Geology 103 Chapters 1-7 Midterm
Why are sandstones and siltstones of desert environments rarely black or gray in color?
Black and dark gray coloration in sedimentary rocks results from the presence of compounds rich in organic carbon and iron. Hence, black sediments represent deposition in an environment where organisms were abundant and where oxygen levels are low enough to prevent destruction of the organic matter by oxidation or bacterial action. The desert environment lacks both the many organisms and the anoxic conditions necessary to preserve organic matter.
Suppose that you collected sponges, brachiopods, nautiloids, primitive conodonts, graptolites, trilobites, and gastropods from a limestone layer in western Utah, but in spite of dedicated searching you were not able to find bryozoans, corals, foraminifera, or crinoids. Given the range of each fossil group, determine the age of the limestone bed. In other words, during which period of geological time were sponges, brachiopods, etc. present, but not crinoids, bryozoans, corals, or foraminifera?
CAMBRIAN
Describe four nonsilicate minerals that are also common in the earth's crust: calcite, dolomite, aragonite, and halite.
Calcite and dolomite are the most important carbonates. Calcite is the main constituent of limestone and marble, and it is secreted as skeletal material by certain invertebrate animals from seawater, or formed as dripstone in caverns. Dolomite is used for carbonate minerals and in it, calcium and magnesium occur in equal proportions. Aragonite is the stuff that's inside the shells of clams where pearls are, and is a carbonate material that occurs in a different form and more rarely than calcite or dolomite. Halite is considered common rock salt and gypsum and is easily recognized by its salty taste and it crystallizes and cleaves to form cubes.
Oldest to youngest periods=
Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian.
The correct order of Paleozoic periods is (from oldest on left to youngest on right)
Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian.
Examine the Geological Time Scale on page 13 of your textbook, and indicate which of the following intervals has the shortest duration.
Cenozoic.
Who's idea was natural selection?
Charles Darwin.
List the clastic sedimentary rocks in order of increasingly finer grain size.
Conglomerate, sandstone, siltstone, shale and claystone.
4. In drilling for oil, geologists recover Devonian conodonts in a stratum known to be Permian in age. Explain how this may have occurred.
Conodonts are made of the durable mineral apatite. The conodont in question was eroded from a Devonian layer (along with quartz sand grains), was transported by wind and water, and was then deposited into a layer of sediment during the Permian. This is known as a reworked fossil.
Summarize the origin and significance of sea-level changes in the sedimentary rock archive.
Figure 3-42 (page 87 of your textbook) shows the pattern of sea-level oscillation over the last 600 million years of Earth's history. Note that the red line represents modern sea level. The blue line represents the position of sea level at any given point of time during the last 600 million years (Cambrian to Recent). When the blue sea-level curve is left of the red line, it indicates a time when sea level was higher than its present level. The blue sea-level curve is right of the red line when sea level is lower than at present. Four important observations emerge from this diagram: (see next cards.)
Explain how fossils are used to reconstruct ancient ecosystems, climates, and geographies.
Fossil are remains of species that once had specific ecological needs. The presence of certain fossils or assemblages of fossils in rocks yields valuable insights into the environment of deposition. The study of fossils as members of ancient communities and ecosystems is called paleoecology. Paleoecologists assume that past biological communities had many of the same physical and biological attributes and requirements of their modern counterparts. The biosphere has been likened to a Shakespearean play wherein the roles and stage requirements remain fixed while different actors reprise the same roles just as different species have evolved to fill ecological niches through geologic time.
List the subdivisions of the Linnean classification scheme in their proper order.
From general to specific the Linnean hierarchy is as follows: domain, kingdom, phylum, class, order, family, genus, and species.
Who's idea was extinction and catastrophism?
Georges Cuvier.
3. A chronostratigraphic (time-rock) unit contains a different fossil assemblage at one locality than at another located 200 km away. Suggest a possible cause for the dissimilarity.
Given that the two fossil assemblages are time equivalent, the difference must be because of ecological differences. A shallow marine location would have different fossils than a time-equivalent, deep-water locality two hundred kilometers away.
Nicolaus Steno
He first discovered the principles of superposition, original horizontality and lateral continuity. He worked as a physician to the Duke of Tuscany.
Understand how igneous rocks are classified.
Igneous rocks are extensively covered by sedimentary rocks and mountains. They are those that have cooled from a molten state. The word "igneous" comes from the Latin word, ignis, which means "fire."
Describe the different origins of igneous, metamorphic, and sedimentary rocks in the context of the rock cycle.
Igneous rocks are those that have cooled from a molten state. Sedimentary rocks consist of materials formed from the weathered products of pre-existing rocks that have been transported, deposited and lithified. Metamorphic rocks are any that have been changed from previously existing rocks by the action of heat, pressure and associated chemical activity.
Of the three rock families—igneous, metamorphic, and sedimentary—which forms from cooling of molten materials (magmas and lavas)?
Igneous.
What is a mineral? What characteristics of a true mineral such as quartz or feldspar would NOT be present in a piece of glass?
It is a naturally occurring, inorganic solid with a specific chemical composition and atomic arrangement. In other words, a mineral is an orderly arrangement of atoms. In a glass, the atoms are not ordered.
Who's idea was uniformitarianism?
James Hutton.
Is modern sea level above or below the Phanerozoic (Cambrian-Recent) average?
below.
The study of processes affecting a fossil organism from the time of its death until final burial is called
biostratinomy.
