Deltaic Region Research Articles

Organic-walled microfossils of doubtful origin in Permian and Triassic sequences on peninsular India

The Permian and Triassic succession of the Indian Gondwana Sequence, with the exception of Lower Permian Talchir Formation, has been considered to be deposited in fluviatile-lacustrine environment-Palynological investigations of these deposits have revealed the presence of rich assemblages of spores, pollen and other organic-walled microfossils of doubtful origin (OMIDO) belonging to the group Acritarcha in its broader sense. Recent discoveries of marine signatures from these deposits depicted by sedimentological, biotic and chemical features strongly prompt for a detailed investigation of OMIDO’s for their authentic application in determining the palaeoenvironment. Sporadic or consistent occurrence of OMIDO’s has been recorded from Talchir to Panchet formations at various time intervals. The increase in the brackish water regime on to the Indian Peninsula near the deltaic sea-shore regions could have provided suitable environment from time to time for growth of OMIDO’s. This could have occurred due to the well-known global transgressions during Permian and Triassic times. It is, therefore, important that the non-marine nature of Indian Gondwana should be skeptically viewed in order to find possible marine signatures in this sequence. The present study reveals that there had been three major diversity acme phases of OMIDO’s during Permian, viz., (i) Talchir/Karharbari, (ii) Upper Barakar, and (iii) Upper Raniganj Formations. They broadly coincide with the onset of regression. Although the data is meager, a similar trend in occurrences of OMIDO’s has been observed in the Triassic.

Relationships between mineral surfaces and organic carbon concentrations in soils and sediments

Relationships between mineral specific surface area and organic carbon (OC) concentration are examined for sediments and soil A-horizons from throughout the world. I found (published elsewhere) that continental shelf sediments from many different regions exhibit downcore loss of OC to a refractory background level which shows a consistent relationship with mineral surface area (slope = 0.86 mg m −2 OC). This trend is equivalent to a monolayer of organic matter over all surfaces, and is termed the monolayer-equivalent (ME) level. Sediments and soils from other environments are compared to this empirically derived relationship. Several continental slope areas show extension of this relationship to considerable depth. Marked excesses of OC above this trend, which persist downcore, were found in sediments with high carbonate mineral content or slope sediments with low dissolved oxygen concentrations in the overlying water column. About half of the soils examined also adhered to this relationship, while soils with high carbonate content, low pH, or poor drainage showed OC concentrations higher than the ME level. OC concentrations below the ME level are found in deltaic regions and areas with low organic matter delivery such as the deep sea or arid soils. The nature of mineral surfaces was examined using N 2 adsorption-desorption isotherms, and most surface area was found to be present as pores with < 8-nm widths. A hypothesis is developed that explains the observed OC concentrations as a saturation of adsorption sites within small pores, which are small enough to exclude hydrolytic enzymes and hence protect organic matter against biological attack. The relationship between this hypothesis and other hypothesized protection mechanisms is discussed. Adsorption is shown to provide a mechanistic and quantitative explanation for spatial and temporal relationships between sedimentation rate and OC burial.

Estimating the extent of floods in Bangladesh using SPOT data

Nine SPOT XS scenes recorded during the dry season (January, February) and after cyclonic storms were analyzed to evaluate both the extent and consequences of floods in Bangladesh, in the deltaic complex of the Ganges. Digital and visual analysis showed the following results: 1) Near the capital, Dahka, within a SPOT scene (3600 km 2), the extent of water varies from 324 km 2 during the dry season to 1303 km 2 after a destructive flood. This means that flood-prone areas in this overpopulated deltaic region are at least four times larger than the hydrographic network observed during the dry season. 2) The Sunderbans are the world's largest mangroves (about 6000 km 2 in a single block); two-thirds of this forest (4050 km 2) are in Bangladesh, and the rest is in India. These ecosystems seem to resist cyclones. No sign of any kind of mangrove alteration is seen on SPOT images recorded a few weeks after disastrous cyclonic storms (20 August 1987 and 6 September 1988). This is an important fact since the protective role of these coastal swamp forests is tremendously important. 3) The islands located in the very exposed area at the mouth of the Meghna are densely populated (more than 1000 inhabitants/km 2). Hathya island has been carefully surveyed. According to the investigations carried out on SPOT images (25 February 1987 and 26 October 1988), the island seems to be at present satisfactorily protected against cyclones and tidal surges, behind newly planted mangroves (Sonneratia apetala Buch.-Ham.) and sheltered by a complex network of embankments which are visible on the images. It was concluded that the spectral separability of classes (water, natural plant communities, land use units) and the geometric accuracy of SPOT are suitable for coastal monitoring in this part of the Bangladesh.

