Spectral analysis of a Precambrian limestone-shale sequence, lower Vindhyan, India

PrecambrianResearch, 39 (1988) 139-149 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

139

SPECTRAL ANALYSIS OF A PRECAMBRIAN LIMESTONESHALE SEQUENCE, LOWER VINDHYAN, INDIA B.K. C H A T T E R J E E

a n d P . K . SEN*

Department of Geology, Banaras Hindu University, Varanasi - 221 005 (India)

(Received August 13, 1986; revision accepted August 26, 1986)

Abstract Chatterjee, B.K. and Sen, P.K., 1988. Spectral analysis of a Precambrian limestone-shale sequence, Lower Vindhyan, India. Precambrian Res., 39: 139-149. The Preeambrian Lower Vindhyan limestone-shale sequence which exhibits predominantly subtidal shelf facies, has been subjected to the power spectrum analysis. The limestone percentages calculated at 20 cm intervals at Pipradih I (Tuira-Pipradih) and Pipradih II (Dhabua) sections form raw data for the analysis. A significant periodicity of approximately 111 cm has been detected by the study of the power spectra. The corresponding sedimentary oscillations are also recorded relative to the position of master bedding planes in the field as well as to the variation of insoluble residue of the limestone. The relative persistence of cycle wavelength of 111 cm, which is independent of facies change throughout the stratigraphic succession, indicates an effect of a long-range rhythmic process during deposition. In view of established worldwide tectonic movements between 1600 Ma and 900 Ma (middle Proterozoic), related eustatic fluctuations of sea level have been suggested as a cause of the cyclicity in the Lower Vindhyan limestone-shale sequence. However, the difference in the pattern of power spectra of lower and upper units (Pipradih I and II, respectively) with respect to Markovian persistence and amplitude of spectral peaks, indicate a greater influence of local environmental factors in the lower unit as compared with the upper sequence.

Introduction

m e n t a t i o n a n d d e p o s i t i o n a l history. In r e c e n t years, a n u m b e r o f statistical t e c h n i q u e s such

It is well k n o w n t h a t m a n y geologic processes a n d e v e n t s are r e p e t i t i v e in n a t u r e . T h e imp r i n t of such oscillatory p r o c e s s e s a n d e v e n t s c o n n e c t e d w i t h basinal tectonics, e u s t a t i c c h a n g e s in sea level a n d climatic v a r i a t i o n s are generally r e f l e c t e d in cyclic lithologic p a t t e r n s of the stratigraphic succession. A detailed s t u d y of the s t r a t i g r a p h i c sections t o g e t h e r w i t h a suitable statistical t e c h n i q u e would provide d a t a for a clearer insight into t h e p r o c e s s o f sedi-

as M a r k o v c h a i n analysis ( Selley, 1970), t i m e series analysis a n d p o w e r spectral d e n s i t y studies (Vistelius, 1961; S c h w a r z a c h e r , 1964, 1975; J a c k s o n , 1965; M a n n , 1967; H a r b a u g h a n d M e r r i a m , 1968; A g t e r b e r g a n d B a n e r j e e , 1969; deBoer, 1982; S c h w a r z a c h e r a n d Fisher, 1982 ) have b e e n utilized for statistically t e s t i n g the s e d i m e n t a r y sequence for M a r k o v i a n persistence a n d periodicity. T h e p r e s e n t i n v e s t i g a t i o n a t t e m p t s to elucidate t h e applicability o f a u t o c o r r e l a t i o n a n d power spectral density functions to decipher the cycle w a v e l e n g t h or p e r i o d i c i t y a n d to e s t i m a t e

"M/s. Parshava Properties Limited, Dalmianagar, Bihar, India.

0301-9268/88/$03.50

© 1988 Elsevier Science Publishers B.V.

140 TABLE I

dhyan, i.e., Kaimur, Rewa and Bhander Groups

G e n e r a l l i t h o s t r a t i g r a p h y of t h e V i n d h y a n B a s i n

are predominantly

Decan

Upper

Vindhyan

Trap

B h a n d e r Group ..... Diamond bearing conglomerate--R e w a Group ..... Diamond bearing conglomerate---

Kaimur Group ........ unconformity ........ Rohtas Formation

......... Kheinjua Formation

Semri LowerV i n d h y a n

Group

.........

PorcellaniteFormation Basal Formation

........ unconformity ........