Which fossil groups are most useful for correlating Cambrian rocks on a worldwide basis?
brachiopods, trilobites.
Of the nuclide pairs listed below, which is best for dating biological materials, such as bone, coal, and soot?
carbon 14:nitrogen 14.
Principle of lateral continuity
claims that strata extends in all directions until they terminate by thinning at the margin of the basin, end abruptly against some former barrier or grade laterally into a different kind of sediment.
These rocks were deposited in what environment?
deep marine.
In which of the following depositional environments would you expect to find the best sorted sediments?
desert.
The sedimentary rocks alluded to in the question before the previous one would be deposited on flat-lying sedimentary strata of late Pleistocene age (those now forming the grass-covered surface of Florida). The surface separating the Pleistocene layers from the hypothetical future deposits would represent an interval of missing time (the time that has lapsed since Florida was flooded during the last interglacial period, approximately 100,000 years). Deposition of a new package of flat-lying sedimentary rocks on top of this surface would result in the formation of
disconformity
Georges Cuvier
discovered extinction and catastrophism
William Smith
discovered faunal succession
Charles Darwin
discovered natural selection.
Charles Lyell
discovered the principle of cross-cutting relationships; wrote a book about Principles of Geology.
James Hutton
discovered uniformitarianism.
Which of the following is the least useful index fossil in Upper Devonian rocks?
echinoids.
When shoreline sands of the Tapeats Sandstone were forming in the eastern Grand Canyon at time T1, what kind of sedimentary rocks were being deposited in the western Grand Canyon?
offshore shale (bright angel shale)
The Tapeats Sandstone in the western Grand Canyon is ___________ the Tapeats Sandstone in the eastern Grand Canyon
older than.
A marine organism that lives in the water column, between a depth of 0 to 1000 meters, and is an active swimmer is best classified as a(n)
pelagic, nektonic organism
A group of closely related classes comprises a taxonomic
phylum.
Carbonization (types of fossil preservation)
process of fossilization wherein original soft parts are flattened and reduced to a film of carbon
Permineralization (types of fossil preservation)
process of infilling of pores within bones and shells with additional mineral material
Metamorphic rocks are classified as either foliated or nonfoliated. Which of the following are nonfoliated metamorphic rocks
quartzite and marble.
Paleoecological studies enable geologists to:
reconstruct ancient ecosystems, track the migration of lithospheric plates, and evaluate climatic events of the past.
Replacement (types of fossil preservation)
fossilization process wherein the original shell of skeletal substance is replaced by a different mineral (e.g., replacement of calcite by pyrite or silica)
Define the term fossil and understand the following types of fossil preservation
fossils,the remains or traces of past life preserved in sedimentary rock strata. Fossils are the most important means of establishing time equivalency of rock layers on a regional and global basis. Fossils that indicate specific or restricted periods of time are called index fossils.
A rock that forms deep underground (intrusive igneous rock) and has a sialic composition is called
granite.
Biological components of marine ecosystems are classified according to their so-called trophic, or feeding, level. Which of the following is a producer organism as contrasted with a consumer organism?
green plant.
Olivine
has an olive green color and is glassy and green also. It is made from iron and magnesium silicate and is present in basalt. It is a component of the ultramafic rock called peridotite.
Oldest to youngest eons
included Hadean, Archean, Proterozoic and Phanerozoic.
According to Lamarck, the driving mechanism of evolutionary change is
inherent needs or wants of the evolving organism.
The marine sedimentary rock formed by incorporation of carbonate shells and ooids into a solid deposit is
limestone.
What type of sedimentary rocks would form in the warm shallow seas that would cover the Everglades? (Hint: What type of sedimentary rock is now forming in the shallow waters covering the Bahamas platform?)
limestone.
The technical term for the intertidal zone is
littoral.
Which of the following is a trace fossil?
mammoth footprint.
As sea level continues to rise, Florida will continue to experience a
marine transgression.
Mica
mica is recognized by its perfect cleavage along one directional plane. There are 2 types of mica, biotite and muscovite. Biotite mica is dark colored and muscovite mica is colorless or pale colored mica. Both are common rock-forming silicates.
During what time interval did the ocean reach its all-time low?
middle oligocene.
If the basal Tapeats sandstone is Early Cambrian (540 million years) in age in the western Grand Canyon and Middle Cambrian in age in the eastern Grand Canyon (520 million years), what was the average speed of the Tapeats transgression across the Grand Canyon area?
10 millimeters per year.
What percentage of Florida would be flooded if the ice caps at the North and South Poles were to melt and sea level were to rise 200 feet?
100 percent.
How deep would the ocean be in central Florida once all of the ice had melted (refer to the question before the previous one)
120 feet.
Indicate how many years ago Midway Island was centered over the spot now occupied by the big island of Hawaii?
18 million years.
The Earth is approximately ____________ years old.
4.6 billion.
Explain the difference between a geochronologic term (sometimes called a time term) and a chronostratigraphic term (sometimes called a time-rock term).
A geochronologic unit is an abstract unit because it is a unit of time. The basic geochronologic unit is the period (Cambrian, Ordovician, and so on). Other geochronologic units include eons, eras, epochs, and ages. Consider the Devonian period, a 56-million-year-long interval that began 418 million years ago and ended 362 million years ago. Just like the year 1999, this interval of time has come and gone, never to be revisited. So how do we know anything about the Devonian period if it happened over 362 million years ago? We know about the Devonian because during that time, geological and biological processes, such as sedimentation, plate tectonics, and organic evolution, were operating and leaving a record of their operation in Earth's rocky crust. The rock strata formed by these processes during this 56-million-year interval comprise the chronostratigraphic unit known as the Devonian System. Hence, a geochronological unit is an increment of pure time, whereas a chronostratigraphic unit is a body of rock (a tangible, nonabstract entity) deposited or otherwise formed during a particular time interval.
