Sediments 2
***The 4 Systems Tract Model +see pic on 38!!!
(sequence boundary) falling stage systems tract hightstand systems tract transgressive boundary lowstand systems tract (sequence boundary) time (hst=short down period so sea level falling slowly) (fst=long under loop so lowest sea level)=constant rate of sediment supply (line), zero rate of sea level change, sea level is falling below this line (line) (lst=short up period, so belwo baseline) (tst=long upper loop, so above baseline) THESE CURVES SHOW THE RATE OF CHANGE IN SEA LEVEL NOT THE POSITION OF SEA LEVEL
Bedding Conformable contact
*forms and spatial position of rocks in the earth's crust. Sedimentary and metamorphic rocks usually occur in the form of layers or strata bounded by roughly parallel surfaces *the smallest lithostratigraphic unit, usually ranging in thickness from 1 centimeter - several meters thick each strata is separated by a bedding plane that represents a change in depositional pattern or short break in deposition It is the single most common and characteristic feature of sedimentary rocks found in coarse sandstone, fossil-rich limestone, black shale bedding is normally a conformable contact because its deposited in the same environment lithologically consistent unit
Falling Stage System Tract
- includes all the regressional deposits that accumulated after the onset of a relative sea-level fall and before the start of the next relative sea-level rise. The falling stage systems tract is the product of a forced regression (one should not confused this with the sediments deposited during a normal regression). The FSST lies directly on the sequence boundary and is capped by the overlying lowstand systems tract sediments
Flexure Origin
-continent-continent collision -subduction zone rollback -ocean-continent andean type margin
hybrid basins aulocogens impactogens wrench basins
-intracontinental wrench basins: formed within continental crust due to distant collisional forces (qaidam basin china), more than 2 lake movements happen -aulacogens: failed arm of a triple junction. it is at high angles to continental margins which are reactivated during convergent tectonics (mississippi embayment) -impactogens: rifts at high angles to orogenic belts without pre-orogenic history (baikal rift) hybrid basins are very rare
intracontinental basins vs. thrust related foreland basins
-intracontinental: slow subsidence, short decay -thrust related foreland basins: slow initial subsidence, accelerated due to loading, long decay?
***why does geophysical data play an important role in sedimentary basin analysis?
-magnetic data over an area can indicate the nature of rocks underlying a sedimentary sequence oceanic crust retains a higher remnant magnetism than continental crust -gravity surveys can provide an indication of the thickness of sedimentary strata present, as they are of lower density than igneous or metamorphic rocks -seismic reflection shave far superceded other geophysical methods by providing subsurface structural data that can be used for structural analysis of succession
passive margins vs. strike slip basins
-passive margins: rapid inital subsidence, long decay -strike slip basins: rapid subsidence, shortlived decay these are the mechanisms of basin formation that cause different basins to have different rates of subsidence
the physical mechanisms forming these depressions can be: pix of this on 9.19
-rifting (extension and faulting) caused by crustal tension. when asthensophere pushes up it starts the tension process like rifting -flexure of the lithosphere (foreland, thermal sag) caused by crustal compensation//The lithospheric flexure (also called regional isostasy) is the process by which the lithosphere (rigid outer layer of the Earth) bends under the action of forces such as the weight of a growing orogen or changes in ice thickness related to (de)glaciations. -downwelling (mantle convection causing thickening of crust) erosion?
***analysis techniques
-structural analysis: tectonic setting deformation during deposition (basin history we look at tectonic activities, compressional? tensional?) -sedimentological analysis: sources of sediment, environments of depositon, facies (their environments and structures) -geohistory analysis: subsidence history (diagenic changes when sediments load on top of stuff can lead to subsidence) big impact on oil -thermal history: burial history (talks about after sedimentary beds it is buried deep so what temps it was exposed to) big impact on oil -geophysical data: basin structure thickness of succession (depositional structures how is changed over time???) -stratigraphic analysis: analysis age of rock units & correlation within basin (depositional structures how is changes over time)
what leads to subsidence and creation of accommodation space in sedimentary basins?
-thinning of underlying crust -sedimentary, volcanic, and tectonic loading (principles of isostasy) -changes in the thickness (or density) of adjacent lithosphere (isostatic compensation)
Eastern Indonesia
2 faults going down; half grabens so the right side is formed by rifting because grabens left side has reverse faults and folds so it must be formed by compressional strength and this is a flexor basin. left=compression right=extension
banded ironstones
2000-3500ma alternating chert and red iron rich hematite, magnetite and iron silicates coexistence of chert, iron (silicates, carbonates and oxyhydrates) indicate an alkaline environment that changed fro reducing to oxidizing frequently
sediment distribution on earth
75% of earth's surface & 5% of the volume of the earth's crust consists of sedimentary rocks
Red Bedsterm-184
>3500ma 1000m thick quartzite-amphibole bands, totally recrystallized. no remnant sedimentary features thought to be chemically precipitated as chert, silica concentration in ancient ocean was about 20 times higher than that of today this is a precipitation of iron rich water
banded quartzite
>3500ma 1000m thick quartzite-amphibole bands, totally recrystallized. no remnant sedimentary features thought to be chemically precipitated as chert. silica concentration in ancient ocean was about 20 times higher than that of today
***porphyry??? (residual)
???Whenever there is a subduction zone, basaltic crust goes down undder continental zone comes out in volcano so igneours rock comes out above water table, this process emplaces the olivine etc. which are more reactive to acid and undergo high temps!???
forearc basin
A forearc is the region between an oceanic trench and the associated volcanic arc. As such, forearc regions are found at convergent margins, and include any accretionary wedge and forearc basin that may be present. Due to tectonic stresses as one tectonic plate rides over another, forearc regions are sources for great thrust earthquakes proximity=on top origin=convergent underlying=oceanic?
***extensional half-grabens
A half-graben is a geological structure bounded by a fault along one side of its boundaries, unlike a full graben where a depressed block of land is bordered by parallel faults.
Paraconformity
A paraconformity is a type of unconformity (gap in the geologic system) in which there is no evidence of a gap in time, because the planes above and below the gap are parallel and there is no evidence of erosion.
flooding surfaces
A surface of deposition at the time the Shoreline is at its maximum landward position bind parasequences surfaces across which there is stratigraphically abrupt deepinging recorded in sedimentary facied maximum transgressive phase
Thrust Fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger.
Conformable Strata
A vertical sequence of rocks in which deposition was more or less continuous
Aggradation
Aggradation is the term used in geology for the increase in land elevation due to the deposition of sediment. Aggradation occurs in areas in which the supply of sediment is greater than the amount of material that the system is able to transport. Aggradation can be caused by changes in climate, land use, and geologic activity, such as volcanic eruption, earthquakes, and faulting. For example, volcanic eruptions may lead to rivers carrying more sediment than the flow can transport: this leads to the burial of the old channel and its floodplain. RATE OF DEPOSITION = SEDIMENTS LOAD
what is sea is too saline?
