Early Eocene Arecoid Palm Wood, Palmoxylon Vastanensis N

Journal of the Palaeontological Society of India ISSN 0522-9630 Volume 58(1), June 2013: 115-123 EARLY EOCENE ARECOID PALM WOOD, PALMOXYLON VASTANENSIS N. SP. FROM VASTAN LIGNITE, GUJARAT, INDIA: ITS PALAEOENVIRONMENTAL IMPLICATIONS M. PRASAD ¹, H. SINGH ¹, S. K. SINGH ¹, DEBI MUKHERJEE ² and EMILIO ESTRADA RUIZ3 1.BIRBAL SAHNI INSTITUTE OF PALAEOBOTANY, 53, UNIVERSITY ROAD, LUCKNOW- 226007, INDIA. 2. CENTRE OF ADVANCE STUDY IN GEOLOGY, LUCKNOW UNIVERSITY, LUCKNOW, 226007, U.P. INDIA. 3.UNITED ACADEMICAEN CIENCIASDELA TIERRAUNIVERSITDAD AUTONOMADE GUERRERO EX HACIENDA DE SAN JUAN BAUSTINA, 40323, TAXCO EL VIEJO, MEXICO. Corresponding author: E-mails: ¹[email protected], ² [email protected] ABSTRACT A new species of fossil palm wood, Palmoxylon vastanensis is reported and described from the Vastan Lignite Mine, Surat, Gujarat, India. The fossil wood is characterized by highly lacunar ground tissue with very large air spaces indicating that plants were growing in an aquatic or the marshy environment. A detailed anatomical study revealed its affinities with the extant arecoid taxa belonging to the family Arecaceae. Among them, it closely resembles Areca catechu as both fossil and living species possess similar anatomical features such as highly lacunar ground tissue, reniform, dorsal sclerenchymatous sheath of the fibrovascular bundles with the frequency of 30-35 per cm². Based on the anatomical characters of the fossil and present day ecology of its modern equivalent, the palaeoenvironmental implications have been discussed. Keywords: Palmoxylon vastanensis n. sp., Arecaceae, anatomy, palaeoenvironment, Vastan Lignite, Lower Eocene, Gujarat, India INTRODUCTION the Gulf of Cambay (Fig.1). The Vastan opencast lignite mine is The subsurface beds of the Lower Cambay Shale exposed situated about 29 km NE of Surat. The lignite, together with in an opencast lignite mine at Vastan in the southern part of the associated sediments containing pollen assemblage, was the basin, include a large number of different types of fossils reported by Samant and Tapaswi (2000, 2001); Samant and such as foraminifers, ostracods, molluscs, fishes and mammals Bajpai (2001); Rana et al. (2004). The marine ostracods from reported by several workers (e.g. Garg et al., 2008; Bajpai et these sediments were recovered by Bhandari et al. (2005). al., 2005; Punekar and Saraswati, 2010; Rana et al., 2004). The Evidence of marine fish remains and mammalian fossils was Palaeogene sediments in the Cambay Basin are exposed in the reported by Sahni et al. (2004); Nolf et al.(2006); Rana et al. form of the strips along the Saurashtra coast and to the east of (2005a,b), while Rose et al. (2006) provided information related Fig. 1. Geological map of the area showing site of palm wood occurrence. Inset shows position of the study area in India. 116 M. PRASAD, H. SINGH, S. K. SINGH, DEBI MUKHERJEE AND EMILIO ESTRADA RUIZ to depositional environment and sedimentation in the Table 1: (Generalised stratigraphy of the Vastan lignite mine (after Palaeogene lignite-rich succession at Surat, Gujarat. Later, these Bhandari et al., 2005). views were also supported by Tom McCann (2010) and Kishor Formation Lithology Age et al.(2011). Alluvium/ Black Soil and Recent alluvium Recent and Sub It has been observed by one of the authors (H. Singh) that soil Nummulitic limestone and Recent occurrence of plant megfossils (especially leaves) was restricted Amrawati marl in the uppermost thin layer of lignite in contact with the shale Calcareous bentonitic Late Eocene bed (Fig.2). A few fragmentary wood specimens were found variegated Clay, associated with the sandy shale bed. In addition, reports of unfossiliferous microfossils from the Vastan lignites have been published by Cambay Shale Greenish grey, whitish clay Early Eocene Tripathi and Srivastava (2006); Samant and Tapaswi (2008); and brown fissile shale, clay Guleria et al. (2008): Mandal and Guleria (2006); Garg et al. and marl (2008). Recently, Singh et al. (2010) reported the occurrence of with carbonaceous zone plant megafossils (fruits) referable to Ziziphus, Combretum, including Terminalia and Lagerstromia belonging to the dicotyledonous lignite seam with vertebrate, famlies Rhamnaceae, Combretaceae and Lythraceae. plant, pollen and spore fossils Vagadkhol Variegated clay Palaeocene-Early Eocene Deccan Trap Basalt Late Cretaceous Recent Alluvium Sandstone Lignite Mine. It is a small piece, black in colour measuring 4x2 cm in size, apparently showing fibrovascular bundles scattered Shale bed in the matrix. The specimen was cut into thin sections (TS and LS). To observe the anatomical characters, these sections were Wood Sample Collected ground to thin slices and polished by standard method for preparation of permanent slides. The important characters were studied under low and high magnifications under the optical Top Lignite (Seam -I) microscope and the photomicrographs for important anatomical features were prepared. SYSTEMATIC DESCRIPTION Family Arecaceae Schultz,1832 Fig. 2. Field photograph showing the lignite layer from where sample Genus Palmoxylon Schenk, 1882 was collected. Type species: Palmoxylon blanfordi Schenk, 1882 Palmoxylon vastanensis n. sp. GEOLOGICAL SETTING (Pl. I, figs.a-k; Pl. II, figs.a-c) The vastan lignite mine is situated about 29 km north east Type specimen (Holotype): Palmoxylon vatsanensis n. of Surat town (Lat 21º 25? 