Okada (1971), Folk (1980) and Dickinson (1985). ..... Ganga sediments (based on Dickinson 1985). .... Professor Edward Derbyshire thoroughly reviewed the.
Tectonic setting and sedimentology of Ganga River sediments, India ADAL SINGH, BISHESHWAR D. BHARDWAJ AND ABUL H. M. AHMAD
Born
Singh, A., Bhardwaj, B. D. & Ahmad, A. H. M. 1993 (March): Tectonic setting and sedimentology of Ganga River sediments, India. Boreas, vol. 22, pp. 38-46. Oslo. ISSN 030-9483, The Ganga basin provides a present-day example of a peripheral foreland basin. The course of the river is controlled by Himalayan tectonics. Three main types of architectural elements, such as channels (CH), sandy bedforms (SB) and overbank fines (OF) have been developed in Ganga River sediments. The channels (CH) include gravelly (Gs) and sandy channel (Ss) lithofacies. The sandy bedforms (SB) include trough crossstratified (St), planar cross-stratified (Sp), horizontal stratified (Sh), sandy massive (Sm) and climbing ripple cross-laminated (Sr) lithofacies, all of which are active channel deposits. The overbank fines (OF) include massive silt and clay (Fm), parallel laminated silt and clay (FI) and climbing ripple cross-laminated (Sr) lithofacies. Mega units have been developed in the lower part of the active channel deposits, while small units have been developed in the upper part of active channel deposits, in inactive channel deposits and overbank fines. This study illustrates the seasonal and tectonic control on sedimentation. Petrofacies studies of the sediments indicate a recycled orogen provenance. The sediments are derived from rapidly uplifted fault blocks comprising granite, gneiss and basic and ultrabasic rocks. Lack of textural and compositional maturity suggests a local source of derivation. The principal control on sand composition is source lithology. The hot and humid climate may slightly increase the content of quartz in sand derived from reworked foreland basin sediments. but the effect is neither sufficient to shift the sand compositions out of the recycled orogen field nor does it obscure composition mixing patterns. Ada1 Singh, Bisheshwar D . Bhardwaj and Ahul H . M . Ahmad, Department of’ Geology. Aligarli Muslim University, Aligarh-202002, India; 2nd February. 1992 (revised 5th October, 1992).
Sedimentation processes and petrography are greatly influenced by tectonic setting and climate, particularly in alluvial basins. The Indo-Gangetic basin, drained by a network of large and small river system provides a classic example of a present-day peripheral foreland basin (Mitchell & Reading 1986: 514), situated south of the rising Himalaya. The floor of the basin is marked by lineaments, faults and regional highs (Fig. 1). The Ganga basin is being filled, over the past 10,000 years, at a fast rate and is rapidly growing out into the Bay of Bengal, where new islands are being deposited, such as the New Moore (Valdiya 1984: 218). The reason is that the rate of basin floor subsidence is less than the sediment supply rate. The basic objective in the study of the Ganga sediments is to generate a modern analogue of an alluvial basin in an existing climatic and tectonic setting, as a model for understanding similar processes in the geological past. The monsoon-type climate causes both very high and very low seasonal water and sediment discharges and provides an example of facies architecture for modern alluvial basins. Recently the Ganga sediments have been studied by Singh & Bhardwaj ( 1991a, b) and by Bhardwaj & Singh (1992). The detrital mineralogy of the Ganga sediments is presented in order to make a petrographic classification and an interpretation for provenance and to describe the depositional history and tectonic setting of this modern peripheral foreland
basin. Much work has been done on sandstone classification during the last four decades, and important contributions have been summarized by Klein ( 1963), Okada (1971), Folk (1980) and Dickinson (1985).
Investigation area The present study was made from Hardwar to Kachhla, which lie in the West Uttar Pradesh as shown in the tectonic map of the Ganga basin (Fig. 1). Upstream of Hardwar, the River Ganga is confined by narrow valleys and downstream it emerges on to a plain. The gravelly zone where the river emerges on to a plain from the mountains is called the bhaber zone, which is a zone of braided channels and infiltration of surface waters.
