Lower Vindhyan Rocks around Hirapur and its Relationship with the Basement Granites

The rocks of Semri Group are well developed in Son valley area with almost all of its succession preserved. These sediments are also substantially exposed in Bundelkhand area around Hirapur. They rest unconformably over Bundelkhand Granite with a profound non-conformity whereas their contact with the Bijawar Group is either a marked angular unconformity or disconformity. Both these unconformities can be mapped for several kilometers where the ferruginous clastic rocks of Bijawar Group mostly comes in contact with Semri Group. The sequence is well exposed along road and river cuts where the hillocks of Semri Group form a conspicuous hogback and cuesta topography. Lower Vindhyan succession starts from a horizon of rippled, thinly laminated, medium to fine grained glauconitic sandstones followed by a similar layer without glauconite. The sinuously crested asymmetric ripple marks and planner cross laminations show a NW directed palaeocurrent. Along Kalidhar River near Chouki village, these rocks grade in to thin layers of siltstones and glauconitic shales which often shows small scale ripple marks. The entire sandstone unit is locally known as Pandwafall Sandstone and is overlained by a rather thin unit of dolomitic limestone best exposed in nearby Tapariya village. The limestone surface shows less developed elephant skin weathering and is plane and thinly laminated. It rarely shows ripple marks and is locally termed as Ken Limestone. This carbonate unit is followed by a thin but prominent lenses of glauconitic shale which is highly weathered in appearance due to which it has poor exposure. It is mappable but limited in areal extent and is called as Olive Shale. The three distinct stratigraphic units described above form the entire Semri Group which is overlained by monomictic conglomerate of Kaimur Group.