Geology2

63. Historical origins of geology: uniformitarianism versus catastrophism, early figures in the history of geology Historical geology examines the origin and evolution of Earth, its continents, oceans, atmosphere, and life. **Charles Darwin** proposed //the theory of organic evolution//, the evidence for which he cited as the way organisms are classified, embryology, comparative anatomy, and to some degree the fossil record. The concept of the theory of organic evolution is that all living organisms are related and have evolved from organisms that existed in the past. This is probably best supported by the evidence of fossils which allows us to interpret physical events and conditions in the geologic past. Geologic time scale subdivides geologic time into a hierarchy of time intervals. Six fundamental geological principles used in relative dating are //superposition//, //original horizontality//, //lateral continuity//, //cross – cutting relationships//, //inclusions//, and //fossil succession.// **Nicolas Steno** established the //principle of superposition// in which the layer at the bottom of the deposit is the oldest layer and the last or top layer of the deposit is the youngest layer. He also established the //principle of original horizontality// and //principle of later continuity//. The discovery of radioactivity in 1895 and development of radiometric dating techniques allowed scientists to assign absolute ages to the subdivisions of the geologic time scale. Based upon the concept that current processes have operated throughout geologic time is //the principle of uniformitarianism.// Uniformitarianism allows us to use present day processes as the stepping stone for interpreting the past and predicting potential future events. Uniformitarianism means that though variation of rates and intensities of geologic processes has prevailed, the physical and chemical laws of nature have remained constant. Early Christian theologians developed the idea that time is linear and that Earth is very young. **Archbishop Ussher** determined the Age of Earth to be about 6000 years old based upon his interpretation of scriptures. **James Hutton** believed that present day processes occurring over time could explain all of Earth’s geologic features. He thought that Earth’s history was cyclical and that Earth was very old. His observations were key to the principle of uniformitarianism. He also established //the principle of cross-cutting relationships.// Uniformitarianism, as interpreted by **Charles Lyell**, became the guiding principle of geology. It provides a better observation for observed geologic phenomena than either //neptunism// or catastrophism. The concept of neptunism was proposed by **Abraham Gottleb Werner**. He was an excellent mineralogist and convincing lecturer who popularized neptunism which included the worldwide ocean corresponding well to the biblical deluge. His inability to explain where all the waters of the worldwide ocean went and incorrect analysis of the origin of igneous rocks, particularly basalt, dispelled the principle of neptunism. **Baron Georges Cuvier** explained that the physical and biological history of the Earth resulted from a series of catastrophic events. Each catastrophe explained significant and rapid changes in Earth, including abrupt creation or importation of new species into an area. His six major catastrophes corresponded to the six days of Earth’s biblical creation, which although popular among theologians, could not be supported by field evidence. Along with the assumption formulated by **Lord Kelvin** that the Earth was originally molten,(he was not aware that Earth has an internal heat source – radioactivity – allowing it to maintain a relatively constant temperature throughout geologic time) neptunism and catastrophism were dispelled by the physical evidence of Hutton and Lyell’s uniformitarianism. The discovery by **Pierre and Marie Curie** of the heat produced during the process of //radioactive decay// disproved Kelvin’s concept of //Earth’s internal heat// as derived from residual cooling of a molten state and gave a dating tool for scientists to place dates upon the time periods established by Lyell and Hutton. Wicander/Monroe: Historical Geology pgs. 13-83 PB

Looks good. The modern view: the principles and laws are the same as they were just the intensity and rate varies. EEC.

64. Fossils: index fossils, Principle of Fossil Succession, interpretation of stratigraphic column through fossil inclusion, preservation types, properties of the fossil record //The fossil record is made up of the physical remains (body fossils) of organisms or traces of organisms (trace fossils) throughout much of Earth's history. Fossils are found in sedimentary rock layers all over the world, and give clues to the past climate of the place in which they are found, in addition to the age of the rock in which they are found.//

//Fossilization is a relatively rare event, as it requires very specific conditions. For the body of an organism to be preserved, it needs: 1) not to be eaten, 2) not to be scavenged/scattered, 3) not to be decomposed quickly by bacterial/fungal action, and 4) quick and total burial, dessication, freezing or entrapment in tar or amber. Some methods by which "body fossils" are preserved are:// //1. Freezing (ex- Wooly Mammoths)*// //2. Entrapment (ex- La Brea tar pits; insects in amber)*// //3. mummification*// //4. Molds and Casts- A mold is a 3-d impression that can form when a buried organism decays and leave behind a cavity. That cavity later// //fills with sediment, and the new "copy" of the body is a cast.// //5. Replacement: Water moves into organic material and biological parts are replaced by mineral crystals like silica or pyrite. (ex- ammonite// //shells)// //6. Recrystallization: Shape/chemical composition of crystals within a biological material changes into new crystals.// //7. Permineralization: Water moves into spaces in organic material and crystals are added into those spaces. (ex- "petrified" wood, dinosaur// //bones)// //8. Carbonization: thin carbon film left as organism decays and decay products leach into sediments under pressure- black silhouette of// //organism (ex- fish, leaves)// //*In these processes, whole bodies, including soft tissues, are preserved without alteration.//

//Trace fossils are any traces of organisms' activities preserved in the rock record, including tracks, burrows, footprints, coprolites (preserved feces), etc.//