Archaean Basement the relative influence of cyclic processes in the deposition of the Precambrian Lower Vindhyan limestone-shale sequence of the Son Valley, India. R e g i o n a l s e t t i n g a n d d e s c r i p t i o n of section The Precambrian Vindhyan rocks consisting of nearly horizontal bedded quartz arenite, shale, limestone, laminated chert and pyroclastics, lie with a marked angular unconformity on highly metamorphosed and folded Archaean rocks of northern India. They cover an area of about 104 000 km 2 in Bihar, Uttar Pradesh, Madhya Pradesh and Rajasthan States. The rocks are unmetamorphosed and devoid of any major structural deformation. They attain a thickness of about 2000 m in the Son Valley (the Type area) and range in age from ca. 1400 to 550 Ma (Crawford and Compston, 1970). These rocks are divided in ascending order into the Semri, Kaimur, Rewa and Bhander Groups (Table I). The Lower Vindhyan Semri Group (Basal-, Porcellanite-, Kheinjua-, and Rohtas Formations) is characterized by argillaceous and calcareous lithofacies while the Upper Vin-

arenaceous.

Auden (1933) did the first systematic geological mapping of the lithostratigraphic units of the Vindhyan basin. Krishnan and Swaminath (1959 ), Lahiri (1964 ), Misra ( 1969 ), Banerjee (1974), Singh (1980) and others have given detailed accounts of the stratigraphy and the depositional environments of these units. Mathur (1981a) first pointed out the cyclic nature of the Vindhyan Supergroup and recognized five cycles in the Semri Group in the Type area. The Rohtas Formation, which forms the topmost unit of the Semri Group, relates to younger cycles IV and V. Recently, Chanda and Bhattacharya (1982) have given a general review of Vindhyan sedimentation and palaeogeography. The stratigraphic sections of the Rohtas Formation of the Semri Group measured for the present investigation lie near Tiura-Pipradih (23 °20', 84 °05') and Dhabua (24 °34', 83 ° 48'), Rohtas District, Bihar ( Survey of India, toposheets 63 P/10 and 63 P/14). These quarry sections are located 66 and 61 km, southwest of Dehri-On-Son railway station, respectively (Fig. 1 ). In these quarry sections, the Rohtas Formation is composed mainly of alterhating layers of limestone and shale of varying thickness (Fig. 2a,b ). The beds are horizontal except for a few small folds. The total exposed thickness of about 100 m of the Rohtas Formation in these areas may be divided into two units on the basis of dominant colour, lithological associations and sedimentary structures. The lower micritic limestone unit is generally dark-grey, alternately bedded with carbonaceous black shale exposed near Tiura-Pipradih (Pipradih I). Framboidal pyrite balls of ~<3 cm in diameter are also commonly associated with limestone and shale. The limestone is characterized by parallel horizontal laminations and the master bedding plane is often marked by very thin (mm dimension ) shaly partings. The amount of insoluble residue in the limestone fluctuates almost regularly from bed to bed and

141 e4°

PIPRADIH

[

~:"..

INDIA

(' ~r" •

~" ~!

25 ©

0

,

,~

DELHI ".-. VARANASI •

i

LOCATION

Insoiubiee'l.

1000 km

! .

I

I0

,! ~-~

, /

~

.

"-,._

-

I

,

o *

( ~

'-

Y

._--..

I

I

-- 26a

ALCUTTA~

• •e

--

:*

._

-.

"--

~ VAR4"~.~aSASARA M

•

•

.-~

~

Dhobuo

--

:

86.°

~=

Be•

"-

""

2So -

.

•

T]U~RA

\):,..o., 26~

SECTION

10 20 30

t I / ~ C A L ~ U T TA I|BOMBAY~

I

MAP

8 o

6°

**

"D

~~

.--

o~

: --

Fig. i. Location map of measured sections Pipradih I and

el

"

'.

.--

"

._.

.._ "-

-

•

"--

_

.tO

0

-~

O

0

=J

JO

n

O ~..

lo C

"o

~ W

O =1

~.

~

I0

o"

>u

~

0

,',

'o

>

"~

0

,

2

•

Q)

~ - ~ ~ It.~o ~ ._: o = ~ . " o z ~ = o E ~. ~ ~ ~ o o ~ ~ ~ ~- ] o ~ o o

". •. • • o • "

e,,P

o ~

~ ~ .o -

,-

-

•

--

o.

~ .o.o~

I.

~~

--

~o.

