Bones of contention

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 akes 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 int