//Fossils are important not only in terms of understanding the evolutionary history of life on Earth, but also in sequencing rock strata by relative age. This is accomplished through the use of index fossils and fossil inclusion. An index (or guide) fossil is one which represents a species that occupied a relatively small geologic time range but was geographically widespread. It must also be easily recognizable and abundant. An assemblage of index fossils can be studied to see where their time ranges overlap, allowing the geologist to determine relative ages of the strata in which the fossils are found. A sedimentary rock is about the same age (but at least a little younger) than the organism whose remains are fossilized within it. For these reasons, most index fossils are shelled marine organisms. These are more likely than terrestrial species to be buried in layers of sediment in oxygen-poor environments that favor preservation. They are also more widespread, since epeiric seas commonly covered most continental areas, while terrestrial species are frequently isolated by wide bodies of water.//

//Due to the nature of preservation processes, the fossil record "favors" shelled marine organisms. Because of this, the fossil record is particularly sketchy prior to the evolution of shells and other hard parts. Therefore, remains of earlier organisms are most certainly missing from the record.//

//The earliest microfossils to date are of members of the archae (prokaryotic cells) found in rock (chert) from Western Australia that dates back around 3.5 billion years. Other early life forms found as fossils are products of the cyanobacteria, which form mounds called stromatolites. These mounds are preserved in precambrian strata. Soft-bodied, multicellular organisms are not well-represented beyond a few notable exceptions, one of which is the Burgess Shale fossil group.// Looks good! EM 65. Relative Age Dating: Transgression and regression sequences and their properties, types of unconformities and identification in the field
 * SMH (most material from Geo 2 notes- preservation methods from Exercise 8 of __Deciphering Earth History- //Exercises in Historical Geology,//__ //fourth ed.)//**
 * Age Dating**


 * __ Transgressive sequence __**** - (fining upward) shoreline migrates landward, offshore facies deposited on top of nearshore facies over vast geographic area. **
 * __ Regressive sequence __**** - (coarsening upward) opposite transgressive sequence **


 * Causes: seafloor spreading, addition or removal of water from oceans during glacial episodes **


 * Unconformities **
 * **__ Disconformity __**** – surface of erosion or nondeposition between younger and older sedimentary rocks which are parallel to one another; can be difficult to recognize without fossil assemblages **
 * **__ angular unconformity __**** - angled rock strata below horizontally deposited rock **
 * **__ nonconformity __**** - sedimentary rock deposited over an erosional surface of metamorphic or igneous rock **


 * MarkW**
 * You might also want to look at the information on the law of Superposition, Original Horizontality, Cross cutting relationships. -EM**

66. Use of 6 principles to interpret cross sections
 * These six principles of relative dating can be applied to a cross-section to determine the sequence of events that occurred, but not how long ago they occurred.**
 * 1. Principle of superposition (Steno) – oldest layer is on the bottom and youngest on the top in an undisturbed section of sedimentary rock**
 * 2. Principle of original horizontality (Steno) – sediments are deposited horizontally due to gravity; if layers are not horizontal, then force(s) acted on them since deposition and lithification**
 * 3. Principle of lateral continuity (Steno) – sediments extend laterally in all directions until they either thin and pinch out, or terminate against the edge of a depositional basin**
 * 4. Principle of cross-cutting relationships (Hutton) – an igneous intrusion or fault must be younger than the rocks it cuts through**
 * 5. Principle of inclusions – inclusions (fragments) of one rock contained within a layer of another are older than the rock layer itself.**
 * 6. Principle of fossil succession - fossil assemblages succeed one another through time in a regular and predictable order; based on these 3 points: life has varied through time, assemblages are recognizably different, and relative ages of assemblages can be determined.**
 * DS**
 * Looks good.**
 * JL**
 * ditto, LK**

67. Interpretation of geologic maps
 * []** This website tutorial has a lot of maps and information on interpretation. I am not totally sure what this question needs, but here goes. On page 212, Chapter 5 (Geologic Map Interpretation) of the Historical Geology Interpretations and Applications Lab Manual, Poort/Carlson, discusses geologic map interpretation followed by a listing of map symbols and map activities. PB

