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On Some Plant Fossils from the Pariwar Formation, Jaisalmer Basin, Rajasthan

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On Some Plant Fossils from the Pariwar Formation, Jaisalmer Basin, Rajasthan ON SOME PLANT FOSSILS FROM THE PARIWAR FORMATION, J AISALMER BASIN, RAJASTHAN HARI K. MAHESHWARI Birbal Sahni Institute of Palaeobotany, Lucknow-226007 & N. P. SINGH Oil and Natural Gas Commission, Jodhpur ABSTRACT The Pari war Formation is named after the Pari war Village (27° 14'30": 70°44'30") The paper reports on plant megafossils found in the lower part of the Pari war (Parihar) Formation and consists of a poorly exposed but exposod in the Jaisalmer Basin, Rajasthan. The stratigraphically thick sequence of sandstone plant fossils belong to the groups Filicales, Cyca• beds. The formation in the north-east dales, Bennettitales and Coniferales. The identi• part around Pariwar Village consists mainly fiable species are: ?Gleichenites sp., Phlebopteris sp., Frond type I, Taeniopteris vitlata, T. densinervis, of pebbly, current-bedded sandstones T. spatulata, Pterophyllum sp., Otozamites imbricatus, but to the south-east it is difficult to Ptilophyllum acutifolium, Elatocladus conferta, establish the stratigraphy dUE to paucity ?Elatocladus sp. and Pagiophyllum sp. In general of the outcrops. The lower fossiliferous composition the fossil assemblage is more akin to that known from the Kutch Basin of Gujarat, member consists mostly of variegated and is probably Upper Jurassic in age. (yellow, yellowish-white, brown and ochreous brown) siltstone, sandstone and shale/clay beds of considerable thickness. Das-Gupta INTRODUCTION (1974) assigned a Lower Cretaceous (Neoco• mian) age to the formation on the basis of subsurface stratigraphical correlation in this area. However, the present study of plant a numbervast Rajasthanof sedimentaryshelf basinsincludesof THEwhich the Jaisalmer Basin is the megafossils collected from the type area largest. In the north-north-west and south suggests an Upper Jurassic affinity of the of Jaisa1mer, is exposed a thick sequence Pari war Formation flora. of marine and continental sedimentaries The fossils are preserved as impressions of post-Triassic age on a truncated, pene• in ochre-yellow, argillaceous shale and in plained basement. The Mesozoic strata buff-coloured siltstone. Some of the comprising Lathi, Jaisalmer, Baisakhi, impressions are partly coloured red, prob• Pari war (formerly Parihar) and Habur ably due to leaching of iron. Preservation (formerly Abur) [ormations have till recently is usually poor but sometimes wetting the not yielded any p1ant fossils though a specimens with xylol or liquid paraffin brings mioflora of probable Lower Jurassic age out certain structures clearly. (Srivastava, 1966) is known from the Lathi Formal ion. DESCRIPTION During the 1972-73 field season, a field party of the Oil and Natural Gas Commission, Genus - Gleichenites Goppert 1836 of which the second author was a member, discovered plant megafossils in the lower Type Species - Gleichenites porsildii part of the Pari war Formation, east of the Seward 1926. Habur Village. The thick arenaceous sequence of Pari war Formation was earlier ? Gleichenites sp. described as the 'Parihar beds' by Oldham PI. 1, fig. 2 (1886) and 'Parihar Formation' by Swami• nathan, Krishnamurthy, Verma and Description - Small fragmentary speci• Chandiok (1956). men, leaf as a whole not known, pinnules 116 MAHESHWARI & SINGH - PLANT FOSSILS FROM PARI WAR FORMAT [ON 117 small, about 2 mm long, margin entire, 1968, p. 22) in having less oblique pinnae. apex: rounded, veins not preserved. Phlebopteris sp. of Roy (1968, p. 110, pI. 1, Remarks - Due to its extremely bad figs. 6-7, pI. 2, fig. 9) is known only from preservation the specimen is doubtfully a fragmentary specimen. Our specimens referred to Gleichenites. are further different from all the other phlebopterids in having a mucronate apex. Genus - Phlebopteris Brongniart 1836 FROND TYPE-1 Type Species - Phlebopteris polypodioides Brongniart 1836. PI. 1, fig. 8; Text-fig. 1975 Cladophlebis sp. (?): Das Gupta et. al., p. 2::36,' fig. 3. Phlebopteris sp. PI. 1, figs. 6-7 Description - This lS another very common type in the present assemblage. Description - This is one of the more Frond bipinnate, main rachis winged, about common plants in this assemblage but 1·75 mm wide, pinna rachis less than 0·5 unfortunately preservation is extremely mm wide at base and gradually tapering poor. All the specimens are incomplete towards apex. Pinnae opposite, arising at and none shows the apical or basal parts an interval of about 9-10 mm and at an of the frond. Specimens pinnate, largest angle of 35°-45°. Most complete pinna specimen measuring 10 cm in length, rachis 5·5 mm long, lanceolate. Typical pinnules stout, up to 1·5 mm broad. Pinnae 5·5 to 6·5 mm long, slightly smaller in the alternate or subopposite, almost at right upper pinnae, apex narrow obtuse, pinnules angles to the rachis, straight or slightly arising at an angle of 30°-35° to the pinna falcate, adjacent pinnae confluent at base. rachis, almost