depositional mechanisms as revealed from grain-size measures of the palaeoproterozoic kolhan...

E L S E V I E R Sedimentary Geology 89 (1994) 181-196

S E D I M E N T A R Y

G E O L O G Y

Depositional mechanisms as revealed from grain-size measures of the Palaeoproterozoic Kolhan Siliciclastics,

Keonjhar District, Orissa, India

S u m i t K u m a r G h o s h , ,a , B . K . C h a t t e r j e e b

a Sedimentology Group, Wadia Institute of Himalayan Geology, Dehra Dun-248001, India b Department of Geology, Banaras Hindu Unicersity, Varanasi-221005, India

(Received May 27, 1992; revised version accepted August 13, 1993)

Abstract

The depositional mechanisms of the Palaeoproterozoic Kolhan Siliciclastics have been examined using grain-size analytical approaches. Grain-size distributions of different lithofacies reveal a somewhat diversified paralic depositional environment including nearshore, beach, macrotidal estuary and inland dunes. These inferences arise from different ways of analysing grain-size data, such as cumulative curves, bivariant plots, linear and multigroup discriminant functions and sediment trend matrix analyses. Sediment trend matrix analysis of various lithofacies taken together appears to be most effective for synthesizing the relationship between facies and sub-environments, taking into account the regional and local variations of lithofacies distribution and primary sedimentary structures. Grain-size distributions and sediment transport paths as revealed from the above statistical parameters suggest overall hydraulic control of the grain-size distribution of the Kolhan Siliciclastics in a fluvio-beach-shallow marine depositional setup.

1. Introduct ion

Grain size is a fundamental physical property of sediments and sedimentary rocks. Its importance in the classification of sediments has been recognized since the end of the 19th century by workers like Udden (1898), Wentworth, (1922), Krumbein (1938) and others.

Interest in grain-size frequency distributions and their implication in depositional environment

* Corresponding author.

interpretation has become more significanct in the course of time as evidenced by the large number of publications on this subject (Fried- man, 1967; Middleton, 1976; Tucker and Vacher, 1980; Bridge, 1981; McLaren, 1981; McLaren and Bowles, 1985; Forrest and Clark, 1989; and others). However, much controversy still exists among researchers regarding the effectiveness of many interpretative techniques available for discrimination and classifying the sedimentary environments.

The present investigation is an at tempt to in- terpret grain-size distribution data of the Palaeo-

0037-0738/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0037-0738(93)E0107-Q

t 82 S.K. Ghosh, B.K, Chatterjee / Sedimentary Geology 89 (1994) 181-190

proterozoic Kolhan Siliciclastics, and to examine the limitations of available graphical and quanti- tative techniques for environmental analysis.

The siliciclastic rocks of the Kolhan Group ( ~ 2100-2000 Ma; Saha and Roy, 1984) are more or less persistently widespread over much of the south Singhbhum, Bihar and adjoining Keonjhar districts in Orissa (Fig. la). The Kolhan Siliciclas- tic rocks lie unconformably over the older Iron Ore Group and Singhbhum Granite (Phase III, ~ 3.1 Ma) and consist of impersistent conglomer- ate and sandstones. The rocks are tectonically least disturbed and generally exhibit a dip of 2 ° to 10 ° to the west (Fig. lb). In general, the siliciclastics are dominantly purple, grey and pale-green coloured quartz arenite (60%) and quartz wacke (40%).

2. Lithofacies

On the basis of sedimentary structures, bed geometry, lithology, bed contacts and grain size, the Kolhan Siliciclastic unit has been subdivided into six lithofacies, namely Granular Lag (GLA), Granular Sandstone (GSD), Sheet Sandstone (SSD), Plane Laminated Sandstone (PLSD), Rip- pled Sandstone (RSD), and Thinly Laminated Si l t s tone-Sandstone (TLSD) (Ghosh, 1983; Ghosh and Chatterjee, 1990).

The Granular Lag Facies (GLA) is represented by laterally impersistent layers of moderately to poorly sorted (0.74-1.28 ~b), oligomictic to polymictic conglomerates. The average thickness of this facies is 0.41 m constituting approximately 7.61% of the measured sections. The polymictic nature of cobbles and pebbles is more pronounced in the northern part (Fig. 2). It occurs in the form of wedge or lensoid bodies sandwiched between sheet sandstones (SSD). It often repre- sents channelled or planar erosional surfaces with SSD and PLSD. Graded bedding, trough cross- stratification (TCS) and pebble imbrication are the common sedimentary structures. Graded bedding is more pronounced than large scale TCS. The occurrence of lag layers and their oligomictic nature suggest extensive reworking by sheet-like flow systems (Anderton, 1976).

