Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Wednesday, 9 August 2017

Thursday, 27 July 2017

"Why I left Electrical Engineering and choose Geology?" with Rana Faizan

About author: Rana Faizan is currently in his third year of under graduation in Applied Geology at Institute of Geology at University of the Punjab in Lahore, Pakistan. He is interested in Petroleum Geology, Structural Geology, Sedimentology and Tectonics.         
  

When I was studying in the 8th grade, my father had a wish to make me an Electrical Engineer. Honestly speaking at that time I have no idea about my future goals and even I didn’t knew anything about Electrical Engineering.
One day I was in my class, my teacher gave us a lecture on future planning which really inspired me to think about future aims. This was the first time I started thinking about my future goals. I reached home and asked my father about this concern. He advised me to choose Electrical Engineering in future and told me that this is his dream about me. At that time, I was not familiar with the Geology. Days were passed and I completed my 10th grade exams with good percentage and took admission in 11th grade (pre-engineering), and I started study hard to fulfill my parent’s dream.

Then a day come, my father was sharing his university life experiences with me and this was the first time I heard about Geology because his hostel mates were Geology students. My father told me about the geology field work experience that his friends shared with him. And his friend is currently settled in Canada and working as a Geologist. He told me about some more people and some of them are now my professors.

These all things sums up and gave me inspiration about geology, I searched about geology on internet and I found it an interesting field as geologists ruin tourism in their daily life. They can work in natural resource companies, environmental consulting companies, government agencies, non-profit organizations, and universities. Many geologists do field work at least part of the time. Others spend their time in laboratories, classrooms or offices. All geologists prepare reports, do calculations and use computers. I found that geology is a practical and professional field, all sciences and engineering required geology work in some disciplines. Another thing is the study of mountains, different rocks, minerals, structures and more over their observations in field with naked eye is so interesting. Moreover thin section study and geological mapping was another cause that inspired me to pursue my career in this field.

Due to all these things, I mentally prepared myself to choose geology in future but my father wanted me to become an engineer.

After few months, I completed my 12th grade with good percentage and I applied for electrical engineering as per my father’s wish. And I also applied for geology as per my wish. Unfortunately, I didn’t get admission in any geology institute and get admission in electrical engineering. My parents were very happy because their wish was near to fulfill at that time but I was not so happy because I wanted admission in geology. Then unwillingly, I have to study the electrical engineering. This was little bit interesting subject for me especially circuits. I liked working on C++ programming. I completed my first semester with good CGPA and got 2nd position but still I wasn’t satisfied in this field. 

Next year, when I was studying 2nd semester in engineering, the admissions in geology get opened and again I tried to get admission in this field but my parents, relatives and friends even my engineering professors advised me that I should not leave this field (engineering) now because that decision would effected my future and one year of my study would be wasted. I listened to my heart voice and applied for admission and I was surprised to know that I got admission in geology. I left engineering and join geology field. My friends and professors of engineering institute asked me again not to leave this field. I still remembered, I simply told them that I don’t want high marks, I want to fulfil my interests so that I can give my 100% in that work. I thought what if I done electrical engineering with good percentages and get job. But what if I am not satisfied with my decision then what is the benefit of that job? Geology may not give me highly paid jobs easily as I could find in electrical engineering but I would definitely find peace and satisfaction in geology.


Me (left) discussing geological map of Pakistan with my class mate (right).
Photo © Rana Faizan 
Describing about Salt Range (Sub-Himalayas) model
Photo © Rana Faizan 
Now, I’m studying geology and I am fully satisfied with my decision. I have completed my two and half years of bachelor’s degree with three field works and I have learnt many things about geology. I found all things as same as I imagined, when I was in 12th grade. This was my dream that one day I will become a geologist and will study from the same institute from my father’s friends have studied. Everyone has its own interest. Some like engineering, some like medical and some go for other. My purpose here is not to degrade anyone especially electrical engineering students, no doubt it is also a good field as technology is becoming a need of everyone. So, I have an advice for everyone, always listen to your own decisions and do not bother what other say.

Selfie at Harno River, Abbottabad, Pakistan.
Photo © Rana Faizan 
Had a rainy fieldwork at Indus River, Pakistan
Photo © Rana Faizan 
I still remember a quote:
                    "Think 100 times before you take a decision,
But once that decision is taken, stand by it as one man."

We have a lot of hidden potential that we don’t know. And if we know then we don’t utilize it because we fear what people would say. More than that there is our own voice shouting inside that you can do this. What if we stop listening to those voices and listen only to our heart.
I have observed many geological things during field work and some pictures below are describing about the beauty of geology. I have many pictures related to rocks, minerals, structures and other features. Some beautiful pictures are given below:
Hammering slates
Photo © Rana Faizan 
Plunging anticline fold observed during fieldwork.
Photo © Rana Faizan


 
Enjoying fieldwork after mapping sedimentary area
Photo © Rana Faizan 

Note: This article is originally written and contributed by Rana Faizan. You can also contribute your article by sending us at geologylearn@gmail.com. We would love to share your field experiences with our readers. See guidelines here.




