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Here Previously asked Question and Answers are saved...
Question : What mfs stands for and what significance it has in Reservoir Geology?
Answer: MFS stands for Maximum Flooding Surface. This is a surface of deposition in a stratigraphic sequence and indicates the deposition at the time shoreline is at its maximum landward position. In other words, mfs is a depositional surface at the time of maximum transgression.
It plays important role in stratigraphic sequence studies as an environmental indicator. Marine shelf and basinal sediments associated with this surface are the results of slow rates of deposition by pelagic- hemipelagic sediments and they are usually thin. MFS is characterized by presence of radioactive and often organic rich shales, glauconite, hard grounds, thin bedded concentration of fauna with high abundance and diversity.
Question : What is Allostratigraphy?
Answer: This system classify the rock stratigraphy on the basis of bounding surfaces that provide the timing of accumulation.
Question : What is Stratigraphic sequence?
Answer: Stratigraphic sequence is a succession of strata that are genetically related and bounded at its top and base by unconformities and their correlative conformities.
Question : What is migmatite?
Answer : A rock that shows characters of both igneous and metamorphic materials is called migmatite. This is probably caused by the partial melting of igneous rock at the upper limit of metamorphism in the presence of water. Such rocks show large crystals with laminar flow structures.
Question : What is fumarole?
Answer : Fumarole is a small vent or opening in the ground from which steam or heated groundwater, hydrogen sulfide or other volcanic gases pour out. However, there is no lava coming out of this vent. Many dormant or inactive volcanos contain active fumaroles.
Question : What are the major uses of petrophysical logs?
Answer : Petrophysical logs are mainly used in exploration to correlate zones and to assist with structure and isopach mapping, logs help define physical rock characteristics such as lithology, porosity, pore geometry, and permeability. Logging data is used to identify productive zones, to determine depth and thickness of zones, to distinguish between oil, gas, or water in a reservoir, and to estimate hydrocarbon reserves. Also, geologic maps developed from log interpretation help with determining facies relationships and drilling locations.
Question : What is BIF?
Answer: BIF stands for Banded Iron Formation. It is a marine sedimentary mineral deposit with alternating light and dark colored minerals where light color is mainly due to silica rich minerals and dark color comes from iron rich minerals. It is considered to be formed as a chemical deposit from the sea around 2 to 3 billion years ago with a increased level of oxygen in the atmosphere.
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Artesian well
Question: What is an Artesian well? Ans: In simple term it is a flowing well. Here water flows out of a well without pump. If hydraulic pressure in an aquifer is enough to expel water out of the well, then such a well is called as an Artesian well. Question: What is Calcarenite? Answer: Calcarenite is a type of sandstone, which is mainly composed of calcite grains. Question: What is catastrophism? Answer:This is a hypothesis for the development of mountains, valleys and other huge structures in the earth crust. As per this hypothesis all these great structures are the result of very strong but short series of upheavals in the earth crust. Question: What is cleavage? Answer: The tendency of certain minerals to split along distinct planes determined by the crystal structure. |
Spheroidal weathering
Question: What is Spheroidal weathering? Answer: In the process of weathering hard rocks such as Basalt develops multiple sets of joints resulting in square shaped blocks. These blocks are then further easily weathered by the action of solution (subsurface water with dissolved chemicals derived from the minerals) along the edges making the process of weathering faster. Such weathering results in roundening of these blocks, forming rounded boulders. In Geological term such weathering is called spheroidal weathering, a typical characteristic of Basalt. Question: What is Contact metamorphism? Answer: Metamorphism that is caused by the heat of magma when it intrudes an igneous rock body. Question: What is Moho? Ans: The outer most layer of the earth is called as Crust and the lower boundary of this crust is defined as the MOHO. From seismic study it is known that there is a seismic discontinuity at this layer and it serve as a reflector. Question: What is a tsunami? Ans: Tsunamis are huge sea waves that are formed due to an earthquake in coastal regions. Such waves are very destructive in nature and cause big damage along the shoreline Question: What is a barchan? Ans: Barchan is a type of dune which is crescent in shape. Such dunes are small in size with the limbs on the downwind side. Focus and Epicenter of an EarthQuake Question: What is the difference between focus and epicenter of an earthquake? Ans: The point of fracture inside the earth where earthquake originates is called the focus of the earthquake and the point on the earth's surface directly above the focus is the epicenter.