The Granular Sandstone Facies (GSD) is characterised by moderately well to poorly sorted (0.68-1.43 ~b) granule-bearing sandstone. It comprises on average 6.85% of the measured section with a thickness of 0.36 m (Fig. 2). Planar cross- stratification is more commonly found with reactivation surfaces as compared to trough cross- stratification. Occasionally, graded bedding is also noted. It shows a gradational contact with GLA and SSD. The grain size varies from 0.20 to 0.35 mm with sandstone composition varying from lithic to sublithic arenite.

The Sheet Sandstone Facies (SSD) consists of 0.32 to 0.60 m thick sandstone sheets separated by TLSD or PLSD either by sharp or gradational contacts and constitutes about 62% of the measured sections. Planar (< 0.45 m in length with concave or occasional reactivation surfaces) and herringbone cross-stratification and symmetrical wave ripples are the common sedimentary structures. The important feature of this facies is the presence of granular lags along planar or channelled bed tops; where lags are absent the bed top frequently shows a mega-rippled bedform ranging in amplitude from 0.10 to 0.75 m. The sandstones are greyish to pale greenish, moderately well sorted (0.51 ~h) compact quartz aren- ires.

The Plane Laminated Sandstone Facies (PLSD) is characterised by 0.27 to 0.30 m thick beds commonly found associated with RSD and SSD (Fig. 2). This facies constitutes about 10.42% in the measured sections. The contact varies from gradational to planar erosional. Parallel lamina- tions, ripple drift cross-lamination, hummocky cross-stratification and reactivation surfaces are well documented. The sandstones are fine- to medium-grained, moderately-well to moderately sorted (0.49-0.89 ~b), sublithic arenites.

The Rippled Sandstone Facies (RSD) comprises 9.31% of the measured sections and is characterised by symmetric or wave-modified current ripples, trough cross-stratification, flaser bedding and mud drapes. The thickness of the bed unit varies from 0.20 to 0.33 m and is mostly lenticular in nature. It shows erosional contacts with all other facies except TLSD. Grain size varies from fine to medium with occasional layers of granules

S.IC Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181-196

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Fig. 2. Areal variation of grain-size parameters and lithofacies distribution of the Kolhar~ Siliciclastics.

S.K. Ghosh, B.I~ Chatterjee /Sedimentary Geology 89 (1994) 181-196 185

along the foreset of rippled surfaces. Composi- tionally, the sandstones are mostly quartz arenite to quartz wacke.

The Thinly Laminated Siltstone-Sandstone Fa- cies (TLSD) is characterised by thinly laminated or plane to wavy bedded siltstone-sandstone with a mean grain size from 0.25 to 0.06 mm. It is commonly found interbedded with RSD with planar or gradational contacts, and erosional and wavy contacts with underlying SSD and PLSD. It comprises about 3.86% of the measured section, with a unit bed thickness less than 0.15 m.

The areal distribution pattern (Fig. 2) suggests that SSD is widely distributed throughout the basin and attains a thickness of about 14 m near the central part (Inganijoran and Surgutaria), thinning towards the northern and southern parts, thus giving a lens-shaped geometry. The thickness of PLSD is almost uniform, except near the Ja- jang-Lonipisi section (Fig. 2), where it attains a thickness of 2 m. The average bed thickness of TLSD is about 0.10 m, except in the central portion where its thickness measures upto 0.20 m. The RSD gradually thicken (0.45 m) towards the southern part. The preponderance of GLA and GSD is noticed towards the northern and to some extent in the southern part (Gurtawa) of the basin (Fig. 2).

3. Grain-size distributions

The thin-section method of grain-size analysis has been used throughout in the present study following the procedure first suggested by Krum- bein (1935), because of the difficulty of disaggre- gation of the compact rocks. This is the only method available for such rocks and has been employed, justified and improved by several workers, such as Friedman (1962), Connor and Ferm (1966) and Textoris (1971).

Grain-size measurements of nearly ninety sandstone samples were carried out by the con- ventional thin-section method. The measured grain-size values were grouped into half-th inter- vals and cumulative and frequency curves were plotted for six lithofacies. The statistical parameters (both graphic and moment measures) were

calculated following Folk and Ward (1957) and Friedman and Sanders (1978).

