Paleocurrent patterns in braid-bar and point-bar deposits: Examples from the Ganga River, India

A braid bar at Bithur and a point bar at Saidpur, both in the Ganga River, were studied for their paleocurrent patterns by making trenches in a grid s ystem and documenting the azimuthal direction of planar and trough cross-be dding. The bars are made up of fine sand and subjected to annual monsoon di scharge fluctuations, The paleocurrent trends in the Bithur braid bar show changes from the upstream to the downstream parts, viz,, the upcurrent part has a unimodal pattern with high variance, the middle part shows a bimodal pattern with very high variance, and the downstream part shows a unimodal pattern with high variance, There is large variance between the paleocurren t directions of planar and trough cross-bedding and a very high variance in the overall paleocurrent trend, The Saidpur point bar shows a polymodal pa ttern with very high variance in the upstream part, unimodal distribution w ith low variance in the middle part, and unimodal distribution with high va riance in the downstream part. There is no difference in the paleocurrent d irection of planar and trough cross-bedding; the variance value for the ove rall paleocurrent is slightly lower than in the Bithur braid bar. Contrary to the existing models, the value of azimuthal dispersion is higher for the Bithur braid bar and lower for the Saidpur point bar. Reconstruction of be dform movement on both Bithur and Saidpur bars shows a prominent movement d irection of bedforms obliquely into the channel in the marginal parts of th e bars. This trend of bedform movement is in contrast to the trends of the theoretical models, where in the marginal parts of bars bedforms move obliq uely on the bars.