Glacial Sedimentation of Late Paleozoic Talchir Diamictite, Pench Valley Coalfield, Central India

SATYENDRA M. CASSHYAP* Department of Geology, Aligarh Muslim University, Aligarh, India HAYAT A. QIDWAI* }

ABSTRACT Permian-Carboniferous diamictite units of the Talchir Forma- tion of the Lower Gondwana group on the Indian peninsula have Three mappable diamictite units occur in the Lower Gondwana been considered glacial in origin (Blanford and others, 1856; Fed- Talchir Formation (Permian-Carboniferous) of the Pench Valley den, 1874; Krishnan, 1960). Subsequent studies of the texture and coalfield of Satpura basin, central India. These diamictite units mineral assemblage of Talchir strata in the Damodar Valley (each about 28 to 45 m thick) are predominantly green, polymictic, coalfields of eastern India recognized both glacial and fluvioglacial and poorly sorted. Portions of the units ':hat are massive diamictite deposits (Rao, 1957; Srivastava, 1961; Niyogi, 1961; Smith, 1963; include a variety of twisted and deformed to tabular and wedge- Ghosh and Mitra, 1970). Locally, evidence for turbidity currents shaped sandstone bodies, as well as thin \enses of conglomerate and was cited by Banerjee (1966). The Pench Valley coalfield of the sandstone that locally exhibit parallel groove markings on the Satpura basin in central India (Fig. 1, inset map) was selected for upper surface. Portions of the units that are stratified diamictite are this investigation because it lies at the western limit of Lower characterized by "grouped" clasts and thin interbeds of siltstone Gondwana deposition and because the Lower Gondwana rocks in and sandstone showing fine, parallel grooves (striae) and linguoid this part have not been studied in detail. ripples where the interbeds occur beneath diamictite. Each diamic- The Talchir diamictite assemblage represents a complex group of tite unit is overlain by an assemblage of interbedded green siltstone, rocks, and a critical re-evaluation is desirable to modify and ex- shale, and sandstone. Such an assemblage contains a variety of pand the sedimentation model and paleogeography. The sedimen- primary depositional structures plus local striated "lonestones." tation model is developed from analysis of stratigraphic and The upper part of the Talchir Formation, the transitional assemb- lithologic characteristics and primary and secondary sedimentary lage, is characterized by horizontally bedded to cross-bedded con- structures of the diamictite units and associated strata. An attempt glomeratic sandstone in which embedded clasts are more rounded is made to reconstruct the sedimentologic evolution of the Talchir than those of the diamictite. strata. A synthesis of the above features discounts the possibility that turbidity currents or mass flows were the sole formative mech- STRATIGRAPHIC SETTING anisms. Alternatively, lithologic and sedimentary characteristics The geologic map of the Pench Valley coalfield was prepared by of the lower Talchir strata and their over-all stratigraphic and tec- C. S. Fox in 1923 to 1925 (Fox, 1934, p. 176). The area was tonic setting strongly favor a glacial origin for the diamictite; this geologically remapped on a scale of 5 cm to 1.58 km (2 in. to 1 mi) corroborates previously published views. We postulate a by one of us (Qidwai) during the winters of 1969 to 1970 and 1970 glaciomarine model, however, to explain the Talchir sedimentation to 1971 (Qidwai, 1972, his Fig. 2). The Talchir Formation overlies in the study area. The ice sheets may have advanced into central Archean rocks and is overlain by the Barakar and Motur Forma- India from the south several times. The overlying transitional as- tions (Fig. 1A). The structural strike is generally southeast; north- semblage may be glaciofluvial in origin. Key words: sedimentology, east dips vary from 3° to 8°. The sedimentary assemblage is over- stratigraphy, diamictite, tillite, Gondwana, late Paleozoic, Talchir, lain by the Cretaceous Deccan Trap. ice transport direction, paleoslope, sedimentary evolution. The Talchir Formation shows a faulted contact with the underlying Archean rocks and is exposed in two patches (Fig. 1A). The INTRODUCTION strata in the western area are better exposed than those in the smaller eastern area; both areas have been examined for this study. The Recent research on diamictite has improved understanding of the Talchir Formation of the Indian peninsula is characteristically geologic processes that result in the deposition of this rock type and olive green and consists of an interbedded sequence of diamictite, control the lithologic succession associated with it. Initial studies of sandstone, siltstone, and shale, with minor lenses of pebble con- diamictite units have been re-evaluated by detailed analysis to de- glomerate. A series of traverses along drainage courses in the west- termine whether their origin was glacial or whether an alternative ern part has yielded an orderly lithologic sequence that is laterally mechanism, such as subaerial mudflows, subaqueous mass move- traceable (Fig. IB). Table 1 records the recognizable subdivisions ment, or turbidity currents, caused their emplacement. The and corresponding lithologic units of the Talchir Formation. Ap- geologic interpretation of this complex group of rocks should be proximate minimum thickness of the Talchir strata in the western based on integrated studies of lithologic and stratigraphic charac- part is about 250 to 300 m. Plant fossils are more common in the teristics and primary sedimentary structures of both the diamictite middle and upper parts of the formation and are mostly fragments and associated rocks, in addition to consideration of the over-all of Glossopteris. stratigraphic framework and tectonic setting (Thornbury, 1954; The age of the Talchir strata and the overlying Lower Gondwana Flint, 1961; Dott, 1961; Crowell, 1964; Harland, 1965; Schwarz- formations cannot be determined with absolute precision because bach, 1964). of the paucity of faunal remains. The discovery of marine inverte- brate fossils in the Talchir diamictite at Umaria, Manendragarh, and Daltonganj in east-central India has enabled Sastri and Shah * Present address: (Casshyap) Ruhr-Universität Bochum, Institute für Geologie, 4630 Bochum-Querenburg, West Germany; (Qidwai) Department of Atomic Energy, (1964, p. 143) to propose Sakmarian to Artinskian (Early Permian) Atomic Mineral Division, R. K. Puram, New Delhi-110022, India. age for these fossiliferous diamictite outcrops, however.

