Pankaj Srivastava

Role of neotectonics and climate in development of the Holocene geomorphology and soils of the Gangetic Plains between the Ramganga and Rapti rivers

Abstract Fifteen soil-geomorphic units have been delineated from the Gangetic Plains between the Ramganga and Rapti rivers. They were identified by remote sensing and field checks. On the basis of degree of profile development, their soils are grouped into five members (QGH1 to QGH5, QGH5 being the oldest) of a soil chrono-association. Tentative ages assigned to QGH1 to QGH5 are 500, > 2500, 8000 and 13,5000 yr B.P., respectively. From the early Holocene to about 6500 yr. B.P. a cold, arid to semi-arid climate prevailed and pedogenic calcrete developed over large areas in the Gangetic Plains. Later, a warm and humid climate and improved drainage resulted in complete removal of calcrete from soil profiles in some areas or its dissolution and re-precipitation in lower horizons in other areas. Neotectonics seems to have played a significant role in the evolution of the geomorphology and soils of the area. It determined areas of active sedimentation, pedogenesis and erosion (in upland regions). It led to tilting and sagging of large blocks resulting in shifting and increase in sinuosity of the rivers. Tectonic slopes/faults determined the courses of large rivers.

SIGNIFICANCE OF THE FORMATION OF CALCIUM CARBONATE MINERALS IN THE PEDOGENESIS AND MANAGEMENT OF CRACKING CLAY SOILS (VERTISOLS) OF INDIA

Micromorphological studies were performed in order to understand the factors and processes involved in the formation of calcium carbonate (CaCO3) in twenty three soil series of Vertisols representing sub-humid, semi-arid and arid climatic regions of Peninsular India. The study indicates that Vertisols contain both pedogenic calcium carbonate (PC) and non-pedogenic calcium carbonate (NPC) irrespective of the ecosystems to which they belong. The NPCs are part of the parent material of Vertisols. Dissolution of NPCs and recrystallization of dissolved Ca2+ ions are responsible for the formation of PCs. Vertisols of arid and semi-arid climates contain more PC in their soil control section (SCS) than those of sub-humid climates. Formation of PC is the prime chemical reaction responsible for the increase in pH, the decrease in the Ca/Mg ratio of exchange site with depth and in the development of subsoil sodicity. Petrographic and scanning electron microscopic (SEM) examination of quartz, feldspars and micas indicate little or no alteration, discounting the possibile formation of smectite during Vertisol formation. X-ray diffraction (XRD) analysis of clays indicates that smectites of Vertisols are fairly well crystallized and do not show any sign of transformation except for hydroxy interlayering. The preservation of the crystallinity of smectite and the lack of transformation of primary minerals thus validate the hypothesis of positive entropy change during the formation of Vertisols.The precise cause-effect relationship between CaCO3 of pedogenic and non-pedogenic origin, and exchangeable Mg, Na and Ca percentages (EMP, ESP and ECP) has been established in the study. This indicates that impoverishment of Ca2+ ions on the exchange sites of Vertisols needs to be controlled by rehabilitation methods that can replenish Ca2+ ions, and thus the study provides relevant information for future land resource management programmes not only on Vertisols of India but also on similar soils occurring elsewhere.

Clay illuviation in calcareous soils of the semiarid part of the Indo-Gangetic Plains, India

Abstract In view of diverse understanding on the movement and accumulation of clay particles in calcareous parent material, a micromorphological study on 28 Alfisols of the semiarid part of the Indo-Gangetic Plains (IGP) was undertaken. The study indicates that the identified clay pedofeatures are typically of the type “impure clay pedofeatures” which have resulted from the impairment of the parallel orientation of the clay platelets induced by dispersion of both clay and silt size layer silicates in slightly to highly sodic environment. The study also indicates that the illuviation of clay particles and their subsequent accumulation in the Bt horizons have occurred in sodic environment caused by the precipitation of soluble Ca 2+ ions as calcium carbonate (CaCO 3 ), thus discounting any role of soluble Ca 2+ ions and the presence of CaCO 3 in preventing the movement and accumulation of clay particles. The study thus suggests that the formation of impure clay pedofeatures and pedogenic CaCO 3 are two pedogenic processes occurring simultaneously in soils of the IGP as contemporary pedogenic events in the semiarid climate since the last 4000 years B.P.

