GENERAL NOTES 1 TO 3.pdf

GENERAL NOTES FOR LECTURES 1 TO 3 Geology is the study of Earth, its solid parts like minerals, rocks and their processes of formation. It is traditionally divided into two broad areas: physical and historical. Physical geology examines the materials composing Earth and seeks to understand...

GENERAL NOTES FOR LECTURES 1 TO 3 Geology is the study of Earth, its solid parts like minerals, rocks and their processes of formation. It is traditionally divided into two broad areas: physical and historical. Physical geology examines the materials composing Earth and seeks to understand the many processes that operate beneath and upon its surface. The aim of historical geology, on the other hand, is to understand the origin of Earth and its development through time. Thus, it strives to establish a chronological arrangement of the multitude of physical and biological past. Scottish naturalist James Hutton (1726-1797) is known as the father of modern geology and published “Theory of the Earth’ in 1795. In this work Hutton put forth a fundamental principle that is a pillar of geology: uniformitarianism. It states that the physical, chemical and biological laws that operate today also operate in the geologic past. In other words, the forces and processes that we observe shaping our planet today have been at work for a very long time. Thus, to understand ancient rocks, we must first understand present-day processes and their results. This idea is commonly stated as “the present is the key to the past”. Importance of geology Geology provides necessary information about the site of construction materials used in the construction of building, dams, tunnel, tanks, reservoirs, highways and bridges. Geological information is most important in planning phase (stage), design phase and construction phase of an engineering project. The role of geology in civil engineering may be briefly outlined as follows:  Geology provides a systematic knowledge of construction materials, their structure and properties.  The knowledge of Erosion, Transportation and Deposition (ETD) by surface water helps in soil conservation, river control, coastal and harbour works.  The knowledge about the nature of the rocks is very necessary in tunnelling, constructing roads and in determining the stability of cuts and slopes. Thus, geology helps in civil engineering.  The foundation problems of dams, bridges and buildings are directly related with geology for the area where they are to be built.  The knowledge of ground water is necessary in connection with excavation works, water supply, irrigation and many other purposes.  Geology maps and sections help considerably in planning many engineering projects.  If the geological features like faults, joints, beds, folds, solution channels are found, they have to be suitably treated. Hence, the stability of the structure is greatly increased.  Pre-geological survey of the area concerned reduces the cost of engineering work. Page1 CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Branches of geology 1. Physical geology As a branch of geology, it deals with the various processes of physical agents such as wind, water, glaciers and sea waves, run on these agents go on modifying the surface of the earth continuously. Physical geology includes the study of Erosion, Transportation and Deposition (ETD). The study of physical geology plays a vital role in civil engineering thus: it reveals constructive and destructive processes of physical agents at a particular site and it helps in selecting a suitable site for different types of project to be under taken after studying the effects of physical agents which go on modifying the surface of the earth physically, chemically and mechanically. 2. Mineralogy As a branch of geology, it deals with the study of minerals. A mineral may be defined as a naturally occurring, homogeneous solid, inorganically formed, having a definite chemical composition and ordered atomic arrangement. The study of mineralogy is most important: for a civil engineering student to identify the rocks, in industries such as cement, iron and steel, fertilizers, glass industry and etc and in the production of atomic energy 3. Petrology As a branch of geology, it deals with the study of rocks. A rock is defined as the aggregation of minerals found in the earth’s crust. The study of petrology is most important for civil engineers’ point of view in the selection of suitable rocks for building stones, road metals, etc. It provides a proper concept and logical basis for interpreting physical properties of rocks, thus, the study of texture, structure, mineral composition, chemical composition, etc. Earth structure and composition There is only one place in the universe, as far as we know, that can support life; a modest-sized planet called earth that orbits