Geology 102 1st assignment

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time-stratigraphic unit 100

A body of strata that was deposited during a specific interval of geologic time; for example, the Devonian System, a time-stratigraphic unit, was deposited during that part of geologic time designated the Devonian Period.

sand dune 117

A ridge or mound of wind-deposited sand.

angular unconformity

An unconformity below which strata dip at a steeper angle than those above. (See disconformity, nonconformity, and unconformity.)

unconformity

An unconformity indicates that the geologic record is ________ at a particular location, and may indicate a period of ________ . incomplete; non-deposition

biogenic sedimentary structures

Any feature such as tracks, trails, and burrows in sedimentary rocks produced by the activities of organisms. (See trace fossil.)

Marine Environments

Continental shelf Inner shelf Mostly cross-bedded sandstone with wave-formed ripples, marine fossils, and bioturbation Outer shelf Mostly mudrocks with subordinate sandstone; marine fossils and bioturbation Continental slope and rise Turbidite sequences in submarine fans with graded bedding in sandstone and mudrocks Carbonate shelf Limestone (dolostone). Limestone varies from coquina (made of shell fragments) to ooliticlimestone to micrite (carbonate mud). Cross-beds, mud cracks, ripple marks common; marine fossils Deep-ocean basin Pelagic clay and calcareous and siliceous oozes Evaporite environments Rock salt and rock gypsum the most common, but others, including potassium and magnesiumsalts, may be present

delta seaward; progradation

Deltas build ________ by a geologic process called ________ .

evaporites deposited? What are the two most common types of evaporite rocks?

Evaporites are mostly rock gypsum and rock salt, formed in saline lakes, playa lakes, and some marginal marine environments. Evaporites form in arid environments with high evaporation rates.

Evaporites 81

Evaporites, such as rock salt, result when evaporation exceeds precipitation, such as in desert regions or along hot, dry shorelines

bioturbation

Extensive burrowing by organisms may produce ________ , in which sediments may be so disturbed that other sedimentary structures are destroyed

Cross-bedding

Layers deposited at an angle to the surface on which they accumulated Deposition on a sloping surface as the downwind side of a sand dune

Laminations (or laminae)

Layers less than 1 cm thick Form mostly as particles settle from suspension

Beds

Layers more than 1 cm thick. Form as particles settle from suspension and from moving sediment as sand in a stream channel

micrite

Many limestones are made up of sand- and gravel-sized particles and calcium carbonate mud called

Lower Sularian Strata 124

New Jersey, Penn. deposited in braided streams that flowed from east to west

deposition

Sedimentary structures are formed during ________ or shortly thereafter.

cross dating 79

The procedure of matching ring patterns from numerous trees and wood fragments in a given area is called cross-dating.

Atrypa 102

and the trilobite Paradoxides are guide fossils because they are well suited for time-stratigraphic correlation

Current ripple marks 110

are asymmetrical in profile and are invariably generated by currents, either water or wind, that flow in one direction

metamorphic rocks 77

difficult to accurately date bc of heat and pressure affect parent daughter ratio

atoms 73

extremely small particles that make up elements

disconformity 87

is an erosion surface in sedimentary rocks that separates younger rocks from older rocks, both of which are parallel to each other

daughter element 73

new more stable element

discontinuities or unconformities

represent times of nondeposition, erosion, or both

depositional environment 117

Any area where sediment is deposited; a depositional site where physical, chemical, and biological processes operate to yield a distinctive kind of deposit.

Numerical dating 66

Assigning an age in years before the present to geologic events before the present; numerical dates are determined by radioactive-decay dating techniques

marine transgression 90

, when sea level rises with respect to the land, a marine transgression takes place that accounts for the vertical sequence of facies

alpha decay 73

2 protons and 2 neutrons are emitted from the nucleus

playa lake 117

A temporary lake in an arid region.

outwash 117

All sediment deposited by streams that issue from glaciers. (See drift.)

stratigraphy

Although the branch of geology known as stratigraphy applies to all the major rock groups, it focuses primarily on ________ rocks. sedimentary

till

Any sediment deposited directly by glacial ice is called

pelagic clay and ooze 121

Beyond the continental shelf, the seafloor is nearly covered by fine-grained deposits known as pelagic clay and ooze

marine transgression vertical sequence of strata can be attributed to a marine transgression

During a transgression, sea level becomes higher, and the shoreline migrates towards land. As the shoreline migrates landward, offshore facies are deposited over nearshore facies, so that in the rock record the nearshore facies sandstone is overlain by shale and then limestone.

Walther's Law

During marine transgressions and regressions, several facies are deposited at the same time, giving rise to vertical and lateral relationships. Which law summarizes these relationships?

John Wesley Powell 66

Grand Canyon,

half-life 1/8

If a radioactive element has a half-life of 32 million years, what fraction of the original amount of parent material will remain after 96 million years?

daughters atoms migrate out 73

If a rock is heated during metamorphism and the daughter atoms migrate out of a mineral that is subsequently radiometrically dated, an inaccurate date will be obtained. Therefore, this date will be younger than the actual date;

members and beds, 98

Many formations are subdivided into members and beds,

geologic history The photograph on the right was taken on Fish Creek Trail in the Sierra Nevada, California. It shows two black metavolcanic erratics on granodiorite bedrock that has been intruded by a white dike. Using your knowledge of igneous rocks and processes, glacial features, and relative dating principles, provide a geologic history of this area based on what is shown in this image

The first event was the emplacement of the intrusive granodiorite batholith. The white dike then intruded this plutonic material. Erosion occurred. Later glacial processes transported the glacial erratics and deposited them on the plutonic material and dike.

rounding 109 texture

The process involving abrasion of sedimentary particles during transport so that their sharp edges and corners are smoothed off.