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Nodules
Question: What is a nodule and how is it formed? Ans: Nodules are small irregular shaped bodies found in a big rock body. Composition of these nodules is different than the main rock body that encloses it. They are formed due to replacement of original mineral by some different matter. They are commonly seen in limestones and dolomite. Here silica replaces the original rock body to form chert or flint nodules. Question: What are polymorphs? Minerals with same chemical composition but different crystal structures are called Polymorphs. A good example of this phenomenon is Carbon, which forms Diamond that is the hardest substance, found in the nature and Graphite, which is a very soft mineral. Both Diamond and Graphite have similar chemical composition but different crystal structure. Question: Define Aquiclude, Aquifuge and Aquifer? Answer: An Aquiclude is a rock formation which contains water but is unable to transmit is to a well or spring. In other words an aquiclude is a formation which has porosity but lacks permeability. On the other hand a rock that has no porosity and permeability is called Aquifuge. That means this type of rock is so tight that it can not hold or transmit water. An Aquifer is a permeable rock formation that has the capability of holding and transmitting groundwater below the water table. In other words a reservoir formation that can produce sufficient amount of water is called an aquifer. Question: What are Vesicles and amygdule? Answer: Vesicles are gas cavities formed in a volcanic rock when gas escapes from lava during its cooling. When such vesicles get filled with mineral matter such as quartz or calcite then the term amygdule is used. |
Sabkha
Question: What is a Sabkha? Sabkhas are saline flat landforms. They are mainly found in arid climates. Such Sabkhas charectestically lie just above the water table. Here crust rich in gypsum and halite veins normally underlie thin layer of sand and silt. Question: What is carbon dating" dating technique and what is it use for? Ans: Carbon dating method is used to determine the age of rocks. This type of dating technique can be used only with the rocks that contain organic material. This is mainly because, carbon is found only in the living organism. Some portion of this carbon is present in the form of an unstable radioactive isotope called carbon 14 or C-14.Once an organism is dead, this C-14 start disintegrating at a steady rate. Since the rate of disintegration for C-14 is known, the age of organism can be determined by measuring the remaining amount of C-14. Once the age of the organism is determined it can be easily correlated with age of the rock as well.
This is considered a reliable and absolute method but it can not be used for the rocks that are formed before the appearance of life on the earth.
This method was introduced by Mr. Willard Libby in 1947.
Question: What is a mineral?
Ans: A mineral is a solid chemical matter with a definite pattern of atoms. Gases and liquid do not have a definite atomic pattern and hence they are not minerals. This atomic arrangement depends mainly on temperature and pressure to which mineral is subjected.
Question: WHAT IS THE MAIN COMPOSITION OF EARTH CORE?
Ans: The central and the inner most part of the earth is called Core and is mainly composed of Iron (Fe) with some Nickel (Ni).
Question: What is Base Level of a Stream?
Answer: Base level of a stream is the lowest level below which a stream can not erode the channel
through which it is flowing. Usually this is equal to the sea level but some times certain local factors such as a hard and resistant rock formation or a lake may become the controlling factor.
Question: What is Batholith?
Answer: A large discordant mass of coarse grained igneous rocks with an exposed surface area of more than 100 square kilometers and a depth of about 30 kilometers. This may result due to intrusion in a country rock or may be formed by the metamorphism of existing rock. They are generally found in elongated mountain ranges and are exposed after the overlying rocks been eroded away.
Question: What is bed load? Answer: A body of coarse-grained sediments that move along the bottom of a stream by rolling and bouncing over the streambed is called the bed-load.
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Unconformity
Question: What is an unconformity? Ans: Any break in rock sequence by an erosional surface is called unconformity. When sediments are deposited on a surface that was exposed to natural agents of weathering and erosion, a clear boundary marks the two rock sequences which is referred to as an unconformity. If the lower sequence of rocks are tilted before the second depositional period, then such unconformity is called as Angular Unconformity. If the older rock sequence is metamorphosed prior to second deposition then the boundary marking two sequences is called Non-conformity. Question: What are Clastic rocks? Answer: Clastic rocks are sedimentary rocks mainly composed of broken fragments of pre-existing rocks, fossils or minerals that were mechanically transported, deposited and compacted to form a sedimentary rock. Question:What is Butte? Answer: A Butte is a flat topped hill with steep sides. Some times when a flat sequence of sedimentary layers undergoes erosion, a resistant layer may cap the softer layers underneath, protecting the sequence from further erosion, resulting in such flat topped hills. Question: What is Craton? Answer: A large segment of the earth's continent that have escaped any tectonic activity for the last two billion years and remained earthquake free. The craton is mainly composed of granite and metamorphic rocks. It is made of continental shield and the surrounding continental platform. |
Mushroom rocks