Explain the difference between a rock and a mineral.
A rock is an aggregate of minerals. These aggregates may be igneous, sedimentary, or metamorphic in origin. Igneous rocks are those that form through cooling of a magma or lava. Sedimentary rocks form when fragments of previously existing rocks and soil are compacted and cemented together. If a rock is subjected to elevated temperatures and high pressure, the mineral composition and texture may be altered, giving rise to metamorphic rocks. Weathering, heat, and pressure continually act on rocks to change them from one type to another. /// A mineral is an orderly arrangement of atoms. By definition, these orderly arrangements must be naturally occurring and inorganic. As a result, neither synthetic diamonds nor amber (solidified tree resin) qualify as minerals. Over three thousand minerals, most of them rare, have been detected thus far. New ones are likely to be discovered in the future. Minerals are identified on the basis of physical properties such as crystal shape, cleavage, hardness, color, luster, and so on. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, an ordered atomic structure and specific physical properties. A rock, by comparison, is an aggregate of minerals and need not have a specific chemical composition. Minerals range in composition from pure elements to very complex silicates with thousands of known forms.
What features in a sedimentary rock might indicate it was developed in each of the following environments of deposition?- A. Shallow marine environment
A shallow marine setting is well-oxygenated and subject to wave and storm energy. The abundance of light would result in an active plant and animal community. If this seafloor were adjacent to a delta or other source of silicate sand and gravel, the resulting deposits would be light-colored (tan or greenish-gray), moderately well-sorted, cross-bedded sandstone with abundant trace fossils. If the seafloor was protected from influx of clay and sand, the dominant sediment source of would be the remains of plants and animals living on the seafloor. As a result, a light gray, fossilrich limestone would be deposited.
In which of the following depositional environments would you anticipate finding red sandstones interbedded with thick layers of poorly sorted, but partially rounded conglomerate (gravel)?
Alluvial fan
What differences in texture and composition serve to distinguish between a mature and an immature sandstone?
An immature sandstone is characterized by poor sorting, angular grains, a high percentage of clay and silt in the matrix, and a mineral composition that includes unstable minerals, such as feldspar and ferromagnesian minerals. A mature sandstone is comprised chiefly of quartz grains that are wellsorted and well-rounded.
Discuss the role of radioactivity in constructing a quantitative geologic timescale.
As things get older, they started to decay?? When the nucleus of an unstable radioactive atom fires off a positively charged particle comprised of two protons and two neutrons (a helium nucleus) it has undergone alpha decay. The process at work in radiometric clocks is the spontaneous decay from parent to daughter isotopes through addition or loss of nuclear particles (protons and neutrons). Lab studies show that decay occurs at a constant rate, regardless of temperature and pressure changes in the test chamber. The measurable result of decay is the increasing abundance of daughter isotope at the expense of parent material. The rate is measured in terms of half-life, the amount of time required for one half of the original parent isotopes in a mineral to decay into daughter product. Precise amounts of parent and daughter materials in a rock or mineral are measured with a mass spectrometer. These amounts are plugged into the equation on the following page to determine the age of the host rock or mineral. t = (t 1/2 /0.693) ln(D/P)+1)
The plastic, partially molten layer upon which lithospheric plates move is the
Asthenosphere.
Which igneous rock best approximates the composition of the continental crust?
Continental=granite. Oceanic=basalt. The igneous rock that best approximates the composition of continental crust is granite. The igneous rock that best approximates the composition of oceanic crust is basalt.
What features in a sedimentary rock might indicate it was developed in each of the following environments of deposition?- B. Deep marine, continental rise environment
Deep marine rocks of the continental rise will reflect deposition by turbidity currents in an oxygen-starved setting. Graded bedding and dark coloration would be the two biggest clues to this setting.
What features in a sedimentary rock might indicate it was developed in each of the following environments of deposition?- C. Transitional, deltaic environment
Deltas are characterized by river and wave energy and an influx of sand, gravel, and mud. Swamps often form on the top of the delta plain. Interbedded sandstones, coals, and clays would result.
What are the differences between the following? E. Domain and kingdom
Domains and kingdoms represent major taxonomic subdivisions of the Linnean classification scheme. Everyone is familiar with the kingdoms Plantae and Animalia. With the invention of the microscope, it became clear that some living things were neither plant nor animal; consequently, the kingdoms of Protoctista, Fungi, and Monera were added. Recently, the term domain has been added to encompass two or more kingdoms. The three domains currently recognized are Archaea, Bacteria, and Eukarya. The domain called Eukarya is divided into four kingdoms known as Protoctista, Plantae, Animalia, and Fungi.
Articulate the differences between the terms shield , craton , and platform.
Each continent is comprised of three parts: shield, stable platform, and marginal mobile belts. The shield is the flat, geologically stable (few earthquakes and volcanoes) region of the continent where Precambrian igneous and metamorphic rocks are exposed at the surface. The surrounding areas, where Precambrian rocks are covered with a thin blanket of sedimentary strata, are called the stable platforms. Like the shield, the platform is geologically quiet. Together the shield and platform form the craton, or stable interior, of the continent. Tectonic activity in the form of mountain building, volcanic eruptions, and earthquakes is generally restricted to the marginal mobile belts.