an average-sized star, the Sun. Earth has a long and complex history. Time and again, the splitting and colliding of continents has resulted in the formation of new ocean basins and the creation of great mountain ranges. Furthermore, the nature of life on The crust is the Earth’s outer surface. It is a cold, thin, brittle outer shell made of rock. The crust is very thin, relative to the radius of the planet. There are two main types of crust: oceanic crust and continental crust. Oceanic crust is composed of magma that erupts on the seafloor to create basalt lava flows or cools deeper down to create the intrusive igneous rock gabbros. Sediments, primarily mud and the shells of tiny sea creatures, coat the seafloor. Sediment is thickest near the shore where it comes off the continents in rivers and on wind currents. Continental crust, on the other hand, is made up of many different types of igneous, metamorphic, and sedimentary rocks. The average composition is granite, which is much less dense than the mafic igneous rocks of the oceanic crust. Because it is thick and has relatively low density, continental crust rises higher on the mantle than oceanic crust, which sinks into the mantle to form basins. When filled with water, Page2 these basins form the planet’s oceans. CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 The lithosphere is the outermost mechanical layer, which behaves as a brittle, rigid solid. The lithosphere is about 100 kilometers thick. The definition of the lithosphere is based on how earth materials behave, so it includes the crust and the uppermost mantle, which are both brittle. Since it is rigid and brittle, when stresses act on the lithosphere, it breaks. This is what we experience as an earthquake. The two most important things about the mantle are: (1) it is made of solid rock, and (2) it is hot. Scientists know that the mantle is made of rock based on evidence from seismic waves, heat flow, and meteorites. The properties fit the ultramafic rock peridotite, which is made of the iron- and magnesium-rich silicate minerals. Peridotite is rarely found at Earth’s surface. Scientists know that the mantle is extremely hot because of the heat flowing outward from it and because of its physical properties. Heat flows in two different ways within the Earth: conduction and convection. Conduction is defined as the heat transfer that occurs through rapid collisions of atoms, which can only happen if the material is solid. Heat flows from warmer to cooler places until all are the same temperature. The mantle is hot mostly because of heat conducted from the core. While, convection is the process of a material that can move and flow may develop convection currents. Convection in the mantle is the same as convection in a pot of water on a stove. Convection currents within Earth’s mantle form as material near the core heats up. As the core heats the bottom layer of mantle material, particles move more rapidly, decreasing its density and causing it to rise. The rising material begins the convection current. When the warm material reaches the surface, it spreads horizontally. The material cools because it is no longer near the core. It eventually becomes cool and dense enough to sink back down into the mantle. At the bottom of the mantle, the material travels horizontally and is heated by the core. It reaches the location where warm mantle material rises and the mantle convection cell is complete. Scientists know that the core is metal for a few reasons. The density of Earth’s surface layers is much less than the overall density of the planet, as calculated from the planet’s rotation. If the surface layers are less dense than average, then the interior must be denser than average. Calculations indicate that the core is about 85 percent iron metal with nickel metal making up much of the remaining 15 percent. Also, metallic meteorites are thought to be representative of the core. If Earth’s core were not metal, the planet would not have a magnetic field. Metals such as iron are magnetic, but rock, which makes up the mantle and crust, is not. Scientists know that the outer core is liquid and the inner core is solid because S-waves stop at the inner core. The strong magnetic field is caused by convection in the liquid outer core. Convection currents in the outer core are due to heat from the even hotter inner core. The heat that keeps the outer core from solidifying is produced by the breakdown of radioactive elements in the inner core. Earth’s evolution through geologic time The history of Earth began about 13.7 billion years ago when the first elements were created during the Big Bang. It was from this material, plus other elements ejected into interstellar space by now- defunct stars, that Earth, along with the rest of the solar system, formed. As material collected, high