The following review article entitled "A Review on the Quaternary Characteristics of Pleistocene Tracts of Bangladesh " covers the answer to your question.
the Barind Tract Formation is most probaly combination beween sedimentation (alluvium) and rubifaction, consequently the red clay are paleosol.
Have a look to:
M. Shafiqul Alam, Eddy Keppens, Roland Paepe, The use of oxygen and carbon isotope composition of pedogenic carbonates from pleistocene palaeosols in NW Bangladesh, as palaeoclimatic indicators, Quaternary Science Reviews, Volume 16, Issue 2, 1997, Pages 161-168, ISSN 0277-3791, http://dx.doi.org/10.1016/S0277-3791(96)00044-3.