Methods The field work was carried out in the months of March and April when the different geomorphic features were well exposed. Trenches were dug using a shovel in order to expose the three-dimensional geometry of the deposits. The different architectural elements, bounding surfaces, sedimentary facies and lithology were observed.
Ganga River sediments
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KmlooSo 0
1 0 0 Km
1
39
T X T T H R U S T S ( L I M l T I N G T H E P L A T F O R M MARGIN) 7 OTHER F A U L T S
I
I
Fig. 1. Tectonic map of the Ganga basin and adjoining areas (mainly compiled from the tectonic map of India, 1968, provided by the Oil and Natural Gas Commission).
Architectural elements and lithofacies classification The term ‘architectural element’ was coined by Allen (1983). Miall (1985, 1988a) described these elements and provided the current state of knowledge of them. The elements that occur in the Ganga sediments are described below. The lithofacies codes given follow Miall (1978).
Channels (CH). - In this element both the gravelly (Gs) and sandy channels (Ss) lithofacies types are
developed in the Ganga sediments. The gravelly channel lithofacies is developed only in the Hardwar area (Fig. 2). However, the sandy channel lithofacies is frequently developed from Hardwar to Kachhla. The lower bounding surfaces of these lithofacies are concave upward (Fig. 2) while the upper bounding surfaces are flat or convex upward. The convex-up form of the upper bounding surface is caused by erosion on the stoss side of the bar, while deposition takes place on the downstream end (Miall 1988a). Sandy channel lithofacies are mainly associated with climbing ripple cross-laminations. The gravelly channel lithofacies in-
40
Ada1 Singh et al.
HARDWAR
BOREAS 22 (1993)
SHERPUR
GARHMUKTESHAR
RAJGHAT
HACHHLA
Fm 8,
SI
FI
.Fc --
-
st Sr ---_
st 8 ss Sh
Sr
st Sm SP
Fig. 2. Vertical lithofacies sequences at Hardwar, Sherpur, Garhmukteshar, Rajghat and Kachhla. For geographical overview, see Fig. I .
dicates high seasonal flood flows, while the sandy channel lithofacies is the result of vertical aggradation (Collinson 1978; Singh & Bhardwaj 1991a). Sandy bedforms (SB). - Sandy bedforms consist of trough cross-stratified (St), planar cross-stratified (Sp), horizontal stratified (Sh), sandy massive (Sm) and climbing ripple cross-laminated (Sr) (Fig. 3) lithofacies (active channel deposits). The bounding surfaces of these lithofacies are parallel. This parallelism suggests that they are accretionary growth surfaces rather than erosion surfaces. The St lithofacies developed due to migration of dunes (lower flow regime conditions), while the Sp lithofacies resulted from migration of straight crested mega-ripples (Miall 1988a; Singh & Bhardwaj 1991a). The Sm and Sh lithofacies developed due to transportation of sediments in planar sheets (upper flow regime conditions) (Casshyap & Kumar 1987; Desloges & Church 1987; Singh & Bhardwaj 1991a) whereas the Sr lithofacies developed due to an abundant supply of sediments in suspension (Lindholm 1987; Singh & Bhardwaj 1991a).
Overbank fines (OF). - Overbank fines are characterized by massive silt and clay (Fm), parallel laminated silt and clay (FI), convolute lamination (Fc), lenticular sandy (Sl) and climbing ripple cross-laminated (Sr) lithofacies (Fig. 3). Bounding surfaces o f these deposits are parallel. These deposits are marked by sheet-like geometry, reflecting their origin by vertical aggradation. The Fm lithofacies result from heavily sediment-laden water currents during waning periods of a flood stage (Morison & Hein 1987; Singh & Bhardwaj 1991a). The FI lithofacies consisting of mica and clayey material indicates suspension conditions, whereas mica-free lamination and silty material indicate high velocity currents and low depth (Collinson 1986; Paola et al. 1989; Singh & Bhardwaj 1991a). Fc lithofacies is the result of pore fluid expulsion generated during loading of overlying sediments (William & Rust 1969; Morison & Hein 1987; Singh & Bhardwaj 1991a). Lithofacies Sp may represent washed-out dunes or upper flow regime planebed deposition over underlying bar deposits ( Miall 1988a).