velocity impacts of chunks of matter called planetesimals and the decay of radioactive elements caused the temperature of our planet to steadily increase. Iron and nickel melted and sank to form the metallic core, while rocky material rose to form the mantle and Earth’s initial crust. Page3 CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Earth’s primitive atmosphere, which consisted mostly of water vapor and carbon dioxide, formed by a process called outgassing, which resembles the steam eruptions of modern volcanoes. About 3.5 billion years ago, photosynthesizing bacteria began to release oxygen, first into the oceans and then into the atmosphere. This began the evolution of our modern atmosphere. The oceans formed early in earth’s history as water vapor condensed to form clouds, and torrential rains filled low-lying areas. The salinity in seawater came from volcanic outgassing and from elements weathered and eroded from Earth’s primitive crust. The Precambrian, which is divided into the Archean and Proterozoic eons, spans nearly 90 percent of Earth’s history, beginning with the formation of Earth about 4.6 billion years ago and ending approximately 542 million years ago. During this time, much of Earth’s stable continental crust was created through a multistage process. First, partial melting of the mantle generated magma that rose to form volcanic island arcs and oceanic plateaus. These thin crustal fragments collided and accreted to form larger crustal provinces, which in turn assembled into larger blocks called cratons. Cratons, which form the core of modern continents, were created mainly during the Precambrian. Supercontinents are larger landmasses that consist of all, or nearly all, existing continents. Pangaea was the most recent supercontinent, but other massive continents including an even larger one, Rodinia, preceded it. The splitting and reassembling of supercontinents have generated most of Earth’s major mountain belts. In addition, the movements of these crustal blocks have profoundly affected Earth’s climate and caused sea level to rise and fall. The time span following the close of the Precambrian, called the Phanerozoic eon, encompasses 542 million years and is divided into three eras: Paleozoic, Mesozoic, and Cenozoic. The Paleozoic era was dominated by continental collisions as the supercontinent of Pangaea assembled; forming the Caledonian, Appalachian, and Ural Mountains. Early in the Mesozoic, much of the land was above sea level. However, by the middle Mesozoic, seas invaded western North America. As Pangaea began to break up the westward-moving North American plate began to override the Pacific plate, causing crustal deformation along the entire western margin of North America. Owing to their different relations with plate boundaries, the eastern and western margins of the continent experienced contrasting events. The stable eastern margin was the site of abundant sedimentation as isostatic adjustment raised the modern Appalachians, causing streams to erode with renewed vigor and deposit their sediment along the continental margin. In the West, the Laramide Orogeny (responsible for building the Rocky Mountains) was coming to an end, the Basin and Range province was forming, and volcanic activity was extensive. The first known organisms were single-celled bacteria, prokaryotes, which lack a nucleus. One group of these organisms, called cyanobacteria, used solar energy to synthesize organic compounds (sugars). For the first time, organisms had the ability to produce their own food. Fossil evidence for the existence of these bacteria includes layered mounds of calcium carbonate called stromatolites. The beginning of the Paleozoic is marked by the appearance of the first life-forms with hard parts such as shells. Therefore, abundant fossils occur, and a far more detailed record of Paleozoic events can be constructed. Life in the early Paleozoic was restricted to the seas and consisted of several invertebrate groups, including trilobites, cephalopods, sponges, and corals. During the Paleozoic, organisms diversified dramatically. Insects and plants moved onto land and lobe- finned fishes that adapted to lad became the first amphibians. By the Pennsylvanian period, large Page4 tropical swamps, which became the major coal deposits of today, extended across North CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 America, Europe and Siberia. At the close of the Paleozoic, a mass extinction destroyed 70 percent of all vertebrate species on land and 90 percent of all marine organisms. The Mesozoic era, literally, the era of middle life, is often called “Age of reptiles”. Organisms that survived the extinction at the end of the Paleozoic began to diversify in spectacular ways. Gymnosperms (cycads, conifers and ginkgoes) became the dominant tress of the