68. Absolute Age dating: limitations of the method, calculation of rock ages with parent/daughter isotope ratios Radioactive dating is the process in which an unstable atomic nucleus is spontaneously transformed into an atomic nucleus of a different element. There are three types of radioactive decay resulting in a change of atomic structure. In alpha decay there are two protons and neutrons emitted from the nucleus, which results in the loss of two atomic numbers and four atomic mass numbers. In beta decay, a fast moving electron is emitted from a neutron in the nucleus, changing that neutron into a proton and changing the atomic number by one, but not changing the atomic mass. Electron decay capture results when a proton captures an electron from an electron shell and converts it to a neutron. This causes it to lose one atomic number, but no change to the atomic mass. Some elements undergo one decay step, whereas some undergo several. These decay rates are called half lives. This is the time it takes for one half of the atoms of the original unstable parent element to decay to atoms of a new, stable daughter element. The half life of a given radioactive element is constant and can be measured accurately. Radioactive decay happens at a geometric rate instead of a linear one, producing a J curve as opposed to a straight curve when graphing the resulting data. When the first half live occurs, the element will divide into equal amounts of atoms for both parent and daughter. After two half lives, the parent divides in half again and those atoms transfer to the daughter. This continues until the remaining parent atoms are so few that they cannot be accurately measured. The most accurate radiometric dates can be obtained from igneous rocks. A mineral crystallizing in a cooling magma wil have radioactive parent atoms and no stable daughter atoms. So the time measured is the time of crystallization of the mineral containing the radioactive toms and not the time at which the radioactive atoms formed. Aside from unusual circumstances, sedimentary rocks cannot be radiometrically dated because the age of a particular mineral would be dated and not the time that it was deposited as a sedimentary particle. Glauconite is the exception as it contains radioactive potassium 40 which decays to argon 40. It forms in some marine environments as a result of chemical reactions with clay minerals as it is converting from sediments to sedimentary rock. This indicates that the glauconite forms when the sedimentary rock forms, giving a radiometric date to the sedimentary rock’s origin. For accuracy, geologists have to make sure they are working with a closed system in which no parent or daughter atoms have been added or removed and that the ratio between them results only from radioactive decay. The closed system is compromised if the rock is heated or subjected to intense heat and pressure in metamorphism. Leakage from the system would result in an inaccurate age determination. Because of this metamorphic rocks are difficult to date accurately. If the minerals in the closed system agree closely, they are said to be concordant. It they do not agree, they are said to be discordant. The measurement error for many radiometric dates is typically less than 0.5% of the age and sometimes is even better than 0.1%. Wicander/Monroe: Historical Geology, pgs. 72-75 PB 69. Organic evolution, Darwin versus Lamarck, natural selection //I would add/stress the idea that the environment exerts selective pressures, which change as the environment changes- those best suited to those pressures survive and reproduce.//
 * Evolution**
 * Organic evolution states that all living organisms are related and have descended with modifications from organisms that lived in the past. (Historical Geology. Wicander/Monroe. p. 13)**
 * Lamark proposed the theory of Inheritance of Acquired Characteristics, whereby physical traits acquired during an individual’s lifetime are inheritable. By contrast, Darwin (along with Alfred Wallace) proposed the theory of Natural Selection, whereby favorable variations in an individual are more likely to survive and be passed on to an organism’s progeny. Another way of looking at it is that Lamark proposed that individuals evolve and Darwin (and Wallace) proposed that populations evolve. (Same reference as above, p. 133-135)**
 * The key points to Natural Selection are: 1) organisms possess heritable traits, 2) some variants in these traits can give an advantage and 3) organisms with favorable traits are more likely to survive and pass those traits to their offspring. (Same reference as above, p. 135)**
 * JL**
 * SMH**

70. Plate Tectonics: plate boundaries, manifestations and characteristics of each boundary type, identification of old boundaries, rates of plate motion, relative motion rates for Archean Eon versus later tectonics; Wilson Cycle and various supercontinents in Earth history


 * __ Types of plate boundaries with associated landforms: __**
 * **__ Divergent __**** - continent/continent (creates rift valley); ocean/ocean (creates mid-ocean ridge with pillow lavas/basalt); no continent/ocean. **
 * **__ Convergent __**** - continent/continent (mountains with minor volcanism), ocean/ocean (trenches and volcanic island arcs), continent/ocean (trenches and volcanic mountain chain) **
 * **__ Transform __**** - slide past each other horizontally (fault valley) **


 * Ancient Evidence for divergence and convergence: **
 * **__ Divergence/Rifting- __**** causes faults, dikes, sills, lava flows and thick sedimentary sequences; also causes ocean formation= divergent separation, faulting with rising magma, linear sea, mid-ocean ridge (mature) **
 * **__ Convergence __**** - presence of ophiolites (during subduction pieces of oceanic crust are accreted onto the edge of the continental crust) **


 * __ Wilson Cycle __**** - the relationship between mountain building and the opening and closing of ocean basins. Involves rifting of a continent, opening an ocean basin with passive margins and then subduction occurs ending with a continent/continent collision. (Ex. ancient ocean closed to form Appalachians then reopened to form Atlantic Ocean) **


 * __ Archean Eon and Continent Formation __**** - 1st crust ultramafic. More residual heat from earth’s formation and more radiogenic heat caused plates to move faster and magma generated more rapidly. As a result continents grew more quickly along their margins (//continental accretion//). More upwelling in mantle caused many ocean/ocean subduction zones forming first andesitic island arcs. Partial melting of andesite yields granitic magma (beginning of //granitic// continental crust!). Those island arcs collide with others thereby creating the nucleus of a continent. This process repeats creating cratons (shield + platform). **


 * __ Supercontinents __**
 * ** Laurentia (2 b.y.a) **
 * ** Rodinia (1 b.y.a.) **
 * ** Pannitia (650 m.y.a) **
 * ** Pangaea (300 m.y.a.) **


 * Gondwana?

(**Historical Geology p.167-186 and notes) MarkW**


 * I will propose 3 supercontinents: Rodinia, Pannotia and Pangaea. I think Laurentia involved only North America, Greenland and northwest Scotland. Gondwana was the result of rifting between Laurasia and itself during the breakup of Pangea. "Supercontinents" are composed of all or most of Earth's landmasses (pg. 180, Historical Geology). Let me know what you guys think and please correct me if I am wrong.**
 * -PM**
 * I would agree with you. Just the 3 supercontinents. The other two did not involve all of Earth's major landmasses.**
 * DS**