Wednesday, 21 June 2017

Fault anatomy

Fault anatomy

Faults drawn on seismic or geologic sections are usually portrayed as single lines of even thickness. In detail, however, faults are rarely simple surfaces or zones of constant thickness. In fact, most faults are complex structures consisting of a number of structural elements that may be hard to predict. Because of the variations in expression along, as well as between, faults, it is not easy to come up with a simple and general description of a fault. In most cases it makes sense to distinguish between the central fault core or slip surface and the surrounding volume of brittlely deformed wallrock known as the fault damage zone, as illustrated in Figure 8.10.
Simplified anatomy of fault.
The fault core can vary from a simple slip surface with a less than millimeter-thick cataclastic zone through a zone of several slip surfaces to an intensely sheared zone up to several meters wide where only remnants of the primary rock structures are preserved. In crystalline rocks, the fault core can consist of practically non-cohesive fault gouge, where clay minerals have formed at the expense of feldspar and other primary minerals. In other cases, hard and flinty cataclasites constitute the fault core, particularly for faults formed in the lower part of the brittle upper crust. Various types of breccias, cohesive or non-cohesive, are also found in fault cores. In extreme cases, friction causes crystalline rocks to melt locally and temporarily, creating a glassy fault rock known as pseudotachylyte. The classification of fault rocks is shown in heading below.
In soft, sedimentary rocks, fault cores typically consist of non-cohesive smeared-out layers. In some cases, soft layers such as clay and silt may be smeared out to a continuous membrane which, if continuous in three dimensions, may greatly reduce the ability of fluids to cross the fault. In general, the thickness of the fault core shows a positive increase with fault throw, although variations are great even along a single fault within the same lithology. 
The damage zone is characterized by a density of brittle deformation structures that is higher than the background level. It envelops the fault core, which means that it is found in the tip zone as well as on each side of the core. Structures that are found in the damage zone include deformation bands, shear fractures, tensile fractures and stylolites, and Figure below shows an example of how such small-scale structures (deformation bands) only occur close to the fault core, in this case defining a footwall damage zone width of around 15 meters.
Damage zone in the footwall to a normal fault with 150–200 m throw. The footwall damage zone is characterized by a frequency diagram with data collected along the profile line. A fault lens is seen in the upper part of the fault. Entrada Sandstone near Moab, Utah.
The width of the damage zone can vary from layer to layer, but, as with the fault core, there is a positive correlation between fault displacement and damage zone thickness (Figure below a). Logarithmic diagrams such as shown in Figure below are widely used in fault analysis, and straight lines in such diagrams indicate a constant relation between the two plotted parameters. In particular, for data that plot along one of the straight lines in this figure, the ratio between fault displacement D and damage zone thickness DT is the same for any fault size, and the distance between adjacent lines in this figure represents one order of magnitude. Much of the data in Figure below a plot around or above the line D=DT, meaning that the fault displacement is close to or somewhat larger than the damage zone thickness, at least for faults with displacements up to 100 meters. We could use this diagram to estimate throw from damage zone width or vice versa, but the large spread of data (over two orders of magnitude) gives a highly significant uncertainty. 
A similar relationship exists between fault core thickness (CT) and fault displacement (Figure below b). This relationship is constrained by the straight lines D=1000CT and D-10CT, meaning that the fault core is statistically around 1/100 of the fault displacement for faults with displacements up to 100 meters.
(a) Damage zone thickness (DT) (one side of the fault) plotted against displacement (D) for faults in siliciclastic sedimentary rocks. (b) Similar plot for fault core thickness (CT). Note logarithmic axes. Data from several sources.
Layers are commonly deflected (folded) around faults, particularly in faulted sedimentary rocks. The classic term for this behavior is drag, which should be used as a purely descriptive or geometric term. The drag zone can be wider or narrower than the damage zone, and can be completely absent. The distinction between the damage zone and the drag zone is that drag is an expression of ductile fault-related strain, while the damage zone is by definition restricted to brittle deformation. They are both part of the total strain zone associated with faults. In general, soft rocks develop more drag than stiff rocks.

Fault rocks

When fault movements alter the original rock sufficiently it is turned into a brittle fault rock. There are several types of fault rocks, depending on lithology, confining pressure (depth), temperature, fluid pressure, kinematics etc. at the time of faulting. It is useful to distinguish between different types of fault rocks, and to separate them from mylonitic rocks formed in the plastic regime. Sibson (1977) suggested a classification based on his observation that brittle fault rocks are generally non-foliated, while mylonites are well foliated. He further made a distinction between cohesive and non-cohesive fault rocks. Further subclassification was done based on the relative amounts of large clasts and fine-grained matrix. Sibson’s classification is descriptive and works well if we also add that cataclastic fault rocks may show a foliation in some cases. Its relationship to microscopic deformation mechanism is also clear, since mylonites, which result from plastic deformation mechanisms, are clearly separated from cataclastic rocks in the lower part of the diagram. 

