tdwy-blog
Heavily Laden
A student of Earth Science at UCL.
Just about to finish my 3rd year :o
I have one year left ;p
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Sooooo, initially all continents were as one in the form of the super continent Pangaea, this was around the Middle Jurassic when the Tethys Ocean was in existence. This was soon to end, as Pangaea began to rift apart, FFWD to 35Ma which is the end of the Palaeogene, by which time the Tethys Ocean had closed and we now have some that resembles the Mediterranean Sea, across which we have Africa and Iberia.
Permian
Triassic
Jurassic
Cretaceous
Palaeogene
Neogene (= Miocene > Eocene)
N.B.// Africa is travelling Northward toward Iberia, but it is rotating anticlockwise as it does so. Apparently this creates a transpressional regime, with a sort of dextral oblique collision.
The collision between the two continents causes crustal thickening which includes thin-skinned thrusting and folding. This is when only the surface sediments (earlier deposited Mesozoic & Tertiary) are involved, becoming detached from the variscan basement via decollement. This stage can be regarded as the formation of the External Zone (no metamorphosis), which can be divided into the Prebetic (shallow water seds) & Subbetic (more basinal seds).
Decollement is the detachment of surface sediments from the basement rock. This may be possible due to the presence of a salty gliding plane between the two, salt can act as a lubricant.
The Internal Zone to the South is composed of Palaeozoic & Mesozoic sediments which have been penetratively deformed and subject to a range of P/T metamorphic conditions to give three sorts of complex:
Nevado-Filabride: pre-Permian graphite mica schist intruded with granite. Permo-Triassic metamorphosed feldspathic sandstones, carbonate rocks and metabasic rocks
Alpujarride: A range of metamorphism (from east to west) greenschist to eclogite facies
Malaguide: unmetamorphosed rocks
These complexes are displayed in elongate slithers running parallel with the cordilleran, between then lies intramontane basins (Neogene Basins) that are filled with both marine and terrestrial sediments.
To explain the formation of the formation of the internal zone one must look to Ar-Ar isotope dating, for which there are some key observations.
Firstly there is a distinct difference in ages of rocks:
Nevado-Filabrides are much younger, dated to around 13Ma - Miocene
Whereas the Alpujarrides show Miocene in the West and Eocene in the East
Looking at P/T conditions:
High P/T for Nevado-Filabrides
Alpujarrides show low P/T in the East and very high P/T in the West
All this lovely info points to TWO events!
The Eocene Event is where Africa ia moving Northward rotating anticlockwise toward Iberia. The Alpujarride Complex is being subducted beneath the Malaguide Complex. Overall forming the Alboran Domain BeeeeeeeeeYITCH!
The Miocene Event (Neogene Tectonics) is the second stage and is responsible for how the Betic Cordilleran looks today.
This second event is a reaction to serious extension leading to the formation of oceanic crust, the initial stages being visible as the Cabo de Gata volcanics, and later stages being visible as the Garnet Volcano at Cerro el Hoyazo where basalt has come through the crust and we have a restite. There is also major faulting throughout the internal zone, this too is a result of this serious extension.
But how the devil do we have extension within a compressional environment???!
Because as the crust thickens it becomes overloaded, there is detachment of the upper lithospheric mantle from below (blob) delamination and also thinning and extension on top to compensate. coincidently the crust in the Alboran basin is thin thin at around 13km. Seismic tomography reveals a negative temp anomaly beneath the Alboran Sea, thought to represent the detached cooler lithospheric body.
The Alboran Domain spreads toward the west btw, overriding the NFC.
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Although tired as fuck, I vow to fully comprehend the initial phases of Betic formation.
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Viva Info
Assessment is to be on:
Basin Evolution
Crustal Deformation
Mountain Collision
;) which basically means just learn the essay I just wrote ;P
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Hello again! Am pleased to say that I am only two days away from finishing my exams - hurrah! Until then I shall mostly be revising the ins-and-outs of the Betic Cordilleran in Southern Spain - Vamos!
Inner Monologue
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Overview of my essay on Introduction to CCS
Why is there is a growing interest in CCS?
There is growing concern for carbon emissions and their effect upon climate. Renewable energies offer a route to reduce carbon emissions, but they do not provide a solution - they have their limitations, they are costly and inefficient, consequently they are not an option for many developing nations, so it is assumed that consumption of fossil fuels such as coal is likely to increase, thus an increase in carbon emissions can also be expected. CCS provides a compromise, as it allows for the consumption of fossil fuels whilst preventing the associated carbon emissions from entering the atmosphere.
What is CCS?
It is the capture and storage of CO2 in geological formations on a geological timescale.
Ideally capture takes place direct from large sources of co2:
coal fired power plants
cement factories
industry
Capture can be one of three methods:
Post combustion scrubbing, involves the use of amine solvents on flue gas which brings the co2 into solution, which can then be separated.
Pre combustion capture, involves oxidising the fuel to produce CO2 and H2. The Hydrogen can go on to be used as fuel whilst the CO2 is extracted.
Oxy-fuel combustion, is the combustion of fuel in pure oxygen opposed to air, so the products received are H2O and CO2. Condensation of H2O leaves pure CO2 to be extracted.
Once captured the gas must be compressed to a supercritical state where density is much greater and therefore volume is much less - more manageable/efficient to transport carbon in this state.
Transport of the supercritical fluid over reasonable distances is most likely to be by pipe, over longer distances the fluid may be shipped. The LNG port in Milford Haven in West Wales is a working example of such a scheme - gas is shipped there via moss-rosenbergs and piped 316km to England.
