KOKO: Keep on Keeping On 🙂
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INTRODUCTION TO GEOLOGY
Introduction to Geology
- Geology as a Discipline
- the relevance of time
- the issue of scale
- the complexity of replicating natural systems and phenomena in a laboratory
- Definition of Geology
- the study of Earth, its origin and history, the processes that shapes it, and the resources that could be obtained from it
- Branches of Geology
- Historical: “origin and history”
- Physical: “processes and resources”; deals with energy, minerals, metals, and environment
- Geologic Theories
- Uniformitarianism
- proposed by James Hutton (Father of Modern Geology)
- the Earth’s features are mostly accounted for by gradual, small-scale processes that occurred over long periods of time
- “the present is key to the past”
- Catastrophism
- proposed by Georges Cuvier
- the Earth’s features are mostly accounted for by violent, large-scale events that occurred in a relatively short amount of time
- Uniformitarianism
The Planet Earth
- Origin of the Universe
- The Big Bang Theory:
- appearance of all matter and energy in an instance
- the universe was in a hot dense state (unstable) then a sudden inflation happened about 15 – 20 billion year ago
- proposed by Georges Lemaitre
- evidences include: Hubble’s Law and Redshift (galaxies moving further away), abundance of Hydrogen and Helium (basic elements), and Remnant Heat (by Arno Penzias and Robert Wilson via the Cosmic Microwave Background Radiation)
- The Nebular Hypothesis:
- the solar system originated from a single rotating cloud of gas and dust starting 4.6billion years ago, which contracted due to gravity and was triggered, probably, by a supernova
- proposed by Immanuel Kant and Pierre Simon de Laplace
- the Earth was brought together by gravity (accretion), was heated (heating) and was segregated into layers while cooling (differentiation)
- differentiation: the denser elements sank while the lighter ones float to the surface which caused the (1) formation of the atmosphere (2) formation of oceans (3) life
- The Big Bang Theory:
- The Solar System
- Sun: made up of hydrogen, where the most of the mass of the nebula got concentrated
- Planets:
- Terrestrial Planets:
- Mercury, Venus, Earth, Mars
- within the asteroid belt, nearest the sun
- rocky composition: silicate rocks and metals (Si, Fe, O)
- Jovian Planets (giant planets):
- Jupiter, Saturn, Uranus, Neptune
- outside the asteroid belt, far from the sun
- gaseous and liquid form, gassy and icy (lacks solid surfaces)
- composed of light elements (H, He, Ar, C, O, NI)
- used to include Pluto (a dwarf planet)
- Terrestrial Planets:
- Isostasy
- “same standing”, concerned with the buoyancy of the blocks of the Earth’s crust as they rest on the mantle
- Theories
- Pratt’s Theory
- elevation is inversely proportional to density
- lighter or less dense materials will float higher
- heavier or denser materials will sink
- Airy’s Theory
- elevation is proportional to the depth of the underlying root
- mountains have roots which extend down into the mantle
- Pratt’s Theory
- Earth’s Vital Statistics
- equatorial radius and circumference: 6378 km, 40 076 km
- polar radius and circumference: 6357 km, 40 008 km
- volume: 260 000 000 000 cu. miles
- density: 5.52 g/cm3
- shape: oblate spheroid (flattened at the poles, bulging at the center)
- chemical composition (by mass): 34.6% Iron, 28.5% Oxygen, 15.2% Silicon, 12.7% Magnesium
- Earth’s External Features
- Continents:
- mountains, mountain ranges, mountain belts
- Oceans
- ocean basins, continental shelf, slope and rise, mid-ocean ridge, trench, transform fault, guyot, seamount
- Continents:
- Earth’s Internal Structure
- based on chemical composition
- Crust:
- Continental Crust: granitic composition, 20 – 60 km thick, 2.7g/cm3
- Oceanic Crust: basaltic composition, 3 – 15 km thick, approximately 3.0g/cm3
- Mantle: composed of iron and magnesium, approximately 2900 km thick,
- Core: composed of iron and some nickel
- Crust:
- based on physical composition
- Lithosphere: solid and rigid
- Upper Crust: brittle, 4 – 15 km depth
- Lower Crust and Upper Mantle: ductile, 15 – 100 or 200 km depth
- Asthenosphere: solid but flows, weak sphere, located beneath the lithosphere and within the upper mantle
- Mesosphere: solid and rigid, rocky layer
- Outer Core: liquid, 2270 km thick
- Inner Core: solid, 1216 km radius
- Lithosphere: solid and rigid
- Discontinuities
- Mohorovicic (Moho): between the crust and mantle
- Gutenberg: between the core and the mantle
- Lehmann: between the outer core and inner core
- based on chemical composition
Plate Tectonics
- Plate Tectonics
- the unifying theory of geology (included theories: Continental Drift, Seafloor Spreading, Paleomagnetism)
- the lithosphere is made up of moderately rigid plates (7 major plates + 7 smaller plates)
- evidences include: hotspots (relatively small, long-lasting and hot regions which exists below the plate, traces the directions of plate motion), GPS (global positioning system)
- Continental Drift Theory
- proposed by Alfred Wegener and was expressed in his book “The Origins of Continents and Oceans” (1915)
- continents are moving relative to each other (there was once a supercontinent, Pangaea, which broke up to Gondwanaland and Laurasia)
- evidences include: jigsaw puzzle fit of S. America and Africa, fossils spread over certain areas, matching mountain belts, similar rock types and ages, and paleoclimatic evidences
- Seafloor Spreading
- proposed by Harry Hess during 1960 through extensive mapping of the ocean floor
- mid-ocean ridges: where new materials are formed
- the younger rocks are near the mid-oceanic ridges
- Paleomagnetism
- Behavior: magnetic mineral rocks align themselves to the existing magnetic field at the time they were formed
Geomagnetic Reversals:- provides us a record of the direction and distance to the magnetic poles at the time a rock wa magnetized
- rocks formed at the same time would have same record of magnetic field
- Earth periodically reverses polarity
- Polar Wandering
- if the poles are relatively fixed, than the continents were to ones that probably moved:
- Behavior: magnetic mineral rocks align themselves to the existing magnetic field at the time they were formed
- Plate Boundaries
- Convergent
- oceanic → continental forms subduction zones and volcanic arcs
- continental → continental forms mountain ranges
- oceanic → oceanic forms island volcanic arcs and volcanic arcs from the bottom of the sea
- Divergent: where plates are being pulled away from each other
- Transform: where plates slide past each other
- **Wilson Cycle: (1) continents break apart (2) oceans fill the gap (3) continents closes back (4) repeat numbers 1 – 3
- Convergent
- Driving Mechanisms
- Convection Currents
- two-layer convection (separated at 660 km/ upper mantle)
- whole-mantle convection
- Slab Pull
- Ridge Push
- Convection Currents
- Philippine Setting
- Manila Trench: top-left side
- Sulu-Negros Trench: left side
- Cotabato Trench: bottom-left
- East Luzon Trough: top-right
- Philippine Trench: right side
MINERALS
Minerals
