Name ______Geology 103

Siliciclastic Rock Identification

Answer the following questions:

Shale

Sample PSR:

What environment (oxygen content) would this green shale

be formed in? ______

Sample MSO:

What depositional environment (oxygen content) would you

expect for thisred, silty shale?______

Sample OBS:

What does the black color indicate in this shale?______

Sample 52:

This shale has fine laminae, but it does not break along the laminae.

What term would you use to describe the way the shale breaks?______

Sample MSP:

These shale chips break alone laminae. List two terms that are

used to describe this weathering texture.______

Sample FWS:

This silty shale contains leaf imprints and fish bones, and is from a

lake (fresh water environment). Since the organic content of shale is

related to color, what estimate would you give for organic content in

this sample? (high = > 10%, medium = 2-10%, low = <2%)______

Sample MSH:

This marine shale effervesces with dilute hydrochloric acid. What adjective

would you use to describe a shale that is almost a limestone?______

Sample PMR:

This silty shale has no identifiable bedding. What is

the rock name when no bedding is visible?______

Siltstone

Sample RSS:

This siltstone has green spots, but is predominantly red.

What geochemical environment might be indicated by

the green spots?______

Sample MSI:

This micaceous, sandy siltstone contains marine fossils (brachiopods).

Look closely, and describe the bedding:______

Sample BSI:

This blocky siltstone has laminae and is thinly bedded. Which are

finer-grained: the laminated or the thinly bedded intervals?______

Sandstone

Sample GVG:

This sample is from isa continental margin of NY, and is matrix-rich,

has abundant chlorite, and may be slightly slightly metamorphosed.

What informal name is often used for this type of rock?______

Sample NGA:

This sample is Triassic in age, and is from the base of the Newark

Group (New Jersey). What informal name is used for a sandstone

that has abundant feldspar grains?______

Sample LAS:

This sample has abundant lithic clasts, and low matrix content.

What is the name of this sandstone, using Gilbert’s classification?______

Sample AA:

There are many granule-sized lithic clasts in this sample, but the

average grains is still sand-sized. Salmon-colored feldspar is the

most common grain type. What name would Gilbert use for this

feldspar and matrix-rich sandstone?______

Sample OSA:

This sample is from the Oriskany Formation in Cuyahoga, NY.

It marks a major systemic boundary, and has abundant quartz grains

in addition to the large brachiopod shells. What is the name of this

sandstone, using Gilbert’s classification?______

Sample KSS:

This sandstone is from the Great Valley Sequence, near LakeBeryessa

It is from the Sites Sandstone member of the Cortina Formation, and is

Late Cretaceous in age. Lithic clasts are very common. If you look closely,

you can see larger clay pieces up to 10 mm in diameter that were ripped up

from the ocean floor during turbidity flows. These are called “rip up clasts”

What name would Gilbert give to a sandstone with high matrix and

high lithic content?______

Sample JSC:

This sample is from the Jurassic Stony Creek Formation, and forms

the base of the Great Valley Sequence near LakeBerryessa. The large,

dark grains are basalt (volcanic rock fragments). Using Gilbert’s

classification system, is this rock an arenite or a wacke?______

Conglomerate

Sample KVS:

This sample is Late Cretaceous in age, and is from the

Venado Sandstone member of the Cortina Formation. It was

collected near the LakeBerryessa spillway. Larger clasts are

clay rip-up clasts from the nearby ocean floor, and basalt.

Sandy matrix approaches 30-40% of the sample. Assuming

that the average grain size is 5-15 mm, what is the Wentworth rock name?

(be specific- 2 words!!)______

Sample UJM:

This sample is Upper Jurassic in age, and is a stream channel

deposit from the Morrison Formation in central Utah. The

Morrison Formation is famous for spectacular dinosaur discoveries.

Estimate the average grain size for this sample. What is the

rock name? (be specific- 2 words!!)______

Sample KPC:

This sample is from the Cretaceous Pigeon Creek Formation

in central Utah. Is it grain supported, or matrix supported?______

Sample F:

What informal name would we give to this conglomerate

with angular clasts?______

Sample UPC:

This sample has a sandy matrix, but the granules are generally

touching each other. What name do we give to a conglomerate

with grain-to-grain contact?______

Sample KBC:

This sample has a sandy matrix, and the cobbles are made of

less resistant metamorphic and limestone clasts. What name do

we give to a conglomerate that is made of unstable clasts?

(Hint- think oligomict, polymict or petromict)______

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