Injection of CO2 is via a bore hole, the part of the bore which is within the formation is covered with a permeable screen which allows CO2 to flow out.
The formation is likely to already contain fluid within it's pore space. In order to allow the CO2 to enter the injection pressure the injection pressure must exceed the native pore fluid pressure.
Once injected the co2 movement depends on:
The density differences i.e. supercritical co2 is less dense than saline water therefore it will rise, and denser than natural gas therefore it will sink.
Movement of CO2 can also be as part of circulations that occur naturally in a reservoir rock.
There are four methods of trapping, each one more secure than the last:
Physical trapping where a cap rock prevents the migration of co2 to the surface. There are two types of cap rock; Aquitardes such as mudstone which have low permeability, and Aquicludes such as Halite which is impermeable.
Immobilisation is where CO2 becomes trapped in dead end pore space.
Dissolution is where the CO2 dissolves in the pore waters to form a weak carbonic acid, which in turn gives way to...
Reaction of minerals present in the formation such as plagioclase precipitates new carbonates e.g. MgCO3. This is mineralization and is the most secure.
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Bit of intel on the exam tomorrow - student was handed his own work and told to talk through essay - why the interest in CCS, what it is all about. A bit about the proposed storage formation. Injection of fluid into a formation.
anon
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IRMS (Isotope Ratio Monitoring Mass Spectrometry)
Infact I just realised that I have sort of covered Isotope Ratio Monitoring Mass Spec in my earlier post on the BEIF, but I appear to have missed a few important details which were highlighted by my flatmate last night.
The Sample:
IRMS only accepts the analyte in gaseous form, and then only a limited number of gases are acceptible:
CO2 & CO
N2 & N2O & NO
H2
SO2
And those gases should be isotopically representative of the original sample.
Sample Preparation at the Gas Bench:
Acid Digestion at the gas bench ( can't find a pic) takes your INORGANIC sample (some sediment) put it in a test tube, seals it air tight, flushes it with Helium to get rid of any other gases (air) then adds a few drops of phosphoric acid. Phosphoric acid (which I believe is a strong acid) reacts with the sample to give CO2 gas.
This is your analyte - from it you can measure the abundance of isotopes:
Heavy Oxygen (18)
Deuterium (Heavy Hydrogen)
Heavy Nitrogen (15)
Sample preparation at the TC/EA (Thermal Combustion Element Analyzer):
ORGANIC matter is subject to pyrolysis (heat in the absence of oxygen) to produce gases:
Carbon Monoxide (CO)
Hydrogen (H2)
This is your analyte which you can analyze to measure the abundance of:
Heavy Oxygen (18)
Deuterium
Sample Preparation with Flash EA (Flash Element Analyzer)
This is the combustion of ORGANIC samples to produce gases:
CO2
N2
SO2
This is your analyte which you can use to measure the abundance of isotopes:
Carbon 13
Deuterium
Sulphur 34
Nitrogen 15
So in summary for sample preparation there are three methods.
1 for inorganic sample - acid digestion at the Gas Bench
Acid digestion uses phosphoric acid, which produces CO2, can use to measure the abundance of oxygen 18, nitrogen 15 and deuterium.
2 for organic samples - pyrolysis with TC/EA (Thermal Combustion/Element Analyzer) & combustion with the Flash EA
Thermal combustion uses pyrolysis which is heat without oxygen to produce gases hydrogen and carbon monoxide. It can be used to measure abundance of isotopes oxygen 18 and deuterium .
Combustion of a sample produces gases CO2, N2 and SO2, which can be used to measure the abundance of isotopes oxygen 18, nitrogen 15, sulphur 34 and deuterium.
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A good morning on the Betics report. Viva is tomorrow, in fact 24hrs from now I shall be viva-ing. Today I am going to start by going back over analytical techniques we were shown in the labs.
inner monologue
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Geochemistry and origin of formation waters in the western Canada sedimentary basin - III. Factors controlling chemical composition*
By Brian Hitchon et al 1971
I included this paper in my annotated bibliography, so there is a chance I may be asked about it in my viva on Wednesday. Here is a saucy overview of the paper to sum up the key points :p
Paper is on the chemical characteristics of samples taken from oil & gas fields in the western Canada sedimentary basin.
Jim Carrey - favourite canadian
Middle part is a load of babble from hitchon et al - incomprehensible shite.
Skip to page 586 for some form of clarity:
There is evidence of a seawater origin, in that the pore waters have a composition similar to that of modern day sea water, and also the basin rocks appear to have been deposited under marine conditions.
Invasion of saline water into a formation can make the formation water more saline than modern day seawater.
Study of fluid flow within the west canadian basin shows that there has been extensive mixing of seawater with fresh water, which has caused the redistribution of salts within the basin, this is known as dilution by freshwater recharge.
There is selective mobility of alkalis and isotopes as they move through shales. The formation waters that had moved through the shales had significantly lower salinity than modern say seawater. This is membrane filtration.
Much of the rock that composes the west canadian basin is Halite, dissolution of this enriches the formation waters with NaCl, making it hella salty - solution of halite.
An observed increase in Ca and a decrease in Mg can be attributed to dolomitization of limestone present within the basin. This is also helped by the formation of chlorites, namely MgCl2.
There has been a reduction of sulphate in formation waters due to bacterial action. Although calculations wrt the presence of H2S in solution fall short when only bacterial action is taken into account. Precipitation of Gypsum is thought to plug the gap with regards to sulphate reduction.
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