How do isotopes of a given element differ from one another in regard to number of protons and neutrons in the nucleus?
Each of the known elements is defined by the number of protons in the nucleus of the atom. For example, each atom in the universe that possesses two protons in the nucleus is, by definition, helium. All atoms in the universe with six protons are carbon. For a given element, the number of protons is in the nucleus is fixed. The number of neutrons may, however, vary within the nucleus of atoms. Isotopes are atoms of a given element that vary in the number of neutrons. For example, some chlorine atoms have eighteen neutrons, while others have twenty. As long there are seventeen protons, these atoms are still chlorine (table 1-2 on page 20 of your text).
What is the name of the biologist who developed the system of binomial nomenclature for naming organisms (e.g., kingdom, phylum, class, order, family, genus, species)?
Linnaeus.
Observation 4
Major transgressions and regressions occur over tens of millions of years.
Principle of faunal (biological) succession
Matching a sedimentary layer with one of the same age located in a different state (or on a different continent) is best achieved using the principle of faunal succession. British canal-builder William Smith noted as early as 1805 that many sedimentary layers contained a unique suite of fossils that distinguished them from overlying and underlying strata.
How does matrix in a rock differ from cement? What are the most common kinds of cements found in sandstones? Which of these is most durable?
Matrix is fine-grained material deposited with sand grains, pebbles, or boulders at the time of sediment deposition. Cement is a post-depositional component of a sedimentary rock. As groundwater percolates through tiny pores in the unconsolidated sediment, tiny crystals precipitate on the walls of the pores much like stalactites and stalagmites form on the walls of a cave. These crystals (cement) eventually fill up the porosity and glue the particles together. Common cements in sandstones are silica and calcite. Of these, the former is much more durable.
Understand how metamorphic rocks are classified.
Metamorphic rocks are classified by the presence or absence of foliation. It is considered rocks that have been altered by physical and chemical changes in the environment that has converted it. They can be foliated or nonfoliated.
Who's idea was superposition of strata?
Nicholas Steno.
Which of the following statements about the earth's crust is false?
Oceanic crust is granitic, while continental crust is basaltic.
Indicate the difference between biological species and paleontological species.
Paleontologists use the same system as biologists in naming and classifying fossil organisms. The fundamental unit of the Linnean system is the species, a group of organisms that look alike and that can produce viable offspring. Since paleontologists cannot determine if fossils could breed when alive, they must rely solely upon similarities in shape and appearance to define species.??
Oldest to youngest eras
Paleozoic, Mesozoic, Cenozoic era.
Which of the following periods of the Paleozoic Era was not defined in Great Britain?
Permian.
Describe the three types of plate margins (convergent, divergent, transform fault) and identify what types of geological activities, geological structures (folds and faults), and rocks occur at each.
Plate margins are defined by relative plate motion as the following: (1) convergent(plates collide), (2) divergent (plates pull apart), and (3) transform fault (plates slide horizontally past one another). Most tectonic activity (earthquakes, volcanism, mountain building) takes place at these plate boundaries.
Visualize the important distinctions between six common silicate minerals: quartz, feldspar, mica, hornblende, augite, and olivine.
Quartz- is a mineral that is most familiar and important of all the silicate minerals. It is common in many different families of rocks. Quartz's appearance is a glassy, colorless, grey or white mineral. It has a hardness of 7 and will not cleave. It's made out of silicon dioxide. (the rest are on separate cards.)
Which of the following techniques is used to determine the absolute or actual age of a geological feature?
Radiometric dating
On a continuum from minor disruption to severe damage, which of the following biostratinomic processes does the least violence to a potential fossil?
Reorientation of the shell
Describe the general steps used by geologists and other scientists in their attempt to solve particular problems or explain natural phenomena
Scientists follow a procedure called the scientific methodfour steps: develop a question about an observation in nature; formulate a hypothesis or plausible explanation to answer the question; test the hypothesis by seeing if it fits the data; accept, reject, or modify the hypothesis. If scientists modify the hypothesis, they test it again to see if it better explains the phenomenon in question.
Observation 1
Sea level is lower at present than it has been through most of Phanerozoic time.
Observation 3
Sea level rises (excursions of the sea-level curve to the left) are more gradual than sea-level drops (excursions to the right).
Observation 2
Sea level rises and falls continuously.
Explain the concept of sedimentary facies.
Sedimentary facies refers to the features of a rock that indicate its environment of deposition. Suppose that a Pleistocene age limestone layer extends across Florida. Suppose further that muddy, laminated limestones prevail in northern Florida while coarser, fossil-rich limestones prevail in southern Florida. These facies relationships suggest that low-energy tidal flat conditions existed in northern Florida while higher energy, perhaps reeflike, conditions existed farther to the south. This limestone is said to grade laterally from a fine-grained or tidal flat facies in the north to a fossiliferous, reefal facies in the south. This twofold example is quite oversimplified, as myriad shallow marine subenvironments, each with its own compliment of sedimentary textures and structures (facies), coexisted in the shallow ocean that covered Florida during the Pleistocene Epoch.
Why are silicate minerals important in geology? Which silicates might one expect to find in granite? Which silicated occur in sedimentary rocks?