- Minerals (NIHDOS)
- Naturally occurring
- Inorganic
- Homogeneous
- Definite chemical composition
- Ordered structure
- Solid
- Physical Properties
- Color: caused by the absorption or reflection of various light wavelengths, may be caused of impurities and therefore not a good diagnostic property
- streak: color of the powdered form of minerals (metals → dark colored), not always identical to the color of the mineral
- hardness: resistance of the mineral to abrasion or scratching
- talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, diamond
- common: fingernail (2.5), copper penny (3.5), wire nail (4.5), knife (5.1), glass (5.5), streak plate (6.5)
- luster: ability of minerals to reflect light
- metallic, submetallic, nonmetal (pearly, waxy, earthy, vitreous, etc)
- cleavage: tendency of a mineral to break in particular directions due to zones of weakness in the crystal structure (fractures occur if bond strength is equal in all directions), parallel repeating planes
- crystal habit and crystal form: shapes and aggregates that a certain mineral is likely to form
- specific gravity: ratio of the density of the mineral to the density of water
- others: magnetism, fluorescence, reaction to chemicals, taste, odor
- Classifying Minerals
- composition: single element, 2 elements or greater than 2 elements
- crystal structure:
- Silicate: largest group in the crust, coposed of silica tet
- Nesosilicate (“islands”): isolated silicate tetrahedra
- Sorosilicate (“group”): double-island silicate tetrahedra
- Inosilicate (“chain”): parallel single chains of silicate tetrahedra
- Cyclosilicate (“ring”): isolated rings of silicate tetrahedra
- Phyllosilicate (“sheet”): parallel sheets of silicate tetrahedra
- Non-Silicate
- native metals: single element
- oxides: oxygen + metal
- sulfides: metal + sulfur (no oxygen); opaque with distinct colors
- sulfates: metal(s) + sulfate (SO4)
- carbonates: metal(s) + carbonate (CO3)
- phosphates: metal(s) + phosphate (PO4)
- halides: metal(s) + halogen element (Cl, F, I)
- hydroxides: metal(s) + hydroxyl (OH)
- Silicate: largest group in the crust, coposed of silica tet
- **Polymorphism: the ability of a specific chemical substance to crystallize in more than one configuration due to changes in temperature, pressure or both
- Most…
- Common Rock-Forming Minerals: olivine, pyroxene, amphibole, mica, feldspars, quartz, calcite, clay
- Abundant elements in the Crust: Oxygen (46.6), Silicon (27.7), Aluminum (8.1), Iron (5.0), Calcium (3.6), Sodium (2.8), Potassium (2.6), Magnesium (2.1)
- Rocks
- naturally occurring aggregate of one or more minerals
- may or may not contain mineraloids (amorphous, naturally occurring and inorganic material), natural glass and organic matter
- types: igneous, sedimentary, metamorphic
- Rock Cycle
IGNEOUS ROCKS
Igneous Rocks
- Magma
- molten material that contain suspended crystals and dissolved volatiles that are composed of mobile ions abundant in the Earth’s crust
- Sources of Heat for melting in the Crust: original heat, radioactive decay, conduction, mantle plumes, frictional heat
- Magma Generation:
- role of heat → hotspots: generates basaltic magma, due to geothermal gradient
- role of pressure → mid-oceanic ridges: generates basaltic magma, pressure is proportional to temperature, low pressure causes low melting temperature (decompression melting)
- role of volatiles → subduction zones: volatile amount is indirectly proportional to temperature, volatiles → dissolved gases
- Classification or Description of Magma
- chemical composition
- felsic, silicic, acidic: continental (x > than 63% SiO2)
- intermediate: continental ( 52% < x < 63% SiO2)
- mafic or basic: oceanic ( 45% < x < 52% SiO2)
- ultramafic or ultrabasic: upper mantle ( x < 45% SiO2)
- viscosity: property to resist flow
- high temperature, low viscosity (indirectly proportional)
- high SiO2, high viscosity (proportional)
- high dissolved H2O, low viscosity (indirectly proportional)
- density:
- mafic (oceanic): heavier, crystallizes at around 1000 – 1200oC
- felsic (continental): lighter, crystallizes at around 600oC
- chemical composition
- Types of Magma
- Felsic, Rhyolitic, Silicic: high SiO2, high viscosity, high amount of contained gases
- Intermediate: intermediate SiO2, intermediate viscosity, intermediate amount of contained gases
- Mafic, Basaltic: low SiO2, low viscosity, low amount of contained gases
- Bowen’s Reaction Series
- Igneous Rock Types:
- extrusive/ volcanic rocks: rocks formed at the surface (basalts, andesites, rhyolites), quick cooling, tiny crystals
- intrusive/ plutonic rocks: rocks that crystallized while underneath the surface (gabbro, diorite, granite); slow cooling, large-crystals
- Intrusive Bodies:
- batholith:
- laccolith: blister-shaped sill
- stock: small discordant pluton
- dike: tabular body cutting across beddings
- sill: concordant tabular body
- volcanic pipe
- Classification of Igneous Rocks:
- Texture/ Crystal Size:
- Aphanitic: very fine-grained
- Phaneritic: coarse-grained
- Porphyritic: larger crystals (phenocrysts) embedded in smaller crystals (groundmass), may be due to two or more cooling rates
- Others: vesicular, glassy, pegmatitic, pyroclastic
- Shape of Crystal Faces:
- Euhedral: well-defined (due to slow cooling)
- Subhedral: intermediate
- Anhedral: no well-formed faces
- Mineral Composition or Color Index:
- orthoclase + quartz + muscovite = rhyolite (extrusive), granite (intrusive), acidic composition and felsic color
- sodium-rich plagioclase + amphibole + biotite = andesite (extrusive), quartz diorite (intrusive), intermediate composition and color
- intermediate plagioclase + amphibole + pyroxene = basalt (extrusive), gabbro (intrusive), basic composition and mafic color
- olivine + pyroxene + calcium-rich plagioclase = komatite (extrusive), peridotite (intrusive), ultrabasic composition and ultramafic color
- Texture/ Crystal Size:
- Pyroclastics: volcanic ejecta or pyroclasts or tephra
- ash: less than 2mm in diameter
- lapilli: 2 – 64 mm in diameter
- block or bomb: greater than 64 mm in diameter
- Resources from Igneous Rocks:
- aggregates
- lahar and tuff
- basalt and andesite
- aggregates + cement = concrete
- dimension stones: basalt, granite, gabbro, diorite
- sulfides : important source of metals
- Volcanic Massive Sulfides (VMS):
- precipitated within a fumarole field or a black smoker
- Cu, Zn, Pb, Au, Ag, Co, Sn, Ba, S, Se, Mn, Cd, In, Bi, Te, Ga, and Ge as mining by-products
- aggregates
Volcanism
- Volcano
- an opening or vent where magma or gases are released
- a mountainous accumulation of materials resulting from successive eruptions of lava from a central vent
- erupts due to (1) influx of magma, (2) melting of surrounding rock, (3) exsolution of gases, and (4) contact with water
- usually found at the Pacific Ring of Fire, hotspots, spreading centers (due to decompression melting) and subduction zones
- magma: hot fluid or semifluid material below or within the earth’s crust from which lava and other igneous rock is formed by cooling
- Types of Volcanoes:
- Shield Volcanoes
- have gentle slopes and big craters (resembles a lying Roman shield)
