UPHESC Assistant Professor Geology PYQs

Concept: In the classical textbook treatment 'Nautilus' stands for the nautilid stock (Nautilidae/Nautilaceae in the broad sense), whose range is given as Triassic to Recent; this is the range the question expects.

1. Cambrian to Recent is the range of the nautiloids as a whole (sub-class Nautiloidea), not of Nautilus.
2. Jurassic and Cretaceous are too late for the start of the nautilid stock in that classical sense.
3. Note: the modern genus Nautilus in the strict sense has fossils only from the Late Eocene onwards; the Triassic start refers to its family-level lineage.
4. Nautilus is the only living cephalopod with an external chambered shell, a central siphuncle and simple sutures.

Short trick: Nautiloids: Cambrian→Recent; Nautilus stock: Triassic→Recent.

Concept: At Kolar, gold occurs in the Champion Reef – auriferous quartz lodes in Dharwar amphibolites; the gold-bearing quartz is characteristically bluish-grey to smoky (the 'Champion lode'), while milky white quartz is generally barren.

1. Native gold is associated with scheelite, pyrrhotite, arsenopyrite in this grey quartz.
2. Kolar mines (now closed, 2001) reached over 3 km depth.

Short trick: Kolar Champion reef: grey-blue quartz = gold; milky quartz = barren.

Concept: Cassiterite (SnO₂) of the Bastar–Koraput tin belt occurs in granite pegmatites and associated quartz veins intruding Precambrian granitic gneisses/metasediments.

1. Tin is a classic granitophile (lithophile) element – it concentrates in late-stage granite, greisen and pegmatite.
2. Basalt, diorite and conglomerate are not tin hosts here (alluvial cassiterite is derived from the pegmatites).

Short trick: Tin ↔ granite–pegmatite–greisen.

Concept: The first tetrapods/amphibians (Ichthyostega, Acanthostega) are known from Late Devonian rocks of East Greenland (~365 Ma).

1. Devonian = 'Age of Fishes'; lobe-finned fishes (Tiktaalik, Eusthenopteron) gave rise to amphibians.
2. Carboniferous is the 'Age of Amphibians' (their peak), not their first appearance.

Short trick: Fish age (Devonian) ends with first amphibian – Ichthyostega.

Concept: A zonule is the smallest biostratigraphic unit – a subdivision of a biozone (subzone) recognised by its fossil content.

1. Biostratigraphic hierarchy: biozone → subzone → zonule.
2. Lithostratigraphic: Supergroup–Group–Formation–Member–Bed.
3. Chronostratigraphic: Eonothem–Erathem–System–Series–Stage–Chronozone.

Short trick: Zone → Subzone → Zonule: all fossil-based.

Concept: In a conoscopic interference figure, the melatope is the point where an optic axis emerges in the field of view; around it the isochromes are centred and the isogyres pass through it.

1. Uniaxial optic-axis figure: one melatope at the cross centre.
2. Biaxial acute-bisectrix figure: two melatopes on the isogyres (on the optic axial plane trace).

Short trick: Melatope = 'black spot' where the optic axis comes out.

Concept: Stromatolites are laminated structures built by cyanobacterial mats; the oldest are Archaean (≈3.5–3.4 Ga, Warrawoona/Strelley Pool, Pilbara; ≈3.2–3.0 Ga in South Africa) – so of the options only ~3200 m.y. fits.

1. 500 and 1000 m.y. are far too young; stromatolites were abundant in the Proterozoic but began in the Archaean.
2. Indian examples: Aravalli (Udaipur) and Vindhyan stromatolites (Proterozoic).

Short trick: Stromatolites = oldest visible evidence of life, >3 billion years.

Concept: The Archaean–Proterozoic boundary is fixed chronometrically (GSSA) at 2500 Ma.

1. Proterozoic: 2500–541 Ma (Palaeo-, Meso-, Neo-).
2. Archaean: 4000–2500 Ma; Phanerozoic begins at 541 (≈538.8) Ma.

Short trick: 2.5 Ga = Archaean ends, Proterozoic begins.

Concept: Bauxite forms by intense chemical (lateritic) weathering of aluminous rocks in hot, humid climates: silica and bases are leached away and Al-hydroxides (gibbsite, boehmite, diaspore) remain behind – a residual concentration.

1. Indian examples: East Coast bauxites (Panchpatmali, Odisha) on khondalite; Deccan-trap cappings in Maharashtra/Gujarat.
2. Not magmatic or replacement; transported bauxite is minor.

Short trick: Leach the rest, Al stays – residual bauxite (and laterite).

Concept: Placers form by mechanical concentration: running water, waves or wind sort grains, and heavy, chemically resistant minerals (gold, cassiterite, ilmenite, monazite, diamond) settle where velocity drops.

