Test: Geomorphology - 3 - UPSC MCQ

• Sediment maturity refers to the length of time that the sediment has become in the sedimentary cycle.

• Texturally mature sediment is sediment that is well rounded (as rounding increases with transport distance and time) and well sorted (as sorting gets better as larger clasts are left behind and smaller clasts arc carried away).

• If the fragments arc angular, it indicates that they have not been transported very far and the sediment is poorly sorted.

• Sedimentary rocks preserve a record of the environments that existed when they formed. By looking at sedimentary rocks of different ages, scientists can figure out how climate and environments have changed through Earth’s history. Fossils of ancient living things are preserved in sedimentary rocks too.

• Quartz, K-feldspar and muscovite are some of the important minerals found there.

• Metamorphic rocks are made by either heating up or squashing the Earth’s crust. They are often found in mountainous regions. One example is slate. Slate was originally a black mud laid down on the bottom of the sea or lake.

• Sometimes, metamorphic rocks are formed when rocks are close to some molten magma, and so get heated up. When metamorphic rock is formed under pressure, its crystals become arranged in layers. Slate, which is formed from shale, is like this. Slate is useful for making roof tiles because its layers can be split into separate flat sheets.

• The Azoic Age was used to describe the age of rocks formed before the appearance of life in the geologic sequence. Also known as Pre-Cambrian rocks, these are the oldest rocks of the Earth’s crust.

• The Archaean period covers over 85 % of the total geological history time of Earth and therefore is very significant. This period marks the development of the first photosynthesis, the life support atmosphere.

• The Archaean or Purana rock system in India is found in Aravallis mountains, two- thirds of the Deccan peninsula and some parts of the North-east.

The Archean or Purana rock system in India is found in Aravallis mountains, 2/3rd of the Deccan peninsula and some parts of north east. These rocks have abundant metallic and non-metallic minerals such as iron, copper, manganese, bauxite, lead, zinc, gold, silver, tin, tungsten, mica, asbestos, graphite, etc.

 The iron-ore reserves of India are associated with the Dharwar rock systems. The Dharwar rocks are rich in iron ore, manganese, gold, zinc, lead, silver, etc. They are named after the Dharwar region of Karnataka.

• In the Himalayas, geological processes have led to the major displacement of rock strata. This has disturbed the arrangement of rocks and made it complex, making the Himalayas poor in mineral resources.

• The rugged terrain and adverse climatic conditions make exploration of minerals difficult and costly, but it can’t be a reason for lack of mineral resources.

• Our rich mineralised zone is largely confined to the old, crystalline rock structures of plateaus and low hills of peninsular India.

• The Siwalik series comprehends the two zones of strata forming the outermost ranges of the Sub- Himalayas.

• Petrologically, this group consists either of coarse conglomerates or fine, brown clays, the latter being indistinguishable, in hand specimens, from the modern alluvium of Punjab. The conglomerates occur mainly on the lines of the large rivers, being replaced in the intervals by the clays.

• A Siwalik system of rockfalls under Cenozoic Era and belongs to the Middle-Miocene, Pliocene and Lowe Pleistocene period or Epoch. This system of rocks is considered to be one of the largest storehouses of mammalian remains and other vertebral fossils.

• Khasi hills, one of the youngest, belong to the Tertiary period (to which a large area in North-east also belongs). Shivalik are part of Himalayas, so given the reasoning below.

• The alluvium which is found in the Indo- Gangetic plain belongs to the Quaternary period. It was eroded from the Himalayas by the rivers and the monsoons since the Himalayas were formed after Deccan traps, and are very young.

• The Deccan Plateau in India is one of the oldest plateaus in India made mainly from igneous rocks.

• Some applied forces determine the physical or mechanical weathering processes. Following are the few applied forces:

(i) Gravitational forces like overburden pressure, load and shearing stress;

(ii) Expansion forces due to changes in temperature, crystal growth or animal activity;

(iii) Water pressures controlled by wetting and drying cycles.

Many of these forces act both at the surface and within different Earth materials, causing fracture of the rocks. Thermal expansion and pressure release are responsible for most of the physical weathering processes. Though these processes are slow and small, rocks suffer continued fatigue due to repeated contractions and expansions that greatly damage the rocks.

• Enrichment of many low-grade ores occurs when the metal-bearing solutions of these valuable metals drain downwards along the vein or other deposits and then are re-precipitated into concentrated, bonanza- grade deposits at shallow depths.

• Some of these enriched deposits are quite large, being the product of long, continued forces of weathering with the descending mineral salts acting to concentrate the metal values from a great thickness of vein matter and rocks that were once located above the current outcrop, but now have been removed by erosion.

• This process of natural concentration is how the action of weathering can produce such amazingly rich ore bodies.

• Weathering processes are responsible for breaking down the rocks into smaller fragments and preparing the way for the formation of not only regolith and soils but also erosion and mass movements. Biomes and biodiversity is basically a result of forests (vegetation) and forests depend upon the depth of weathering mantles.

• Without weathering taking place, the concentration of the same valuable material may not be sufficient and economically viable to exploit, process and refine since they would be scattered across a large area.

• Weathering aids mass wasting, erosion and reduction of relief and changes in landforms are a consequence of erosion.

• The catchments of large rivers are called river basins while those of small rivulets and rills are often referred to as watersheds.

• There is, however, a slight difference between a river basin and a watershed. Watersheds are small in area while the basins cover larger areas.

• River basins and watersheds are marked by unity. What happens in one part of the basin or watershed directly affects the other parts and the unit as a whole.

• That is why they are accepted as the most appropriate micro-, meso- or macro-planning regions. Every tributary too has a watershed. Sum of watersheds gives rise to river basin.