- made up of successive solid lava flows
- have relatively quiet eruptions (fluid basaltic lava)
- Cinder Volcanoes
- also called “tephra cones”
- tephra: solid material ejected into the air a during volcanic eruption
- have steep slopes
- relatively small volcanoes
- made up of pyroclastics/ cinders (no lava)
- have relatively explosive eruptions (pyroclastics)
- Composite Volcanoes
- have gentle slopes near the base and steep slopes near the crater
- also known as the “strato-volcano”
- a hybrid of shield and cinder volcanoes
- most beautiful and well-formed volcanoes
- made up of layers of solid lava flows mixed with layers of volcanic rocks (cinders and volcanic ashes)
- have relatively explosive eruptions (fluid lava and pyroclastics)
- Shield Volcanoes
- Types of Volcanic Landforms:
- Fissure Volcano
- a long crack in the earth’s surface through which magma erupts
- flat on the land surface (making it look like a simple crack)
- produce lava eruptions (not explosive)
- Lava Dome
- has a steep, convex slope due to thick and fast-cooling lava
- relatively small bulbous masses formed from viscous lava (intermediate and felsic: andesite and rhyolite)
- produce dangerous explosive eruptions (usually Pelean)
- Caldera Volcano
- caldera: larger circular or elliptical depressions in a volcano as a result of explosions emitting gases and cinders (larger craters)
- formed as a result of the collapse of a volcanic structure due to evacuation of the underlying magmas
- lakes are often formed in a caldera due to the closed depression
- Fissure Volcano
- Types of Volcanic Eruptions:
- Hawaiian Eruption
- effusive and relatively safe eruptions of fluid lava (mafic: basalt)
- characterised by lava fountains, fissure eruptions and lava flows
- Strombolian Eruption
- short-lived explosive outbursts of pasty lava (looks like fireworks)
- ejection of fluid lava (mafic: basalt or basaltic andesite) reaches tens to hundreds of meters in the air
- created due to large gas bubbles at the vent of the volcano
- no eruption column
- Vulcanian Eruption
- high-velocity ejection of bombs and blocks (“like cannon fire at irregular intervals” -Mercalli)
- short, violent and relatively small explosion of viscous magma (intermediate and felsic: andesite, dacite and rhyolite)
- produces tephra, ash clouds and pyroclastic density currents
- Plinian or Vesuvian Eruption
- extremely destructive, violent and large eruptive columns reaching heights of around 45km
- releases very viscous magmas (felsic: dacite and rhyolite), gases, ashes, scoria and lava bombs (that may reach miles from the volcano)
- eruptive column are mushroom-shaped (like a nuclear explosion)
- Pelean Eruption
- large amounts of gas, dust, ash and lava fragments are blown out of the volcano’s crater accompanied by massive pyroclastic flows
- violent eruptions of viscous lava (felsic – intermediate: rhyolite and andesite) and fast moving pyroclastic flows (tends to form lava domes)
- ejection of large volumes of dust, ash, rock and gas
- Phreatic Eruption
- caused by water suddenly turning into steam due to heat of magma causing sudden increase in pressure
- an explosion of vapor and pyroclastics (no magma)
- Phreatomagmatic Eruption
- similar to phreatic eruption it is caused by magma and surface water interaction
- an explosion of vapor, pyroclastics and magma
- Hawaiian Eruption
- Lava (molten magma) Types
- Aa Lava
- composed of broken lava blocks and has a rubbly surface
- indicates a slow fluid flow of mafic magma
- Pahoehoe Lava
- smooth, billowy, undulating or ropy surface lava
- indicates low viscosity and fluid flow (mafic magma)
- Pillow Lava
- lava emerges from an underwater volcanic vent
- as soon as lava contacts the water, lava is cooled down and forms pillow-like rocks with pointed portions (points to the magma source)
- Aa Lava
SEDIMENTARY ROCKS
Sedimentary Rock Formation
- Weathering
- physical breakdown (disintegration) and chemical alteration (decomposition) of igneous or metamorphic rocks at or near the Earth’s surface
- leads to increase in surface area
- two types of weathering:
- Mechanical Weathering: physical breaking leading to increase in surface area; seen in cold climates, high altitudes and dry regions
- frost wedging: due to cycles of freezing and thawing of water inside a rock causing the rock to crack
- heating and cooling: due to expansion (heating) and contraction (cooling) causing rocks to crack since rocks are not good conductors of heat
- wetting and drying: due to swelling (wetting) and contracting (drying) of soil particles creating surface cracks or circular holes on soil
- organisms and biological weathering: due to flora and fauna digging up rocks for nutrients or protection causing rocks to weather
- unloading or unroofing: due to removing of thick layers resulting to pressure release
- abrasion: scraping of rock surface due to transport of rocks/ moving particles
- Chemical Weathering: always aims towards stability (from less stable to more stable); breaking components and altering internal structure; agents include water, chemicals dissolved in water and gases
- dissolution: solute (rock) and solvent (water) interaction
- hydrolysis: formation of hydroxides (-OH)
- acidification: due to hydrogen ions from water (from carbonic and organic acids)
- hydration: water added to a solid mineral resulting to a softer mineral
- oxidation and reduction
- ion exchange
- Differential Weathering: less stable rocks weather first
- Soil: a layer of weathered rocks and loose materials; composed of rock, air, water and organic materials
- O horizon: composed of leaf litter and humus (organic)
- A horizon: humus and mineral particles
- E horizon (eluviation): light colored, leaching layer (lost its minerals and clay due to water flow)
- B horizon (accumul) contains clay and mineral deposits from the eluviation horizon
- C horizon: slightly broken bedrock
- R horizon: unweathered rock layer
- Soil: a layer of weathered rocks and loose materials; composed of rock, air, water and organic materials
- Mechanical Weathering: physical breaking leading to increase in surface area; seen in cold climates, high altitudes and dry regions
- Factors Affecting Weathering:
- Climate: precipitation and temperature
- Relief: affects the amount of rock exposure and period of exposure (steep slopes means less rock exposure and less weathering)
- Rock Type: due to the Goldich Stability Series and joints (planar cracks); fine-grained rocks are chemically more ready to decompose
- ** Goldich Stability Series: high temperature and pressure forming minerals are less stable (an upside down Bowen’s Reaction Series)
- Erosion
- meant to “eat away”
- movement of rock or soil
- agents include: gravity, water, ice, wind and organisms (anthropogenic)
- prevention includes cover management and seawalls
- Transport
- competence: biggest size an agent can transport
- capacity: minimum load an agent can transport
- Transport Types:
- suspension
- saltation
- traction
- creep/ rolling
- grain size:
- coarser grain size needs high energy for transport
- finer grain size needs low energy for transport
