indicate that the sediments during the Lariakantha ... order, are exposed in a number of structural basins extending ..... Principles of sedimentary Basin Analysis.,.
Bulletin of the Indian Geologists' Association 29 (1,2) : 37- 46 , June-December 1996, Chandigarh-160
014
Detrital Modes and Provenance Interpretation of the Lariakantha Member (Blaini Formation), Nainital Hills, Kumaun, Lesser Himalaya Charu C. Pant and Pradeep K Goswami
\
Department
of Geology, Kumaun
University, Nainital 263 002
Abstract The upper Proterozoic Lariakantha lithicwacke
and siltstone,
Quartzites ("= 1000 m thick) in the N aintal syncline consists of medium to coarse quartzarenite,
locally containing well-rounded
to sub-rounded
quartzite,
chert and silty lithic pebbles, Forming
an
integral part of the Blaini Formation these rocks overlie the regressive Nagthat Formation with a sharp contact The quartz typology, mineralogical
and detailed petrofacies parameters
of parameters metasedimentary
indicate that the sediments
were used to determine the provenance of the sedimentary
during the Lariakantha
terrain. The ternary plots of the detrital modes reveal recycled orogenic provenance
Introduction The Krol belt sedimentaries comprising Nagthat
- Blaini - Krol
, 1
- Tal
formations, in an ascending
order, are exposed in a number of structural basins extending from Solan in Himachal Pradesh upto Naintal in Kumaun. In Naintal syncline the Nagthat Formation belonging to the Jaunsar Group (Auden, 1934) is overlain by the diamictite bearing Blaini Formation of the Mussoorie Group (Valdiya, 1980). The contact has been shown as very sharp to locally erosinal and even as unconformable (Rupke, 1968; Fuchs and Sinha, 1974). , The Blaini Formation in the Naintal area is divisible into four members (Valdiya, 1980). The oldest Bhumiadhar Member comprising quartzwacke, qurtzarenite, diamictite, siltstone and shale is followedby predominantly arenaceous Lariakan!ha Akmber. It is made up of medium to coarse grained, profusely cross-bedded, wave and current rippled quartzarentes, siltstone and shale with local pebbly horizons. The Lariakantha Member in turn is followed up by the diamictites, purple-grey slates, silstone and lenticular pink siliceous dolomitic limestone of the Pango! Member. The uppermost Kailakhan lvfember
fill. A combination
times were derived chiefly from a granitic
and low garde
for these rocks.
comprises dark grey, carbonaceous-pyritous slates and siltstone. The Blaini Formation grades transitionally into the Krol Formation in present area. The Lariakantha Member has its. excellent development in the Lariakantha ridge (east of Nainital) extending through Kilberry
- Binayak -
Badanthali - Kunjakhark in the northwest of Nainital (Fig. 1.), Although the strcutural set-up and the stratigraphic setting of the Blaini rocks in the Nainital Hills have been discussed by large number of workers, however detailed lithofacies, petrographic and petrofacies analyses have not been attempted. The Blaini rocks of the Mussoorie and Garhwal synclines have been studied in some detail (Valdiya, 1973, Rupke, 1968; Tangri and Singh, 1982; Jain and Varadraj, 1978) and aspects of palaeoenvironment, sediment dispersal pattern and palaeogeographic setting were discussed. Y.:'lriousdepositional models ranging from glacial (Auden, 1934; Bhargava, 1972; Srikantia, 1975; Brookfield, 1987) glaciomarine (Jain and Varadraj, 1978), turbidite (Rupke, 1968; Niyogi and Bhattacharya, 1971)toshallow marine (Singh, 1979; Tangri and Singh, 1982) have been
PANT AND GOSWAMI
38
° 79° 25'
I
79 30
LEGEND Dolerite
dyke
H9°, 30
Upper Kro I
ffiIIIIIII] Honumongorhi
M.
Monoro M.
° ° ° I:':.
Pongot M. BI'olnl . hailakha" M 1 .::1 Loriokontho M. Fm.
1:--:-::1
Bhumiodhor
M.