3.1. Cumulative curves

Representative cumulative curves (CC) for different lithofacies are shown in Fig. 3. The CC of the SSD, PLSD, RSD and TLSD facies are characterised by initially (coarse size) steep, straight lines with a concave middle part and again a steep straight end (fine size) portion. The GLA and GSD facies are characterised by moderately steep, straight initial curves with a concave middle and steep straight end part. Such curves show many local truncations as compared to the former CC. However, all curves show a major concave-up slope break (C.T.) near 0.25 mm (+ 2.0 ~b) and reflects the transition from traction or surface creep to intermittent suspension. This size corre- sponds approximately to the mid-point of the transition between Rubey's Impact Law and Stokes' Law of particle settling (Sagoe and Visher, 1977, p. 296). A second major slope break, con- vex-up, separates transportation by true suspension from that by intermittent suspension. In all curves, it occurs near +3.5 th, lying approximately at the silt-clay boundary, i.e., the lower limit of the transition between Rubey's Impact Law and Stokes' Law. The slight variation in the two principal slope breaks may be interpreted in terms of current velocities, flow separation, flow regime velocity, velocity gradient and grain shape. According to Middleton (1976) and Lambiase (1982), saltation population A is actually trans- ported by intermittent suspension or turbulence generated by velocity fluctuations in water. In the present case, the observed shift towards a coarser grain size at the C-A (traction to saltation popu- lations) and A-B (saltation to suspension popula- tions) boundaries from GLA-GSD to SSD on- wards, and steepness of the curve segment reflect that transport gradually changes from traction to primarily by intermittent suspension in response to greater flow strength. The probable depositional environments deduced from the shapes of the cumulative curves are shown in the Table 1. The overall depositional environment may be comparable with beach shoreface sands/shallow

186 S.K. Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181 - 190

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S.K. Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181-196 187

marine sands from wave zones (Visher, 1969) or macrotidal estuaries (Lambiase, 1980).

3.2. Statistical parameters and bivariate plots

The representative ninety samples of the different lithofacies of the Kolhan Siliciclastics were plotted on bivariate diagrams based on six different combinations of grain-size statistical parameters. Mean size plotted against standard deviation (sorting) is generally considered to be an effective discriminator between recent river, dune and beach sands by Friedman (1961) and Moiola and Weiser (1968). This plot (Fig. 4a) indicates that most sandstones are of a mixed river and dune (Friedman's diagram) and river environment (Moiola and Weiser's plot). Skewness versus mean size has been used for differentiating between river, wave and slack water processes (Stewart, 1958), between beach and dune sands (Friedman, 1961, 1967; Moiola and Weiser, 1968) and between inland and coastal dune sands (Moiola and Weiser, 1968). Since median and meansize for the Kolhan Siliciclastics are almost identical,

Stewart's discriminating boundaries based on median and skewness may be safely used. Accord- ingly, most samples cluster in the zone of river and wave processes (Fig. 4b). Beach sands are more prominent according to the plots of Fried- man and of Moiola and Weiser. However, when the data are plotted in the diagram of Friedman and Sanders (1978) much of the samples cluster in the river sand zone (Fig. 5a). The plots of kurtosis versus mean size and standard deviation versus kurtosis do not lead to any environmental interpretations.

Mason and Folk (1958) and Moiola and Weiser (1968) have proposed a plot of kurtosis versus skewness to distinguish among beach, dune and aeolian flat sands and between inland dune and beach sands, respectively. In the present case, such plots yield inconclusive results because most samples lie outside the three fields discriminated by Mason and Folk (1958). However, according to Moiola and Weiser's diagram sandstones plot mostly in inland dune environments (Fig. 5b).

Friedman's plot (1967) of standard deviation versus mean cubed deviation (third moment) is

Table 1 Probable depositional environment of the Palaeoproterozoic Kolhan Siliciclastics based on cumulative curve analysis (after Visher, 1969)

Lithofacies Saltation population (A) Suspension population (B) Surface creep population (C) Probable

percent ST C.T. F.T. percent ST mixing F.T. percent ST C.T. mixing environ- th ~b A a n d B q~ th A a n d C ment

GLA

GSD

SSD

PLSD

RSD

TLSD

15-45 G 1.9 2.5 nil to 5 G much 4.50 52-94 P 0.50 little fluvial/ to to to no limit tidal inlet 2.0 3.5 G

20-30 F 2.0 3.3 nil to 4 F much 5.00 58-95 P 0.0 to average fluvial/ to to to - 0.50 tidal 2.4 4.4 G chanel

30-50 F 2.50 3.0 4-20 F much 5.00 40-84 P no limit much shoal / to to to tidal 3.0 5.0 F channel

3-60 F 2.5 3.5 5-6 F much 3.0 52-97 F 0.0-1.0 average wave zone to to G 5.0

18-60 P 1.5 2.5 2-5 G much 4.0 40-94 P - 0.5-0.5 average plunge zone to to to 2.5 4.0 F

0-38 G 2.5 > 5.0 2-98 G much 5.0 - - no limit - plunge/wave to zone 3.5

C.T. = coarse truncation point; F.T. = fine truncation point; ST = sorting; G = good; F = fair; P = poor.

