On the Karharbari Age of Coal-Measures of Ray-Bachra Area, North Karanpura Coalfield*
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ON THE KARHARBARI AGE OF COAL-MEASURES OF RAY-BACHRA AREA, NORTH KARANPURA COALFIELD* H. S. PAREEK Geological Survey of India, Lucknow ABSTRACT probably because it has been explored only recently, The age of these coal-measures In the south-eastern portion of the North Karanpura coalfield, Bihar, two coal seams, known has been described as Barakars by Jowett as Rav seams in Ray (23 0 40': 85 0 4') and Bachra (1925) and Banerjee (1958), and as Karhar seams in Bachra (23 0 41'19": 85 0 5'17") areas, occur baris by Puri (1952), Ghosh (1958) and in Lower Gondwana coal-measures that comprise Mehta et at, (1963). The author studied a maximum thickness of 140 metres. Coal petro graphy has established that Bachra seams are the Jitbology of these coal-measures and ex eastward extension of Ray seams, vVhile some amined bore hole cores and logs of Bachra workers have described them as Barakars, others area in detail, along with the palaeobotanical have regarded them as Karharbaris. and palynological evidences to arrive at a The author examined their geology, field relations of coal seams, borehole logs of Bachra area, and conclusion, This paper discusses the petrography of Ray and Bachra seams in detail, evidences for the inferred Karharbari age and studied the available palaeobotanical and of the coal-measures. In order to provide palynological data. This paper presents conclusive the lithological evidences, a geological ac evidences of their being of I(arharbari age. count of the less-known Bachra area, as revealed by bore hole logs, is also incorpo INTRODUCTION rated. HE Ray-Bachra area is a strip of the GEOLOGY OF THE BACHRA AREA Lower Gondwana coal-bearing forma T tions in the extreme south-eastern The Bachra area is a triangular block of part of the North Karanpura coalfield, about 3·62 sq, km, extent bordering the •Bihar. In the area around Ray (23° 40': right bank of the Saphi nata (see FIG, 1) . 85° 4') in Ranchi district, t",,·o coal seams It is confined between the parallels 23° 41' named as Ray Top and Ray Bottom are 16" and 23° 42' 48" N. Latitude and 83° 3' being worked at localities Manki, Churi, Ray 45" and 85° 5' 41" E. Longitude, falling just and Bishujhapa by private enterprises, In north-east of the Ray area. It has an un the adjoining Bachra area, named aiter the dulating topography with a slope towards nearby.village (23° 41' 19": 85° 5 17") in the Saphi and has a soil cover in vvhich Hazaribagh district, the existence oi two coal quartz pebbles have reconsolidated. seams, Upper Bachra and Lower Bachra, The general nature of the underground has been proved by drilling operations by sedimentary strata appears in Fig, 2 in the Geological Survey oi India (PAREEK, a bore hole section. The geological sequence 1962); these seams are now being worked by of formations, as interpreted from bore hole the National Coal Development Corpora cores and as established is given in Table 1. tion Ltd, The general strike direction of the sedi The geology and field relations of the coal mentaries is N.E.-S.W. The surface dips seams of the two contiguous areas are indicate horizontal nature of the beds, but indicative of the Bachra seams being the core dips and bore hole sections suggest eastward extension of Ray seams (PAREEK, their rolling nature and even a minor folded 1964a) ; coal petrography has confirmed pattern of the formations, There is no this conclusion (PAREEK, 1964b), evidence of any major faulting. While much has been published on geology The bore hole data indicates that the of the Ray area (BANERJEE, 1958; GHOSH, Talchirs vary in thickness from one metre 1958; MEHTA et at., 1963), practically to 2·55 metres in north-western to eastern nothing is known about the Bachra area, portions of the area, But they are absen t 'Published by permission of the Director-General, Geological Survey of India. 73 .•....BORf HOlE :+: .NO; I~ .• CHRA ·.f . f :1 ./ . .1 ./ : ./ .I : .1 r ../ .j- ../ I : r. :I: GE OLOGICAL MAP OF RAY-BACHRA AREA, :I: NORTH KA RANPURA COALFIELD BIHAR. @TER GHOSH (1'350) ANO MEHTA [T. Al. (1963), MOOlflEO 8'( H.g. PAREEO INDEX: c=J 8araku StBge. @ Burnt coal outcrop. CoaL outcrop. 10()01 ~ karhol"bBri Stage. --- ProbabLe coal outcrop. ,.........-F Fault. SCALE Tel chir Stage. Illl01li''''US. , -F Suspl2cted F8ult. // 6 i Metamorphics. F+ l-IorizontBL Sed: I ..... 