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The AAPG/Datapages Combined Publications Database

Houston Geological Society

Abstract


Deltas in Their Geologic Framework, 1966
Pages 125-157

Lithological and Chemical Facies Changes in the Recent Deltaic Sediments of the Godavari River, India

A. S. Naidu

Abstract

Along the 52-mile river course of the modern Godavari Delta the median and mean size of the sands decrease, sorting increases, skewness changes from negative to positive, and kurtosis remains unchanged downstream. Sands of the offshore barrier islands are very well sorted and unskewed, those of the mainland beach are moderately sorted and negatively skewed, and the dune sands are well sorted and positively skewed. Percent silt and clay in the mainland beach is less (0.1 to 0.8 percent) than in the dunes (7.0 to 1.5 percent). An anomalously high content of sand in the lagoonal facies is attributed to earlier deposition in a shallow marine environment. Consideration of the present geomorphology of the river and its bed load indicates that the change in the river course over the past century is a result of coarsening of the bed load.

Heavy minerals indicate a provenance of khondalite, charnockite, and calc-granulite. The downstream decrease in opaques and garnet and the corresponding increase in amphibole and sillimanite are assumed to be controlled by sorting based on mineral specific gravity and shape. An increase in quartz/feldspar ratios downstream is due to the greater instability of. feldspar.

Increased salinites along the river correspond with an increase in illite, chlorite, and Na+ montmorillonite, and a decrease in mixed Ca++ Na+ montmorillonite and kaolinite. Na+ montmorillonite is predominant in the swamps and illite in the backwater. Chemical analyses of the clay fraction substantiate the assumption that the increase in Na+ montmorillonite, illite, and chlorite is due to the cation exchange of Na+, K+, and Mg++ by the respective clay minerals.

The variations in iron, phosphate, and uranium content in the various environments are related to the changes in clay mineralogy, organic matter, and hydrography. Trace elements analysed do not show any variation from one environment to another.


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