GEOLOGY FREE NOTES

 1) The Earth’s magnetic field originates from convection in which one of the following layers? (A) Inner core (B) Outer core (C) Lithosphere (D) Asthenosphere Solution: Outer core of the earth produces magnetic field because the molten metals present within the core are are in motion circulating in convection currents that produce electrical current. The mechanism by magnetic field is generated is known as Dynamo. 2) Which one of the following logging tools is used to measure the diameter of a borehole? (A) Sonic (B) Density (C) Neutron (D) Caliper Solution: Density, Sonic and Neutron logs are porosity logs Sonic log : measure interval transit time Neutron log : measure hydrogen concentration in the formation Density log : measure the density of the formation SP log : measure DC potential difference Gamma ray log : measure volume fraction of shale 3) The given figure depicts an array used in DC resistivity surveys, where the current electrodes are denoted by C1 and C2, and potenti...

 SEDIMENTARY STRUCTURES Large scale features Laminae < 1 cm, Beds > 1cm UPPER BEDDING : Rain print, Ripple marks, Mud cracks LOWER BEDDING - (Erosional structures) S cour marks : Flute cast : have a bulbous nose at their upstream end helps to infer paleocurrent direction Obstacle scour / Current crescent Longitudinal scour , Gutter casts Tool marks : Groove cast, Chevron marks, Prod casts, Bounce marks, Skip marks (Can’t identified in vertical section) SYN-DEPOSITIONAL : Graded bedding, Cross bedding/lamination POST DEPOSITIONAL/DEFORMATIONAL Load cast - gravitational instability Convolute bedding Dish and pillar structure - water escape structures, fluidisation Ball and pillow structure Slump structure BASED ON ENVIRONMENT Tidal : Herringbone, Sub-tidal : Double mud drapes Inter-tidal : Rain print, Mud crack, Adhesion ripple Storm : Hummocky cross Fluvial : Epsilon cross stratification TOP AND BOTTOM CRITERIA Oscillation ripple Load cast - soft sediment deformation...

  Basins are divided into 5 types: 1) Basins in divergence settings : Terrestrial rift valleys and Proto oceanic rift troughs 2) Basins in Intraplate settings : Intracratonic, Passive margins, Active ocean basin, Dormant ocean basin 3) Basins in convergent settings : Trenches, Trench-slope basins, Fore arc basins, Intra arc basins, Back-arc basins, Retroarc foreland basin, Remnant ocean basins, Retro-arc foreland basins, Piggyback basins, Foreland intermontanne basins 4) Basins in transform and transcurrent settings : Transtensional, Transpressional, Transrotational basins 5) Basins in Hybrid settings : Auloacogens, Impactogens 1) Basins in divergence settings : Terrestrial rift valleys : East african rift Proto oceanic rift troughs : Red sea 2) Basins in Intraplate settings : Intracratonic : Vindhyan basin Passive margins : Kerala-Kankan , Krishna-Godaveri basin Active ocean basin : Indian ocean Dormant ocean basin : Gulf of Mexico 3) Basins in convergent settings : Trench...

  TERMINOLOGY A steroid belt : region between mars and jupiter Kuiper belt : region between neptune and pluto Meteoroids : asteroids collides with each other result in formation of smaller pieces Meteors : when meteroids enters the earth’s atmosphere at high speed and burn up, they are called meteors Meteorite : don’t vapourize completely, has survived passage through atmosphere finally landed on earth TYPES OF METEORITES Siderites or Iron meteorites : 98% metal Siderolites or stony irons : 50% metal and 50% silicates Aerolites or stony meteorites : include silicates Tektites : 75% tectoslicates IRON METEORITES Shows widmastatten texture Differentiated meteorites, represent the core of differentiated asteroids Two nickel alloys present Kamacite : Ni poor Taenite : Ni rich Further divisions Hexahedrites (4-6% Ni) Octahedrites (6-12 % Ni) Ataxites ( >12% Ni) STONY-IRON METEORITES Equal amount of silicates and metals (Fe-Ni alloys) Two groups Pallasites : characterized by...

ORE MINERAL : a mineral from which one or more metal can be extracted (Chalcopyrite - Cu, Galena - Pb) GANGUE : Unnecessary material associated with ore TENOR : Total metal content of an ore GRADE : Concentration of metal in an ore CUT OFF GRADE : Grade below which it is not possible to mine, i.e lowest grade which will be mine HOST ROCK : Rock which contain ore deposits COUNTRY ROCK : Rock which surrounds the ore deposits BENEFICIATION : Process of removal gangue to produce a high grade ore deposit ORE GENESIS : Process of formation of ore deposits HYPOGENE Primary mineral deposition ascending hydrothermal solution SUPERGENE Secondary mineral deposition descending hydrothermal solution SYNGENETIC : Formed during same time of formation of host rock EPIGENETIC : Formed after formation of host rock STRATIFORM : Reflect stratification Concordant in nature Ex: Stratiform copper, Kupferscheiper STRATABOUND: Restricted to a particular lithology Mostly discordant Ex: MVT deposit, Z...