Kerala Plus Two Geology cheat sheet

Earth's internal layers by composition: crust (oceanic ~7 km, continental ~35 km), mantle (to ~2900 km), core (Fe-Ni); by rheology: lithosphere, asthenosphere, mesosphere, outer core (liquid), inner core (solid).

Moho = seismic discontinuity between crust and mantle; Gutenberg discontinuity at ~2900 km depth marks core-mantle boundary; Lehmann discontinuity separates inner and outer core.

P-wave velocity drops sharply and S-waves cannot pass the outer core - evidence that the outer core is liquid; S-wave shadow zone spans 103°-142° from the epicentre.

Isostasy: Airy model = crustal roots of varying thickness; Pratt model = lateral density variation at constant depth. Mountains have low-density roots floating in denser mantle.

Plate boundary types: divergent (ridges, normal faults, basaltic volcanism), convergent (trenches, subduction, andesitic arcs, thrust faults), transform (strike-slip, no volcanism).

Sea-floor spreading (Hess, 1960s): magnetic stripe symmetry about mid-ocean ridges, age increasing away from ridge, pillow basalts and ophiolite sequences.

Weathering: mechanical (frost, salt, exfoliation) vs chemical (hydrolysis of feldspar to clay, oxidation, carbonation of limestone). Chemical weathering is dominant in Kerala's humid climate.

River erosion forms V-shaped valleys; glaciation forms U-shaped valleys and cirques; wind forms yardangs and barchans. Kerala's laterite caprock is a product of intense tropical chemical weathering.

Earthquake focus is the point of rupture; epicentre is its surface projection. Magnitude (Richter/Mw) is logarithmic energy; intensity (Mercalli) measures observed damage.

Mineral = naturally occurring, inorganic, solid, definite chemical composition, ordered internal structure. Quartz, feldspar, mica, amphibole, pyroxene, olivine, calcite, garnet, kyanite, sillimanite are common rock-formers.

Mohs hardness scale: talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10.

Silicate tetrahedron SiO4^4- is the fundamental unit. Classification: nesosilicate (isolated, olivine, garnet), sorosilicate (Si2O7), cyclosilicate (ring, beryl), inosilicate (chain, pyroxene single, amphibole double), phyllosilicate (sheet, mica, clay), tectosilicate (framework, quartz, feldspar).

Cleavage is controlled by weak planes in crystal structure: mica = one perfect basal cleavage; calcite = three rhombohedral cleavages; halite = three cubic cleavages; quartz = no cleavage (conchoidal fracture).

Feldspar group: orthoclase (K), plagioclase series albite (Na) to anorthite (Ca). Striations on plagioclase distinguish it from orthoclase.

Bowen's reaction series (from high to low temperature): olivine, pyroxene, amphibole, biotite, then K-feldspar, muscovite, quartz.

Polymorphism: same composition, different structure - diamond/graphite (C), calcite/aragonite (CaCO3), kyanite/sillimanite/andalusite (Al2SiO5).

Optical properties under crossed nicols: isotropic minerals (cubic, e.g. garnet, halite) stay dark; anisotropic minerals show interference colours. Birefringence = difference of refractive indices.

Specific gravity: quartz 2.65, feldspar 2.55-2.76, calcite 2.71, galena 7.5, magnetite 5.2. Streak of hematite = red-brown; of pyrite = greenish black.

Igneous classification by SiO2: ultrabasic <45%, basic 45-52%, intermediate 52-65%, acidic >65%. By texture: phaneritic (coarse, plutonic), aphanitic (fine, volcanic), porphyritic, glassy, vesicular, pyroclastic.

Common igneous rocks: granite (acidic, plutonic), rhyolite (acidic, volcanic), diorite/andesite, gabbro/basalt (basic), peridotite (ultrabasic), pegmatite (very coarse).

Magma series: tholeiitic, calc-alkaline (subduction, andesite), alkaline (within-plate, basalt-nepheline). Differentiation by fractional crystallisation, assimilation, magma mixing.