Tree-ring dating

The process of determining the age of a tree or wood in a structure by counting the number of annual growth rings.

Relative dating

The process of placing geologic events in their proper chronological order with no regard to when the events took place in terms of the number of years ago. (See numerical dating.)

marine transgressions and regressions

Uplift and subsidence of continents, the amount of water frozen in glaciers, and the rate of seafloor spreading are responsible for marine transgressions and regressions

ripple marks

Wavelike structure on a bedding plane, especially in sand, formed by (1) unidirectional flow of air or water currents or (2) by oscillating currents as in waves.

ripple marks 110

Wavelike structure on a bedding plane, especially in sand, formed by (1) unidirectional flow of air or water currents or (2) by oscillating currents as in waves.

fossil footprint

What is the best example of a biogenic sedimentary structure

discordant 77

ages do not agree

Carbon-14 dating 78

can be used only on organic matter such as wood, bones, and shells, and is effective back to approximately 70,000 years ago

conformable 86

conformable Refers to a sequence of sedimentary rocks deposited one after the other with no discontinuities, or only minor ones.

James Hutton 70

considered the founder of modern geology

uranium thorium dating 78

cross check d=carbon 14 dating

uranium-lead and thorium-lead 77

date igneous rocks lunar sample and meteorites

samarium - neodymium dating 78

date old igneous and metamorphic rocks and meteorites

Niobrara Formation 124

deposition in a marine environment

continental rise 121

detrital marine env The gently sloping part of the seafloor lying between the base of the continental slope and the deep seafloor.

Mud cracks are one type of biogenic sedimentary structure.

false

igneous rocks 75

gives most accurate radiometric dates

sedimentary rocks are important because they

may contain fossils

rock ages 103

rocks of Ordovician age are younger than those of the Cambrian and older than Silurian rocks,

Eras Eras are subdivided into periods.

true

unconformities All unconformities are created during periods of erosion and/or non-deposition.

true

George Lewis De Buffon 67

Earth Gradually cooled, 75,000 years old

original horizontality

Imagine a stack of tilted sedimentary beds. We know that these beds were deposited horizontally, and then later tilted, because of the principle of ________ .

superposition 72

Imagine that you are standing in front of a stack of sedimentary beds. You know the beds at your feet are older than those above your head because of the principle of ________

lithostratigraphic unit 97

Lith and litho mean "stone" or "stonelike."

Till 117

Sediment deposited directly by glacial ice, as in an end moraine.

lagoons

Silt and clay are fine-grained sediment and tend to be deposited in low-flow environments such as

sedimentary facies

Simultaneous deposition in adjacent but different environments yields sedimentary facies, which are bodies of sediment (or sedimentary rock) with distinctive lithologic and biologic attributes.

Ripple marks

Small (< 3 cm high) ridges and troughs on bedding planes

Navajo sandstone 124

Studies show that the Navajo sandstone is made up of well-rounded, well-sorted quartz grains with tracks of land dwelling animals, including dinosaurs, and it has cross-beds up to 30 meters high. These are good indicators that this was formed in a ________ environment. coastal dune

Fission-track dating

The dating process in which small linear tracks (fission tracks) resulting from alpha decay are counted in mineral crystals.

fossil succession - allows geologists to determine the relative ages of sedimentary rocks in widely separated areas.

The fossil record reveals that animal and plant species (or assemblages of species) have occurred in a specific, non-repeating sequence that is consistent from area to area. Therefore, by correlating fossils or fossil assemblages from one area to another area, geologists can conclude the rocks in both locales were deposited at similar times.

period 101

The fundamental unit in the hierarchy of time units; part of geologic time during which the rocks of a system were deposited.he most commonly used time unit

superposition and faunal succession;

The geologic column and relative geologic time scale were established by the 1840s based on

Radioactive decay 73

The spontaneous change in an atom by emission of a particle from its nucleus (alpha and beta decay) or by electron capture, thus changing the atom to a different element.

Paleogeography

The study of Earth's ancient geography on a global as well as a regional scale.

Paleogeography 125

The study of Earth's ancient geography on a global as well as a regional scale.

till poorly; glaciers

Till is ________ sorted sediment deposited by ________

Tillites 81

Tillites (glacial sediments) result from glacial activity and indicate cold, wet environments.

elements 73

all matter is made up of elements

Stratigraphy is primarily the study of sedimentary rocks.

false

Unconformities can only develop between layers of sedimentary rock.

false

Uniformitarianism is a limited concept, because it fails to account for sudden events such as earthquakes, volcanoes, and tsunamis.

false

correlation The strongest evidence that rocks are time correlated is derived from lithological similarities.

false

Continental Environments 117

*Fluvial * Braided stream Mostly horizontally bedded conglomerate and cross-bedded sandstone; mudrocks not common Meandering stream Mostly mudrocks deposited on floodplains; subordinate but distinctive lenticular sandstones deposited in point bars *Desert * Alluvial fan Poorly sorted conglomerate from debris flows and sandstone- and conglomerate-filled channels Sand dune Well-sorted, rounded sandstone with large-scale crossbeds Playa lake Laminated mudstone/siltstone; evaporites such as rock salt, rock gypsum, and others *Glacial* Outwash Much like braided stream deposits Moraines Unsorted, nonstratified deposits of sand and gravel

sorting 109 texture

, which refers to the size variation in a sedimentary deposit or rock. If most of the particles are of about the same size, the sediment or rock is well sorted, but if a wide range of sizes is present, the material is poorly sorted

sedimentary rocks are important because 108

1.they preserve evidence of the surface processes responsible for deposition (for example, running water, wind, waves, and glaciers) and 2.many contain fossils that are rare or absent in most other rocks. So here we focus on areas where sediment is deposited—that is, depositional environments—as well as the criteria used to recognize deposits of specific environments.

