(a) Describe the stratigraphy of Singhbhum Craton and discuss its economic significance. (20 marks) (b) Discuss the effects on…

(a) Stratigraphy and economic significance of the Singhbhum Craton

The Singhbhum Craton in Jharkhand–Odisha is a Precambrian nucleus that records an Archaean to Proterozoic evolution from about 3.5 Ga, with older zircon inheritance, to about 1.0 Ga. Its basement is the Older Metamorphic Group (OMG), a high-grade gneissic suite, intruded by the Older Metamorphic Tonalite Gneiss (OMTG). The ~3.3–3.1 Ga Singhbhum Granite batholith intrudes this basement. The Palaeo–Mesoarchaean Iron Ore Group (IOG) forms three greenstone-BIF belts around the batholith: the western Noamundi-Joda-Koira (Bonai-Keonjhar) belt, the eastern Gorumahisani-Badampahar belt and the southern Daitari belt. The Neoarchaean to Palaeoproterozoic Dhanjori volcano-sedimentary basin lies along the southern margin of the shear zone, and north of it the Singhbhum Group (Chaibasa and Dhalbhum formations) and the Dalma volcanics make up the North Singhbhum mobile belt. The Kolhan Group is a younger Proterozoic platform cover resting unconformably on the Singhbhum Granite and the IOG, and several swarms of Newer Dolerite dykes, dated between about 2.8 and 1.1 Ga, cut the craton.

The Singhbhum Shear Zone is a major structural boundary that localises deformation and mineralisation. Economically, the craton is central to India’s mineral security. The IOG BIFs supply most of India’s hematite iron ore, chiefly from the Noamundi, Kiriburu-Meghahatuburu, Gua, Chiria and Joda-Barbil mines of the western belt, with magnetite-bearing ores at Gorumahisani-Badampahar; chromite of the Sukinda ultramafic belt on the southern margin of the craton supports ferrochrome production; the Singhbhum Shear Zone hosts hydrothermal vein-type copper deposits, with associated nickel and uranium, at Mosabani, Rakha and Surda; uranium is mined along the same shear zone at Jaduguda, Bhatin and Turamdih; kyanite occurs at Lapsa Buru; and manganese ores occur in the Joda-Barbil area. These resources make the craton central to India’s steel, ferrochrome, copper and nuclear-fuel sectors.

(b) Effects on a dead organism after burial

After burial, a dead organism enters taphonomy, from biostratinomy to fossil diagenesis. First, biostratinomy controls transport, orientation, sorting and initial exposure; physical agents such as water and wind, together with scavenging and bioturbation, modify the assemblage. Soft tissues decay by microbial action, producing gases, autolysis and selective preservation of hard parts; microbial decay pathways include aerobic decomposition, anaerobic sulphate reduction and methanogenesis. In the sediment, compaction and pressure solution reduce pore space and flatten remains, while early diagenesis alters minerals. Authigenic mineralization may replace or coat the organism: pyritization in anoxic muds, phosphatization in phosphate-rich settings, and silicification where silica is available. Permineralisation fills pores with mineral matter, as in the silicified (petrified) wood of the Rajmahal Hills and the Akal fossil wood park near Jaisalmer, while dissolution and replacement can destroy original material and substitute silica, calcite, pyrite or phosphate. If decay is inhibited, burial is fast, oxygen is low, and sediment is fine-grained, exceptional preservation in Konservat-Lagerstätten can retain soft tissues, feathers, skin or stomach contents. These processes determine whether a body is destroyed, partially preserved, or fossilised. Under normal conditions, only resistant shells, bones, teeth or mineralised tissues survive as fossils, as in the dinosaur eggs and bones of the Lameta Formation.

(c) Types, factors and mitigation of landslides

Landslides are mass movements classified by Varnes according to mode of movement and material into falls, topples, slides, spreads, flows and complex movements. Falls are free-falling rock or debris; topples involve forward rotation about a pivot; slides include rotational slides along curved surfaces and translational slides along planar surfaces; spreads are lateral spreading of weak material; flows involve fluid-like movement of saturated debris; complex landslides combine two or more movement types, often in weathered slopes. In India, the 1998 Malpa landslide in Pithoragarh district, Uttarakhand, the 2013 Kedarnath debris flows, and the debris flows of Pettimudi near Munnar (2020) and Mundakkai-Chooralmala in Wayanad (July 2024) in weathered charnockites and gneisses of the Western Ghats illustrate these types.

Causal factors are geological, topographic, climatic and anthropogenic: shear zones, weak weathered schists, steep escarpments, intense monsoon rainfall, road cutting and deforestation. Mitigation requires hazard zonation mapping, drainage control, rock bolting, benching and retaining structures, bio-engineering, slope monitoring and early warning systems, with land-use regulation in susceptible zones. In India, such measures rest on the GSI’s National Landslide Susceptibility Mapping at 1:50,000, ISRO’s Landslide Atlas of India (2023) and the NDMA landslide guidelines.