Fault breccia is an unconsolidated fault rock consisting of less than 30% matrix. If the matrix fragment ratio is higher, the rock is called a fault gouge. A fault gouge is thus a strongly ground down version of the original rock, but the term is sometimes also used for strongly reworked clay or shale in the core of faults in sedimentary sequences. These unconsolidated fault rocks form in the upper part of the brittle crust. They are conduits of fluid flow in non-porous rocks, but contribute to fault sealing in faulted porous rocks.
Pseudotachylyte consists of dark glass or microcrystalline, dense material. It forms by localized melting of the wall rock during frictional sliding. Pseudotachylyte can show injection veins into the sidewall, chilled margins, inclusions of the host rock and glass structures. It typically occurs as mm- to cm-wide zones that make sharp boundaries with the host rock. Pseudotachylytes form in the upper part of the crust, but can form at large crustal depths in dry parts of the lower crust. 

Crush breccias are characterised by their large fragments. They all have less than 10% matrix and are cohesive and hard rocks. The fragments are glued together by cement (typically quartz or calcite) and/or by microfragments of mineral that have been crushed during faulting.
Cataclasites are distinguished from crush breccias by their lower fragment–matrix ratio. The matrix consists of crushed and ground-down microfragments that form a cohesive and often flinty rock. It takes a certain temperature for the matrix to end up flinty, and most cataclasites are thought to form at 5km depth or more. 
Mylonites, which are not really fault rocks although loosely referred to as such by Sibson, are subdivided based on the amount of large, original grains and recrystallised matrix. Mylonites are well foliated and commonly also lineated and show abundant evidence of plastic deformation mechanisms rather than frictional sliding and grain crushing. They form at greater depths and temperatures than cataclasites and other fault rocks; above 300 C for quartz-rich rocks. The end-member of the mylonite series, blastomylonite, is a mylonite that has recrystallized after the deformation has ceased (postkinematic recrystallization). It therefore shows equant and strain-free grains of approximately equal size under the microscope, with the mylonitic foliation still preserved in hand samples.
Credits: Haakon Fossen (Structural Geology)

Sunday, 11 June 2017

Deformation bands and fractures in porous rocks

Deformation bands

Rocks respond to stress in the brittle regime by forming extension fractures and shear fractures (slip surfaces). Such fractures are sharp and mechanically weak discontinuities, and thus prone to reactivation during renewed stress build-up. At least this is how non-porous and low-porosity rocks respond. In highly porous rocks and sediments, brittle deformation is expressed by related, although different, deformation structures referred to as deformation bands.
Kinematic classification of deformation bands and their relationship to fractures in low-porosity and non-porous rocks. T, thickness; D, displacement.
Deformation bands are mm-thick zones of localised compaction, shear and/or dilation in deformed porous rocks. Figure above  shows how deformation bands kinematically relate to fractures in non-porous and low-porosity rocks, but there are good reasons why deformation bands should be distinguished from ordinary fractures. One is that they are thicker and at the same time exhibit smaller shear displacements than regular slip surfaces of comparable length (Figure (a) below). This has led to the term tabular discontinuities, as opposed to sharp discontinuities for fractures. Another is that, while cohesion is lost or reduced across regular fractures, most deformation bands maintain or even show increased cohesion. Furthermore, there is a strong tendency for deformation bands to represent low permeability tabular objects in otherwise highly permeable rocks. This permeability reduction is related to collapse of pore space, as seen in the band from Sinai portrayed in Figure (b) below. In contrast, most regular fractures increase permeability, particularly in low-permeability and impermeable rocks. This distinction is particularly important to petroleum geologists and hydrogeologists concerned with fluid flow in reservoir rocks. The strain hardening that occurs during the formation of many deformation bands also makes them different from fractures, which are associated with softening. 
(a) Cataclastic deformation band in porous Navajo Sandstone. The thickness of the band seems to vary with grain size, and the shear offset is less than 1 cm (the coin is 1.8 cm in diameter).
(b) Cataclastic deformation band in outcrop (left) and thin section (right) in the Nubian Sandstone, Sinai. Note the extensive crushing of grains and reduction of porosity (pore space is blue in the thin section). Width of bands 1 mm.
The difference between brittle fracturing of nonporous and porous rocks lies in the fact that porous rocks have a pore volume that can be utilised during grain reorganisation. The pore space allows for effective rolling and sliding of grains. Even if grains are crushed, grain fragments can be organised into nearby pore space.
The kinematic freedom associated with pore space allows the special class of structures called deformation bands to form.

What is a deformation band?

How do deformation bands differ from regular fractures in non-porous rocks? Here are some characteristics of deformation bands: 
  • Deformation bands are restricted to highly porous granular media, notably porous sandstone.
  • A shear deformation band is a wider zone of deformation than regular shear fractures of comparable displacement.
  • Deformation bands do not develop large offsets. Even 100 m long deformation bands seldom have offsets in excess of a few centimetres, while shear fractures of the same length tend to show meter-scale displacement. 
  • Deformation bands occur as single structures, as clusters, or in zones associated with slip surfaces (faulted deformation bands). This is related to the way that faults form in porous rocks by faulting of deformation band zones.