Animals do not survive. No source for limestone to deposit
macerals
As minerals are to rocks...macerals are similar components to coal A maceral is a component, organic in origin, of coal or oil shale. The term 'maceral' in reference to coal is analogous to the use of the term 'mineral' in reference to igneous or metamorphic rocks. Examples of macerals are inertinite, vitrinite and liptinite. vitrinite reflectance is directly proportional to thermal increase
backarc basin
Back-arc basins are geologic features, submarine basins associated with island arcs and subduction zones. They are found at some convergent plate boundaries, presently concentrated in the Western Pacific ocean. Most of them result from tensional forces proximity=close!! origin=convergent underlying=transitional?
Bauxite (residual)
Bauxite, an aluminum ore, is the world's main source of aluminum It consists mostly of the minerals gibbsite beta??? Al(OH)3, boehmite AlO(OH) and diaspore alpha AlO(OH), mixed with the 2 iron oxides goethite and haematite, the clay mineral kaolinite and small amounts of anastase TiO2 They were formed by lateritic weathering and residual accumulation of intercalated clays or by clay dissolution residues of the limestone laterite can be increased by aluminum
calcite compensation depth (CCD)
Carbonate deposition diminishes below water depths of 3 km. At the CCD, pressure is great which is the cause for complete dissolution of carbonates. Carbonates will also not form if there is a large influx of silica material or debris from the land.
***Planar or Irregular Surfaces Separating Different Types of Rock Contacts Can Be ***picture?
Conformable (abrupt, gradational) Unconformable (unconformities) pattern is dif above and below Lateral Contacts ( abrupt: faults, basin boundaries ++gradational: pinchouts, intertongings)
evaporites
Deposits (non-carbonate) formed out of precipitation are Evaporites Seawater contains 35g/l of salts in solution Depositional Environment Playa lakes Marine lakes
Absolute Age//Absolute Dating
Determined through radioactive isotope methods dating methods which are both time consuming and expensive Absolute dating=finding the exact time of stratigraphy is radiometric dating
***what is the difference between weathering and erosion?
Erosion - the wearing away of rocks and other deposits on the earth's surface by the action of water, ice, wind, etc. There are such types of erosion: -glacial erosion -soil erosion. Weathering - the mechanical and chemical breakdown of rocks by the action of rain, snow, cold, etc.
***Placer Deposits
Gravity separation during sedimentary processes ideally deposited at bends of flow or at slope inflection points types of placer deposits: alluvial placers beach placers deposits: diamonds gold iron heavy metals and minerals rare earth elements
what if water depths are more than 200m? what about the carbonates that formed deeper than abyssal plains?
Greater depths do not allow light penetration. Planktons cannot proliferate, hence aquatic animals that feed on planktons are rare. The organisms forming these deposits would not have lived there. They were perhaps floating or swimming organisms which after death sank into the deeper water and slowly accumulated as oozes (very fine carbonate sediments)
Principles of Stratigraphy
Help us interpret relative ages of geologic features and events Also helps determine the relative age of geologic events
Relative Age
Helps establish the sequence of events in a sedimentary basin and is often used to correlate and amend errors in absolute dating
Highstand System Tract
Highstand systems tract (HST) forms when sediment accumulation rates exceed the rate of relative sea-level rise and an increase in accommodation constitutes the upper systems tract in either a type 1 or type 2 sequence
Retrogradational Parasequence Set
In a single outcrop, a retrogradational parasequence set can be recognized by the progressive appearance of deeper water facies upwards within the parasequence set as well as the progressive loss of shallower water facies upwards in the parasequence set this lack of overall facies change results in no net vertical trend in water depth sedimentation rate LAGS rate of accomodation
Strike Slip Fault
In a strike-slip fault, the movement of blocks along a fault is horizontal.
Progradation
In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. RATE OF DEPOSITION < SEDIMENTS LOAD *In sedimentary geology and geomorphology, the term progradation refers to the growth of a river delta farther out into the sea over time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is greater than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result, progradation can be caused by: Periods of sea-level fall which result in marine regression. This can occur during major continental glaciations within ice ages, periods during which mass anomalies cause the local geoid to rise, or due to an overall deepening of ocean basins that can often be caused by the presence of older, deeper sea floor.
formation of limestones
In the geological past shallow seas were widespread and limestone could be deposited over stretched of 1000 km2. Organisms with carbonate skeletons occur throughout the world, so in theory carbonate sediments can be deposited anywhere e.g. seas and oceans. fringing-->barrier-->atoll Limestones tend to form in warm seas. These conditions are proved by the presence of index fossils such as corals. Therefore most limestones form in Warm seas (tropical/sub-tropical belts between 0 - 300 north/south of the equator) Water depths up to 200m (till the shelf edge) Reefs (where carbonate shelled life forms proliferate) Zones where clastic sediment influx is low
*Chronostratigraphy
Integrated approach to establishing the time relationships among geologic units to establish relative position dating Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time. The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of the Earth.
Lowstand System Tract
It is deposited during an interval of relative sea-level fall at the offlap break, and subsequent slow relative sea-level rise
Each stratigraphic technique classifies rocks into different units Lithostratigraphy Allostratigraphy Biostratigraphy Magnetostratigraphy Chronostratigraphy
L-classifies units into compositional units like GROUPS//FORMATIONS//MEMBER//BEDS+FLOWS A-classifies units into SEQUENCES ie SYNTHEM+CYCLOTHEM B-classifies rocks into zones like RANGE ZONES//INTERVAL ZONES//LINEAGE ZONES//ASSEMBLAGE ZONES//ABUNDANCE ZONES//other biozones M-produces polarity zones (NORMAL//REVERSE) C-divides rock units based on their time of deposition with respect to geologic time scale EONOTHEM (EON)//ERATHEM (ERA)//SYSTEM (PERIOD)//SERIES (EPOCH)//STAGE (AGE)//SUBSTAGE (SUBAGE or AGE)
***heat flow inferences
McKenzie demonstrate mathematically that the heat flow within a basin was related to the amount of crustal stretching, termed the beta value. the higher the rate of stretching, the higher the heat flux during the initial phase of rifting the beta value for a basin may be discovered by constructing a burial history curve for the basin and comparing it with known curves calculated for given beta factors the accurate predication of the history of heat flow in a sedimentary basin is a prerequisite to the accurate modeling of petroleum generation
silicates
Non-clastic silicates are called CHERT Forms below the CCD Originates from siliceous skeletons of microscopic organisms like Diatoms (lacustrine) and Radiolaria (marine)
Normal Faults
Normal faults generally occur in places where the lithosphere is being stretched. Consequently they are the chief structural components of many sedimentary rift basins (e.g. the North Sea) where they have major significance for hydrocarbon exploration.
tar sands
Once was oil and gas but regenerated which left tar behind Heated so comes out of sand
***Hydro-Thermal Alteration
Plenty of acidic water and have magma going out which is hot obvi so this changes the rock and this hot water transports dissolved material this is how we get copper gold etc. deposits Different degrees of heat lead to different types of mineral deposits
Retrogradation
Retrogradation is the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. during periods of sea-level rise which results in marine transgression. This can occur during major periods of global warming and the melting of continental ice sheets. with extremely low sediment input. RATE OF DEPOSITION > SEDIMENTS LOAD
Reverse Faults
Reverse faults are exactly the opposite of normal faults. If the hanging wall rises relative to the footwall, you have a reverse fault. Reverse faults occur in areas undergoing compression (squishing).
