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

V. Singa Raju ¹, B. M. Shah ¹

Affiliations
1 Geological Survey of India, Hyderabad - 500 068, IN

Abstract

A thick sequence of Upper Pleistocene and Holocene Litho-Assemblages(50 m) are recorded while evaluating the Quaternary geology of the Eleru delta Classified under fluvial, marine and aeolian facies, these sediment assemblages indicate the transgressive and regressive phases in the process of coastal evolution. The marine regressive phase is indicated by predominant fluvial sediment characteristics in these assemblages during Upper Pleistocene times. The sediment characteristics of the channel-Fill deposits are suggestive of prevalence of aggraded fluvial channels that might be consequent to the rise in the sea level, subsequent to the last glacial maximum ( 18000 years B P). The sea level reached its peak during climatic optimum (6500 years B P). The landward geornorphological observations suggest a palaeoshoreline which existed at around 2 5 km away from the present coastline. However, the present systematic evaluation of the sediment parameters and microfossils in the coastal Litho-Assemblages brought to light a Palaeo-Coastline extending even beyond 4 km from the present coastline. This transgressive marine phase is typified by the consistent predominance of organic Matter-Rich, greyish black silty clays right up to the inferred coastline. The marine Micro-Fauna, represented by benthic and planktonic foraminifera, ostrocods and pteropods in these clays further strengthens this observation. The recurrence of dominant fluvial processes along the coast might be due to subsequent gradual recession of the sea. The presence of the palaeo-beach ridges and present beach ridge marks the standstill points in the upper Holocene coastal evolution.

Keywords

Marine Transgression, Holocene, Eleru Delta, East Godavari District, Andhra Pradesh.

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M. Anand Rao ¹, S. Ramamurthy ¹, B. M. Shah ¹, V. Hanumantha Rao ¹

Affiliations
1 Geological Survey of India, Hyderabad, IN

Abstract

Geomorphic expression of the variety of landform units exposed in the Krishna Delta is a manifestation of complex interplay of riverine and marine processes in space and time. The dominance of fluvial processes is largely responsible for the progradation of the delta. This is evidenced by the presence of a series of Palaeo-Delta lobes and strand plains across the deltaic plain. Systematic study of geomorphic maps, aerlal photographs, toposheets spanning a period of right decades and satelite images (IRS-1D) indicates operation of highly dynamic nature of coastal processes Superimposition of data sets of different periods, clearly exhibits remarkable changes in the configuration of the lower deltaic plan. It is observed that towards the eastern margin and in close proximity to the easternmost distributary a substantial part of about 15 km has been eroded away. At the same time the western part of the lower deltaic plain shows accretion. There is an enlargement and further westward growth of the spit. The width of the spit which was approximately 120 m during the 1920s had grown to 620m in the 1970s and in the year 2001 its width is around l km. Another spit with bars enclosing a lagoon, which is a new development, was observed. Impact and possible causes of the changes in the deltaic region on environment are also discussed. The attempt here is to highlight only the morphological changes along the delta coast.

Keywords

Morphology, Coastal Processes, Erosion, Accretion, GIS, Image Processing, Krishna Delta.

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