Inclusions /B

3.Which one of the following statements is correct? a. A formation is made up of two or more biozones; b. Inclusions are older than the rock layer containing them; c. Time units are defined by rock type and thickness; d. Guide fossils have very long geologic ranges; e. A disconformity is the fundamental type of lithostratigraphic unit.

unconformities 86

A break or gap in the geologic record resulting from erosion or nondeposition or both; the surface separating younger from older rocks where a break in the geologic record is present. (See angular unconformity, nonconformity, and disconformity.)

Tidal flats 119

A broad, extensive area along a coastline that is alternately water-covered at high tide and exposed at low tide

drift 117

A collective term for all sediment deposited by glacial activity; includes till deposited directly by ice, and outwash deposited by streams discharging from glaciers. (See outwash.)

Walther's law 90

A concept holding that the facies in a conformable vertical sequence will be found laterally to one another.

alluvial fan 117

A cone-shaped accumulation of mostly sand and gravel where a stream flows from a mountain valley onto an adjacent lowland.

mud cracks

A crack in clay-rich sediment that forms in response to drying and shrinkage.

mud cracks 110

A crack in clay-rich sediment that forms in response to drying and shrinkage.

varve 117

A dark-light couplet of sedimentary laminations representing an annual deposit in a glacial lake.

prograding delta explain why prograding deltas yield a deposit that becomes coarser-grained upward, whereas in prograding tidal flats, sediments become finer-grained upward.

A delta commonly forms by the deposition of sand and clay as a river or stream enters the quiet water of an ocean or lake. Hence, near-shore deposits, which commonly include sands and silts deposited at the river mouth, prograde over deep water deposits, which commonly include clay minerals that remain in suspension as the river water moves away from the coast toward deeper water. In contrast, tidal flats commonly prograde over beach deposits. The fine-grained sediments of the tidal flats overlie coarser-grained sands of the beach.

delta

A deposit of sediment where a stream or river enters a lake or the ocean.

delta 118

A deposit of sediment where a stream or river enters a lake or the ocean.

geologic column 96

A diagram showing a composite column of rocks arranged with the oldest at the bottom, followed upward by progressively younger rocks. (See geologic time scale.)

biozone 98

A general term referring to all biostratigraphic units such as range zones and concurrent range zones.

rocks

A geologist is least likely to collect good data on recent climate change (within the past 1,000 years) from what source?

barrier islands 119

A long sand body more or less parallel with a shoreline but separated from it by a lagoon.

carbon-14 dating 78

A numerical dating technique relying on the ratio of to in organic substances; useful back to about 70,000 years ago.

principle of cross-cutting relationships 72

A principle holding that an igneous intrusion or fault must be younger than the rocks it intrudes or cuts across.

principle of inclusions 86

A principle holding that inclusions or fragments in a rock unit are older than the rock itself—for example, granite inclusions in sandstone are older than the sandstone.

principle of lateral continuity 72

A principle holding that rock layers extend outward in all directions until they terminate.

principle of superposition 72

A principle holding that sedimentary rocks in a vertical sequence formed one on top of the other so that the oldest layer is at the bottom of the sequence whereas the youngest is at the top.

principle of original horizontality 72

A principle holding that sediments are deposited in horizontal or nearly horizontal layers.

graded bedding

A sediment layer in which grain size decreases from the bottom up.

graded bedding 109

A sediment layer in which grain size decreases from the bottom up.

graded bedding

A sediment layer in which grain size decreases from the bottom up. Most graded beds are deposited by turbidity currents, which are underwater flows of sediment and water that have a greater density than sediment-free water.

meandering streams 116

A stream with a single, sinuous channel with broadly looping curves.

braided streams 116

A stream with an intricate network of dividing and rejoining channels.

cross-bedding

A type of bedding in which individual layers are deposited at an angle to the surface on which they accumulate, as in sand dunes.

cross-bedding 110

A type of bedding in which individual layers are deposited at an angle to the surface on which they accumulate, as in sand dunes.

Biostratigraphic units 98

A unit of sedimentary rock defined solely by its fossil content.

nonconformity

A(n) ________ is an erosional surface cut into plutonic or metamorphic rocks that is overlain by sedimentary rocks.

superposition; younger 72

According to the principle of ________, the sedimentary rocks on the top layer, are ________ than those on the bottom layer. .superposition; younger

sedimentary structures

All features in sedimentary rocks, such as ripple marks, cross-beds, and burrows, that formed as a result of physical or biologic processes that operated in a depositional environment.

sedimentary structures 109

All features in sedimentary rocks, such as ripple marks, cross-beds, and burrows, that formed as a result of physical or biologic processes that operated in a depositional environment. formed during deposition or shortly thereafter, but before lithification.

guide fossils 102

Any easily identified fossil with a wide geographic distribution and short geologic range; useful for determining relative ages of strata in different areas.

biogenic sedimentary structures 110

Any feature such as tracks, trails, and burrows in sedimentary rocks produced by the activities of organisms. (See trace fossil.)

trace fossils 92

Any indication of prehistoric organic activity such as tracks, trails, burrows, and nests. (See biogenic sedimentary structure, body fossil, and fossil.)