Law of Lateral Continuity
Sediment forms into continuous lateral layers in every direction. This layering effect continues until the sediment encounters a contact which can be due to thinning (edge of an alluvial fan/gradual thinning owing to deficiency in sediment supply as in the case of fans), depositional boundary of basin (at the boundaries of a sedimentary basin where the slope of the topography restricts is lateral extension), a faulted surface (a fault where the depositional basin is downthrown against the footwall)
coal and swamps
Sediments and sedimentary rocks with high proportion of organic matter are called carbonaceous. Organic matter is formed and preserved in Low relief High water table Anaerobic conditions Slow subsidence Types Land plants form PEAT which is diagentically transformed into COAL Shallow marine planktons form Sapropel which generates Petroleum Swamp/Flood plains In between the distributary channels are swamps and slightly elevated areas with trees/vegetation. These swamps are stagnant water and are therefore anaerobic/anoxic. Which is perfect for preservation of organic matter (peat accumulation) Peat ultimately turns into coal on burial/diagenesis.
Law of Original Horizontality
States that sedimentary rocks are deposited horizontally on top of each other. This means that the boundary between two adjacently deposited sedimentary rocks shall have a planar horizontal boundary. Ex. Grand Canyon where the rocks are found to be horizontally layered Elsewhere the rocks may be inclined due to tectonic deformation. At places the rock may be tilted beyond vertical (90*), in which case we say they are overturned.
Laws of Stratigraphy
Steno's 6 laws of stratigraphy Law of original horizontality Law of superposition, Law of cross-cutting relationships Law of lateral continuity Law of inclusion (rock b younger than rock a) Law of faunal succession (this is the most important piece of evidence)
Subsidence
Subsidence is the motion of a surface (usually, the Earth's surface) as it shifts downward relative to a datum such as sea-level. The opposite of subsidence is uplift, which results in an increase in elevation.
factors that contol depositon of cabronates
Temperature Salinity Water depth Amount of silica input
dunham's limestone classification
Texture based classification which is useful for field descriptions
Transgressive System Tract
The maximum rate of rise of sealevel occurs some time within the transgressive sytems tract, and the end of the systems tract occurs when the rate of topset accomodation volume decreases to a point where it just matches sediment supply, and progradation begins again. • This point is known as Maximum Flooding Surface.
Law of Superposition
This law implies that the rock layer on top is deposited after the rock layer underneath and therefore is younger of the two The law of superposition holds good in all places except where the rock overturned. This is the case in the bottom left picture where the layers are extremely deformed and a limb of the fold is overturned.
Principle of Inclusion
This law states that when a sedimentary rocks has inclusions of another rock then it is younger than that rock from which the inclusion have come from in this example* the granite batholith was eroded and its granules are found as inclusions in the sandstone bed. This means that the granite batholith is older than the sandstone On the other hand, the purple rock bed below the sandstone is devoid of any granitic inclusions which indicate that the granite batholith is younger than the purple bed
Radiometric Half-Life
Time taken for half of the original (parent) isotope to decay to the new (daughter) isotope the decay series of most interest to geologists are those with half lives of tens, hundred, or thousands of millions of years. carbon, potassium the half life is based on composition ic ration a to b
Aggradational Parasequence Set
Vertical build up of a sedimentary sequence. Usually occurs when there is a relative rise in sea level produced by subsidence and/or eustatic sea-level rise, and the rate of sediment influx is sufficient to maintain the depositional surface at or near sea level sedimentation rate MATCHES rate of accomodation
conformable vs. unconformable
When layers of rocks are deposited in a continuous succession through time without any significant break in deposition they are conformable. But if deposition is interrupted or there is an episode of erosion between deposition then the boundary between the older and younger rocks is unconformable, in essence part of the geologic record is missing.
Folded Tectonism
Will have sediments of all horizontal pieces
Disconformity
a surface separating younger from older rocks, both of which are parallel to one another with a clear erosional surface most important
how are unconformities formed?
a). sediment is deposited below sea level b). rocks are uplifted and tilted c). erosion exposed folded rocks d). rocks sink below sea level and new rocks are deposited
Qadim Basin, China
all the faults in qadim basin are vertical intracontinental wrench basin
***Clay mineral analysis
also helpful as these are formed by characteristic of a particular bedrock -smectite group clays indicate a basaltic source rock use electron probe microscope to study clay minerals
Nonconformity
an erosional surface cut into metamorphic or intrusive rocks and covered by sedimentary rocks nonsedimentary rock below is a nonconformity
Angular Unconformity
an erosional surface on tilted or folded strata over which younger rocks were deposited
Arc-Related Basins
are most likely to contain matter derived from volcanic activity in their sediments whenever there is arc subdection we find volcanoes. forearc vs backarc
parasequences
are relatively conformable successions of genetically related beds or bedsets bounded by marine flooding surfaces and their correlative surfaces commonly meters-10s of meters thick and shallowing upwards (the basin becomes shallow). deposited in single environment facies transitions within parasequences obey walther's law but transitions across the upper and lower bounding surfaces do not parasequences are bounded by definition by flooding surfaces which are surfaces across which there is stratigraphically abrupt deepening recorded in sedimentary facies
depositional sequences
are relatively conformable successions of genetically related strata bounded by sub aerial unconformities and their basincorrelative surfaces. depositional sequences may be composed of parasequences
oxygen isotope
atmospheric water contains more oxygen 16 than oxygen 18 snow precipitation in glacial periods have oceans with high oxygen18 this has been created by measuring the 18O/16O ratio in carbonate materials formed directly from seawater by organisms and dating the deposits in which they occur by other means
why is silica concentration reduced today?
because at that time we don't expect any lifeforms that contribute to carbonate component of oceans
chemostratigraphy
bulk chemical analysis heavy mineral analysis clay mineral analysis Chemostratigraphy, or chemical stratigraphy, is the study of the variation of chemistry within sedimentary sequences.
burial chart
burial charts are critical to evaluate time of deposition and depth of burial in a basin which is critical to estimate the sequence of events and thermal exposure of rocks
thermal history what does the burial of sediments result in?