1. Residual liquid segregation – magmatic (e.g. chromite, Ti-magnetite).
2. Residual concentration – weathering in place (bauxite, laterite).

Short trick: Placer = Heavy + Hard + Hydraulic sorting.

Concept: Spreading methods let surface water spread over or into the ground and infiltrate: basins, ditches & furrows, flooding, pits/shafts. Induced recharge instead pumps wells sited near a river/lake so that the lowered water table draws (induces) surface water into the aquifer.

1. Basin, ditch-furrow and pit methods all spread water to infiltrate.
2. Induced recharge works by pumping – an indirect method, no spreading.

Short trick: Induced = pump-induced bank infiltration, not spreading.

Concept: The LGM, when the last (Weichselian/Wisconsin) ice sheets were at their greatest extent and sea level ~120 m lower, was about 26,000–19,000 years ago, centred near 21–22 ka B.P.

1. Holocene (last 11,700 yr) is post-glacial.
2. 110–60 ka is the early part of the last glaciation, not its maximum.
3. 280 Ma is the Permo-Carboniferous (Gondwana) glaciation.

Short trick: LGM ≈ 22 ka; Holocene starts 11.7 ka.

Concept: A metabasite (dolerite/basalt) in the amphibolite facies becomes an amphibolite: hornblende + plagioclase (andesine) ± garnet, epidote.

1. Opx + Cpx + Pl – granulite facies.
2. Chlorite + actinolite + albite (± epidote) – greenschist facies.
3. Lawsonite + glaucophane – blueschist facies.

Short trick: Amphibolite facies → Hornblende + Plagioclase (= amphibolite rock).

Concept: In fractional (Rayleigh) fusion each increment of melt is removed as soon as it forms, so it cannot re-equilibrate with the residual solid; in equilibrium (batch) fusion the melt stays in contact and reacts with the residue until it is extracted.

1. Fractional fusion gives melts that jump from eutectic to eutectic in a phase diagram.
2. 'Differentiated melt' describes a product, not the melting process.

Short trick: Fractional = remove instantly; Equilibrium/Batch = keep together.

Concept: Connate water is water trapped in the pores of sediments at the time of their deposition and isolated from the hydrological cycle for a long time – hence called 'fossil water'.

1. Juvenile (magmatic) water – new water from magma, never in the hydrological cycle before.
2. Meteoric water – derived from precipitation; the bulk of groundwater.
3. Cosmic water – from space (comets/meteorites), negligible.

Short trick: Connate = 'born with' the sediment = fossil water.

Concept: Hydraulic conductivity K = Q/(iA); with Q in m³/day, i dimensionless and A in m², K has the units of velocity – m/day (or m/s, cm/s).

1. m²/day (or m²/s) is the unit of transmissivity T = Kb.
2. m³/s is the unit of discharge Q.

Short trick: K – velocity (m/d); T – m²/d; Q – m³/d.

Concept: A pleochroic scheme (colours for X, Y, Z vibration directions) can be written only for coloured anisotropic minerals; hornblende is strongly pleochroic: X = light yellow-green, Y = green/olive, Z = dark green/blue-green.

1. Quartz and muscovite are colourless in thin section – no pleochroism.
2. Garnet is isotropic (cubic) – cannot be pleochroic.

Short trick: Pleochroic scheme needs colour + anisotropy: hornblende, biotite, tourmaline.

Concept: Three 4-fold axes (along the three crystallographic axes) are characteristic of the holohedral (normal) class of the cubic/isometric system; galena (PbS) is cubic (m3m).

1. Gypsum – monoclinic (one 2-fold axis).
2. Baryte – orthorhombic (three 2-fold axes).
3. Rutile – tetragonal (only one 4-fold axis).

Short trick: 3 × 4-fold axes = cube: galena, halite, fluorite, garnet.

Concept: Indian (Gondwana) coals – which form over 98% of Indian coal – are generally regarded as of drift origin: plant material was transported by rivers and deposited in lakes/basins (Fox, Krishnan).

1. Evidence: high ash content, absence of true seat-earths/underclays with roots, interbanding with sandstones, and great seam thickness with splitting.
2. In-situ (autochthonous) coal, typical of Carboniferous coals of Europe/USA, shows rootlet beds (Stigmaria) below seams.

Short trick: Gondwana coal = drifted (high ash); Euro-American Carboniferous = in-situ.

Concept: Know the crystal system of common minerals.

1. Garnet – cubic (isometric) → (2).
2. Cassiterite (SnO₂) – tetragonal, rutile group → (3).
3. Axinite – triclinic → (4).
4. Orthoclase – monoclinic → (1). Code: 2-3-4-1.

Short trick: Garnet cube, Cassiterite = Rutile-tetragonal, Axinite 'axe' = triclinic, Orthoclase = 'right-angle' cleavage but monoclinic.