Exam 3 Intro Geology Spring 2018 Tulsa

Rank the following steps describing how a clastic sedimentary rock forms from its pre-existing parent rock.

Weathering --> Erosion --> transportation --> Deposition --> Lithification

Place the units shown in the diagram into their order of occurrence by dragging labels into the correct position in the ranking (youngest at the top; oldest at the bottom).

YOUNGEST Bed E Dike H Batholith G Fault F Bed A OLDEST To put the events in their correct order, you had to make the following observations: - Bed E must be younger than Dike H because Dike H is erosionally truncated below it. - Dike H must be younger than Batholith G because Bed D truncates Batholith G but is cross-cut by Dike H. - Batholith G must be younger than Fault F because it cuts across Fault F. - Fault F must be younger than Bed A because it cross-cuts Bed A.

This outcrop of Precambrian and Paleozoic rocks in northern Cape Breton, Nova Scotia, provides a great example of the kinds of relative age relationships that geologists observe in the field. Put the features in order from oldest (bottom) to youngest (top). The rocks have not been overturned.

YOUNGEST Fault Cong. MAfic. Felsic. Oldest In order to successfully answer the question, you had to make the following observations and interpretations: 1. The felsic crystalline rocks are cut by the mafic intrusion (the felsic crystalline rocks are older than the mafic intrusion). 2. The conglomerate was deposited atop the mafic intrusion and the felsic crystalline rocks (the conglomerate is younger than both the mafic intrusion and the felsic crystalline rocks). 3. The fault cuts across the felsic crystalline rocks and the conglomerate (the fault is younger than both the conglomerate and the felsic crystalline rocks).

Classify the prominent unconformity shown in this illustration.

angular unconformity The prominent unconformity shown in this illustration is an angular unconformity. At this boundary, beds that were folded into a syncline were eroded, and horizontal layers were deposited on top of the erosional surface.

Rocks formed dominantly from the calcium carbonate shells of marine organisms are classified as __________ and called __________.

biochemical; limestone Biochemical limestones are made from the calcium carbonate shells of marine organisms.

A clastic sedimentary rock composed of angular pebble-sized fragments surrounded by matrix is

breccia

Which of the following rock types does not contain the mineral calcite?

chert Chert is composed of the mineral quartz (i.e., it is siliceous). The others are examples of biochemical limestone, all composed of the mineral calcite or its polymorph aragonite.

Which of the following lists accurately describes grain size increasing from smallest to largest?

clay, silt, sand

You should be able to number the events in the accompanying figure in the proper order of occurrence. If the first (oldest) event is number 1, and the last (most recent) is number 8, which occurred fifth in the sequence?

intrusion (batholith G)

Uniformitarianism

is illustrated by scientists' seeing pillow lava form only underwater, then theorizing that pillow lava found high in the mountains today did nevertheless form underwater.

The image shows cross beds in the Navajo sandstone in Zion National Park. Note the person for scale near the bottom right corner of the image. Which of the following best describes the direction that the wind was blowing when these cross beds were formed?

left to right The inclined layers dip toward the right, which means that the wind was blowing from left to right.

An unconformity develops when

new strata are deposited atop eroded strata. An unconformity occurs when sedimentary layers are deposited on top of a surface of erosion or nondeposition.

Sedimentary rocks can form by each of the following processes EXCEPT

solidification from a melt.

Match A,B,C,D to the picture

A - Coal is a sedimentary rock that is formed in areas that were once rich in terrestrial forests with sufficient amount of water that resulted into marshy conditions. B - Marine shales are found in undisturbed environments in the ocean that are mostly observed in deep sea environment. C - Red beds are those sedimentary rocks that are terrestrial in origin and clastic in nature. They are typically composed of sandstones, Arkoses, Siltstones and Wackes. However, the predominance of Red color marks the distinguishing characteristic from the main group of sedimentary rocks. This red color is due to the presence of high amount of ferric oxides. D - Marine Sandstones could be deep marine or shallow marine in origin. However, one of the pics show coastal environment which is suitable for formation of marine sandstone. C,A,D,B is the order

Consult the stratigraphic column for the Grand Canyon in your text or ebook. The A represents the Supai Group. The B represents the Redwall Limestone. The C represents the Mauv Limestone. The D represents the Tapeats Sandstone. The E represents the Unkar Group.