Sedimentary rocks: clastic (sandstone, shale, conglomerate), chemical (limestone, dolomite, rock salt, chert), organic (coal, chalk). Grain size: gravel >2 mm, sand 2-0.0625 mm, silt 0.0625-0.004 mm, clay <0.004 mm.

Sedimentary structures: cross-bedding (current direction), graded bedding (turbidites, way-up), ripple marks, mud cracks (subaerial exposure), bioturbation.

Metamorphism types: contact/thermal (around intrusions, hornfels, marble), regional/dynamothermal (mountain belts, schist, gneiss), dynamic (fault zones, mylonite), burial.

Metamorphic grade indicators: slate -> phyllite -> schist -> gneiss (increasing grade); index minerals chlorite, biotite, garnet, staurolite, kyanite, sillimanite.

Protolith to product: limestone -> marble; sandstone -> quartzite; shale -> slate -> schist; basalt -> greenschist/amphibolite; granite -> gneiss.

Foliation forms by preferred orientation of platy minerals under directed stress; lineation by alignment of elongate minerals. Granoblastic texture is non-foliated (hornfels, marble, quartzite).

Strike = compass direction of a horizontal line on a bedding plane; dip = maximum angle of inclination perpendicular to strike, measured from horizontal. Apparent dip is always less than true dip.

Folds: anticline (older rocks in core, limbs dip away), syncline (younger in core), monocline, isoclinal, recumbent. Plunge is the angle of the fold axis from horizontal.

Fault types by stress: normal (tension, hanging wall down), reverse/thrust (compression, hanging wall up), strike-slip (shear, lateral). Hanging wall = block above the fault plane.

Unconformities: angular (tilted older beds below), non-conformity (sedimentary over igneous/metamorphic), disconformity (parallel beds with erosion surface).

Plate tectonics evidence: palaeomagnetism, sea-floor spreading, Wadati-Benioff zones, matching continental margins, glacial striations, fossil correlation across continents.

Wilson cycle: rifting -> ocean opening -> subduction -> continental collision -> suturing. Himalayas formed by India-Eurasia collision; Western Ghats relate to India's rifting from Madagascar.

Stress vs strain: elastic, plastic (ductile, folding), brittle (faulting). Confining pressure promotes ductile behaviour; low temperature and high strain rate promote brittle failure.

Strike and dip recorded with a Brunton/clinometer compass; true thickness = apparent thickness x cos(dip) when measured perpendicular to strike.

Lineaments and joints: systematic joint sets indicate palaeostress directions; Kerala's NNW-SSE and ENE-WSW lineaments control drainage and laterite distribution.

Fossil preservation types: petrifaction (permineralisation), mould, cast, carbonisation, amber, trace fossils (ichnofossils), replacement.

Index fossils are wide-ranging geographically but short-lived stratigraphically: ammonites, graptolites, trilobites, foraminifera.

Geological time scale (eras): Archaean, Proterozoic, Palaeozoic (Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian), Mesozoic (Triassic, Jurassic, Cretaceous), Cenozoic (Palaeogene, Neogene, Quaternary).

Major extinctions: end-Ordovician, Late Devonian, end-Permian (~252 Ma, largest), end-Triassic, end-Cretaceous (~66 Ma, dinosaurs, iridium anomaly at K-Pg boundary).

Gondwana supercontinent included India, Africa, South America, Australia, Antarctica; its breakup explains the Talchir boulder beds and glossopteris flora in India.

Stratigraphic principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, faunal succession, inclusion.

Lithostratigraphy (formations, groups) vs biostratigraphy (zones) vs chronostratigraphy (systems, series). Kerala's Warkalli and Quilon beds are Tertiary fossil-bearing horizons.

Fossils of India: Gondwana plant fossils (Glossopteris, Gangamopteris), Cretaceous marine fossils of Trichinopoly, Siwalik vertebrates (Ramapithecus, Stegodon).

Radiometric dating: U-Pb in zircon (oldest, most reliable), K-Ar and Ar-Ar in volcanic rocks, Rb-Sr, Sm-Nd, C-14 for young organic material (<50 ka).