The Effect of Mississippi River Delta Lobe Development on the Habitat Composition and Diversity of Louisiana Coastal Wetlands

The patterns of habitat changes that occur during the growth and decay of Mississippi River deltaic lobes were examined by comparing different-aged lobes using habitat maps constructed from aerial photographs. Mudflats and fresh marshes dominated young delta lobes (10-1000 years old). Intermediate-aged lobes (1000-2000 years old) contained higher proportions of brackish and salt marshes. Old lobes (2000-4000 years old) contained large areas of salt and brackish marshes and open water. The number of habitat types (N) and Shannon-Wiener index of habitat diversity (H') were lowest in the youngest lobe (N = 14, H' = 0.68), highest in a medium-aged lobe (N = 56, H'= 1.77), and intermediate in the oldest lobe (N = 44, H' = 1.38). A new cycle of vegetation change is initiated approximately every 1000 years when upstream river diversion reintroduces fresh water and sediment into an old lobe. INTRODUCTION This study examines the effect of the large-scale disturbance caused by major shifts in the course of the Mississippi River on the distribution of plant communities in the Mississippi River deltaic plain region of Louisiana. Land in the Mississippi River delta region was formed during the last 6000 years by sediment deposited in major deltaic lobes by the Mississippi River (Fig. 1). Together the delta lobes built a broad plain of approximately 3 million ha. The nature and timing of these deltaic deposits control the long-term dynamics and persistence of the habitats found in this predominantly wetland coastal region. The five delta lobes that today make up the Mississippi River deltaic plain range in age from 10-4000 years. New delta lobes begin to form approximately once every 1000 years in response to a major change in the course of the river (Fig. 1). Each delta lobe undergoes a cycle of geological development (Kolb and van Lopik, 1966; Frazier, 1967; Gagliano and van Beek, 1975) and each of the existing five lobes lobes represents a different stage of development (Fig. 2). The initial phase includes below-water (subaqueous) deposition and limited above-water (subaerial) development. This is followed by a second phase of sustained land building. Land building continues until the river's hydraulic gradient becomes too flat to efficiently transport water and sediment to the Gulf of Mexico. This sets the stage for an upstream diversion to a new stream course with a steeper gradient (Morgan, 1967). A third phase of prolonged subsidence, land erosion and lobe decay follows diversion of the river course. During this stage of delta abandonment, progressively less water and sediment are transported by the dying distributary. The reduced quantity of sediment at its mouth cannot compensate for subsidence and wave attack, and erosion becomes the dominant process acting on a delta lobe (Morgan, 1967). Salinity decreases as a delta lobe develops, is lowest during time of greatest land building because of large riverine freshwater input, and increases again as freshwater input declines (Fig. 2). Land deposition and erosion and changes in salinity during this geologic cycle pro'Present address: Department of Forestry and Wildlife Management, University of Massachusetts, Amherest, 01003

210Pb Flux in an Arctic Coastal Region

Seven marine coastal cores and one lake core were collected from a deltaic region in northern Alaska and analyzed for 210Pb. The 210Pb activity levels at the surface in all cores were less than the levels generally observed in coastal sediments of nonpolar regions. The attenuated flux of 210Pb to this region, as deduced from analyses of snow deposits, is probably responsible for these reduced activity levels. Yet the calculated flux of this nuclide to the sediments (about 1 and 4 dpm/cm&sup2;/yr in the marine and lake sediments respectively) is in excess of that accountable from the atmospheric flux (0.08 dpm/cm&sup2;/yr). Presumably processes such as advection of 210Pb contribute importantly to the sedimentary flux.Key words: lead, cores, arctic coastal plain, radionuclide flux, air masses, lake sediments

Development and Ecodisaster: A Lesson from Cochin Backwater System

Kerala, with a unique climate, has rich and varied ecosystems with luxuriant and diverse plant and animal communities. This has led to a high density of human population. The State has resorted to modern technological methods for its economic development which include industrialization and improvement of agricultural production. The establishment of a modern port at Cochin has transformed the region into the industrial capital of the State. Simultaneous with economic progress, the environmental conditions have become deranged due to large scale shipping operations. Of late the environmental problems are increasing in the highly productive backwater system, due to industrial effluents. How developmental programs can undermine the ecological balance and cause deleterious effects as well as unforseen consequences are well illustrated by the deltaic region of Kuttanad - “the rice bowl of Kerala”. Dams, at the upper reaches of the rivers, provide power for industry and water for irrigation. But inadvertent denudation of the forests due to continuous human settlement and related activities will not only damage the dams, the industry and agriculture but also the climate of the region. The high density of population exerts undue pressure on the ecosystem whether it be terrestrial, aerial or aquatic and causes serious imbalances.

