This website is made to help students prepare for their competitive exams with ease and confidence.
Q61. Which of the following statement(s) is/are correct for a plot of (87Sr/86Sr) versus (87Rb/86Sr) of a rock which has evolved in a closed system?
The correct answers are The slopes of the lines of evolution for the minerals in the rock are all equal and negative, The slope of the isochron is opposite in direction to the slope of the lines of evolution for the minerals in the rock. As radioactive Rubidium (Rb) decays into Strontium (Sr), the amount of Rb decreases (moving left on the x-axis) while Sr increases (moving up on the y-axis). This trajectory creates a negative slope for an individual mineral's evolution over time. However, the 'isochron' line that connects all the different minerals at the present day slants upwards to the right (positive slope), making it exactly opposite in direction.
Q62. Major mass extinction events occurred in the
The correct answer is end Permian. The 'end Permian' extinction (about 252 million years ago) is infamous as the greatest mass extinction event in Earth's history, often called the Great Dying, where over 90% of life was wiped out. While other periods had minor extinctions, the end Permian was by far a 'major' mass extinction event.
Q63. Which of the following is/are true for crystallization of plagioclase phenocrysts from a basic magma forming a layered intrusion?
The correct answer is Cumulus texture at the base, Anorthite-rich early plagioclase at the base, Albite-rich late plagioclase at the top. In a layered magma intrusion, minerals crystallize and sink to the bottom to form a 'cumulus' texture. High-temperature, calcium-rich plagioclase (anorthite) forms first and settles at the base. As the magma cools, the leftover liquid becomes richer in sodium, so sodium-rich plagioclase (albite) forms later at the top. Quench texture happens during rapid volcanic eruptions, not slow underground cooling.
Q64. Choose the characteristic mineral(s) formed in the supergene enriched zone of a sulphide deposit.
The correct answer is Covellite, Chalcocite. When a sulfide ore deposit is weathered by rain, metals wash downwards and concentrate just below the water table, creating a super-rich 'supergene enriched zone'. Covellite and Chalcocite are the two classic, diagnostic copper-sulfide minerals that form in this specific zone. Psilomelane is a manganese oxide, and Cassiterite is a tin oxide, making them incorrect.
Q65. Hermatypic corals are typically found in
The correct answer is the photic zone, warm and clear water, reefs. Hermatypic corals are the famous 'reef-building' corals. To survive, they have tiny algae living inside them that require sunlight for photosynthesis. Therefore, they strictly must live in shallow sunlit water (the photic zone) that is warm and clear. They actively build reefs. They cannot survive in cold, dark, deep water.
Q66. Which of the following change(s) when a dipping bed with a plunging lineation is rotated about a vertical axis?
The correct answer is Plunge direction of lineation, Strike of bed. Imagine a tilted ramp with a line drawn down it. If you spin that entire ramp around a vertical axis like a merry-go-round, the compass direction the ramp faces (Strike) changes, and the compass direction the line points (Plunge direction) also changes. However, the steepness of the ramp's tilt (Dip amount) and the steepness of the line drawn on it (Plunge amount) physically remain identical.
Q67. P and S waves originate at earthquake focus and travel through the earth. Which of the following statements for these waves is/are correct?
The correct answer is S-wave shadow zone is 154° wide, P-wave velocity abruptly drops downward at mantle-core boundary. Because the Earth's outer core is liquid, S-waves completely stop when they hit it, creating a massive 'shadow' on the other side of the planet measuring roughly 154 degrees wide. P-waves can travel through the liquid, but because liquid is less rigid than solid rock, the P-waves suddenly slow down (drop velocity) when they cross from the solid mantle into the liquid core.
Q68. Which of the following is/are NOT true for texturally immature sandstone?
The correct answer is Little or no clay present, Grains are well sorted, Grains are rounded. An 'immature' sandstone is like dirt just washed off a mountain: it's messy, full of sticky clay mud, has mixed-up grain sizes (poorly sorted), and sharp, jagged edges (angular). Because an immature sand is full of clay, options B, C, and D describe a clean, highly 'mature' beach sand, making them completely untrue for an immature rock.
Q69. The Toposheet No(s). immediately adjacent to Toposheet No. 55J/8 is/are
The correct answer is 55J/12, 55K/5. Toposheets are mapped in a specific grid system. Sheet 55J/8 is surrounded by neighbors. Moving south on the grid takes you to 55J/12. Moving exactly east crosses into the next main block (55K), landing specifically on 55K/5. The other options (55K/2 and 55J/6) are located further away or diagonally and do not immediately touch the borders of 55J/8.
Q70. Which of the following stratigraphic unit(s) is/are coal/lignite bearing?
The correct answer is Barakar Formation, Barail Group, Cuddalore Formation. India has several major coal deposits. The Barakar Formation holds massive amounts of high-quality coal. The Barail Group in Assam is famous for its Tertiary coal and oil. The Cuddalore Formation in the south is well-known for its brown lignite deposits (like in Neyveli). The Ariyalur Formation is a marine deposit famous for dinosaur bones and sea fossils, not thick coal swamps, making it the wrong choice.