E

-

'--

limestone is dominantly microsparite or sparite in which carbonate grains measure 4-15/~. Its insoluble residue ranges from 7.5 to 19.5% coarse silt-sized detrital quartz grains, chert, and illite-clay mineral. Occasionally, it exhibits small-scale wave ripples, micro-cross lamina-

,.

• .

H.

varies from l4 to 21% fine silt-sized quartz, carbonaceous material, illiteand globular pyrites. The carbonaceous black shale is thinly laminated, silty and contains < 10% carbonates. The limestone becomes nodular and siliceous together with a decrease in the amount of carbonaceous materials in the shale in the upper part of the lower unit. The nodular limestone is greyish black, pyritiferous, fine-grained, hard and massive in nature. Ellipsoidal or irregular limestone nodules measuring 5-95 cm in length, are embedded parallel to wavy laminations within the carbonaceous shale bands. T h e upper unit consists of alternating thickbedded limestone and calcareous shale. It is well exposed at Dhabua quarry section (Pipradih II), about 5 km N E of Tiura-Pipradih. The

w JO

ee

a.

I ~

---

Sha,,

~l,,tone position

Relative

of

,,,a.*.," be~,,"~n~ p'a.B

Fig. 2a. Diagrammatic section of the lower unit of the Rohtas Limestone-shale at Pipradih I (Tiura-Pipradih).

tions, parallel laminations, algal laminations, few scattered brownish micritic intraclasts, peloids and laminoid fenestral fabric. The lime-

142 II SECTION

PIPRADIH

,~,ub,,../. ~ '~ ~ 3'0 "- : .... . .-- " .... : = g ._ " o: ~ , q) .l,,. • E ~ -~ o ,-

2e4 m "

---

.o

o

.~ oE = 2

...;

"

v~

=

•

~ '~ -~

E

~ = ~- ~ ~,

_~

3~, ~.- ~o = ~

~,

_

,owe,:t

.._ .

s

[

.

= ~ ~ -" 0 N ~ ~= := "~ ~ s

•

:

-

.-• .__ -

0..i

i I

--

o =o ~ ~ o ~ ~ .~ 0

~

°o '~" "a E "~

~ ~

a.

U

O

s_

&,,.

"

-•

N

O

~

~

E

~°"

~,

o ~ ~

~

~ ~ ~ ~ ~

~

-§ ~ E ~ = ~ ~= -~ o~ >. o ::. ~

==

.

.

~ ~

o

-~ ~ ~ ~ = = ~ E ~, ~ ~ ~= ._ ..~ 0 0 ¢~

~

~ ~ - ~ •.= ~

•

--

•

• .

• "

~

o

~

=

•

531 m

I~

"~

.

__

_. __

o

E

o ~ ~ =

•

- - .

~

~ ~

---

• .

--

---

O~

3 3 u

°~ o __

--

careous or marly, grey to yellowish grey, mode r a t e l y h a r d a n d c o n t a i n s a b u n d a n t coarse siltsized s u b - a n g u l a r q u a r t z grains. Acid insoluble residues of t h e lower u n i t do not show appreciable v a r i a t i o n as c o m p a r e d to the u p p e r l i m e s t o n e unit. H o w e v e r , bed to b e d insoluble residue analysis shows a n approxim a t e l y regular f l u c t u a t i n g t e n d e n c y in the seq u e n c e m e a s u r e d in the field. T h e l i m e s t o n e shale a l t e r n a t i o n s are more f r e q u e n t in t h e

~

z z ' ~

~

~

.~

~

~= ~

§ .o

~

.~

o

~, -o ~

"~

E ~:

~= ._~ ~ ~

°o

~,-, o~'

' ~otto~ Shot, Limesto.¢ ---

ReLative position of

mo,t,r

b,ddingp[on¢

Fig. 2b. Diagrammatic Section of the upper unit of the Rohtas Limestone-shale at Pipradih II (Dhabua).

stone is p a r t i a l l y d o l o m i t i z e d a n d c o n t a i n s irregularly a n a s t o m o s i n g micro-stylolite sets in t h i n sections. T h e shale is l a m i n a t e d , m o r e cal-

aoiot

eu

e,'uo*t'r

e,i

estooeas

well as shale in the lower u n i t are more darker, t h i n a n d s t r u c t u r e l e s s ( e x c e p t parallel lamin a t i o n s ) in c o m p a r i s o n with t h e u p p e r unit. T h e sequence grades a b r u p t l y u p w a r d into well sorted, p r o f u s e l y cross-bedded U p p e r Vind h y a n K a i m u r q u a r t z arenite. T h e regular cyclic a l t e r n a t i o n of shale and fine-grained argillaceous l i m e s t o n e a p p e a r s t o