burial of sediments results in diagenetic changes effected by increased temp with burial depth. an indication of this can be determined by: fission-track analysis vitrinite reflectance of organic
pH of ocean crust
but oceanic crust more basic so that means the top layer in pic are more reactive to acids. So those will disinitegrate whenever there is an acid. That means if acid rain those minerals will get digested much faste rand other ones are far more stable
how is calcareous different from carbonaceous?
calcaereous=limestones and sediments which solidify to form them are called calcareous. //Calcareous rocks or limestones are mainly composed of the shells or skeletons of animals or plants, and are formed of carbonate of lime. Limestones belong to the group of organic rocks. It is the most abundant non-clastic rock. carbonaceous=Carbonaceous rocks are formed from the remains of plants converted by heat and pressure into coal. Peat, lignite and coal are carbonaceous deposits of organic origin. All these rocks are composed of plant debris in different stages of alteration.hydrocarbons
Limestones
calcium carbonate typically composed of abundant marine fossils most common type of chemical sediment forming today by biogenic processing of seawater -dolomite (or dolostone) is created by replacement of calcium by magnesium after shallow burial of limestone in tropical shallow marine environmets
geologic time scale Picture 11.4 why did the water cycle begin?
cambrian: multi-celled organisms ordovician: plants emerge in sea, fish with teeth silurian: plants start to occur on land so the water cycle starts to happen devonian: vertebrated and first amphibians cenozoic: evolution of the atmosphere, hydrosphere, and climate
Nicholas Steno
came up with first three laws of stratigraphy. horizontality, continuity, superposition 1669
where can sediments come from other than land to sea and wave disperal?
can come from volcanoes in the oceans can originate from mid oceanic ridge will find different facies where these features are located these special environments give rise to special minerals like green marine clays
heavy mineral analysis
certain heavy minerals help us identify the source of sediment sand sized grain distribution is a challenge quartz is of little value for provenance studies certain heavy minerals help us identify the source of sediment
what may affect the relative sea level on a shorter time scale?
changes in sediment accumulation
colloid
chemical weathering a colloid we use every day is milk, it doesnt have a single composition because its a mixture of many. the minute you change the pH it changes to butter or milk A colloid is a solution that has particles ranging between 1 and 1000 nanometers in diameter, yet are still able to remain evenly distributed throughout the solution. These are also known as colloidal dispersions because the substances remain dispersed and do not settle to the bottom of the container.
diagenic can be mechanical or chemical
chemical=cementing that relates pores Diagenesis the change of sediments or existing sedimentary rocks into a different sedimentary rock during and after rock formation (lithification), at temperatures and pressures less than that required for the formation of metamorphic rocks.
energy and economic potential
coal petroleum tar/oil sand shale gas understanding sediments, sedimentary processes, their facies and depositional environments and the evolution of the basin provides us valuable insights into the economic potential of the sediments
***sandy shoreline parasequences
coarsening upward flooding surfaces record a rapid relative rise in sea level without deposition of sediment parasequences record a period of shoreline progradation under static to slowly rising relative sea level parasequences may be produced by: eustatic sea level changes episodic earthquake-induced subsidence delta switching
green marine clays
common today but the cause of the green coloration agent differs in the ancient deposits green particles in oceans are authigenic aluminum silicates rich in iron and magnesium normal seawater cannot be the source of iron -sourced from detrital fluvial systems -volcanic activity in oceanic trenches and island arcs -present day green particles are derived from early diagenesis of pyrite and siderite in ocean trenches and island arcs in sediments in conjunction with organic matter in reducing conditions but in the past it was more from volcanic activity than fluvial deposition
zonation of earth. compositional and mechanical layers
compositional layers: continental crust (10-70km; aluminum Al silicate), oceanic crust (5-7km; silicates), mantle, core (nickel Ni and iron Fe). this is based on composition mechanical layers: lithosphere, aesthenosphere (viscous more like liquid), mesosphere (seismic waves do not cross this), outer core, inner core. mainly concern elasticity
reverse faults/folds indicate
compression
Conformable Contacts ***picture?
conformable strata form unbroken depositional sequences layers are deposited in an uninterrupted manner pattern is same below and above *Between Beds of sedimentary rocks may be either abrupt of gradational
Peripheral Foreland Basins
contain high proportion of re-worked sediments where there is a wedge and normally have sediments here that compose the wedge
Rift Basins
contain material derived from surrounding cratonic area and are likely to include plutonic igneous and metamorphics rift basins happen in cratons not a plate boundary
***Accomodation
created by tectonism space available for sediments to fill in area at margin of the basin marine accommodation is controlled by: -basin tectonics -eustasy changes in accomodation is referred to relative sea level changes accommodation space equation: T+E+S+W T=is rate of tectonic subsidence E=is rate of eustatic sea level rate S=is rate of sedimentation W=is rate of water depth increase (deepening) sea level fall=negative accommodation sea level rise=positive accommodation
Uranium Roll-Front Deposits (residual)
cup shaped roll-front lies perpendicular to fluvial axis uranium was sourced from volcanic asshes though subsequent migration and concentration by percolating acid groundwater all sandstone that was deposited and water percolates from top and goes into sediment. this is rich in solution of uranium
***what is the dead sea transform an example of? north sea? red sea? persian gulf? rocky mtns? alpine mtns?
dead sea=transform/vertical north sea=normal rifting red sea=normal rifting persian gulf= rocky mtns=flexural/reverse fault alpine mtns=flexural/reverse fault
history of compaction can be calculated by
decompacting the sedimentary succession in a series of stages accounting for the palaeobathymetry
***peripheral foreland and forearc basins both comprise
deepwater facies in the lower part of the basin....shallowing up to shallow-marine or continental deposits
***4 system tracts
depositional sequnces are composed of a characteristic succesion of 4 systems tracts (sets of all contemporaneous depositional facies), always in the same stratigraphic order: lowstand LST transgressive TST highstand HST falling-stage FST
burial of sediments results in what?
diagenic changes effected by increased temp with burial depth. an indication of this can be determined by fission-track analysis, vitrinite reflectance of organic (these act as paleothermometers)
geophysical survery are useful for distinguishing what?
different basin types amount of subsidence
different basin types can be expected to show what?
different patterns of sedimentation -a rift or strike-slip basin may be expected to have coarse facies such as alluvial fans or fan-deltas at its margins -a backarc basin would have an apron of volcaniclastic deposits at one margin -a passive margin succession would be dominated by shallow marine clastic or carbonate facies
***estimating subsidence
difficult to make absolute measurements assuming sea level to be constant, subsidence owing to compaction resulting from the water column can be estimated
Types of unconformities
disconformity paraconformity nonconformity angular unconformity these are all contacts
***triangle diagram?
dunite=comething rich? react to acid
Principle of Cross-Cutting Relationship
dykes and faults cut across sedimentary rocks the principle of cross cutting relationship says that the feature which cuts across a sedimentary layer is always younger than the sedimentary layer
What is distance transported inferred from?
