ROCK COMPOSITION - SEDIMENTARY

WHAT ARE ROCKS MADE OF?
~ SEDIMENTARY ROCKS ~

"To understand what sedimentary rocks are made of, the processes that lead to their formation must be understood!"

"I'm willing to go there, Lulu!

"Good man, Lou! The recipe for sedimentary rocks is:

Weather a pre-existing rock to make sediment.
Transport and deposit the sediment.*
Turn the sediment into rock (lithify the sediment).

Each of these steps plays a part in determining the composition of the sedimentary rock! Let's learn about or review each of the steps!"

*Actually, in a small number of cases, step 2 is omitted. The weathered materials stays where it is and turns into rock.

PRODUCTION OF SEDIMENT BY WEATHERING

Weathering is the disintegration (mechanical weathering) and/or decay (chemical weathering) that all rocks undergo when exposed to the air, water, and living organisms of the Earth's surface environment.

Mechanical and chemical weathering commonly act on rocks at the same time.

The end products of weathering are sediment and/or dissolved mineral matter.

	MECHANICAL WEATHERING: Example - Frost Shattering
	CHEMICAL WEATHERING: Example - Solution
	CHEMICAL WEATHERING: Example - Alteration

In the 'Salt Lake' rollover, it was noted that the dissolved salts originate through the weathering of rocks. Examine the 'Chemical Weathering - Solution' rollover and determine which three minerals are most soluble. These are amongst the most important materials that are carried by groundwater and streams to the ocean and to salt lakes and make them salty. Name the three minerals:

TRANSPORT AND DEPOSITION OF SEDIMENT

Once it is produced by weathering, sediment may be transported from its place of origin.

Sediment may gradually or rapidly work its way downslope due to the pull of gravity.
Sediment may be picked up and carried by 'agents of transport': streams, wind, flowing ice, tides, waves, or living organisms.
When the ground becomes level or agents of transport lose their energy, the sediment comes to rest (is deposited).
Transport and deposition may occur repeatedly until the sediment comes to its 'final' resting place, where it is turned into rock.

REVIEW SOME OF THE WAYS IN WHICH SEDIMENT MAY BE TRANSPORTED AND DEPOSITED
	BY FLOWING ICE AND MELTWATER
	BY LANDSLIDES
	BY FLOWING WATER
EXAMINE WHAT HAPPENS TO SEDIMENT DURING TRANSPORT
	THE EVOLUTION OF SEDIMENT
List three ways in which the sediment changed during transport. My answer:
TRANSPORT AND DEPOSITION OF DISSOLVED MINERAL MATTER
	THE FATE OF DISSOLVED MINERAL MATTER

LITHIFICATION OF SEDIMENT

Once sediment comes to rest, it may be turned into rock. Lithification is most likely if a great thickness of sediment accumulates. The sediment grains that are buried are protected from being picked up and moved some more, and so have a chance to become attached to one another. As you have learned, the attachment is accomplished by cementation or by grains growing until they interlock.

REVIEW SOME OF THE WAYS IN WHICH SEDIMENT GRAINS MAY BECOME ATTACHED TO ONE ANOTHER
	BY INTERLOCKING GRAINS
	BY CEMENTATION
Sediment accumulates and and has the chance to turn into rock in diverse locations on land and the floors of lakes and oceans. These locations will be described

"So, Lou, what do you think?! Can sedimentary rocks be identified as such on the basis of the minerals they contain?! I'll provide some help in the form of some questions!"

"As always, you're a great help! OK, serve me up the questions!!

Here are six questions that will help you decide if the mineralogy of a rock can provide clues as to whether it is sedimentary in origin. A distinction will be made between sediment that is 'fragmental' (composed of broken pieces of rock) and sediment that is 'precipitated' (composed of material precipitated from solution).

(1) Fragmental sediment originates through the breakup of rock. The fragments then begin a journey to the place where they will be deposited and turned into sedimentary rock. Can any rock exposed at the earth's surface be a source material for fragmental sediment? (Yes/No):

(2)How do the distance and duration of transport of fragmental sediment affect the diversity of minerals present?:

(3)Under the right circumstances, can any mineral whatsoever that is present in the source rocks be present in fragmental sediment  when it is deposited? (Yes/No):        What are those 'right' circumstances?:

(4)Does the lithification of sediment affect the mineralogy of the sediment? (Yes/No/Maybe):     If your answer is 'yes' or 'maybe', explain in what way or under what circumstances the mineralogy is affected:

(5)Can precipitated sediment be composed of any mineral whatsoever? (Yes/No):       If your answer is 'no', explain your reasoning.:

(6)What is your conclusion as to whether the mineralogy of a rock may be used to identify a rock as sedimentary? (You may want to return to this question after you've thought about the minerals present in metamorphic rocks.)

To check your answers and get additional hints and information, click on the link.