Types of deformation bands 

Similar to fractures, deformation bands can be classified in a kinematic framework, where shear (deformation)bands, dilation bands and compaction bands form the end members (1st Figure). It is also of interest to identify the mechanisms operative during the formation of deformation bands. Deformation mechanisms depend on internal and external conditions such as mineralogy, grain size, grain shape, grain sorting, cementation, porosity, state of stress etc., and different mechanisms produce bands with different petrophysical properties. Thus, a classification of deformation bands based on deformation processes is particularly useful if permeability and fluid flow is an issue. The most important mechanisms are:
  • Granular flow (grain boundary sliding and grain rotation) 
  • Cataclasis (grain fracturing) 
  • Phyllosilicate smearing 
  • Dissolution and cementation 
The different types of deformation bands, distinguished by dominant deformation mechanism.
Deformation bands are named after their characteristic deformation mechanism, as shown in Figure above.
Brittle deformation mechanisms. Granular flow is common during shallow deformation of porous rocks
and sediments, while cataclastic flow occurs during deformation of well-consolidated sedimentary rocks and non-porous rocks.
  
Disaggregation bands develop by shear-related disaggregation of grains by means of grain rolling, grain boundary sliding and breaking of grain bonding cements; the process that we called particulate or granular flow (Figure above a). Disaggregation bands are commonly found in sand and poorly consolidated sandstones and form the “faults” produced in most sandbox experiments. Disaggregation bands can be almost invisible in clean sandstones, but may be detected where they cross and offset laminae (Figure below). Their true offsets are typically a few centimeters and their thickness varies with grain size. Fine-grained sand(stones) develop up to 1 mm thick bands, whereas coarser-grained sand (stones) host single bands that may be at least 5 mm thick. 
Macroscopically, disaggregation bands are ductile shear zones where sand laminae can be traced continuously through the band. Most pure and well-sorted quartz-sand deposits are already compacted to the extent that the initial stage of shearing involves some dilation (dilation bands), although continued shear-related grain reorganization may reduce the porosity at a later point.
Right-dipping compaction bands overprinting left-dipping soft-sedimentary disaggregation bands (almost invisible). The sandstone is very porous except for thin layers, where compaction bands are absent. Hence, the compaction bands only formed in very high porosity sandstone. Thin section photo shows that the compaction is assisted by dissolution and some grain fracture. Navajo Sandstone, southern Utah.
Phyllosilicate bands (also called framework phyllosilicate bands) form in sand(stone) where the content of platy minerals exceeds about 10–15%. They can be considered as a special type of disaggregation band where platy
minerals promote grain sliding. Clay minerals tend to mix with other mineral grains in the band while coarser phyllosilicate grains align to form a local fabric within the bands due to shear-induced rotation. Phyllosilicate bands are easy to detect, as the aligned phyllosilicates give the band a distinct color or fabric that may be reminiscent of phyllosilicate-rich laminae in the host rock.
If the phyllosilicate content of the rock changes across bedding or lamina interfaces, a deformation band may change from an almost invisible disaggregation band to a phyllosilicate band. Where clay is the dominant platy mineral, the band is a fine-grained, low-porosity zone that can accumulate offsets that exceed the few centimeters exhibited by other types of deformation bands. This is related to the smearing effect of the platy minerals along phyllosilicate bands that apparentlycounteracts any strain hardening resulting from interlocking of grains. 
If the clay content of the host rock is high enough (more than 40%), the deformation band turns into a clay smear. Clay smears typically show striations and classify as slip surfaces rather than deformation bands. Examples of deformation bands turning into clay smears as they leave sandstone layers are common.
Cataclastic bands form where mechanical grain breaking is significant (Figure b). These are the classic deformation bands first described by Atilla Aydin from the Colorado Plateau in the western USA. He noted that many cataclastic bands consist of a central cataclastic core contained within a mantle of (usually) compacted or gently fractured grains. The core is most obvious and is characterized by grain size reduction, angular grains and significant pore space collapse (Figure b). The crushing of grains results in extensive grain interlocking, which promotes strain hardening. Strain hardening may explain the small shear displacements observed on cataclastic deformation bands (3–4 cm). Some cataclastic bands are pure compaction bands (Figure above), while most are shear bands with some compaction across them. 
Cataclastic bands occur most frequently in sandstones that have been deformed at depths of about 1.5–3 km, although evidence of cataclasis is also reported from deformation bands deformed at shallower depths. Comparison suggests that shallowly formed cataclastic deformation bands show less intensive cataclasis than those formed at 1.5–3 km depth. 
Cementation and dissolution of quartz and other minerals may occur preferentially in deformation bands where diagenetic minerals grow on the fresh surfaces formed during grain crushing and/or grain boundary sliding. Such preferential growth of quartz is generally seen in deformation bands in sandstones buried to more than 2–3 km depth (>90 C) and can occur long after the formation of the bands.