be due to p r i m a r y s e d i m e n t a r y processes. T h e s e d i m e n t a r y origin is f a v o u r e d b y a lateral persistence of individual b e d or bedding over rem a r k a b l y wide distances ( m a s t e r bedding p l a n e s ) , wave ripples, c r o s s - l a m i n a t i o n s a n d shale parting. T h e diagenetic process, however, has modified t h e sequence as i n d i c a t e d b y stylolites, d o l o m i t i z a t i o n a n d c r y s t a l l i n i t y ofillite. T h e R o h t a s l i m e s t o n e - s h a l e sequence carr e s p o n d s to a s e d i m e n t a t i o n w i t h i n 'Zone Z' of the I r w i n - L e s s M o d e l (Flugel, 1982) indicating d e p o s i t i o n in a shallow water, low e n e r g y shelf area. H o w e v e r , the sedimentological feat u r e s such as d a r k colour, p y r i t e framboids, mon o t o n o u s r e p e t i t i o n of parallel a n d u n i f o r m l y thick l a m i n a t i o n s of micritic limestone (or lime m u d s t o n e ) a n d d a r k shale, absence of f e n e s t r a l fabrics indicate t h e deposition of lower u n i t below wave base in a r e d u c i n g deep subtidal env i r o n m e n t . Local instability in t h e basinal c o n d i t i o n is i n d i c a t e d b y silty i n t e r c a l a t i o n s in shale a n d a p p e a r a n c e of nodular limestone n e a r the j u n c t i o n of lower a n d u p p e r l i m e s t o n e - s h a l e sequence. T h e c h a n g e in s e d i m e n t a r y c o n d i t i o n is f u r t h e r reflected in the gradual c h a n g e of l i t h o - u n i t s f r o m d a r k to light coloured micritic to m i c r o s p a r i t i c limestone, c h a n g e in average

143 bed thickness, occasional intraclasts and peloids, algal laminations, laminoid fenestral fabric, small-scale wave ripples, micro-cross laminations and dolomitic nature of the upper unit. This suggests a gradual shallowing of the sea floor with a change in the depositional milieu from a deep subtidal to an open shallow subtidal or an intertidal marginal marine environment. Lastly, terrigenous influx increased during regression and uplift of the basinal floor. E x p e r i m e n t a l design and collection of data For the quantitative analysis of a vertical section, it is necessary to express equally-spaced petrographic variables of the lithological units in ordered numerical terms. At Pipradih I quarry, 35.8 m of measured section contains 66.8% limestone and 33.2% black to grey shale, The average thickness of limestone and shale beds are about 32.5 cm and 8.5 cm, respectively. The quarry section at Pipradih II represents the upper limestone-shale unit which contains 51.4% limestone and 48.6% calcareous shale in 33 m of the section. The average thickness of limestone beds is 37.5 cm whereas that of shale bed is about 50 cm. The vertical gap in measurement between two horizons or units is ~25 m of nodular limestone and shale. The sections are completely exposed in both Pipradih I and II quarries and horizontal beds of limestone and shale were measured with a metrestick to the nearest centimetre. The master bedding planes are traceable for long distances and are usually marked by mm dimension shaly partings. As the average cornbined thickness of limestone-shale couplets is about 41 cm in the lower unit, and thickness of sections are 35.8 m and 33 m, it would be suitable to examine the above sections for periodicities ranging from a wavelength of 1000 cm to 40 cm. The sampling interval, Ax, may be found from the following relationship (Schwarzacher, 1975 )

1 Ax =

2o)0 where COo stands for the Nyquist frequency which is the highest frequency that can be detected with data sampled at an interval Ax. Thus, in the present situation Ax-- 2

1

- 2 0 cm

1/40 Thus, the entire sequence at both Pipradih I and Pipradih II was subdivided into 20 cm intervals. For each 20 cm interval, the percentage of limestone is calculated from the measured thickness data in centimetres. The values for limestone percentage form the raw data for auto-correlation and spectral analyses. Figure 3 shows the limestone percentage trends for two measured sections at 20 cm intervals. The graph indicates that the fluctuations are approximately systematic about the mean value. This has been tested by the 'statistic K' (Kendall, 1946). It is defined as 3 R - 2n + 2.5 K= x / ( 1 6 n - 2 9 )/10 where R = number of runs between turning points, n = number of observations. In the present case, the values o f K f o r Pipradih I (R=68, n=179) and II (R=17, n=165) sections are -8.997795 and - 17.111693, respectively. The probability of these values of K as read from the table of normal probability integral is < 0.001. Therefore, the limestone percentage fluctuations as shown for the sections follow a nonrandom distribution.

