CHAPTER 8 SEDIMENTARY ROCK

CHAPTER 8:
SEDIMENTARY ROCK


Sedimentary
Sedimentary rock
rock is
is formed
formed from
from the
the weathered
weathered and
and
eroded
eroded remains
remains of
of other
other rocks
rocks

Many of the rock layers in this
photograph are composed of
sediments that accumulated
on the seafloor.

What evidence would reveal
to a geologist that a rock
formed in a marine
environment?

Sedimentary Rock

•
•

Most of Earth’s surface is covered with layers
of loose sediment
>75% of the land surface is Sedimentary Rock


•

They reflect physical and chemical characteristics of
their source environments and depositional
processes

Steven Earle

Why study sedimentary rocks?
Fossiliferous Cambrian Burgess Shale at Mt.

Planetary nebula remaining

Stephen, BC

mineral particles and gas after a star

•

They contain direct and indirect evidence of life

and its evolution

•

They can be interpreted to understand geological
history

•

The are the source of important resources,
including metals, building materials and energy
Steven Earle

explodes

Triassic limestone being quarried for cement at Texada Island, BC


There are three common types of sediment:
Clastic, Chemical, and Biogenic

•
•

CLASTIC SEDIMENTS are broken and eroded pieces of rocks and minerals
deposited by water, wind, ice, or some other physical process

What is the main mineral in this sandy sediment?
What else might be present?

Chemical and Biogenic Sediments

CHEMICAL SEDIMENTS are produced by inorganic (nonbiological)
precipitation of dissolved compounds (e.g., through evaporation)

BIOGENIC SEDIMENTS are produced by organic
(biological) precipitation of the remains of living
organisms
Comet exhibiting coma (tail)


Change in Sediments

•

Sediments change as they are transported across Earth’s
surface… en route to their depositional environment

What are the likely depositional environments of
these three types of sediment?


Particle Size Reflects
Depositional Energy


Sorting

Particles separated

based on grain size


Decreasing grain size with
increased transport distance and
decreased energy level


?

Steven Earle

Coral Pink Sand Dunes, southern Utah

What does multi-generational mean in
this context? Why are these grains so
well rounded and so dominated by
quartz?

0.1 mm

Close-up view of the multi-generational fine-grained sand at
the Coral Pink Sand Dunes

Steven Earle


Clastic Grains

•

•

Clastic grains combine with
chemical and biogenic sediments
through either organic or inorganic
precipitation.
The black material in these thin
sections photographs is organic
matter.


Sedimentary Basins

•

Dissolved compounds are transported from weathering sites into Sedimentary Basins


Sediments evolve during transportation and deposition

•
•
•
•

.

Unstable grains (olivine, pyroxene, feldspar, amphibole, and others) become less abundant
Stable grains (quartz, clays, muscovite) become more abundant
Biogenic sediments accumulate

Chemical sediments may become more abundant


The Sedimentary Cycle

•

Sediment becomes sedimentary rock
during the sedimentary cycle

Sediments typically accumulate at rates
of less than 1 mm per year. How long
would it take to accumulate 1000 m of
sediment at a rate of 0.2 mm/year?


Lithification

•

Lithification is caused by compaction and cementation


The important types of clastic sedimentary rock

•

Distinguished by:

–

–
–

grain size and shape
grain type (mineralogy)
texture of the grains, matrix and cements

Why are they called clastic sedimentary rocks? What is a clast?


Types of Sediment

•
•

Specific combinations of texture and composition for each type.
Determined by sediment’s history: transport energy and distance, weathering intensity, and composition of source rock.


Important clastic sedimentary rocks

conglomerate

breccia

quartz sandstone

What is the textural difference between conglomerate and breccia?
What are the compositional differences between quartz sandstone, arkose and lithic sandstone?

lithic sandstone

siltstone

claystone

shale

arkose


Chemical sedimentary rocks

Rock salt

Gyspum

Chert

Travertine


Biogenic Sedimentary Rock

Skeletal
limestone

Chalk

What do skeletal limestone, chalk and

coquina have in common?

Coquina

Coal


Sedimentary rocks preserve evidence of past environments and ecology


Continental depositional environments

Wetland, alluvial fan, stream, desert, lake, glacier – which is which?
Do all of these environments exist in Canada?


Coastal depositional environments

Barrier island, carbonate lagoon, beach, tidal wetland, delta – which is which? Do all of these environments exist in
Canada?


Marine Environments of deposition