Geological Society of America Bulletin, v. 85, p. 749-760,10 figs., May 1974

749

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TABLE 1. LOWER GONDWANA SEQUENCE AND LITHOLOGIC SUBDIVISIONS OF THE TALCHIR FORMATION -| Cyclic units

Approximate Description of main lithologie types thickness (m) Cycllc units 800 Red and green mudstone and thin interbeds of gray and green, coarse sandstone in the lower p.jrt, and gray to white, pebbly, coarse to medium sandstone in the upper part 120 Interbedded, coarse to fine, gray sandstone, siltstone, shale, carbonaceous shale, and coal Transitional assemblage D1 40 Interbedded fine, green sandstone, (D) siltstone, and shale D 10 Gray to white, pebbly, coarse sandstone i • A •. Û • Fine clastic rocks C3 60 Predomirantly olive-green laminated shale • A* » • • C2 10 Interbedded sandstone, siltstone, and shale CI 15 Olive-green sandstone Coarse clastic rocks C 28 Olive-green, poorly sorted diamictite Fine clastic rocks B1 6 Gray sandstone, lower contact wavy Coarse clastic rocks B 38 Olive-graen, poorly sorted diamictite Fine clastic rocks A3 5 - 10 01ive-gr<»en sandstone A2 12 - 22 Interbedded green sandstone, siltstone, and shale r=31 IHTERBCODCD SANDSTONE A1 35 Olive-groen sandstone bud AND SHALC Coarse clastic rocks r.v.;| &ANOSTONE A 30 Olive-green, poorly sorted diamictite mAMtcTire