Two interesting coins of Śaśāṅka

Śaśāṅka, who flourished in eastern India, was one of the most important rulers in the post-Gupta epoch. He was a rival and opponent of the Maukharis of Kānyakubja, Rājyavardhana and Harṣavardhana of Thāneśvara, and Bhāskaravarman of Kāmarūpa. Śaśāṅka is known from a large number of sources and among these coins are very important. Śaśāṅka is generally known to have issued coins made of gold only. In course of our recent exploration in the deltaic regions of West Bengal, we have, however, come across two examples of the hitherto unnoticed silver coins of Śaśāṅka. These coins were discovered along with the two other coins made of gold, and of these one belongs to Śaśāṅka and the other to a class of coin with the legend Śrī the obverse.

A study on the suitability of two short duration Russian Hirsutum varieties for rice fallows in Madras State

The cultivation of P216F cotton as an off-seasonal orop in the rice fallows of Madras state is of recent origin, within the last two decades. With all its proved merits for successful utilisation of rice fallows (Balasubramanian, 1952; Iyengar et al, 1958; Neelakantan et al, 1959 and Iyemperumal et al, 1960), only a total area of 16,100 acres is estimated to be under this cotton (Fifth and Final Forecast Report 1963-64, Madras State) in the State. The progress made in this direction is reported to be not quite satisfactory (Ramachandran et al, 1960). They have, therefore, stressed the need for evolving a cotton strain shorter in duration than the present P216F cotton for a planned approach towards the problem of solving the varietal bottleneck in the cotton cultivation in wet lands after the harvest of thalady or to suit the short fallow periods in the deltaic regions. Sikka and Avtar Singh (1961) have observed that increased yields were obtained in U. S. S. R. by increasing plant population per unit area facilitated by short branch character and enrliness possessed by varieties grown there. The short branch trait with extreme earliness under our conditions is considered valuable for exploiting the advantageous habit of growth to suit the growing demand for a cotton strain earlier than P216F in the rice fallows of the State. The paper summarises the study undertaken to explore the possibility of directly introducing short branching, short duration and early maturing varieties in the rice fallows of the State.

The amphipods of the deltaic region of the rivers rhine, meuse and scheldt in relation to the hydrography of the area part II. The talitridae

Resume Dans la region du delta du Rhin, de la Meuse et de l'Escaut, 13 especes de la famille des Gammaridae ont ete trouvees. Leur distribution et leur ecologie sont discutees. L'auteur a etudie en particulier l'influence de la salinite et de la concurrence interspecifique sur la distribution des especes dans les eaux d'estuaires. Dans l'etage sublittoral des estuaires le passage progressif de l'eau marine a l'eau douce est jalonne par la serie suivante d'especes du genre Gammarus: G. plumicornis - G. locusta - G. salinus - G. zaddachi - G. pulex. Une serie analogue du genre Melita est representee en Hollande seulement par 2 especes: M. obtusata dans les eaux marines hors des passes et M. palmata, qui penetre dans l'eau saumâtre jusqu'a la zone mesohaline. Dans l'etage eulittoral une autre serie de Gammaridae se presente. Marinogammarus obtusatus et M. marinus sont des habitants de la zone marine. M. marinus penetre notablement plus loin dans l'eau saumâtre que M. obtusatus, mais dans les zones meso- et oligohalines des estuaires il est remplace par Gammarus duebeni. G. duebeni et G. zaddachi sont aussi tres communs dans les eaux saumâtres a l'interieur des iles du delta, qui n'ont pas une communication libre avec la mer. Melita palmata est assez commun dans les eaux interieures meso- et polyhalines, tandis que Gammarus locusta et G. salinus sont rare dans les eaux interieures ou ils n'apparaissent seulement que dans des conditions ecologiques speciales. Dans l'etage eulittoral de la zone euhaline des estuaires, Marinogammarus marinus et M. obtusatus se presentent en zonation prononcee, provoquee par concurrence interspecifique. Dans la partie septentrionale des eaux estuairines du delta, toutes les especes de Gammarus ont disparu soudainement au printemps de 1960, probablement par suite d'une maladie epidemique. L'auteur a etudie le repeuplement de ces eaux; G. salinus a reparu en moins d'une annee, et G. duebeni au bout de 3 ans, mais G. zaddachi n'a pas encore reoccupe son aire ancienne et il semble que cette espece se soit eteinte dans cette region.