- sorting: variation or similarities in grain sizes
- poorly sorted grains (greatly varied grain sizes) indicate short distance of transport and inconstant energy for transport
- moderately sorted grains (between similar and varied grain sizes) indicate average distance of transport and average constance of energy for transport
- well-sorted grains (greatly similar grain sizes) indicate transportation long distance of transport and constant energy for transport
- grain shape: roundness (or angularity) and sphericity (closeness of grain size to a sphere)
- angular or non-spherical grains indicate near the source transportation
- sub-angular or subrounded grains indicate moderately near or far (respectively) from the source transportation
- well-rounded or spherical grains indicate far from the source transportation
- Deposition
- happens when transported materials settles or rests
- happens when the agent loses energy for transport
- Diagenesis
- process in which the sediments are lithified into a rock
- has two stages: early (shallow burial) stage, and late (deep burial and uplift) stage
- Diagenetic Processes:
- compaction: due to pressure increase when the sediments are buried, sediment grains are squeezed and compacted
- cementation: precipitation of mineral components (like silicates, carbonates and iron oxides) in pore spaces that binds and joins the sediments
- recrystallization of unstable elements: existing mineral in a rock changes in volume or size
- dissolution and replacement: opposite of cementation wherein silicate or carbonate minerals dissolve under certain conditions and are replaced by carbonate or silicate minerals respectively
- bioturbation
Sedimentary Structures
- Definition and Characteristics:
- formed right after deposition
- reflects the different sedimentary processes undergone by a sediment
- Sedimentary Structure Types:
- Stratification
- layers of different compositions and grain sizes (sorting) or color
- different sediment layers are stacked over each other
- caused by changes in deposition processes
- Varves
- different colored layers of dark and light due to difference in oxidation
- usually found in lacustrine environments
- light: due to oxidation during summer (abundant sunlight therefore abundant oxygen)
- dark: due to reduction during winter (less sunlight therefore less oxygen)
- Graded Bedding
- normal graded bedding: coarser rocks at the bottom, finer rocks at the top (a good indicator on identifying the top bedding)
- reverse graded bedding: finer rocks at the bottom, coarser rocks at the top
- caused by turbidity currents
- Tilted Bedding
- a tilted stratified bedding
- caused by plate tectonic activity
- Cross Bedding
- formed in an angle at a main bedding plane
- caused by currents that flow over the sediment surface and therefore indicates flow direction
- inclination to the left indicates flow direction to the right
- inclination to the right indicates flow direction to the left
- Bioturbation
- presence of trace-fossils in a sedimentary rock
- caused by the disturbance of sediment by organisms that were once alive
- Mud Cracks
- formed on top of a bedding and is therefore a good indicator on identifying the top bedding
- caused by wet and dry seasons
- Ripple Marks
- formed on top of a bedding and is therefore a good indicator on identifying the top bedding
- stoss (longer; going to the crest) and lee (shorter; going to the trough) can be used as indicator of flow direction
- caused by flowing water or wave action on a smaller scale
- current produces asymmetrical ripples wherein flow direction of the current can be identified
- wave produces are symmetrical and can branch in a “tuning-fork” fashion
- Raindrop Marks
- formed on top of a bedding and is therefore a good indicator on identifying the top bedding
- caused by raindrops
- Stratification
- Sedimentary Products and Resources
- sand and gravel
- pure clays
- fossil fuels
- food additives (salt)
- building stones
- gas deposits
- ** Malampaya Palawan → sedimentary basin in the Philippines (rich in gas deposits)
Sedimentary Rock Classification
- Classified through:
- Texture: the physical properties like roundness, sphericity, size, sorting and color
- Composition: the chemical composition and mineral assemblage
- Classification of Sedimentary Rocks
- Siliciclastic/ Clastic/ Detritus/ Detrital Rocks: formed through cementation of rock fragments; composed of the clast (large materials), matrix (finer grains) and cement (binding material)
- Breccias: rocks with angular gravel-sized grains
- Conglomerates: rocks with well-rounded gravel-sized grains
- Sandstones: rocks with sand-sized grains (may be identified through the QFL diagram)
- Quartz Sandstone: quartz-abundant sandstone
- Arkosic Sandstone: feldspar-abundant sandstone
- Lithic Sandstone: rock fragments-abundant sandstone
- Arenites: “true sandstones” (either 100% quartz, feldspar or rock)
- Siltstones/ Claystones/ Mudstones: rocks with silt-sized, clay-sized and mix of silt and clay-sized grains respectively
- Shale: fissile (breakable along cleavage planes) siltstones and claystones
- Chemical Rocks: formed through the precipitation of ions to form minerals
- Carbonates (Chemical Limestones): mainly composed of calcium carbonate (CaCO3) due to calcite cementation and therefore effervesces with acid (HCl)
- crystalline limestone: made up of coarse-grained CaCO3 crystals
- micrites: made up of fine-grained CaCO3 crystals
- oolitic limestone: composed of oolites (spherical grains) and CaCO3
- Dolostone: magnesium-rich limestone (CaMg(CO3) which effervesces with acid when in its powdered form; formed via the replacement by Mg
- Rock Salt: formed by the precipitation of halite (NaCl) from ocean water
- Rock Gypsum: formed by the precipitation of gypsum (CaSO4.H2O) from ocean water
- Ironstone: a dark-colored amorphous or cryptocrystalline rock composed of iron-bearing minerals (hematite and limonite)
- Carbonates (Chemical Limestones): mainly composed of calcium carbonate (CaCO3) due to calcite cementation and therefore effervesces with acid (HCl)
- Biochemical Rocks: formed via recrystallization of organic elements
- Carbonates (Skeletal Limestones): carbonate rocks with shell fragments cemented with calcite which effervesces with acid (HCl)
- calcirudite/ calcarenite/ calcisiltite: carbonate biochemical rocks with gravel-sized, sand-sized and silt-sized grains respectively
- coquina: composed mainly of broken shells
- micrite: clay-sized carbonate rock
- chalk: porous carbonate rock with silt and clay-sized grains
- Chert: multi-colored siliceous rocks which are formed due to the recrystallization of dissolved skeletons of siliceous organisms (eg. glass sponges, radiolarians, diatoms, silicoflagellates); can also be biochemical due to its origin
- Coal: composed of plant remains and forms in the presence of clastic rocks
- peat: lowest grade of coal
- lignite
- bituminous coal
- anthracite: highest grade of coal; safest and most environment friendly
- Carbonates (Skeletal Limestones): carbonate rocks with shell fragments cemented with calcite which effervesces with acid (HCl)