Influence on fluid flow 

Very dense cluster of cataclastic deformation bands in the Entrada Sandstone, Utah.
Deformation bands form a common constituent of porous oil, gas and water reservoirs, where they occur as single bands, cluster zones or in fault damage zones. Although they are unlikely to form seals that can hold significant hydrocarbon columns over geologic time, they can influence fluid flow in some cases. Their ability to do so depends on their internal permeability structure and thickness or frequency. Clearly, the zone of cataclastic deformation bands shown in Figure above will have a far greater influence on fluid flow than the single cataclastic band shown in Figure a or b at the top.
Cataclastic deformation bands show the most significant permeability reductions.
Deformation band permeability is governed by the deformation mechanisms operative during their formation, which again depends on a number of lithological and physical factors. In general, disaggregation bands show little porosity and permeability reduction, while phyllosilicate and, particularly, cataclastic bands show permeability reductions up to several orders of magnitude. Deformation bands are thin, so the number of deformation bands (their cumulative thickness) is important when their role in a petroleum reservoir is to be evaluated. 
Conjugate (simultaneous and oppositely dipping) sets of cataclastic deformation bands in sandstone. Note the positive relief of the deformation bands due to grain crushing and cementation. The bands fade away downward into the more fine-grained and less-sorted unit. Entrada Sandstone, Utah.
Also important are their continuity, variation in porosity/permeability and orientation. Many show significant variations in permeability along strike and dip due to variations in amount of cataclasis, compaction or phyllosilicate smearing. Deformation bands tend to define sets with preferred orientation (Figure above), for instance in damage zones, and this anisotropy can influence the fluid flow in a petroleum reservoir, for example during water injection. All of these factors make it difficult to evaluate the effect of deformation bands in reservoirs, and each reservoir must be evaluated individually according to local parameters such as time and depth of deformation, burial and cementation history, mineralogy, sedimentary facies and more.
The influence of deformation bands on petroleum or groundwater production depends on the permeability contrast, cumulative thickness, orientations, continuity and connectivity.

What type of structure forms, where and when? 

Given the various types of deformation bands and their different effects on fluid flow, it is important to understand the underlying conditions that control when and where they form. A number of factors are influential, including burial depth, tectonic environment (state of stress) and host rock properties, such as degree of lithification, mineralogy, grain size, sorting and grain shape. Some of these factors, particularly mineralogy, grain size, rounding, grain shape and sorting, are more or less constant for a given sedimentary rock layer. They may, however, vary from layer to layer, which is why rapid changes in deformation band development may be seen from one layer to the next. 
Other factors, such as porosity, permeability, confining pressure, stress state and cementation, are likely to change with time. The result may be that early deformation bands are different from those formed at later stages in the same porous rock layer, for example at deeper burial depths. Hence, the sequence of deformation structures in a given rock layer reflects the physical changes that the sediment has experienced throughout its history of burial, lithification and uplift. 
Different types of deformation bands form at different stages during burial. Extension fractures (Mode I fractures) are most likely to form during uplift. 
To illustrate a typical structural development of sedimentary rocks that go through burial and then uplift, we use the diagram and add characteristic structures (Figure above). The earliest forming deformation bands in sandstones are typically disaggregation bands or phyllosilicate bands. Such structures form at low confining pressures (shallow burial) when forces across grain contact surfaces are low and grain bindings are weak, and are therefore indicated at shallow levels in Figures above and figure at the end. Many early disaggregation bands are related to local, gravity-controlled deformation such as local shale diapirism, underlying salt movement, gravitational sliding and glaciotectonics. 
Cataclastic deformation bands can occur in poorly lithified layers of pure sand at shallow burial depths, but are much more common in sandstones deformed at 1–3 km depth. Factors promoting shallow-burial cataclasis include small grain contact areas, i.e. good sorting and well-rounded grains, the presence of feldspar or
other non-platy minerals with cleavage and lower hardness than quartz, and weak lithic fragments. Quartz, for instance, seldom develops transgranular fractures under low confining pressure, but may fracture by flaking or spalling. At deeper depths, extensive cataclasis is promoted by high grain contact stresses. Abundant examples of cataclastic deformation bands are found in the Jurassic sandstones of the Colorado Plateau, where the age relation between early disaggregation bands and later cataclastic bands is very consistent (Figure above).
When a sandstone becomes cohesive and loses porosity during lithification (left side of Figure above), deformation occurs by crack propagation instead of pore space collapse, and slip surfaces, joints and mineral-filled fractures form directly without any precursory formation of deformation bands. This is why late, overprinting structures are almost invariably slip surfaces, joints and mineral-filled fractures. Slip surfaces can also form by faulting of low-porosity deformation band zones at any burial depth. 
Joints and veins typically postdate both disaggregation bands and cataclastic bands in sandstones. The transition from deformation banding to jointing may occur as porosity is reduced, notably through quartz dissolution and precipitation. Since the effect of such diagenetically controlled strengthening may vary locally, deformation bands and joints may develop simultaneously in different parts of a sandstone layer, but the general pattern is deformation bands first, then faulted deformation bands (slip surface formation) and finally joints (tensile fractures in Figure above) and perhaps faulted joints. 
The latest fractures in uplifted sandstones tend to form extensive and regionally mappable joint sets generated or at least influenced by removal of overburden and cooling during regional uplift. Such joints are pronounced where sandstones have been uplifted and exposed, such as on the Colorado Plateau, but are unlikely to be developed in subsurface petroleum reservoirs unexposed to significant uplift. It therefore appears that knowing the burial/uplift history of a basin in relation to the timing of deformation events is very useful when considering the type of structures present in, say, a sandstone reservoir. Conversely, examination of the type of deformation structure present also gives information about deformation depth and other conditions at the time of deformation.
Tentative illustration of how different deformation band types relate to phyllosilicate content and depth. Many other factors influence the boundaries outlined in this diagram, and the boundaries should be considered as uncertain.
Credits: Haakon Fossen (Structural Geology)

