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Q81. Which one of the following predicts the correct tectonic settings for development of the positive flower structure and the negative flower structure?
Flower structures are associated with strike-slip faults. Transpression (compression + strike-slip) creates uplift (positive flower), whereas transtension (extension + strike-slip) creates subsidence (negative flower).
Q82. A river with a 2 km wide flood plain and 10 m channel depth flows with a velocity of 2 m/s. What will be the flow condition in the river?
Flow condition is determined by the Froude number (Fr = V / sqrt(g*D)). Fr = 2 / sqrt(9.8 * 10) = 2 / sqrt(98) = 2 / 9.9 = ~0.2. Since Fr < 1, the flow is tranquil/sub-critical.
Q83. The following is a list of important events in organic evolution: (A) First appearance of mammals (B) First appearance of fishes (C) First appearance of birds (D) First appearance of flowering plants. Which one of the following is correct in ascending stratigraphic order (oldest to youngest)?
Fishes appeared first (Ordovician/Silurian), followed by Mammals (Triassic), then Birds (Jurassic), and finally Flowering plants / Angiosperms (Cretaceous).
Q84. Places A and B receive rainfall of 1200 mm/y and 1000 mm/y, respectively. Rainfall is spread over 6 months at A and for 2 months at B. The erosivity will be:
Erosivity depends on the intensity of the rainfall. Place B receives 500 mm/month, while Place A receives 200 mm/month. Higher intensity causes greater surface runoff and erosion.
Q85. Which of the following statements are correct about epeirogenic movements? (a) Very little deformation involved. (b) More localized than orogenic movements. (c) Result due to tangential forces. (d) Involve regional uplift.
Epeirogenic movements are broad, slow, vertical (radial) crustal movements that cause regional uplift or subsidence with virtually no folding or severe deformation. Orogeny is localized and tangential (compressional).
Q86. During glacial intervals, which of the following statements is true regarding oceanic isotopic records?
During glacial periods, massive amounts of isotopically light water (16O) are locked up in continental ice sheets. This leaves the remaining global ocean enriched in heavy 18O, leading to higher d18O values in benthic foraminifera shells.
Q87. During a glacial stage, the average salinity of the ocean:
During a glacial period, massive amounts of fresh water are locked up in continental ice sheets. Removing this fresh water from the oceans increases the global ocean salinity.
Q88. In the sea, equal quantities of two water masses of the same density 'di' mix. Before mixing they had temperatures of 3.8 C and 8.5 C and salinities 34.7 and 35.4, respectively. The mixture will have a density 'dm' such that:
Due to the non-linear equation of state for seawater (cabbeling), mixing two water masses of the exact same density but different temperatures/salinities always produces a mixture that is denser than its parent masses.
Q89. It is observed that high pressure (HP) and ultra high pressure (UHP) metamorphism is generally younger and in mostly post-Archean times. Which of the following could be the most likely reason for this?
Due to higher radioactive heat production in the Archean, the Earth's geothermal gradient was steeper. Subducting slabs heated up too quickly before they could reach the extreme depths/pressures needed for HP/UHP facies (like eclogite).
Q90. Given below are two statements: Assertion (A): To a large degree the Earth's surface possesses relief because the geomorphic processes operate at differential rates. Reason (R): The rocks of the Earth's crust vary in their lithology and structure and hence offer varying degrees of resistance. Which is correct?
Differential erosion occurs exactly because different rock types (lithologies) have different hardness and structural weaknesses, explaining why high relief topography is created.