- Siliciclastic/ Clastic/ Detritus/ Detrital Rocks: formed through cementation of rock fragments; composed of the clast (large materials), matrix (finer grains) and cement (binding material)
Sedimentary Environments
- Definition and Characteristics:
- always distinct from adjacent sedimentary environments
- defined by the flora and fauna, geology, geomorphology, climate, weather and temperature
- if subaqueous, it is defined by the depth salinity and current system of the water
- sedimentary facies:
- mass of sedimentary rock which can be defined and distinguished from others
- characterised by geometry, lithology, fossils, paleocurrents and sedimentary structures
- three types: terrestrial, transitional and marine environments
- Methods of Diagnosis
- Geometry: a function of pre-depositional topography, geomorphology and its post-depositional history
- Lithology (rock type): parameters easily observed and has environmental significance (grain size, sorting, shape and texture)
- Sedimentary Structures: important indicators of sedimentary environment
- Fossils: geologists assume that the fossil lived where it was buried, the habitat of the fossil can be deduced either from its morphology or from studying its living ascendants; trace fossils: occur “in situ” or in place
- Terrestrial Environments
- Alluvial
- contain rocks with coarse particles (high energy transport) and poor sorting
- deposited by floods, stream flows, debris flows or mudflows
- usually found in tectonically active regions or near the base of a mountain
- alluvial fan: a cone-shaped deposit of coarse stream sediment, sheet-flood deposits and debris flows
- alluvial fan parts: apex, scarps and toe
- alluvium: very young sediments that accumulate at the alluvial fan (nearer to the base of the fan = older sediment)
- Fluvial (rivers)
- Braided
- young (near the source), wide and shallow river
- has high gradient or slope, multiple channels (caused by bar deposits) and low sinuosity
- contain rocks with coarse particles (high energy)
- Meandering
- older river than the braided rivers and is therefore farther from the source
- has low gradient (flat) and a single channel
- through time the river shifts in location leaving oxbow lakes (cut-off lakes from the river by bar deposits) and meander scars (oxbow lakes with no water)
- deposition happens on the inner circle of a meandered part while erosion happens on the outer circle
- Straight
- oldest river and is therefore farthest from the source
- thalweg: the deepest part of a river
- point bar deposits: islands of deposit
- laminar vs. turbulent rivers:
- laminar: parallel streamlines and are harder to cross (more dangerous)
- turbulent: intersecting and swirling streamlines due to rocks along the river’s way
- River Drainage Patterns:
- dendritic: looks like tree branches and are formed in flat and uniform bedrock
- radial: formed due to a circular elevation or depression (high grounds to low grounds)
- rectangular: rivers with right-angled bends that are formed on faulted or jointed bedrocks
- trellis: parallel with vine-looking drainage that are formed due to folded topography
- Braided
- Lacustrine (lakes)
- landlocked body of standing non-marine water that are circular or elongated in plan view
- fault graben or basins with internal drainage or limited flows
- has rocks with finer grains (low energy) at the topological center and coarser grains (high energy) at the edges
- exhibits coarsening upwards (shallower waters will have coarser grains) until there comes a time that the lake is dried out
- due to fine grains, fossils are well-preserved
- Paludal (swamps and marshes)
- heavily vegetated due to high amount of biological activity
- rocks has fine grains (low energy) and high organic content
- Others: eolian (desert), glacial (glacier)
- Alluvial
- Transitional Environments
- Delta
- location where the river meets the ocean therefore the energy is low to moderate (contain fine-grained rocks)
- parts: plane, front and prodelta
- types of delta:
- river-dominated: has moderate sediment supply due to the river
- tide-dominated: has less deposited sediments (no bars) due to tides
- wave-dominated: the sediment supply are deposited at the sides due to the waves (looks like a duck-foot)
- Beach
- shore of a body of water formed and washed by waves and tides
- has rocks with sand-sized or pebble-sized grains (high energy) and are well-sorted
- white sand indicates that the beach is near a coral reef while dark sand indicates that the beach is near a volcanic
- sediments are moved by:
- waves: a body of water in an arched form breaking on the shore
- longshore drifts: movement of sediments along the beach by angled swash and backswash of waves
- longshore currents: current that moves parallel to the shore
- types of beach:
- spit: a narrow coastal land formation that is tied to the coast at one end; a long ridge of sand deposited by longshore currents and drifts
- tombolo: sand/ gravel way that connects a mini-island to the mainland
- Lagoon
- an area between barrier islands and mainland with brackish and shallow water
- contain fine-grained rocks (low energy)
- separated from terrestrial environment by reefs, barrier islands, sandbanks and spits
- Tidal Flats
- marshy or barren tract of land that is alternately covered and uncovered by tied
- contain fine-grained rocks (low energy)
- three zones: supratidal, intertidal, subtidal
- Delta
- Marine Environments
- Coral Reefs
- wave-resistant, mound-like structure that builds up on continental shelves
- composed of carbonate structures due to carbonate secreting organisms
- formed at warm, shallow and sunlit environment
- types:
- fringing:
- barrier:
- atoll:
- Continental Margin
- three parts:
- Continental Shelf: nearly flat, gently sloping edge of the continent that extends under the ocean where coarse-grains are washed up to the continent leaving fine-grains at the shelves
- Continental Slope: a steeply sloping edge of shelf that extends down to the ocean flow with fine grained sediments (low energy)
- Continental Rise: a fan shaped deposit of sediment at the base of the continental slope with sediments of sand, silts and clay (low energy)
- three parts:
- Abyssal Plain
- the flat-region of the ocean floor that is covered with pelagic mud
- contain rocks of fine-grained sediments (eg. limestone and chert) and microscopic shells of marine plankton (low energy)
- abundant in calcareous and siliceous deposits
- Carbonate Compensation Depth (CCD)
- a barrier between the depth wherein carbonates are precipitated or dissolved
- above the CCD is where carbonates are precipitated and silicates are dissolved
- below the CCD is where carbonates are dissolved and silicates are precipitated
- Coral Reefs
Groundwater
- Definition
- freshwater located underground that is stored and transmitted through cracks and spaces of sediments, sands and rocks
- water table: the upper boundary of groundwater and the barrier between the vadose and phreatic zones
- vadose/ unsaturated zones: little water (soil moisture) are found in the open spaces
- phreatic/ saturated zones: abundant water fills the open spaces:
- porosity and permeability
- porosity: the volume of water held by rocks in its voids and spaces that is affected by the sorting, grain size and shape (well-rounded, well-sorted, and coarse-grained rocks have high porosity)
- permeability: the ability of a rock to transmit fluids due to the interconnection of voids in the material (large spaces allow water to pass through)
- Transporting Groundwater
- Aquifer: stores and transmits sufficient amount of water
- Confining Units
- aquitard: stores and transmits in low amounts of water
- aquiclude: stores but does not transmit water
- aquifuge: does not store nor transmit water
- Types of Aquifers
- Unconfined Aquifer: open to receive water from the surface
- Perched Aquifer: located a a vadose zone leading to discontinuous permeability (ephemeral)
- Confined Aquifer: due to pressure a piezometric water level is formed; created due to confining layers top and under the aquifer
- Springs: found at the surface and water table intersection where water flows out of the ground
- Artesian Wells: a confined aquifer where natural pressure causes water to just flow out of the well
- Geologic Activity → Caverns
- formed due to acidic water “eating away” limestones
- can be found through Karst topography (sinkholes and disappearing streams)
- has speleothems: stalactites and stalagmites
- Groundwater-Related Problems
- cone of depression: a depression in water levels due to groundwater pumping
- pollution and salt water intrusion
- CAMANAVA “enhanced” flooding: excessive groundwater extraction through compaction of aquifers, land subsidence and excessive floods
- Conservation of Water
- avoid taking showers
- avoid doing laundry on a daily basis
- stop buying bottled water
- collect rainwater
- Sources of Groundwater
- meteoric water: water from atmospheric precipitation such as rain and snow
- connate water
- fossil water that is entrapped in sediments during deposition
- has two types: syngenetic (trapped in the sediments containing it) and epigenetic (entered from basins into rocks)
- juvenile or magmatic water
- water, called virgin water, was formed due to the cooling of magma where water vapor is separated out from the magma
Mass Wasting
- Definition
- mass movement or slope movement
- downslope movement of rock, regolith and soil due to gravity
- mass-wasting processes may be sudden or slow but often leads to disastrous results
- Factors
- Slope: increasing the slope will create more mass wasting due to instability of rocks and soil particles
- Water: water washes away soil particles and therefore more water will create more mass wasting
- Soil Cover: a decrease on vegetation will create more mass wasting since vegetation stabilizes the soil particles on the surface and anchors the soil particles under the surface due to the root system
- Geologic Features:
- Lithology: based on the degree of weathering, type of material and degree of movement of the rocks
- Types of Mass Wasting
- Slope Failures
- Sediment Flow
- Type of Mass Wasting Movements
- Based on Rate of Movement
- debris avalanche: very rapid due to air trapped under rocks
- mudflow: rapid and highly fluid due to combination of mud and water
- rock fall: rapid dislodging of rock from a steep slope
- rock/ debris slides: rapid rock movement across a plane (translational slide)
- slumps: rapid rock movement along a curved surface (rotational slide)
- creep: a gradual and very slow rock movement that is caused by expansion and contraction of the surface sediments and gravity
- Based on Material Involved: (1) debris, (2) mud, (3) earth, (4) rock
- Based on Material Movement: (1) falls, (2) slides, (3) flows
- Based on Rate of Movement
- Hazards include typhoons, landslides and earthquakes
- Mitigation
- through hard and soft engineering
- Hard Engineering
- through providing technology and techniques
- use of hazard maps, chicken wires, weep holes, retaining walls, rock barriers, benching
- Soft Engineering
- through providing information
- through information and education campaigns, monitoring and early warning systems
- Hard Engineering
- through hard and soft engineering
METAMORPHIC ROCKS
Metamorphic Rock Formation
- Metamorphism
- change undergone by an existing rock in the solid state to another rock
- a change in structure or constitution of a rock due to natural agencies (pressure and head) especially when the rock becomes harder and more completely crystalline
- Agents of Metamorphism:
- Heat
- from (1) geothermal gradient (temperature increases with depth), (2) large bodies of molten rock or intrusive bodies
- provides the energy to drive chemical reactions that results in recrystallization
- may convert the rock minerals into a different mineral with more stable atomic structures at the specific temperature gradient (recrystallization)
- Pressure
- confining pressure: equal stress from all sides due to overlying rocks in the crust of the earth (due to burial)
- differential stress (compressional stress):unequal stress in different directions due to converging plates
- pressure increases with depth
- rocks become denser and mineral grains become realigned, flattened out and elongated
- if pressure is combined with heat, the rock flows instead of breaking
- Chemically Active Fluids
- changes the crystallization and composition in rock due to deposition/ recrystallization of dissolved minerals and dissolving the existing minerals
- due to (1) water trapped from the rock, (2) water trapped from the micas or amphiboles, (3) due to water from magmatic bodies
- Heat
Metamorphic Rock Types
- Contact Metamorphism
- happens when magma invades pre-existing rocks (magmatic intrusive bodies)
- the zone of alteration is called metamorphic or contact aureole
- takes place at shallow depths and low pressures but at high temperatures
- produces non-foliated and fine-grained metamorphic rocks (eg. hornfels, marble)
- closer to the magmatic body meant a higher metamorphic grade
- Regional Metamorphism
- takes place at considerable depths over an extensive area
- takes place at high pressure and low to intermediate temperature locations
- accompanied by deformation due to differential stress (mountain building)
- produces foliated metamorphic rocks (eg. slate, phyllite, schist, gneiss)
- Hydrothermal Metamorphism
- takes place at high temperature and moderate pressure locations
- produces non-foliated chemically altered metamorphic due to hydrothermal fluids (hot, ion-rich water)
- Shock or Impact Metamorphism
- sudden impact of extraterrestrial bodies (such as meteorites and comets) or large volcanic explosions produces ultrahigh pressures
- produces rocks with minerals that are only stable at very high pressures
Metamorphic Rock Classification
- Texture
- the size, shape, relationships and arrangement of mineral grains
- foliation: any planar arrangement of minerals or structural features within a rock
- Types of Texture:
- Foliated Texture
- nearly parallel alignment of platy and/or elongated minerals
- compositional banding or layering
- slaty cleavage where rocks can be easily split into thin, tabular sheets