Figure 2. Stratigraphic sections of Talchir Formation showing lithologic composition and cyclic units in the western (A, B, and C) and eastern (D) areas. A, Chatua- LITHOLOGIC TYPES AND Hinautia section; B, Budhwara-Naulakhapa section; C, Bhadri section; D, Khirsadoh SEDIMENTARY CHARACTERISTICS section. Columnar sections illustrate gross lithologic composition and cent) units. The most important lithologic types are porphyritic sedimentary characteristics of the Talchir Formation (Fig. 2). The granite (22 to 50 percent), granite gneiss (15 to 44 percent), lime- Talchir strata (Table 1) can be grouped into three lithologic types: stone (5 to 9 percent), quartzose sandstone (2 to 15 percent), basic (1) diamictite units A, B, C; (2) a fine-grained assemblage of sand- extrusive igneous rocks (5 to 9 percent), red sandstone (less than 1 stone, siltstone, and shale occurring above each diamictite (units to 11 percent), banded hematite quartzite (less than 1 to 11 per- A1 to A3, Bl, and CI to C3); and (3) coarse- and fine-grained clas- cent), and shale (less than 1 to 11 percent). Relative proportions tic rocks of the transitional assemblage, represented by units D and persist in groups of clasts of different size fractions. Clast round- D1 (Figs. IB and 2). ness was estimated visually from the chart after Krumbein (1941). Roundness appears to be independent of clast composition—a Diamictite Units feature observed by several workers elsewhere (Frakes and The three diamictite units (about 28 to 45 m thick) constitute Crowell, 1967, p. 43; Lindsay, 1970, p. 1158). Larger boulders of about 55 percent of the Talchir strata. They are uniformly polymic- 0.5-m diam and more are conspicuously better rounded (round- tic in composition; pebbles, cobbles, and boulders are sparsely dis- ness, 0.7 to 0.8), but smaller clasts (large cobbles to fine-sized peb- tributed in a tough clayey to silty and calcareous matrix. According bles) exhibit a wider variation in roundness (0.2 to 0.6). to the scale of sorting by Folk and Ward (1957), the matrix of the Shapes of 110 clasts were determined following the method out- diamictite is poorly sorted except in certain parts of unit B and C, lined by Sneed and Folk (1958, p. 123). Figure 3A shows a compos- where it is moderately well sorted (Qidwai, 1972). ite plot of shapes for igneous, sedimentary, and metamorphic clasts Clast Assemblage. Generally, the three diamictite units cannot of the three diamictite units. Among the most abundant shapes are be differentiated either on the basis of clast sorting and lithologic bladed (26 percent), compact bladed (22 percent), elongated (12 type or clast roundness, shape, and sphericity. The clasts are poorly percent), and compact platy (10 percent). Clasts ranging in size sorted; by volume, pebbles exceed cobbles and boulders. The most from 2 to 12 cm have triangular or pentagonal "flatiron" shapes widespread pebbles are those ranging iri size from 8 to 64 mm, with smooth, abraded edges and a conspicuous basal facet (Fig. whereas the most abundant cobbles range between 64 to 128 mm 4A). Quartzite, basic igneous rocks, and some limestone clasts are in maximum diameter. Boulders are relatively less common than particularly well faceted and may bear subparallel striae (Fig. 4B). cobbles and seldom exceed one meter in diameter. The largest Clast sphericity was obtained by interpolating the points be- boulder was pink porphyritic granite; it measured about 4 m across tween isosphericity contours (Sneed and Folk, 1958, their Fig. 2), and occurred in the basal part of the lower diamictite unit A. and the percentage of clasts in each sphericity class was plotted on Percentage (by volume) of embedded clasts in the diamictite units a histogram (Fig. 3B). The distribution is unimodal and skewed; was determined in several outcrops by following the method of about 35 percent of the clasts are in the modal sphericity class of pebble counts used by Casshyap (1969, p. 15) in his study of Gow- 0.7 to 0.8 and correspond mostly to elongated, compact bladed to ganda tillite of southern Ontario. For each outcrop, clast percen- compact platy forms. Generally, sedimentary clasts are more tage was determined in two or three areas of 4 m2, and an average equant (compact and compact bladed) and show higher sphericity was taken for the outcrop. Usually clasts constitute about 10 to 15 (0.9 and higher) than igneous and metamorphic clasts, which are percent of the rock and represent igneous, sedimentary, and commonly elongated and bladed to platy, and seldom show metamorphic source rocks. Combined percentages of igneous and sphericity in excess of 0.8. Some large-sized embedded clasts show metamorphic clasts (60 to 75 percent) are constant in the diamictite fractures that are oriented parallel to the long axis of the clasts and units, whereas sedimentary clasts show a systematic variation in usually do not extend into the surrounding diamictite matrix. Wide that they are more common in the lower unit (average 30 percent) fractures may be filled with the same material that constitutes the than in the middle (average 18 percent) and upper (average 14 per- matrix (Fig. 4C). There is little evidence in the study area to suggest

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Compact 9 Igntciss o Staiimntmrf « Mt1om*rphic

0 •0 .33 l -1 .67 1.0 PLATY us ELONGATED Figure 3. A, triangular plot for shape analysis of clasts. B, histogram showing frequency distribution of clast sphericity 'or samples plotted in A.

•1 2 -3 -4 "t ^ ^ 3 '9 Sphericity class

that clast fractures are due to regional tectonic stress; an alternative explanation for the origin of clast fractures is necessary. Whereas clast texture and rock type may provide useful clues to the possible mode of deposition (Pettijohn, 1957; Krinsley and Takahashi, 1962; Harland and others, 1966; Landhim and Frakes, 1968; Frakes and Crowell, 1970), shapes of clasts may reflect an inherited feature from systematic jointing in the source area. Internal Structure. Two types of internal structure may be recognized in the diamictite of the study area: massive diamictite and stratified diamictite. Of the three diamictite units in the western area (Fig. IB), the lower unit A, middle and upper parts of unit B, and the lower and middle parts of unit C are massive (Fig. 5A). The undivided diamic- Figure 4. A, faceted, flatiron-shaped pebbles from diamici:ite units, showing trian- tite unit of the eastern area is hard, compact, and apparently mas- gular, rectangular, and pentagonal outlines. B, rounded limestone clast (20 cm long) sive. In nonstratified diamictite, embedded clasts are sparsely scat- showing subparallel striae; clasts like this are common in diamictite. C, fracture in a tered and form about 12 to 16 percent of the rock by volume. Such large (1 m long) boulder filled with diamictite matrix (unit A). About 1.5 km west- southwest of Hinautia. diamictite may contain local inclusions of sandstone in twisted masses, isolated tabular blocks, or wedge-shaped (triangular) bodies. Deformed bodies of earthy white, medium-grained sand- much as 10 m long and 3 m thick and have the apex tapering stone may range in size from less than 1 to about 2 m; some are downward. In some places, massive diamictite includes thin sharply bent at one end (Fig. 5B) and form a hook-shaped structure laminae of sandstone that exhibit well-developed, finely parallel (Crowell, 1957). Apparently, the host diamictite is not disturbed or striae or miniature grooves on the upper surface (Fig. 6). There is deformed anywhere along the contact of sandstone inclusions. no evidence of faulting that might account for the grooves. Occa- Larger sandstone bodies are less deformed and occur as isolated sional lenses of faintly bedded or cross-bedded sandstone and con- tabular blocks in diamict.te (Fig. 5C) or appear as vfredge-shaped glomerate may also occur in massive diamictite. bodies in cross section (Fig. 5D). Wedge-shaped sand masses are as The occurrence of t wisted sandstone bodies has been attributed