Time units 101

Any of the units such as eon, era, period, epoch, and age referring to specific intervals of geologic time.

parent vs daughter isotopes decreases; increases

As a rock ages, the percentage of parent isotopes ________ , whereas the percentage of daughter isotopes ________ .

Current ripple marks

Asymmetric ripple marks Result from deposition by water or air currents flowing in one direction

Baculites reesidei biostratigraphic zone 103

Baculites reesidei biostratigraphic zone in the Bearpaw Formation in Saskatchewan, Canada, is about 72 to 73 million years old because numerical ages have been determined for associated volcanic ash layers

coals 81

Coals form in freshwater swamps where climatic conditions promote abundant plant growth.

Transitional Environments 117

Delta (marine) Mudrocks and sandstone in coarsening-upward sequences; associated rocks of marine origin;fossils of marine and land-dwelling organisms Beach Rounded sandstone with variable sorting, commonly with shells or shell fragments, wave-formed ripple marks, and small-scale cross-bedding Barrier island Beach As above Sand dunes Much like desert dunes but with sand-sized shell fragments Tidal flat Mudstone and sandstone in fining-upward sequences; distinctive herringbone cross-bedding in sandstone

Paleocene-Eocene Thermal Maximum 80

Earth has also undergone large-scale periods of soaring global temperature, such as during what is known as the Paleocene-Eocene Thermal Maximum (Figure 4.15), beginning around 56 million years ago and lasting more than 150,000 years

continental shelf, continental slope, and continental rise

From land to sea, the order of marine environments is ________

radiometric

Geologists depended solely on relative dating methods prior to the development of ________ dating techniques.

rock sample closed; long

Geologists use a rock sample that is a(n) ________ system to date events that occurred early in Earth's history as well as a radioactive isotope with a relatively ________ half-life.

graded bedding? How does it form? In which sedimentary environment would you expect it to be common

Graded bedding is a sedimentary structure characterized by rock layers that become progressively finer in an upwards direction and is usually the result of turbidity currents. These sediment-laden currents move along the bottom of the seafloor. As the velocity diminishes, they deposit large particles followed by progressively smaller ones, forming graded bedding.

uniformitarianism 70

Hutton viewed Earth history as cyclical, with periods of uplift, erosion, and deposition. He believed Earth was old, and the cycles had vast amounts of time to operate. Lyell supported Hutton and postulated a "steady-state" Earth system in which the same geologic processes operating today have prevailed at the same rate over geologic time. By accepting this, if we understand Earth's processes today, we can use them to reconstruct Earth's history. However, it is now accepted that the rates of some geological processes may vary with time. In this way, the principle of uniformitarianism has been adapted to incorporate processes that may be relatively rare, such as major bolide impacts. Uniformitarianism is significant because it allows geologists to use current observations to interpret the rock record and determine past conditions.

younger than; cross-cutting relationships

If a fault cuts three beds of rock, it must be ________ the three beds of rocks. We know this because of the principle of ________ .

Johannes Walther (1860-1937). 90

In our discussion of marine transgressions and regressions, we considered both vertical and lateral facies relationships, the significance of which was first recognized by Johannes Walther (1860-1937).

Graded-bedding

Individual layers with an upward decrease in grain size Deposition by turbidity currents or during the waning stages of floods

sedimentary deposits of the inner and outer continental shelf differ? Do they share any features

Inner shelf deposits are mostly sand, contain marine fossils, are bioturbated, and are commonly cross-bedded. Bedding planes are marked by wave-formed ripple marks. This is the high-energy area that is periodically stirred up by waves and tidal currents. Outer shelf deposits are typically mud with marine fossils. This is the low energy part of the shelf. Both inner and outer shelf environments are marine environments where fossils and bioturbation are present.

Mud cracks

Intersecting cracks in clay-rich sediments Drying and shrinkage of mud along a lakeshore, on a floodplain, or on tidal flats

Lord Kelvin 71

Kelvin assumed that Earth had begun as a molten mass, and then he calculated the temperature under those conditions. By estimating Earth's current temperature and rate of heat loss, Kelvin determined how long it would have taken for Earth to cool to its present temperature. His calculations appeared scientific and convincing, but the calculations produced a date that was far too young. Kelvin's basic flaw was his failure to account for a heat source within Earth since its formation. He was unaware that radioactive decay within the Earth generated heat. However, even if radioactivity had not been discovered, there is other scientific evidence for the ancient age of Earth. Scientists eventually would have accumulated more data, which would have led to acceptance of the ancient age of Earth.

cooling; refuted

Lord Kelvin analyzed ________ rates for Earth to determine the age of Earth. He believed that his work ________ uniformitarianism as outlined James Hutton-Charles Lyell.

Marine environments 119

Marine environments include the continental shelf, slope, rise, and the deep seafloor

Mold—93

Mold—a cavity with the shape of a bone or shell;

turbidity currents 109

Most graded beds are deposited by turbidity currents, which are underwater flows of sediment and water that have a greater density than sediment-free water

point bar 116

One of the most distinctive features of meandering streams is point bar deposits consisting of a sand body overlying an erosion surface that developed on the convex side of a meander loop

relative dating; 66

Placing geologic events in sequential or chronologic order as determined by their position in the geologic record is

Charles Lyell 70

Principles of Geology changes over long periods of time have cumulative effects

fluvial 116

Relating to streams and rivers and their deposits.

elongate, or shoestring, geometry, 115

Some sand deposits have an elongate, or shoestring, geometry, especially those deposited in stream channels or barrier islands.

