UPSC Geology 2026 — Paper I

(a) Define transform and transcurrent (wrench/strike-slip) faults and bring out the essential difference between them; 'illustrate using neat sketches' makes labelled diagrams compulsory, not optional. (b) Two linked demands: (i) discuss all three types of plate boundaries with suitable sketches, and (ii) append a separate note on mid-oceanic ridges. Both parts must appear; sketches are compulsory. (c) Describe every type of unconformity with neat sketches and then add a separate note on their geological significance. Both the typology (with diagrams) and the significance note are separately marked. (d) Describe the major geomorphic (physiographic) provinces of the Indian subcontinent and then add a note on why each is geologically significant. Both the description of provinces and the significance note are marked. (e) Name and define all the resolutions used in remote sensing (spatial, spectral, radiometric, temporal) and explain the significance of each, preferably with geological relevance and sensor examples.

• Transform fault: strike-slip fault forming a plate boundary between two offset boundary segments (ridge–ridge, ridge–trench, trench–trench)
• Transform slip constant on the active segment and ending at the junctions, with an inactive fracture zone beyond; slip opposite to ridge offset
• Transcurrent fault: intra-plate strike-slip fault whose displacement dies out towards its tips
• Labelled sketches of both, with examples such as San Andreas and Great Glen or Karakoram faults
• Divergent, convergent (with ocean–ocean, ocean–continent, continent–continent) and transform boundaries with examples
• Sketches or cross-sections of the boundary types, labelled
• Mid-oceanic ridge: about 65,000 km long, central rift, spreading, pillow basalts, shallow earthquakes, transform offsets
• Magnetic stripes, ocean-floor age increasing away from the ridge, spreading rates
• Angular unconformity, disconformity, nonconformity and paraconformity, each defined
• Labelled sketches showing the erosion surface for each type
• Significance: hiatus, uplift and erosion, orogenic movement, stratigraphic subdivision, correlation problems
• Economic or palaeogeographic importance, with an example
• Himalayan mountain belt with its subdivisions and the MCT, MBT and HFT
• Indo-Gangetic-Brahmaputra plain, Peninsular plateau, coastal plains and islands
• Geological character of each: young fold-thrust belt, alluvial foreland basin, ancient shield with Deccan Traps
• Significance: collision tectonics, groundwater and hydrocarbons, mineral wealth
• Spatial resolution: pixel size or IFOV, with example sensors and effect on mapping scale
• Spectral resolution: number and width of bands (multispectral versus hyperspectral) and mineral identification
• Radiometric resolution: number of bits and discrimination of small radiance differences
• Temporal resolution: revisit period and monitoring applications, with the trade-offs

(a) Two parts of roughly equal weight: (i) describe the guiding principles and procedure of geological mapping, and (ii) using sketches, describe the different categories of symbols used on a geological map. Drawn symbols are compulsory for the second part. (b) Two linked demands: (i) discuss how drainage systems are controlled by the underlying lithology and structure, and (ii) explain the concepts of antecedent and superimposed drainage with examples. Examples are explicitly required. (c) Two demands: (i) a balanced comparison giving both merits AND limitations of aerial photographs versus satellite imagery, and (ii) an explanation of how multispectral data assist in identifying lithology and structure. A one-sided list will not do.

• Principles: base map and scale, prior study, traverses and contact tracing, location of observations
• Recording of lithology, contacts, strike and dip, structures and samples; laws of superposition, original horizontality and cross-cutting; V-rule
• Symbol categories: bedding attitude, contacts, faults, folds, unconformity, other features
• Drawn symbols: strike and dip, horizontal and vertical beds, solid, dashed and dotted contacts, fault and fold signs
• Lithology control: drainage density and permeability, dendritic pattern on homogeneous rocks
• Structure control: trellis, rectangular, radial, centripetal and annular patterns with their causes
• Antecedent drainage defined, with Himalayan examples (Indus, Sutlej, Brahmaputra)
• Superimposed drainage defined, with an example
• Aerial photographs: high resolution and stereo as merits; small coverage, distortion and limited spectral range as limitations
• Satellite imagery: synoptic, repetitive, multispectral and digital as merits; coarser resolution, clouds and cost as limitations
• Multispectral lithology: iron oxide, clay/carbonate SWIR and thermal-infrared silicate signatures
• Processing and structure: composites, ratios, lineaments and fold patterns