Sunday, 30 April 2017

Equipment for Geological Field Work

Following is a list of all equipment that is likely to be needed in the field:

1. Adhesive tape
2. Aerial photographs
3. Altimeter
4. Binoculars
5. Calculator
6. Camera, tripod, film, etc
7. Chemicals for staining rocks
8. Cold chisel
9. Color pencils
10. Colored tape or paint for marking localities
11. Brunton compass or other
12. Drawing Board
13. Erasers
14. Field case for maps and photographs
15. Field glasses
16. First aid kit
17. Flashlight
18. Gloves
19. Gold pan
20. Grain-size card
21. Geologists Hammer
22. Hand lens
23. Dilute Hydrochloric Acid
24. Ink, waterproof; black, brown, blue, red and green
25. Insect repellent
26. Jacob staff
27. Knapsack
28. Lettering set
29. Loose-leaf blinder
30. Magnet
31. Maps, topographic, geologic
32. Microscope
33. Mineral hardness set
34. Field notebooks
35. Paper, lined
36. Paper, quadrille
37. Paper, scratch
38. Pen, drop circle
39. Pen, holders
40. Pen, ruling
41. Pens, ballpoint
42. Pen, inkflow, for photographs
43. Pencils, 3B to 9H
44. Pencil pointer
45. Pick or mattock
46. Pocket knife
47. Protractors
48. Rain gears
49. Rangefinder, Camera
50. Reference library
51. Sample bags
52. Scale, plotting, 6 in.
53. Shovel
54. Stereo-graphic net
55. Tally counter
56. Tape, 6-ft
57. Tape, 100-ft
58. Triangles, drawing
59. Satellite phone
60. Watch

Estwing Hammer and Hand lens


A hammer with a pick or chisel end is used for cleaning exposures, for digging, for breaking rocks, and for trimming samples. Standard geologists hammer have heads weighing 1.5 to 2 lb (0.68 to 0.9 kg) and are adequate for most geologic work. A small sledge--- for example a 2 or 3 lb head on a 14-in. handle may be needed to collect fresh  samples of especially hard rocks.
While using hammer, it is important,
1. to wear safety goggles
2. not to strike heavy blows when people are nearby
3. never to strike one angular rock edges

A cold chisel maybe used with a hammer to split rocks parallel to bedding or foliation and to free fossils or specific mineral samples from unfoliated rocks.

A map holder must be large enough to carry 9*9 in. aerial photographs and should be made of masonite rather than metal( which in uncomfortable to carry) or plastic (which may break when cold).

A scale, used for measuring features or laying off distances on maps and photographs, should have fine, distinct graduation marks that are equivalent to even increments at the map scale used.

A protractor is used for plotting structural symbol maps and for measuring angles between structures in rocks.

A camera, for, photo-geologic interpretation, is an important equipment for geological field work and should be compact and strong. All 35 mm cameras have a great depth of focus than cameras with longer focal length and this is a decided advantage in photographing irregular outcrops at closer range.

Samples bags of cloth or plastic maybe obtained through most suppliers, or bags maybe of extra heavy paper, the variety often used as nail bags.

Hydrochloric acid will be needed and should be diluted just to the strength that causes effervescence of calcite but not dolomite (except when powdered).

Of the hand lenses, 10X and 14X lenses are used most widely. The depth of focus of the 14X lens, however, is only 0.8 mm, whereas that of 10X lens is 2.5 mm.
Good quality triplet lenses typically give excellent images. In testing a lens, and in all other viewing, the following are important:

1. Hold the sample so that the area being viewed is in full light --- in sunlight, if possible.
2. Hold the lens exactly at the distance of sharp focus, with its optical axis perpendicular to the surface being viewed
3. Bring the eye to the point where the eyelashes are mostly touching the lens (this is the only position from which the entire field of view will be sharply and comfortably in focus)


Saturday, 29 April 2017

3D Geological Model of Pakistan

We are GLAD to inform you that one of our admin, Muhammad Qasim Mehmood with his team have prepared a geological model which was presented at All Pakistan Science Fest hosted by UET Science Society at 20/04/17. 