Wave-formed ripple marks

Symmetric ripple marks; generally with sharp crests and broad troughs Formed by oscillating currents (waves

facies 89

Tapeats Sandstone is overlain by the Bright Angel Shale and finally by the Muav Limestone (Figure 5.7). Each of these rock units represents a facies,

formation 97

The basic lithostratigraphic unit; a mappable unit of strata with distinctive upper and lower boundaries

lithostratigraphic unit

The basic, mappable, lithostratigraphic unit is the ________ , which has ________ upper and lower boundaries. formation; distinct

determine numerical ages of sedimentary rocks

The best way to determine numerical ages of sedimentary rocks and their contained fossils is to obtain dates for associated igneous rocks and metamorphic rocks.

bioturbation

The churning of sediment by organisms that burrow through it.

bioturbation 111

The churning of sediment by organisms that burrow through it.

sorting

The degree to which all the particles in a detrital sedimentary rock are of about the same size

meandering stream deposits

The deposits of a meandering stream system consist mostly of mud with subordinate sand;

cross-bedding and ripple marks

The direction of ancient wind and water currents can be deduced from analyzing ________

average sedimentation rate Suppose that the upper ash layer in Figure 5.21 formed 1.7 million years ago and the lower one is 1.9 million years old. What was the average sedimentation rate in cm/yr for the deposits between the ash beds for the column on the right? Do you think your calculated average is accurate for the actual rate of sedimentation? Explain.

The distance between the upper and lower ash beds is approximately 21m using the scale between the columns. Therefore, in 0.2 my, 21m of sediment were deposited. Rate of sedimentation=21m×102cmm×1200,000yr=0.011 cm/yr . This is probably not the average actual rate. It is obvious from the column on the left that either much less deposition or much more erosion took place at another location.

radioactive decay 73

The element changes to a new element.

relative geologic time scale 96

The geologic time scale as deduced from the geologic column, showing only relative time; that is, Silurian rocks are younger than those of the Ordovician but older than those designated Devonian.

rock

The geologic time scale is a dual scale based on ________ sequences with radiometric dates expressed as years before the present

stratification .

The layering in sedimentary rocks; layers less than 1 cm thick are laminations, whereas beds are thicker

stratification

The layering in sedimentary rocks; layers less than 1 cm thick are laminations, whereas beds are thicker.

stratification or bedding 109

The layering in sedimentary rocks; layers less than 1 cm thick are laminations, whereas beds are thicker.

dust 121

The main sources of deep-sea sediments are dust blown from continents or oceanic islands, volcanic ash, and shells of microorganisms that dwelled in the ocean's surface waters.

radiometric dating techniques 66

The most common method used for numerical ages, enabled geologists to determine numerical ages for rock units and geologic events

numerical dating

The most common way to numerically date a sedimentary rock is to ________ .numerically date an associated igneous or metamorphic rock

system 100

The most commonly used time-stratigraphic unit is the system, which is based on a stratotype consisting of rocks in the area where the system was first described.

different ages A volcanic ash fall was radiometrically dated using the potassium 40-argon 40 and rubidium 87-strontium 87 isotope pairs. The isotope pairs yielded distinctly different ages. What possible explanation could be offered as to why these two isotope pairs yielded different ages? What would you do to rectify the discrepancy in ages?

The most likely explanation for the discrepancy between the calculated ages is that the potassium 40-argon 40 system involves a gas as a daughter product. It is more likely that argon gas escaped from the system resulting in depletion in the daughter product. In order to confirm this hypothesis, the calculated dates using the two isotope systems should be compared. If argon gas has escaped from the system since the deposition of the ash, the date for the ash using the potassium 40-argon 40 method should be younger than the date calculated using the rubidium 87-strontium 87 isotope pair.

present is the key to the past"?

The natural laws that operate today operated precisely the same in the past

rounding

The process involving abrasion of sedimentary particles during transport so that their sharp edges and corners are smoothed off.

sorting

The process whereby sedimentary particles are selected by size during transport; deposits are poorly sorted to well sorted, depending on the range of particle sizes present.

relative age While doing geologic field work, you make the following observation: a thick layer of sandstone lies adjacent to a large body of granite, and the sandstone contains small pieces of the granite. How can you determine the relative ages of the sandstone and granite? What additional information at this rock exposure would support your conclusion?

The relative dating principle of inclusions reveals that the granite is older and the sandstone is younger. In order for the sandstone to contain inclusions of the granite, the granite had to be present first. Additional evidence supporting your conclusion could come from examining the sandstone for contact metamorphism. If the granite intruded after the sandstone, you would expect the underside of the sandstone to be baked.

progradation 118

The seaward (or lakeward) migration of a shoreline as a result of nearshore sedimentation.

Study the illustration at right and determine the relationship that exists between the tilted older rocks and the overlying horizontal rock layers. What sequence of events can you infer that led to the origin of these rocks and their present relationships?

The sedimentary rocks below the angular unconformity represent an early period of deposition and lithification. Afterward, deformation tilted these strata and erosion removed the upper portion of the section. A second period of deposition deposited the sediments above the angular unconformity. The limestone at the bottom of this upper section was probably deposited in a marine environment.

body fossils 92

The shells, teeth, bones, or (rarely) the soft parts of organisms preserved in the fossil record. (See fossil and trace fossil.)

global warming Given the current debate over global warming and the many possible short-term consequences for humans, try to visualize how the world might look in 10,000 or even 1 million years. To make your prediction, use what you have learned about plate tectonics and the direction and rate of movement of plates as well as what you know about how plate movement and global warming will affect ocean currents, weather patterns, weathering rates, and other factors. Do you think that such short-term changes can be extrapolated to long-term trends in trying to predict what Earth will be like using a geologic time perspective?