(a) Two parts: (i) discuss the importance of remote sensing AND GIS in geological mapping, and (ii) elucidate the specific role of both in mineral exploration. The GIS component must be treated separately from remote sensing, not merged into it. (b) Two demands: (i) discuss the types of folds — i.e. the standard geometric classifications — and (ii) add a separate note classifying folds by the mechanism of folding. The mechanism-based note is separately marked and cannot be skipped. (c) Describe homogeneous and heterogeneous deformation (strain) of rocks, contrasting them, and then add a distinct note on progressive deformation — the accumulation of incremental strain and its structural consequences.

• RS in mapping: synoptic view, lithological discrimination, lineaments and structure, photogeological base map, less field time
• GIS in mapping: layered spatial database, integration of geology, geophysics, geochemistry and RS, digital updating, DEM and 3D analysis
• RS in exploration: host rocks, structural controls and hydrothermal alteration (iron oxide, clay, alunite) from spectral signatures
• GIS in exploration: data integration, overlay and buffer analysis, weights-of-evidence or fuzzy prospectivity modelling, target ranking
• Geometric types: anticline and syncline, dome and basin, monocline, and forms such as chevron, box and isoclinal
• Classification by axial plane attitude (upright, inclined, overturned, recumbent), plunge and interlimb angle (gentle to isoclinal)
• Ramsay's classes or parallel versus similar folds
• Mechanism: buckling (flexural slip and flow), passive or shear folding, bending, drape or forced folds
• Homogeneous strain: uniform, straight parallel lines stay straight and parallel, circle becomes an ellipse
• Heterogeneous strain: variable, lines curve, with folds, boudins and shear zones as examples
• Contrast of the two, including the effect of scale
• Progressive deformation: incremental strains along a strain path, finite strain, coaxial versus non-coaxial, structural consequences

(a) Three explicit demands: define an earthquake; explain HOW the epicentre is located (the method, not just the definition); and discuss the disaster risk associated with earthquakes of different magnitudes. All three must be answered. (b) Two parts: (i) discuss the currently most accepted hypothesis for the origin of the Earth — the modern nebular/solar-disc accretion model — with reasons for its acceptance, and (ii) add a note, WITH a sketch, on the internal structure of the Earth. (c) Three demands: define foliation, classify the various types of foliation, and discuss the processes/mechanisms by which foliations form. The mechanism part is as heavily weighted as the typology.

• Definition: sudden release of elastic strain energy giving seismic waves; focus and epicentre defined
• Epicentre by S–P interval at three or more stations, distance circles and triangulation
• Magnitude scale is logarithmic (10× amplitude, about 32× energy); risk graded from minor to great earthquakes
• Other controls on risk: depth, soil amplification and liquefaction, construction, population, secondary hazards; Indian examples and seismic zones
• Nebular (solar-nebula) hypothesis: collapse of a cloud into a rotating disc, planetesimals, protoplanets
• Supporting evidence: planetary orbits, meteorite age of 4.56 Ga, compositional zoning, observed protoplanetary discs
• Early Earth: accretion, differentiation into core, mantle and crust, and the giant impact origin of the Moon
• Interior with a labelled sketch: crust, mantle, outer core (liquid) and inner core (solid), with depths and seismic evidence
• Definition: planar fabric of aligned minerals or layering, normal to maximum shortening
• Types: slaty cleavage, phyllitic foliation, schistosity, gneissic banding, spaced or crenulation cleavage
• Processes: mechanical rotation, pressure solution, recrystallisation and neocrystallisation
• Further processes: flattening, metamorphic differentiation and shear-zone (mylonitic) foliation

(a) Discuss the special conditions — sedimentological, geochemical, biological and diagenetic — that permit the preservation of the soft (non-mineralised) parts of organisms, which are normally destroyed by decay and scavenging. (b) Discuss the principles on which magnetostratigraphy rests — how rocks record the geomagnetic field, why polarity reversals give globally isochronous datum planes, how a polarity column is built and how it is correlated with the geomagnetic polarity time scale. (c) Two linked tasks: (i) mark and label the cratons and the mobile belts of India correctly on the outline map supplied in the answer booklet, and (ii) list, craton by craton and belt by belt, the major economic minerals associated with each. Both the map and the mineral list are marked. (d) Two demands: define and describe the hydrologic cycle with its components, and then explain specifically why rainwater harvesting matters for GROUNDWATER management — not merely for water supply in general. (e) Explain what drainage-basin morphometry is, name and define its linear, areal and relief parameters (with formulae), and explain how these parameters are used in groundwater studies — the second half is as important as the first.

