GRAIN-SIZE FREQUENCY-DISTRIBUTION IN ANCIENT DEPOSITIONAL ENVIRONMENT- A CASE-STUDY FROM LOWER GONDWANA SEDIMENTS, PRANHITA GODAVARI BASIN, ANDHRA-PRADESH

Environmental significance of grain-size frequency distribution of anc ient terrigenous deposits has been examined in the light of applicabil ity as one of the tools of environmental analysis. Synthesis of result s obtained from grain-size analysis of 71 subsurface samples of Barren Measures Formation in Bellampalli-Chinnur area of Pranhita-Godavari L ower Gondwana basin points to the interplay of various sedimentary dyn amics of diverse microenvironments within a broad fluvial system. Form ative processes were controlled by availability of different sizes of particles and competency of flow. Channel pattern deduced from the stu dy conform to the model of ''mixed load anabranching river pattern.'' This study reaffirms the reliability of grain-size analysis of sands i n interpreting ancient depositional environment.