Silicate minerals comprise over 90 percent of Earth's crust. As a result, they are called the rock-forming minerals. Granite is comprised of potassium feldspar, quartz, and muscovite mica, all of which are silicate minerals. The common silicates in sedimentary rocks are quartz, mica, and clay.
Roderick Impey Murchison was instrumental in naming three of the Paleozoic periods. Which ones were named by him?
Silurian, Permian and Devonian.
List the foliated metamorphic rocks in order of increasingly coarser foliation.
Slate, phyllite, schist, and gneiss.
Indicate the role of fossils in establishing the age equivalence of sedimentary strata.
Some species existed for only a few million years and are diagnostic of a particular slice of Earth's history. If these short-ranging species are also abundant, geographically widespread, and environmentally robust, they are given the status of index fossil, those fossils that are most useful in determining time equivalence of sedimentary layers in geographically separated areas.
Discuss the principles that Steno, Lyell, and Smith formulated for the development of the geologic time scale.
Steno established superposition of strata, original horizontality, and lateral continuity. Lyell popularized uniformitarianism by showing how it applied to the real world. He did this in his famous book Principles of Geology , the founding document of the geological sciences.William Smith demonstrated equivalency of strata by noting consistencies in their stratigraphic position relative to overlying and underlying layers, and by the unique assemblage of fossils they bore. He is best remembered for recognizing that strata were often characterized by particular fossils and that there was a general progression toward more modern-looking fossils in successively younger strata (faunal succession).
What species is most useful in demonstrating time equivalence between the three sections?
Streptognathodus isolatus.
5. Understand the concept of lithostratigraphy (subdivision of the rock record into formations, members, and so on).
The basic unit of lithostratigraphy is the formation, a layer or rock body distinguished from overlying and underlying units on the basis of rock type (e.g., sandstone vs. limestone). Formations are named after geographic localities where they are well exposed. If the vertical succession is divided on the basis of age rather than rock type, the units are chronostratigraphic. Such units form during a specific interval of geological time. For example, all rocks formed during the Ordovician Period (505-441 million years ago) constitute a time-stratigraphic (chronostratigraphic) unit called the Ordovician System.
Understand the nature and importance of silicate minerals (the most abundant of the common rock-forming minerals).
The bulk of the earth's crust is comprised of a dozen or so rock-forming minerals. Chief among these minerals is a group of related minerals known as the silicates. All silicates share a common building block, the silicon-oxygen tetrahedron. This is a four-sided pyramid comprised of four oxygen atoms (located at the corners of the pyramid) surrounding a single silicon atom. /// In addition to the silicates, a second family of common rock-forming minerals is the carbonates. The basic building block of these minerals is a ring of three oxygen atoms with a carbon atom in the center. These structures are glued together most commonly with calcium atoms (calcite and aragonite), or an even mixture of calcium and magnesium (dolomite). Calcite is the most common of these three carbonate minerals and the dominant constituent of limestones.
What is meant by uniformitarianism?-Cite an example of a process occurring on the Earth today that did not occur in the geologic past.
The essence of uniformitarianism is embodied in the phrase, "The present is the key to the past." In other words, we can apply our knowledge of modern geological and biological processes (and their products) to the rock and fossil record. Under uniformitarianism, we can assume that 400-million-year-old basalt flows were the product of volcanic eruptions just like those basalts forming on Hawaii today. Without uniformitarianism we have no intellectual basis for studying past events.
Discuss the completeness of the fossil record.
The fossil record is incomplete. Most individual organisms and a large percent of species that once resided on Earth have left no record of their existence
Principle of cross-cutting relationships
The general principle that a geologic feature that cuts across or penetrates another body of rock must be younger than the rock mass penetrated. The feature that is cut is older than the feature that crosses it. It applies not only to rock bodies but also to geologic structures such as faults and unconformities.
In a columnar section of sedimentary rocks, a limestone is overlain by a shale, which in turn is overlain by sandstone. What might this coarsening upward sequence indicate with regard to the advance or retreat of a shoreline?
The limestone represents deposition furthest from shore, the shale represents deposition closer to shore, and the sandstone represents deposition at the shoreline. The vertical succession reflects an upward transition from offshore limestone to nearshore sandstone; thus, the water was becoming increasingly shallow as the rock column was deposited. This would reflect the retreat of the shoreline towards the ocean (regression).
What conditions in the Bahama Banks carbonate platform result in the high production of calcium carbonate sediment?
The main condition required for the development of a Bahama-like carbonate platform is clear, warm, shallow seawater. Carbonate production is so prolific in the Bahamas because there are no rivers dumping clay and sand into the region. As a result, the waters are quite clear. The top of the carbonate platform is covered with nutrient-rich water that is no deeper than thirty or forty feet, well within the photic zone. Since it is located at low latitudes, the surface water is warm. The warm, clear water promotes production of marine plants and algae, which in turn support a prolific community of carbonate secreting invertebrates that, upon death, donate their shells to the growing layer of seafloor sediment.
1. What factors determine whether or not a particular fossil will be valuable as an indicator of the age and correlation of a stratum?
The most valuable index fossils (indicators of age) are those that had a short geological range (existed only a short time) and a widespread geographical distribution. If they are easily identified and abundant, they are even more valuable.
Outline the significance of color, texture, and sedimentary structures in determining the environment of deposition for any given sedimentary rock.