BOREAS 22 (1993)
Ganga River sedimenrs 41
Fig. 3. Section showing mega-unit (active channel) and small scale unit (inactive channel) of climbing ripple cross-laminated sandy facies.
Composition of sands
Quartz is the most abundant grain type. The variIn the present study, the detrital mineral composition ous quartz types include common quartz, vein quartz, of the Ganga sands was evaluated in 84 thin sections. recrystallized metamorphic quartz and stretched metaThese include, 34 samples from the Hardwar sector, morphic quartz. Quartz grains are subangular to sub25 samples from the Rajghat sector and 25 samples rounded. Both sedimentary and metamorphic rock fragments from the Kachhla sector. For quantitative analysis about 400-500 grains were counted, as recommended occur. Sedimentary rock fragments include shale and by Griffiths (1967). K-feldspar grains were identified chert. Metamorphic rock fragments include phyllites, by staining with sodium nitrocobaltate solution. The micaceous quartzite and schists. The feldspars include orthoclase, plagioclase and recent sediments are coarse to fine grained, and moderately well sorted to moderately sorted. The grains microcline. Feldspar grains are generally subequant are generally subangular to subrounded. The detrital with mostly subrounded to well-rounded outlines. constituents include mainly several varieties of quartz, Some angular to subangular grains also occur. The sedimentary and metamorphic rock fragments, feld- feldspars are mostly fresh, but altered ones are also spar, mica and heavy minerals (Table 1). According to seen in some samples. Muscovite occurs as tiny to large elongate flakes Folk’s ( 1980) classification, the sandstones are predominantly sublitharenite. with frayed ends. Table 1. Ranges and averages of detrital minerals in the Ganga River sediments.
Hardwar sector: Range average Rajghat sector: range average Kachhla sector: range average
Monocrystalline quartz
Polycrystalline quartz
Common quartz
Vein quartz
Recrystallized metamorphic quartz
Stretched metamorphic quartz
Mica
Feldspar
Rock fragments
Heavy minerals
59 - 82 70
0-2 1 .o
3-18 8.0
1-2 2.0
2-6 3.0
2-4 3.0
1-5 2.0
5-14 II
68-76 73
-
4-9 6.0
0-2 2.0
3-4 3.0
2-3 3.0
5-7 6.0
5 - 10 7.0
64-84 74
0-2
2-9 5.0
1-6 3.0
1-4 2.0
2-4 2.0
2-9 5.0
2- I4 7.0
1 .o
42 Ada1 Singh et al.
Heavy minerals Tourmaline. - Tourmaline is the most abundant heavy mineral in the Ganga sands. The green variety is dominant, others are greenish brown and blue. The grains are prismatic, subrounded to well rounded. Garnet. - The colourless variety is most abundant, followed in frequency by light pink, brown and red coloured varieties. Grains are marked by pitted surfaces, and are sharply chipped and subangular to subrounded. Zircon. - The most commonly occurring variety is colourless, followed in frequency by pink and light yellow varieties. Most grains show abraded margins and are angular to subrounded. Some are pyramidal in shape. Opaques. - Three varieties of opaques (in reflected light) are hematite (reddish brown), magnetite (silver black) and limonite (yellowish brown). The grains are angular to subrounded. Titanite. - Titanite shows brown, brownish yellow or yellowish green colours. The grains are irregular in shape. Spinel. - Red, reddish yellow and light green spinel varieties occur in the Ganga sands. The grains are rounded to slightly worn octahedra, marked by conchoidal fractures. Sillimunite. - A colourless variety is dominant, followed by a green variety. The grains occur as slender prisms or fibers with fractured or irregular terminations. Chlorite. - Occurs as flat, rounded and irregular flakes. The grains are pale green to dark green, with black spots. Hornblende. - Shows a characteristic green colour. Usually the grains are elongated and irregularly terminated. Kyunite. - Only colourless kyanite has been identified in the Ganga sands. The grains are subangular to subrounded and elongated, marked by rectangular outlines. Epidote. - Pale greenish yellow, lemon yellow, and dark green varieties have been identified. The grains are irregular, subangular to subrounded. Stuurolite. - Two varieties, straw yellow (dominant) and brownish yellow have been identified. The grains are irregular, subangular to subrounded, with subconchoidal fractures.
