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A chain of lentiform deposits of coarsely crystalline magnesite extends at least for 130 km northwest from the Kali Valley to the Alaknanda Valley. The deposits have uniform average thickness and chemical and mineralogical composition throughout. The magnesite rock is restricted to a narrow stratigraphic interval in the upper part of the Gangolihat Dolomites of the Calc Zone of Pithoragarh-Tejam and is almost invariably associated with the biohermal stromatolite-bearing dolomites. A situation similar to the modern Coorong Lagoon and its associated ephemeral lakes of southeast South Australia is visualized for the lagoons and barred embayments in the back-reef shelf of the Gangolihat sea. Development of these barred basins is attributed to the biohermal barriers built by algae. The Mg/Ca ratio of the basin-waters progressively increased with the passage of time as a cumulative result of biogenic and inorganic precipitation of CaCOa during the aqueous stages of sedimentary process. Accumulation of algal debris further added to the concentration of magnesium. The Mg/Ca ratio became so high that during periods of high pH the earlier-formed carbonates were converted into carbonate-assemblages of higher magnesium content including magnesite. The high pI-I is attributed to prolific growth of the algae. Magnesium-rich basin-waters were potent enough to react upon the susceptible framework of algal bioherms and associated limestone beds and gave rise to discordant bodies of magnesite deposits. Coarse granularity of magnesite is attributed to later recrystallization during regional metamorphism.

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India collided with mainland Asia at 65 Ma. The pressure rose to 9-11 kbar in the collision zone. As the Indian lithosphere bent down and its upper crust buckled up as an upwarp in the period 35-45 Ma, the southern margin of Asia became the water-divide of the Himalayan rivers. A variety of Eurasian fauna migrated to the Indian landmass. The southern margin of the Himalayan province synchronously sagged to give rise to the foreland basin that was linked with the Indian sea. In this Paleocene foreland basin 48-49 Ma ago, the whales from one of the species of the immigrant terrestrial mammals evolved. The sea retreated from the Himalayan province by the early Miocene, even as the crust broke up along faults 20-22 million years ago. The basement rocks, which had attained high-grade metamorphism at 600-800°C and 6-10 kbar, were thrust up to give rise to what later became the Himādri or Great Himalaya. Differential melting of the high-grade metamorphic rocks of the Himadri extensively produced 21 ± 1 Maold granites. Rivers carried detritus generated by the denudation of the fast emerging Himalaya and deposited it in the foreland basin which turned fluvial around 23 Ma. Another fluvial foreland basin, the Siwalik, was formed at ~18 Ma in front of the rapidly rising orogen and was filled by river-borne sediments at the rate of 20-30 cm year-1 in the early stage and at 50-55 cm year-1 later when the Himadri was uplifted and briskly exhumed in the Late Miocene (9-7.5 Ma). The Himadri then became high enough to cause disruption of wind circulation, culminating in the onset of monsoon. The climate change that followed caused migration of a variety of quadrupeds from Africa and Eurasia, bringing about considerable faunal turnovers in the Siwalik life. Spasmodic uplift of the outer ranges of the Lesser Himalaya and tectonic convulsion in the Siwalik domain at 1.6 Ma resulted in widespread landslides with debris flows and emplacement of the Upper Siwalik Boulder Conglomerate. Strong tectonic movements at 0.8 Ma caused the partitioning of the foreland basin into the rising Siwalik Hills and the subsiding IndoGangetic Plains, and also the initiation of glaciation in the uplifted domain of the Great Himalaya. After the end of the Pleistocene ice age around 0.2 Ma, there was oscillation of dry-cold and wet-warm climates. This climatic vicissitude is recorded in the sediments of the lakes that had formed because of reactivation of faults crossing rivers and streams. Activeness of faults, continuing uplift and current seismicity imply ongoing strain-buildup in the Himalayan domain.