Texture, composition and provinance of innershelf sediments between Narakkal and Purakkad, Kerala with special reference to the formation of Mud Banks

The continental shelf of southwest coast of India (Kerala) is broader and . flatter compared to that of the east coast. The unique characteristic feature of the study area (innershelf between Narakkal and Purakkad) is the intermittent appearance of 'mud banks' at certain locations during southwest monsoon. The strong seasonality manifests significant changes in the wind, waves, currents, rainfall, drainage etc., along this area. Peculiar geomorphological variation with high, mid and lowlands in the narrow strip of the hinterland, the geological formations mainly consisting of rocks of metamorphic origin and the humid tropical weathering conditions play significant role in regulating the shelf sedimentation. A complementary pattern of distri bution is observed for clay that shows an abundance in the nearshore. Silt, to a major extent, depicts semblance with clay distribution . Summation of the total asymmetry of grain size distribution are inferred from the variation of skewness and kurtosis.Factor I implies a low energy regime where the transportation and deposition phases are controlled mostly by pelagic suspension process as the factor loadings are dominant on finer phi sizes. The second Factor is inferred to be the result of a high energy regime which gives higher loadings on coarser size fractions. The third Factor which might be a transition phase (medium energy regime) representing the resultant flux of coastal circulation of the re-suspension/deposition and an onshoreoffshore advection by reworking and co-deposition of relict and modern sediments. The spatial variations of the energy regime based on the three end-member factor model exhibits high energy zone in the seaward portion transcending to a low energy one towards the coast.From the combined analysis of granulometry and SEM studies, it is concluded that the sandy patches beyond 20 m depth are of relict nature. They are the resultant responses of beach activity during the lower stand of sea level in the Holocene. Re-crystallisation features on the quartz grains indicate that they were exposed to subaerial weathering process subsequent to thei r deposition

Studies on the, Physical Aspects of the Mud Banks along the Kerala Coast

A detailed survey of the present knowledge on the physical aspects of the mud banks has been presented in chapter 1.The physical geographical and geological aspects of the kerala coast, the shore-line and the sea bed and the various views on the formation,movements and dissipation of the mud banks have been discussed.The scope of the present work and a description of the area of study have also been given in this chapter. The horizontal and vertical distribution and the seasonal variations of the concentration of suspended matter in the mud bank region are discussed in chapter 3.it is seen that the mud bank reses above the bottom in the form of a ridged ,irregular,solid come with a flat top. Chapter vi deals with waves and currents in the region of the mud bank. The orientation of the breakers on either side of the mud bank suggests the possibility of formation of opposing alongshore currents and convergence of energy caused by wave refraction.The distribution of currents during the formative nature and dissipating stages of the mud bank show that the converging alongshore currents give rise to offshore flows

Provenance, Sedimentation and Geochemistry' of the Modern Sediments of time Mud Banks Off the Centrai Keraia Coast, India

This thesis is an attempt to Provenence, Sedimentetion and Geochemistry of the Modern Sediments of the Mud Banks off the Central Kerela Coast, India. In the present doctoral work, an attempt has been made to study in detail the mud banks of central Kerala, i.e. of Narakkal, Saudi and Purakkad areas which are reported as permanent mud banks, since olden days. The studies have been conducted during the years 1985 and 1986. The important findings of the study is stated as clay mineralogical studies of the rivers, lake and mud bank sediments reveal that the dominant clay mineral is kaolinite followed by montmorillonite, illite and gibbsite. Geochemical analysis of the Vembanad lake and mud bank sediments show that the iron and manganese are widely distributed both in the lake and mud bank sediments

Studies on the benthose of the mud bank regions of the Kerala coast

There is very little information on the subtidal bottom fauna of the shelf regions in the seas around India. What little is known is restricted to macro benthos. The paucity of the work on bottom fauna and the importance of mud banks in the fishery of the South West Coast of India has initiated the present study. Attempts have been made to obtain a picture of the bottom fauna of a mud bank region of the Kerala Coast. The difficulties involved in the sampling and analysis, especially the availability of a suitable vessel during the S.W. Monsoon, resulted in the work being restricted mainly to the Narakal mud bank region 6 Km. north of Cochin Detailed sampling is conducted using grab, dredge and to a small extent beam trawl, to assess the qualitative and quantitative nature of the macro benthos. Important species contributing to the fauna are identified and the standing crop estimated for different seasons. The meiobenthos was studied using core samples taken from the grab. Animals were identified to the major taxa. Standing crop of meiobenthos and the quantitative importance of different groups were also studied. The data collected have been interpreted and discussed. As an understanding of the physico-chemical aspects of the environment is essential in order to obtain a true picture of the benthos, attempts were made in this direction. Environmental parameters such as temperature of the sediment, salinity, temperature, and dissolved oxygen in the overlying water were studied .during the period of benthos investigation. Monthly observations on the dissolved inorganic and organic phosphorus in the area of investigation have been made. The physico-chemical nature of the sediment was also studied. Influence of these ecological variables on the bottom fauna is discussed.