Method of analysis Power spectrum analysis using autovariance functions has been used extensively for varved sediment of varied geological ages (Anderson and Koopmans, 1963; Preston and Henderson, 1964; Jackson, 1965; Agterberg and Banerjee, 1969). Schwarzacher (1964) a n d M a n n (1967) have also applied this technique to cyclic stra-

144 PIPRADIH

2J

I

20 0

,

0

5

10

15

20

25

30

35 36

Z'5

30

3'5

Elevation in metres above base

PIPRADIH I I

60 4O ~

20

0

5

10

15

ZO

Elevation in metres above base

Fig. 3. Limestone percentage calculated for 20 cm intervals. tigraphic sequences other than varves. Since most geological data arranged in a stratigraphic sequence denotes some relationship with time, the application of power spectrum analysis (Blackman and Tukey, 1958; Mitchell et al., 1966; Chattopadhyay, 1970) can discern the probable time periodicities in the repetitive sequence, Let us consider a series of observations Xl, x2, X3...Xn recorded at time interval At (or/ix in case of stratigraphic measurement w h e r e / i x refers to thickness) • The serial ( or auto- ) correlation coefficients or normalised covariances p (0), p ( 1 ) , p ( 2 ) ........ , p ( m ) were calculated f r o m t h e data and these were used to obtain spectral estimates at m discrete frequencies. For this, a T u k e y - H a n n i n g window was used (Tukey, 1950). The number of lags m was kept to between 10 and 15% of the original number of observations n (Schwarzacher, 1975). The results of the power spectrum analysis can be assessed by means of a suitable statistical significance test. I f p (1) does not differ from zero by a statistically significant amount, the time series has no persistence• In this case, the appropriate 'null continuum' is a horizontal line

(i.e. 'white noise' in the spectrum), the ordinate value of which is equal to the average of ( m + 1 ) raw spectral estimates. But if p (1) > 0 by a statistically significant amount, find w h e t h e r p ( 2 ) ~ - p 2 ( 1 ) ; p ( 3 ) ~ p 3 ( 1 ) etc. In such a case, a Markovian type of persistence in the series is indicated. The 'null continuum' is estimated by the equation 1 _p2 (1) s~=g

~k 1 +p2 (1) - 2p (1) cos -m-

where gis the average of all ( m + l ) raw spectral estimates (sk). The smooth curve passing through these values, represents a 'null continuum' level below which all spectral peaks are highly unreliable. To check other forms of non-randomness of the time series, in addition to persistence, we compared each smoothed spectral estimate sk, with the corresponding value of the 'null continuum' s~. According to Tukey (1950), the ratio of these two values has a distribution similar to the chi-square divided by degrees of freedom (p). The number of degrees of freedom (~) is

145 related to n and m according to the equation (Tukey, 1950) v = (2n-m/2)/m

The 95% confidence limit for v is obtained from the standard table of the chi-square distribution. This value is multiplied with ordinate value of 'null continuum' at each harmonic to obtain a smooth curve of the '95% confidence limit' for the spectrum. From the graph, the spectral peaks 95% confidence limit represent real oscillations in the observations. P o w e r s p e c t r u m a n d geological interpretation The power spectrum or a plot of spectral estimates versus harmonic numbers enables us to detect the possible frequencies at which most variance of an observed series is located. The power of pure random variation (white noise) tends to be constant for the whole spectrum. If a pure sine wave is present in the time series, the spectrum would show sharp and definite peaks at appropriate wave lengths. If quasi-periodicities or irregular oscillations are present in the series, then the spectrum contains less sharply defined maxima, In general, a peak in the spectrum above the 95% confidence limit (C.L.) and above indicates that oscillation with corresponding frequency is more plausible in the series than those below C.L. with neighbouring frequencies. Several peaks in the spectrum indicate the influence of different physical mechanisms generating a given time series. I f a time series does not show any periodicity other than Markovian persistence, i.e. each value of the series is influenced by its immediatelypreceding value, the spectrum would exhibit distortion towards a lower frequency. Conversely, the amplitude of the spectrum decreases from longer to shorter wavelengths. The spectrum resembles that of 'red noise'. It further indicates that the process generating the time series is partly deterministic and partly random. It should be pointed