Role of microtopography in the formation of sodic soils in the semi-arid part of the Indo-Gangetic Plains, India

Abstract In the northwestern part of the Indo-Gangetic Plains (IGP), India, non-sodic and moderately sodic soils occur on microhigh (MH) and highly sodic soils on microlow (ML) positions under a semi-arid climate. The main soil-forming processes have been clay illuviation, deposition of pedogenic calcium carbonate and concomitant development of sodicity. The microlows are repeatedly flooded with surface water during brief high-intensity showers, so the soils are subject to cycles of wetting and drying. This provides a steady supply of alkalis by hydrolysis of feldspars, leading to precipitation of calcium carbonate at high pH and development of subsoil sodicity. This impairs the hydraulic conductivity of soils and eventually leads to the development of Natrustalfs with exchangeable sodium percentages increasing rapidly up the profile. The semi-arid climate and topography interact to facilitate greater penetration of bicarbonate-rich water in microlow than microhigh positions. Thin sections show deformational pedofeatures such as cross and reticulate striation of plasmic fabric, disruption of clay pedofeatures and carbonate nodules and elongation of voids as a result of tectonic activity during the Holocene. In view of the persistent build up of stresses in the IGP in general, and the study area in particular, it seems that the neotectonics have caused the microtopographical variations (0.5–1 m) that control the formation of sodic soils.

Polygenetic Vertisols of the Purna Valley of Central India

The Purna Valley, a part of the Payanghat Plain, is an oval basin covering an area of about 1.9 Mha in central India. The soils are deep, calcareous, clayey and very dark greyish brown to dark brown in colour, and meet criteria for the Vertisols order of Soil Taxonomy. Cracks extend down to the slickenside zones in soils of the northeastern part of the valley, but cut through the slickenside zones in the soils of the southwestern part. Soils of the southwestern part are strongly alkaline with exchangeable sodium percentages (ESPs) of 5–26, whereas those of the northeastern part are moderately alkaline and have ESP values <5. Despite their similar coefficients of linear extensibility, volumetric shrinkage potentials, clay contents and amounts of fine clay smectite, the plasmic fabric of the slickenside horizons in soils of the northeastern part is porostriated, whereas in soils of the southwestern part, it is stipple-speckled to mosaic-speckled, indicating weak plasma separation. The soils have both pedogenic and nonpedogenic calcium carbonate, but those of the southwestern part have more pedogenic carbonate than those in the northeastern part. The semiarid climate removes Ca2+ ions from the soil solution by precipitating carbonate, and also causes the ESP and sodium absorption ratio to increase with depth. The lack of soil water in soils of the southwestern area is thought to be the reason for weak swelling of smectite, for larger amounts of pedogenic carbonate and for cracks cutting through the slickenside zones. The Vertisols of the southwestern part of the of the Purna Valley are, therefore, polygenetic because they exhibit distinctly different soil properties resulting from increasing aridity in the valley during the late Holocene.

Role of zeolites in persistence of high altitude ferruginous Alfisols of the humid tropical Western Ghats, India

Abstract The high altitude ferruginous Alfisols associated spatially with shrink–swell soils on the Deccan basalt plateau and dissected table lands in the Western Ghats of India were analysed for their morphological, chemical and mineralogical properties with a view to comprehend their formation and persistence in the tropical humid climate prevailing since the early Tertiary. The study indicates that despite their acidic pH the soils have high bases and their clay fractions are dominated by interstratified smectite-kaolin. The persistence of these non-kaolinitic and/or non-oxidic Alfisols has been possible due to the presence of base-rich zeolites of amygdoloidal basalt. It suggests that for an open system such as soil, the existence of steady state is a more meaningful concept than thermodynamic equilibrium. The knowledge gained on the role of zeolites in soils provides a check on the reasoning of models on the formation of soils in tropical humid climate. The study also indicates that the supply of bases from zeolites can prevent the soils from losing their productivity even in intense leaching environment.