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Anatase. - Anatase grains are rectangular, subhedral in form and frequently show ‘geometric patterns’. Hypersthene. - Of greyish green and pale green colour. Usually occurs as prismatic, subangular or subrounded. Actittolitel Tremolite. - Actinolite is green, whereas tremolite is colourless. Generally the grains are irregular, elongated and prismatic. Actinolite grains have a fibrous structure. Zoisite. - Various varieties of zoisite, such as yellowish brown, pale green and colourless, have been identified. It occurs as prismatic grains. Rutile. - Rutile grains are angular to subangular. Elongate prismatic forms occur with rounded pyramidal ends. Apatite. - The apatite grains are colourless, hexagonal. Most of the grains are rounded.
Petrofacies and tectonic setting Dickinson & Suczek (1979) and Dickinson (1985) have emphasized the role of plate tectonics in determining the composition of the sandstone suite on a regional scale. Plate tectonics control the distribution of different types of sandstones because they govern the key relations between provenance and basins. However, the composition of sandstones is also affected by factors others than tectonic setting, including transport history (Suttner 1974; Franzinelli & Potter 1983), sedimentary process within the depositional basin (Davies & Ethridge 1975) and palaeoclimate (Basu 1976, 1985; Suttner et ul. 1981). Classification of sandstones according to Dickinson’s (1985) scheme was attempted and detrital modes were recalculated to 100%)as the sum of Qt, Qm. F, L, Lt (Tables 2 and 3). When plotted (Figs. 4A, 4B, 5A, 5B), the sands show compositional field characteristics of different provenances, Qt- F-L emphasizes maturity, whereas Qm- F- Lt emphasizes primary deposition from source rocks. Both Qt-F-L (Fig. 4C and E) and Qm-F-Lt (Fig. 5C and E) plots show that the studied samples fall mainly within the recycled orogen area. Both fields further suggest that the sediments were derived mainly from recycled orogen provenance.
Provenance The present study reveals that the Ganga sediments derive from a variety of Himalayan rocks. The occurrence of brown tourmaline reveals derivation from
Ganga River sediments
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Table 2. Explanation of recalculated petrographic parameters of sandstone point counts (after Dickinson 1985). A. Quartzose grains
B. Feldspar grains
C. Unstable lithic fragments
D. Total lithic fragments
43
Table 3. Ranges and averages of percentages (see Table 2) in the Ganga sediments (based on Dickinson 1985).
(Qt = Qm + Qp) Qt =total quartzose grains Qm = monocrystalline quartz grains Qp = polycrystalline quartz grains ( F = P + K) F = total feldspar grains P = plagioclase feldspar grains K = potassium feldspar grains ( L = Lv + Ls) L = total unstable lithic fragments Lv = volcanic/metavolcanic lithic fragments Ls = Sedimentary/metasedimentarylithic fragments (Lt = L + Q p ) Lc = extrabasinal detrital limestone clasts (not included in L or Lt)
Hardwar sector: range average Rajghat sector: range average Kachhla sector: range average
Qt
F
L
Qm
F
Lt
90-96 93
2-5 3.0
2-7 4.0
72-90 834
2-5 4
8-25 13
89-94 91
3-4 3
2-8 6
83-88 85
3-4 3
8-14 12
88-96 92
2-4 3.0
2-10 5
76-90 83
2-6 3
8-20 14
wise, the occurrence of various shades of garnet indicates different source rocks; colourless garnet is derived from schists, light pink from acid igneous rocks, such as granite, and red garnet from crystalline gneisses and schists. Apatite may have been derived from acid igneous rocks and pegmatites ( Friedman & Johnson 1982). Muscovite indicates low-grade metamorphic rocks whereas epidote indicates crystalline metamorphic rocks. Hypersthene may have been derived from intermediate to basic and ultrabasic
pegmatized injected metamorphic terranes, green from granitic rocks and blue from pegmatites (Singh & Bhardwaj I991b). The occurrence of well-rounded tourmaline reveals its derivation from a pre-existing sedimentary source (the Siwalik rocks), indicating polycyclic transport (Singh & Bhardwaj 1991b). Like-
CONTINENTAL
INCREASING
L
B
A
C
Qt
Qt
D
E
Fig. 4. Classification (Qt) of sandstone ( A and B) according to the principles of Dickinson ( 1985). Plot C is of samples from the Hardwar sector, D of samples from the Rajghat sector and E of samples from the Kachhla sector.