out here that all spectra exhibit variance or power concentration toward the low frequency end, and hence peaks in the low frequency region may not be representative of a significant periodicity in the spectrum (Schwarzacher, 1983). In the present investigation, although the rate of sedimentation or actual time involved in deposition is unknown, the spectral analysis gives some insight into the conditions under which the sequence was laid down. In the case of the lower unit, the limestone percentages are calculated at 20 cm thick intervals. The 35.8 m long section of Pipradih I gave therefore 179 points. The maximum lag 'm' chosen for autocorrelation and spectral estimates is 25. The serial or autocorrelations with different lag values are shown in Fig. 4a. The lag one serial correlation [p (1) = 0.30] is not significantly greater than zero, butp(2) _~p2(1) and p ( 3 ) -~p 3 (1) indicate a linear Markov type of persistence. The autocorrelation coefficients do not show a tendency to damp out. It indicates that the process responsible for deposition was of harmonic character. The power spectrum plot in Fig. 4b exhibits a significant spectral peak at 9 cycles 1000 m - 1 corresponding to the wavelength of 111 cm. Other peaks at 14 and 24 cycles 1000 m -1 are subdued in nature because they occur below the 95% confidence limit. For the 3300 cm sequence of thick limestone and shale at Pipradih II, the serial or autocorrelation coefficient is significantly greater than zero [p(1) =0.86] with p ( 2 ) ~p2(1) and p ( 3 ) -~p 3 (1) ( Fig. 5a). The above relationship indicates that the series contains a strong linear Markov type of persistence, with a negative slope. The power spectrum in Fig. 5b exhibits the presence of spectral peaks at 9, 11, 13, 15, 22 and 24 cycles 1000 m - 1corresponding to the wavelengths of 111, 91, 77, 67, 45 and 42 cm, respectively. The spectral peak at 9 cycles 1000 m-1, which corresponds to a wavelength of 111 cm, appears to be more significant.

146 10 1 0.8.

c~ 0"6" l....... .9 o.z,

u "3 0 . 2

O} \;zO) p

o

P

Log

in c m

-~-

-0.2

-0.4

Fig. 4a. Autocorrelations of limestone percentages in Pipradih I section. 0.14 •

0.10

E

~"'c'v~ . .......... o . ~

...~<.

0.08

O

"-o.:~

"o. "~,

'b. OO

" ~

l

'71 c m

Q. m 0.0~-

---~-...o.__o_

10

__o. __a_ - --o--

r

E0.02

~'

q)

o

2

4

1'4

6 k

Harmonics

2'o

2'6

(Cycles per ]000crn)

Fig. 4b. Power spectrum of the limestone percentage in Pipradih I section. Prominent peaks are shown by vertical lines.

The analysis therefore demonstrates a significant periodicity of ~ 111 cm in both stratigraphical units. The corresponding sedimentary oscillations are also recorded in the field as the grouping of limestone and shale into distinct units marked by master bedding planes and fluctuations in insoluble residue percentage (Fig. 2a,b). However, the variation in spectral pattern of the two units with respect to Markovian persistence and amplitude of peaks may

be attributed to local tectonics or environmental factors. It has already been concluded from lithological and sedimentary attributes that the repeated sequence of limestone-shale was deposited in low energy deep subtidal shelf to open shallow subtidal or marginal marine environments. However, it is interesting to note that although there are variations in lithological characteristics, thickness of component

147 1.0 ,.p (11

0.8

0.6

~V,,., p 2 (1)

e'X~ ~'p~(~I

C

,~ 0.4 t.

0.2

uo

5

20

-0.2

Log

25

in cm

0.4 Fig. 5a. Autocorrelations of limestone percentages in Pipradih II section. 0.16 0.16

t I

,, 0.14

. f,

~ 0.12

E

o.1o

0.08

~-,.. ,-6. \

W

~

0.06

O\

= ~o.o,

~

111cm

%~I',,"% I ~:"I'~% I ' " °'

0.02

4~cm

I ".°" -.=1 I I 2. J "'0--

0

2

4

6

..

..