188 S.K. Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181--190

generally considered to be an effective discriminator between beach and river sands. In the present case, GLA and GSD fall mostly in the river-field whereas the SSD, PLSD, RSD and TLSD samples plot both in river and beach environments.

3.3. C-M diagram

The C - M plot in the case of GLA and GSD facies indicates a resemblance with Passega's (1964, 1977) basic bed load pattern V of the fluvial environment and the alluvial fan deposits of Bull (1962). Facies SSD, PLSD, RSD and TLSD all reflect typical beach or nearshore environments (Fig. 6).

3.4. Discriminant functions

Bivariant plots of grain-size parameters could not yield an effective differentiation between the depositional environments of the six lithofacies. The discriminant function analysis of Sahu (1964) is helpful here because this method combines all statistical parameters into a single linear equa- tion. Sahu (1964) empirically established four discriminant functions to differentiate between sediments from aeolian, beach, shallow agitated marine, fluvial (deltaic) and turbidite environments. Based on the discriminant function values, different lithofacies mostly represent shallow marine, beach, turbidity current and fluvial environments (Table 2).

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Fig. 4. (a) Bivariate plot of mean size versus graphic standard deviation. (b) Bivariate plot of mean size versus graphic skewness.

S.I( Ghosh, B.I£ Chatterjee / Sedimentary Geology 89 (1994) 181-196 189

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Fig. 5. (a) Bivariate plot of simple sorting measures versus simple skewness measures. (b) Bivariate plot of graphic skewness versus graphic kurtosis.

190 s.K. Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181 - 196

A log-log plot of mean 4' deviation versus the ratio of standard deviation of kurtosis to standard deviation of mean size multiplied by the standard deviation of variance (Sahu, 1964) of all samples belonging to six different lithofacies has been used for further differentiation between the environments. Unlike various predications given in Table 2, it places GLA and GSD facies in the fluvial domain, whereas SSD and PLSD fall in shallow marine and transitional marine-fluvial environments. The RSD and TLSD occur along the border zone between fluvio-deltaic and turbidity current deposits (Fig. 7). Further, the ap- plication of the multivariate method of environment discrimination after Sahu (1983) in the form of a graphical plot of V] versus V 2 reveals that except facies TLSD, all suggest a beach environment (Fig. 8).

3.5. Spatial and stratigraphic grain-size (statistical parameters) uariations

A brief account of the regional (spatial) variation of different statistical parameters is given

below and is shown by an areal distribution map (Fig. 2).

Mean grain size (M~). Towards the central, southern and western portions the M z value de- creases, whereas it increases towards the northern part of the basin.

Mode (M,,). An overall variation of M o suggests that sands are mostly polymodal to bimodal towards the central and northern parts, and more unimodal nearer the southern portion of the basin.

Standard deviation ((rt). No significant variation is seen in the areal distribution of sorting. It may be inferred that sands are comparatively moderately well sorted in the northern and southern parts, while in the central portion of the basin they are mostly poor to moderately sorted. This almost parallels the distribution of the mean size (Mz).

Skewness (SKI). The skewness values range from finely to coarsely skewed. However, areal distribution shows that the sediments are mostly finely skewed near the northern region, but are

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SANDSTONE FACIES

l ,l , , I() l C~ I0 I0 2 10 3 I0 'I I I0 2 I0 S 1 4

M=MADIAN IN MICRONS M = MEDIAN IN MICRONS

Fig. 6. (a) C-M pattern of the GLA and GSD facies. (b) C-M pattern of the SSD, PLSD, RSD and TLSD facies.

S.I~ Ghosh, B.BL Chatterjee / Sedimentary Geology 89 (1994) 181-196 191

I0"0

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SKG/ SMZ. S(o-12) Fig. 7. Log-Log plot of mean (h deviation versus the ratio of s tandard deviation of kurtosis to s tandard deviation of mean size t imes the s tandard deviation of variance, showing the depositional environment of six lithofacies of the Kolhan Siliciclastics.

nearly symmetrical to coarsely skewed towards the southern part. The frequency curves are coarsely skewed in the north-central part and finely skewed to near symmetrical towards the south-central part of the basin.

Kurtosis (Kc). The areal pattern of K o suggests that the (frequency) curves are more platykurtic ( < 0.90 (k) in the northern part, but that they are more leptokurtic (0.67-0.90 4)) and

80

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Fig. 8. Partitioning of discriminant space by an Euclidean distance measure showing the dominance of a beach environment in the Kolhan Siliciclastics.

mesokurtic (0.90-1.11 4)) in the central and southern parts of the basin.

The general temporal (stratigraphic) variation of the grain-size statistical parameters in a com- posite lithosection is shown in Fig. 9. M z values vary from 1.75 to about 4.0 ~b. From the base to the middle of the section the mean size increases,

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C = C amman, r = rare , a : abundant , U = Unimodot, B = Bimodal , P = Polymodal

Fig. 9. Stratigraphic variation in grain-size parameters of the Kolhan Siliciclastics.

192 S.K. Ghosh, B.K. Chatterjee / Sedimenta~ Geology 89 (1994) 18I 196

Table 2

Environment interpretation based on Sahu's (1964) linear discriminant functions

Lithofacies and test used Y-value Discriminant function

decision

Granular Lag Facies (GLA) Aeolian: beach 1.729888

Beach: shallow marine 107.71972 Shallow marine: fluvial -9.247016

Fluvial: turbidite 4.23008

Granular Sandstone Facies (GSD) Aeolian: beach 1.172523 Beach: shallow marine 108.49227

Shallow marine: fluvial -8.573734

Fluvial: turbidite 6.237003

Sheet Sandstone Facies (SSD) Aeolian: beach 0.865002 Beach: shallow marine 93.751199 Shallow marine: fluvial -5 .76964 Fluvial: turbidite 5.689443

beach shallow marine

fluvial (deltaic)

turbidite

beach shallow marine fluvial (deltaic)

turbidite

beach

shallow agitated shallow marine turbidite

Plane Laminated Sandstone Facies" (PLSD) Aeolian: beach - 0.73225

Beach: shallow marine 87.693177

Shallow marine: fluvial -5 .71018 Fluvial: turbidite 6.392462

Ripple Sandstone Facies (RSD) Aeolian: beach - 0.642181 Beach: shallow marine 87.37054

Shallow marine: fluvial - 5.223746 Fluvial: turbidite 6.403154

Thinly Laminated Siltstone- Sandstone Facies" (TLSD) Aeolian: beach - 7.398084 aeolian Beach: shallow marine 87.976496 shallow marine Shallow marine: fluvial - 1.70106 shallow marine

Fluvial: turbidite 7.716936 turbidite

beach

shallow marine shallow marine

turbidite

beach shallow marine shallow marine

turbidite

while fining as well as coarsening in the upward direction. M z erratically fluctuates at about the 2 ~b boundary between medium and fine sand in the middle where the TLSD facies predominates. The sorting is slightly poorer towards the base and top of the sequence near the contacts with the GSD facies whereas the TLSD facies in the middle is generally well sorted. A wide-ranging standard deviation from 0.40 to 1.30 ~b is a characteristic feature. Skewness and kurtosis show

almost similar trends for the sequence. SK l is generally finely skewed to near symmetrical at the base and middle, while gradually passing up- wards into coarsely skewed SSD facies. K c is generally mesokurtic near the base and becomes platykurtic towards the top. The fluctuations in mode of the sand is not systematic. However, GLA and GSD facies near the base show poly- modality whereas other facies are commonly bimodal or unimodal towards the top of the stratigraphic section.

It is generally believed that regional and stratigraphic variations in single grain-size parameters depend on regional palaeoslope and topographic relief of the depositional site. The overall picture which emerges from the study of such variations is a slight depression in the west-central part and a general palaeoslope towards the northwestern side with an occasional undulating pre-Kolhan erosional surface. The stratigraphic changes .in the variability of size parameters (Fig. 9) probably indicate changes in environmental energy condi- tions such as water depth, wave intensity or velocity of the depositing currents. The slight basin- ward increase in the average grain size (GLA and GSD facies) towards the west-central part may be comparable with the shallow marine shelf border- ing the Florida Panhandle (Tanner, 1961)where sediments of the Apalachicola River are being reworked into submarine shoals. The slight coarsening shoreface is attributed to a lag effect due to the landward segregation of finer sands by storm-generated waves or strong tidal currents. Sorting values on an average range from 0.40 to 1.43 4', indicating the influence of beach, river and shallow marine environments (Folk, 1966). A palaeocurrent analysis proves that the dispersal of sandy materials took place from all three sources, viz., the Singhbhum Granite to the northeast, and the Older Metamorphics and Iron Ore Group to the southeast and southwest (Fig. 2). The relative contributions from the Singhb- hum Granite and Older Metamorphics are however more prominent (Ghosh, 1983). It is there- fore quite likely that sand was initially deposited by rivers from east and north of the basin, where sedimentation was periodically disturbed by tidal waves or currents.