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Figure 5. A, typical outcrop of massive diamictite (upper part of unit B) in which dasts of different size are sparsely dispersed. About 1.8 km southwest of Khairwani. B, small, twisted sand body in massive diamictite in the middle part of unit B. About 3 km south of Chatua. C, tabular blocks of conglomeratic sandstone included in the massive diamictite unit A. About 1 km southwest of Khairwani. D, wedge-shaped sand body included in massive diamictite (unit C); in the background is, perhaps, a channel sandstone. About 2 km east-northeast of Chatua.

perhaps disrupted remains of fluxoturbidite beds, or load-casted masses of formerly continuous sand beds that were mobilized into incompetent (probably water-saturated) fine sediment (Chester A. Wallace, 1973, written commun.). Talchir diamictite exhibits at least partial stratification (Fig. 7A) at three stratigraphic levels: the lower and upper parts of diamictite unit B and the upper part of diamictite unit C. Stratification is small scale and results from alternation of thin, silty shale, sandstone, and conglomerate. Embedded clasts in stratified diamictite seldom exceed 12 percent of the total rock; locally, there are patches as large as 4 m2 in which the embedded clasts are greater in number and closely spaced (Fig. 7B) forming "grouped" clasts (Frakes and Crowell, 1967, p. 44). The matrix is generally better sorted in stratified than in massive diamictite units. At one outcrop of upper diamictite unit B, thin (5 to 10 cm) sandstone interbeds show on upper bedding surfaces asymmetric to interfering (linguoid) ripple marks (Fig. 7C); the interbed subjacent to the diamictite exhibits fine unidirectional, miniature grooves. These parallel grooves or striae are as much as 8 cm wide and 2 cm deep and occur beneath a diamictite unit or within it (Fig. 6); they resemble drag marks on soft sediment. The north-south orientation of grooves closely cor- responds with the fabric of embedded clasts (see Fig. 9). Other features of stratified diamictite are spherical nodules of silty limestone (5- to 20-cm diam.), which occur on the upper surface of diamictite unit B (Fig. 7D). Polished sections through the nodules show internal faint laminations that pass laterally into the host rock. This suggests that the nodules are syngenetic and that the local environment allowed deposition of carbonate (mainly cal- cite) around centers of nucleation.

Fine-Grained Clastic Assemblage The fine-grained clastic assemblage is predominantly medium- to fine-grained sandstone, interbedded sandstone and shale, and relatively pure shale (Table 1). The sandstone, commonly called "Tal- chir sandstone," forms distinct units (Al, A3, Bl, and CI) above to soft-sediment deformation caused by mass movement in either a the diamictite units (Figs. IB and 2). These sandstone units may be nonglacial or glacial environment of deposition (Crowell, 1957, massive or horizontally bedded, but occasionally they show small- 1964; Lindsay, 1966; Frakes and Croweli, 1967, 1970, Table 1). and large-scale cross-bedding and symmetric or asymmetric ripple Wedge-shaped sand bodies plus sandstone and conglomerate lenses marks. Lower and upper contacts are usually even and conforma- in diamictite have been related to glacial deposition by Frakes and ble, which implies continuous deposition. The lower surface of the Crowell (1967, p. 47), Frakes and others (1968), Casshyap (1969), third sandstone unit (Bl) is strikingly uneven and irregular at sev- and Lindsay (1970). Alternatively, the wedge-shaped sand bodies eral places, however. Fluid-laden, unconsolidated diamictite, be- may represent outwash channels cut into till, eskerlike bodies, or neath more competent sand, flowed laterally or was differentially

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stone, shale, and carbonaceous shale (unit Dl). The lower conglomeratic sandstone assemblage (about 10 m thick) includes small patches of pebble- and cobble-conglomerate in the basal part at some localities. Most of the clasts show, however, polymictic composition and a range of shape and sphericity similar to those of the underlying diamictite units. Significantly, the abundance of sedimentary clasts decreases and roundness of clasts increases slightly (0.5 to 0.7) without regard to size or lithologic type. The conglomeratic sandstone is both cross-bedded and horizontally bedded and contains a small proportion of reworked underlying material including small fragments of green shale. The 40-m-thick uppermost unit (Dl) consists of interbedded sandstone, siltstone, and shale. It exhibits sedimentary characters grossly similar to those observed in the fine-grained clastic assemblage described earlier. This sequence commonly includes lenses of carbonaceous shale in the upper part near the contact with the overlying coal-bearing Barakar Formation.

