Introduction to Geology - Introductory Lectures PDF

Introduction to Geology Introductory Lecture Benedict Yankyerah Content: Course outline Course description Objectives Course basics Assessment Course materials & references Why this course Course outline: Background/ Introduction Structure of the...

Introduction to Geology Introductory Lecture Benedict Yankyerah Content: Course outline Course description Objectives Course basics Assessment Course materials & references Why this course Course outline: Background/ Introduction Structure of the earth Plate tectonics Faulting Geologic Time Minerals #dauntlessnattie Rocks Geologic Structures Course description: This undergraduate course provides an overview of the fundamental concepts of the earth’s structure, processes and history Objectives: To students gain in-depth understanding of the fundamentals of rock formation and deformation and how rock characteristics are related to modern geological processes and applied to ancient record Course basics: Course code: PENG 151 Class: Petroleum Engineering Year 1 (Sem 1) Credits: 3 Lecture schedule: Wed 9-10pm, SH6; Fri 9-11am, LTS3 Assessment: Total (100%) 5 5 10 20 60 #dauntlessnattie Final exams Mid Sem Quizzes Assignments Attendance Course materials & references: PPT slides Blyth, F.G.H. & De Freitas, M (2017). A Geology for Engineers Bonewitz, R. (2012). Rocks and Minerals. DK Publishing Fossen, H. (2016). Structural Geology. Cambridge University Press Why this course: Intoduction to Geology: What is Geology? Physical Geology Historical Geology Structure of the earth Content: Cross-section of the earth The Crust The Mantle The Core Cross-section of the earth The earth is composed of three basic layers: the core, the mantle, and the crust. The Crust  The crust is differentiated into oceanic crust and continental crust. Oceanic crust – This lies under the oceans and is thin about 8-11 km and is made up primarily of heavy rock that is formed when molten rock (magma) cools e.g. basalt rich in silica and magnesium Contenental crust – This about 16-48 km thick and is composed of rock that is relatively light as compared to oceanic crust e.g. granitic rock and is rich in silica and alumina The Mantle This is the layer below the crust. It is about 2,885 km thick. It is mostly solid rock, with some of the rocks molten. It contains iron, magnesium, silicon, and oxygen compounds. There is movement of the molten rock in the mantle from the hot lower part of the mantle to the cooler shallower parts above through a process known as mantle convection which is responsible for the continental drift and sea floor spreading (Plate Tectonics) The Core  Divided into inner and outer core, It is the innermost part of the Earth – The outer core is liquid and is made mainly of molten rocks – The inner core is solid and is made mostly of iron and nickel – The outer core is cooler than the inner core with a temperature range between 4,500 degrees Celsius and 5,500 degrees Celsius – Temperature in the inner core is about 5,200° with pressure of about 3.6 million atm What makes the inner core solid though hotter than the outer core? Plate tectonics Content Plate tectonics theory Theory of contenental drift Types of plate boundaries Divergent boundaries Convergent boundaries Transform boundaries Plate tectonics theory  Earth's lithosphere comprises a number of large tectonic plates These plates have been slowly moving since about 3.4 billion years ago There are seven major plates and a number of smaller plates. – Pacific, North American, Eurasian, African, Antarctic, Indo-Australian, and the South American Plate. While most plates are comprised of both continental and oceanic crust the giant Pacific Plate is almost entirely oceanic. Theory of contenental drift The theory was proposed by Alfred Wegener in the early 20th century, suggesting that continents move around on Earth's surface Wegener's theory was based on the fit of the continents, fossil evidence, and the matching of geological features across continents The theory explains the similarity between the Western coastline of Africa and the Eastern coastline of South America The theory of plate tectonics expanded on Continental Drift by providing a mechanism;- convection currents in the Earth's mantle that drives the movement of tectonic plates Types of plate boundaries There are three (3) types of plate boundaries: 1. Divergent/ Constructive/ Spreading: These are associated with volcanoes. New crust is generated as the plates pull away from each other. 2. Convergent/ Destructive: These are associated with earthquakes. The impact of the colliding plates can cause the edges of one or both plates to buckle up into mountain ranges or one of the plates may bend down into a deep seafloor trench. 