energy of the environment particle shape and size of clasts density & composition of clasts
what do syn sedimentary folds and faults indicate?
evidence of tectonic activity during deposition
basin forming mechanisms mechanism that creates surface depression are:
extension: driven by plate boundary forces (passive rifting) thermal lithospheric cooling and contraction--thickens mantle lithosphere crustal extension driven by buoyancy of relatively thin mantle lithosphere (active rifting) metamorphic reactions flexure (foreland basins) dynamic topography driven by convecting mantle
How do you know the water depth?
find a rock.... take sedimentological evidence shale deposited must be more water sandstone on beach, no water
***muddy shoreline parasequences
fining upward and shallowing upward a parasequence developed on a muddy shoreline would have a different suite of facies, but they would also be arrayed vertically in a shallowing upward order typically starts with a cross bedded subtidal sands, continue with interbedded bioturbated mudstones and ripples sands of the intertidal and pass upwards into entirely bioturbated and possibly coally mudstones of the supratidal rocks lying above and below a flooding surface commonly represent non-adjacent facies, such as a foreshore sands directly overlying offshore mud
***Lariang Basin
flexure basin. this is not a pic of a rift basin because we see folding and reverse faulting. not normal faulting
Flexural Basins (vs tensional)
flexures are related to compressional tectonics which leads to crustal thickening the width and depth of the foreland basin is determined by the flexural rigidity of the underlying lithosphere and the characteristics of the mountain belt proximity: far? origin: compressional underlying: continental?
sequence stratigraphy
focuses on analyzing changes in facies and geometric character of strata identification of key surfaces to determine the chronological order of basin filling and erosional events
vitrinite
forms from old trees and bark so when its heated it becomes shinier.
forced regression normal regression pix on 32 ch8
fr: progradation with downstepping. progradation driven by relative sea level fall (negative accomodation). the coastline forces to regress nr: stacking pattern: progradation with aggradation interpretation: progradation driven by sediment supply-sedimentation rates outpace the rates of relative sea-level rise (positive accomodation) at the coastline
earth processes
geodynamics: plate tectonics (movement of plates or crustal) isostasy (crustal density-thickness equilibrium climate change: eustasy (sea level changes)
Graded Bedding Conformable Bedding
gradational contact the characteristics of the sediments within the single strate gradually changes the changes can be from bottom to top or horizontally the difference is that contact is not sharp as in bedding
Gradational conformable contact
gradual change in depositional conditions with time progressive gradual contact one lithology grades into another
***why does oceanic crust retain a higher remnant magnetism than continental crust? and why is the strength of the magnetic field proportional to the density?
has more metal.
lateral contacts
has to do with principle of lateral continutity and abrupt contacts include faults ++basin boundaries tectonic events results in faults, occurs if rock is brittle but if rock is elastic then they do not break apart law of horizontality does not apply to these lateral contacts
3D architecture of a sequence and what decides how they vary
how facies, surfaces, and systems tracts are arrayed internally--varies depending on: -rates of eustatic sea-level change -tectonic subsidence -the type and volume of sediment supplied -the configuration of the shelf
evolution of the atmosphere, hydrosphere & climate
icehouse to greenhouse inflicts minor gradual changes to the composition and temperature of atmosphere and oceans
Progradational Parasequence Set
in a cross section, a progradational parasequence set can be recognized by the seaward movement of a particular facies contact at an equivalent position in a parasequence sea level changes then sea level becomes so low that it erodes and becomes sequence boundary sedimentation rate EXCEEDS rate of accomodation
where are sediments deposited?
in basins basins are accommodation space for sediments
parasequence sets and stacking patterns
in most cases, there will be a series of parasequences sets of successive parasequences may display consistent trends in thickness and facies composition which may be classified as progradational // the moving of the sediments where the sediments move towards the sea in lateral movement aggradational || move on top of each other retrogradational \\ backwards toward land
Ironstones
iron oxide minerals, usually magnetite or hematite interlayered with chert and clay minerals
geohistory
is about if we find certain thickness of rocks we want to go back to find what was happening when they were deposited. we find this by decompaction
Sedimentary Basin Analysis
is the aspect of geology that considers all the controls on the accumulation of a succession of sedimentary rocks to develop a model for the evolution of the sedimentary basin as a whole
rate of sediment accumulation
is the thickness of strata deposited between two datable horizons can be an indicator of basin setting Rift basin sediments will commonly accumulate at a faster rate than passive margin deposits
chalk=calcium carbonate
it forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates (coccoliths) shed from micro-organisms called coccolithophores
what is assumed about iron in prehistoric oceans?
it is assumed that initially the earth started out with vast amounts of iron dissolves in the world's acidic seas. eventually as photsynthetic organisms generated oxygen, the available iron in the earth's oceans was precipitated out as iron oxides
why is geohistory analysis important in hydrocarbon exploration?
it provides information on the porosity and permeability changes through time it provides the thermal history of any part of the succession, that is critical to the generation of oil and gas
oolitic ironstones
known throughout phenerozoic but seldom in neogene sediments mined for iron, most of these belong to the precambrian era as recent deposits are low in iron content oolitic ironstones is an enigma and its origin is debatable -they occur predominantly in clastic sequences. most of the iron appears to have been supplied by rivers draining deeply weathered lateritic soils where the iron was enriched -the ooids and other iron-rich particles probably formed in coastal waters under repeatedly changing environmental conditions, partially at the sea bottom and partially within the sediment -transgressive-regressive cycles led to winnowing, repeated migration and final deposition of oolitic bodies in the form of offshore bars or more widely extended sand sheets during the deepest sea level stands 2mm occur in clastic environments, not chemical. could be diagenic form of ironstones
which way would the coast move if sea level rises?
landward marine transgression
Gradational Contacts Include
lateral facies change=Walther's law pinch out = The termination of a bed that thins gradually intertonguing = intergradation of different rock bodies laterally by splitting into many thin tongues that individually wedge out.
