Ooids in Sillakkudi Formation of Ariyalur Group of Tiruchirapalli Cretaceous, Tamil Nadu: Implications for Origin and Depositional Environment

An ooid-rich limestone band of Sillakkudi Formation is encountered in a well section near Ariyalur. The ooids are believed to be deposited in a marine regime. They contain berthierine as the major mineral and haematite, siderite and quartz as minor minerals. They exhibit alternate rings of berthierine and haematite which shows that these minerals were developed under changing physico-chemical conditions. In the present paper, the petrographical characters, mineralogy, origin and depositional environment of the ooids are discussed.