3. Transform/ Conservative: Also associated associated with earthquakes, when plates slide side by side. Divergent boundaries These boundaries are also known as spreading centres. Examples are the East Pacific Rise and the Mid-Atlantic Ridge. This is formed as a result of heated mantle material upwelling as a result of convection from below the lithosphere. The older lithospheric rock is spread apart and newly generated volcanic material fills the fracture of the spreading centre. #dauntlessnattie Convergent boundaries This is the compensating destruction of the older ocean- floor crust so that the earth does not expand as the new oceanic crust is formed at spreading centeres. This destruction takes place at subduction zones A subduction zone is an area where a cold slab of ocean floor is forced back into the mantle beneath another plate. As this happens the plates moves towards each other. magma erupts at the surface as a chain of volcanic islands or volcanoes along a continental margin. Examples are the Andes of South America. Geothermal heat and friction increase the temperature of the liding plate and creates magma. Transform boundaries Transform Boundaries are where two plates are sliding horizontally past one another as a result of transform faulting Most transform faults are found on the ocean floor. They commonly offset active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes A few, however, occur on land. The San Andreas fault zone in California Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr Faulting Content Faults Definition of terms Types of faults Faults A fault is a fracture or zone of fractures between two blocks of rock which causes the blocks to move relative to each other. or A fault is a discontinuity in a rock along which there has been displacement. Dip & Strike dip: the inclination angle of a rock layer or fault surface from the horizontal The dip direction is the compass direction down which the steepest part of the rock layer or fault surface inclines. strike: the compass direction of a horizontal line on that inclined surface It is measured relative to true north and is perpendicular to the dip direction. Types of faults Dip slip (Normal or Reverse) Strike-slip and Oblique-slip Dip slip faults Dip-slip faults are caused by tensional and compressive forces. There are two types: Normal fault ▪ Faulting is caused by tensional forces and leads to extension. ▪ The block above the fault line (hanging wall) moves down relative to the block below the fault line (foot wall)  #dauntlessnattie Reverse fault ▪ Faulting is caused by compressional forces and leads to shortening. ▪ The block above the fault line (hanging wall) moves up relative to the block below the fault line (foot wall) Strike-slip This type of fault is caused by shearing forces. The fault blocks are displaced horizontally/ laterally with respect to each other. Strike-slip faults are also known as lateral/transcurrent/tear/wrench fault Oblique-slip Oblique-slip faults are a combination of dip-slip and strike slip faults They occur as a result of combination of shearing and tensional/compressional forces Geologic Time Contents The Age of the earth What is Geologic Time? Catastrophism Uniformitarianism Geologic Timescale Principles Behind Geologic Time Relative Age Dating Relative Age dating with index fossils Uncomformities Absolute Age Dating Carbon Dating The Age of the earth? Prior to the 19th century, accepted age of Earth based on religious beliefs ~6,000 years for Western culture (Biblical) Old beyond comprehension (Chinese/Hindu) – James Hutton, realized geologic processes require vast amounts of time and challenged the then popular idea... What is geologic time? Geologic time refers to the vast expanse of time over which Earth's geological events and developments have occurred, spanning billions of years. Geologic time and Earth’s geologic history are concepts that need to be clearly understood and how they relate to the petroleum industry. It takes millions of years and specific conditions for organic and sedimentary materials to be converted to recoverable hydrocarbons Catastrophism Catastrophism is a geological theory that suggests that Earth's geological features and landscapes were primarily formed by largescale sudden, short-lived, and catastrophic events. It proposes that geological processes in the past were significantly more violent and rapid compared to those observed today. Evidence such as the presence of marine fossils on mountaintops and large meteorite impact structures, evidence of mass extinctions in the fossil record have been cited as support for the theory. Uniformitarianism “...the present is key to the past” James Hutton in the late 18th century, introduced the principle of uniformitarianism to challenge the prevailing belief in catastrophism. Uniformitarianism is a fundamental principle in geology that posits that the same natural processes observed today have operated throughout Earth's history at the same rate and intensity. This principle suggests that by studying present-day geological processes, such as erosion, sedimentation, volcanic activity, and tectonic movements, we can infer and understand past geological events and formations. Geologic Timescale The geologic time scale divides up the history of the earth based on life-forms that have existed during specific times since the creation of the planet. These divisions are called geochronologic units  Eons: Longest subdivision; based on the abundance of certain fossils, spans about 1 billion years. Eras: Next to longest subdivision; marked by major changes in the fossil record. Spans hundreds of millions of years. Periods: Based on types of life existing at the time. Lasts tens of millions of years. Epochs: Marked by differences in life forms and can vary from continent to continent. Spans several million years. Age: The lowest rank unit of time for the geologic time scale. Ages are usually between two and ten millions years in length- subsections of longer epochs.  