71. Main “themes” of plate tectonics during various eras 72. Main areas of orogenic activity in North America during various eras . Main areas of orogenic activity in North America during various eras. Wicander/Monroe: Historical Geology, pgs pgs 59, 212, 335, 346, 430, 431, 433, 434, 436 [] [] [] An orogeny is an episode of intense rock deformation or mountain building. Orogenies are the consequence of compressive forces related to plate movement. Usually, orogenies take place along oceanic-continental plate boundaries or continental-continental plate boundaries. The Appalachian Mobile Belt was where the first Phanerozoic orogeny began during the Middle Ordovician. The mountain building during the Paleozoic Era had a distinct influence on the climate and sedimentary history of the craton. Beginning with the subduction of the Iapetus plate beneath Laurentia which is an oceanic-continental convergent plate boundary, the Appalachian mobile belt was created. The resulting //Taconic// orogeny was the first of many orogenies to affect the Appalachian region. The **Grenville** orogeny occurred during the Neoproterozoic producing deformation and mountain building in the area of the Appalachian Mountains. The area was deformed again during the //Taconic// and //Acadian// orogenies and in the late Paleozoic with the closure of the Iapetus Ocean resulting in the **Hercynian-Alleghenian** orogeny. The North American part of this orogeny – **Alleghenian** – was a period of mountain building in the Appalachian mobile belt from New York to Alabama which resulted from the collision of Baltica with Laurentia during the Pennsylvanian to the Permian. The **Taconic** orogeny occurred during the Ordovician. It was a mountain building episode which caused deformation of the Appalachian mobile belt. The **Acadian** orogeny was a mountain building period in the Appalachian mobile belt during the Devonian. It was the result of the collision of Baltica with Laurentia. The **Antler** orogeny took place from the late Devonian to the Mississippian. It involved mountain building affecting the Cordilleran mobile belt from Nevada to Alberta, Canada. The **Cordilleran** orogeny divided into three phases known as the **Nevadan,** **Sevier,** and **Laramide** orogenies. It was a time of deformation that affected western North America occurring from the Jurassic into the Early Cenozoic time. **Nevadan** orogeny most strongly affected the western part of the Cordilleran belt. It took place in Late Jurassic to Cretaceous. The //Nevadan// orogeny was the first of three major mountain building episodes to transform Western North America between the Late Mesozoic and Early Cenozoic Eras, the latter two being the //Sevier// and //Laramide// orogeny, chronologically. **Sevier** orogeny was the Cretaceous phase of the //Cordilleran// orogeny affecting the continental shelf and slope of the Cordilleran mobile belt. The //Sevier// meets the //Laramide// orogenic belt on its eastern side. The //Sevier// fold and thrust belt was active between late Jurassic through Eocene time. The **Laramide orogeny** was the late Cretaceous to Early Paleogene segment of the //Cordilleran// orogeny and was responsible for many of the structural features we see in the Rocky Mountains. **Ouachita** orogeny was a mountain building period in the Ouachita mobile belt during the Pennsylvanian period. **Sonoma** orogeny was caused by the collision of an island arc with the SW margin of North America during the Permian-Triassic periods. **PB** 73. Precambrian 74. Development of shelled organisms, possible reason(s) and benefits Shelled organisms developed in the late Proterozoic-early Cambrian. The exact biological and environmental factors that lead to their development at this time are unknown; it might have been in response to a rise in predators. Having a shell provides UV protection, prevents desiccation, allows an increase in size, provides attachment points for muscles and provides protection from predators. (Historical Geology. Wicander & Monroe. p. 242) JL
 * Wicander/Monroe: Historical Geology, pgs 2, 15, 259, 282-291, 339, 378**
 * The interrelated themes of Historical Geology are plate tectonics, organic evolution and long periods of time also known as deep time. The main theme of plate tectonics during the Paleozoic was the coming together of the Earth’s crust to form a supercontinent. Earth’s outermost part is made up of a series of moving tectonic plates whose interactions have impacted Earth’s biological and physical history. During the Mesozoic Era the supercontinent rifted into individual continents by tectonic plate movement. During the Cenozoic Era the continental movement slowed and moved to the current positions. The central theme of the theory of organic evolution is that all living organisms are related and evolved (descended with modifications) from organisms that existed in the past. During the Permian Period, at the end of the Paleozoic Era most animals became extinct. During the Mesozoic Era mammals emerged and the marine life flourished. In the Cenozoic, mammals continued to evolve and man emerged. The third theme is that physical and biological changes that occurred did so over long periods of time.** **PB**
 * Earth History**
 * Wicander/Monroe: Historical Geology, pgs 154, 155, 156, 173-195 PB**
 * When used in reference to time, Precambrian includes all geologic time from the origin of Earth at 4.6 billion years ago to the beginning of the Phanerozoic Eon 542 mya. It also includes all of the rocks that lay below the rocks of the Cambrian system. Precambrian encompasses the eons Archean and Proterozoic. Of the Archean there are the Eoarchean, Paleoarchean, and Neoarchean Eras. There are no periods defined for the Archean Eons. Within the Proterozoic Eon there are the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic Eras. Each of these eons is subdivided into 3 to 4 periods. As defined within the concept of continental foundations, a Precambrian shield is composed of an area or multiple areas of exposed ancient rocks which is found on all continents. Moving outward from the shields are broad platforms of buried Precambrian rocks that are under all continents. Together, a shield and a platform create a craton, which can be referred to as a continent’s ancient nucleus. The following is taken from the summary on pg 192. This outlines the Proterozoic geologic and biologic events.**
 * **The crust-forming processes that created Archean granite-gneiss complexes and greenstone belts continue into the Proterozoic but less than previously.**
 * **Paleoproterozoic collisions between Archean cratons formed larger cratons that functioned as nuclei, around which crust is accreted. One large landmass formed in this fashion was Laurentia, consisting mostly of North America and Greenland.**
 * **Paleoproterozoic amalgamation of cratons, followed by Mesoproterozoic igneous activity, the Grenville orogeny, and the Midcontinent rift, were important events in the evolution of Laurentia.**
 * **Ophiolite sequences marking convergent plate boundaries are first well documented from the Neoarchean and Paleoproterozoic, indicating the establishment of plate tectonic movement similar to what we experience now.**
 * **Sandstone-carbonate-shale-assemblages deposited on passive continental margins were very common by Proterozoic time.**
 * **The supercontinent Rodinia assembled between 1.3 and 1.0 bya, fragmented, and then reassembled to form Pannotia about 650mya, which began fragmenting 550mya.**
 * **Glaciers were widespread during both the Paleoproterozoic and Neoproterozoic.**
 * **Photosynthesis continued to release free oxygen into the atmosphere, becoming much more oxygen rich through the Proterozoic.**
 * **Fully 92% of Earth’s iron ore deposits in the form of banded iron formations were deposited between 2.5 and 2.0 bya.**
 * **Widespread continental red beds dating from 1.8 bya indicate that Earth’s atmosphere had enough free oxygen to oxidate iron compounds.**
 * **Most of the known Proterozoic organisms are single celled prokaryotes (bacteria). When eukaryotic cells first appeared is uncertain, but they were probably present by 1.2 bya. Endosymbiosis is a widely accepted theory for their origin.**
 * **The oldest known multicelled organisms are probably algae, some of which might date back to the Paleoproterozoic.**
 * **Well-documented multicelled animals are found in several Neoproterozoic localities. Animals were widespread at this time, but because all lacked durable skeletons, their fossils are not common.**
 * **Most of the world’s iron ore production is from Proterozoic banded iron formations. Other important resources include nickel and platinum.**