The principal features that you see when examining a sedimentary rock are color, texture, and composition. These features, particularly texture and composition, are the criteria used in classifying sedimentary rocks. Together with sedimentary structures (cross-bedding, graded bedding, layering, and so on), these features yield clues about the origin of any given sedimentary rock or rock layer. // Color is usually a reflection of sediment interacting with oxygen. If sediments are deposited where oxygen is abundant (usually the case in continental environments), the iron-bearing minerals are oxidized or rusted. The resulting red color is a tip-off that the rocks were deposited on land. Black rocks reflect the deposition of organic carbon or iron-bearing sediments in anoxic settings, such as deep marine basins or oxygen-starved estuaries and lakes. Shallow marine rocks are typically green, gray, tan, or white.
How is the texture of a sedimentary rock found?
The sedimentary rock's texture is determined by the size, sorting, and shape of the sedimentary particles that comprise the rock. Conventionally, geologists use the Wentworth Scale (see table 3-1, page 69 of your text) to determine sedimentary grain size. The Wentworth Scale ranges from boulders on the coarse end to clay on the fine end. Notice that sand has a specific meaning to geologists: sediment of any type that falls between 2 and 1/64 millimeters. Similarly clay is the technical term for sediment that is finer than 1/256 of a millimeter. Sedimentary particle size is a function of the energy of the sediment-transporting medium. As a general rule of thumb, the coarser the sediment, the higher the energy required to move it.
Discuss the three major depositional environments that exist on the earth now and that existed in the geological past.
The three main environments of deposition on Earth are marine, continental, and transitional. These are the main areas where sedimentary rocks are currently forming and are the settings where sedimentary rocks have accumulated throughout most of Earth's history. Each of these three main environments is subdivided into several subenvironments. For example, marine sedimentary rocks form around reefs, on the shallow marine shelf, or on the deep ocean floor. Continental sediments, those deposited above sea level and away from the sea's influence, might be deposited in a lake, stream, alluvial fan, or desert. Environments that transition between the sea and land include deltas, beaches, tidal flats, barrier islands, and lagoons
Explain the difference between the three structural (tectonic) elements of the North American continent (shield, platform, and orogenic belt).
The three principal tectonic elements of the North American continent are the Canadian Shield (flat area of exposed Precambrian igneous and metamorphic rocks), the platform (interior of continent where Precambrian crystalline rocks are covered with a thin veneer of layered sedimentary rocks), and orogenic belts (elongated mountainous regions parallel to the east and west coasts). Together, the Canadian Shield and platform constitute the craton, a relatively flat, low-lying area with little modern earthquake and volcanic activity. The other major continents also contain a shield, platform, and one or more orogenic belts.
If a lava with a mafic composition solidifies at the Earth's surface, like the lavas in Hawaii, what type of igneous rock will form?
basalt.
Indicate the major differences between clastic sedimentary rocks (sandstone, shale, conglomerate) and carbonate sedimentary rocks (limestone).
The two main families of sedimentary rocks are clastic and carbonate. Both types are important and abundant. They form, however, by different means. Clastic rocks (sandstones, siltstones, shales, and conglomerates) form when weathered material (quartz grains, felspar grains, mica flakes, rock fragments, and so forth) is brought from a sediment source area to a basin of deposition by streams, glaciers, or wind. Texture and sedimentary structures indicate conditions within the basin of deposition, while the clastic rock's composition reflects the nature of the sediment source area, which may be located hundreds of miles from the final resting place of the sediment. Consider that the Mississippi River delta receives sediment from areas as far away as the Rocky Mountains. While in transit, these sedimentary particles are rounded, sorted, and chemically altered. // Clastic rocks are classified by texture and composition. Classification begins with assessing particle size. If grains comprising a rock are larger than 2 millimeters in diameter, the rock is diagnosed as a conglomerate. If sedimentary particles fall between 1/16 and 2 millimeters, the rock is called a sandstone. Siltstone and shale are comprised of even smaller grains. Sandstones have been further subdivided based on the mineralogy of the constituent sedimentary grains. Sandstones dominated by quartz grains are simply called quartz sandstones. These sandstones are compositionally mature in the sense that they lack unstable mineral grains (mica, feldspar, and so forth) and are relatively well sorted. Since only durable quartz is present, these rocks suggest deposition only after a long period of sediment alteration and transport. Pinkish or reddish sandstones containing abundant feldspar (>25 percent) reflect deposition in close proximity to a granitic (feldspar rich) source region. Such sandstones are called arkoses. A third type of sandstone, known asgraywacke, is a poorly sorted sandstone, containing up to 30 percent clay material. Quartz is typically present, but so is a host of unstable silicate minerals such as mica, chlorite, feldspar, and volcanic rock fragments. // By contrast, limestone (the most important carbonate rock) is comprised of biologically produced carbonate grains (mainly calcite and aragonite) in the form of shells and carbonate muds that accumulate in clear, warm, shallow seawater (and to a much lesser degree in lakes). Unlike the grains in a sandstone, those comprising carbonate rocks are produced in the basin of deposition in close proximity to their final resting place by organic activity. Little if any transportation, with its concomitant sorting and rounding, takes place. Because the grains are both formed and buried in the same area, they are sensitive indicators of past environments.
What are the eight most abundant elements found in rocks and minerals?
They are, in order of decreasing abundance, oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium (table 2-1 in your text).
11. Using fossils for age correlation is dependent on a priori knowledge of their age ranges. How has this knowledge been obtained?