Mesozoic because they could adapt to the drier climates. Reptiles became the dominant land animals. The most awesome of the Mesozoic reptiles ware the dinosaurs. At the close of the Mesozoic, many large reptiles, including dinosaurs, became extinct. The Cenozoic is often called the “Age of Mammals” because these animals replaced the reptiles as the dominant vertebrate life-forms on land. Two groupd of mammals, the marsupials and the placentals, evolved and expanded during this era. One tendency was for some mammal groups to become very large. However, a wave of late Pleistocene extinction rapidly eliminated these animals from the landscape. Some scientists suggest that early humans hastened their decline by selectively hunting the larger animals. The Cenozoic could also be called the “Age of Flowering Plants”. As a source of food, flowering plants (angiosperms) strongly influenced the evolution of both birds and herbivorous (plant-eating) mammals throughout the Cenozoic era. Continental drift and plate tectonics In the early 1900s Alfred Wegener set forth his continental drift hypothesis. One of its major tenets was that a supercontinent called Pangaea began breaking apart about 200 million years ago. The rifted continental fragments then “drifted” to their present positions. To support his hypothesis, Wegener used the fit of South America and Africa, fossil evidence, rock types and structures, and ancient climates. One of the main objections to the continental drift hypothesis was its inability to provide an acceptable mechanism for the movement of continents. By 1968, continental drift was replaced by a far more encompassing theory known as plate tectonics. According to plate tectonics, Earth’s rigid outer layer “lithosphere” overlies a weaker region called the asthenosphere. Further, the lithosphere is broken into several large and numerous smaller segments, called plates, that are in motion and continually changing in shape and size. Plates move as relatively coherent units and are deformed mainly along their boundaries. Divergent plate boundaries occur where plates move apart, resulting in upwelling of material from the mantle to create new seafloor. Most divergent boundaries occur along the axis of the oceanic ridge system and are associated with seafloor spreading. New divergent boundaries may form within a continent (for example, the East African Rift Valleys), where they may fragment a landmass and develop a new ocean basin. Convergent plate boundaries occur where plates move together, resulting in the subduction of oceanic lithosphere into the mantle along a deep-ocean trench. Convergence of an oceanic and continental block results in subduction of the oceanic slab and the formation of a continental volcanic arc such as the Andes of South Africa. Oceanic-oceanic convergence results in an arc- shaped chain of volcanic islands called a volcanic island arc. When two plates carrying continental crust converge, the buoyant continental blocks collide, resulting in the formation of a mountain belt as exemplified by the Himalayas. Page5 Transform fault boundaries occur when plates grind past each other without the production or destruction of the lithosphere. Most transform faults join two segments of a mid-ocean ridge where CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 they provide the means by which oceanic crust created at a ridge crest can be transported to its site of destruction; a deep-ocean trench. Still others, like the San Andreas Fault, cut through continental crust. The theory of plate tectonics is supported by (1) the ages of sediments from the floors of the deep- ocean basins; (2) the existence of island groups that formed over hot spots and that provide a frame of reference for tracing the direction of plate motion, and (3) Paleomagnetism, the direction and intensity of Earth’s magnetism in the geologic past. Page6 CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Geological History of the Earth Geology is an earth science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which they change. Geology is the study of the Earth - how it works and its 4.5-billion-year history. Geologists study some of society's most important problems, such as energy, water, and mineral resources; the environment; climate change; and natural hazards like landslides, volcanoes, earthquakes, and floods. The geological history of Earth follows the major events in Earth's past based on the geologic time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Page7 CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Cambrian Period (570-510 Million Years Ago) An explosion of life populated the seas, but land areas remained barren. Animal life was wholly invertebrate, and the most common animals were arthropods called trilobites (now extinct), with species numbering in the