Jurassic Of Kutch

Introduction The Mesozoic rocks ranging in age from Middle Jurassic to Lower Cretaceous are particularly well developed in Kutch, where they exhibit a complete succession and a total thickness of 600ft. These rocks are regarded as the oldest and the most important stratigraphical formation in Kutch. These sedimentary rocks represent a phase of marine transgression along the western part of India during the Jurassic Period. The individual rock beds appear to have been deposited under a relatively shallow stretch of marine water and exhibit a gentle slope towards the sea. The enormous thickness of the sedimentary column is probably due to the gradual sinking of the basin along with the deposition of marine sediments. In Kutch region, the Jurassic rocks are exposed in three anticlinal chains of ridges trending in east-west direction. The northern chain comprises the islands of Patcham, Karrir, Bela and Chorar. The middle chain consists of the most prominent ridge extending for about 193km from Habo in the east to Lakhpat in the west. The southern most chain forms a 64km long Katrol – Charwar range in the south of Bhuj. Lithology Characteristically the Mesozoic succession of Kutch region has been intruded by various sills and dykes which are genetically related with the overlying Deccan Traps. The basal conglomerate of the Patcham Formation contains pebbles of crystalline rocks, suggesting a Precambrian basement for the Mesozoic succession of the region. Classification The Jurassic sequence of Kutch is divided into four main divisions, as follows – UMIA FORMATION

-

3000ft

KATROL FORMATION

-

1000ft

CHARI FORMATION

-

1200ft

PATCHAM FORMATION

-

1000ft

(Including Kaurbet beds)

Stratigraphic Succession (after Shastry and Mamgain, 1971)

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Formation (age)

Subdivisions

Leading fossils

Deccan Traps ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~ Umia

Post - Aptian

Bhuj beds

Palmoxylon, Ptillophylum

(Umia plane beds) Sandstones and Shales Aptian

Ukra beds

Australiceras, Tropaeum

Marine Calcareous Shales

Katrol

Upper Neocomian

Umia beds – barren sandstones and shales

Unfossiliferous

Valanginian

Trigonia beds – barren sandstones

Trigonia

Upper Tithonian

Umia ammonite beds

Virgatosphinctes, Umiaites

Middle Tithonian

Upper Katrol Shales

Hildoglochiceras, Heploceras

Gajansar beds

Belemnopsis, Streblites

Lower Tithonian `

Upper Katrol Sandstone (barren sandstone)

Mainly unfossiliferous

Middle Kimmeridgian

Middle Katrol Sandstone (red sandstones)

Torquatisphinctes, Katroliceras

Lower Katrol Shale (s.s.t, shales, marls)

Aspidoceras, Torquatisphinctes

Kantkote (Bimammatum zone)

Epimayaites, Prososphinctes

Upper Oxfordian Chari

Upper to Oxfordian

Dhosa Oolite (green and brown oolites)(Transversarium zone)

Mayaites, Dhosaites

Upper Callovian

Athleta beds (marls and gypseous shales)

Metapeltoceras, Peltoceras

Middle Callovian

Anceps beds (limestones and shales)

Kinkeliniceras, Hubertoceras

Rehmanni limestone)

Reineckeia rehmanni, tyranniformis, Shivajiceras

Lower Callovian

Lower

Sandstone

beds

(yellow

Macrocephalus beds (shales with calcareous bands, with golden oolite – Diadematus zone in the

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Macrocephalites, Dalicocephalites

R.