Meteorological aspects of mud bank formation along south west coast of India

The study mainly intends to investigate the meteorological aspects associated with the formation of mud banks along southwest coast of India. During the formation of mud bank, the prominent monsoon organized convection is located in the equatorial region and relatively low clouding over Indian mainland. The wind core of the low level jet stream passes through the monsoon organized convection. When the monsoon organized convection is in the equatorial region, the low level wind over the southwest coast of India is parallel to the coastline and toward south. This wind along the coast gives rise to Ekman mass transport away from the coastline and subsequently formation of mud bank, if the high wind stress persists continuously for three or more days. As a result of the increased alongshore wind stress, the coastal upwelling increases. An increase in chlorophyll-a concentration and total chlorophyll can also be seen associated with mudbank formation

Geotechnical properties of the Cassino Beach mud

Knowledge of the marine soils properties, together with hydrodynamic and climatic data, plays an important role for a better understanding of the dynamic behavior of sandy and muddy coasts. This paper deals with reporting and basic interpretation of two campaigns of exploration and characterization of the mud of Cassino Beach, southern Brazil, carried out during the years of 2004 and 2005. Samples were obtained by means of cores collected at some locations offshore, and were submitted to various laboratory geotechnical tests, including determination of the physical index, grain size distribution, Atterberg limits, and shear resistance by both triaxial and shear vane tests. Results confirm the existence of a very soft soil deposit offshore Cassino Beach, highly plastic, compressible, and viscous, forming an important database for further studies.

Mapping oil spill environmental sensitivity in cardoso island state park and surroundings areas, São Paulo, Brazil

This study presents an environmental oil spill sensitivity map of Cardoso Island State Park, located in São Paulo state, Brazil, including some of its surrounding areas. This map was designed following the procedures determined by the Brazilian Federal Environment Organ (Ministry of the Environment), which separates coastal habitats in different littoral sensitivity indexes (LSI) to oil spills. We have also analysed some seasonal variations in morphologic and textural parameters at the local marine beaches that could affect their sensitivity, having found that they are more sensitive during summer due to a wider foreshore zone during these periods. Local most sensitive habitats are estuarine mangroves (LSI 10) and estuarine mud banks (LSI 9). Marine beaches were ranked LSI 3, and littoral rocky shores were subdivided in exposed flat rocky shores (LSI 1), boulder rocky shores (LSI 6) and sheltered rocky shores (LSI 8). Due to the elevated sensitivity of an estuarine system in the area, we considered necessary the installation of an Environmental Emergency Centre and the design of an emergency plan for the region in case of an accident resulting in oil spills within its vicinities. (C) 2007 Elsevier Ltd. All rights reserved.

Distribuição dos foraminíferos recentes associados à vegetação na faixa estuarina do Rio Itapanhaú, Bertioga, São Paulo

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Mineralogical-sedimentological and chemical investigation of sediments from Cross Bank off Florida

