Geology 2021 Paper II 50 marks State

Q7

(a) State the characteristic features of cosmic abundance of elements. What are the bases of estimation of cosmic abundance of elements? (20 marks) (b) Discuss briefly with examples about different types of chemical bonds observed in natural minerals. (10 marks) (c) Describe briefly the geology, structure and mode of occurrence of hydrocarbons in western oil fields of India. (20 marks)

हिंदी में प्रश्न पढ़ें

(a) तत्वों की ब्रह्मांडीय बहुलायत की विशेषताएं बताइए। तत्वों की ब्रह्मांडीय बहुलायत के आकलन का क्या आधार है? (20 अंक) (b) प्राकृतिक खनिजों में पाए जाने वाले विभिन्न प्रकार के रासायनिक बंधों के बारे में उदाहरण सहित संक्षिप्त चर्चा कीजिए। (10 अंक) (c) भारत के पश्चिमी तेल-क्षेत्रों में हाइड्रोकार्बन के भूविज्ञान, संरचना और प्राप्ति स्वरूप का संक्षिप्त वर्णन कीजिए। (20 अंक)

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Directive word: State

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How this answer will be evaluated

Approach

The directive 'state' in part (a) demands precise, factual presentation of cosmic abundance characteristics and estimation bases. Allocate approximately 40% of time/words to part (a) given its 20 marks, 20% to part (b), and 40% to part (c). Structure as: brief introduction linking cosmochemistry to mineral chemistry and petroleum geology; three distinct sections for each sub-part with clear sub-headings; and a concluding synthesis on how elemental abundance governs mineral formation and hydrocarbon source rock potential.

Key points expected

Part (a): Characteristic features of cosmic abundance — H and He dominance (~98% by mass), even-odd atomic number pattern, iron peak at Z=26, exponential decrease with atomic number, and rarity of Li-Be-B due to nuclear instability
Part (a): Bases of estimation — spectroscopic analysis of stellar atmospheres, meteorite composition (especially CI chondrites), solar wind measurements, and cosmic ray abundance data
Part (b): Types of chemical bonds with mineral examples — ionic (halite, NaCl), covalent (diamond, C), metallic (native Au, Cu), van der Waals (graphite, phyllosilicates), hydrogen bonds (ice, kaolinite), and mixed bonding in silicates
Part (c): Western Indian oil fields — Mumbai High (Bombay High) fractured basement and carbonate reservoirs, Cambay Basin rift-related Tertiary sediments, and Kutch-Saurashtra region with Mesozoic and Tertiary sequences
Part (c): Structural controls — listric faults, rollover anticlines, and stratigraphic traps in Mumbai High; rift graben geometry in Cambay Basin with Eocene-Oligocene source rocks

Evaluation rubric

Dimension	Weight	Max marks	Excellent	Average	Poor
Concept correctness	25%	12.5	Demonstrates accurate understanding of nucleosynthesis processes explaining cosmic abundance patterns (Big Bang, stellar nucleosynthesis, supernova r-process); correctly identifies CI chondrites as standard for non-volatile element estimation; precisely classifies bond types with correct electronegativity reasoning; accurately describes Mumbai High as offshore carbonate platform and Cambay Basin as continental rift with Olpad/Kadi formations.	States basic abundance features (H/He dominance, iron peak) but confuses estimation methods; lists bond types with generic examples but misses mixed bonding in silicates; describes western oil fields with some field names but conflates structural styles or misidentifies source-reservoir relationships.	Fundamental errors such as stating cosmic abundance based on Earth's crust composition; confuses ionic-covalent-metallic bonding definitions; describes eastern Indian oil fields (Assam-Arakan) instead of western fields or makes gross geological errors like calling Mumbai High a volcanic structure.
Diagram / cross-section	15%	7.5	Includes a well-labelled graph of cosmic abundance vs. atomic number (log scale) showing iron peak and even-odd effect; sketches crystal structure diagrams for at least two bond types (e.g., diamond cubic for covalent, NaCl structure for ionic); provides clear cross-section of Mumbai High or Cambay Basin showing trap types, source rock intervals, and migration pathways.	Provides rough sketch of abundance curve without proper axes or labels; mentions bond types without structural diagrams; includes simplified block diagram of western oil fields but lacks detail on structural geometry or reservoir-seal relationships.	No diagrams despite clear visual requirements; or diagrams with major errors (e.g., abundance curve increasing with atomic number, incorrect coordination numbers in crystal structures, cross-sections showing impossible geometries).
Field evidence	20%	10	Cites specific meteorite evidence (Orgueil CI chondrite for volatile-corrected abundances); references spectroscopic data from specific stellar classes (G-type stars matching solar photosphere); names specific Indian mineral localities for each bond type (e.g., diamond from Panna for covalent, graphite from Palamu for van der Waals); details specific wells/fields in western India (e.g., Mumbai High L-III pay, Gandhar field in Cambay Basin) with depth and lithology data.	Mentions meteorites and spectroscopy generically without specific examples; names common minerals without Indian localities; lists western oil field names (Bombay High, Cambay) but lacks specific well or formation data.	No field evidence cited; confuses meteorite types (uses iron meteorites for abundance estimation); provides no Indian examples for minerals; describes Assam or Cauvery basin instead of western fields.
Quantitative reasoning	20%	10	Provides numerical data: H (~70%), He (~28%) by mass in cosmic abundance; Si normalized to 10^6 atoms with corresponding abundances for Fe, O, C; electronegativity differences explaining bond character; reserves and production figures for Mumbai High (~300,000 bpd peak) or Cambay Basin; depth ranges for reservoirs (e.g., 1000-1500m for Mumbai High pay zones).	States approximate percentages for H/He without precision; mentions relative abundances qualitatively; provides rough depth estimates for oil fields without specific numbers; lacks quantitative bond character data.	No quantitative data; or incorrect orders of magnitude (e.g., Fe more abundant than H); absurd depth/reserve figures; confuses atomic number with atomic mass in abundance discussions.
Indian / economic relevance	20%	10	Explicitly connects cosmic abundance to India's mineral resources: explains why Fe, Al, Si abundance translates to abundant iron ore (Odisha), bauxite (Eastern Ghats), and silicate minerals; discusses strategic importance of western offshore fields for India's energy security (~15% of domestic production); mentions ONGC's role and recent discoveries (e.g., ultra-deepwater UD-1); links bond types to industrial mineral applications (graphite for electrodes, diamond for cutting).	Mentions Indian oil fields and some minerals but misses strategic energy security angle; notes ONGC presence without production significance; describes mineral uses generically without industrial context.	No Indian context; or irrelevant discussion of foreign oil fields (Middle East, Venezuela); fails to mention ONGC, western offshore significance, or Indian mineral localities; discusses eastern Indian geology for part (c).

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