India's geological framework: Archaean cratons (Dharwar, Singhbhum, Bundelkhand, Aravalli), Proterozoic basins (Cuddapah, Vindhyan), Gondwana basins, Deccan Traps, Tertiary Himalayan belt.

Dharwar Craton: oldest rocks of peninsular India, greenstone belts (Kolar, Hutti) with gold, banded iron formations, granitic gneisses.

Deccan Traps: ~66 Ma flood basalts, ~500,000 km2, erupted near the K-Pg boundary; related to the Réunion hotspot.

Kerala's geology: Precambrian crystalline basement (charnockites, khondalites, gneisses) of the Southern Granulite Terrain; Western Ghats escarpment; coastal Tertiary sediments (Warkalli and Quilon beds); laterite capping; Recent alluvium and beach sands.

Charnockite (hypersthene-bearing granulite) is Kerala's state rock; khondalite = garnet-sillimanite-graphite gneiss.

Wayanad and Periyar lineaments, Achankovil shear zone, and Bavali lineament control structure and drainage. Nilgiri and Anaimalai hills form the Western Ghats.

Kerala mineral occurrences: monazite-rich beach sands (Thiruvananthapuram-Kollam), graphite (Chavara), china clay (kaolin) in Kollam and Thiruvananthapuram, bauxite/laterite in Kasaragod and Kannur.

Kerala has almost no coal; limited limestone (Thiruvananthapuram, Palakkad) and no major metallic ore mining. Seismic zone III for most of Kerala (zone II for parts of the coast).

The Kerala coast is a submergent-emergent coast with lagoons (Vembanad, Ashtamudi), barrier beaches, and backwaters formed by Recent sea-level change.

Ore = mineral aggregate from which a metal can be extracted economically. Gangue = waste minerals. Grade = metal content; cut-off grade controls economic viability.

Ore genesis types: magmatic segregation (chromite, magnetite), hydrothermal veins (gold, base metals), porphyry copper, sedimentary (banded iron formation, phosphorite), residual/lateritic (bauxite, nickel), placer (monazite, gold).

India's key resources: iron ore (Bailadila, Singhbhum, Bellary), manganese (Balaghat), bauxite (Koraput), coal (Jharia, Raniganj, Neyveli lignite), mica (Koderma), gold (Kolar, Hutti), petroleum (Bombay High, Assam).

Atomic minerals: uranium (Jaduguda), thorium from monazite beach sands of Kerala, Tamil Nadu, Odisha.

Kerala's heavy mineral sands contain ilmenite, rutile, monazite, zircon, garnet; Chavara is a major source of monazite and ilmenite.

Industrial minerals: kaolin (paper, ceramics), limestone (cement), silica sand (glass), graphite (crucibles), talc, gypsum.

Reserves vs resources: reserve = proved and economically mineable; resource = total including sub-economic. Classification by confidence: measured, indicated, inferred.

Laterite (bauxite ore when Al-rich) forms by tropical leaching of silica and enrichment of iron and aluminium oxides; Kerala laterite is used as building brick.

Mineral conservation: beneficiation, recycling, substitution, and preventing illegal beach-sand mining are key policy concerns in Kerala.

Porosity = volume of voids / total volume. Permeability is the ability to transmit fluid; high porosity does not guarantee high permeability (clay is porous but impermeable).

Aquifer types: unconfined (water table), confined (artesian, piezometric surface), perched. Aquiclude, aquifuge, aquitard are relative terms of transmissivity.

Darcy's law: Q = K i A, where K = hydraulic conductivity, i = hydraulic gradient, A = cross-sectional area.

Kerala's aquifers: laterite (shallow, dug wells), weathered crystalline (limited, fractured), coastal alluvium (saline intrusion risk), river banks.

Groundwater quality parameters: TDS, hardness, pH, chloride, fluoride, nitrate, iron. Fluoride >1.5 mg/L causes fluorosis; nitrate >45 mg/L indicates contamination.

Seawater intrusion occurs when pumping lowers the freshwater head below the Ghyben-Herzberg relation (freshwater lens depth ~40 times the height above sea level).