The sediments of a core of.1.55 m length taken on the windward side of the Cross Bank, Florida Bay, are clearly subdivided into two portions, as shown by grain size analysis: silt-sized particles predominate in the relatively homogeneous lower two thirds of the core. This is succeeded abruptly by a thin layer of sand, containing fragments of Halimeda. They indicate a catastrophic event in the Florida Bay region, because Halimeda does not grow within Florida Bay. Above this layer, the amount of sand decreases at first and then continuously increases right to the present sediment-water-interface. The median and skewness increase simultaneously with the increase in the sand and granule portion. We assume that the changing grain size distribution was determined chiefly by the density of the marine flora: during the deposition of the lower two thirds of the core a dense grass cover acted as a sediment catcher for the fine-grained detritus washed out of the shallow basins of the Florida Bay, and simultaneously prohibited renewed reworking. Similar processes go on today on the surface of most mud banks of Florida Bay. The catastrophic event indicated by the sand layer probably changed the morphology of the bank to such an extent that the sampling point was shifted more to the windward side of the bank. This side is characterized by less dense plant growth. Therefore, less detritus could be caught and the material deposited could be reworked. The pronounced increase in skewness in the upper third of the core certainly indicates a strong washing out of the smaller-sized particles. The sediments are predominantly made up of carbonates, averagely 88.14 percent. The average CaCO3-content is 83.87 percent and the average MgCO3-content amounts to 4.27 percent. The chief carbonate mineral is aragonite making up 60.1 percent of the carbonate portion in the average, followed by high-magnesian calcite (33.8 percent) and calcite (6.1 percent). With increasing grain size the aragonite clearly increases at the cost of high-magnesian calcite in the upper third of the core. Chemically, this is shown by an increase of the CaCO3 : MgCO3-ratio. This increase is mainly caused by the more common occurrence of aragonitic fragments of mollusks in the coarse grain fractions. The bulk of the carbonates is made up of mollusks, foraminifera, ostracods, and - to a much lesser extent - of corals, worm-tubes, coccolithophorids, and calcareous algae, as shown by microscopic investigations. The total amount of the carbonate in the sediments is biogenic detritus with the possible exception of a very small amount of aragonite needles in the clay and fine silt fraction. The individual carbonate components of the gravel and sand fraction can be relatively easy identified as members of a particular animal or plant group. This becomes very difficult in the silt and clay fraction. Brownish aggregates are very common in the coarse and medium silt fraction. It was not always possible to clarify their origin (biogenic detritus, faecal pellets or carbonate particles cemented by carbonates or organic slime, etc.). Organic matter (plant fragments, rootlets), quartz, opal (siliceous sponge needles), and feldspar also occur in the sediments, besides carbonates. The lowermost part of the core has an age of 1365 +/- 90 years, as shown by 14C analysis.

Benthic invertebrates that form habitat on deep banks off southern California, with special reference to deep sea coral

There is increasing interest in the potential impacts that fishing activities have on megafaunal benthic invertebrates occurring in continental shelf and slope ecosystems. We examined how the structure, size, and high-density aggregations of invertebrates provided structural relief for fishes in continental shelf and slope ecosystems off southern California. We made 112 dives in a submersible at 32−320 m water depth, surveying a variety of habitats from high-relief rock to flat sand and mud. Using quantitative video transect methods, we made 12,360 observations of 15 structure-form-ing invertebrate taxa and 521,898 individuals. We estimated size and incidence of epizoic animals on 9105 sponges, black corals, and gorgonians. Size variation among structure-form-ing invertebrates was significant and 90% of the individuals were <0.5 m high. Less than 1% of the observations of organisms actually sheltering in or located on invertebrates involved fishes. From the analysis of spatial associations between fishes and large invertebrates, six of 108 fish species were found more often adjacent to invertebrate colonies than the number of fish predicted by the fish-density data from transects. This finding indicates that there may be spatial associations that do not necessarily include physical contact with the sponges and corals. However, the median distances between these six fish species and the invertebrates were not particularly small (1.0−5.5 m). Thus, it is likely that these fishes and invertebrates are present together in the same habitats but that there is not necessarily a functional relationship between these groups of organisms. Regardless of their associations with fishes, these invertebrates provide structure and diversity for continental shelf ecosystems off southern California and certainly deserve the attention of scientists undertaking future conservation efforts.

(Table 2) Age determination of brock-red sandy mud beds and detrital carbonate beds in the Scotian margin

Piston cores from the continental margin off Nova Scotia show up to four discrete intervals of "brick-red sandy mud", which are up to 20 cm thick. The ages of these intervals are bracketed by several radiocarbon dates, and three fall in the range 12.5-14.1 ka (radiocarbon years with -0.4 kyr reservoir correction). The youngest dates from ~10.4 ka, placing it within the Younger Dryas. The distribution of the beds and their petrographic character indicate a source in the Gulf of Saint Lawrence. The grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers. Graded brick-red beds in some cores were probably redeposited from turbidity currents. The lowermost bed on the Laurentian Fan and East Scotian Rise is immediately overlain by a carbonate-rich interval that can be identified all around the margin of the Grand Banks. This interval is correlated with detrital carbonate bed DC-1 in the Labrador Sea and Heinrich event H1 in the North Atlantic. The sequential occurrence of the two beds suggests that they may be a response to the same trigger, probably sea level rise, but that the Gulf of Saint Lawrence source was more easily destabilized.