The earliest time of the Earth is called the Hadean and refers to a period of time for which we have no rock record, and the Archean followed, which corresponds to the ages of the oldest known rocks on earth. These, with the Proterozoic Eon are called the Precambrian Eon. The remainder of geologic time, including present day, belongs to the Phanerozoic Eon. EONS LENGHT CHARACTERISTICS MAJOR EVENTS Cenozoic Era: The age of mammals, where mammals and birds rise to dominance and modern forms of life Formation of the Himalayas, ice appear. ages, and the evolution of hominids. Phanerozoic About 541 million Mesozoic Era: The age of reptiles, dominated by Breakup of Pangea, dominance of (current years ago to the dinosaurs and the first appearance of birds and dinosaurs, and the Cretaceous- eon) present mammals. Paleogene extinction event that ended the Mesozoic. Paleozoic Era: The era of ancient life, where we see the Cambrian Explosion, the formation of development of most major animal groups and the Pangea, and the Permian mass colonization of land by plants and animals extinction. Great Oxygenation Event, snowball Oxygen begins to accumulate in the atmosphere, 2.5 billion to 541 Earth periods, and the emergence of Proterozoic eukaryotic cells emerge, and multicellular life begins to million years ago more complex life forms leading up to develop. the Cambrian Explosion Emergence of the first simple life 4.0 to 2.5 billion The crust solidifies, early continents form, and the first Archean forms, development of stromatolites, years ago known life forms (microbial life) appear. and significant volcanic activity. The Earth's formation and early development, Formation of the Moon, cooling of About 4.6 to 4.0 Hadean characterized by a molten surface eventually cooling to Earth’s surface, and the beginnings billion years ago Principles Behind Geologic Time Nicholas Steno, a Danish physician (1638-1687), postulated that the position of a rock layer could be used to show the relative age of the layer based on 3 main principles: 1. The principle of superposition: The layer on the bottom was deposited first and so is the oldest 2. The principle of horizontality: All rock layers were originally deposited horizontally. 3. The principle of original lateral continuity: Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.  William Smith, later, upon understanding that certain rock units could be identified by the particular assemblages of fossils they contain, applied that knowledge to correlate strata with the same fossils for many miles, giving rise to a 4th principle, 4. The principle of biologic succession: Each age in the earth’s history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species.  Charles Lyell also, later presented these principles in addition: 5. The principle of cross-cutting relationships: A rock feature that cuts across another feature must be younger than the rock that it cuts. 6. Inclusion principle: Small fragments of one type of rock but embedded in a second type of rock must have formed first, and were included when the second rock was forming. These 6 principles are known as Principles of Stratigraphy Relative Age Dating When rock layers are in their original sequence, the age of one layer in relation to another, could be determined. This is called “Relative age”. This is not the actual age of the rock layer in question. All six of the original stratigraphic principles may be applied to determine the age of a rock. This process is called age dating.  Scientists correlate strata by rock unit type (lithology) - composition, texture of sediments fossil type (biology) to extrapolate relationships over large areas of land. Because rock layers can be “matched up,” we can guess that they were formed during the same period, so they usually are the same age. Relative Age dating with index fossils An index fossil is any animal or plant preserved in the rock record of the Earth that is characteristic of a particular span of geologic time or environment. Characteristics of Index fossils widespread short temporal durations resulting from rapid life spans, abundant throughout their geographic and geologic ranges Distinctive and easily recognized. Examples of index fossils Unconformities Deciphering the sequence of a rock outcrop is sometimes complicated by a feature within rock record called unconformities, which are specific contacts between rock layers. Unconformities are a type of geologic contact or boundary between rock strata caused by a period of erosion or a pause in sediment accumulation, followed by the deposition of sediments anew.  