Geology: Quiz Questions & Answers (Test 3)

After 3 half lives, how much daughter product will you find in a sample (assuming it is a closed system)?

87.5%

__________ forms in seawater when carbon dioxide reacts with water, and dissolves (chemically weathers) the shells of many sea creatures.

Carbonic Acid

Which of the following options lists sediment grain sizes in order from smallest to largest?

Clay-silt-sand-cobbles

Layers of sedimentary rocks are ______ if they were deposited without interruption. An _____ represents an interruption in deposition, and therefore a time gap in the depositional record in that location.

Conformable; unconformity

A sedimentary rock consisting of rounded grains >2mm in diameter (pebbles or larger) cemented together is called a ___________________

Conglomerate

Radiometric dating techniques are based on:

Decay of radioactive elements

You come across an outcrop and observe layers of chert and shale. The beds are thin, and have no other notable sedimentary structures. You don't see any large fossils, but after you take it back to the lab and study it under the microscope, you see it is full of micro-fossils of planktonic algae. Which of the following is the likely depositional environment of these rocks?

Deep marine

Which of the following is a non-radiometric dating technique, that can provide absolute ages?

Dendrochronology

The image above shows an angular unconformity exposed in the Grand Canyon, AZ. Identify the correct order of events that must have occurred in order to create this angular unconformity.

Deposition - Tilting - Erosion - More deposition

Several types of unconformities exist. In a ________, the sedimentary layers above and below the unconformity are parallel.

Disconformity

You come across a rock in the field that you are pretty sure is a chemical sedimentary rock (it occurs in beds - as is typical of sedimentary rocks, but it is not made of small grains cemented together, so you know it is not a clastic sedimentary rock). However, you are trying to figure out whether it is limestone, dolostone or chert. You drip dilute HCl (acid) on it and it does not appear to effervesce (fizz and bubble). However, when you powder a bit of the sample by scratching it with a pen knife to increase the surface area that can react with the acid, and then drip acid on that, it does effervesce! What rock is it?

Dolostone

You come across an outcrop and observe 2-3 m thick cross-bedded sandstone beds. The sandstone is very well sorted and very well rounded. Which of the following is the likely depositional environment of these rocks? You look, but don't find any fossils. Which of the following is the likely depositional environment of these rocks?

Dune field

True or false: The minerals of Bowen's reaction series that crystallize at the highest temperatures are the most stable at Earth's surface conditions (i.e. they are resistant to chemical weathering)

False

You come across an outcrop of very poorly sorted sediment, with grain sizes ranging from clay all the way to refrigerator-sized boulders. There are no sedimentary structures, layering, or fossils within this deposit. Of the following options, which is the most likely depositional environment?

Glacier terminus

One way to increase chemical weathering rates is to:

Increase surface area by mechanically weathering a rock

Based on what you know about the chemical composition of limestone and chert, combined with what you know about chemical weathering - which of these two rock types do you think is more easily broken down by chemical weathering?

Limestone

Caves occur where groundwater has dissolved away pre-existing _____________. This same rock, can also be formed later in the cave by abiologic processes.

Limestone

____________ breaks rocks down into smaller pieces.

Mechanical weathering

If a radioactive isotope has a half-life of 10 years, is it a good idea to use it to date a sample that you are pretty sure is >100 years old?

No

A _______ is an unconformity in which sedimentary rocks lie on crystalline igneous or metamorphic rocks

Nonconformity

Which of the following is an example of chemical weathering?

Oxidation (aka. rusting)

You come across an outcrop of thin beds alternating between mudstone that contains mudcracks, gypsum and rock salt (halite). You look around but cannot find any fossils. Which of the following is the likely depositional environment of these rocks?

Playa lake

Any geologic feature that cuts across another, must be younger than the feature that it cuts

Principle of cross cutting relationships

If a clast is included in a sedimentary layer, the clast must be older than the layer which includes it

Principle of inclusions

Sedimentary layers are originally deposited over large spatial areas. These layers thin and eventually pinch out gradually, they do not end abruptly

Principle of lateral continuity

Sedimentary beds are originally deposited in flat, horizontal layers

Principle of original horizontality

If multiple sedimentary layers are stacked, the layer at the bottom is the oldest

Principle of superposition

You come across an outcrop that consists of moderately sorted and very well rounded conglomerate. The conglomerate bed is not laterally extensive - it is about 1 meter thick and only about 10 m wide, where it thins and pinches out. To the sides of the conglomerate bed, there is shale that is rich in terrestrial plants and contains mudcracks. At the base of the conglomerate bed you observe scour marks in the underlying layer. Which of the following is the likely depositional environment of the conglomerate bed?

River channel

What is chalk made of?

The carbonate skeletons of microscopic planktonic algae

Which of the following statements is an example of relative dating of strata?

The dike is younger than the sedimentary beds, but older than the unconformity

What is a good inference you can make about the sediment that is very rounded and smooth?

The sediment has been transported far from its original source & the sediment has likely been transported by water

Which of the following processes can form a very well sorted deposit?

Transport by water (rivers)