CHAPTER 8 SEDIMENTARY ROCK

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

CHAPTER 8:

SEDIMENTARY ROCK

Sedimentary rock is formed from the weathered and

eroded remains of other rocks

Sedimentary rock is formed from the weathered and

eroded remains of other 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?

• They reflect physical and chemical characteristics of

their source environments and depositional

processes

• 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

Why study sedimentary rocks?

Planetary nebula remaining

mineral particles and gas after a star

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)

Comet exhibiting coma (tail)

BIOGENIC SEDIMENTS are produced by organic (biological) precipitation of the remains of living organisms

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

Particles separated based on grain size

Decreasing grain size with

increased transport distance and decreased energy level

0.1 mm

Coral Pink Sand Dunes, southern Utah

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

Steven Earle

What does multi-generational mean in

this context? Why are these grains so

well rounded and so dominated by

quartz?

?

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 is caused by compaction and cementation

The important types of clastic sedimentary rock

• Distinguished by:

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 arkose

lithic sandstone siltstone claystone shale

What is the textural difference between conglomerate and breccia?

What are the compositional differences between quartz sandstone, arkose and lithic sandstone?

Chemical sedimentary rocks

Rock salt

Travertine

Gyspum

Chert

Biogenic Sedimentary Rock

Skeletal limestone

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

Primary sedimentary structures record modern and ancient sedimentary processes

Ripples

Mud Cracks

Cross-bedding in eolian sandstones, Zion Canyon,

Utah

Graded bedding in submarine fan rocks, Gabriola Island ,BC

Bedding in fluvial and lacustrine deposits, Horseshoe Canyon, Alberta

Haiti, 2010

Choose four depositional environments in this figure For

each, describe the texture of the sediments likely to form

there.

Consider the beach and glacier If the sediment source for each was granitic mountains, predict the composition of sediments in each case.

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