4(--

I I

='.°° 1 l

22

24

-44--

8 10 12 14 16 18 k - H o r m o n i c s ( C y c l e s p e r 1 0 0 0 crn)

20

26

Fig. 5b. Power spectrum of the limestone percentages in Pipradih II section. Prominent peaks are shown by vertical lines.

lithic units, and physical environments of deposition, the persistence of the oscillatory time series indicates a long-range independent rhythmic process during deposition. Major processes controlling cyclic sedimentation (Duffet al., 1967) are: (1) eustatic changes in sea level;

(2) changes in climate; and (3) the effect of large-scale tectonic movements of the Earth's crust. However, the changes in sea level themselves may be induced by either changes in climate (i.e. by alternating glaciation and deglaciation) or by global tectonic movements.

148

The record of Precambrian glaciation is vague and uncertain in the Vindhyan Supergroup although Mathur (1981b,c) has reported localized Lower Vindhyan diamictite (Basal conglomerate of Auden, 1933). Lower Vindhyan sedimentation commenced at c. 1400 Ma ago (Crawford and Compston, 1970) when the metamorphic and plutonic events were active at depth in the Eastern Ghats, Satpura and Aravalli-Delhi Orogenic belts (c.900-1600 Ma, Sarkar, 1980). During this time interval ( middie Proterozoic), tectonic movements took place in the Baltic and Ukranian shield Ripheides 1/Marealblan), Australia (Musgrave, Bangemall), Africa (Kibaran, Burundian, Karagwe-Ankolean), North America ( Greenville/Older B l a c k H i l l s ) , and Scotland (Gairlochean) accompanied by igneous intrusions, metamorphism and development of intracratonic basins. In discussing the palaeogeography of Vindhyan times, Sahni (1941) and Krishnan and Swaminath (1959) indicated a wide extension of the Vindhyan sea and the existence of its Himalayan equivalents (Tals, Krols, Blaines, Jaunsars) further eastwards through Assam, Burma ( Chaung Mogyi Series) and into the provinces of Shanshi, Shantung and Manchuria in China (Sinian System). An extensive development of lithic units over a wide area, and shallow water facies with alternating lithologic changes (Duff et al., 1967) further imply eustatic control of sea level during the deposition. It is therefore, suggested that, although the fluctuations of calcium carbonates could result from local changes in depth, water-mass composition, and terrigenous clay sedimentation, the worldwide tectonic movements during the middle Proterozoic (Windley, 1981) w e r e mainly responsible for eustatic sea-level fluctuations and resultant cyclicity in the Lower Vindhyan limestone-shale sequence. This assertion could be proved if similar cyclicity could be found on a worldwide basis.

Acknowledgements The authors record their appreciation to Prof. P. Enos, University of Kansas, and Prof. W. Schwarzacher, Queen's University of Belfast, for critically reviewing an early version of the manuscript and offering many constructive suggestions. Thanks are also extended to Dr. J. Chattopadhyay, Geophysics Department, B.H.U. for his invaluable discussion on power spectrum analysis.

References Auden, J.B., 1933. Vindhyan sedimentation in the Son Valley, Mirzapur District. Mem. Geol. Surv. India, 62: 141150. Agterberg, F.P. and Banerjee, I., 1969. Stochastic model for the deposition ofvarves in glacial lake Barlow-Ojibway, Ontario, Canada. Canada. J. Earth Sci., 6: 625-652. Anderson, R.Y. and Koopmans, L.H., 1963. Harmonic analysis of varve time series. J. Geophys. Res., 68: 877893.

Banerjee,I., 1974. Barrier coastline sedimentationmodel and the Vinhyan example. Geol. Min. Met. Soc. India,

GoldenJubilee Volume,46: 101-127.

Blackman, R.B. and Tukey, J.W., 1958. The Measurement of Power Spectrum. Dover,New York, 190 pp. Chanda,S.K. and Bhattacharya, A., 1982.Vindhyan sedimentation and paleogeography: Post-Auden developments, In: S.B. Bhatia, V.K. Gaur and K.S. Valdiya (Editors), Geology of Vindhyanchal. Hindustan, (India): pp. 88-101. Chattopadhyay, J., 1970. Power spectrum analysis of atmospheric ozone content over North India. Pure Appl. Geophys., 83: 111-119. Crawford, A.R. and Compston, W., 1970. The age of the Vindhyan system of Peninsular India. Q. J. Geol. Soc. London, 125:351-372. DeBoer, P.L., 1982. Cyclicity and the storage of organic matter. In: G. Einsele and A. Sellacher (Editors), Cyclic and Event Stratification in Middle Cretaceous Pelagic Sediments. Springer-Verlag, Berlin, pp. 456-475. Duff, P.McL.D.,HaUam, A. andWalton, E.K.,1967. Cyclic Sedimentation. Elsevier, Amsterdam, 280pp. Flugel, E., 1982. Microfacies Analysis of Limestones. Springer, Berlin, 633 pp. Harbaugh, J.W. and Merriam, D.F., 1968. Computer Applications in Stratigraphic Analysis. Wiley, New York, 282 pp.