Question: What are mushroom rocks? Ans: Mushroom rocks are the characteristic rocks of desert with a narrow base and broad top giving mushroom like structure. They are formed due to differential wind erosion. When a rock comprised of alternate layers of hard and soft beds, under goes wind erosion, the softer layer tends to get eroded faster than the harder layer, resulting in such mushroom shaped rocks (see picture to the right). Question: What are stalactites and stalagmites? Ans: These are commonly seen in limestone caves. Rainwater in its down course dissolves Co2 from the air, forming a weak acid called carbonic acid (CO2+H2O=H2CO3). This mild acid when flows under ground it dissolves some soluble mineral matters from the rock its passing through. This gradually corrodes the limestone and the natural fractures in the rock slowly widen over a period of time. This finally results in a network of underground channels and at places widen up to form big caves. When water, carrying dissolved mineral matter flow through such channels some part of the dissolved matter may get deposited. As water drips from the roof of a cave, some part of it evaporates leaving behind a small part of its load. This material is known as dripstone or flowstone. Continuos deposition of such material on a roof of a cave results in hanging structures called stalactite. When this water drips on the floor of the cave, it results in growth of inverted cone shaped structures called stalagmite. If such deposition continue the stalactite and stalagmite may join together to form a continuos single structure called column. Question: What is PLAYA? Ans: This is a Spanish term used for large flat depression in a desert which is periodically filled with water. When such depression is filled with water then the term Playa Lake is used. Question: What are Concretions? Answer: Concretions are spherical mineral bodies embedded in a host rock formed by precipitation of mineral matter around a nucleus such as fragment of shell or bone or a leaf. Question: What is Diatreme: Answer: Sometimes highly volatile gas escapes with an explosion from a volcanic vent leaving behind angular rock fragments in the vent. A vent filled with such angular fragments is called Diatreme. Question: Define the term Aphinitic? Answer: Aphinitic is a term used to describe fine grained texture in igneous rocks. Question: What is Caldera? Answer: A Caldera is a large depression in a volcanic terrain, which is more or less circular in shape and is mainly formed due to the collapse of a volcanic cone. When a magma reservoir beneath a cone becomes empty after an eruption, the top part of the cone may collapse resulting in a huge basin like depression called Caldera. A Caldera may measure more than 15 kilometers in diameter and more than 1000 meters in depth. Question: What is Atoll? Answer: Atoll is a roughly circular reef that may be continuous or broken, surrounding a shallow lagoon. When an island in an ocean, which has barrier reefs at the margins, sinks below sea level, such structures are created.
Question: What is Asrobleme? Answer: Astrobleme is a circular erosional feature, which is considered to form due to the impact of a meteorite or comet.
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Weathering and Erosion
Question: What do you mean by weathering and erosion. Ans: Weathering is the process of breaking of rocks into smaller fragments by some natural agents such as wind, water etc. etc. EROSION is the transport of rocks or broken fragments of rocks by natural agents of transport. Wind, water and ice act as agents of transport and shift rock fragments or sediments from one place to another. Picture to the left is a beautiful example of such natural processes. This picture is of mountains at the border of United Arab Emirates and Oman. Here cretaceous limestone layers were subjected to tectonic forces resulting in upliftment and folding of the strata. These rocks then further underwent weathering and erosion giving rise to eroded crest part with beds of fold dipping in either direction, as seen in the picture. Question: What are plutonic rocks? Ans: Rock that are formed due to cooling of magma beneath the earth surface are called Plutonic rocks. Granite and Gabbro are the examples of such rocks. Question: What is a Geosyncline?
Ans: A huge depression in the earth crust that may serve as depositional basin for sedimentary or igneous rocks. Thickness of such deposition may reach in thousands of meters and length of such a depression may be over a thousand of kilometers
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Focus and Epicenter of an EarthQuake
Question: What is the difference between focus and epicenter of an earthquake? Ans: The point of fracture inside the earth where earthquake originates is called the focus of the earthquake and the point on the earth's surface directly above the focus is the epicenter.Question: What is a Geosyncline? Ans: A huge depression in the earth crust that may serve as depositional basin for sedimentary or igneous rocks. Thickness of such deposition may reach in thousands of meters and length of such a depression may be over a thousand of kilometers Question: What is the difference between MAGMA and LAVA? Ans: Deep within the earth due to high temperature and pressure conditions, earth material is formed in molten condition which is called magma. Magma is always associated with gasses and liquids, which make it more volatile, and it tries to move upwards. When this magma escapes to the earth surface through a weak zone or fracture, it is called volcano. In other words volcano is the passage of molten earth material to the surface.When magma is erupted on the surface from a volcano then it is called LAVA. Question: What is the difference between a HOT SPRING and a GEYSER? Ans: A hot spring is heated ground water that comes out on the ground surface.A geyser is sort of a fountain that erupts with force at certain times. The eruption may shoot up to 30-60 meters into the air. Eruption is then followed by steam flow. Question: What is the calculated radius of earth? Ans: The approximate calculated radius of the earth is around 6370 kms. However, radius at the equator is around 22 km more than at the poles. Question: What is Pangea? Ans: In 1912, a German scientist, Alfred Wegner proposed a theory that all the continents were once together forming a huge supercontinent which he called PANGEA. This is now a widely accepted theory through out the world. Question: What is Agate? Answer: Agate is a colorful variety of siliceous rocks, which is made of alternate bands of chalcedony and chert of various colors. Question: What is Alluvium? Answer: Alluvium is sedimentary deposit composed of sorted or unsorted gravel, sand and clay that had been deposited by a stream on the stream's channel or flood plain.
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