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Observations on the Post-Triassic Gondwana Sequence of India

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Observations on the Post-Triassic Gondwana Sequence of India OBSERVATIONS ON THE POST-TRIASSIC GONDWANA SEQUENCE OF INDIA S. C. SHAH, GOPAL SINGH & M. N. GURURAJA Geological Survey of India ABSTRACT istic lithology, vertebrate remains and The post-Triassic Gondwana sequence of India rarity of plant fossils. The overlying Juras• is one of the well developed in the Gondwanaland. sic-Cretaceous sequence of rocks have a Its flora has been helpfuLin establishing the strati• rich and distinct floral assemblage commonly graphy of thick continentaL deposits of this period. designated as the Ptilophyllnm flora and The sedimentary sequences containing this flora their stratigraphy is mainly based on floral are developed in widely scattered Gondwana basins evidences. of the Peninsula namely, the RajmahaL hills, Bihar; Satpura and South Rewa Gondwana basins, Madhya Recent studies have indicated that the Pradesh; Pranhita-Godavari basin of Andhra sequence proposed earlier for these J urassic• Pradesh and Maharshtra; East Coast and Gujarat. Cretaceous deposits in India is rather con• In the light of the recent studies the stratigraphic position of the floral assemblages has been reviewed fusing and as such the dating done on floral in the paper. evidences has been a matter of great dispute. The flora is known to continue without any Palaeo botanists like Oldham & Morris, Feist• break throughout the Jurassic and the Lower mantel, Sahni, Jacob, Bose and others Cretaceous. The lower age limit of the floral sequence commences in Lower Jurassic and as such assigned a Jurassic age to these deposits, the views expressed by Spath (1933) and Arkell whereas Spath, Arkell and many others on (1956) suggesting the absence of entire Jurassic the basis of faunal evidences suggested a continental deposits of India is no more tenable. The flora associated with Lower Cretaceous Lower Cretaceous age to them. marine fauna on the East Coast indicates the range Here, the post-Triassic sequences are of the Jurassic floral elements into the Lower being dealt as developed in different basins Cretaceous rather than suggesting any palaeonto• and the problem of age of this sequence is logical contradiction between the faunal and floral being discussed in the light of geological evidences as thought earlier. history and recent palaeontological evidences. INTRODUCTION Pranhita-Godavari Basin The post-Triassic Gondwana sequenc2 111 of Indiapost-TriassicembodyingGondwanaa rich sequenceflora is this basin is as follow..>: THEone of the best of its kind developed in the Southern Continent. In Australia, King Kutty this sequence is represented by a great (1881) (1969) development of continental deposits of Jurassic-Cretaceous age, while in Africa Post Chikiala Gangapur formation! Triassic Kota ? Chikiala and South America, this was a period of Gondwanas Kota formation enormous volcanic activity, resulting in Dharmaram forma• limited deposition of continental deposits. tion In India, the post-Triassic Gondwana Up. Triassic Maleri Maleri formation sequence is developed in widely scattered basins: in Rajmahal hills, Bihar; South King (1881) made collection of fossils Rewa - Satpura basins, Madhya Pradesh; including plants from Kotas only and Pranhita - Godavari basin, Andhra Pradesh Chikialas were devoid of fossils. The plant and Maharashtra; Jaisalmer, Rajasthan; fossils were studied by Feistmantel (1877): Cutch, Kathiawar and Himmatnagar, Guja• rat; and along the East Coast in Orissa, Localities Fossils Andhra Pradesh and Tamil Nadu. In these basins, the Triassics, wherever they are Annaram Elatoclad~~s (Palissya) , seen, are distinguished by their character- Chirolepis 221 221 THE PALAEOBOTANist Localities Fossils CHART 1 - DISTRIBUTION OF POST TRIASSIC GONDWANA FLORA FROM Naogaon T acnioj>teris (A ngiojJt;ri- PRANHITA-GODAVARI BASIN dimn) , Ptilophyllttm awtifolimn NAME OF SPECIES KOTA FM. GANGAPUR Chirakunt Cycadites sp., (=? Elatocladrts (Palissya) CHIKIALA jabalpttrensis FM.) Between the Pagiophyllwn percgrilZ{t'}'It, Equisetites sp. X X villages Maor A raftcarit:;s ettichcnsis Gleichenites gleichenoides X G. rewahens is and Balhanpur X G. sp. X Coniopteris hymeno- x Later on, Rao & Shah (1959a), listed phylloides additional plant fossils from Kota-Maleri Coniopteris sp. X formation and Bose (1966) observed that Cladophlebis indica X X there is an admixture of flora in the assem• Sphenopteris sp. X Hausmannia sp. X X blage given. To remove this confusion Ptilophyllum acutifolium X (Rao & Dutt, 1955-56 and Rao & Shah, Otozamites sp. X X 1957-60, the unpublished reports in the Dictyozamites sp. X Taeniopteris spathulata X Geological Survey of India) the collection is ? Nilssonia sp. X being studied and the results of the