GEOLOGICAL MAP OF THE STUDVAREA (Aftl!rVoldiyo,
1988
,~
Thrust
~
Motorobll! Rood
+"
2rf
)
Fault
Dip
0
1
,
2 km I
29° :,125'
Fig. 1. Geological map of the northwestem part of Naintal (After valdiya, 1988)
proposed for the sedimentation
"
of these rocks.
The present work deals with the petrographic and petrofacies analysis of the :1:1000 m thick Lariakantha Member of the Blaini Formation along the Kilberry
-Pangot
- Binayak,
Badanthal!-
Kunjakharak, and Lariakantha sections. An attempt has been made to reconstruct the nature of the source area, using mineralogical composition, quartz typology, framework modal parameters and characters of the associated petrofacies.
Petrography Methodology
A large number of thin sections were made of samples collected systematically along different sections and severely deformed, altered thin sections were discarded. A total of fifty thin sections were selected for petrofacies analaysis. In the present study 500 points in each thin section, using Swift Point Counter, were counted
PROVENANCE
Q
INTERPRET ATION OF THE LARIAKANTHA
39
Q
abraded overgrowth of silica. The population showsa large variation in grain size (Fig. 3b) from 0.1 mm to 3.3 mm. Majority of the grains (80%) of the populationshow weak undulatory extinction (Fig. 3d) and remaining poluation exhibits straight to moderate undulosity.
lorMx>15'/,
F
MEMBER
F
Fig. 2. Ternary plots (QFL) of the sandstones ofthe Lariakantha Member (Q=(Qm+Qp);
F= (P+K); L=(Lv+Ls+Lm).
to characterize the detrital modes of sandstones. The points counting parameters are mostly those defined by Dickinson (1970, 1988). The grid spacing used in point counting exceeded the grain size so that the individual grains were not counted more than once (Cf Vander Plas and Tobi, 1965). Metamorphic lithic fragments (Lm) were distinguished from sedimentary lithic fragments (Ls) by the preferred alignment of the grains (Metamorphic fabric) in the former. The quartz grains having'more than two extinction directions were categorised as polycrystalline quartz. The detrital modes of the arenites and wackes are shown in Tables 1 and 2 respectively. Framework Modal Parameters The ternary plots (Fig. 2) of the sandstones of the Lariakantha Member reveal that the rocks chiefly belong to quartzarenite (0.25-1.0 mm) and quartzwacke (0.25 - 0.45 mm) types. The detrital framework elements of these rocks being almost same (Table 1.). The chief framework elements are described below in order of decreasing aboundance. (i) Monocrystalline Quart (QM): The monocrystalline quartz grains, constituting 51 to 76 modal percent in arenties and 36 to 66 modal percent in wackes, are generally subrouunded to rounded in shape (Fig. 3a). A few grains manifest
(ii)Polycrystalline Quartz (QP): Constituting 6 to 21 modal percent in arenites and 2 to 26 modal percent in wackes the grains being subrounded to rounded (Fig. 3e). The grains generally comprise more than eight internal crystals which show variation in size. The internal crystals vary in size from fine sand to coarse silt. Generally the polycrystalline quartz are bigger than monocrystalline quartz. The population generally is composed of the follwing four varieties of polycrystalline quartz. (a) Internal crystals with random arrangement, (b) Intercrystalline boundaries having sutured nature and showing strongly undulose nature, (c) Internal crystals showing preferred alignment, and (d) Internal crystals showing moderate to strong elongationand strong crystallographic orientation. (iii) K-Fledspar (K): The K-feldspar population of the sandstones comprises untwinned orthoclase and micro cline along with a few twinned orthoclase. The grains are almost equal to the quartz grains in size and generally show corroded margins (Fig. 3a and d). K-feldspar pseudomorphs comprising largely sericite are also observed (Fig. 3b and f.) The modal percenatage ofK-feldspar in the rock is highly variable being 0-11.5% in wackes and 0.5 to 14% in arenites (Table 2,3). (iv) Plagioclase Feldspar (P) : The population mainly comprises altered and fresh labradorite, albite and subordinate amount of oligoclase. Sericite and chlorite are the chief alteration products. Significantly, the size of the grains is almost equal to the quartz grains. The modal
40
PANTAND GOSWAMI
Table 1. Recalculateddetrital modes for Arenites. QmFLt(%)
QFL(%) Qm
%Op
%P
%K
%L
%Mx
Q
F
L
Qm
F
Lt
GB 53
70
6
2
9
6
7
82
12
6
76
12
12
GB52
68.5
6.5
2.5
9.5
6
7
81
13
6
71
13
16
GB51
64.5
8
1
11.5
5
10
81
14
5
72
14
14
GB43
63.5
16
0.5
8.5
6.5
5
84
10
6
67
9
24
60
12
28
65
10
25
63
9
28
SampleNo.