marine deposits
limestone banded iron formations chalk
DEPTHS OF THE SEA
littoral: The littoral zone is the part of a sea, lake or river that is close to the shore. In coastal environments the littoral zone extends from the high water mark, which is rarely inundated, to shoreline areas that are permanently submerged. neritic: The neritic zone is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately 200m in depth. bathyal: The bathyal zone or bathypelagic -is the part of the pelagic zone that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface. It lies between the mesopelagic above, and the abyssopelagic below. abbysal: An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 m. Lying generally between the foot of a continental rise and a mid-ocean ridge,
***PIX ON 10.7 & 8 & 9! what do magnetic, gravity, and seismic rata tell us?
magnetic data tell us about the nature of underlying rocks. magnetic data shows us a pattern in the sea. sedimentary rocks are no magnetic! don't look at rocks themselves but what is below? gravity surveys tell about the thickness of strata, ie the density. gravity does not show elevation but high density. low density indicates sedimentary rocks seismic reflection are best because provide subsurface structural data that can be used for structural analysis of succession. accostic impodence. used to study the sediment itself, not the rock below -colors indicate amplitude, it roughly follows bedding, can see 2 patterns. the differences between the 2 is that the ones at the top are sedimentary and the ones at the bottom are metamorphic so this shows us that the basement and everything below that line will not be sedimentary. so these lines show faults. thats why the curves start to occur when being filled with sediments its called syn-sedimentary, theres 3 types of sedimentation....the top layer was deposited when the faults ceased
magnetostratigraphy
magnetic reversals & remnant magnetism
***rheology of crustal types oceanic vs continental lithosphere
max rock strength what is brittle at shallow depth becomes more tactile max rock properties change with depth the study of the flow of matter, primarily in a liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force.
paleobathymetry
micropalaeontological evidence lead to the depth of deposition of lithic sections *try to find if rock was in neritic, bathyal or abyssal zone! resolution depends on the organism -forams -ostracods -microfacies
***lithospheric stretching why will faults always be normal faults?
mid-oceanic:thermal intra-cratonic:thinning -in the brittle upper crust, extension is accomodated by normal faulting -faults will always be normal faults because it is an area of tension where blocks move away from each other -normal faulting is driven by gravity
evaporites
mineral precipitated from saline water in arid environments with high evaporation rates (ie playa lakes) gypsum halite anhydrite potash
Salveson Model
model of passive crustal separation (passive not associated with any plate boundary) the continental crust was deemed to deform by brittle failure, while the sub-crsutal lithosphere is thinned by ductile necking model was largely based on studies of the red sea and gulf of suez rift system (rigid crust, ductile lithosphere)
forearc vs. backarc
mostly find volcanic and metal in backarc
precambrian rocks dolomites
mostly metamorphic or igneous, no sedimentary rocks during this time because they were a part of the early crust, we find some sediment dating back to pre-cambrian because deposited by not active plate process could be similar but materials is totally different archean and proterozoic rocks are known from all continents and represent a major part of the so-called shields or cratons banded quartzites: so old that they are all metamorphic rocks (***SHOULD KNOW THESE) dolomites: similar processes created dolomites not limestones, the similarities is magnesium, that means early earth materials was magnesium rich. must have been oceanic crust!!! banded ironstones placers & paleosols red beds
bioclasts vs non-biogenic clasts
non biogenic clasts nclude ooids, pisoids, peloids, oncoids, intraclasts
Perth Basin
normal fault so must be tensional tectonics which is rifting
which will create basins of high depth? rifting? flexor or transform folding?
normal faults is rifting, reverse faults is flexor, vertical fault is transform faulting so transform=deepest the dead sea was formed by this transform
Erlian Basin, Mongolia
normal faults. the minute you see normal faults, it must be rifting!!!
Walther's Law
noticed that the same facies he found laterally were also present in a vertical sequence holds that the facies seen in a conformable vertical sequence will also replace one another laterally, ie. lithologs represent vertical sequences of rocks. SO THE SAME FACIES THAT CAN BE FOUND LATERALLY WILL ALSO REPRESENT A VERTICAL SEQUENCE (this is in violation with horizontal continuity) applies to marine transgressions and regressions also known as law of correlation of facies 7th law of stratigraphy, only in places of sea facies *As laterally-adjacent sedimentary environments shift back and forth through time, as a result of sea level change, facies boundaries also shift back and forth. Given enough time, facies which were once laterally adjacent will shift so that the deposits of one environment come to overlie those of an adjacent environment. In fact, this is how many (if not most) vertical sequences of sedimentary rocks were formed. This concept was first stated by Johannes Walther in 1894, and is called Walther's Law. Basically, in a conformable sedimentary sequence (i.e., one without unconformities), sedimentary units which lie in vertical succession represent the deposits of laterally adjacent sedimentary environments migrating over one another through time.
types of peripheral pro foreland basins
occur on the late that is subjected or underthrust during plate collion
coal swamps
occurs in swampy environments and if it is compacted can expect sort of thick but if it is sooooo thick its hard to imagine where, must have been full of vegetated swamp during deposition
marine regression
occurs when sea level recedes with respect to the land it is represented by: -water receding inwards into the sea -shore environment migrates inwards to the sea yields a vertical sequence where: -near-shore facies overlying offshore facies -sand overlying silt-mud-carbonates *representing progressively shallower water environments (shallowing-upward sequence). As a result, a regressive sequence will have coarser-grained facies overlying finer-grained facies (coarsening-upward). Regression can be caused by a buildup of ice in the polar ice caps, or localized uplift of the land in coastal areas.
marine transgression
occurs when sea level rises with respect to the land during a marine transgression: -the shoreline migrate landward -the environment paralleling the shoreline migrate landward as the sea progressively covers more and more of the continent each laterally adjacent depositional environment produces a sedimentary facies the facies forming offshore become superposed upon facies deposited in near shore environments sea level change is not absolute, no way to measure how sea level goes up or down * facies representing progressively deeper water environments (a deepening-upward sequence). As a result, a transgressive sequence will have finer-grained facies overlying coarser-grained facies (fining-upward from sand at the bottom, and then to silt, and then to shale). Transgressions can be caused by melting of polar ice caps, displacement of ocean water by undersea volcanism, or by localized sinking or subsidence of the land in coastal areas.
***placers vs paleosols
older than 2200 ma placer deposits of uranium in fluvial sandstone is indicative of oxygen poor environment as it is unstable in oxidizing environment placer is a deposit that has been selectively deposited. such as a river because can cover certain things depending on flow etc. so some of the heavier metal may be placed earlier pyrite placer deposits also indicate a reducing environment paleosol art soils. difference from sandstone is that sandstone is weathered and deposited there to here but soil is residual so it does all that in one place
Index Fossils
organisms which proliferated on earth for a short geological time before going extinct all together organisms come into existence, proliferate, and then get extinct as a part of the cycle of evolution
how are sedimentary basins classified?