S.K. Ghosh, B.K~ Chatterjee / Sedimentary Geology 89 (1994) 181-196 193

4. Sediment trend matrix analysis

Krumbein (1938) first gave a list of environmental elements such as depth, shape of bay, configuration of depositional surface, medium of sedimentation, and energy factors which influ-

ence the grain-size distribution, and also recognized the importance of progressive changes in the statistical measures from source to final deposit. In this context, McLaren (1981) and McLaren and Bowles (1985) emphasized the util- ity of the above idea in recognizing the probable

S E D I M E N T S O U R C E GrainSize Choract-

~es G L A G SD SSD PLSD RSD T L S D ,eristics

G ,Coarser ~, C_,o9 rser/ m /(.~oar ser., ~.,oorsfl(/ / , " . . . . /p t~o~e ' r /~ /Poorgr / /Poore ' r / SD (,~) ,~ L ,P~o~¢r" ~oo~r ~'

,_ G /,rf~{~ / 4 / / / / ' / / / / / " / / / / / < I L I A , / , /k.oarser m (,~) - ,~oarser /Coorser/~.J~,oorser" / , ,. / c -- S /B~ t t ; r ~ / / / P o o r e ~ ' . P o o r e r / / P ~ o r e ? / , /.Poorer., SD (~'1 o "~

o ~ , .

' " / F i n e r / / Finer .Coarser r~ S Seet~e~, ( Better ,Po'oiei~ " ' / / ~Pogr.er/ ~.P.'o~r~-~, SO (~) o

Coarser /Coorser~'C~'~4s~/~r// m ('~')i~, ~ ~ I-- ~ /B'etter// /Bette~// Better /Bette~/'/ . . . . . . /poore'r/~, SD (~) Z / / / / / ~ v

:ER/////~ /////'///'//'//////" ii -- / r / m e r / , ~ Finer / F i n e r / / ~ F i n e r ~ /Coarser, m (,~) ~ '..7. r~ S / = / " / - /~ / i / l / B e t t e r ' / Better /Bette'r/~/Poorer/ /.15Darer// SD (~) ~ , . , o _ "/X+/A "//-/// SK

T Finer Finer Finer Finer Finer / m (,~') --' "De ~:~ S Better Better Better Better Better SD (,21) ~ / E~ D . . . . . SK (~') E m

(A)

(B)

Breaker Zone /Beach Face

' ~ - ~ . . . . ' - P L S - ~ Of f Shore Berm GSD Bar

(C) Trough

Fig. 10. (A) Sediment trend matrix, (B) corresponding sediment transport paths and (C) probable depositional model for the Kolhan Siliciclastics.

194 S.K. Ghosh, B.K. Chatterjee / Sedimenta~' Geolo~' 89 (1994) 1 8 l l¢)O

Table 3 Grain size statistics from six lithofacies of the Kolhan Silici- clastic rocks (based on moment measures, Friedman and Sanders, 1978)

Litho- Average Average Average Probable facies mean size stand, dev. skewness environment

(&) SD (~b) SK (~h)

GLA 1.49 1.06 - 0.1 l fluvial GSD 1.67 0.97 0.08 fluvial/beach SSD 1.80 0.~3 0.06 shallow marine PLSD 1.69 0.77 0.31 shallow marine RSD 1.86 0.84 - 0.03 shallow marine TLSD 3.08 0.60 -0.26 shallow marine/

aeolian

All values are in & units.

source and sediment transport paths of sedimentary deposits. According to them, the characteristics of a deposit are closely related to its source and are dependent on sedimentary processes like winnowing, selective or partial deposition and total deposition. These trends indicate the probable transport paths for sediment movement which may be indicative of a model for environments of deposition.

In the present study, the idea of sediment paths has been applied to six lithofacies of the Kolhan Siliciclastics. Table 3 shows statistical parameters of average grain size (moment measures) together with probable depositional environments. As these facies are interrelated, a sediment trend matrix and corresponding sediment transport paths have been plotted in Fig. 10. GLA contribute sediments to TLSD facies by total deposition (Case I, McLaren, 1981; Fig. 10B). The sediments thus formed are better sorted than the source (GLA) and negatively skewed. However, the mean size of resultant sediments is finer, indicating that the energy level or turbulence of the eroding processes is incapable of transporting sediments coarser than the mean size of the source (GLA). The Granular Sand- stone (GSD) facies contributes sediment to all facies except GLA, the reason for this being that the GSD is finer, better sorted than the GLA and positively skewed. The responsible processes are total deposition (Case I, McLaren, 1981 ) for SSD, RSD and TLSD. However, the SSD facies also contributes sediments for PLSD and TLSD by