There are three types of unconformities that help us determine relative ages of rock layers: Angular unconformity: Horizontal beds are uplifted and tilted or eroded followed by new deposition of horizontal beds. Disconformity: The unconformity between two parallel layers of stratified rocks, representing a considerable period of erosion or non-deposition between the layers. Nonconformity: Sediment is deposited on top of eroded volcanic or metamorphic rock indicating a very long passage of time. Identify the chronologic succession of the rock layers of this titlted outcrop Absolute Age Dating On the basis of the characteristics of the atoms that make up a rock's minerals, absolute ages, or geochronometric ages, of rocks can be assigned to the geologic time scale. Absolute dating produces an exact age in years. The number of neutrons in a nucleus of an atom determines the isotope of the element. Unstable isotopes break down into other isotopes through a process called radioactive decay. The original isotope is called the parent and the new isotope product is called the daughter Half-Life The specific and measurable rate at which parent elements decay into daughter elements is referred to as half-life. The half-life of an isotope is the time it takes for ½ of the parent atoms in the isotope to decay. For instance: If an isotope has a half-life of 4000 years, then after 4000 years ½ of the parent isotope remains. After another 4000 years, ½ of ½ remains, or ¼ of the original amount of parent isotope.  In another 4000 years (12,000 years total), ½ more of the remaining amount decays, so after 3 half-lives, there only remains 1/8 (½ of ½ of ½) of the original parent isotope. If a scientist knows the half-life of the parent and measures the proportion of parent isotope to daughter isotope, he/she can calculate the absolute age of the rock. This valuable method is called Radiometric dating.  Scientists use the proportion of parent material remaining to the proportion of daughter material produced in order to predict the age of the rock Isotopes with very long half-lives are not suitable for dating rocks younger than ~1 million years because there are too few daughter atoms to be measured accurately. Scientists generally aim for a minimum of 12 half-lives to have passed for accurate dating. This ensures a sufficient amount of daughter isotope has accumulated to be measured reliably compared to the remaining parent isotope. Carbon Dating Carbon dating is used to date anything that was once alive and up to 70,000 years old. All living things take in carbon from the environment in the form of carbon-12 and carbon-14. When an organism dies, carbon intake stops and the carbon-14 begins to decay at a known rate. Scientists can determine how much C-14 remains in an organism by measuring radiation emitted by the C-14 isotopes. The half-life of C-14 is 5,730 years. Because of this, it should not be used with material older than ~70,000 years or 12 half-lives Rocks Contents Definition A rock is a natural occurring solid cohesive aggregate of minerals. Types of Rocks Rocks are broadly classified into three types based on based on how they are formed: Igneous rocks Sedimentary rocks Metarmoprphic rocks Igneous Rocks Igneous rocks are formed from solidification and cooling of magma derived from partial melts of pre-existing rocks in either a planet's mantle or crust. The melting of rocks is caused by; an increase in temperature, a decrease in pressure, or a change in composition. Igneous rocks are therefore associated with volcanic activity and their distribution is controlled by plate tectonics.  Divergent plates are usually associated with creation of basalts and gabbros especially in the oceanic crust e.g. in the mid-Atlantic ridges. In the convergent plates usually granites and andesites magmas are produced e.g. In the South America, Indonesia etc Forms/Classes of Igneous Rocks based on their Physical Properties Felsic: light colored rocks that are rich in elements such as aluminum, potassium, silicon, and sodium Mafic: dark colored rocks that are rich in calcium, iron, and magnesium, poor in silicon Coarse-grained: takes longer to cool, giving mineral crystals more time to grow Fine-grained: cools quickly with little to no crystals Types of Igneous Rocks Igneous rocks are divided into two main categories: Plutonic or intrusive rocks: result when magma cools and crystallizes slowly within the Earth's crust. Eg. granite. Volcanic or extrusive rocks: result from magma reaching the surface either as lava or fragmental ejecta, forming rocks such as pumice or basalt Metamorphic Rocks Metamorphic rocks are rocks that have experienced change due to high pressure and temperature below the zone of diagenesis The original rock that underwent