features

Question 32

volcaniclastic Sediments

Answer 32

Volcaniclastics reworked by water
horizontal bedding
cross-bedding
graded bedding
flame structures

Question 33

Clastic deposition

Answer 33

commonly in water

Question 34

common constituents of clastic sedimentary rocks

Answer 34

quartz, clay, iron, ( to minor degree feldspar, mica & lithic fragments)

Question 35

factors in classification of clastic sedimentary rocks

Answer 35

grainsize, grain shape & amount of matrix, mineralogy

Question 36

common clastic rock types

Answer 36

breccia, conglomerate, quartz arenite, arkose, wacke, shale, tillite, diamictite