GB42
54
20
1
10
6
9
81
12
7
10
6
9
4
GB41
58
17
0.2
8.8
5
11
84
GB39
59
21
1
&
4
7
87
\.
GB38
56
21
--
10
3
10
86
11
3
63
11
26
GB37
57
21
--
11
5
6
83
12
5
60
12
28
GB34
54.5
16.5
2.5
7.5
4.5
14.5
84
11
5
64
11
25
GB33
52.5
17
1.5
10
4.5
14.5
81
14
5
61
14
25
GB25
66
11
7
5
6
11
87
6.5
6.5
74
6.5
19.5
GB23
69
13
5.5
0.5
5
7
88
7
5
74
7
19
GB 19
60
17
2.5
5
4.5
11
86
9
5
68
9
23
GN7a
55.5
6.5
3
9.5
14
11.5
70
14
16
63
14
23
GN7
51
12.5
I
14
8
13.5
73
17
10
70
4
24
GN4
65
14.5
I
3
9
7.5
86
4
10
70
4
26
GNI
60
8
3
6.5
11
11.5
77
11
12
68
11
21
11.5
--
0.5
11.5
5
87.5
0.5
12
75.5
0.5
24
5
GGl6
71.5
GP 12
76
6
0.5
2.5
4
11
92
3
85
3
12
GK9
56
11
0.5
12
11.5
9
74
14
13
61
14
25
Mean
82.5
10
7.5
67.5
10
22.5
percentage of population varies from 0-5% in wackes and 0-5.5% in arenites. (v) Lithic Fragments (L) : Constituting 3 to 14 modal percent in arenites and 1.5 - 18% in wackes the lithic fragments are primarily of the sedimentary affinity alongwith a few low grade metamorphic grains. Significantly, no igneous rock fragments (iv) were encountered. Most dominant lithics are the shale fragments (Fig. 3b) which commonly occur as flakes (upto 7.5 mm
long). In some thin sections these labile flakes are severely squashed and it becomes difficult to distinguish between detrital matrix and the clasts (Fig. 3g). The other important lithic fragments being siltstone (Fig. 3c), chert, quartzose wacke, quartzites (Fig. 3c) and a few carbonate. The nature of polycrystalline quartz grains and schistose fabric of siltstone and arenites manifest derivation terrain
of a few clasts from metamorphic
(quatzose
schist).
41
PROVENANCE INTERPRETATION OF THE LARIAKANTHA MEMBER
Table 2. Recalculated detrital modes for Wackes. QmFLt(%)
QFL(%) %1
%Mx
Q
F
1
Qm
F
Lt
11.5
3
17
77
19
4
63
19
18
5
7.5
4
19
79
16
5
63
15
72
26
2.5
5
1.5
22
88
10
2
55
10
35
45.5
8.5
0.8
0.2
18
27
74
2
24
62
2
36
GB40
55
17
I
8
4
15
85
10
2
64
II
25
GB32
51
10
I
10
5
23
80
14
6
66
14
20
GB31
49.5
13
1.5
II
8
17
76
15
9
60
15
25
GB27
56
7
1.5
11.5
4
20
79
16
5
71
16
13
GB24
60.5
15.5
I
5
2
.