75. Biological trends in each geologic era; important evolutionary events in Earth history, influences of Earth’s geology on evolutionary trends and developments __Wicander/Monroe: Historical Geology, pages noted throughout the text of this response.__ Many events that began during the **Cenozoic** continue to the present, including the ongoing erosion of the Grand Canyon, continued uplift and erosion of the Himalayas in Asia and the Andes in South America, the origin and evolution of the San Andreas Fault, and the origin of the volcanoes that make up the Cascade Range. Moving tectonic plates affect the biosphere because the geographic locations of continents profoundly influence the atmosphere and hydrosphere. In the Cenozoic, spreading ridges such as the Mid-Atlantic Ridge and East Pacific Rise were established along which new ocean crust formed and continues to form. Another important plate tectonic event was the northward movement of the Indian plate and its eventual collision with Asia. Northward movement of the African plate caused the closure of the Tethys Sea and began the tectonic activity that currently takes place throughout an east west zone from the Mediterranean through northern India. Neogene rifting began in East Africa, the Red Sea, and the Gulf of Aden. Meanwhile, the North and South American plates continued their westerly movement as the Atlantic Ocean widened. Cenozoic orogenic activity took place largely in the Alpine-Himalayan orogenic belt and the circum Pacific orogenic belt. Formation of the Alps in Switzerland, Pyrenees between France and Spain, Apennines in Italy, and the Himalayas in India were forming as a result of movement in the Alpine-Himalayan orogenic belt. The Andes in South America continue to form due to plate convergence along the circum-Pacific orogenic belt. During the Cretaceous, Japan separated from mainland Asia, moving eastward over the Pacific plate forming oceanic crust in the Sea of Japan. A protracted episode of deformation known as the Cordilleran orogeny began during the Late Jurassic as the Nevadan, Sevier, and Laramide orogenies progress from west to east, The progression of faulting, uplifting, and volcanism yielded the Rocky Mountains, Cascade Mts., Sierra Nevadas, Grand Canyon, Rio Grande, and Appalachian Mts. on the North American continent. Pg 351 summary. Pg 398 summary Pg 170 summary Pg 192 summary The Cenozoic marine invertebrate community became more provincial due to changing ocean currents and latitudinal temperature gradients. Coccolithophores, diatoms, and Dinoflagellates recovered from their Late Cretaceous reduction to flourish during the Cenozoic. Diatoms were plentiful during the Miocene due to increased volcanism. Echinoids were plentiful during the Cenozoic. Changing climatic conditions caused the geographic distribution of some plants to change their structures in order to adapt. Paleocene rocks in the western interior of North America have ferns and palms, indicating a warm, subtropical climate. Seafloor sediments and geochemical evidence indicate that about 55mya an abrupt warming trend, the Paleocene-Eocene Thermal Maximum. Large scale oceanic circulation was disrupted diminishing heart transfer from equatorial regions to the poles. Oceanic water became warmer and many deep water foraminifera went extinct. Subtropical conditions persisted into the Eocene in North America. At the end of the Eocene a major climatic change plummeted mean annual temperatures as much as 7ºC over 3 million years. A general decrease in precipitation during the last 25 million years changed the midcontinental climate of North America to savannah conditions and then to steppe resulting in herbivore adaptations to their new diets. First ducks, penguins, owls evolved during the Paleogene. The age of mammals begins in the Cenozoic Era. By the Miocene and Pliocene time most mammals were quite similar to those in existence now. By the Paleocene primates were evident. Hoofed mammals, ungulates, were in the early Cenozoic. Horses, camels, elephants, and other mammals spread across the northern continents because land connections existed between those landmasses at different times. By the Oligocene, elephants were becoming larger and growing tusks. Ice Age mammals were large. A very important trend in the Pleistocene was the change of mammals and some birds towards giantism. Pleistocene deposits contain frozen mammals. Pleistocene Extinctions began about 14,000 years ago. In Australia, 15 of the 16 genera of large mammals died out. North America lost 33 of 45, and South America lost 46 of 58. Europe only lost 7 of 23 and south of the Sahara in Africa only 2 of the 44 went extinct. The questions of what cause the Pleistocene extinctions, why were mostly large mammals affected, and why the extinctions were most severe in Australia and the Americas are speculated with two hypotheses. One is the climatic change hypothesis, wherein the rapid climatic changes at the end of the Pleistocene killed them and the other is prehistoric overkill implying that human hunters were to blame. The animals had no previous experience with human hunters until about 11,000 years ago. Also the separation of Pangaea isolated Australia, so no migration could take place. The southern continents were mostly separate during the Cenozoic. Africa remained somewhat close to Eurasia and some faunal exchange took place, but most of the large mammals had already migrated to northern continents. South America was isolated until about 5 million years ago when a land bridge was established. The Isthmus of Panama allowed the exchange, but most of South America’s mammals came from the north, while only a small percentage of North America’s mammals crossed over from the south. Pgs 376-398 Pleistocene glaciers covered about 30% of the landmass, prominently on the Northern