Oligocene Flora from Makum Coalfield, Assam, India
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Oligocene flora from Makum Coalfield, Assam, India N. Awasthi & R.C. Mehrotra Awasthi N & Mehrotra RC 1995. Oligocene flora from Makum Coalfield, Assam, India. Palaeobolanist44 . 157-188 The coal-bearing Oligocene sediments exposed in the Makum Coalfield, Assam contain rich assemblage of mega-plant remains. Out of a large number of leaves and fruits collected from the-associated sediments at Baragolai. Ledo-Tirap and Tipongpani collierics of the Makum Coalfield, 24 species ofdicotyledonous taxa have been identified. Of these, 22 arc represented by leaves belonging to the genera Sau:opellilum (Anonaceae); Calophyl/um. Ganinia, Kayea (Clusiaceae); Pleryxota (Sterculiaceae); Sanliria (Burseraceae); Hevnea (Meliaceac); Nephelium (Sapindaceae); Lannea, Mangijera, Parishia (Anacardiaceae); Rhizophora (Rhizophoraceae); Ter lIIinalw (Combretaceae); Memecylon (Memecylaceae); Avicennia (Avicenniaceae); AlslOnia (Apocynaceae); Myri.Hica (Myristicaceae). Apol/oJlias(Lauraceae) and Bridelia (Euphorbiaceae). The remaining two taxa are based on fruit/seed comparable (0 those of Dalberxia and Entada of Fabaceae. The distribution pallem ofcomparable modern taxa of fossils and keeping in view the great amount and variety of plants preserved in the sediments, it is inferred that thick tropical evergreen to moist deciduous forest existed in this part of northeast India during Oligocene. Occurrence ofAvicennia, Rhizophora and Terminaliacalappa suggests deltaic, mangrove or lagoonal deposition ofcoalseams amI associated sediments in the Makum Coalfield. Key-words- Megafossils, Angiosperms, Fossil leaves and fruits, Oligocene, Makum Coalfield, Assam. N "'mslhi & R.C. Mehrotra, Birbal Salllli Instilule ojPalaeobotany. 53, Universily Road. LuclulOW 226 007. 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In fact, there is no other Oligocene outermost flank of the Patkoi range, Tinsukia District, sedimentary basin in India which contains such a rich Assam (Text-figure I). The coalfield houses the largest and diversified Oligocene flora. The present systematic Tertiary coal deposit of India. The Makum Coalfield, study of plant fossils from this Coalfield has been under apart from being the most important for coal resourcs in taken in order to fill the gap in our existing knowledge northeastern India, the area is equally important for of the Oligocene floristics and its environment in the palaeobotanical studies as the coal-bearing Oligocene Tertiary floral history of India. 158 THE PALAEOBOTANIST Tipam Variegated clay, sandy clay, shale, 90' 92' 96' '" Sandstone coaly streaks, silicified woods and [H NA Formation conglomeratic sandstone (+ 1000m) Barail Tikak Parbat Hard and Iight coloured quartose Oligocene Formation sandstone. Alternations of siltstone, sandy shale, shale, mudslOne, carbonaceous shale and thin impersistent coal seams (+ 409m). Allernations of siltstone, mudstone carbonaceous shale, clay and workable coal seams. Occasional clayey sandstone, clay and sandy shale (+ 200 m) Baragolai Alternations of buff, bluish green Formation and grey coloured sandstone, sandy BUR M A shale, carbonaceous shale, sandy clay, clay and thin impersistent , 'c seams of coal and shal y coal. Herd " massi ve and Ooggy, grey o~100 Kll'I micaceous and ferruginous sandstone and oilsand (± 2743 m) BAY OF BENGAL \ \ I Naogaon Hard compact and Ooggy dark grey Formation fine-grained sandstone and interbeds of grey splintery shale (± Text-figure 1- Map showing location of Makum Coalfield (after Awasthi 1525 m) etal., 1992). Disang Dark grey splintery shale with GENERAL GEOLOGY Eocene interbeds of dark grey and finegrained sandstone (± 300m) The Makum Coalfield encompasses Baragolai, The present study is concerned with the coal-bearing Tikak, Ledo-Tirap and Tipong collieries which are well Tikak Parbat and Baragolai formations of Barail Group served by roads and railways. The National Highway No. (Oligocene) (Text-figure 2). The Tikak Parbat Forma 38 passes through this coalbelt and continues further east tion has five coal seams confined within the basal 200 m up to Myanmar border. The following lithostratigraphic section (Misra, 1992a). sequence of sediments exposed in the area has been given by Raja Rao (1981) and later modified by Misra Seam no, 5 (2.4 mJ8 ft thick 1.3-2.5m ( 1992a). abondoned AGE/GROUP FORMATION LITHOLOGY Parting 30.0-40.0m Seam no. 4 Recent·Pleistocene Alluvium Alluviiim and high level terraces (1.5 mJ5ft thick) 1.2-1.8mJ often Dihing Allernating pebble beds, coarse merges with seam no. Pliocene bluish green felspalhic and ferruginous sandstone and grey to 3 brown clay. abondoned Tiparn Girujan Variegated clay, silly clay. bluish Parting 3.0-18.0m Miocene Clay Formation green and grey sandstone (+ 470 m) Seam no. coarse, gritty and massive bluish 3(6 mJ20 ft thick) 2.0-7.5m worked green to grey felspathic and composite seam out in 2 sections micaceous sandstone. Parting 38.0-68.0m AWASTHI & MEHROTRA - OLIGOCENE FLORA FROM MAKUM COALFIELD, ASSAM 159 Of the five seams only Seam nos 1 and 3 are ex ploited throughout the field. According to Evans (1932) the 18 m seam (Seam no. 1) is demarcating horizon between the Tikak Parbat Formation and the ~nderlying Baragolai Formation (Text-figure 3). The Baragolai For mation has several thin to very thin coal bands of highly 09.00 impersistent nature. 50.30 52.60 ~ The Tikak Parbat Formation comprises alternations 55.00 53' of sandstone, siltstone, mudstone, shale, carbonaceous 65.20 66.80 69.80 shale, clay and coal seams (Misra, 1992a). Although the 75.60 occurrence ofplant-remains in grey carbonaceous shales and sandy shales in the field is known since long, they ~ ~. = :;:. 53 C1 :- = ~ .; ; remained practically uninvestigated until recently. In 9670 mD early 1989 the present authors made an extensive colIec 9730 tion of plant fossils comprising mostly leaves, a few fruits and seeds, with a view to reconstruct the Oligocene plant communities which served as source for coal for mation besides, deducing palaeoclimate and deposition al environment of the Oligocene sediments. From this colIection, recently Awasthi et at. .(1992) descri bed 1l.2.35 leaves of Podocarpus of Podocarpaceae and a leaf and fruit of Mesua of Clusiaceae. Of the remaining large '60.50 number of fossils, an account of two fruits Entada and '61.60 ~ Dalbergia and twentytwo dicotyledonous leaves belong ing to 20 genera, distributed among 15 families is presented in the present paper. The Terminology used in describing the leaves is :. .: = = after Hickey (1973) and Dilcher (1974). The identifica 20035 INDEX tion of leaves and fruits was done by comparing them 200.80 with fhe herbarium sheets at the Forest Research In Iv:dAlluvium stitute, Dehradun; Central National Herbarium, Howrah 61° 0 Sandstone 217·90 and the National Botanical Research Institute, Lucknow. I~ ~ ~I Clay 227.85 l-\.ll the type and duplicate specimens of fossils are ~ Coal 233.70 ... deposited in the Museum, Birbal Sahni Institute of I~ : ;1 Mudstone & Silty clay Palaeobotany, Lucknow. -- Shale 245."'0 2'-"·95 o Gr..y Shal.. 258.25'1 SYSTEMATIC DESCRIPTION Text-figure 2- Lilholog or Makum Coalfield (TiIap) (provided by Coal Family - Anonaceae India Limited, Northeastem Coalfield, Margherila, Assam). Genus - Saccopelalum Benn. Seam no. 2 (New Seam) Saccopetalu/11 palaeolongiflorum sp. nov. 2. i ml7ft thick 1.5-2.6 ill PI. 1, fig. I P;:,ning 5.0-20.0m Description- Leaf symmetrical, seemingly elIiptic :;eam no. 1 to wide elliptic, preserved length about 18 cm, width of (J 8 m/60 ft thick 10.0-20.8 m!worked one side of midrib about 6 cm; apex broken; base broken; (Composite seam) out in 2 or 3 sections margin entire; texture chartaceous; venation pinnate; 160 THE PALAEOBOTANIST y \:!)y ~ "~A~ Q ALLUVIUM fRECENJ) PARBA! } IF .f1 FAUll u...i!..!LU.J~ FORIrl4ATrON BARA60LAI iARAIL DIH'NG GROUP ~ L ~..-I ANTICLINE AXIS I..%:Q:I FOR"'AIION GROUP ~ !>CALE NAOGAON (OLIGOCENE I ['TT7'l G,RUJArI CLAY } SYNCLINE AXIS , o.~ 0 J~m IL:L.:L..:.dFORJolIATtQN TIPAJ04 l:...:...:....: FORMATION k-\1 l_ 1iiiioiI' I .... f1PA"4 SANDSrON[ GROUP CROP OF THRUST , ,... _! OUT o FOR"'AIION (""OCENE) I..... ....,...4' ;' THICI( COALS[AM Text-figure 3- A geological map of Makum Coalfield (after Misra, 1981) brochidodromous; primary vein seemingly moderate in 1973). It consists of 5 species. Saccoptealum thickness, more or less straight; secondary veins 9 pairs longiflorum, with which the fossil shows resemblance, visible, each IA-2.5 cm apart, angle ofdivergence mod is found in Eastern Bengal near Purneah (Hooker, 1872) erately acute (50°-65°), more or less uniform, moder ately thick, curving sharply before reaching the margin Family - Clusiaceae and joining superadjacent secondary veins at acute to Genus - Ca/ophyllutn Linn. right angles; intersecondary veins prominent, simple; tertiary veins percurrent, angle of origin AA-AR, close, Calophyllum suraikholaensis Awasthi & Prasad 1990 mostly alternate, oblique, simple. PI. I, fig. 2; PI. 3, fig. I Holotype - Specimen no. BSIP 37085.