straight, pointing forwards, Pinnae longer in the middle part of the leaf pinnule margin smooth, adjacent pinnules (up to 2·5 cm) and becoming smaller to• confluent at base. First pinnule arises on wards apical and basal parts; typically 2-5 the basiscopic side and sometimes is almost mm broad at the widest. Pinna apex on the rachis (Text-fig. 1). Each pinnule characteristically mucronate. Midrib pro• served with a distinct midrib which con• minent, persisting up to apex. Veins arising tinues up to apex, further secondary veins at an angle of approximately 75°-80° to not seen. the midrib, almost parallel, a few cross Remarks - Due to nonpreservation of connections observed in some specimens secondary veins, assignment of these speci• (PI. 1, fig. 6). mens to a genus is not possible. In habit Remarks - Harris (1961, p. 101, 112) these fronds resemble Pachypteris, Onychi• has remarked that the genera Phlebopteris, opsis, Scleropteris and Cladophlebis. Pachy• Matonidium and Matonia appear to pteris as instituted by Brongniart (1828), intergrade. Matonidium can be distin• is characterized by the absence of veins or guished from Phlebopteris only by its indusi um by the presence of only a single primary formed from the expanded end of the vein in the pinnules. Later st udies have placenta. In sterile condition the distinc• shown that Pachypteris is in its venation, tion between these two genera is difficult as well as in other characters, very much to make. We have provisionally referred like Thinnfeldia. Pachypteris, can further our specimens to Phlebopteris on the basis be ruled out altogether as the fronds of of their general similarity with the figured that genus are thick and coriaceous. specimens of Phlebopteris from India (see Scleropteris is an ill-defined genus, but the Bose &Sah, 1968,pI. 5,fig. 31; Sukh-Dev, 1970, midrib in that genus is usually indistinct or pI. 1, figs. 6, 7, 9) and due to occurrence of lacking. Onychiopsis has a typical venation. occasional anastomoses. Our specimens, Because of the welldefined midrib the however, differ from those of Phlebopteris specimens could belong to Cladophlebis but polypodioides Brongniart (in Sukh-Dev, 1970, the preservation being imperfect a definite p. 201) and Phlebopteris sp. (Bose & Sah, determination is not possible. 118 THE PALAEOBOTANIST TEXT-FIGS. 1-5 MAltESHWARI & SINGH - PLANT FOSSILS FROM PARiWAR FORMATION 119 Genus - Taeniopteris Bron~niart 1832 then gradually tapers to form an acute apex, margin entire except in basal reGion where Type Species - Taeniopteris vittata Brong• it is slightly wavy. Midrib strong, about niart 1832. 3·5 mm wide at base and gradually narrow• Remarks - Nathorst (1909) described the ing towards apex, fine longitudinaUy running cuticle of a specimen which he believed to striations seen. Secondary veins arising be an example of Nilssonia tenuinervis. from midrib almost at right angles, slightly As it had sinuous cell walls he created a new curved forwards almost reaching margins, genus Nilssoniopteris for it. Thomas (1913, simple or occasionally once-forked. p. 241) found, on re-examination, that thi.s Remarks - This species has been reported particular specimen resembled ~ore .Taen:• from Kutch under the name Oleandridium opteris vittata. The genus N~lssomopterzs (Taeniopteris) vittatus (Feistmantel, 1876, was therefore later abandoned (Thomas & p.15, pI. 1, figs. 1-3; pI. 2, figs. 1-5). Bancroft, 1913; Seward, 1917). H(~.rris (1932) and Florin (1933a, 1933b) recogmzed the need for separate genera for taeniop• Taeniopteris densinervis Feistmantel 1876 terid leaves with different types of cuticle. PI. 1, fig. 5; Text-fig. 4 While Harris (1932) created a new genus Taeniozamites for taeniopterid leaves with Description - Simple leaf, oval spathu• bennettitalean cuticle, Florin (1933a, 1933b) late, base and apex not preserved, incom• retained Nilssoniopteris for such leaves. plete specimens 4'6-7·9 cm long and 1·6-3·1 We think that it is prudent to retain cm broad at the widest. Midrib stout, 1·5 Nilssoniopteris for forms with bennet.titalean mm broad at base and gradually tapering cuticle as cuticle of the type specImen of towards apex, finely pitted. Veins arise the type species of the genus Taeniopteris from midrib at angles of 75°-80° and then (i.e. T. vittata) is probably not known. curve sharply forwards meeting the margins Further under prevalent botanical practices, at low angles, mostly simple, rarely once• the species vittata (with same holotype) must forked. At one or two places there is slight not be taken as type for two similar though appearance of an anastomosis but it could unrelated genera, i.e. Taeniopteris and as well be a preservation artefact, concen• Nilssoniopteris. It is suggested that vittata tration of veins 22-24 per cm. should be retained as type species of the Remarks - In general appearance and the genus Taeniopteris and that a new type angle of emergence of the veins, the figured species should be designated for the genus specimen resembles those of Taeniopteris N ilssoniopteris. densinervis from Kutch (Feistmantel, 1876, pI. 2, fig.
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