Bellemnites,

upper part) Patcham

Lower Callovian Lower Callovian Bathonian

to

Coral bed

Macrocephalites, Procerites

Shelly Limestone

Macrocephalites, Trigonia

Kuarbet beds

Corbula, Eomiodon, Trigonia

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Unconformity~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Precambrian basement (not exposed) Lithological Description Patcham Formation The formation is named after the type section, the Patcham Island of the Rann. The rocks are best exposed in the Patcham, Khan and Bela Islands of the Great Rann of Kutch. The formation represents a narratic facies of transgressive sea comprising a 300m thick succession of dark pisolitic limestones, yellow sandstones and olive green shales overlying by nodular fossiliferous cherly limestones and marls. The lowest bed, seen here in Khera, is known as Kuarbet beds. It is made up of principally of limestones and some sandstones and shale and constitutes a total thickness of about 100ft. This formation is as a whole rich in limestone. Chari Formation This formation takes its name from a village 50km NW of Bhuj. It conformably succeeds the Patcham Formation and consists of about 400m thick succession of sandy limestones, marls, calcareous and sandy shales and oolitic limestones. The formation represents five groups. The lowest is the Macrocephalus beds are made up of shales, calcareous bands and oolites. It can be subdivided into several zones by means of the ammonite fauna. The upper part of the middle division of this group contains a few layers of ‘golden oolites’ constituting the Diadematus zone, which is calcareous oolite, the grains of which coated with thin films of ferric oxides giving them a golden colour. Above this occur, dark shales and sandy shales with calcareous and ferruginous nodules. The Rehmanni beds overlying the golden oolites are composed of dark shales and sandy shales with calcareous and ferruginous nodules. The Anceps beds lies above the Rehmanni beds are consists of limestones and shales. This horizon contains Perisphinctes anceps. White limestone marls and gypseous shales occurring above the Anceps beds are known as the Athleta beds. The topmost beds of Chari Formation are the Dhosa oolites, composed of green and brown oolitic limestone. The lithology of the formation of relatively deeper water facies represents a change in the depositional environment from a transgressive facies. Katrol Formation The Katrol Formation succeeds the Chari Formation presumably with an interrupted deposition demonstrated by the presence of pebbly beds in the basal part of the succession (Rajnath 1932). The Katrol Formation is named after the east-west trending Katrol Charwar range in the south of Bhuj, comprising of about 750m thick shallow marine succession of shales, limestones, sandstones and sand grits. The Formation includes the Kankote Sandsotnes, Katrol beds proper and Gajansar beds in the ascending order, and range in age from Upper Argovian to Portlandian. The oldest division is known as Kantkote sandstone. It indicates a horizon below the Katrol beds proper.

