Acknowledgement
SB and KD acknowledge the Department of Science & Technology, Government of India for funding a research project (ESS/16/251/2005). SK acknowledges the CAS of the Department of Geological Sciences, Jadavpur University and SDG is thankful for the support obtained through J.C. Bose Fellowship from the Department of Science & Technology, Government of India. We thank Prof. Talat Ahmad for inviting us to write this review.