Charcoalified Wood of Hopenium pondicherriensis (Dipterocarpaceae) from Neyveli Lignite Formation

. The Neyveli lignite is one of the largest brown coal field of India, Cuddalore district of Tamil Nadu. The lignite is one of tertiary formation found in the Neyveli. So far many mega and micro fossils reported from this formation. The Neyveli lignite well preserved and recognizable entities are mainly woody and non-woody tissues of different angiosperm plants, spore and pollen, cuticles of leaves, resins, fungal spores and fungal fruiting bodies. The present study is about the charcoalified angiospermic wood is identified as Hopenium pondicherriensis (Dipterocarpaceae). This is a first report of Hopenium pondicherriensis from the Neyveli formation.


Introduction
Neyveli lignite, the single largest brown coal field. So far known in India lies in the Cuddalore district of Tamil Nadu, India. It is roughly estimated that around 3000 million tons of lignite reserve spread beneath an area of 300 sq. km. with an average thickness of 23 m of seams [3]. Until recently the lignite was considered to be a part of the Cuddalore Formations. However, Siddhanta [9] divided the Cuddalore Formations into two parts and named the lower part, which includes lignite, as the Neyveli Formation and the retained the term Cuddalore Formation for the upper part. The Neyveli Formations consists of semi consolidated sand stones and clay beds with occasional limestone intercalations followed by carbonaceous clay (abouve1m thick) and brownish block lignite (up to 23m thick). It is overlain by the Cuddalore Formation (60 to 120m thick), which is made up of ferruginous, arkosic, semiconsolidated sand stone exhibiting some herring tone types cross laminations. The contact between the two Formations is marked by erosional unconformity [9]. The age of the Neyveli lignites (belonging to the Neyveli Formation) has remained a subject of dispute. Until 1973 these deposits were believed to be of Miocene age. However, Venkatachala [10], Deb et al. [4] and Siddhanta [9] on the basis of palynological and geological evidences inferred a Palaeocene -Eocene age. The lignite contains well preserved and recognizable entities of mainly woody and nonwoody tissues of different angiosperm plants, spores and pollens, cuticles of leaves, resins, fungal spores and fungal fruiting bodies [6].

Materials and Method
The charcoalified angiospermic wood were collected from the Neyveli lignite sediments of Mine-I A, Tamil Nadu, located at the Cuddalore District. A piece of charcoalified wood was placed in Sodium hypochlorite (for softening). The length of time necessary for this should be empirically tested. Sections (TS, TLS & RLS) were prepared using razor blade. The sections were immersed in sodium hypochlorite solution to get the transparency. After cleaning, sections were immersed in a solution of 1% safranin for 3-5 minutes. Then rinsed in water, 50 % alcohol and then 96 % alcohol until excess stain was removed. Dehydrated sections then immersed in xylene before being mounted on glass slides in Canada balsam. Olympus Trinocular Microscope magnification was used to observe the fossil materials and slides. Microphotographs were taken using Olympus SLR Camera attached with Trinocular Microscope. Species: Hopenium pondicherriensis Awasthi.

Affinities
The characteristic features of the present wood are, small vessels, they are in radial multiples, presence of vasicentric tracheids, gum canals vertical and heterocellular rays. These features indicated that the present wood is having affinity with the family Dipterocarpaceae. The genera of this family were assigned into two groups based on the arrangement of gum canals (Ghosh, 1956) (i) Gum canals always in concentric rings (eg. Shorea Roxb., Doona Thwaites., Hopea Roxb., Parashorea Kurz., Pantacme A.DC., Balanocarpus Bedd, and Dryobalanops C.f. Gaertn) and (ii) Gum canals diffuse and in short tangential rows in Anisoptera Korth., Dipterocarps Gaert.f., Vatica L. Vateria L. and Cotylelobium Pierre. The present fossil wood possessing gum canals in concentric rings, so it is placed in the first category. Among the genera of the first category, the fossil shows the best resemblance to the genus Hopea Roxb. Fossil wood resembles with wood of living genus Hopea placed under the genus Hopenium Awasthi.
International Letters of Natural Sciences Vol. 75

Discussion
In the present work charcoalified fossil wood belonging to the family Dipterocarpaceae (Hopenium pondicherriensis) were analysed. The fossil wood were recovered from the lignite samples collected from neyveli lignite mines. So far five Dipterocarpaceous woods (Table 1) [2] differ from the present specimen in having closely spaced parenchyma bands. The present wood more closely related Hopenium pondicherriense reported from the Cuddalore Formation. So it is assigned to this species.

Conclusion
The observation of present work charcoalified wood of Hopenium payangadiensis, (Dipterocarpaceae). This is the first report of Hopenium pondicherriensis from the Neyveli lignite formation. Based on the fossil floral elements collected from Neyveli lignite the palaeovegetation palaeoclimate and the age of this region during the tertiary period was worked out.