Shiyali Fm
Type Locality and Naming
SUBSURFACE: The type section is located at exploratory well Madanam-A(depth interval: 998-546 m), in the Nagapattinam subbasin. The hypostratotype is in the well Karaikal-E (depth interval: 857-521 m). It was named after the Shiyali village by ONGC team steered 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
Claystone. It is predominantly consists of claystone. Its thickness varies from 452-840+ 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 Niravi Fm.
Upper contact
Conformable with the Vanjiyur Fm.
Regional extent
Present in Kumbakonam-Madanam ridge, Tranquebar sub-basin and Kaaikal-Mannargudi ridge.
GeoJSON
Fossils
Diagnostic foraminifera: M. (Miogypsinoides) complanata, M. formosensis, Globigerina angulisuturalis and Turborotalia opima.
Age
Depositional setting
Inner neritic.
Additional Information
This unit was first reported as Shiyali Claystone by R. P Rao et l. (1972) in ‘Progress report on studies in the Cauvery and Godavari basins (Field season 1971-72), unpublished ONGC report’, and later Venkatarengan et al. (1993) have adopted as-is.