A. between A and B B. between B and C D. between D and E There are three unconformable contacts in the photograph. The unconformable contacts occur between Supai and Redwall strata (disconformity), between Redwall Limestone and Mauv Limestone strata (disconformity), and between Tapeats Sandstone and Unkar Group strata (angular unconformity).

The image shows sedimentary rocks exposed in Death Valley National Park. In which of the following environments was this deposit was likely laid down?

Alluvial fan Alluvial fans are composed of sand, gravel, and in this case, large angular blocks deposited when a mountain stream spilled into a broad, unconfined area.

deposits are wedge-shaped deposits consisting of coarse sediments and a large amount of feldspar, typically at the foot of an eroding mountain range, whereas deposits consist mostly of clay and the skeletons of planktonic microorganisms.

Alluvial-fan; deep-marine In arid regions, where there is not enough water for a stream to flow continuously, the stream deposits its load of sediment near a mountain front, producing an alluvial fan. How do these deposits compare to those in a shallow marine environment?

The image shows photographs of sandstones taken with a petrographic microscope (a special type of microscope used by geologists). Match the adjective describing grain shape with the appropriate specimen.

B,A,C

The image shows photographs of sandstones taken with a petrographic microscope (a special type of microscope used by geologists). Match the description of sorting with the appropriate specimen.

B,A,C The image in the center has a very uniform distribution of grain sizes, the one on the left has a combination of silt- and sand-sized particles, and the one on the right has a wide distribution of grain sizes, ranging from clay to sand. Remember that a well-sorted specimen has grains of very similar sizes and a poorly sorted one has a wide range of grain sizes.

Which of the following characteristics describe biochemical chert but not physically precipitated chert?

Biochemical chert is bedded (layered). Biochemical chert is made up of the skeletons of foraminifera and radiolaria. and Biochemical chert does not occur as small nodules within bodies of limestone.

If a sedimentary rock consists of solid fragments and grains broken off of preexisting rocks that are cemented together, is it clastic, biochemical, organic, or chemical?

Clastic

_____ forms when _______ is altered chemically such that half of the calcium atoms are replaced with magnesium.

Dolostone; Limestone

Identify the FALSE statement. Radiometric dating

FALSE can be used only if there is some uranium present in the rock. (Many different radioactive isotopes of many different minerals can be used.) TRUE B. of metamorphic rock tells when the high temperatures of metamorphism cooled below the closure temperatures of the minerals involved. C. can begin only when the isotopes cool enough to lock into the crystal lattice. D. of sedimentary rock dates the time of crystallization of the sedimentary minerals, not the time of sedimentary rock formation.

Which of the following statements is FALSE? The principle of

FALSE: inclusions says rock containing inclusions is older than the inclusions. The principle of inclusions states that the inclusions are older than the surrounding rock. TRUE THINGS B. cross-cutting relations says the feature doing the cutting is younger than the feature it cuts. C. original continuity says sedimentary layers began as continuous expanses of sediment. D. superposition says in a sequence of sedimentary beds, the youngest is on top.

Order the steps in the formation of an angular unconformity.

In an angular unconformity, the rock layers below are tilted and the layers above are horizontal. A typical angular unconformity is produced via a sequence such as this: First, sediments are deposited and lithified. Folding or faulting then disturbs the originally horizontal sediments, tilting them at an angle. Erosion takes place, truncating the tilted strata. Sediments are deposited on the erosional surface.

Which of the following is NOT one of the major classes of sedimentary rocks?