This knowledge has been obtained through carefully observing fossil occurrences in rock layers during the last 200 years. For example, dinosaur bones have been found in Mesozioc rocks, but to date, no dinosaurs have been found in Paleozoic rocks. Similarly conodonts have been found in late-Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, and Triassic strata. They have not been found in Jurassic or younger formations, in spite of efforts to find them there.
Hornblende
This rock type is a glassy, black or very dark green mineral. It's the most common member of a family of amphiboles, and it is designated a ferromagnesian or mafic mineral. It is usually long and narrow.
Consider the skeletal elements of the forelimbs of birds, bats, whales, horses, and humans (figure 4-20 on page 124 of your text). This list includes representatives of two classes (Aves and Mammalia) and comprises organisms that fly, swim, run, and walk. Which of the following statements is true?
Whales and humans possess the same complement of limb bones (with exception of the metacarpals), but they have taken on different shapes that fit their respective uses.
Which statement below correctly portrays the most important contribution of the fossil record to our understanding of evolution?
While modern genetics demonstrates how the process of evolution occurs, the fossil record illustrates the patterns of these changes through time.
Who's idea was faunal succession?
William Smith.
What features in a sedimentary rock might indicate it was developed in each of the following environments of deposition?- D. Continental, desert environment
Wind is the dominant means of sediment transport in a desert. Desert sediments are readily distinguished by the high degree of sorting. Coarse sand and gravel cannot be moved, and silt and clay are blown into the atmosphere, leaving behind the fine - to medium-sized quartz particles. These grains are bounced along the ground through a process known as saltation. As the grains bounce, the corners are knocked off, leaving the grains rounded. The surface is scratched and pitted giving a frosted appearance under the microscope. Wind shapes the sand into large dunes with internal cross-beds that might be tens of feet high. Hence, sedimentary rocks deposited under desert conditions will be well-rounded, quartzose, well-sorted, light colored (tan to reddish-tan), and crossbedded.
Examine the fossil occurrences. Is it now possible to correlate the Red Eagle Limestone with the other sections?
YES. The fossils make it possible to approximate time equivalence between sections.
Which of the following is classified as a transitional depositional environment (transitional between land and ocean)?
a Beach.
The ocean transgressed from west to east across a flat surface of eroded Precambrian granites and metamorphic rocks. As the shoreline moved eastward, a veneer of shoreline sands (Tapeats Sandstone) was laid down on top of this surface. The planar boundary between the Precambrian crystalline rocks and the tapeats is thus classified as
a nonconformity.
The sedimentary particles comprising the rockwere most likely eroded from
a source area where granite was exposed at the surface.
Define historical geology and explain why it is an eclectic science.
a.) Historical geology addresses the Earth's origin, evolution, changes in the distribution of lands and seas, growth and destruction of mountains, succession of animals and plants throughout time, and developmental history of the solar system. B.) Because geology incorporates the information of so many other scientific disciplines, it is considered an eclectic science, which means a body of selected information drawn from a variety of sources.
2. Fossil A occurs in rocks of Cambrian and Ordovician age. Fossil B occurs in rocks that range in age from early Ordovician through Permian. Fossil C is found in Mississippian through Permian strata. What is the maximum possible range of age for a stratum containing only fossil B? What is the maximum possible range of age for a stratum containing both A and B? Which is the better guide fossil, A or C?
a.Silurian and Devonian, Ordovician, This is difficult to evaluate given the scanty data. A would be a better guide fossil than C for Cambrian and Ordovician rocks and vice versa.
Approximately what percentage of the map area would have been above sea level during the last glacial period, when sea level was 200 feet lower than it is today?
about 90 percent
When the nucleus of an unstable radioactive atom fires off a positively charged particle comprised of two protons and two neutrons (a helium nucleus) it has undergone
alpha decay.
Augite
an important member of the pyroxene family; it is a ferromagnesian mineral also, and is dark colored and stumpy in shape.
At what rate (miles per year) would the ocean encroach from south to north across Florida (from point A to point B) if sea level continued to rise at a rate of 0.04 feet (0.5 inches) per year. Assume that the land surface slopes southward from point B at a rate of 0.06 feet per mile. In other words, for every mile that you travel southward, you lose 0.06 feet in elevation. Or, for every mile that you travel northward, you gain 0.06 feet in elevation.
approximately 0.66 miles per year.
How long would it take to completely flood the portion of Florida shown on the map if sea level continued to rise at a rate of 0.04 feet (0.5 inches) per year?
approximately 1900 years
A sedimentary rock comprised of well-sorted, sand-sized grains of feldspar (30 percent), quartz (65 percent), mica (3 percent), and chert (2 percent)
arkose.
Understand the essential difference between the two major families of sedimentary rocks: clastic and carbonate.
clastics = clasts of pieces of rock that range from microscopic particles to huge boulders. These include conglomerates, sandstones and shales. Carbonates are biogenic, from organisms that live in the ocean who secrete carbonate. Dolomites or limestones are carbonate.. reefs, which are built from organisms. Carbonates fracture more easily than clastics and have pores in them. Clastics= the small space between pieces of sand. Think: Calcite, aragonite, and limestone.
Sedimentary rocks are composed of consolidated sedimentary particles through a process known as lithification. Which of the following processes are most important in converting loose sediment into solid rock?
compaction and cementation.
The arkose rock is
compositionally immature but texturally mature.
Clastic sedimentary rocks comprised of sedimentary particles that are larger than 2 mm in diameter are classified as
conglomerate.
Which two groups are useful index fossils throughout essentially all of their geological range?
conodonts and ammonoids.