- developed in areas of directed or differential stress (regional and/or shock metamorphism)
- eg. slate, phyllite, schist, and gneiss
- Non-foliated Texture
- lacks foliation and usually develops in environments where deformation is minimal (contact and hydrothermal metamorphism)
- eg. marble, quartzite, hornfels, amphibolites, skarns, serpentinites
- Porphyroblastic Texture
- textures with large grains (porphyroblasts) surrounded by a fine-grained matrix
- Foliated Texture
- Protolith
- the original rock prior to metamorphism (parent-rock)
- the parent rocks of metamorphic rocks are more identifiable at lower grades
- as the grade of metamorphism increases, the original textures are replaced with metamorphic textures
- the protolith may be determined through identifying the bulk composition or mineralogy
- Mineralogy
- the mineral composition of the rocks
- some examples:
- pelitic rocks: abundant in clay minerals, micas, kyanite, sillimanite, andalusite and garnet (sedimentary rocks)
- quartzo-feldspathic rocks: abundant in quartz and feldspars (granitic rocks and arkosic sandstones)
- calcareous rocks: rocks that are calcium rich (carbonate rocks)
- basic rocks: abundant in biotite, chlorite, hornblende, plagioclase and epidote or low silica minerals (mafic igneous rocks like basalts and gabbros)
- magnesian rocks: magnesium-rich and iron-poor rocks, abundant in serpentinite, brucite, talc, dolomite and tremolite (ultramafic igneous rocks like peridotite, dunite, and pyroxenite)
- ferruginous rocks: iron-rich and magnesium-poor rocks (cherts and ironstones)
- manganiferous rocks: manganese-rich rocks
Rock Deformation
- Stress vs. Strain
- Strain: change in size, shape or both as a result of stress
- Stress: a force acting on a material or rock that produces a strain
- Types of Stress:
- uniform stress: equal stress from all directions
- differential stress: unequal stress from different directions
- compressional stress: rocks are squeezed or compressed together
- tensional stress: rocks are pulled apart
- shear stress: slippage and translation of rocks
- Stages of Deformation:
- Elastic
- temporary change in shape or size that is recovered when the deforming force is removed
- returns to original shape when stressed is removed (reversible)
- Ductile or Plastic
- permanent change in shape or size that is not recovered when the stress is removed (irreversible and permanent)
- occurs by the slippage of atoms or small groups of atoms past each other in the deforming material without loss of cohesion
- Brittle
- loss of cohesion of a body under the influence of deforming stress (permanent rock breaks or ruptures)
- usually occurs along sub-planar surfaces that separate zones of coherent material
- Elastic
- Ductile or Plastic Deformation
- Strike and Dip:
- strike: the intersection of the tilted bed and an imaginary horizontal bed
- dip: the angle between the horizontal bed and the tilted bed usually perpendicular to the strike
- Parts of a Fold:
- axial plane: the fold axis that divides the fold as symmetrical as possible
- fold axis: a line connecting all the points on the hinge (fold)
- limb: the sides of the fold
- Types of Fold:
- monocline: two limbs of the fold are still horizontal
- anticline: the rock was folded upwards and the two-limbs dip away from the hinge
- syncline: the rock was folded downwards and the two-limbs dip inward toward the hinge
- plunging fold: when the fold axis is not horizontal
- Other Types of Fold:
- symmetrical
- asymmetrical
- isoclinal
- overturned
- recumbent
- chevron
- dome
- basin
- Strike and Dip:
- Brittle Deformation
- Joint vs. Fault
- Joint:
- smaller compared to faults and can occur in almost all kinds of rock formation
- have very little to no movement since they do not completely separate rock formations
- formed when a rock is stretched to its breaking point
- Fault:
- bigger compared to joints and may extend up to miles on end
- prone to lateral movement caused by tectonic forces beneath the surface of the Earth
- may move upwards, downwards, and sideways (often the cause of earthquakes)
- Joint:
- Fault Types:
- dip-slip faults:
- faults that have an inclined fault plane
- parts:
- hanging wall: moving part of the fault
- footwall: stationary part of the fault
- movement:
- normal: hanging wall moves down relative to the footwall
- reverse: hanging wall moves up relative to the footwall
- thrust: hanging wall moves up relative to the footwall where the dip is less than 45o
- strike-slip faults:
- faults whose movement are horizontal
- movement:
- right-lateral movement: when facing towards the other side of the fault, the fault moves to the right
- left-lateral movement: when facing towards the other side of the fault, the fault moves to the left
- oblique-slip faults:
- faults whose movements have both a dip-slip and strike-slip component
- dip-slip faults:
- Joint vs. Fault
Earthquakes
- Earthquakes
- intense ground shaking caused by sudden release of energy
- occurs when the stress exceeds the strength of the rock, and the rock fractures along a fault releasing its stored energy as an earthquake
- can be generated by bomb blasts, volcanic eruptions and sudden slippage, along faults
- Elastic Rebound Theory
- tectonic earthquakes occur when strains in rock masses have accumulated to a point where the resulting stresses exceed the strength of the rocks and sudden fracturing results
S1. Original Position
S2. Build-up of Strain
S3. Rupture/ Slippage
S4. Release of Energy
- Kinds of Seismic Waves
- Body Waves: travels at the earth’s interior
- primary waves: emanates from the focus and travel in all directions through the body of the earth
- also known as compressional waves
- travels faster than the secondary waves
- consists of contraction and expansion movements
- travels through land and water
- the motion of the particles is parallel to the direction of the wave
- secondary waves:
- also known as shear waves
- travels slower than the P-waves
- can only travel through land
- transverse waves meaning the particles moves perpendicular to the direction of the wave
- primary waves: emanates from the focus and travel in all directions through the body of the earth
- Surface Waves: travels along paths that are nearly parallel to the surface
- rayleigh waves :
- causes the ground to shake in an elliptical motion (no transverse or perpendicular motion)
- moves like an ocean wave
- love waves:
- having a horizontal motion that is transverse (or perpendicular) to the direction the wave is travelling
- moves side to side
- rayleigh waves :
- Body Waves: travels at the earth’s interior
- Intensity vs. Magnitude
- Intensity:
- ground-shaking strength based on the amount of damage at a certain location
- measures the violence of seismic shaking over a single affected area (local)
- determined from the effects on people, human structures and natural environment
- uses the Mercalli Scale
- Magnitude:
- measures the energy released from the focus of the earthquake (logarithmic)
- measures the “size” or amplitude of the seismic waves generated by an earthquake source
- determined from the measurements on the seismographs
- uses the Richter Scale