44 Ada1 Singh et al.
BOREAS 22 (1993)
B
C
D
E
Fig. 5. Classification (Qm) of sandstone ( A and B) according to the principles of Dickinson ( 1985). Plot C is of samples from the Hardwar sector, D of samples from the Rajghat sector and E of samples from the Kachhla sector.
igneous rocks. Zircon and rutile derive from sialic igneous and crystalline metamorphic rocks.
Depositional regime On the basis of observations from the vertical sequences (Fig. 2), from Hardwar downstream to Kachhla, the depositional regime of the Ganga river is described as follows. The basal part of the vertical sequences (proximaldistal) is dominated by mega-units, with lithofacies such as Gs, St, Sp, Sr, Sm and Sh. Small-scale units with lithofacies such as Fc, Sr, F1, St and Fm in fine sand, silt and clay have developed in the upper part of the various channel bars and overbank deposits (proximal -distal). The study area, which lies on the West Uttar Pradesh (Fig. 1) is separated from the tectonically rising Siwalik hills by the Himalayan Frontal Fault (HFF). The presence of the H F F leads to the deepening of the Gangetic basin while the Siwalik hills are rising. These active tectonic processes, leading to the uplift of source areas, are responsible for the high
sediment discharge (gravels and coarse sand) during flood season, resulting in the deposition of mega-units in active channels (Singh & Bhardwaj 1991a). However, the small-scale units consisting of medium to fine sand, silt and clay laid down in inactive channels or in overbank deposits were deposited during low water periods. The variation in water level, as represented by sharp or erosional contacts between the lithofacies, results in periodic/seasonal emergence and subsequent erosion of channel bars. All the sequences described are sand-dominated, which is a characteristic feature of braided river deposits (Walker & Cant 1984; Miall 1988b; Singh & Bhardwaj 1991a).
Discussion The study of Ganga River sediments illustrates the seasonal and tectonic control of sedimentation. The basin is tectonically unstable, as it is progressively deepened due to movements along the Himalayan Frontal Fault. The uplift of the Himalaya, deepening of the basin and high seasonal flood discharges are responsible for the development of mega-units in
Ganga River sediments
BOREAS 22 (1993)
active channels. The scale and distribution of lithofacies types within active channels varies vertically as well as with the distance downstream. The river emerges from the mountains on to the plain upstream of Hardwar and when its competency is suddenly controlled, this results in the deposition of thick active channel sediments (gravels and coarse sand). However, downstream of Hardwar, the sediment load available for transportation is small, resulting in only thin active channel deposits (mainly medium to fine sand). The sedimentation of the small-scale units of inactive channel and overbank deposits occurs during the low water period. The composition and maturity of the sands is primarily controlled by the source rocks and tectonics. Secondary processes, such as climate and weathering and depositional reworking and abrasion, acting singly or in combination, tend to destroy the labile constituents and produce quartz rich sands. Intense weathering under a warm and humid climate and long residence time in soils may destroy feldspars and other labile constituents, resulting in a high degree of compositional maturity of the sediment. The ratio of rock fragments and feldspars present in the sediments is the result of a balance between the rate of decomposition and the rate of erosion. Most litharenites arise from the denudation of a mixed sedimentary terrane. With deeper dissection, the plutonic and high-grade metamorphic sources are exposed with the result that the derived sands become increasingly feldspathic. In general, the main recycled orogen sources contain sedimentary strata and subordinate volcanic rocks and their metamorphic derivatives, which are exposed to erosion by orogenic uplift of fold belts and thrust sheets (Dickinson et al. 1982; Dickinson 1985). The modal composition of the Ganga sands matches that of the Appenine Cretaceous of Italy (Sestini 1970), the Carboniferous lithic sandstones of Ouachita Mountains in Arkansas (Graham et al. 1976), and the Ordovician Plynliman Group of Wales (James 1971). All these examples from the geological record were interpreted as being derived from recycled orogen provenances. According to Dickinson & Suczek (1979), recycled sands, rich in chert and other rock fragments derived from subduction complexes, orogenic collision belts and uplifted forelands, are found in closing ocean basins, various successor basins, and foreland basins. The textural maturity (rounding, sphericity and sorting) of the Ganga sands is low to medium, with subangular grains, while the sediments are compositionally immature as testified by the presence of rock fragments (chert, phyllite, schist). Both textural and compositional attributes suggest that depositional reworking was not prolonged. The detritus was mainly locally derived and was not subjected to long transport or reworking.