origin (divergent, convergent, transform, intra-plate) proximity of the basin to the active plate margins type of crust underlying the basin (oceanic, continental or transitional)
types of flexural basins
peripheral (pro) foreland basins, which occur on the plate that is subducted or underthrust during plate collision -examples include the north alpine foreland basin of europe of the ganges basin of asia retroarc (retro) foreland basins, which occur on the plate that overrides during plate convergence or collision (ie situated behind the magmatic arc that is linked with the subduction of oceanic lithosphere) when fold fails it becomes brittle and results in fault and the nature of these are normal rivers -examples include the andean basins, or late mesozoic to cenozoic rocky mountain basins of north america
Phase Evolution
phase 1: subduction of oceanic lithosphere phase 2: partial subduction of continental margin phase 2: end of partial subduction of continental margin phase 3: collisional orogen (obduction)
decompaction
porosity changes in sediments on burial reduction of porosity leads to reduction in bed thickness to calculate the thickness of a sediment layer at any time in the past, it is necessary to move the up the appropriate porosity-depth curve this is equivalent to sequentially removing overlying sediment layers and the layer of interest to decompact
differentiating basins
post-depositional basin: sediments came into basin after it was already formed so the sediments make the same shape syn-depositional basin: sediments were coming in as the basin was being depressed and formed. makes wedges shape
***phases of stretching and stretching models
pre-rift idyllic phase rift phase cooling collapse phase temp v depth? divergence of continental landmasses leads to surface extension and therefor thinning of the continental lithosphere the geometry of extension can follow a variety of modes the most significant stretching models are: Salveson Mckenzie Werkicke
dolomites
precambrian era had more dolomites than limestones high magnesium calcium ratio thought to be caused by high mg/ca ratio and high pH of early ocean such dolomites are also rich in iron and silica and sometimes alternate with chert and ironstone pH of early oceans very high and crust is more basic because it has more metals so that means the pH would be high dolomites are high in iron and silica and sometimes with chert and ironstones because earth core is mostly composed of iron
Marine evaporites and carbonates
precambrian era had more dolomites than limestones thought to be caused by high mg/ca ratio and high pH of early ocean such dolomites are also rich in iron and silica and sometimes alternative with chert and ironstones ex. death valley canada not happening at the same degree today.
why were there more dolomites during the pre-cambrian than today?
presumed to be formed in isolated oceans where depth of water was pretty high. thought to be caused by high mg/ca ratio and high pH of early ocean
***rifts and backarc basins show
progressive change from continental deposits (at early rifting) to shallow marine and sometimes deeper facies
***main aspects of sedimentological analysis of basins
provenance studies facies distribution (sequence stratigraphy) palaeoenvironments changes in the above 3 through time during the basin evolution
***Mud analysis
provides the average composition of large continental areas geochemical fingerprinting using rare earth elements and isotopic dating (Sm-Nd) is useful kandite and smectite group
***pro wedge toward what and retro wedge toward what???
pw=continental rw=ocean
dating and correlation techniques
radiometric dating uses the decay of isotopes of elements present in minerals as a measure of the age of the rock. in order to arrive at a fair calculation, must have: rate of decay, properties of parent to daughter isotope at mineral formation, present day proportion
geologically, sediment basins are
regions of longterm subsidence creating accommodation space for infilling of sediments sedimentary basins occur in diverse geological settings usually associated with plate tectonic activity
causes of sea level change
relative change: local tectonics, fault moves land down so water goes down eustatic change: continental ice caps (decrease in ice volume raises sea level); global scale thermo tectonic (slow mid-ocen ridge spreading, oceanic crust cools and contracts) or (fast mid ocean ridge spready, more hot, buoyant oceanic crust occupies more space in the ocean basin, sea water displaced onto continental shelves); exchange with water on continents
non conformable contacts
represents a broken depositional sequence, layers deposited are uninterrupted by a non-depositional and erosional period commonly called unconformities abrupt sudden distinctive changes in lithology often local changes
normal faults indicate
rifting
Basins are Formed Due to
rifting, flexure and mantle down welling rifting is associated with normal faults and shear resulting grabens and half grabens flexure is associated with thrusts and folds mantle down welling is not associated with plate margins sea level change has been changing ever since cambrian. whenever sea level rises, it gives rise to basin base level of erosion is the water table or sea level, anything below that, process of deposition will be stronger than erosion
eustatic compensation micro-palaeotological data
sea level change relative to a reference. if an ocean with initial water depth h is filled with water to a new depth h, the sea-level rise compensated for isostatic depression of the ocean floor is....(equation) micro-palaeontological data is used to estimate paleobathmetric changes through time. evidence leads to the depth of deposition of lithic sections, resolution depends on the organisms: forms, ostracods, microfacies *Micropaleontology (also sometimes spelled as micropalaeontology) is the branch of palaeontology that studies microfossils, or fossils that require the use of a microscope to see the organism, its morphology and its characteristics details
gypsum pix???
sedimentary
Sequence Boundaries
sequence boundaries within a parasequence are defined by unconformities that record subaerial exposure and erosion (red lines in pic) correlative marine erosion surfaces and correlative conformities. Sequence boundaries form from a relative fall in sea level Types: Flooding surfaces maximum flooding surfaces transgressive surface sequence boundary
Phanerozoic case studies differences between precambrian and phanerozoic stratigraphic frameworks
sequence stratigraphy was developed as a new method of stratigraphic analysis based on this differences between precambrian and phanerozoic stratigraphic frameworks are explained by the evolution of the planet's hydrosphere atmosphere-biosphere system: -changes in environmental energy conditions and the related physical processes -changes in the rates and intensities of processes controlling various aspects of sedimentation at different scales of observation
Weathering selectively breaks down rocks into allocthonous authocthonous
soluble chemicals transported in solution insoluble residue: -allocthonous: removed from original site and deposited at a distance authocthonous: stay at same place forming residual deposits
provenance quartz*
source of the sediment how we go about it: study of clasts (texture&composition) During the transportation, minerals can be sorted by their density, and as a result, light minerals like quartz and mica can be moved faster and further than heavy minerals (like zircon and tourmaline).
*Allostratigraphy
study of rock units defined by unconformities and related feature which impact base level of deposition / base level change An allostratigraphical unit is a body of sedimentary rock that is defined and identified only by its bounding discontinuities.
*Biostratigraphy
study of the fossil record with emphasis on faunal succession to establish relative time relationships --uses fossil assemblages and their evolutionary characteristics to establsh position in time
*Magnetostratigraphy
study of the magnetic properties of rock units for the purpose of correlation using magnetic polarity reversals --uses remanent magnetism of rocks to establish age
*Lithostratigraphy
study of the physical relationship among rock units to establish relative position. this would include compositional and tectural characteristics No time connotation other than superposition Physical properties and stratigraphic position relative to other lithostratigraphic units
Abrupt conformable contact
sudden distinctive changes in lithology often a local change
how was the earth formed how old is the earth? and what was happening during this period?
sun emits gases like sulfur. sun is made of gas so planets that came from that are also gaseous. (present is key to the past does not apply to this because up until the mesozoic not similar to present, but start to look similar near cenozoic) 4.6 million years old crust was being formed in this period, no life except single celled organisms. life started in the water but no sign of life on land.
what controls the changes in facies and palseo-geography in time?
tectonic settings in other words, changing palaeo geography within a basin reflects the tectonic evolution
what is accommodation space created by?