Here is the brief introduction of model:

It is a 3D geological model of Pakistan that shows mainly tectonic division of mountain ranges of Pakistan. The model demonstrates the major/famous deposits of Pakistan like Petroleum, Minerals/Gemstones, Uranium, Coal including other geographical features like dams and rivers.

It is a non-working model (size: 5
×
6 ft approximately) supported mainly by wooden boards and other cementing material. It is using thermocol sheets, maps, large paper sheets, graphs, paints and mechanical and scientific goods as per the requirement of a particular model.

This unique model cover the topics of Plate Tectonics, Structural Geology, Economic Geology and others. Also the students have added the future aspects of Geo-economics like Kalabagh Dam, CPEC route, oil and gas wells in Baluchistan and offshore wells in Arabian Sea near Gwadar.


The model is showing the following geological aspects of Pakistan:

1. Major Geological Basins of Pakistan i.e. Indus Basin and Balochistan Basin
2. Major Thrusts in Northern Pakistan
     Main Karakoram Thrust (MKT)
     Main Mantle Thrust (MMT)
     Main Central Thrust (MCT)
     Main Boundary Thrust (MBT)
     Salt Range Thrust / Himalayan Frontal Thrust
3.  Mountain Ranges of Pakistan
     Some mountain ranges of Pakistan is shown on the model located in North-West to              South-West of Pakistan which has important geological significance in distinguishing            Indus Basin from Balochistan Basin
4.  Famous Peaks of Pakistan
     Mount Godwin-Austen (k2) - World's 2nd highest peak
     Nanga Parbat ( The Killer Mountain) - World's 9th highest peak
     Tirich Mir - highest peak in Hindukush Range

5. Major Fuel of Pakistan
     Oil wells in Potwar Plateau and in Balochistan
     Gas wells in Sui, Balochistan - biggest gas reserve in Pakistan
     Coal reserves in Thar - World's 16th largest coal reserve in Pakistan
     Uranium reserves in Siwalik Hills west of Dera Ghazi Khan
6. Famous Gem Stone of Pakistan
    Emerald from Mingora, Swat 
    Aquamarine from Hunza Valley,Gilgit-Baltistan    Tourmaline from Skardu District, Gilgit Baltistan

And two future prospects for the improvement of Geo-economics of Pakistan:
1. Kalabagh Dam (to be made)
2. China Pakistan Economic Corridor -CPEC (construction under process) western route.

Following are some of the maps (obtained from internet) which we consider during the preparing of our model

Map showing Geological Basins of Pakistan
Source: GSP

Tectonic Map of Pakistan
Source: GSP

Political Map of Pakistan
Source: Unknown
Tectonic Map of Pakistan & India showing major regional thrusts
Source: Unknown
CPEC map
Source: CPEC website
And some photos captured during the preparation of model

Cutting of thermocol sheet

coloring thermocol sheet with finishing paint

Hasan creating "finishing of paint" with paint spatula scraper

final look of Stage 1
Umer Amin sketching map on model and fixing sticks for projections and heights


sketches of mountain ranges and river tributaries and sticks for average height of each range and peak
all things are made perfect due to plotting of each point according to longitude and latitude


 a great Atlas Book

maps and maps


a rough look of model showing mountain ranges made with Plaster of Paris
Completion of Stage 2

team work!!!


after using distemper paint

And finally after painting and drawing river tributaries, fixing sign boards of cities and much more, the model is:

 3D Geological Model of Pakistan




 3D Geological Model of Pakistan


Legend for the model



Geological tools, Gemstones, Rocks and Fuel (Coal and Crude Oil)
Featuring Qasim Mehmood (Co founder of Learning Geology), on left
and
Rana Faizan Saleem, my class mate and CEO of Geology for Beginners
Students of Institute of Geology, University of the Punjab

Pyrope

What is Pyrope?

Pyrope is the most well-known gemstone form of Garnet. The term Garnet describes a group name for several closely related minerals that form important gemstones, and Pyrope is an individual member mineral of the Garnet group. Its dark, blood-red colour is distinct and attractive, and makes a fine Garnet gemstone. In the gem trade, the term Pyrope is rarely used on its own. It is either generically called "Garnet", or "Pyrope Garnet".
The mineral pyrope is a member of the garnet group. Pyrope is the only member of the garnet family to always display red colouration in natural samples, and it is from this characteristic that it gets its name: from the Greek for fire and eye. The composition of pure pyrope is Mg3Al2(SiO4)3, although typically other elements are present in at least minor proportions-these other elements include Ca, Cr, Fe and Mn. Pyrope forms a solid solution series with almandine and spessartine, which are collectively known as the pyralspite garnets (pyrope, almandine, spessartine). Iron and manganese substitute for the magnesium in the pyrope structure. The resultant, mixed composition garnets are defined according to their pyrope-almandine ratio. The semi-precious stone rhodolite is a garnet of ~70% pyrope composition.
The origin of most pyrope is in ultramafic rocks, typically peridotite from the Earth's mantle: these mantle-derived peridotites can be attributed both to igneous and metamorphic processes. Pyrope also occurs in ultrahigh-pressure (UHP) metamorphic rocks, as in the Dora-Maira massif in the western Alps. In that massif, nearly pure pyrope occurs in crystals to almost 12 cm in diameter; some of that pyrope has inclusions of coesite, and some has inclusions of enstatite and sapphirine.
Pyrope is common in peridotite xenoliths from kimberlite pipes, some of which are diamond-bearing. Pyrope found in association with diamond commonly has a Cr2O3 content of 3-8%, which imparts a distinctive violet to deep purple colouration (often with a greenish tinge) and because of this is often used as a kimberlite indicator mineral in areas where erosive activity makes pin pointing the origin of the pipe difficult. These varieties are known as chrome-pyrope, or G9/G10 garnets.