SEDIMENTARY CYCLES Previous workers did not recognize sedimertary cycles in the Talchir strata. It is clear from this investigation that the Talchir strata in the area studied are composed of four distinct cycles, all of which are lithologically similar. Ideally, the lower part of each of the first three cycles contains diamictite overlain by an interbedded assemblage of fine-grained clastic rocks, which include sandstone, siltstone, and shale. Tiese repetitive diamictite subsequences are characterized by a vertical decrease in grain size; and are similar to fining-upward cycles (Fig. 2). The lithologic types in a Talchir cycle in ascending order are (1) diamictite; (2) sandstone; (3) interbedded fine-grained sandstone, siltstone, and shale; and (4) shale. The fourth cycle forms the upper part of the Talchir Formation (transitional assemblage) and demonstrates a vertical gradation of size from coarse to fine; the only difference is that the diamictite of lower cycle units is replaced by conglomeratic sandstone. A similar lithologic sequence was recently reported for the Dwyka tillite series in Rhodesia (Bond and Stocklmayer, 1967). Figure 6. Groove marking on a sandstone sliver embedded in a massive diamictitc in This proposed cyclic sequence for the Talchir Formation should eastern part of study area. About 1 km northeast of Khirsadoh railway station. be regarded as "idealized" (Duff and others, 19(57) in that cycles do not always contain all the lithologic types in the same sequence. In compressed by weight of the sand body (Fig. 8A). Thus, blocks of the study area, cyclic units commonly occur in the following se- sand foundered into the soft, muddy substrate (Lawrence A. quence: 1—»2—»3;l--»2—»4;1—»2—>3—»4. Frakes, 1973, written commun.). Interbedded sandstone and shale (12 to 15 m thick) occur prominently in the lower diamictite unit SEDIMENT TRANSPORT DIRECTION above sandstone A1 and in the upper diamictite unit above sand- AND PALEOSLOPE stone CI. The latter contains some asymmetric ripple marks or Paleoslope determination is based on systematic measurements successive bedding planes. of (1) dimensional pebble fabric (982 azimuths of apparent long Shale beds are typical of green "Talchir shale" or "needle shale," axes of embedded clasts after the method suggested by Pettijohn so-called because they weather into small, needlelike fragments. [1962]); (2) 26 azimuths of parallel striations on clasts and upper These laminated and calcareous shale beds locally include thin surfaces of sandstone interbeds; and (3) 62 cross-bedding dip lenses of marl. The laminations are closely spaced and parallel, azimuths, 24 azimuths of ripple asymmetry, and 8 ripple-crest regular to uneven, and moderately continuous in outcrop. There azimuths from sandstone. are minor, thin (1.0 m), discontinuous interbeds of shale in diamic- Figure 9 is a composite representation of the paleocurrent data. tite unit C. The interbeds show fairly regular alternation of coarse- Azimuthal distribution of apparent clast long axes is bimodal with and fine-grained silty laminations. These laminite beds closely re- both modes confined to the northwest-scutheast quadrants. semble varves (Fig. 8B). Isolated clasts, sometimes showing Bimodal fabric in Talchir diamictite has been reported from several scratches or subparallel striations, also occur in the shales as other areas (Ganju arid Srivastava, 1959; Srivastava, 1961; Ghosh "lonestones" (Fig. 8C). Penetration and deformation of lamina- and Mitra, 1967), and, with a few exceptions, :he principal mode is tions below a lonestone are slight or indistinguishable from the approximately north-south. The regional similarity of Talchir fab- later effects of compaction. Several workers elsewhere (see Oven- ric is a significant and possibly primary feature, inasmuch as post- shine, 1970) have noted such possibilities in laminated shale beds depositional deformation of Gondwana rocks is known to be mini- containing lonestones. mal throughout the Indian peninsula. Striations are also oriented southeast-northwest (Fig. 9). Conglomeratic Transitional Assemblage The sediment-transport direction and the paleoslope can be de- This sequence forms the upper part of the Talchir Formation in termined from primary depositional structures in sandstone as- the study area and is particularly well exposed south of the village sociated with diamictite. Cross-bedding foresets and ripple-mark of Nazarpur (Fig. IB). Its lower contact with the underlying green asymmetry yield vector mean values of 355° and 345°, respectively. laminated shale is uneven and possibly erosional (Fig. 8D). It has been shown elsewhere (Casshyap and Qidwai, 1971) that the Lithologically, this subdivision is composed of a lower conglomera- paleocurrent system was practically constant throughout Early tic sandstone (unit D) and an upper interbedded sandstone, silt- Gondwana time in the Pench Valley coalfield, flowing predomi-

Figure 7. A, typical outcrop of stratified diamictite (lower part of unit B) showing and asymmetric straight ripples; the uppermost bed in the foreground shows also thin, discontinuous intercalations of fine sandstone and mudstone. Pebbles and cob- parallel groove markings. Note on the left side of hammer hollows made by cobbles. bles are sparingly distributed. About 2 km southeast of Khairwani. B, grouped clasts Bhangi rivulet, about 200 m northeast of Chatua. D, small spherical calcareous in the lower part of stratified diamictite (unit B). About 1 km northwest of Khajri vil- nodules contained in diamictite unit C. Alongside of creek about 1 km north of Budh- lage. C, thin sandstone interbeds in diamictite unit B. Each sandstone shows linguoid wara.