45
Conclusion It is concluded that the mega-units were developed in the lower part of active channels as a result of high sediment discharge during flood season. Small-scale units have been developed in inactive channels and as overbank deposits during low water periods. The modal compositions of the fluvial sand samples from the Ganga River provide supporting evidence from a modern foreland basin for Dickinson & Suczek’s (1979) ‘recycled orogen provenance model’. The principal control on sand composition in the Ganga basin is source lithology. The hot and humid climate may slightly increase the content of quartz in sand derived from reworked foreland basin sediments. However, the effect is neither sufficient to shift the sand compositions out of the recycled orogen provenance field, nor does it obscure composition mixing patterns. Acknowledgements. - The authors are grateful to Professor S. N. Bhalla, Chairman, Department of Geology, Aligarh Muslim University for providing the research facilities. We are also thankful to Professor S. M. Casshyap for fruitful discussions and valuable suggestions. Professor Edward Derbyshire thoroughly reviewed the manuscript, which was considerably improved by his comments and suggestions.
References Allen, J. R. L. 1983: Studies in fluviatile sedimentation: bars, bar complexes and sandstone sheets (low-sinuosity braided streams) in the Brownstones (L. Devonian), Welsh Borders. Sedimentary Geology 33, 237-293. Basu, A. 1976: Petrology of Holocene fluvial sand derived from plutonic source rocks: implications to paleoclimatic interpretation. Journal of Sedimentary Petrology 46, 694-709. Basu, A. 1985: Influence of climate and relief on composition of sands released at source area. In Zuffa, G. G. (ed.): Provenance of Arenites, 1 - 18. Reidel, Dordrecht. Bhardwaj, B. D. & Singh, A. 1992: Sedimentology of a recent alluvial fan of Ganga River, Rishikesh, India. Journal of the Geological Society of India 39, 457-465. Casshyap, S. M. & Kumar, A. 1987: Fluvial architecture of the Upper Permian Raniganj Coal measures in the Damodar Basin. Eastern India. Sedimentary Geology 51. 181 -213. Collinson, J. D. 1978: Alluvial sediments. In Reading, H. G. (ed.): Sedimentary Environments and Facies, 15-60. Blackwell Scientific, Oxford. Collinson, J. D. 1986: Alluvial sediments. In Reading, H. G. (ed.): Sedimentary Environments and Facies, 20-60. Blackwell Scientific, Oxford. Davies, D. K. & Ethridge, F. G. 1975: Sandstone composition and depositional environments. American Association of Petroleum Geologists Bulletin 59, 239-264. Desloges, J . R. & Church, M. 1987: Channel and flood plain facies in a wandering gravel-bed river. In Ethridge, F. G., Flores, R. M. & Harvey, M. D. (ed.): Recent Development in Fluvial Sedimentology. Society of Economic Paleontologists and Mineralogists Special Publication 39, 99- 109. Dickinson, W. R. 1985: Interpreting relations from detrital modes of sandstones. In Zuff, G. G. (ed.): Provenance of Arenites. 333-361. Reidel, Dordrecht. Dickinson, W. R. & Suczek, C. A. 1979: Plate tectonics and sandstone composition. American Association of Petroleum Geologists Bulletin 63, 2164-2182.