thousands. Multiple collisions between the Earth's crustal plates gave rise to the first supercontinent, known as Gondwanaland. When Pangaea broke up, the northern continents of North America and Eurasia became separated from the southern continents of Antarctica, India, South America, Australia and Africa. Ordovician Period (510-439 million years ago) The predecessor of today's Atlantic Ocean began to shrink as the continents of that time drifted closer together. Trilobites were still abundant; important groups making their first appearance included the corals, crinoids, bryozoans, and pelecypods. Armored, jawless fishes—the oldest known vertebrates—made their appearance as well; their fossils are found in ancient estuary beds in North America. Silurian Period (439-408.5 million years ago) Life ventured on to land in the form of simple plants called psilophytes, with a vascular system for circulating water, and scorpion-like animals akin to now extinct marine arthropods called eurypterids. Trilobites decreased in number and variety, but the seas teemed with reef corals, cephalopods, and jawed fishes. Devonian Period (408.5-362.5 million years ago) This period is also known as the age of fishes, because of their abundant fossils in Devonian rocks. Fishes had also become adapted to fresh water as well as to salt water. They included a diversity of both jawless and jawed armored fishes, early sharks, and bony fishes, from the last of which amphibians evolved. (One subdivision of the sharks of that time is still extant.) On land areas, giant ferns were widespread. Permian Period (290-245 million years ago) Page8 The Earth's land areas became welded into a single land mass that geologists call Pangaea, and in the North American region the Appalachians were formed. Cycad-like plants and true conifers CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 appeared in the northern hemisphere, replacing the coal forests. Environmental changes resulting from the redistribution of land and sea triggered the greatest mass extinction of all time. Trilobites and many fishes and corals died out as the Palaeozoic era came to an end. Triassic Period (245-208 million years ago) The beginning of the Mesozoic era was marked by the reappearance of Gondwanaland, as Pangaea split apart into northern (Laurasia) and southern (Gondwanaland) supercontinents. Forms of life changed considerably in the Mesozoic, known as the age of reptiles. New pteridosperm families appeared, and conifers and cycads became major floral groups, along with ginkgoes and other genera. Such reptiles as dinosaurs and turtles appeared, as did mammals. Jurassic Period (208-145.6 million years ago) As Gondwanaland rifted apart, the North Atlantic Ocean widened and the South Atlantic was born. Giant dinosaurs ruled on land, while marine reptiles such as ichthyosaurs and plesiosaurs increased in number. Primitive birds appeared, and modern reef-building corals grew in coastal Page9 shallows. Crab-like and lobster-like animals evolved among the arthropods. CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Cretaceous Period (145.6-65 million years ago) Dinosaurs flourished and evolved into highly specialized forms, but they abruptly disappeared at the end of the period, along with many other kinds of life. (Theories to account for these mass extinctions are currently of great scientific interest.) The floral changes that took place in the Cretaceous were the most marked of all alterations in the organic world known to have occurred in the history of the Earth. Gymnosperms were widespread, but in the later part of the period angiosperms (flowering plants) appeared. Tertiary Period (65-1.64 million years ago) In the Tertiary, North America's land link to Europe was broken, but its ties to South America were forged towards the end of the period. During Cenozoic times, life forms both on land and in the sea became more like those of today. Grasses became more prominent, leading to marked changes in the dentition of plant-eating animals. With most of the dominant reptile forms having vanished at the end of the Cretaceous, the Cenozoic became the age of mammals. Thus, in the Eocene epoch, new mammal groups developed such as small, horse-like animals; rhinoceroses; tapirs; ruminants; whales; and the ancestors of elephants. Members of the cat and dog families appeared in the Oligocene epoch, as did species of monkeys. In Miocene times, marsupials were Page10 numerous, and anthropoid (human-like) apes first appeared. Placental mammals reached their zenith, in numbers and variety of species, in the Pliocene, extending into the Quaternary period CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Quaternary Period (1.64 million years ago to present) Intermittent continental ice sheets covered much of the northern hemisphere. Fossil remains show that