Intrusive

After completing the "Beginner," "Intermediate," and "Expert" exercises in the Biostratigraphy Simulation, think about the logic you used. Today we know that the reason why fossils occur in an ordered succession in the fossil record (rather than being randomly distributed throughout) is because of evolution. Different species evolve, live, and go extinct, only to be replaced by others through time. However, when William Smith discovered fossil succession in the eighteenth century, the idea that organisms evolved was still in its infancy. It wasn't until the mid-nineteenth century that evolution became widely accepted among scientists. In recreating the fossil succession based on your outcrops, did you ever need to think about the fossils' "evolutionary position" relative to one another, or did you ever place a more "highly evolved" fossil above a "less evolved" fossil? Is knowledge of evolution necessary to reconstruct a stratigraphic reference section using the principal of fossil succession?

No, fossil succession is a pure geometric and logical exercise. Knowledge of evolutionary relationships is not necessary to reconstruct the stratigraphic reference section. An understanding of evolution is not required to reconstruct the relative order in which the fossils occur inside the rocks.

What is the difference between numerical age and relative age?

Numerical age gives the elapsed time between an event and the present, whereas relative age places events in sequential order. Numerical age for a rock is a number estimating the time of the rock's formation in years before the present. Relative age is a statement of ordinal (or sequential) timing; for example, Ordovician sedimentary rocks were deposited after those of the Cambrian, but before those of the Silurian.

Given the relationships shown in the block, what is the relative age of the features labeled, from oldest to youngest?

OLDEST sed rocks pluton fault dike YOUNGEST

Sorting question. Worst to best

Poorly sorted bascially means big and small rocks in the microscope while well sorted they will all look like the same size.

Which slide has travled the least distance?

Sample 1, because it contains both resistant and nonresistant minerals.

Which of the following statements about the formation of cross beds is correct?

Sand blows over the crest of a dune and accumulates on the slip face. -- Wind carries the sand over the crest to the leeward side of the bedform, where gravity pulls the sediment down the slip face.

Why are geologists not able to date sedimentary rocks directly?

Sedimentary rocks are younger than their composite minerals. Isotopic dating provides the ages of minerals (grains or crystals) within a rock. Igneous rocks form at the same time as their composite minerals and thus are datable. Sedimentary rock grains, such as sand, mud, and gravel, are derived from the physical and chemical weathering of preexisting rocks at relatively low temperatures. The mineral components within sedimentary rocks are generally much older than the rocks themselves (principle of inclusions).

Order the steps in the formation of a disconformity.

Sediments are deposited in a marine environment. When sea level falls, exposing the marine sediments, erosion takes place. When sea level rises again, the erosional surface is buried by more marine sediments, creating a disconformity.

As sediment is transported downstream, away from its point of origin, the particles become

Smaller Clastic sediments increase in maturity as they are transported farther from their point of origin. Along the way, they become smaller, increasingly well rounded and well sorted, and easily weathered grains (like feldspar) are gradually destroyed.

Which of the following is TRUE?

Specifying the age of one feature with respect to another is called its relative age.

A corpse with flesh intact, found in the Alps in 1991, was dated by the carbon-14 method and showed a parent-daughter isotope ratio of approximately 1:1, with slightly more parent material than daughter material. The half-life of carbon-14 is 5,730 years. Which of the following statements is TRUE?

The age could logically be 5,300 years. Since there was still more parent material than daughter, one half-life had not quite been reached. The carbon-14 method is used on organic material, not rock.

An area of slightly dipping sedimentary rock layers has large inclusions and is intruded by an igneous dike. Apply the basic principles for determining relative ages and identify the FALSE statement.

The dike is older than the sedimentary rock layers it cuts across. The dike must be younger than the sedimentary rock layers that it cuts across because the rock layers need to be there before they can be cut by the intrusion.

The image shows an outcrop of granite and basalt with a pink area between them that records contact metamorphism. Use the concepts of inclusions and baked contacts to select which of the following statements best describes the relative age relationship between the granite and basalt.

The granite is older than the basalt. The granite is older than the basalt. Notice that the granite has experienced contact metamorphism and that a fragment of it is contained within the basalt, both indicating that the granite was in place before the intrusion of the basalt.

Select statements true of unconformities.

Unconformities represent periods of nondeposition in the rock record. Unconformities represent periods of erosion in the rock record. There are three major types of unconformities.