• Rapid burial in fine sediment or ash, sealing the body from scavengers
• Anoxic bottom water and absence of scavengers and bioturbation
• Early diagenetic mineralisation (phosphate, pyrite, silica, carbonate concretions) replacing soft tissue
• Special media (amber, permafrost, asphalt, hypersaline water) and examples of Lagerstätten such as Burgess Shale
• Rocks acquire remanent magnetisation (thermoremanent and detrital) that records field polarity
• Geomagnetic polarity reversals are global and near-instantaneous, hence isochronous markers
• Sampling, demagnetisation and construction of a polarity column of normal and reversed chrons
• Correlation with the geomagnetic polarity time scale using radiometric or fossil anchors
• Map with cratons marked: Dharwar, Bastar, Singhbhum, Bundelkhand and Aravalli
• Map with mobile belts marked: Aravalli–Delhi, Central Indian Tectonic Zone, Eastern Ghats, Southern Granulite and Himalaya
• Minerals craton by craton (gold and iron in Dharwar, iron ore in Bastar and Singhbhum, and so on)
• Minerals belt by belt (copper in Khetri and Malanjkhand, manganese, bauxite, graphite, sillimanite)
• Definition of the hydrologic cycle driven by solar energy and gravity
• Components: evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater flow
• Rainwater harvesting recharges aquifers and raises the water table (check dams, percolation tanks, recharge pits, rooftop)
• Benefits: reduces runoff and erosion, sustains base flow, improves quality, checks seawater intrusion
• Definition of morphometry as quantitative basin and network measurement
• Linear parameters: stream order, bifurcation ratio, stream length
• Areal parameters (drainage density, stream frequency, form factor, circularity and elongation ratios) and relief parameters (relief, relief ratio, ruggedness)
• Groundwater significance: high Dd and steep relief mean low recharge; watershed prioritisation and recharge site selection with RS and GIS

(a) Two demands: (i) COMPARE the major morphological characters that separate the human family (Hominidae in the traditional sense, i.e. the bipedal hominins) from the ape-like primates, and (ii) discuss the evolutionary trend of the group, illustrating it with fossil evidence from India. (b) Three demands: define Continental Flood Basalt with its characteristics and global examples; give the stratigraphic classification of the Deccan Trap; and comment specifically on why inter-trappean beds are important. (c) Discuss the hydrogeological properties (porosity, permeability, specific yield, transmissivity, storativity) of the main rock types — unconsolidated sediments, sandstone, shale, limestone, crystalline hard rock and basalt — and explain how this knowledge is used in groundwater studies.

• Locomotion and posture: bipedalism, foramen magnum, S-shaped spine, pelvis and foot compared with apes
• Brain size (about 450 cc to 1350 cc), dentition (small canines, no diastema, parabolic arch), face and skull compared
• Evolutionary sequence from Australopithecus and Homo habilis through Homo erectus to Homo sapiens with increasing brain size and tool use
• Indian evidence: Siwalik Sivapithecus and Gigantopithecus, Narmada skull cap (Hathnora), and Acheulian tools
• CFB defined: huge volume of basalt from fissures in a short time, tholeiitic, horizontal flows, red boles, dyke feeders
• Global examples: Deccan, Siberian, Columbia River, Paraná–Etendeka, Karoo–Ferrar, Ethiopian
• Deccan stratigraphy: Lower, Middle and Upper Traps, and Sahyadri Group with Kalsubai, Lonavala and Wai subgroups and their formations
• Inter-trappean beds: freshwater sediments with fossils that give age and palaeoenvironment, mark pauses and act as aquifers
• Definitions: porosity, permeability or hydraulic conductivity, specific yield, transmissivity and storativity
• Sand and gravel, sandstone and clay or shale with typical properties (aquifer versus aquitard)
• Limestone (karst), crystalline hard rock and basalt: secondary porosity in fractures, weathered zones and vesicular flow tops
• Uses: aquifer identification, well siting, pumping tests for T and S, Darcy flow, recharge and resource estimation