nantly from south to north. A northward-directed paleoslope is evidence cited in support of glacial origin includes the occurrence therefore most likely for the Lower Gondwana rocks of the Pench of striated bedrock (reported with certainty from only one locality Valley basin. In terms of provenance, the embedded clasts of the in central India; Fedden, 1874; Smith, 1963), the presence of diamictite and mineral assemblages of sandstone of the Talchir and striated and faceted clasts, and poorly sorted texture and polymic- succeeding Lower Gondwana formations correspond to Precam- tic composition of the diamictite units. Despite intensive search, brian source rocks exposed south of the study area (Qidwai, 1972, striated bedrock could not be found in the study area, nor has it his Fig. 39). been reported from the adjoining Kanhan Valley coalfield to the west. Striated bedrock may not be developed at subaqueous dep- ORIGIN ositional sites (Harland, 1965; Frakes and Crowell, 1969). In other The origin of rocks containing such a great disparity of particle parts of Gondwanaland where the equivalent Permian- sizes must be the depositional product of a high-density or high- Carboniferous and Permian deposits have been ascribed to glacial viscosity medium, namely, a glacier, turbidity current, or mass origin, striated bedrock seldom occurs (Frakes and Crowell, 1967, movement. Poor sorting of clasts and abundant detrital matrix in 1969,1970). the Talchir diamictite, described earlier, suggests transport by a Numerous depositional features in the Talchir diamictite units high-density medium. Features, such as the abundance of basal and associated strata suggest a glacial origin. The following fea- facets in embedded clasts, their pentagonal flatiron shape, and pres- tures are of particular genetic significance: (1) parallel miniature ence of subparallel striae, as well as the nature of clast fractures, grooves or striae on upper surfaces of sandstone lenses that lie tend to imply ice transport (Thornbury, 1954; Flint, 1961; Frakes within or beneath a diamictite, (2) stratified diamictite units that and Crowell, 1967). locally contain grouped clasts, (3) wedge-shaped sandstone bodies and other sandstone and conglomerate lenses embedded in diamic- Glacial Origin tite, (4) striated and fractured embedded clasts, (5) laminite beds Blanford and others (1856) perhaps first reported the possibility enclosing lonestones, and (6) a wide geographic distribution of of glacial origin for the Talchir "Boulder Bed" in the type area of diamictite units across the Indian peninsula. the Talchir coalfield of Orissa State. Subsequently, the glacial con- Striated sandstone bodies are of particular interest, inasmuch as cept was extended to include all Talchir diamictite of the Indian the grooves or striae show north-south orientation that corre- peninsula (Fedden, 1874; see also Fox, 1931; Pascoe, 1959). The sponds with the principal maximum of pebble fabric (Fig. 9); in

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Figure 8. A, outcrop showing dismembered sandstone with lower contact highly irregular. The diamictitc below lias been injected between blocks. About 1.5 km east of Chatua. B, more or less rhythmic alternation of coarse- and fine-grained siltstone locally characterizes a shale interbed in diamictite. Such sequences, not too common, closely resemble "varves." Bhanjii rivulet, about 2 km east of Cha tua. C, Talchir shale, which breaks into needle-like fragments, shows as lonestones a cobble and a pebble; 0.5 km west of Bhadri village. D, Uneven upper contact of gr;en shale overlain by conglomeratic sandstone of th - transitional assemblage. Ahnit 2 km south of Nazarpur.

diamictite may indicate sand fillings in open fissures of frozen till (Frakes and others, 1968), but ice wedges causing fissures generally are much deeper than wide. Alternatively, these wedge-shaped bodies may be outwash-channel fillings in till or eskerlike bodies that have been engulfed by till at a later stage. Likewise, thin sandstone and conglomerate lenses that are moderately sorted and thinly bedded to cross-bedded can be interpreted as eskerlike sand and gravel bodies. The surfaces of pebbles; and larger clasts in diamictite and shale often include facets; some facets are striated like those developed in till and may be attributed to grinding action of clasts in the matrix during ice transport (Longwell and others, 1969, p. 269). Some some outcrops, cobbles are embedded or their molds occur near the clasts showing wide fractures are filled with the same material grooves or at their far end (Fig. 7C). Elsewhere, striated sand bodies which constitutes the matrix of the enclosing diamictite. This fea- similar to these have been interpreted as soft-sediment pavement ture may represent fracturing by freezing and thawing of ice (Har- developed when individual clasts were "dragged by the ice at the land and others, 1966; Lindsey, 1969). Laminated green shale depositional interface" (Lindsay, 1970, p. 1161). Stratified diamic- above diamictite, containing striated lonestones (possibly drop- tite showing local concentration of stones similar to grouped clasts stones), resembles varves and implies that lacustrine conditions de- may represent subaqueous deposition by iceberg rafting (Reading veloped locally and favored seasonal deposition of coarse and fine and Walker, 1966), and (or) overturned fragments of icebergs silt. [Ovenshine, 1970, p. 891). Wedge-shaped sand bodies in massive Apart from the above characteristics, Talchir diamictite units