Which fossil group has the more cosmopolitan (widespread) geographic distribution at the species level?
conodonts.
When _________ occurs, two or more unrelated lineages acquire similar morphological characteristics through time.
convergent evolution.
Geologists recognize three major types of plate boundaries defined by the relative plate motion at these plate interfaces. These are
convergent, divergent, and transform fault.
The principle of relative dating which indicates that faulting (fault B) occurred after the mass of granite (D) had been emplaced is
cross-cutting relationships.
As a consequence of the previous question, which of the following depositional environments is poorly represented in the modern world?
epieric sea
The most abundant mineral in the Earth's crust is
feldspar.
Recrystallization (types of fossil preservation)
fossilization process wherein the original crystals comprising a shell have been enlarged while retaining their original mineralogy (transition from small calcite crystals to larger calcite crystals); this process often results in obliterating the original internal structure of a shell (such as layering)
Principle of original horizontality
most strata are tilted today; but this principle reasons that most sedimentary particles settle from fluids under the influence of gravity. The sediment must have then been deposited in layers that were nearly horizontal and parallel to the surface on which they were accumulating. Hence, steeply inclined strata indicate an episode of crustal disturbance after the time of deposition.
Minerals are recognized on the basis of physical properties such as color, crystal form, cleavage, and hardness. If you find a crystal that has a hardness of 2-3, perfect cleavage in one direction (so as to form transparent sheets) and a specific gravity of 2.8 to 3.0, which of the following minerals have you found?
muscovite.
The fourth limestone from the top of the Kansas section is named the Red Eagle limestone. Is it possible to find the time-equivalent rock layers in the Usolka River and Aidaralash Creek sections by simply looking at rock types or stratigraphic thicknesses? In other words, based on rock type alone, is it possible to find the rock layers at Usolka and Aidaralash that were deposited at exactly the same time as the Red Eagle limestone was being deposited in Kansas?
no.
Imagine finding a large brachiopod comprised of fool's gold (pyrite). Since brachiopods make their shells out of calcite, it is obvious that this shell has undergone some kind of change during the fossilization process. The specific alteration process displayed by this brachiopod is
replacement.
Which of the following parent-daughter nuclides has the longest half-life?
rubidium 87:strontium 87.
Feldspar is the most abundant mineral in the Earth's crust. During the weathering process, feldspar is altered to sedimentary clay. As a result, the most abundant sedimentary rock on Earth is
shale.
Which family of minerals comprises nearly 92 percent of the Earth's crust?
silicates.
The most abundant elements in rocks of the Earth's crust are
silicon and oxygen.
Igneous rocks come in two main varieties, intrusive (where magmas cool slowly deep in the crust) and extrusive (where lavas cool quickly at the Earth's surface). What physical characteristic of a rock specimen can be used most readily to distinguish whether it is an intrusive or extrusive igneous rock?
size of crystals.
Clastic sedimentary rocks are classified on the basis of texture. Texture is defined as the _______ and shape of the sedimentary particles.
size.
Of the following foliated metamorphic rocks, ____________ reflects the least intense grade of metamorphism?
slate.
A(n) __________ is a group of organisms that look alike and are able to interbreed. This entity constitutes the basic unit of biological classification.
species.
Principle of superposition of strata
states that in any sequence of undisturbed strata, the oldest layer is at the bottom, and successively higher layers are successively younger.
Shale layer C is older than limestone layer E. This can be determined by applying the concept of:
superposition.
Absolute dating
the actual age, expressed in years, of a geologic material or event.
A half-life is defined as
the amount of time it takes for half of the original parent atoms to decay to more stable daughter products.
The atomic number of an atom is determined by adding up
the number of protons in the nucleus.
Relative dating
the placing of an event in a time sequence without regard to absolute age in years.
Uniformitarianism
the scientific pillar (or operational assumption) upon which the study of Earth history rests. This concept, which states that the laws of nature do not change through time, was authored by James Hutton and later popularized by Charles Lyell. Hutton, a Christian, saw God's handiwork in the creative process, but could not see the process completed in a paltry six thousand years.
Feldspar
these are the most abundant constituents of rocks, comprising about 60% of the total weight of the Earth's crust. There are 2 types of feldspars, the Orthoclase (potassium) group and the plagioclase group. They are both a 6-6.5 hardness and they cleave well in both directions. Orthoclase is pink or white, while plagioclase is white or gray.
You are on a field trip to the southwestern United States. The first stop is high in the Inyo Mountains of southern California. Along each side of the dusty Cerro Gordo road, you examine a thick succession of black shales and black limestones of Pennsylvanian and Permian age assigned to the Keeler Canyon Formation. Individual limestone beds are 1-2 meters thick, and each one grades from coarse (3-8 millimeters) abraded and broken fossil particles at the bottom to mud-size carbonate material at the top (i.e., they display graded bedding). These rocks are deposited by?
tidal currents
Which of the following fossil groups would not be present in Triassic rocks?
trilobites.
Metamorphism adjacent to a mass of molten magma constitutes contact metamorphism.
true.
Understand the general process by which the geological eras and periods were determined and named
units were named as they were discovered and studied. Sometimes they were named or borrowed by the geologist who discovered it; sometimes they were named by a certain rock from that age.
What is the youngest (most recent) event on this diagram?
venting of basaltic lava from the volcanic throat (J)???
Wisdom teeth in humans, the appendix in humans, and the pelvis in whales (figure 4-21) are considered
vestigial structures.