selective deposition (Cases IIIB and I; Fig. 10B). The energy level of the eroding and transport capabilities of the processes, however, must have been fluctuating. From the nature of its pebble size, roundness and sedimentary structures, the GLA facies appears to represent fluvial channel lag deposits of a braided river (Fig. 10C). The GSD facies exhibits features characteristic of a transitional environment. To explain the nature of the sediment trend from GSD, SSD and RSD (Case 1), the deposition of GSD must be visual- ized as near estuary mouths or breaker zones. The breaker zone (GSD), the highest energy point in this depositional system, appears to be the immediate source for sediments (especially SSD and RSD). The sediment trends from the SSD further reveal the possibility of its accumulation as offshore bar deposits and the TLSD as berm deposits as a result of tidal waves in this shoreline environment (Fig. 10C). RSD and PLSD may be comparable with beach face and trough sub-environments. The aforesaid interactions of sediment transport paths indicate the dominance of nearshore depositional environments, comparable with the beach and nearshore profile of South Haven, Michigan (Fox et al., 1966; McLaren, 1981). The above interpretation based on a sediment trend matrix appears to correspond with the depositional environments deduced from the lithological and sedimentary features of the sandstone (Ghosh, 1983; Ghosh and Chatterjee, 1990).

5. Conclusion

The study of the Palaeoproterozoic Kolhan Siliciclastics by bivariant and multivariant analyses indicates somewhat diversified sedimentary environments. The different interpretations for a given sample or lithofacies are obtained merely by switching to different sets of grain-size parameters. Moreover, such tests are restricted to recent beach, river, dune and shallow marine sands only, and ignore the effects of regional variation in grain size, sedimentation rate, climate, and tectonic and energy fluctuations within the environment. In this connection, it is pertinent to note that the boundaries of the different environ-

S.K Ghosh, B.K. Chatterjee / Sedimentary Geology 89 (1994) 181-196 195

ments in bivariant plots are neither theoretical nor statistical and thus indicate totally subjective or empirical lines of approach in the recognition of depositional environments. Moreover, the bivariant plots for recognising ancient depositional environments suffer from limitations such as diagenetic and post-diagenetic alteration and subse- quent modification which framework particles undergo, and lastly the lack of reliable techniques for precisely measuring the particle size in such hard and compact sediments.

The linear and multigroup discriminant functions and the log-log plot of ~ii -2 versus SKG/ SMZ, S(tr 2) and V t versus V2, the C-M diagram, the standard deviation plotted against mean cubed deviation and the shape of cumulative grain-size distribution are, however, applicable for distinguishing between broad depositional environments of the Kolhan Siliciclastics. The sediment trend matrix analysis as suggested by McLaren (1981) and McLaren and Bowles (1985) is found to be relatively more effective and simple in analysing the relationship between facies or sub-environments. However, the present investigation of grain-size variation and sediment transport paths as revealed by the sediment trend matrix of the Kolhan Siliciclastics suggests an overall hydraulic control of grain-size distribution in fluvio-beach-shallow marine depositional environments.

6. Acknowledgements

Authors are thankful to the Head, Depart- ment of Geology Banaras Hindu University for providing the necessary facilities to carry out this work. Thanks are also due to the Director, Wadia Institute of Himalayan Geology, Dehra Dun for allowing to finalise the manuscript. Authors are thankful to Prof. G.M. Friedman, U.S.A. and Dr. Patrick McLaren, Canada for useful comments and suggestions.

7. References

Anderton, R., 1976. Tidal-shelf sedimentation: an example from the Scottish Dalradian. Sedimentology, 23: 429-458.

Bridge, J.S., 1981. Hydraulic interpretation of grain size distributions using a physical model for bed load transport. J. Sediment. Petrol., 51: 1109-1124.

Bull, W.B., 1962. Relation of textural (C-M) pattern to depositional environment of alluvial fan deposits. J. Sediment. Petrol., 32: 211-216.

Connor, C.W. and Ferm, J.C., 1966. Precision on linear and aerial measurements in estimating grain size. J. Sediment. Petrol., 36: 397-402.

Folk, R.L., 1966. A review of grain-size parameters. Sedimen- tology, 6: 73-93.

Folk, R.L. and Ward, W., 1957. Brazos River bar: a study in significance of grain size parameters. J. Sediment. Petrol., 27: 3-26.

Forrest, J. and Clark, N.R., 1989. Characterizing grain size distribution: evaluation of a new approach using multivariate extension of entropy analysis. Sedimentology, 36: 711- 722.

Fox, W.T., Ladd, J.W. and Martin, M.K., 1966. A profile of the four moment measures perpendicular to shoreline, South Haven, Michigan. J. Sediment. Petrol., 36: 1126- 1130.

Friedman, G.M., 1961. Distinction between dune, beach and river sands from textural characteristics. J. Sediment. Petrol., 36: 514-529.