metamorphism is refered to as protolith The Role of Temperature & Pressure in Metamorphism The increasing temperature is responsible for: Breaking and reforming the chemical bonds of the protolith. Driving new chemical reactions that changes the rock's chemistry during metamorphism. Causing amalgamation of small crystals which results in the formation of a rock of with coarser grains. Causing unstable minerals to chemical form new minerals  The pressure is in two forms: Lithostatic: Caused by overlying rocks Directed pressure: Caused by tectonics When pressure conditions during metamorphism exceed a mineral’s stability range the mineral will transform to a new phase. These solid-state reactions cause minerals to transform into new minerals with the same chemical properties but different crystalline structures. Contact Metamorphism Vs Regional Metamorphism Contact Metamorphism: Contact metamorphism occurs adjacent to igneous intrusions and results from high temperatures associated with the igneous intrusion Metamorphism occurs only in the zone surrounding the intrusion, called a metamorphic or contact aureole  Regional Metamorphism: Regional metamorphism is the creation of metamorphic rock from large geographically significant processes like plate tectonics This results in forming metamorphic rocks that are strongly foliated, such as slates, schists, and gneisses. Tectonic forces produce compressional stresses in rocks, generating the differential stress which causes regional metamorphism. They result in folding of rock and thickening of the crust, which tends to push rocks to deeper levels where they are subjected to higher temperatures and pressures. Foliation Foliation is the thin layering and parallel alignment of rock minerals as the rock undergoes increasing heat and pressure as a result of metamorphism. Gneiss An example of a non-foliated Matamorphic Rock: Marble SEDIMENTARY ROCKS Sedimentary rocks are formed by the deposition of material at the Earth's surface and (or) within bodies of water. These materials are called sediments and are obtained from the weathering and erosion of igneous, metamorphic, and other sedimentary rocks, exposed at the earth’s surface.  Types of Sediments Clastic sediments: These are made up of fragments of rocks and minerals that have been weathered and eroded from their original source. Chemical sediments: These sediments are formed from the precipitation of minerals from water, such as calcite, gypsum, and halite. Biogenic sediments: These sediments are made up of the remains of organisms, such as shells, coral, and plant material. Organic sediments: These sediments are composed of organic material, such as peat and coal.  Processes that form Sedimentary Rocks Weathering: It is the breakdown and dissolution rocks and minerals in the earth’s surface. This is done by Water, ice, acids, salts, plants, animals, and changes in temperature Erosion: This is the transportaion of weathered materials by wind or water or ice (glaciers), and the influence of gravity. Sedimentation: Sedimentation is the deposition of rock fragments, soil, organic matter, or dissolved minerals that has been weathered and eroded.  Deposition: Sediments are transported according to the energy of the transporting medium. Sediments of a given size are deposited whenever they move into an environment with insufficient energy to transport them. Sediments are deposited layer upon layer, horizontally – Sorting: the process by which sediments of similar size are naturally segregated during transport and deposition according to the velocity and transporting medium.  Compaction and Cementation: As sedimentation continues, the overburden pressure on the earlier deposited sediments increases. They are compacted, reducing the available pore space and expelling much of the pore-water as a result. Dissolved minerals eg. Calcite, Silica, Hermatite, in the ground water precipitate (crystallize) from water in the pore spaces forming mineral crusts on the sedimentary grains, which cements the sediments together, thus forming a rock. Sedimentary Structures Bedding or Stratification: Bedding is the arrangement of sedimentary rocks in beds or layers of varying thickness and character. Stratification may range from a bed thickness of many meters down to fine millimeter-size laminations  Cross-stratification: The internal stratification within a layer bed can be parallel or cross- stratified. Cross- stratification is layering within a stratum at an angle to the main bedding plane. This is caused by ripples, sand  Ripple Marks: Ripple marks are caused by water flowing over loose sediment which creates bed forms by moving sediment with the flow  Mudcracks: Sedimentary structures formed as muddy sediment dries and contracts #dauntlessnattie  Fossil structures: These include preserved portions of the bodies of the organism like skeletal fragments or plant roots, or trace fossils which are impressions of the life and activities of pre-exsting organisms, eg burrows, footprints, leaf impresssions, etc.