Polygenetic Soils of the North-Central Part of the Gangetic Plains: A Micromorphological Approach

Micromorphology indicates that soils of the central part of the Gangetic Plains are polygenetic. They occur on surfaces originating at 13 500, 8000, 2500, >500 and <500 BP (QGH5 to QGH1, respectively). The QGH5 soils on upland interfluves show degraded illuvial clay pedofeatures of an early humid phase (13 500–11 000 BP) and thick (150–200 μm) microlaminated clay pedofeatures of a later humid phase (6500–4000 BP). The earlier clay pedofeatures were degraded by bleaching, loss of preferred orientation, development of a coarse speckled appearance and fragmentation, whereas those of the later phase are thick, smooth and strongly birefringent microlaminated clay pedofeatures. The illuviation was more extensive during the later phase, as indicated by enrichment of groundmass as discrete pedofeatures of clay intercalations. Pedogenic carbonate was formed during the intervening dry phase from the early Holocene to 6500 BP. It forms irregularly shaped nodules of micrite and diffuse needles with inclusions of soil constituents. The subsequent change to wetter conditions caused dissolution–reprecipitation, which resulted in partial to complete removal of carbonate from soils over large areas.