There are a variety of answers for this question. Using the principles of uniformitarianism, we can attempt to extrapolate conditions 10,000 years into the future. Many researchers attempt to do this in an attempt to show human effects on the Earth system. However, the conclusions are not yet definitive, so students may produce a variety of answers based upon their reading and understanding of current science news articles. It would be much more difficult to extrapolate one million years into the future, since student models will probably not include possible catastrophic events that we cannot accurately predict. Additionally, geologic time is so immense that it would not be representative to take conditions over a short-term period and apply them to a long-term period.

Trace fossils

Tracks, trails, tubes, and burrows Indications of organic activity. Intense activity results in bioturbation involving disruption of sediment

depositional environments Geologists are able to interpret depositional environments not only by the sedimentary structures they contain, but also by comparing ancient deposits with present-day deposits.

True

Unconformity 86

Unconformity is a general term that encompasses three distinct types of surfaces: disconformity, nonconformity, and angular unconformity.

radiometric dating 73

What is being measured in radiometric dating is the time of crystallization of a mineral containing an isotope;

period

What is the correct time unit for the Quaternary, Pennsylvanian, Ordovician and Cretaceous?

marine transgression

When a marine transgression occurs, the shoreline migrates ________ , and sea level ________ . landward; rises

continental shelf

Which depositional environment is considered to be marine?

sedimentary structures

Which feature of sedimentary rocks would be most useful to determine the depositional environment?

species-identical fossil assemblages

Which piece of evidence would best illustrate that rocks in widely separated areas were deposited at the same time? species-identical fossil assemblages

deep ocean basin pelagic clay and calcareous and siliceous oozes

Which rock type is predominant in deep ocean basins?

cities and time record

Why are cities unlikely to be preserved in the geologic record? They are situated on land, which tends to erode.

marine regression 90

Withdrawal of the sea from a continent or coastal area caused by emergence of the land with a resulting seaward migration of the shoreline.

Philip Henry Gosse, 85

a British naturalist, who in 1857 claimed that such features were created to look as if Earth had a long history. He proposed that Earth is only a few thousands of years old and that all features in rocks, including fossil bones and shells, that looked as though they formed long ago were created with that appearance.

sedimentary facies 88

a body of sediment with distinctive physical, chemical, and biological attributes.

Navajo Sandstone 124

a coastal dune deposit, wind blew from northeast

biostratigraphic unit;

a concurrent range zone is a type of biostratigraphic unit;

beta decay 73

a fast moving electron is emitted from a neutron in the nucleus, increases atomic number by 1

erosional surface 70

a gap in geologic record- Hutton

outcrops 86

a number of separate rock exposures, or what geologists call outcrops.

concordant 77

ages obtained from parent daughter ratios agree closely, reflects time of crystallization of the magma

radioactive decay 3 types 74

alpha, beta, electron capture

nonconformity 87

an erosion surface cut into plutonic rocks or metamorphic rocks that is overlain by sedimentary rocks is a nonconformity

Range zones

are most beneficial for identifying ________ . the total time species existed

Body fossils

are the actual remains of organisms, most of which are bones, teeth, and shells.

most reliable dates

are those obtained by using at least two different radioactive decay series in the same rock.

Desert dunes 81

are typically well sorted and exhibit large-scale cross-bedding.

Numerical dates for rocks

are usually obtained by determining how many half-lives of a radioactive parent element have elapsed since the sample originally crystallized.

fossil 92

as the remains or traces of prehistoric organisms preserved in rocks. They are by far most common in sedimentary rocks, but they may also be found in volcanic ash deposits and volcanic mudflows—but rarely in other igneous rocks or metamorphic rocks.

lateral gradation 88

as their composition and/or texture becomes increasingly different

relative geologic time scale 71

at first just relative dating then radiometric dating helped with numerical dating

bedding planes 86

bedding planes separate individual strata from one another (Figure 5.1) or the strata grade vertically from one rock type into another.

trace fossil a. shells b. teeth c. burrows d. bones e. jellyfish

burrows, tracks,

James Ussher, archbishop 67

calculated Earth's age at approximately 6,000 years, thus providing the idea that Earth was very young .Based on Old Testament genealogies, October 23, 4004

sedimentary rocks 75

cannot be radiometrically dated bc it would measure a mineral rather than time

ooids 123

carbonate barriers from in high energy area and may be reefs, skeletal particles or accumulations of spherical carbonate grains

cast—93

cast—a mold filled by minerals or sediment

chemical sedimentary rocks 109

chemical sedimentary rocks are composed of minerals extracted from solution by inorganic chemical processes or by the activities of organisms

color 108

color is a useful feature of some sedimentary rocks: red rocks likely were deposited on land, whereas greenish ones more likely were deposited in a marine environment. However, exceptions are numerous, so color must be used with caution.

atomic mass number 73

combined # of protons and neutrons

nucleus 73

composed of protons and neutrons with electrons encircling it

fossil record ________ are least likely to be preserved in the fossil record because ________ . a. Horse teeth; horses live in areas not conducive to fossilization b. Corals; they frequently undergo mineral replacement c. Brachiopods; they frequently undergo mineral replacement d. Jellyfish; they consist mainly of soft parts e. Clams; they are very scarce

d. Jellyfish; they consist mainly of soft parts

potassium-argon 77

date fine grained volcanic rocks

argon-argon dating 78

date fined grained volcanic rocks and metamorphic rocks

fission track dating 78

date samples 40k to 1.5 million years old

Madison Group 124

deposition in a shallow marine env.