N bidity currents may have redistributed glacial debris to form the Talchir sandstone and shale of Raniganj coalfield in West Bengal (Banerjee, 1966). Subaqueous or subaerial mass-flow processes are unlikely agents of Talchir diamictite deposition because (1) the Dimensional diamictite shows a wide areal distribution across the shield area of Fabric the peninsula, and no local or regional evidence exists for size gradation of embedded clasts from the proximal (south) to the distal N = 982 (north) end; (2) twisted and deformed inclusions of sandstone and ?v = 324° —144° shale in diamictite beds are not abundant and rarely exceed 2 m in L -28% greatest dimension; (3) striae showing subparallel patterns on the S2 • 2265 surfaces of embedded clasts are common; (4) clasts in diamictite S • 47 show preferred orientation locally in the area studied and region- ally in other areas of Talchir exposures; and (5) inverse grading, which characterizes debris-flow deposits (Fisher, 1971), seldom occurs in diamictite. Nevertheless, the presence of small deformed and partially broken lenses of sandstone in diamictite suggests that mass movements may have been active periodically during or after deposition. It is clear that neither turbidity currents nor mass movements can account for the origin of Talchir diamictite and associated rocks. On the other hand, lithologic, sedimentary, and stratigraphic features provide evidence that is strongly suggestive of glacial origin. LEGEND 157° Subaqueous (Possibly Marine) Origin Mean pebble orientation (5182) Some Talchir diamictite units show stratification and include Mean cross - bedding azimuth (62) thin intercalations of shale and sandstone. Moreover, each diamic- Mean ripple asymmetry (24) tite unit is associated with a thick assemblage of sandstone, interbedded fine-grained clastics, and shale. The most common primary \ Mean striation azimuth (26) depositional structures are horizontal bedding; thin, continuous laminations; cross-bedding; grouped clasts and lonestones; as well as fragments of plant fossils. These features, which suggest suba- ( Figures in parenthesis refer to queous deposition, characterize the Talchir strata in most other the total number of readings) parts of the Indian peninsula and indicate that, during Talchir Figure 9. A composite rose diagram for Talchir rocks showing the azimuthal dis- time, subaqueous environments existed in the area studied and tribution of apparent long axes of clasts embedded in diamictite; plotted also are mean elsewhere. Massive diamictite units lack direct evidence of suba- values of other paleocurrent data recorded from interbedded sandstone. N = number 2 queous deposition, and they could have been laid down terrestrially of readings; 9V = vector mean; L = vector strength; S = sample variance; S = stan- dard deviation. but not far from the shoreline. In several coalfields of eastern India, the diamictite assemblage and associated deposits show a wide geographic distribution across and related sediments have been interpreted by previous workers as the Indian peninsula and are known to occur from Maharashtra in glaciofluvial deposits. The discovery of marine fossils in Talchir the west through West Bengal in the east, for about 2,000 km. diamictite in some parts of east-central India indicates a marine en- Throughout this length, however, th; diamictite deposits do not vironment of deposition for these areas, however (Krishnan, 1960, show any striking change in lithologic type or other sedimentary p. 280; Sastri and Shah, 1964; Ahmad, 1970). Marine fossils simi- characteristics. Wide areal distribution and uniformity of diamic- lar to these have also been reported in the area near Rangit valley of tite have often been cited as strong evidence for glacial origin (Har- Sikkim from strata reportedly equivalent to Talchir (Krishnan, land, 1965; Harland and others, 1966), and several ancient tillites, 1960, p. 283). Marine fossils in Talchir diamictite have not been including the well-known Gowganda tillite of Ontario, Canada, widely reported from the Indian peninsula, nor were any found in and the Dwyka tillite of southern Africa, are known to occur over a the study area. The lack of marine fossils in the study area is no vast area comparable to that of Talchir diamictite. criterion to discount a marine environment. There are numerous examples in other parts of the world where the regional distribu- Turbidity-Current or Mass-Movemeni: Origin tion of diamictite and the related sedimentary evidence have been Turbidity currents or mass movements, either subaqueous mass employed to invoke a glaciomarine environment for unfossilifer- movements, subaerial mudflows, or debris flows, can produce de- ous tillites (Frakes and Crowell, 1967; Lindsey, 1971; Aalto, posits resembling diamictite and related sedimentary rocks 1971). (Kuenen, 1950; Crowell, 1964; Dott, 1961; Lindsay, 1966; Fisher, 1971). Sedimentary characteristics of turbidity-current deposits are EVOLUTION OF TALCHIR SEDIMENTATION distinctive and generally diagnostic ol the corresponding process. A series of interpretative diagrams demonstrates the progression Subaqueous or subaerial mass-flow deposits are often difficult to of glacial, interglacial, and postglacial sedimentation (Fig. 10). The separate from glacial deposits on the basis of texture as well as in character of Talchir diamictite can satisfactorily be explained by terms of primary bedding structures, especially if mass flows were envisioning a glaciomarine model of sedimentation (Carey and fluid-laden and interbedded with terrestrial deposits such as sand- Ahmad, 1961; Reading and Walker, 1966). A comparable though stone and shale. For Talchir diamictite, no one has yet postulated not identical interpretation, as far as the climate and environment turbidity currents or mass movements £.s the only process of deposi- of deposition are concerned, exists for other diamictite units of tion. Talchir rocks seldom exhibit repeatedly graded and convolute Gondwanaland recently examined by John C. Crowell and Law- bedding, sole marking, or regular alternation of thin beds; indi- rence A. Frakes and referred to above. vidual strata lack lateral continuity. This discounts turbidity cur- In view of the faulted contact, the oldest Talchir strata that may rents as a dominant mechanism of Talchir deposition. Locally, tur- have rested directly on the Precambrian basement are not exposed