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The overlying Katrol group is subdivided into three parts, of which the lowest portion is composed of sandstone, shale and marls. The middle Katrol group is composed of red sandstones. The upper Katrol lies above middle Katrol division, composed of gritty sandstone but contain no fossil because it is tapped by gritty sandstone. The Gajansar beds formed the uppermost horizon of the Katrol Formation. Umia Formation The Umia Formation succeeding the Katrol Formation, with a slight unconformity is composed of mixed rock facies of marine and continental origin. It is 900m thick and consists of sandstones, conglomerates and shales, and considered by Arkell as similar to the Nubian Sandstone of Egypt, which is partly of Lower Cretaceous age. The Lower part of the succession is composed of Umia beds. The bottommost horizon made up principally of shales, called formerly the Jamia Shales, really form part of the Gajansar beds. They are better called as the Upper Katrol Shales. The Umia bed consists mainly of barren sandstone, with fossiliferous intercalations. The ammonite bed lies above Jamia Shales is composed of sandstone and oolites and characterised by presence of remains of numbers of ammonites. Trigonia beds are overlain above Ammonite beds. It comprised of sandstones and conglomerates. Unfossiliferous sandstones, about 1000ft thick, lie above the Trigonia beds and these together constitute the Ukra bed, which comprises about 23m thick succession of greenish sandstone, calcareous shales, grits and marls. Ukra beds are followed upward by a fossiliferous horizon of sandstone and shale. This horizon is known as Umia Plant Beds. The overlying Bhuj beds contain sandstone and shales, and are probably estuarine. They contain Ptillophylum and other plants closely related to Jabalpur Formation, and are presumably of post-Aptian age. The regression which was taking place here seems to be contemporaneous with the transgression of the Trichy Coast. The Jurassic and Lower Cretaceous rocks in Kutch are overlain in some places by Deccan Trap lava flows; with a distinct unconformity. In certain regions, they are overlain unconformably by younger rocks of Tertiary age. The workers in the field of Indian Stratigraphy are of the opinion that the Jurassic rocks of Kutch and the Salt Range were deposited under marine transgression over a vast area. The geosynclinals basin in Himalayan region appears to have witnessed a regression of sea during the same period. Palaeontological Description Patcham Formation: The lowest beds of Patcham Formation, seen near Khera, Kuarbet beds which yield a rich pelecypod fauna (Corbula lyrata, and other species, Eomiodon, Protocardia, Trigonia etc) and corals. The only ammonite found in these beds was a Stephanoceratid. Overlying the Shell and Coral limestone are the Patcham Beds proper. They are characterized by the presence of Macrocephalites triangularis, Sivajiceras congener, etc. Chari Formation: The Chari Formation contains five groups. The lowest is the Macrocephalus beds, which have yielded a rich collection of Callovian ammonites and gastropods. They chiefly yield ammonite - Indocephalites diadematus. The species of Nucula and Astarte are also very common in the Macrocephalus group. The lower portion of this bed is the Rehmanni zone in which Macrocephalites persists and Phylloceras and Lytoceras begin to appear; Idiocycloceras and Subkossmatia are characteristics, as also some Terabratulids and Trigonias. Anceps beds succeeding the Rehmanni zone contain ammonites, brachiopods and lamellibranches. The Athleta beds above them composed of white limestone with a similar fauna. The topmost bed of the Chari Formations are the Dhoja Oolites, very rich in Oxfordian fossil assemblage like Mayaites maya, Epimayaites polyphemus, Perisphinctes indogermanus, Peltoceretoides semirugosus, Paracenoceras kumagunense, Evaspidoceras waageni, and some teribratulites. The Dhosa Oolites contains the late Macrocephalitids such as Mayaites, Epimayaites and Dhosaites. Katrol Formation: This formation includes the Kankote Sandstone, Katrol beds proper and Gajansar beds. The Kankote Sandstone indicate a horizon below the Katrol beds proper and the chief fossil being Epimayaites transience, Prososphinctes virguloides and Torquatisphinctes torquatus of Upper Oxfordian Age. The lower and middle Katrol Beds Proper contains Oppelides and Perisphinctids (Taramelliceras, Glochiceras, Streblites, Aspidoceras; Torquatisphinctes, Pachysphinctes, Katroliceras, Subplanites, etc.) but the upper part tapped by gritty sandstone so it is generally devoid of fossils. The Gajansar beds contain a fauna in which appear species of Glochiceras, Phylloceras, Belemnopsis etc. The Katrol succession has also Mioflora and other plant fossils.

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The microfaunal record however suggests an uninterrupted phase of sedimentation between the Katrol and the Chari Formations. Umia Formation: The bottommost horizon of Umia Formation is Jamia Shales really form part of the Gajansar beds. They contain Haploceras elimatum, Hildoglochiceras spp., Phylloceras, Belemnopsis etc. and are of Portlandian Age. The Umia Group consists mainly of barren sandstones with fossiliferous intercalations. The Ammonite beds are green oolites with abundant ammonites some brachiopods and corals. Large Virgatosphinctes are characteristics but Aulacosphinctes, Ptychophylloceras, Umiaites and Micracanthoceras also occurs; other fossils are Acanthorhynchia, Lobothyris and Trigonia retrorsa. The Trigonia beds are characterized by Trigonia ventricosa and T. crassa. The Umia group is therefore Upper Tithonian and Neocomian. The Ukra beds contain Australiceras, Cheloniceras, Tropaeum. It also contains remains of plants so this is known as Umia Plant Beds. The overlying Bhuj beds yields abundant plant fossils including Philicales, Cycadophyta, Conifers etc. The Saurian remains of Pleisiasaurus indica have also been reported and also contain Ptilophyllum. The plant fossils are closely related to those from the Jabalpur Formation of Post Aptian Age.

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