principle of superposition 86

determine the correct relative ages of underformed strata by their position in a sequence; the oldest layer is at the bottom of the sequence with successively younger layers upward in the sequence

numerical age 73

determined by measuring the decay rate of unstable isotopes

mass spectrometer 75

determines parent daughter ratio

Lithostratigraphic correlation involves

determining the original lateral extent of a formation or group;

continental shelf 119

detrital marine env The area where the seafloor slopes gently seaward between a shoreline and the continental slope.

continental slope 121

detrital marine env The relatively steep part of the seafloor between the continental shelf and continental rise or an oceanic trench.

Correlation of biostratigraphic zones,

especially concurrent range zones, demonstrates that rocks in different areas are of the same relative age even though they may differ in composition.

Alpha decay involves the emission of two protons and two electrons.

false

Evaporites form in moist, humid marine environments. 123

false

Fossil evidence must be examined for accurate determinations of depositional environments.

false

Fossils are useful to a point in that they tell scientists what types of animals and plants existed in the past, but they can't provide climatological data.

false

Geologists expect the most noticeable changes that present-day activities will leave in the geologic record will be the relics of concrete and steel from cities, factories, and utilities.

false

Grand canyon Rocks in the Grand Canyon are in undisturbed horizontal sedimentary layers. Therefore, the youngest rocks are at the bottom of the sequence, and the oldest rocks are at the top.

false

Relative dating principles like superposition are rarely applied by stratigraphers, as they rely mostly on numerical dates.

false

Sedimentary structures are unique to specific environments. For example, ripple marks are only found in stream channels.

false

William Smith's principle of fossil succession states that fossil assemblages succeed one another through time in regular and determinable order.

false

carbonate rocks Unlike detrital sedimentary rocks, carbonate rocks do not have cross-bedding, ripple marks, or other sedimentary structures.

false

earths date Early naturalists used various scientific methods to date Earth, and erred by only +/- 2-3 million years.

false

fossils Soft-bodied organisms are less well represented in the fossil record because they were less common in ancient geologic history.

false

geologic time scale Originally, the geologic time scale was developed using numerical dates.

false

numerical age Lava flows and ash falls interbedded with sedimentary rocks are most useful for determining numerical ages.

false

uranium 238 The short half-life of uranium-238 allows it to be used to date ancient events.

false

Sedimentary structures form during lithification.

false- before lithification

Rocks in a formation can belong to multiple lithostratigraphic units.

fasle

geologic record 85

geologic record—that is, the evidence for physical and biological events preserved in rocks.

Cross-bedding;

geologists cross bedding to determine ancient current directions

William Smith 95

had found a way to determine the relative ages of rocks in different areas by matching up fossil assemblages

Paleogeography deals primarily with producing maps of ________ 125

historical distribution of the continents at various times

Uniformitarianism 70

holds that the laws of nature have been constant through time, and that the same processes operating today have also operated in the past, although not necessarily at the same rates.The uplift mechanism was thermal expansion

Amanz Gressly, 88

in 1838, was the first to use the term facies when he carefully traced sedimentary rocks in the Jura Mountains of Switzerland and noticed lateral changes such as sandstone grading into shale.

Lithostratigraphic correlation

involves demonstrating the original continuity of a rock unit over an area even though it may not now be continuous over this area.

stratigraphy 86

is a branch of geology concerned mostly with the composition, origin, age relationships, and geographic extent of layered, or stratified, rocks. It deals primarily with sedimentary rocks because almost all of them are stratified

Period

is a time unit

Lingula 102

is a type of brachiopod that meets the first two criteria, but its geologic range makes it of little use

Tree-ring dating 79

is another useful method for dating geologically recent events. The age of a tree can be determined by counting the growth rings in the lower part of the trunk. Each ring represents one year's growth, and the pattern of wide and narrow rings can be compared among trees to establish the exact year in which the rings were formed

range zone 102

is defined as the geologic range (total time of existence) of a particular fossil group, such as a species or a group of related species called a genus.

angular unconformity 87

is present if the strata below an erosion surface are inclined at some angle to the strata above

fossil record

is strongly biased toward those organisms that have durable skeletons and that lived where burial was likely.

William Smith

is the basis for the principle of fossil succession, which holds that fossil assemblages succeed one another through time in a predictable order.

banded iron formation, 108

is the main source of the world's iron ore and is important in the economies of Minnesota, Michigan, and Ontario, Canada

half-life 73

is the time it takes for one-half of the original, unstable radioactive parent element to decay to a new, more stable daughter element

Tree-ring dating

is useful for ________ dating of ________ events. numerical; recent

Evaporites are ________ common than limestone in the geological record, and consist mostly of ________

less, rock salt and rock gypsum

micrite 123

limestones are made up of gravel and sand sized grains and microcrystalline carbonate mud called micrite

marine transgression

marine transgression, a vertical sequence of facies results with offshore facies superposed over nearshore facies.

groups and supergroups 98

more inclusive units such as groups and supergroups

closed system 75

needed for accurate radiometric dates neither parent or daughter has been removed or added since mineralization

numerical ages for sedimentary rocks 103

numerical ages for sedimentary rocks and their contained fossils must be determined indirectly by dating associated igneous and metamorphic rocks

