Madanam Fm
Type Locality and Naming
SUBSURFACE: The type section is located at exploratory well Madanam-A (depth interval: 546-255 m), on the Madanam horst. The hypostratotype is in the well Chidambaram-A (depth interval: 880-306 m). It was named after the Chidambaram town by ONGC team guided by Venkatarengan et al.(1993) and issued as Document-VII by KDMIPE, ONGC, Dehradun (1993).
[Figure 1: Type-section Map of Subsurface Formations]
Lithology and Thickness
Limestone. Mainly limestone with alternations of thin silt and silty clay. Limestone is earthy gray, pale cream, slightly argillaceous, vuggy, moderately hard and compact and richly fossiliferous. It is a sand and clayey biomicrite with pyrite encrustations within silt. Its thickness varies from 291-574 m. Part of Narimanam Gr.
[Figure 2: Generalized Stratigraphy and Petroleum System of Cauvery Basin (from dghindia.gov.in)]
[Figure 3: Generalized Stratigraphy of Cauvery Basin (Provided by A. Nallapa Reddy & R. Nagendra)]
Relationships and Distribution
Lower contact
Unconformable with the Tirutturaipundi Fm / Vanjiyur Fm.
Upper contact
Conformable with the Tittacheri Fm.
Regional extent
Present in parts of south Arcot Basin, Kumbakonam-Shiyali Ridge, Karikal Ridge, Nagapattinam sub-basin, Tirupndi high and Tirutturaipundi areas.
GeoJSON
Fossils
Mollusks, Pelecypods, corals and foraminifera- Miogypsina cushmani antillea and Globigerinoides primordius.
Age
Depositional setting
Inner neritic.
Additional Information
This unit was first reported by R. P. Rao et al. (1971) (Progress report on studies in Cauvery Basin (Field season 1)70-71, unpublished ONGC report), and later adopted by Venkatarengan et al. (1993).