Mirroring weak trend in the global markets, the Sensex opened with a significant negative gap of 330 points at 16,212. Unabted selling, thereafter, saw the index slip below the 16,000-mark to a low of 15,690 - down 852 points from the previous close.Selective buying helped the index cut some losses towards the close. The Sensex finally ended (provisional) with a huge loss of 628 points at 15,913.The NSE Nifty dropped 163 points to end (provisional) at 4,758.