Nicolas Steno 71

oldest layer at bottom youngest on top, principle of superposition

Wave-formed ripple marks 110

on the other hand, tend to have symmetrical profiles and, as their name implies, are generated by the to-and-fro motion of waves

parent element 73

original unstable elem

Relative dating 66

places geologic events in sequential order as determined from their position in the geologic record.

preservation of body fossils 92

preservation of body fossils are (1) that an organism has a durable skeleton and (2) that it lives where burial in sediment is likely.

principle of fossil succession 95

principle of fossil succession A principle holding that fossils, especially groups or assemblages of fossils, succeed one another through time in a regular and determinable order.

principle of lateral continuity 88

principle of lateral continuity, meaning that layers of sediment or sedimentary rock extend outward in all directions until they terminate

electron capture 73

proton captures one electron from an electron shell converting the proton to a neutron

Numerical dating 66

provides specific dates for geologic rock units or events that are expressed in years before the present.

radioactivity

radioactivity provided a reliable geologic clock with which we now assign numerical ages to many ancient events.

correlation 101

refers to the act of matching up the same rock unit in areas where it is no longer continuous (lithostratigraphic correlation), or determining which events took place at the same time in different areas (time-stratigraphic correlation).

Texture 109

refers to the size, size distribution, shape, and arrangement of clasts in detrital sedimentary rocks

evaporate environments 123

rock salt and rock gypsum, are found in playa and saline lakes, but mostly formed in seas, found in Mediterranean sea, Michigan Ohio, New York, Gulf coast states western Canada

detrital sedimentary 109

rocks as those made up of detritus, that is, the solid particles of preexisting rocks such as gravel, sand, silt, and clay

blanket, or sheet, geometry 115

rocks cover hundreds or thousands of square kilometers but are perhaps only a few tens to hundreds of meters thick. That is, they are not very thick compared with their dimensions of length and width and thus have a blanket, or sheet, geometry

John Joly 69

salt in streams, 90 million years

sedimentary rocks 85m

sedimentary rocks because those rocks preserve evidence of surface processes (running water, glaciers, and wind) responsible for deposition.

Guide fossils

should be geographically ________ , with a relatively ________ geologic range. widespread; short

sill—86

sill—a sheetlike intrusive body—it is younger than the layers below it and younger than the layer immediately above it

Adam Sedgwick 95

studied rocks in northern Wales and described what he called the Cambrian System, and Sir Roderick Impey Murchison named the Silurian System in southern Wales

Charles Lapworth 96

suggested that the strata in the area of overlap be assigned to a new system, the Ordovician

Transgressions and regressions

take place in response to any tectonic movement that elevates the land with respect to sea level or causes subsidence (downward movement) of the land Another cause of transgressions and regressions is the volume of water in the oceans..

Transgressions and regressions 91

take place in response to any tectonic movement that elevates the land with respect to sea level or causes subsidence (downward movement) of the land.

Walther's law,

the facies in a conformable vertical sequence replace one another laterally

James Hutton- 70

the principle of uniformitarianism

time transgressive, 90

time transgressive, meaning that as the shoreline migrated landward, the facies were not deposited simultaneously over their entire geographic extent.

Cross-bedding allows geologists to determine ancient wind directions.

true

Fluvial systems, lakes, and deserts are classified as continental environments

true

Larger particles indicate higher energy depositional environments

true

Lord Kelvin's estimates of Earth's age were incorrect because he did not account for heat supplied to Earth by radioactive decay.

true

Marine transgressions and regressions are events where sea levels change due to tectonic or climatic events

true

Numerical dating was not used until the discovery of radioactive decay.

true

Paleogeographic maps show the distribution of land and seas at various times in Earth's history

true

Range zones indicate the total time a species existed in the geologic record.

true

Relative dating principles allow geologists to correlate rock units and interpret the geologic history of an area.

true

Sand is commonly found in fluvial deposits.

true

Sedimentary rocks are important because they preserve evidence of the surface processes responsible for deposition.

true

Sediments are originally deposited in horizontal layers.

true

Systems of rock units were established on the basis of superposition and fossil content.

true

Walther's law states that facies seen in a conformable vertical sequence will also replace one another laterally.

true

deep sea sediments The main sources of deep-sea sediments are dust blown from continents or oceanic islands, volcanic ash, and shells of microorganisms that lived in the ocean's surface waters.

true

fossils Dinosaur bones would be body fossils, and dinosaur tracks would be trace fossils.

true

fossils Guide fossils are confined to a narrow range of time.

true

metamorphosed rock After a rock is metamorphosed, it is impossible to determine an accurate date for when the original rock formed.

true

sedimentary rates One reason sedimentation rates cannot be used to calculate the age of Earth is variations in erosion rates.

true

varve consists of a pair of dark and light colored laminations that represent deposition in lakes produced by glacial processes over a one-year period.

true

long-lived radioactive isotope pairs

uranium 238-lead 206, uranium 235-lead 207, thorium 232-lead 208, rubidium 87-strontium 87, and potassium 40-argon 40

James Ussher

used an unscientific method to determine the age of Earth. In the 1600s, ________ analyzed the Old Testament and determined that Earth was formed on October 23, 4004 B.C.

isotopes 73

variable forms of the same element

Superposition and fossil succession

were used to piece together a composite geologic column, which is the basis for the relative geologic time scale.

La Brea Tar Pits in Los Angeles, California, 93

where hundreds of fossil mammals, birds, insects, and other organisms have been recovered


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