Hemisphere continents. The additional weight of the glacial ice on the continents caused the crust to sink lower into the mantle. It is thought that isostatic rebound is continuing in some areas to elevate the Earth’s crust back to its proglacial position. There were about 20 warm-cold cycles during the Pleistocene. Sea level fluctuated considerably. The glacial episodes were separated by tens or hundreds of millions of years resulting from moving tectonic plates and in turn affecting oceanic and atmospheric circulation patterns. The Milankovitch Theory indicates that minor changes in Earth’s rotation and orbit creates climatic changes that produce the glacial-interglacial intervals. Solar energy variation and volcanism are credited with short term climatic changes. Pgs 373-374 PB 76. Mass extinctions: major mass extinctions (Permian-Triassic, CretaceousPaleogene), possible causes, results and effects on the evolution of life forms There are several common themes associated with mass extinctions. First, mass extinctions typically affect both land and sea organisms. Secondly, tropical organisms – especially marine – appear to be more affected than those from the temperate and high-latitude regions. Thirdly, some groups of organisms experience multiple extinctions. Several extinctions took place during the **Cambrian**, affecting only marine life, especially trilobites. Three other marine extinctions took place during the Paleozoic Era; at the end of the **Ordovician** involving many vertebrates; one at the end of the **Devonian** affecting major barrier reef building organisms and primitive armored fish; and the largest one at the end of the **Permian** when about 90% of all marine invertebrate species and more than 65% of all land mammals became extinct. It is believed that an episode of deep sea anoxia and increased oceanic CO ₂ levels resulting in a highly stratified ocean in the late Permian. Very little if any circulation of oxygen rich waters reached the deep ocean. Also at this time stagnant waters covered the shelf regions, affecting the shallow marine fauna. This may be attributed to increased global warming during the late Permian. Widespread volcanism and continental fissure eruptions released additional carbon dioxide into the atmosphere which contributed to continued climatic instability and ecological collapse. The Mesozoic Era had several mass extinctions, the worst at the end of the **Cretaceous**, when almost all large animals including dinosaurs, flying reptiles, and seagoing animals like plesiosaurs and ichthyosaurs became extinct. This one is believed to have been caused by a meteorite impact. Several mass extinctions also took place during the Cenozoic Era. The most severe was near the end of the **Eocene Epoch** and is related to global cooling and climatic change. The most recent one occurred towards the end of the **Pleistocene Epoch.**
 * Archean Eon** consists of **Eoarchean, Paleoarchean, Mesoarchean, and Neoarchean Eras**. Rocks from the latter part of the Eoarchean indicate that crust existed then, but very little of it has been preserved. Archean greenstone belts are linear, syncline like bodies of rock found within much more extensive granite gneiss complexes. Ideally they have two lower units of igneous rocks and an upper sedimentary unit. It is believed that Archean plate tectonics happened, only at a much faster rate and with more igneous activity due to more radiogenic heat within Earth. Outgassing was responsible for the early atmosphere, but also contributor to the hydrosphere. The atmosphere that formed was high in carbon dioxide and water vapor. Early life models deem this oxygen deficient atmosphere relevant to the formation of organic molecules such as amino acids, linked together to form polymers including nucleic acids and proteins. RNA molecules may have been the first self replicating molecules. The only known Archean fossils are of single celled prokaryotic bacteria such as blue green algae; however chemical compounds in some Archean rocks indicate archaea. Stromatolites that formed from photosynthesizing bacteria are found in 3.5 by rocks. Archean mineral resources include gold, chrome, zinc, copper, and nickel. Pg. 172 Table 8.2
 * Proterozoic Eon** Consists of the **Paleoproterozoic Era**, **Mesoproterozoic Era**, and **Neoproterozoic Era**. The crust forming processes that gave Archean granite gneiss complexes and greenstone belts continued but at a much reduced rate. Paleoproterozoic collisions between Archean cratons formed larger cratons that served as nuclei, around which crust accreted. One large landmass forming in this manner was Laurentia, which was mostly North America and Greenland. Paleoproterozoic amalgamation of cratons, followed by Mesoproterozoic igneous activity, the Granville orogeny, and the Midcontinent rift, were important events in the evolution of Laurentia. Ophiolite sequences marking convergent plate boundaries well marked from the Neoarchean and Paleoproterozoic, proving tectonic movement similar to what we have now. Sandstone carbonate shale deposits on passive continental margins were common by Proterozoic time. The supercontinent Rodinia assembled between 1.3 and 1.0 bya, fragmented, and then reassembled to form Pannotia about 650mya, which began fragmenting about 550mya. Glaciers were widespread during both the Paleoproterozoic and the Neoproterozoic. Photosynthesis continued to release free oxygen into the atmosphere becoming richer through the Proterozoic. 92% of Earth’s iron ore deposits in the form of banded iron formations were deposited between 2.5 and 2.0 bya. Most of the world’s iron ore production comes from this. Other resources include nickel and platinum. Widespread continental red beds dating from 1.8 bya indicate enough free oxygen in the atmosphere for the oxidation of iron compounds. Most of the known Proterozoic organisms are single celled prokaryotes (bacteria). They were probably present by 1.2 bya. Endosymbiosis is the accepted theory for their origin. The oldest known multicelled organisms are probably algae dated back to the Paleoproterozoic. Multicelled animals are found in several areas of the Neoproterozoic, but lacked durable skeletons making their fossils uncommon to find. Pg. 195 Table 9.2