Landslides in Kerala occur in high-rainfall Western Ghats slopes with thick laterite/soil cover; triggers include deforestation, slope cutting, and intense monsoon rainfall.

Coastal erosion and backwater pollution (Vembanad, Ashtamudi) are major environmental issues; sand mining and saline intrusion affect groundwater.

Environmental impact assessment (EIA) stages: screening, scoping, baseline study, impact prediction, mitigation, EMP, public hearing, clearance.

Geological field equipment: Brunton compass/clinometer, hand lens (10x), hammer, GPS, topographic sheet, acid bottle (10% HCl for calcite), streak plate, magnet.

Field mapping procedure: establish base map, record strike/dip, lithology, structure, contacts; use traverses, cross-sections, and sketch logs.

Rock identification in hand specimen: colour, grain size, texture, mineralogy, hardness, reaction with acid, cleavage, and foliation.

Thin-section petrography: identify minerals by relief, cleavage, twinning (plagioclase), extinction angle, pleochroism, and interference colours under crossed nicols.

Sieve analysis for grain-size distribution; plotting cumulative curves gives sorting, skewness, and median grain size.

Geological cross-sections are constructed perpendicular to strike; apparent dip must be corrected to true dip using tan(apparent) = tan(true) x sin(angle between section and strike).

Topographic maps: contour interval, scale, spot heights, and drainage patterns reveal structure; V-shaped contours pointing upstream indicate valleys.

Remote sensing and GIS: satellite imagery (Landsat, Sentinel) for lineament mapping, land-use change, and groundwater potential zoning.

Report writing and data quality: record coordinates, photographs with scale, sample numbers, and field notes; use standard stratigraphic nomenclature.

Geological field equipment: Brunton compass/clinometer, hand lens (10x), hammer, GPS, topographic sheet, acid bottle (10% HCl for calcite), streak plate, magnet.

Field mapping procedure: establish base map, record strike/dip, lithology, structure, contacts; use traverses, cross-sections, and sketch logs.

Rock identification in hand specimen: colour, grain size, texture, mineralogy, hardness, reaction with acid, cleavage, and foliation.

Thin-section petrography: identify minerals by relief, cleavage, twinning (plagioclase), extinction angle, pleochroism, and interference colours under crossed nicols.

Sieve analysis for grain-size distribution; plotting cumulative curves gives sorting, skewness, and median grain size.

Geological cross-sections are constructed perpendicular to strike; apparent dip must be corrected to true dip using tan(apparent) = tan(true) x sin(angle between section and strike).

Topographic maps: contour interval, scale, spot heights, and drainage patterns reveal structure; V-shaped contours pointing upstream indicate valleys.

Remote sensing and GIS: satellite imagery (Landsat, Sentinel) for lineament mapping, land-use change, and groundwater potential zoning.

Report writing and data quality: record coordinates, photographs with scale, sample numbers, and field notes; use standard stratigraphic nomenclature.

Geological field equipment: Brunton compass/clinometer, hand lens (10x), hammer, GPS, topographic sheet, acid bottle (10% HCl for calcite), streak plate, magnet.

Field mapping procedure: establish base map, record strike/dip, lithology, structure, contacts; use traverses, cross-sections, and sketch logs.

Rock identification in hand specimen: colour, grain size, texture, mineralogy, hardness, reaction with acid, cleavage, and foliation.

Thin-section petrography: identify minerals by relief, cleavage, twinning (plagioclase), extinction angle, pleochroism, and interference colours under crossed nicols.

Sieve analysis for grain-size distribution; plotting cumulative curves gives sorting, skewness, and median grain size.

Geological cross-sections are constructed perpendicular to strike; apparent dip must be corrected to true dip using tan(apparent) = tan(true) x sin(angle between section and strike).

Topographic maps: contour interval, scale, spot heights, and drainage patterns reveal structure; V-shaped contours pointing upstream indicate valleys.

Remote sensing and GIS: satellite imagery (Landsat, Sentinel) for lineament mapping, land-use change, and groundwater potential zoning.

Report writing and data quality: record coordinates, photographs with scale, sample numbers, and field notes; use standard stratigraphic nomenclature.