many primitive pre-human types existed in south-central Africa, China, and Java by Lower and middle Pleistocene times; but modern humans (Homo sapiens) did not appear until the later Pleistocene. Late in the period, humans crossed over into the New World by means of the Bering land bridge. The ice sheets finally retreated, and the modern age began. IMPORTANT PRINCIPLES OF GEOLOGY There are a number of important principles in geology. Many of these involve the ability to provide the relative ages of strata or the manner in which they were formed. PRINCIPLE OF UNIFORMITARIANISM - states that the geologic processes observed in operation that modify the Earth's crust at present have worked in much the same way over geologic time. A fundamental principle of geology advanced by the 18th century Scottish physician and geologist James Hutton, is that "the present is the key to the past." In Hutton's words: "the past history of our globe must be explained by what can be seen to be happening now." PRINCIPLE OF INTRUSIVE RELATIONSHIPS - concerns crosscutting intrusions. In geology, when an igneous intrusion cuts across a formation of sedimentary rock, it can be determined that the igneous intrusion is younger than the sedimentary rock. There are a number of different types of intrusions, including stocks, laccoliths, batholiths, sills and dikes. PRINCIPLE OF INCLUSION AND COMPONENTS - states that, with sedimentary rocks, if inclusions (or clasts) are found in a formation, then the inclusions must be older than the formation that contains them. For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer. A similar situation with igneous rocks occurs when xenoliths are found. These foreign bodies are picked up as magma or lava flows, and are incorporated, later to cool in the matrix. As a result, xenoliths are older than the rock which contains them. PRINCIPLE OF ORIGINAL HORIZONTALITY - states that the deposition of sediments occurs as essentially horizontal beds. Observation of modern marine and non-marine sediments in a wide variety of environments supports this generalization (although cross-bedding is inclined, the overall orientation of cross-bedded units is horizontal). PRINCIPLE OF SUPERPOSITION - states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. Logically a younger layer cannot slip beneath a layer previously deposited. This principle allows sedimentary layers to be viewed as a form of vertical time line, a partial or complete record of the time elapsed from deposition of the lowest layer to deposition of the highest bed. PRINCIPLE OF FAUNAL SUCCESSION - is based on the appearance of fossils in sedimentary rocks. As organisms exist at the same time period throughout the world, their presence or (sometimes) absence may be used to provide a relative age of the formations in which they are found. Based on principles laid out by William Smith almost a hundred years before the publication of Charles Darwin's theory of evolution, the principles of succession were developed independently of evolutionary thought. The principle becomes quite complex, however, given the uncertainties of fossilization, the localization of fossil types due to lateral changes in habitat (facies change in Page11 sedimentary strata), and that not all fossils may be found CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3 Continental Drift and Plate Tectonics The Earth is divided into three chemical layers: the core, the mantle and the crust. The core is composed of mostly iron and nickel and remains very hot, even after 4.5 billion years of cooling. The core is divided into two layers: a solid inner core and a liquid outer core. The middle layer of the Earth, the mantle, is made of minerals rich in the elements iron, magnesium, silicon, and oxygen. The crust is rich in the elements oxygen and silicon with lesser amounts of aluminum, iron, magnesium, calcium, potassium, and sodium. There are two types of crust. Basalt is the most common rock on Earth. Oceanic crust is made of relatively dense rock called basalt. Continental crust is made of lower density rocks, such as andesite and granite.  The outermost layers of the Earth can be divided by their physical properties into lithosphere and asthenosphere. Page12  The lithosphere (from the Greek, lithos, stone) is the rigid outermost layer made of crust and uppermost mantle. The lithosphere is the "plate" of the plate tectonic theory. CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA GENERAL NOTES FOR LECTURES 1 TO 3  The asthenosphere (from the Greek, asthenos, devoid of force) is part of the mantle that flows, a characteristic called plastic behavior.  The flow of the asthenosphere is part of mantle convection, which plays an important role in moving lithospheric plates. Page13 CE 212 – Geology for Civil Engineers PREPARED BY: ENGR. REJOICE G. MATA