(a) Three demands: give the stratigraphic classification of the Cuddapah Supergroup; discuss the depositional environment of its units; and add a note on the tectonic evolution of the Cuddapah Basin, illustrated with a suitable sketch (map and/or cross-section). (b) Two demands: classify the important microfossil groups specifically on the basis of the COMPOSITION of their tests/walls (calcareous, siliceous, phosphatic, organic-walled), and then discuss how microfossils are applied in hydrocarbon exploration. (c) An applied engineering-geology question in two parts: identify the geological problems specific to tunnelling through limestone (karst) terrain, and then PROPOSE specific remedial and preventive measures. Generic tunnelling problems will not earn full credit; the answer must be karst-specific.

• Classification: Papaghni, Chitravati, Nallamalai and Kurnool Groups with their formations in order
• Depositional environments: fluvial and shallow marine quartzites, stromatolitic carbonates, shelf shales, deeper turbidites, Kurnool shelf
• Tectonic evolution: intracratonic rift, thermal subsidence, unconformities, eastern compression and Eastern Ghats thrusting, undeformed west
• Sketch: labelled W–E section or map showing groups, basement and Eastern Ghats
• Calcareous groups: foraminifera, nannofossils, ostracods
• Siliceous (radiolaria, diatoms), phosphatic (conodonts, fish remains) and organic-walled (palynomorphs, chitinozoa) groups
• Applications: biostratigraphy and well correlation, palaeoenvironment and facies, source-rock and maturity studies
• Advantages such as recovery from cuttings and use at the well site
• Karst cavities and caves, empty or filled, causing collapse and irregular rock quality
• Water and mud inrush, sinkholes and settlement from dewatering, irregular weathered rockhead
• Investigation: karst mapping, resistivity, GPR, microgravity, seismic and probe drilling ahead of the face
• Measures: pre-grouting, cavity backfilling, realignment, heavy support (pipe roof, shotcrete), drainage and monitoring

(a) Four demands: define landslides AND avalanches (both), discuss the causes of landslides, discuss their effects, and enumerate remedial/preventive measures. All four must appear; the avalanche definition is routinely forgotten. (b) Explain the various methods by which palaeogeography is reconstructed — sedimentological, palaeontological, palaeomagnetic, palaeoclimatic and plate-tectonic — and illustrate the answer with at least one worked example, which the question explicitly requires. (c) Two demands: give the stratigraphic classification of the Siwalik Group with its formations, lithology and ages; and comment on its palaeogeographic setting and its fossil assemblage. Named fossils are expected.

• Landslide defined as gravity-driven downslope movement of rock, debris or earth, and avalanche defined separately as rapid flow of snow and ice
• Causes, natural and human: steep slope, weak or weathered rock, adverse dip and joints, rain and pore pressure, earthquakes, undercutting, road cuts, deforestation
• Effects: loss of life and property, damage to roads and hydropower, river blockage and outburst floods, siltation
• Remedial and preventive measures: zonation, slope modification, retaining structures, drainage, bioengineering, monitoring and early warning, snow sheds for avalanches
• Sedimentological methods: facies, palaeocurrents, isopach and lithofacies maps
• Palaeontological methods: fossil assemblages, faunal and floral provinces, index fossils
• Palaeomagnetic method: palaeolatitude and apparent polar wander paths
• Palaeoclimatic and plate-tectonic evidence, with at least one worked example such as Gondwana
• Three divisions: Lower (Kamlial, Chinji), Middle (Nagri, Dhok Pathan), Upper (Tatrot, Pinjor, Boulder Conglomerate) with lithology and ages
• Neogene to early Quaternary foreland molasse between the MBT and HFT, up to about 5–6 km thick
• Palaeogeography: rivers draining the rising Himalaya, coarsening upwards as uplift increased
• Named fossils: Sivapithecus, Gigantopithecus, Stegodon, Sivatherium, Hipparion, Hexaprotodon