Informatics Publishing Limited

Antonio Mascarenhas ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, 403 004 Goa, IN

Abstract

This article presents granulometric data of pelites (less than 40 microns) of mixed composition from a volcano-sedimentary environment. The Sedigraph serves as an useful tool in the analyses of silt-clay fraction of marine sediments. A cumulative curve from 40 to 1 micron can be obtained in 20 minutes. Pelites analysed show wide variations in grain size characteristics with the median value oscillating between 22 and 3 microns. In general, two fine grain size facies, each showing significant variations, are deciphered. Parabolic facies represents coarse silts whereas logarithmic facies comprise medium to fine silts. The type of grain size curves largely depends on the abundance of carbonate and pyroclastic mineral content of individual pelites. As compared to total pelites, their decalcified fractions sometimes show a significant shift of the grain median towards finer sizes. The intricacies of grain size studies of pelites of mixed composition are described in this paper.

Keywords

Sedigraph, Sedimentology, Pelites.

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Antonio Mascarenhas ¹

Affiliations
1 National Institute of Oceanography, Dona Paula-403004, Goa, IN

Abstract

Peat layers 2 to 30 cm in thickness, 22 to 46 m below present sea level, are found along the inner shelf of India, up to 27 km from the coast. They are rich in plant debris, organic carbon and sulfur. These organic-rich layers are not sedimentary deposits. Lack of favourable substrates, absence of sheltered habitats, high energy physical environments, and a very rapid sea level rise during early Holocene indicate an unfavourable paleogeography and adverse oceanographic conditions for mangrove development and in situ peat formation. On the contrary, significant siliciclastic minerals, lithogenous elements and type III kerogen suggest a continental origin of peat. Restricted thickness, limited lateral distribution, absence of matted structures and laminated deposition imply transport of organics. Anomalous ages of wood with respect to present sea level are evidences of sediment reworking. Hence, peats on the continental shelf are not transgressive deposits.

Keywords

Economic Geology, Peat, Western Continental Shelf, India.

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Antonio Mascarenhas ¹

Affiliations
1 National Institute of Oceanography, Dona Paula - 403 004, IN

Abstract

An experiment to rebuild a dune field is attempted at Miramar beach, Goa. Installation of sand fences, a simple, cheap and environment friendly method of inducing accretion of sand is proposed as a remedial management option.

Keywords

Sand Fences, Coastal Dunes, Environment, Goa.

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Antonio Mascarenhas ¹, Nitin Dabholkar ¹, Jayu Narvekar ¹, Shivanand Prabhudesai ¹, Siddharth Ghatkar ¹, Sadaf Ansari ¹, Pramod Maurya ¹, Elgar Desa ¹, Anand Lokapure ¹, Surekha Nagvekar ¹, Gajanan Navelkar ¹, R. Madhan ¹, Fernando Vijayan ¹, Vidish Shetye ¹, Llewellyn Fernandes ¹, Sanjeev Afzulpurkar ¹, T. Suresh ¹

Affiliations
1 National Institute of Oceanography, Dona Paula, Goa 403 004, IN

Abstract

The seabed resident event-driven profiling system (SREP) was deployed in the northeastern Arabian Sea for winter convention studies. SREP is an autonomous profiling system consisting of two parts: a stationary seabed unit and a positively buoyant tethered profiling unit (profiler). It offers a novel and optimized approach to profiling in coastal waters from close to seabed (14.63 m above seabed) to the sea surface. The seabed unit houses an underwater winch system, underwater acoustic modem, pressure sensor, low-power electronics, batteries and divinylcell hydraulic crush point foam for subsea applications. The profiler houses a suite of oceanographic sensors: conductivity– temperature–depth, DO, chlorophyll, PAR, underwater acoustic modem, low-power electronics, batteries and divinylcell hydraulic crush point foam for subsea applications. The underwater winch system on the seabed unit spools out and spools in the profiler throughout the water column. Data acquisition on the profiler is done during ascending. The profiler ascends gradually in the water column at an average velocity of 20 cm/s. The seabed unit and the profiling unit communicate using a pair of underwater acoustic modems operating at 18–34 kHz. SREP was developed to obtain time-series water column measurements of coastal waters during the summer monsoon season (June–September) when the sea wave and wind conditions are extreme, thus making it difficult to deploy profiling packages from the ship. A description of SREP and observations made during the field deployment are presented in this article.

Keywords

Coastal Waters, Profiling System, Seabed Unit, Technology Demonstration, Winter Convention Studies.

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