Lateritic soils of Kerala, India : their mineralogy, genesis, and taxonomy

In this study, we report the chemical and mineralogical characteristics of 4 benchmark Ultisols of Kerala to elucidate their genesis and taxonomy. The taxonomic rationale of the mineralogy class of Ultisols and other highly weathered soils on the basis of the contemporary pedogenesis is also explained. The Ultisols of Kerala have low pH, low cation exchange capacity, low effective cation exchange capacity and base saturation, with dominant presence of 1 : 1 clays and gibbsite. Presence of gibbsite along with 2 : 1 minerals discounts the hypothesis of anti-gibbsite effect. Since the kaolins are interstratified with hydroxy-interlayered vermiculites (HIV), the formation of gibbsite from kaolinite is not tenable. Thus, gibbsite is formed from primary minerals in an earlier alkaline pedo-environment. Therefore, the presence of gibbsite does not necessarily indicate an advanced stage of weathering. On the basis of a dominant amount of gibbsite, a mineralogy class such as allitic or gibbsitic does not establish a legacy between the contemporary pedogenesis and the mineralogy. The dominance of kaolin–HIV in the fine clays of Ultisols and their persistence, possibly since early Tertiary, suggests that ‘steady state’ may exist in soils developed on long-term weathered saprolite. Since the present acid environment of Ultisols does not allow desilication, the chemical transformation of Ultisols to Oxisols with time is difficult to reconcile as envisaged in the traditional model of tropical soil genesis.

Role of weathering of fine-grained micas in potassium management of Indian soils

Abstract Although the major soils of India (alluvial, ferruginous and black soils), endowed with fine-grained micas, are known as natural K suppliers to plants, crop response to K fertilizer treatment has been anomalous. The silt and clay fractions of 14 benchmark soils were subjected to repeated batch type Ba–K exchange to study the rate of K release. The significant positive correlation between cumulative K release in 25 extractions and X-ray intensity ratio of peak heights of the 001 and 002 basal reflections of mica in the silt ( r =0.629 at 1% level) and clay ( r =0.729 at 1% level) suggested that although the fine-grained muscovite and biotite co-exist in soils, the rate of K release and crop response to K are related primarily to the presence of biotite only while muscovite remains as an inert source of K in soils justifying the crop response to K fertilizers. Soil micas under a scanning electron microscope (SEM) indicated that biotite particles were generally thick, showing layer separation with bending at edges due to the formation of vermiculite around their rims. The muscovites, on the other hand, were characterized by very minor layer separation at their edges. To resolve the issue of layer separation of micas through the release of K during the formation of soils, experimental studies of repeated Ba–K exchange were conducted with specimen muscovite and biotite and also on the mixture of the two micas. Experimental studies indicated that at ambient temperature and pressure, muscovite released negligible amount of K from its exposed surfaces and the weathering of muscovite was inhibited in the presence of biotite. This confirmed the observation that when muscovite and biotite co-exist, muscovite hardly weathers in soil environments. Hence, its enrichment in soils does not enhance the supply of K. Therefore, weathering products like di- and trioctahedral vermiculite and smectite are generally the products of the weathering of biotite mica. The X-ray intensity ratio of 001 and 002 basal reflections of mica has been found to be an effective diagnostic parameter to find out the quality of mica and therefore to judge the K releasing potential of soils. However, actual quantification of fine-grained biotites of soils appears to be mandatory for the precise determination of K reserves in soils in order to predict release of K for sustainable K management.

Palynology and clay mineralogy of the Deccan volcanic associated sediments of Saurashtra, Gujarat: Age and paleoenvironments

The intertrappean sediments associated with Deccan Continental Flood Basalt (DCFB) sequence at Ninama in Saurashtra, Gujarat yielded palynoassemblage comprising at least 12 genera and 14 species including Paleocene taxa such as Intrareticulites brevis, Neocouperipollis spp., Striacolporites striatus, Retitricolpites crassimarginatus and Rhombipollis sp. The lava flows of Saurashtra represent the northwestern most DCFB sequence in India. It is considered that the Saurashtra lava flows represent the earliest volcanic activity in the Late Cretaceous of the Reunion Mantle Plume on the northward migrating Indian Plate. The present finding of the Paleocene palynoflora from Ninama sediments indicate Paleocene age for the associated lava flows occurring above the intertrappean bed which suggests that the Saurashtra plateau witnessed eruption of Deccan lava flows even during Paleocene. The clay mineral investigation of the Ninama sediments which are carbonate dominated shows dominance of low charge smectite (LCS) along with the presence of mica and vermiculite. Based on the clay mineral assemblage it is interpreted that arid climatic conditions prevailed during the sedimentation. The smectite dominance recorded within these sediments is in agreement with global record of smectite peak close to the Maastrichtian–Paleocene transition and climatic aridity.