preli• ? Cycadites sp. X minary study are summarized here. Elatocladus plana X The plant fossils as mentioned from E. conferta X E. rjabalpurensis X X Kota-Male! i formation belong to Kota E. ? tenerrima X , stage' of King. The list of fossils is given Elatocladus sp. X X in Chart 1. Brachyphyllum sp. X It is observed that there are clearly three Pagiophyllum peregrinum X X Pagiophyllum sp. X and not two zones, as inferred earlier by Torreyites d. constrictus x X Rao and Shah (1959a), namely: A raucarites cutchensis x X Zone C - Fossils from Gangapur Sandstone Araucarites sp. X and Chikiala Sandstone Pagiophyllum peregrinum X Pagiophyllum sp. X Zone B - Fossils from Kota formation (as Podozamites sp. X defined by Kutty, 1969) Zone A - Fossils from Acheli and Ganaram Zone A is characterized by few species of Glossopteris, Thinnfeldia hughesi, Dicroidimn Zone B has plant fossils which are repre• lwghesi, Dicroiditlm odontopteroides, Noegge• sented by about a dozen genera. They are rathiopsis cj. httghesi etc. This assemblage mostly found in limestone. The fossil is from the lower part of the Kota formation forms are fragmentary and the assemblage which is underlain by Maleri formation of consists of: Equisetiies sp. Sphenopteris sp., Carnic-Noric age. Similar floral assemblage Hausmannia sp., Coniopteris hymenophyl• has also been known from the Parsora for• loides, Coniopteris sp., Otozamites sp., Pagio• mation which is overlying the Tiki forma• phyllum cf. peregrium, Pagiophyllum sp., tion (Shah et al 1970; Dutt, P. K. pers. Araucarites cftichensis, Elatocladus sp. comm). This assemblage can easily be The beds containing this flora overlie the assigned as a part of Dicroidium flora which lower Kotas yielding the Rhaetic flora. is prevalent in the Triassic period. Since Associated with this flora arefishes, sauro• the beds yielding the flora similar to that pod dinosaur and ccocodilian remains which from Parsora formation is overlying the are considered as Lower Jurassic (? early formation of Carnic-Noric age, it can be middle Jurassic). Hence this flora is of assigned to Rhaetic age. upper Liassic age or in other words the The lower Kotas have elsewhere been genera represented in this flora were thriv• differentiated as Dharmaram formation ing during this period. (Kutty 1969) and this has not yielded any Zone C has the assemblages of plant plant fossils. But it has been assigned fossils which belongs to the Gangapur for• Rhaetic on the basis of vertebrate mation, Chikiala sandstone and some loca• fossils. lities of Kota ' stage' of King. Gangapur SHAH el at.-OBSERVATIONS ON THE POST-TRIASS1C GONDWANA SEQUENCE 22~ 1G POST- TRIASSIC GONDWANAS IN INDIA Scole km 320 160 0 l\20km I , 28 Rajasthan Upper Narmada Volley ROJrnllhol ReqlOn 20 I Satpuro/1Sansa- Pars oro \ ,<11),---L",' - - -- --;) -- _ .. ..' , -~ / '<'b; ,.•. ~ ..• ",,, --r Lower Narmada Valle)' Cutch Wardha '" Cutlack Godavan Volley Baroda EfloreO"gOI'~ ~\\ West Coast ~EQstCoost ~:~,:,::7Rornnod formation was considered by King (1881) developed in the western part of the basin as the basal member of the Kota 'stage' and is provisionally considered as equivalent (of King) but Kutty (1969) separated them to Chikiala Sandstone which is developed from the Kota 'stage' and considercd in eastern part of the basin. Kutty had not them a~ overlying the Kota formation with recorded any fossils but observed that the an unconformity. Gangapur formation is flora of Anaram belonged only to Kota 224 tHE pALAE0I30TAN1st formation and flora from other localities as Laterite (Level above given by King belonged to Gangapur for• sea-level mation. i1tfeet) Further, Chikiala Sandstone was con· sidered to be unfossiliferous till Rao & Shah VI Trap 625 (1959b) recorded some fossils. The fossils Sandstone 600 from some localities given by Rao and Dutt V Trap 530 (1955-56, unpublished report) seemed to Ferruginous, friable belong to Gangapur formation. The assem• sandstone 500 blage, if taken as one unit, is characterized VI Trap 425 by the predominance of conifers. This is Chert beds 420 younger than Lower Jurassic and its exact III Trap 320 age or the upper limit on the basis of consi• Oolitic iron-ore 310 derations other than plants can not be II Trap 250 inferred. This floral assemblage clearly Plastic, white, resembles the flora from Nipania of Ra]• iron-stained 210 mahal' region and also to the flora frGm I Trap 210 Raghavapuram Mudstone, Vemavaram Shales cnd Sriperumbudur beds from cast The number of flows exceeds 15 in number coast and EI1U] fOlmation of west coast. and the total thickness of flows is around 1500 feet or so. The individual flow may vary in thickness from 50 to 300 feet. The Rajmahal Region older flows are represented in the eastern half of the Rajmahal hills while in the The general sequence of the pest-Triassic western half higher flows are recorded
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