The amphipods of the deltaic region of the rivers rhine, meuse and scheldt in relation to the hydrography of the area part I. Introduction and hydrography

Une description de la topographie des territoires de l'embouchure du Rhin, de la Meuse et de l'Escaut a donné les résultats suivants: La région deltaïque peut être divisée en trois systèmes hydrologiques, 1. l'estuaire de l'Escaut, 2. le système de l'Oosterschelde, n'ayant pas une décharge des eaux fluviatiles, et 3. la régime deltaïque s.s. , englobant les embouchures du Rhin et de la Meuse. Une classification des sections de salinité, tenant compte des caractéristiques biologiques, mais seulemant valables pour les eaux d'estuaires, est décrite. L'auteur mentionne également quelques donnés sur les eaux saumâtres à l'intérieur des îles deltaïques.

Some studies of salt-affected soils of Canning, West Bengal

Six profiles from a representative area in the southern part of the deltaic region of Gangetic West Bengal, India, were examined. Of these, one can be termed as normal, another as non-saline alkali, and the remaining four as saline alkali. Of the saline alkali ones, there was one profile which had a rather low pH. The acidic condition of the soil is due to the presence of decaying organic matter in the soil giving rise to what has been termed as a degraded saline alkali soil. In designating the soils as such, the broad conditions of total soluble salts expressed as percentage of sodium chloride per hundred grams of soil and the exchangeable sodium percentage have been used as the criterion. The soils have thus been classified taking into consideration the dominant soil-forming factors active here. Remedial measures to improve these soils include the incorporation of green-manuring crops and the application of soil ameliorants like lime, gypsum and sometimes other chemical amendments. The soils must be surveyed in order to delineate the types of salt-affected soils, and during reclamation, drainage and irrigation measures should not be lost sight of either.

Venezuela in 1940

THE Republic of Venezuela, bordering on the Caribbean Sea, has come into special prominence in this century, thanks to the discovery of vast resources of petroleum, a commodity more vital to us in this war even than in the last. The country is of particular interest to us to-day because what one may call its modern development dates from the discovery of oil. Approaching Venezuela from the sea, whether from the east, as did Columbus, or from the north at Cumana, like Humboldt and Bonpland, or landing from a liner at La Guiara to-day, one is confronted by formidable mountains. These, the Andes and the Maritime Ranges, together divide the country into two regions. To the north of these mountains lie the Caribbean Sea, the desert ranges of Falcon, the desiccated peninsula of Paraguana and the basin of the Lake of Maracaibo. South of this range lie the Llanos with their Mesa plateaux, the great river basins of the Orinoco and the Apure, and rising to the south-east, the Guiana highlands. The capital of Venezuela, Caracas, centrally situated in the Distrito Federal, is the political, financial, and social centre of the country. But the natural resources which have brought Venezuela to the forefront among South American Republics are derived primarily from the regions of the Lake of Maracaibo, and secondarily from the Llanos plains of Eastern Venezuela, the States of Anzoategui and Monagas. The Maracaibo Lake Basin includes most of the State of Zulia, economically the most important physiographical province in the country. It occupies a shallow topographical and structural depression formed by the north-east divergence of the Venezuelan Andes from the Eastern Cordillera, lying between the Sierra de Perija to the west, the Sierra del Norte to the south, and the hills of the State of Falcon to the west. Intermittently since Eocene times it has received the sediments from the surrounding hills, and the ancient seas, rich in life, have been the origin of the vast reservoirs of petroleum we are tapping to-day. These seas have always been shallow. To-day, the lake in the centre is about 90 feet deep; 5 miles from shore the depth averages 30 feet. Much of the margin stands at lake level, much is swampy, even tidal, though tides are slight. The flat deltaic regions of the south-western rivers (the Rio Catatumbo and Escalante) come second in size to the Amacuro Delta of the Orinoco, and appear from the air an immense flat of partly forested swamp, lagoon-studded and cut by meandering river channels. The entrance into the Lake of Maracaibo, cut through the dry, sandy, scrub-country of North Zulia, is shallower even than the lake itself. An uplift outside the entrance, bringing to the surface older rocks which form the Island of Toas, has all but closed it. A submerged bar of shifting sand has left a narrow channel navigable to vessels of 14-foot draught which can pass at high tide. Oil companies working in the Lake of Maracaibo have fleets of