47?N Long. 73º 7? 30?) in Gujarat, sp; BSIP Museum No.39901. western India. The shale referable to the Cambay Shale Type locality: Vastan lignite mine, Gujarat, India. Formation is variable in thickness (20-145m), consisting of Horizon and Age: Cambay Shale Formation; Lowe Eocene. lignite bands of various thicknesses alternating with Parts available: Sub-Dermal and Central zones. carbonaceous and grey shales (Fig.2).There are two main lignite Derivation of name: The specific name is based on the seams in this mine; lignite seam-1 lies at the top and lignite locality, Vastan, from where the specimen was recovered. sean-2 at the bottom of the mine (Rana et al., 2008). The Cambay Diagnosis: Wood blackish in colour; comprising sub- Formation overlies the Palaeocene-Lower Eocene Vagadkhol dermal and central size 4x2.6cm, fibro-vascular bundles in sub- Formation and is overlain by the upper Eocene Nummulitic dermal zone irregularly oriented with one metaxylem vessel limestone and marl which denotes the Amravati Formation sometimes two may be present; size of the bundles ranges (Sudhakar and Basu,1973) (Table 1). The foraminifer, from 440x500-700-800µm; dorsal sclerenchymatous sheath Nummulites burdigalensis occurs as an indicator of Shallow reniform; cells of this sheath generally not preserved. A layer Benthic Zone of middle Ypresian (Early Eocene) age, about 18- of tabular parenchyma present around the fibrous part of the 20 m above the rodent-bearing horizon (Sahni et al., 2006); bundle; auricular lobes round, auricular sinus absent; Berggren and Pearson, 2006). The succession, in turn, is diminutive fibrovascular bundles rare, fibrous bundles absent, overlain by the recent alluvium. According to Sahni et al. (2006) leaf-trace bundles rare. Fibrovascular bundles of central zone the sediments of lower half of the Vastan lignite mine were irregularly dispersed in ground tissue, bigger in size as deposited in an estuarine to lagoonal environment, whereas compared to sub-dermal zone; 1000x900-1200x1000µm; the those of the upper half were deposited under the shallow sclerenchymatous sheath reniform, cells of this sheath partly marine conditions. preserved; frequency of the fibrovascular bundles is 30-35 cm² and the f/v ratio varies 4/1-5/1; tabular parenchyma present; MATERIAL AND METHODS stegmata absent. Ground tissue highly lacunar; cells rod to The material was collected by one of the authors (HS) cylindrical and variously shaped forming large air spaces; from the sediments of Lignite seam 1 exposed at the Vastan secretory cells present in the ground tissue; diminutive fibro- 1 to 1.4mm (Pl. I, fig.a). I, (Pl. 1.4mm to 1 in size than the bundles normal and fibro-vascular from extend part with many smaller vessels. xylem are They slightly larger vascular protruded by distinguished be and can stem the in seen vascular bundles (Pl. I, fig.c). fibro- normal, that of is almost similar to structure Their size. in arranged in the ground tissue, measuring less than 250-300µm fibrovascular bundles, rarely seen in this zone, irregularly are also present in (Pl. this I, fig.i; zone Pl. II, fig.a). sometimes present in this zone. are bundles At k). Leaf-trace fig. I, (Pl. size) x100-410x250µm (50 places, secretory glands formed by union of cylindrical parenchyma of various shapes ground tissue is highly lacunarparenchyma cells with of the very groundlarge tissue air (Pl.I, vascularspacesfigs.e,g,h). The part zone; ofare absent.the Radiating bundlesparenchyma 4/1-5/1.Thepresent ranges ratio fibrousaround andfibro-vascular bundles The the cm². and per 35 stegmata30- anastomos from arevary bundles absent in this with the rarely two may be present. The frequencyfibro-vascular of fibro-vascularbundle has generally lumen and thin one cell wall.auricular sinusThe is indistinct; each metaxylem vessel, cells can be observed, they are polygonal in shape with larger exact nature (Pl. II, fig.a). However, a few sclerenchymatous reniform sclerenchymatous sheath of elongatedperipherally theof fibro-vascularlayer a with tabularmeasure1000x900-1200x1000µm bundles they is parenchymafibro-vascular bundles

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