Sillakkudi Formation
| Sillakkudi Formation | |
|---|---|
| Stratigraphic range: Campanian ~ | |
| Type | Geological formation |
| Unit of | Ariyalur Group |
| Underlies | Kallankurichchi formation |
| Overlies | Anaipadi Formation |
| Location | |
| Country |  India |
The Sillakkudi Formation is a sandstone-dominated succession bounded by unconformities, located in the state of Tamil Nadu, India.[1][2]
Description
[edit]The Sillakudi Formation is a sandstone-dominated succession bounded by unconformities. It represents the oldest unit of the Ariyalur Group deposited during the Early Campanian under passive margin depositional conditions. The Sillakudi Formation is subdivided into four facies associations, each represented by a distinct ichnology and environment of deposition.
Unit 1 comprises conglomerates grading upwards into pebbly sandstones almost devoid of trace fossils except a few Planolites isp. indicating a high-energy foreshore-to-shoreface environment.
Unit 2 consists of glauconitic sandstones with Ophiomorpha nodosa, O. annulata, Thalassinoides isp. and Skolithos linearis, belonging to the Skolithos ichnofacies indicating deposition in shoreface to offshore transition environments.
Unit 3 comprises pebbly to very coarse-grained massive sandstones, characterised by an almost monospecific Skolithos ichnofacies indicating rapid colonisation of beds in a delta-front associated debris flows and calcareous sandstones alternating with claystones containing a diverse Cruziana ichnofacies with an ichnoassemblage comprising of Trichichnus isp., Scolicia prisca var. laminites, S. ?prisca, S. vertebralis, Palaeophycus tubularis, Planolites beverleyensis, P. montanus, Taenidium isp., Thalassinoides suevicus, Ophiomorpha isp., Chondrites isp. and Phycodes isp., pointing towards deposition in calmer, possibly dysoxic outer shelf prodeltaic environments.
Unit 4 has pebbly to gritty cross-bedded sandstones exhibiting the development of networks of Thalassinoides isp. and Ophiomorpha isp., indicating shallow sub-tidal to intertidal conditions of deposition. The overall succession is interpreted to show initial deepening followed by shallowing.[3]
Fossil content
[edit]| Genus | Species | Material | Location | Notes | Images |
|---|---|---|---|---|---|
| Inoceramus | I. Sp[2] | A pteriomorphian bivalve | |||
| Bivalva | Bivalva indet.[2] |
| Genus | Species | Material | Location | Notes | Images |
|---|---|---|---|---|---|
| Karapadites | K. karapadense[2] | A Kossmaticerid Ammonite |
References
[edit]- ^ Paranjape, Amruta R.; Kulkarni, Kantimati G.; Kale, Anand S. (2023). "Facies and trace fossils of the Upper Cretaceous Sillakudi Formation (Cauvery Basin, S. India) and their palaeoenvironmental significance". Journal of the Palaeontological Society of India. 68 (2): 262–272. doi:10.1177/05529360231205315. ISSN 0552-9360.
- ^ a b c d "Sillakkudi Formation". indplex.geolex.org. Retrieved 2024-12-12.
- ^ Paranjape, Amruta R.; Kulkarni, Kantimati G.; Kale, Anand S. (2023). "Facies and trace fossils of the Upper Cretaceous Sillakudi Formation (Cauvery Basin, S. India) and their palaeoenvironmental significance". Journal of the Palaeontological Society of India. 68 (2): 262–272. doi:10.1177/05529360231205315. ISSN 0552-9360.