History and Introduction

Pyrope garnet is the best known of the red garnets. It has a distinctive red colour that often resembles the colour of ruby or pomegranate seeds. The word "pyrope" comes from the Greek word "puropus", made up of "pur" (fire) and "ops" (eye) meaning "fiery-eyed". This refers to the impressive brilliance of pyrope garnet, which is a result of its high refractive index.
The use of red garnet dates back thousands of years, when it was used by Egyptian pharaohs for both decorative and ceremonial purposes. The ancient Romans also wore garnet rings and traded garnet gemstones. In ancient times, garnet and other red gemstones cut en cabochon were called "carbuncles", which is not the prettiest of names because it was also used to define pus-filled boils. Nowadays, any natural red gemstone cabochon can be traded as carbuncle stones.
The Latin word, "carbunculus" alludes to a burning piece of coal or ember. This may have been used to refer to garnet because of its bright colour large deposits of pyrope garnet were discovered in Bohemia (Central Europe) around the 16th century, which became the focus of the jewellery industry in the area. Bohemian pyrope garnet from the Czech Republic continues to be mined today.

Identifying Pyrope Garnet

Pyrope garnet is magnesium aluminium garnet. Iron can substitute for the magnesium and become more like almandine, which is iron aluminium garnet. Pure pyrope and pure almandine are rare in nature and most specimens are a mixture of the two. The change in density from almandine (4.3) to pyrope (3.6) is the only good test to determine a specimen's likely identity. Garnet can be distinguished from other gem types by its occurrence in metamorphic rock, its hardness (6.5 - 7.5 on the Mohs scale), colour, refractive index and cubic crystal structure. However, the quickest way to identify garnet is with the use of strong neodymium magnets. Garnet is attracted to neodymium magnets because it contains high concentrations of iron and/or manganese.

Origin and Gemstone Sources

Pyrope garnet sources include China, Madagascar, Myanmar, South Africa, Sri Lanka, Tanzania and the United States. Deposits in the Czech Republic do still exist, but are of minor importance.

Determining Pyrope Garnet Gemstone Value

Pyrope Garnet Colour

The characteristic dark-red of pyrope garnet is found in small sized stones. Bigger gems tend to be very dark, coming close to black.

Pyrope Garnet Clarity and Luster

Pyrope garnet is often inclusion free, so buyers should seek an "eye clean" stone. Pyrope garnet has a beautiful glossy vitreous luster.

Pyrope Garnet Cut and Shape

Pyrope garnet is versatile and can be cut into a wide variety of shapes. Pyrope garnet is not often seen in large sizes. It can be faceted or cut en cabochon. Faceted cuts best exhibit the beauty of pyrope garnet.

Pyrope Garnet Treatment

Pyrope garnet is not known to be treated or enhanced in any way.

Pyrope Metaphysical and healing properties

Pyrope Garnet offer us physical, emotional and spiritual support. Use its healing powers to boost circulation and blood disorders, as well as the digestive tract and immune system. Pyrope emotionally relieves anxiety, and promotes composure, courage and endurance. It lightens the overall mood. It protects the Base and Crown Chakras, and may balance the Heart and Brow Chakras as well.
Pyrope Garnet stimulates warmth and gentleness, unifying the creative forces of the self. On the spiritual path, it also helps open the heart to love - from Divine Love, as well as love of others.
Pyrope Garnets range in colour energies from rose red to deep crimson, including shades of scarlet, amethyst and indigo. It attracts a host of Angels and honours four Goddesses.
Garnet is the traditional birthstone of January, and Pyrope, in various hues, is a natural birthstone for many born at the end of summer through the winter. It is the zodiac stone for those born under the sign of Aquarius and it brings you Fire energy. As an Enhancer Strengthener crystal, it is a talisman of protection.

Properties of Pyrope

Chemical FormulaMg3Al2Si3O12
ColourRed
Hardness7 - 7.5
Crystal SystemIsometric
Refractive Index1.720 - 1.760
SG3.5 - 3.6
TransparencyTransparent to translucent
Double RefractionNone
LusterVitreous
CleavageNone
Mineral ClassPyrope (Garnet)