Portonovo Fm
Type Locality and Naming
SUBSURFACE: The type section is located at exploratory well PYH-B (depth interval: 3165-2260 m), in the Portonovo SUBSURFACE area of the Ariyalur-Pondicherry subbasin. The hypostratotype is in the well PH-C-A (depth interval: 2255-1970 m). It was named after the PortoNovo 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. Dominantly argillaceous shale with minor siltstone. The shale is dark gray, hard, compact, laminated, micaceous, parting easily along the planes showing occasionally inclusions of crystalline carbonate material, fossiliferous. Siltstone is dark gray and soft, at some places lime mud is seen and is laminated. Its thickness varies from 285-905 m. Part of Ariyalur 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 Nannilam Fm.
Upper contact
Unconformable with the Kamalapuram Fm / Karaikal Fm.
Regional extent
The formation has wide distribution with main depocenters in the northern part of Ariyalur-Pondicherry subbasin, west of Karaikal ridge and Palk Bay subbasin.
GeoJSON
Fossils
Diagnostic foraminifera: Globotruncanita stuartiformis, Abathomphalus mayaroensis, Racemiguembelina fructicosa, Rugglobigerina rugosa, Globotruncana arca.
Age
Depositional setting
Outer neritic-Upper bathyal.
Additional Information
It is equivalent (biostratigraphic) to the exposed Sillakkudi Fm (partly), Kallankurichchi Fm, Ottakovil Fm and Kallamedu Fm in the outcrops.