- Intensity:
- Epicenter vs. Focus
- Epicenter: part of the earth’s surface that is directly above the earthquake’s origin (focus)
- Focus (or Hypocenter): the origin of the earthquake; deep seated rupture or source of earthquake
- **the focus may be on the epicenter
- Locating the Epicenter
S1. three seismic stations will detect the earthquake using the seismometer (graph of the vibrations is called the “seismogram”)
S2. the seismic station will measure the arrival interval and draw a circle with the radius as the approximate distance of the station from the epicenter
S3. the intersection of the three circles from the three different seismic station is where the epicenter is located
- Factors affecting the Damage on Structures
- wave amplitudes: high amplitudes results to high damage
- duration of vibration (wavelength and frequency)
- smaller buildings are more prone to damage in high frequencies or low wavelength earthquakes
- taller buildings are more prone to damage in low frequencies or high wavelength earthquakes
- nature of material upon which the structure rests
- finer grains are more prone to liquefaction of making the building sink
- coarser grains are tougher than the finer grains
- Short-Term Predictions
- observed patterns of recurrence (earthquake cycles)
- strange animal behaviors
- increase in seismic tremors or mini-earthquakes
- seismic gaps
- gas emissions
- electromagnetic signals
- Secondary Effects
- tsunamis
- landslides
- ground subsidence
- fire
HISTORICAL GEOLOGY
Fossils and Fossilization
- Historical Geology
- deals with the origin of Earth and its development through time
- strives to establish an orderly chronological arrangement of the historical changes and events on earth
- Fossils
- remains or traces of prehistoric life preserved in sedimentary rocks
- important time indicators and play a key role on correlation of rocks
- any evidence of a once-living organism
- remains of organisms (eg. bones and shells)
- Fossilization or Preservation Requirements
- rapid burial to prevent decomposition
- presence of protective cover or preserving medium (eg. amber)
- possession of hard parts (bones, etc) and durable tissues
- Index Fossils
- fossils that are widespread geographically
- fossils that occur in a certain range of rocks (lived during one specific time period)
- fossils that are easily recognizable
- usually used for correlation
- Uses of Fossils
- evolutionary traces
- reconstructing paleoclimates and paleoenvironments
- energy resource
Types of Fossilization
- Preservation of Unaltered Body Parts
- hard parts (shells, bones, teeth or pollen) preserved through encasement in asphalts (tar), peat and the durability of the hard parts themselves
- soft parts (tissues) preserved through mummification, freezing and encasement in amber (polymerization)
- Chemical Alteration of Hard Parts
- Carbonization: soft tissues are compressed and heated driving off all volatiles and leaving a carbon film
- Recrystallization: original structure is lost due to the rearrangement of the crystal lattice of the minerals (the composition remains the same) from one unstable lattice to another
- Replacement: original composition is lost due to the dissolution of the original minerals and deposition of a replacing mineral (usually due to groundwater)
- Permineralization: pore spaces within the fossils are filled with minerals from groundwater
- Petrification: an organic materials is converted into stone or any similar material
- Imprints in Sediments or Trace Fossils
- Mold: organism is buried then dissolves leaving a mold with the organism’s shape imprinted in the sediment
- Cast: filling of mold by other minerals or materials
- Borings and Burrows: holes in shells or wood or ground made by animals
- Coprolites: fossil excrement
- Gastroliths: stomach stones used for digestion
Relative Dating
- Relative Dating
- dating of rocks and rock units for fossils and correlation of different strata
- only able to find out if the strata is younger or older in relation to another strata (no absolute numerical age)
- needs knowledge of stratigraphic succession (the way rock strata are built up and changed by geologic processes)
- Principles of Stratigraphic Succession and Relative Dating
- Principle of Uniformitarianism
- “present is key to the past”
- former changes of the earth’s surface may be explained by reference to causes in operation
- Steno’s Laws
- Law of Superposition: the oldest layer of rocks is at the bottom and the youngest is at the top if the strata is undisturbed
- Law of Original Horizontality: due to flow and gravity, most layers (of sedimentary rocks) are deposited horizontally
- Law of Lateral Continuity: sediments would spread out until (1) they thin at the edge of a basin, (2) stop at a barrier, (3) grade into another type of sediment due to change in depositional environment
- Principle of Inclusion
- if an igneous rock or magmatic body included a sedimentary rock, then the igneous rock or magmatic body is younger than the sedimentary rock
- Principle of Faunal Succession
- fossil organisms succeed one another in definite and determinable order (a time period has its own fossil content) even at different locations
- Cross-Cutting Relationships
- igneous intrusions and faults existed after the deposition of the rocks
- Unconformity
- the surface between two rock layers
- gaps in the rock record
- a period of non-deposition
- hiatus: time not represented by the rock layers
- Principle of Uniformitarianism
- Types of Unconformity
- Angular Unconformity: tilted rocks are overlain by younger and more flat strata
- Disconformity: jagged layer of strata in between rock layers (a sign of erosion)
- Paraconformity: no observable characteristics but can be identified due to lack of fossil diagnosis of a certain period or time
- Non-conformity: metamorphic and igneous rocks overlain by sedimentary rocks
- Correlation
- the matching of the rocks of the same age based on similarities of lithologic and paleontological features
- shows correspondence in character and in stratigraphic position as well as between geographically separated parts of a geologic unit
- important in constructing the geological timescales
Absolute Dating
- Absolute Dating
- numerical dating of rocks, minerals and fossils with the use of radioactive isotopes
- determines the an estimation of the numerical age of rocks through radioactive decay
- assumes that nothing is added or taken away and that the fossil at hand is found at a closed system
- Radiometric Dating
- radioactive isotopes: variants of the same atom but with different mass numbers which undergo spontaneous decay due to unstable atomic nuclei (leans towards stability)
- half-life: length of time required for one-half of the nuclei to decay
- radioactive isotopes then serve as geological clocks and are used to date fossil rocks through the calculation of the proportion of parent and daughter isotopes in rocks
- Geologic Time Scale
| Time | Rock System |
| Eon | Eonothem |
| Era | Erathem |
| Period | System |
| Epoch | Series |
| Age | Stage |
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