 * Early Paleozoic Era** consists of the **Cambrian, Ordovician, and Silurian periods**. Six major continents and many microcontinents and island arcs existed at the beginning of the Paleozoic Era, all of which were dispersed around the globe at low latitudes during the Cambrian. During the Ordovician and Silurian, Gondwana moved southward and began to cross the South Pole as indicated by Upper Ordovician tillite deposits. The microcontinent Avalonia separated from Gondwana during the Early Ordovician colliding with Baltica during the Late Ordovician-Early Silurian. Baltica with the newly attached Avalonia moved northwest relative to Laurentia and collided with it to form Laurasia during the Silurian. The first major marine transgression onto the craton of North America resulted in deposition of the Sauk sequence. The Tippecanoe Sequence began with deposition of extensive sandstone over the exposed and eroded Sauk landscape. During this time, extensive carbonate deposition took place. Large barrier reefs enclosed basins, resulting in evaporite deposition within these basins. During Tippecanoe time an oceanic continental convergent plate boundary formed, resulting in the Taconic orogeny, the first of three major orogenies to affect the Appalachian mobile belt. The newly formed Taconic highlands shed sediments into the western epeiric sea producing the Queenston Delta clastic wedge. Early Paleozoic age rocks contain a variety of minerals including building stone, limestone for cement, silica sand, hydrocarbons, evaporites, and iron ore. At the beginning of the Paleozoic Era, the sudden appearance of animals with skeletons is called the Cambrian Explosion, although it took place over millions of years during the Early Cambrian Period. During the Cambrian, the earliest vertebrates evolve – jawless fish. Many trilobites become extinct near the end of the Cambrian. During the Ordovician, major adaptive radiation of all invertebrate groups takes place. Middle Ordovician plants move to land. The end of the Ordovician finds extinction of many marine invertebrates. During the Silurian we have early land plants, seedless vascular plants. And the first jawed fish evolve. Pg 216 Table 10.1
 * Late Paleozoic Era** consists of **the Devonian, Carboniferous (subdivided into the Mississippian and Pennsylvanian), and Permian periods.** Laurasia and Gondwana underwent a series of collisions beginning in the Carboniferous. During the Permian, the formation of Pangaea was completed. Surrounding the supercontinent was the global ocean, Panthalassa. The Devonian period was a time of major reef building in western Canada, southern England, Belgium, Australia, and Russia. Widespread black shales were deposited over large areas of the craton during the Late Devonian and Early Mississippian, which was dominated mostly by carbonate deposition. Transgressions and regressions, probably caused by advancing and retreating Gondwanaland ice sheets, over the low lying North American craton, resulted in cyclothems and the formation of coals during the Pennsylvanian Period. Cratonic mountain building, specifically the ancestral Rockies occurred during the Pennsylvanian Period resulting in thick nonmarine detrital sediments and evaporites being deposited in the intervening basins. By the Early Permian, the Absaroka Sea occupied a narrow zone of the south central craton. Here several large reefs and evaporites developed. By the end of the Permian Period this epeiric sea had retreated from the craton. The Cordilleran Mobile Belt was the site of the Antler orogeny, a minor Devonian orogeny during which deepwater sediments were thrust eastward over shallow water sediments. During the Pennsylvanian and Early Permian, mountain building occurred in the Ouachita mobile belt. This tectonic activity was partly responsible for the cratonic uplift in the southwest, resulting in the ancestral Rockies. The Caledonian, Acadian, Hercynian, and Alleghenian orogenies were all part of the global tectonic activity that resulted from the assembly of Pangaea. During the Paleozoic Era, microplates and terranes like Avalonia, Iberia-Amorica, and Perunica played an important role in forming Pangaea. Late Paleozoic age rocks include minerals like petroleum, coal, evaporites, silica sand, lead, zinc, and metallic deposits. The Devonian experienced the following progressing from early Devonian to late: Early land plants – seedless vascular plants, all major groups of fish present (Age of Fish), Amphibians evolved, and the extinction of many reef building invertebrates. The Mississippian had the evolution of gymnosperms and reptiles. The Pennsylvanian had abundant coal swamps with seedless vascular plants and diverse and abundant amphibians. The Permian had abundant and diverse gymnosperms, many invertebrates went extinct. Many vertebrates go extinct and the largest mass extinction event to affect the invertebrates. Pg 237 Table 11.1 and Pg 259 Table 12.2 Pg 280 Table 13.3 Pg 302 Table 14.1
 * Cenozoic Era** is divided into the **Paleogene and Neogene and Quaternary Periods**. These periods are further subdivided into epochs. Chronologically, the **Paleogene has the Eocene and Oligocene epochs**. **The Neogene has the Miocene and Pliocene epochs.** The **Quaternary has the Pleistocene, the Holocene and current time** which is 2.588mya to present time.
 * Wicander/Monroe: Historical Geology, pgs 255-257 PB**