50· Dip. @ Fossil locality. TEXT-FIG. 1 - Geological map of Ray-Bachra area, North Karanpura Coalfied, Bihar. PAREEK - KAIZHARBARI AGE OF COAL-MEASURES OF RAY-BACHRA AREA 75 SCALE IN METRE S GROUND LEVEL o · ·.··. ··..... COARSE GR~NED SANDSTONE ·. BARAKAR CARB. SHALE WITH THIN BANDS OF COAL SHALY SANDSTONE CARB. SHALE SHALY SANDSTONE COARSE GRAINED SANDSTONE FIRECLAy 000 COARSE GRAINED SANDSTONE 0·0·0·0·0.0·0·0·0·() 0 PEBBLE BED 25 0·0·0·0·0 t 0·0·0·0·0·0·0·0·0· COARSE GRAINED PEB BLY SANDSTONE i •• FINE GRAINED SANDSTONE WITH BANDS OF SHALE CARB. SHALE WITH BANDS OF COALlUPPER BACHRA SEAM) SHALY SANDSTONE CARB. SHALE WITH BANOS OF COAL (UPPER BACHRA SEAM) SHALY SANDSTONE S HA LE SHALY SANDSTONE • CARB. SHALE WITH THIN BANDS O~ COAL 50 SHALY SANDSTDNE COAR SE GRAINED SANDSTONE COAL SANDSTONE WITH STREAKS OF CARB. MATTER }LOWER BACHRA SEAM CO AL COARSE GRAINED SANDSTONE WITH KARHARBARI BAN OS 0 F S HAL Y SANDSTONE 0·0.0·0·0 SHALY SANDSTONE WITH BANDS OF COAL 0.0·0·0··0. 0.0.0 -0-0-0-0·0·0·0·0 15 O··0·0·0·00·0·0· .0.0.0.0 6 ) 10·0.0·0.01 0.0·0·0·0-0-0-0.0. 10-0·0-0-0·0· a ·0. o. • c· 0 ·0·0· o • 0 .0.0.01 COARSE GRAINED TO PEOBLY S ANOST ONE 0·0·0·0·0·0·0·0·0· ·0·0·0·0·cl·o·o·o·o 0·0·0·0·0.0·0·0·0· 0·0·0·0·0·0·0·0·0. 0·0·0·0.0.0· o· O· O· .0· .0· O. 100 0·0·0·0·0a o· O· 0·0. 0·0·0·0·0•.0·0 ·0·0· 0'0'0'0'0'0'0'0'01 CONGLOMERATIC SANDSTONE 106 - TALCHIR +++++++ BIOTITE GNEISS - ARCHAEAN TEXT-FIG. 2 - Description of strata in bore hole No. 12, Bachra area, North Karanpura Coalfield. 76 THE PALAEOBOTANIST TABLE 1 AGE DESCRIPTION OF STRATA THICKNESS (METRES) Recent Surface soil with quartz pebbles reconsolidated. 1,5-3'5 rUnconformity I Barakar stage - fine to medium-grained and occasionally Increases from 2·0 in coar~e-grained sandstone, thin bands of shale and of coaly southern to 29·0 in I shale. northern portions. I Unconformity \ H:arharbari stage - Coarse-grained, gritty and pebbly Lower sandstones with angular and subanglliar quartz and Gondwana ~ felspars. The matrix is of yellow or light grey colour I containing in places soft, greenish-yellow material. I Carbonaceoll~ shale, coal seams, and fireclay. 75·0-105·0 I Unconformity . I Talchir stage - fine-grained, khaki-grey to gre('nish sand- I ston(' and boulder bed, occasionally containing vaf\'('d l bands of clay. up to 3·0 Archaean Unconformity Metamorphics - Biotite-gneiss. in the extreme east near the Damodar River Towards the north-east of Bachra area, all where all rocks outcrop. Towards the these seams are reported to have disappeared south, near Bachra and Ray, outcrops of completely. The general seam character Talchir shales with bands of varved clay istics appear in Table 3. • have been recorded by Ghosh (1962). Fireclay - It invariably overlies the Mos't of the area is covered with soil, Upper Bachra seam. Its maximum thick which prevents examination of outcrops, ness is 11·60 metres that is gradually reduced except along the streams and nalas. The to 10 metres in the southern portion and has bore hole data, however, indicates that the thinned further towards northern, north Talchir-Karharbari boundary is generally eastern and north-western portions with well-marked by a band of conglomerate of simultaneous developmen t of partings and thickness up to 25 em. The Karharbari shaly character of the underlying seam. and Barakar junction is similarly marked by a pebble bed of thickness varying from a few DISCUSS10N centimetres to 3·5 metres. Table 2 shows its thickness and location from the base of The coal-measures of Bachra and Ray Upper Bachra and Lower Bachra seams in areas have similar sequence of rock forma the differen t portions and bore holes of the tions. The criteria discussed here for area. It is of greater thickness in the inferring their Ka~harbari age are based on portion adjoining the Saphi and has appa their lithological character, presence of dis rently thinned out towards north-western tinctive plant fossils and micro-fossils, and and south-western portions. petrological nature of the coals. Coal seams - The Upper Bachra and 1. Ldhological evidences - The sandstones Lower Bachra, exhibit tendencv to thicken of the coal-bearing formations are persis or thin out commonly laterafly and also tently coarse-grained, gritty to pebbly along the dip. The Upper Bachra splits containing angular to sub-angular pieces into thin bands in the north-eastern, south and fragments of quartz and of felspar, eastern and eastern portions, and disappears usually kaolinised. Their ou tcrops are in the northern and north-western portions. marked by the weathered product of the The Low~r Bachra splits laterally in to two felspars that covers the entire surface.