Friedman, G.M., 1962. On sorting, sorting coefficients and the log-normality of the grain size distribution of sandstones. J. Geol., 70: 731-753.

Friedman, G.M., 1967. Dynamic processes and statistical parameters compared for size frequency distribution of beach and river sands. J. Sediment. Petrol., 37: 327-354.

Friedman, G.M. and Sanders, J.R., 1978. Principles of Sedi- mentology. Wiley, New York, N.Y., 792 pp.

Ghosh, S.K., 1983. Sedimentological Studies of Precambrian Rock Formations Around Chamakpur, Keonjhar District, Orissa With Special Reference to Sandstone and Chert. Unpubl. Ph.D. thesis, Banaras Hindu University, 171 pp.

Ghosh, S.K. and Chatterjee, B.K., 1990. Palaeoenvironmental reconstruction of the early Proterozoic Kolhan Siliciclastic rocks, Keonjhar district, Orissa, India. J. Geol. Soc. India, 35: 273-286.

Krumbein, W.C., 1935. The use of quartile measures in de- scribing and comparing sediments. Am. J. Sci., 32: 98-111.

Krumbein, W.C., 1938. Size frequency distribution of sediments and the normal phi curve. J. Sediment. Petrol., 18: 84-90.

Lambiase, J.J., 1980. Hydraulic control of grain-size distributions in a macrotidal estuary. Sedimentology, 27: 433-446.

Lambiase, J.J., 1982. Turbulence and generation of grain size distributions. Abstr., l l t h Int. Congr. Sedimentology, Hamilton, pp. 80-81.

Mason, C.C. and Folk, R.L., 1958. Differentiation of beach, dune and aeolian flat environments by size analysis, Mus- tang Island, Texas. J. Sediment. Petrol., 28: 211-226.

McLaren, P., 1981. An interpretation of trends in grain size measures. J. Sediment. Petrol., 51: 611-624.

McLaren, P. and Bowles, D., 1985. The effects of sediment

196 S.K. Ghosh, B.K. Chatterjee / Sedimentao' Geology 89 (1994) 181 190

transport on grain size distributions. J. Sediment. Petrol., 55: 457-470.

Middleton, G.V., 1976. Hydraulic interpretation of sand size distributions. J. Sediment. Petrol., 84: 405-426.

Moiola, R.J. and Weiser, D., 1968. Textural parameters an evaluation. J. Sediment. Petrol., 26: 45-53.

Passega, R., 1964. Grain size representation by C - M patterns as a geological tool. J. Sediment. Petrol., 34: 830-847.

Passega, R., 1977. Significance of C - M diagrams of sediments deposited by suspension. Sedimentology, 24: 723-733.

Sagoe, K.O. and Visher, G.S., 1977. Population breaks in grain-size distributions of s and - - a theoretical model. J. Sediment. Petrol., 47: 285-310.

Saha, A.K. and Roy, S.L., 1984. Early-Middle Archean crustal evolution of the Singhbhum, Orissa Craton. J. Earth. Sci., CEISM Seminar Vol., pp. 1-18.

Sahu, B.K., 1964. Depositional mechanisms from the size analysis of elastic sediments. J. Sediment. Petrol., 34: 73-83.

Sahu, B.K., 1983. Multigroup discrimination of depositional environments using size distribution studies. Indian J. Earth Sci.. 10 (1): 20-29.

Sarkar, S.N. and Saha, A.K., 1962. A revision of the Precam- brian stratigraphy and tectonics of Singhbhum and adja- cent regions. Q. J. Geol. Min. Metall. Soc. India, 34: 07-136.

Stewart, H.B., Jr., 1958. Upstream bottom currents in New York Harbor. Science, 127: 1113-1115.

Tanner, W.F., 1961. Offshore shoals in area of energy deficit. J. Sediment. Petrol., 31: 87-95.

Textoris, D.A., 1971. Grain size measurement in thin section, In: R.E. Carver (Editor), Procedures in Sedimentary Petrology. Wiley, New York, N.Y., pp. 95-108.

Tucker, R.W. and Vacher, H.L., 1980. Effectiveness of discriminating beach, dune and river sands by moments and the cumulative weight percentages. J. Sediment. Petrol.. 50: 165-t72.

Udden, J.A., 1898. Mechanical Composition of Wind De- posits. Augustana Library Publications, No. 1, 69 pp.

Visher, G.S., 1969. Grain-size distribution and depositionat processes. J. Sediment. Petrol., 39: 1074-1106.

Wentworth, C.K., 1922. A scale of grade and class terms for elastic sediments. J. Geol., 30: 377-392.

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