46 Ada1 Singh el al. Dickinson, W. R., Ingersoll, R. V., Cowan, D. S., Helmhold, K. P. & Suczek, C. A. 1982: Provenance of Franciscan greywackes in coastal California. Geological Society of America Bulletin 93, 5 - 107. Folk, R. L. 1980: Petrology of Sedimentary Rocks, 170 pp. Hemphill, Austin, Texas. Franzinelli, E. & Potter, P. E. 1983: Petrology, chemistry and texture of modern river sands, Amazon river system. Journal of Geology 91, 23-40. Friedman, G. M. & Johnson, K. G.1982: Exercises in Sedimentology, 71 -99. Wiley, New York. Graham. S . A,, Ingersoll, R. V. & Dickinson, W. R. 1976: Common provenance for lithic grains in Carboniferous sandstones from Ouachitd Mountains and Black Warrior basin. Journal of Sedimenrary Petrology 46, 620-632. Griffiths, J. C. 1967: Scientific Method in Analysis of Sediments, 508 pp. McGraw-Hill, New York. James. D. M. D. 1971: Petrography of the Plynliman Group west-central Wales. Sedimentary Geology 6, 255-270. Klein, G. dev. 1963: Analysis and review of sandstone classification in the North American literature, 1940- 1960. Geological Society of America Bulletin 74, 555-576. Lindholm, R. C. 1987: A Practical Approach to Sedimentology, 20-34. Allen & Unwin, London. Miall, A. D. 1978: Lithofacies type and vertical profile models in braided river deposits: a summary. In Miall, A. D. (ed.): Fluvial Sedimentology. Canadian Society of Petroleum Geologists Memoir 5. 597-604. Miall, A. D. 1985: Architectural element analysis: a new method of facies analysis applied to fluvial deposits. Earth Science Reoiew 22, 261-308. Miall, A. D. 1988a: Architectural elements and bounding surfaces in fluvial deposits: anatomy of the Kayenta Formation (Lower Jurassic), Southwest Colorado. Sedimentary Geology 55, 233262. Miall. A. D. 1988b. Reservoir heterogenies in fluvial sandstone:
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lessons from outcrop studies. American Association of Petroleum Geologists Bulletin 72 (6). 682-697. Mitchell, A. H. G. & Reading, H. G. 1986: Sedimentation and tectonics. In Reading, H. G.(ed.): Sedimentary Environments and Facies, 471 -519. Blackwell Scientific, Oxford. Morison, S. R. & Hein. F. J. 1987: Sedimentology of the white channel gravels, Klondike area, Yukon Territory. In Ethridge, F. G., Flore’s, R. M. & Harvey, M.D. (ed.): Recent Developments in Fluvial Sedimentology. Society of Economic Paleontologists and Mineralogists Special Publication 39, 205 -2 16. Okada, H. 1971: Classification of sandstone, analysis and proposal. Journal of Geology 79, 509-525. Paola. C., Wiele, S . M. & Reinhart. M. A. 1989: Upper-regime parallel lamination as the result of turbulent sediment transport and low-amplitude bedforms. Sedimentology 36, 47- 59. Sestini, G. 1970: Flysch facies and turbidite sedimentology. Sedimentary Geology 4, 559-597. Singh, A. & Bhardwaj, B. D. 1991a: Fluvial facies model of the Ganga River sediments, India. Sedimentary Geology 72, 135- 146. Singh, A. & Bhardwaj, B. D. 1991b: Textural attributes, depositional processes and heavy mineral study of the Ganga sediments between Hardwar and Kachhla. Bulletin of Indian Geologists Association 24, 41 -54. Suttner, L. J. 1974: Sedimentary petrographic provinces: an evaluation. Society of Economic Paleontologists and Mineralogists Special Publication 21. 75-84. Suttner, L. J., Basu, A. & Mack, G. H. 1981: Climate and the origin of quartz arenites. Journal of Sedimentary Petrology 51. 12351246. Valdiya, K. S. 1984: Aspects of Tectonics, 218 pp. Tata McGrawHill, New Delhi. Walker, R. G. &Cant, D. J. 1984: Sandy fluvial systems. In Walker, R. G. (ed.): Facies Models, 2nd edn. 71-89. Geoscience Canadian Reprint Series 1. William, P. F. & Rust, B. R. 1969: The sedimentology of a braided river. Journal of Sedimentary Petrology 39. 649-679.
