Andimadam Fm
Type Locality and Naming
SUBSURFACE: The type section is located at exploratory well Andimadam-A, in the Ariyalur-Pondicherry subbasin (depth: 4500 (+)-3590 m). Hypostratotype is the well Sattappadi-A (depth interval 4700-3860 m). It was named after Andimadam village by ONGC team steered by Venkatarengan et al., (1993) and was issued as Document-VII by KDMIPE, ONGC, Dehradun (1993).
[Figure 1: Type-section Map of Subsurface Formations]
Lithology and Thickness
Sandstone and shale. The Andimadam Formation consists of predominantly sandstone and minor shale alternations. Abundant pebbles and granules floating at some intervals, angular to subrounded fine to coarse sands are feebly calcareous. Shales are hard, silty with abundant mica. The type section has a thickness of 900 m+.
[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
Undefined or unconformable on Archean Basement.
Upper contact
Conformable with Sattappadi Fm.
Regional extent
Entire basin: This formation is present in the entire basin. Its equivalent is Terani Fm in the outcrops.
GeoJSON
Fossils
Age
Depositional setting
Predominantly neritic in the subsurface and continental in the outcrops.
Additional Information
The serrated log response against this litho unit is the diagnostic feature for recognizing this formation. The Andimadam Formation consists of effective petroleum source rocks and comprises clastic reservoirs hosting hydrocarbons.
This unit developed during Late synrift phase. (Valanginian-Aptian) is developed in a transitional marine transgression, while Albian strata developed in open marine transgressive phase.