Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

M. Ramkumar ¹, P. Sudha Rani ¹, M. S. Gandhi ¹, M. Pattabhi Ramayya ¹, V. Rajani Kumari ¹, K. V. S. Bhagavan ¹, A. S. R. Swamy ¹

Affiliations
1 Delta Studies Institute, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Textural data of the sediments of Godavari delta indicate the control of energy over grain size and other statistical parameters. These parameters also explain the regional energy conditions, which are indicative of many sub-environments. The prime environmental factors viz. transportation, deposition and preservation vary in time and space, which in turn, produce variability as well as shared nature of grain size characteristics. Many sub-environments have similar depositional/energy regimes making their distinction a difficult task. It is also established that only groups of environments could be delineated, rather than individual environments, based on manual observations and discriminant plots of textural data.

Keywords

Texture, Grain Size, Statistics, Sedimentary Environments, Godavari Delta.

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M. Ramkumar ¹

Affiliations
1 Delta Studies Institute, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Recent mapping of the Kakinada spit and the adjoining regions has revealed that the spit has reached its mature state and would not grow lengthwise. Another spit paralleling the Kakinada spit is growing to its east. Futuristic projections show that the new spit would form another bay like the Kakinada bay.

Keywords

Deltaic Landforms, Sedimentation, Recent Changes, Sea Level, Godavari Delta, Andhra Pradesh.

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M. Ramkumar ¹, M. Pattabhi Ramayya ¹

Affiliations
1 Delta Studies Institute, Andhra University, Visakhapatnam - 530 003, IN

Abstract

A simple, manually operated water sampler, that can be used for collection of water sample at desired depths from estuaries, near shore regions, lagoons, bays and lakes has been designed by the authors. The instrument is operated successfully in the Krishna estuary and Nizampatnam bay for collection of water samples to determine suspended sediment transport and nutrient diffusion. The instrument is found to be quite useful to sedimentologists and environmental researchers.

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M. Ramkumar ¹

Affiliations
1 Humboldt Environmental Research Organisation, D-371, Gandhiadigal Street, Annanagar, Tiruchirapalh - 620017, IN

Abstract

Sedimentary micro-environmental characteristics, landforms and morphostrati graphic details of the Godavari delta reveal that the progradational trends of the delta are favoured by channel bifurcation and lengthening in upper deltaic plain. In the lower deltaic regime, formation of barrier bar followed by lagoon and lagoon infilling lead to deltaic progradation over sea. The progradational process was such that, initially, the delta front deposits developed low gradients in continental shelf over which spit and distributary mouth bars were deposited that paved way for the development of lagoonal conditions. It was followed by creation of swamps and marshes that in turn were overlapped finally by flood plain as a complete sequence of delta progradation. The neotectonic activity has played a pivotal role in this progradational process by tilting fault blocks that provided adequate gradient and alternative activation of various distributaries of the river. On the basis of facies architectural elements, sedimentary processes and the pattern of sedimentation, the Godavari delta can be considered as modern analog of abandoned Lafourche delta of Mississippi delta complex. Analyses of shoreline features, ongoing sedimentary pattern and the role of depositional and erosional agents over different sedimentary environments indicate that the delta currently engages erosional phase in view of rising sea level coupled with subsidence and is not prograding over sea as happened during its evolutionary history.

Keywords

Deltaic Environments, Landforms, Neotectomcs, Sea Level Godavari Delta.

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M. Ramkumar ¹

Affiliations
1 Delta Studies Institute, Andhra University, Visakhapatnam - 530 003, IN

Abstract

Documentation of the textural and geochemical criteria of individual sub-environments of the modern Godavari delta shows that in view of prevalent shared nature of transportation, deposition and preservation processes, the textural and geochemical characteristics are not distinct enough to have these sub-environments separated by visual methods on the basis of measurements of constituent variables. Multivariate discriminant function analyses of these data show that the sub-environments of the modern deltaic system could be separated practically to the tune of 80.26% accuracy. The percentage of distinctness depends on the sensitivity of each parameter to different sub-environments and also the ability to separate between sample variations. These results have enabled the construction of a scheme for recognition of environments of unknown samples.

Keywords

Granulometry, Geochemistry, Sedimentary Environments, Statistical Discrimination.

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