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Second Interglacial Shallow-water Zone

Second Glaciation Shallow-water Zone Lower Tillite 13

First Interglacial Marginal and deeper water Zone

High Shore Line

First Glaciation Terrestrial Zone Tillite A

m 250

Approximate Scale # Q 20 km Figure 10. Diagram marie sections illustrating the evolution of Talchir sedi men cation in the Pench Valley area.

in the Pench Valley area. Diamictite unit A probably represents the the final withdrawal of the shoreline from the area because of iso- first glacial advance in the study area. The 32-m-thick diamictite is static recovery. The transitional assemblage is a fining-upward se- massive and unstratified, laterally extensive, exhibits a bimodal quence in which the lower conglomeratic feldspathic sandstone fabric, and is practically devoid of twisted sandstone inclusions. (unit D) is profusely cross-bedded and the upper medium- to The evidence suggests that this diamictite may have been deposited fine-grained sandstone, siltstone, and shale (unit Dl) show small- as a till from a terrestrial wet-based glacier. The shoreline, because scale cross-bedding and parallel lamination and include pebbles of eustatic adjustment to ice-sheet growth, may have receded to the and cobbles. Much of the transitional assemblage exhibits charac- north and east. Wedge-shaped sandstone inclusions and sporadic teristics similar to glaciofluvial outwash. There is evidence in the cross-bedded sandstone lenses in the tillite may be interpreted as Pench Valley coalfield (Fox, 1934; Casshyap and Qidwai, 1971; channel sand and subglacial esker sand deposited locally by melt- Qidwai, 1972) and elsewhere in the Indian peninsula (Fox, 1931; water. Alternatively, wedge-shaped sandstone inclusions might Krishnan, 1960; Casshyap, 1973) that the overlying Lower Gond- have formed as sand fillings in open fissures in frozen till. As the ice wana strata, from the Barakar Formation upward, are typically melted and receded southward, the shoreline transgressed south- fluvial in origin and laid down in extensive alluvial plains. ward into the study area, heralding the first interglacial period during which an assemblage of sandstone (unit Al), alternating thin CONCLUDING REMARKS beds of green shale and fine-grained sandstone (unit A2), plus sand- The glacio-marine model visualized in this paper calls for re- stone (unit A3) was deposited successively on top of lower diamictite examination of Talchir diamictite in several other critical regions of (tillite) unit A. Ripple-marked medium- to fine-grained sandstone east-central and eastern India and in the type area of Orissa. To of unit Al may represent deposition under shallow water; the al- what extent the glaciomarine model proposed herein is applicable ternating shale and fine-grained sandstone (unit A2) suggest depo- in these areas is a matter of future research. Those areas where Tal- sition under quiet and relatively deeper water. Sandstone unit A3 chir diamictite lies directly on the Precambrian basement are of contains isolated lenses of ripple marks; this could reflect a gently vital genetic and paleogeographic interest. In addition to a clearer turbulent environment. Increased turbulence may indicate a slight understanding of paleogeography during Talchir time, future re- withdrawal northward of the shoreline because of isostatic recov- search should help locate the area(s) within or beyond the present ery or, more probably, in response to the second advance of the ice limits of the Indian peninsula where the ice sheets originated. that resulted in the deposition of the overlying middle diamictite (tillite) unit B. ACKNOWLEDGMENTS The middle diamictite represents the second glacial advance. In We are grateful to N. Ahmad, V. K. Srivastava, and F. Ahmad the lower part, it is partially stratified, locally includes grouped for encouragement, discussions, and advice at different stages of clasts and lenses of conglomerate, and contains matrix that is silty, the work. Zahid A. Khan assisted us in the field and in rechecking sandy, and calcareous. This unit is probably of subaqueous origin. computations. John C. Crowell, Lawrence A. Frakes, M. Schwarz- It is possible that the ice advanced or calved into the adjacent body bach, and Chester A. Wallace critically read an early version of the of water and icebergs may have rafted till seaward. The overlying manuscript and made helpful suggestions for its improvement. diamictite is massive and structureless. Locally, it includes twisted This research was accomplished when one of us (Qidwai) was a and slumped lenses in the middle part, and thin interbeds of sand- Senior Research Fellow of the Council of Scientific and Industrial stone showing ripple marks and soft-sediment pavement in the Research, Government of India. We gratefully acknowledge the upper part. The above characters suggest deposition first in a ter- financial support of the CSIR during this research. restrial or grounded-shelf zone and subsequently in the adjoining inner margin of the shallow-water (possibly floating shelf) zone. 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