The Kota Formation is a geological formation in India. The age of the Kota Formation is uncertain; it is commonly considered to date to the Early Jurassic, but some studies have suggested it may extend into the Middle Jurassic or even later. It conformably overlies the Lower Jurassic Upper Dharmaram Formation and is unconformably overlain by the Lower Cretaceous Gangapur Formation. It is split into a Lower Member and Upper Member. The Lower Member is approximately 100 m thick while the Upper Member is 490 m thick. Both subunits primarily consist of mudstone and sandstone, but near the base of the upper unit there is a 20-30 metre thick succession of limestone deposited in a freshwater setting.
Stratigraphy The lower boundary of the Kota Formation is made of pebbly sandstone, covering the topmost clay seen in the Dharmaram Formation. The Kota Formation has been traditionally divided into 2 main members, the Lower and Upper members, yet more recent work have redivided it into 3. The Lower member can be seen at locations such as Adamilli, Kamavarapukota and Sudikonda, being made of sandstones, with clay clasts, with greater or lower stratification. The Middle Member is well developed along the Continental Gondwana basin, specially towards the northwestern part, and is made of medium to fine white sandstone with clay and concretionary limestone, suggesting the development of paleosols associated with alluvial floodplains. The last member is mostly made of broad sandstone sheets with large clay casts associated with fluvial channels, and has an extension that can be easuly seen on several continuous kilometers. The Uppermost section of the unit is mostly made of limestones and is overlain on an angular unconformity by the Gangapur Formation.
Age The age of the Kota Formation is controversial. There are no magmatic rocks or volcanic ash beds associated with the Kota Formation, which means that its age cannot be determined directly through radiometric dating. The maximum age of the Kota Formation is constrained by the underlying Upper Dharmaram Formation, which is Early Jurassic, probably Hettangian or Sinemurian, in age. Various researchers have attempted to date the Kota Formation using biostratigraphy. Krishnan (1968), Jain (1973), and Yadagiri and Prasad (1977) favored an Early Jurassic age based on the fish fauna. Govindan (1975) suggested a Middle Jurassic age based on ostracods. In 2006, Bandyopadhyay and Sengupta argued that the fish fauna suggested a Toarcian age for the Upper Kota Formation, possibly extending into the Aalenian, and in turn estimated the Lower Kota to be Sinemurian to Pliensbachian in age. Guntupalli V. R. Prasad, along with various coauthors, has argued for a younger age. In 2001, Vijaya and Prasad proposed based on palynological evidence that the Kota Formation was deposited between the Callovian age of the Middle Jurassic and the Barremian age of the Early Cretaceous. In 2002, Prasad and Manhas argued that the mammal genus Dyskritodon, known only from the Kota Formation and the Early Cretaceous of Morocco, provides evidence for a young age for the Kota Formation. In 2020, Prasad and Parmar argued that the similarity of the dinosaur fauna of the Kota Formation to that of the Middle Jurassic of the United Kingdom supported a Middle Jurassic age for the Kota Formation.
Paleoenvironment
The Kota Formation represents mostly a Continental succession related to a continental rift basin, the Pranhita-Godavari Gondwana Basin of peninsular India. The associated facies of sandstone and limestones are likely related to playa-type lake, with nearby fluvial currents, part of low gradient hanging wall alluvial fans, being deposited on it´s margin. There have been records of freshwater lue green algal stromatolites and oncolites, suggested to be deposited on low energy and low bathymetry lacustrine settings. More recent works have proven the basin hosted in the Early Jurassic a freshwater carbonate wetland marked by the presence of limestones. The environmental model proposed include a depositional cycle marked by several facies types, A for the sublittoral zones of shallow water bodies, followed by palustrine environments, including surfaces with abundance of influence of both plants and animals, specially rhizobrecciation indicating active colonization of the margins by plants, having a similar deposition to the modern Las Tablas de Daimiel wetlands. Associated with the lacustrine facies have recovered microbial bioherms and lacustrine spring mounds, shallow ephemeral ponds with carbonated mud and Phyllopods, pedogenic calcrete under arid seasons and short-lived distributary channels. The depositional setting may have been partially sheltered from the input of siliciclastic materials, except on flooding seasons. Microbial biomats likely developed on shallow waters, while rhizoliths increased it´s presence of abandoned channel fills and pedogenic facies indicate drought seasons.
The carbonate layers with iron-rich grains and mudstones suggest a transition zone between a lake margin and wetland in a rift valley, in a marsh that experienced periodic influxes of iron-rich and barium-rich waters through faults. These waters briefly increased acidity but were neutralized by mixing with alkaline surface water, allowing carbonate formation. Iron-oxidizing microbes likely helped deposit iron oxides, cementing the sediment. During high water flow, these deposits were eroded and transported to deeper waters, forming iron-rich coatings. Thin sandy layers suggest that freshwater influxes occurred, forming carbonate bodies near water discharge points. As the water returned to being more alkaline, carbonates could form again, supporting freshwater Bivalvia, similar to modern geothermal areas of New Zealand.