149 Jackson, T.A., 1965. Power-spectrum analysis of two "verved" argillites in the Huronian Cobalt Series (Precambrian) of Canada. J. Sediment Petrol., 35: 877-886. Kendall, M.G., 1946. The Advanced Theory of Statistics, II. Griffin, London, 521 pp. Krishnan, M.S. and Swaminath, J., 1959. The Great Vindhyan basin of northern India. J. Geol. Soc. India, 1: 10-30. Lahiri, D., 1964. Petrology of the Vindhyan rocks around Rohatasgarh. India. J. Sediment Petrol.,34: 270-280. Mann, C.J., 1967. Spectral-density analysis of stratigraphic data. Kansas Geol. Surv., Comput. Contrib., 18: 41-45. Mathur, S.M., 1981a. Cyclic sedimentation in the Vindhyan Supergroup. Rec. Geol. Surv. India, 112, VIII: 16.

Mathur, S.M., 1981b. Basal Vindhyan diamictite in the Son Valley, Central India, In: M.J. Hambrey and W.B. Hatland (Editors), Earth's pre-Pleistocene Glacial Record. Cambridge University Press, Cambridge, pp. 424-427. Mathur, S.M., 1981c. The Middle Precambrian Gangau tillite, Bijawar Group, Central India. In: M.J. Hambrey and W.B. Harland (Editors), Earth's pre-Pleistocene Glacial Record. Cambridge University Press, Cambridge, pp. 428-430. Misra, R.C., 1969. The Vindhyan System: Proc. Indian Sci. Congress (56th Session, Bombay), pp. 111-142. Mitchell, Jr., J.M., Dzerdzeevskii, B., Hofmeyr, W.L., Lamb, H.H., Rao, K.N. and Wallen, C.C., 1966. Climatic Change. W.H.O. Technical Note No. 79 (Geneva), 100 pp. Preston, F.W. and Henderson, J.H., 1964. Fourier series characterization of Cyclic sediments for stratigraphic correlation. In: D.F. Merriam (Editor), Symposium on cyclic sedimentation. Kansas Geol. Surv. Bull., 169 (2): 415-425. Sahni, M.R., 1941. Palaeogeographical revolution of the

Indo-Burmese region and neighbouring lands (Vindhyan to Devoaian). Presidential Address, Ind. Sci. Congr. 28th Session, Varanasi, pp. 121-128. Sarkar, S.N., 1980. Precambrian stratigraphy and geochronology of peninsular India. Ind. J. Earth Sci., 7: 1226. Schwarzacher, W., 1964. An application of statistical timeseries analysis of a limestone-shale sequence. J. Geol., 72: 195-213. Schwarzacher, W., 1975. Sedimentation Models and Quantitative Stratigraphy. Elsevier, Amsterdam, Dev. Sedimentology, 19,382 pp. Schwarzacher, W. and Fischer, A.G., 1982. Limestone-shale bedding and perturbations of the Earth's orbit. In: G. Einsele and A. Seilacher (Editors), Cyclic and Event Stratification. Springer-Verlag, Berlin, pp. 72-95. Schwarzacher, W., 1983. The principles and the treatments of single sections. Fourth Int. Short Course on New Concepts and Methods in Stratigraphy IGCP 148 (I.I.T., Kharagpur, India, 14-17 December 1983), 34 pp. Selley, R.C., 1970. Studies of sequence in sediments using a simple mathematical device. Q. J. Geol. Soc., London, 125: 557-581. Singh, I.B., 1980. Precambrian sedimentary sequences of India: their peculiarities and comparison with modern sediments. Precambrian Res., 12: 411-436. Tukey, J.W., 1950. The sampling theory of power spectrum estimates. Symposium on applications of autocorrelation analysis of physical problems (U.S. Office of Naval Research, Washington, DC ), pp. 47-67. Vistelius, A.B., 1961. Sedimentation time-trend functions and their application for correlation of sedimentary deposits. J. Geol., 69: 703-728. Windley, B.F., 1981. Precambrian rocks in the light of the plate tectonic concept. In: A. KrSner (Editor), Precambrian Plate Tectonics, Elsevier, Amsterdam, pp. 1-16.