mumbai, Aug. 20 -- The Securities and Exchange Board of India (SEBI) has barred Copthall Mauritius Investment Ltd and Mansi Share and Stock Broking Pvt. Ltd from accessing the securities market and ordered them to deposit a combined Rs.3.68 crore over alleged manipulative trading during a Sensex closing auction session (CAS). This is the first time SEBI has launched formal proceedings against any entity trading in the auction session. In an ex-parte interim order issued on Wednesday, the market regulator said that the two entities had manipulated the CAS on August 13, which was a weekly Sensex expiry day for derivatives contracts on the bourse. Copthall has allegedly made an illegal gain of Rs.2.96 crore while Mansi Share made unlawful profits of Rs.71.65 lakh. Per the order, on the weekly Sensex expiry day of August 13, SEBI spotted three sharp spikes in the indicative equilibrium price. Sensex rose 362 points in two seconds, 132.67 points in 12 seconds and another 405.08 points in 28 seconds. The order logs showed that Copthall was behind most of the aggressive buying. During the first spike, it accounted for 99.91% of the Rs.66.64 crore buy-order value, placing orders across all Sensex constituents at prices around 3% above their reference prices. It repeated the strategy during the later spikes, accounting for 96.09% and 85.21% of buy-order value, respectively. It subsequently cancelled Rs.98.12 crore of buy orders across 30 stocks. Mansi took the opposite approach. It placed 12.65 lakh shares worth Rs.143.44 crore in sell orders across eight Sensex stocks at prices below reference levels, then cancelled the entire block within four seconds. SEBI said the orders appeared intended to suppress the index, with their cancellation triggering a 232.96-point surge in the IEP....