Fossil content
Ostracoda + Ostracods Genus Species Location Stratigraphic position Material Notes ImagesClinocyprisC. sp.DaroghapalliUpper MemberSix carapacesA freshwater ostracodan of the Family Pontocyprididae.CypredeaC. sp.DaroghapalliUpper MemberFourteen incomplete carapacesA freshwater ostracodan of the Family Palaeocytheridae.DarwinulaD. cf.sarytirmenensisAklapalli Daroghapalli Kanchelli Metpalli PotepalliLower Member Upper MemberMore than 200 carapaces and valvesA freshwater ostracodan of the Family Darwinulidae. The most dominant genus locally and the main indicator of both fluvial and lacustrine settingsD. kingiAklapalli Daroghapalli Kanchelli Metpalli PotepalliLower Member Upper MemberAround 120 carapaces and valvesA freshwater ostracodan of the Family Darwinulidae. D. spp.DaroghapalliLower Member Upper MemberNineteen CarapacesA freshwater ostracodan of the Family Darwinulidae. EucandonaE. sp.DaroghapalliUpper MemberEight incomplete carapacesA freshwater ostracodan of the Family Candoninae.LimnocythereL. spp.DaroghapalliLower MemberThree complete carapacesA freshwater ostracodan of the family Limnocytheridae.Stenocypris?S. sp.DaroghapalliUpper MemberSingle incomplete carapaceA freshwater ostracodan of the family Cyprididae.TimiriaseviaT. digitalisDaroghapalliLower MemberTwenty complete carapaces and thirty-six partly broken carapaces.A freshwater ostracodan of the family Limnocytheridae.
Phyllopoda + Phyllopods Genus Species Location Stratigraphic position Material Notes ImagesEstheriinaE. alibadadensisBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Estheriininae. The most abundant Estheriid in the region and the key element of the Estheriina biozoneE. indijurassicaBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Estheriininae. E. bullataBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Estheriininae. E. pranhitaensisBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Estheriininae. LioestheriaL. kotaensisBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Lioestheriidae. The second key element of the Estheriina biozoneL. crustabundisBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Lioestheriidae.L. ssp.Kota limestone ridgeLower MemberValvesA freshwater clam shrimp of the family Lioestheriidae.PaleolimnadiaP. spp.Kota limestone ridgeLower Member Upper MemberValvesA freshwater clam shrimp of the family Estheriininae. PseudeasmussiataP. andhrapradeshiaKadamba VillageLower Member Upper MemberValvesA freshwater clam shrimp of the family Lioestheriidae.
Insecta +Insects Genus Species Location Stratigraphic position Material Notes ImagesArchimesoblattaA. shivaTasch outcrop K-2 bed 8Upper MemberRight forewing tegmenA mesoblattinid cockroachBlattodea indet.IndeterminateTasch outcrop K-l, K-2, K-4 and K-5 Upper MemberIsolated wingsIndeterminate Blattodean remainsColeoptera indet.IndeterminateTasch outcrop K-l, K-2 and K-5Upper MemberIsolated wingsIndeterminate Beetle remains ColeopteronC. sp. Kota limestone ridge Lower MemberIsolated wingsAn Indeterminate Coleopteran.Ephemeroptera indet.IndeterminateTasch outcrop K-l, K-2 and K-5Upper MemberIsolated wingsIndeterminate Mayfly remainsHemiptera indet.IndeterminateTasch outcrop K-l & K-2Upper MemberIsolated wingsIndeterminate Hemipteran remainsHeteroptera indet.IndeterminateTasch outcrop K-l & K-2Upper MemberIsolated wingsIndeterminate Heteropteran remainsNeuroptera indet.IndeterminateTasch outcrop K-l, K-2 and K-5Upper MemberIsolated wingsIndeterminate Neuropteran remains KotaphialtitesK. frankmortoni Sirpur Taluka, Tasch's K1 outcrop bed 2(A) Upper MemberMCZ 11909, Isolated wingAn ephialtitid hymenopteran.Protogryllus P. lakshmi Kota Formation outcrop K-2 Upper MemberMCZ 3046, Isolated wingA protogryllid cricket TaschigatraT. bharataja Sirpur Taluka, Tasch's K1 outcrop bed 3(A) Upper Member No.2013(3013), part and counterpart of well preserved wingA rhagionid dipteran.T. tulyabhijanaSirpur Taluka, Tasch's K1 outcrop bed 2(A) Upper MemberNo. 5034, well preserved wingA rhagionid dipteran. XyelulaX. alexandri Kota Formation outcrop K-2 Upper MemberMCZ 11831, well preserved wingA sepulcid hymenopteran.
Fish +Fish Taxon Species Location Stratigraphic position Material Notes ImagesIndocoelacanthus I. robustusBoraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberISI P. 39. Impression of the caudal fin ISI P. 40. Nearly complete head and trunk squamation ISI P. 41-45. Fragments of fin-rays ISI P. 46. Neural arches, isolated scales and girdle elementsA robust freshwater coelacanth of the family Latimeriidae. Represents the largest member of the local freshwater fauna, measuring up to 70 cm.IonoscopusI. spp.Boraigudem limestone ridge Kota limestone ridge Lingal-Metpalli ridgeLower Member Upper MemberTeethA freshwater neopterygian of the group Amiiformes.LepidotesL. deccanensisKota limestone ridge Paikasigudem villageLower Member Upper MemberComplete Specimen Isolated RemainsA freshwater neopterygian of the family Lepisosteiformes.L. spp.Kota limestone ridge Paikasigudem villageLower Member Upper MemberIsolated remainsA freshwater neopterygian of the family Lepisosteiformes.LonchidionL. indicusPaikasigudem village Yamanpalli bonebedUpper MemberGSI.TI.2, tooth Isolated TeethA freshwater elasmobranch of the family Lonchidiidae.ParadapediumP. egertoniBoraigudem limestone ridge Kota limestone ridge Near AnkishaLower Member Upper MemberBMNHP12146, Partial specimen BMNHP12147, Almost complete specimen BMNHP12148, Partial specimen ISIP.32 Nearly complete specimen ISIP.33 Nearly complete specimen ISIP.34 Nearly complete specimen