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Mascarenhas, Antonio
- Granulometric Analyses of Pelites Using a Sedigraph: Examples from a Volcano-Sedimentary Environment
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1 National Institute of Oceanography, Dona Paula, 403 004 Goa, IN
1 National Institute of Oceanography, Dona Paula, 403 004 Goa, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 42, No 4 (1993), Pagination: 392-404Abstract
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.- Significance of Peat on the Western Continental Shelf of India
Abstract Views :179 |
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Authors
Affiliations
1 National Institute of Oceanography, Dona Paula-403004, Goa, IN
1 National Institute of Oceanography, Dona Paula-403004, Goa, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 49, No 2 (1997), Pagination: 145-152Abstract
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.- Sand Fences: An Environment-Friendly Technique to Restore Degraded Coastal Dunes
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Authors
Affiliations
1 National Institute of Oceanography, Dona Paula - 403 004, IN
1 National Institute of Oceanography, Dona Paula - 403 004, IN