tectonism (plate tectonism) eustatic changes isostatic balance
palaeothermometers
temperature helps estimate the depth of burial as well, leading to understanding of the subsidence history of the sediments in the basin
whats the difference between tension and compression?
tension is pulling apart compression is pushing together
which part is the bedding?
the contact between the two bodies, one is a body because it was deposited in a body
***what do the patterns of deformation within a sedimentary succession provide information about? what do syn-sedimentary faults and folds show evidence of? normal faulting indicates what? folds and thrusts indicates what?
the crustal stresses that existed in the area during and after deformation evidence of tectonic activity during deposition tension during sedimentation compression as the strata were accumulating
***isostatic compensation
the deficiency of mass in the earth's crust below sea level that exactly balances the mass above sea level
foreland basin
the foreland basin receives sediment that is eroded off the adjacent mountain belt, filling with thick sedimentary successions that thin away from the mountain belt this forms mtns A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure. The width and depth of the foreland basin is determined by the flexural rigidity of the underlying lithosphere, and the characteristics of the mountain belt. The foreland basin receives sediment that is eroded off the adjacent mountain belt, filling with thick sedimentary successions that thin away from the mountain belt. proximity=on the margin origin=flexure? underlying=continental
strata stacking patterns respond to what? and what do these patterns reflect?
the interplay of changes in rates of sedimentation and sea level these patterns reflect combination of depositional trends which include: progradation, aggradation, retrogradation
Accommodation curves
the natured of reference curve that is utilized to define a sequence stratigraphic surfaces and system tracts highstands system tract transgressive systems tract falling-stage systems tract lowstand systems tract
geo-history analysis
the quantitative study of the history of subsidence and sedimentation in a basin
backstripping
the sediment and water load above a horizon of interest in a sedimentary basin causes an isostatic effect so that the total subsidence observed is made of a tectonic driving force component and a sediment/water load component *a geophysical analysis technique used on sedimentary rock sequences - the technique is used to quantitatively estimate the depth that the basement would be in the absence of sediment and water loading.
Wernicke Model
the simple shear extension model involves a low-angle shear zone which extends through the entire lithosphere this is much more simple because it doesnt result in symmetric structures faulting occurs along a detachment surface that extends through the entire lithosphere observe the half-grabens on the left flank of the forming basin, which is a result of asymmetric collapse due to extensional thinning of the crust this model was largely based on studies of the basin and range tectonic province of north america gradaitional mechanical property, bractile into more and more brittle more likely of having a sheer here. but only sheer on one side, because of stretching the brittle part starts breaking ex. red sea rift basin
Stratigraphy and why sedimentary rocks are essentially the study of stratigraphy
the study of stratified rocks. ex. rocks that are layers on top of each other. since sedimentary rocks are deposited in this fashion it is essentially the study of sedimentary rocks
Middle East Example
there are normal fault so was created by rifting
Residual Deposits
these are sediments which are weathered but not eroded. laterite (Fe, Ni, Mn) Kaolinite When percolate into porous sandstone the Not moving the sediment we are depositing the material in solution
fission-track analysis
these are the marks that alpha particles leave on minerals. sediments contain heavy minerals like apatite & zircon which have traces of radioactive material technique: radioactive decay of uranium isotopes in these minerals releases alpha particles alpha particles pass through the lattice of the crystals leaving a trace if the mineral is heated then these tracks become obscure (apatite 110*, zircon 300*) as it cools, new tracks start to form as a result of continued fission *The method involves using the number of fission events produced from the spontaneous decay of uranium-238 in common accessory minerals to date the time of rock cooling below closure temperature.
McKenzie Model
this is a mirror model basically the same the finite uniform extension model also called pure-sheer models, as in these models large-scale lithospheric extension is symmetric and does not involve rotation this results symmetric collapse on both flanks as a result pure grabens result sub-crustal lithosphere thins as a result of isostatic compensation this model was largely based on studies of the north sea basin
Principle of Faunal Succession
this is the most important law we look at fossil assemblages not fossils alone This law using the fossil content of sedimentary rocks to establish the relative age the fossils which are helpful are called INDEX FOSSILS Evolution of species and their fossilization in sedimentary rocks therefore helps us classify rocks into 3 units A-One that was deposited before the species came into existence (oldest) B-One that was deposited when the organism proliferated (intermediate) C-And the one that was deposited after it was extinct (youngest) Assemblages of index fossils and their distribution
***Changes in Clast Composition
through time can be used as an indicator of depth of erosion in the hinterland source area and hence provide a record of the uplift and un-roofing history of an orogenic belt
anatomy of a basin basin axis depocentre why does the sediment come from one side?
topographic axis, water, basin axis, depocentre a sedimentary basin in the restricted sense of the term is an essentially saucer-shaped area of sedimentary rocks. it is therefore surrounded in plan view. strata dip and thicken centripetally toward the centre of the basin sediment comes from one side of the basin because transport is only on one side basin axis is the deepest part of the basin depocentre=point where thickness of sediments is thickest centripetally dipping (dipping toward center) strata, concave upward
What is geology all about?
unraveling the happenings of the past
what can laterite be used for? (residual)
used as construction material
carbon14 dating
used for dating bone or organic matter living organisms continuously accumulate carbon14, which decays after death (half-life 5730) years use carbon to date human bodies
what can you use kaolinite for? (residual)
used to make china clay and porcelain
uranium series dating
utilizes fractionation of 234 and 238 isotopes seawater is abundant with these isotopes which are trapped in carbonates and marine organisms half life is a million years
compaction effect
varies considerably with different lithologies clay-rich sediments decreasing in volume by up to 80% through time sandstone typically lose between 10-20% of their porosity as a result of compaction
*Geochronology
various techniques, especially isotope geochemistry, to establish the absolute age of rock units and their components (minerals, elements)
paleobathymetry
water depth in basin impacts both compaction and subsidence palaeobathymetry: because when rocks deposited on top of each other, top part always has some water but if we dont have idea of water depth on top we cant analyze how much it was compacted *Paleobathymetry is the study of past underwater depths
Chemical Weathering ***Picture 11.13 quartz
when magma cools down, magma is a mix of immisible minerals at high temperature. cholerate? colloid? when you cool it down the first thing that comes out is olivine, then pyroxene then amphibole... QUARTZ is the last thing to come out and olivine is the first so this is natural when you have mantle and temp increases with depth and the first thing that crystallized out is olivine so primary component of oceanic crust because it is deeper and it melts fast. olivine pyroxene common in oceanic crust.
what is magnetism?
when minerals crystallize they go with earth's magnetic field from magma. oceanic crust tend to have more metals so allign more field of earth. magnetic axes has changed in the past. these poles can switch
if its just uplift+sag but if theres compression then if sagging then
wont have many faults will have many faults not many singapore happens because areas of sediment put weight on