77. Sauk and sequence stratigraphy: cratonic sequences, transgressions and regressions in the rock record Rocks of the Sauk Sequence (Neoproterozoic-Early Ordovician) record the first major transgression onto the North American craton. During this period, deposition of marine sediments was limited to the passive shelf areas of the Appalachian and cordilleran borders of the craton. The craton was above sea level and was subjected to considerable weathering and erosion. North America was part of a tropical climate with no evidence of any terrestrial vegetation. Thus, weathering and erosion of the exposed Precambrian basement rocks took place quickly. During the Middle Cambrian, the transgressive phase of the Sauk began with epeiric seas coming across the craton. These seas had covered most of North America by the Late Cambrian. The few large islands exposed were collectively named the Transcontinental Arch. They stretched from New Mexico to the Lake Superior region. There is much evidence of shallow water deposition in the sediment deposits on the craton and along the shelf area of the craton. The shelf deposits are thicker. Both areas have clean well sorted sands, ripple marks and small scale cross bedding. Shallow water deposition is evidenced in the fragments of organic remains and oolitic textures. The Grand Canyon region occupied the passive shelf and western margin of the craton during Sauk time. During Neoproterozoic and Early Cambrian the majority of the craton was above sea level and the marine sediment deposits were mostly on the margins of the craton which were the continental slopes and shelves. In the Grand Canyon region, the Tapeats Sandstone represents the basal transgressive shoreline deposits that accumulated as marine waters transgressed across the shelf and just onto the western margin of the craton during the Early Cambrian. The sediments are typical of those found on a beach in modern time. As transgression continued into Middle Cambrian, Bright Angel Shale muds deposited over the Tapeats Sandstone. By Late Cambrian, the Sauk Sea transgression had advanced to where Muav Limestone carbonates were depositing over the Bright Angel Shale muds. The vertical succession of the sandstone, shale, and limestone formed a transgressive sequence representing a progressive migration of offshore facies toward the craton over time. Grand Canyon Cambrian rocks show that many formations are time transgressive and not the same age in all places. Deposition of the Muav Limestone was occurring on the shelf before Tapeats Sandstone deposition had finished on the craton. For example, Bright Angel Shale faunal analysis indicated Early Cambrian deposition in California and Middle Cambrian in the Grand Canyon region. A similar event was taking place in another area of the craton as the seas transgressed from the Appalachian and Ouachita mobile belts onto the interior craton. Carbonate deposition was over most of the craton as the Sauk transgression progressed to the Early Ordovician, soon covering the Transcontinental Arch. Most of the craton was submerged under a warm, equatorial epeiric sea by the end of Sauk time. 78. Reef environments of the various eras, reef-building organisms throughout geologic time
 * Wicander/Monroe: Historical Geology, pgs 202-206 PB**
 * Cambrian **
 * - Archaeocyathids (filter feeders like corals, but related to sponges) were main reef builders **
 * - Archaeocyathids went extinct at end of Cambrian **
 * Ordovician – one of most important reef building times **
 * - Tabulate and rugose corals; bryozoans, stromatoporoids (sponge-like) **
 * - Barrier, patch and pinnacle reefs, **
 * - Sensitive ecosystems – warm, clear, shallow, normal salinity **
 * Silurian/Devonian – major reef building **
 * - Recovery and diversification **
 * - Massive reefs larger than earlier ones **
 * - Dominated by tabulate and colonial rugose corals and stromatoporoids; brachiopods **
 * - General composition similar to present-day reefs **
 * Carboniferous and Permian Periods **
 * - Catastrophic decline/extinction at end of Devonian of stromatoporoids and tabulate and rugose corals **
 * - Large organic reefs replaced by small patch reefs **
 * - Dominated by crinoids, blastoids, lacy bryozoans, brachiopods and calcareous algae **
 * Mesozoic Era **
 * - Permian extinction of tabulate and rugose corals, fusulinids, lacy bryozoans **
 * - New coral: Schleractinians – modern, solitary and colonial; developed symbiotic relationship with algae and could move into shallow water **
 * - Reef-forming rudists (bivalves) **
 * - Rudists became extinct at end of Cretaceous **


 * Cenozoic Era **


 * - Corals once again became dominant reef builders **
 * DS **