16
90
8
2
72
7
21
GB21
51.5
10.5
2
3
4
29
87
7
6
72
8
20
3.5
27.5
86
9
5
78
9
13
Qm
%Op
%P
GB48
52
11.5
5
GB47
51
13.5
GB46
43
GB45
SampleNo.
%K
"
GB 16
56.5
5.5
3
4
GB 15
69
II
---
0.5
3
16.5
96
0.5
3.5
82
0.5
17.5
GB 14
50
8
2.5
7.5
2
30
83
14
3
72
14
14
GB 13
54
9
4.6
4.4
5
23
83
II
6
70
II
19
GB 9
63
12
I
2
22
96
1.5
2.5
81
1.5
17.5
GB5
66
10
0.5
1.5
6
16
91
2
7
79
2
19
52.5
5.5
2.4
4
II
24.5
77
9
14
69
9
22
Gg15
51
II
---
1.5
10
26.5
84
2
14
70
2
28
Gg10
53
16.5
---
I
8.5
21
88
I
13
81
II
67
I
32
G:--J8
Gg9 Gg8
49 55
--
6
---
---
7.5
37.5
88
15
---
15
5
24
92
2
6
72
2
26
---
1.5
41
26
93
2
5
72
2
26
0.5
7
37.5
85
.4
4
38
80
5
Gg7
53.5
15
Gg3
36
17
2
10.5
--
G8
56.5
19
--
4
12.5
16.5
II
58
15
68
5
27
9
15
56.5
2
I
5.5
9.5
25.5
79
9
12
76
GK5
60
6.5
--
3.5
8
22
85
5
10
77
5
18
GK7
56.5
7.5
--
I
15
20
79
2
19
70
2
24
GKIO
56.5
8.5
--
4
II
20
81
5
14
71
5
24
Mean
84.4
7
8.6
70
7
23
G2
42
PA"T .\NO ti:
44
PANT AND GOSWAMI
opaques were excluded.
Provenance
Interpretation
It has long been recognized that the sandstone composition is useful to unravel source area lithology and, indirectly, to characterize the palaeotectonic setting of the siliciclastic deposits (Krynine, 1942). Other factors such as .climate and relief of the source area, abrasion and reworking in some specific environments and diagenesis also control and alter the detrital composition of sediments (Folk, 1980; Stunner, 1979; Basu, 1985; Pettijohn et al., 1980). The petrofacies analysis in conjucture with petrographic data has been helpful to unravel the source area lithology and a elucidate the tectonic setting for ancient detrital sequences. Petrographic evidence The Lariakantha sadnstones on an average comprise 58% monocrystalline and 12.3% polycrystalline quartz. The non undulose to slightly undulose character of the monocrystalline quartz represents a plutonic source (Folk, 1974; Abdel Wahab, 1992). However, the derivation of no undulose quartz grains from a sedimentarty terrain can not be ruled out. The abraded overgrowths also support this deduction.
attributed to their transformation into clay minerals during the locomorphic stage of diagensis (McBride, 1987). The rock fragments conclusively prove their derivation from sedimentary and metamorphic parentage. The rounded to subrounded hornblende grains persist throughout the succession. Other common accessories are ziron; muscovite and magnetite (opeque). Evidnece from petrofacies analysis The recalculated detrital modes of the arenites and wackes when plotted in the QFL and QmFLt diagrams (Dickinson and Suczek, 1979; Dickinson, 1988) (Fig. 4) manifest striking similarity of the modes. The two rock typesbelong to a single petrofacies (Q 84.4 F 7 L 8.8 QM 70 F 7 Lt 23 for wackes and Q 82.5 F 10 L 7.5; Qm 67.5 FlO Lt 22.5 for arenite). The petrofacies being mineralogically mature (Fig. 4). The QFL and Qm FLt ternary plots for Larikantha Quatzites show that 94% of the total plots fall within the field of recycled orogen provenance suggesting their derivation from a recycled orogen.
Conclusion
The undulose polycrystalline quartz ponits to a metamorphicderivation as they contain more than five internal crystals (Scholle, 1979; Blatt et al., 1980).The bimodal sizedistributionof the internal crystals and sutured intracrystalline boundaries further corroborate a metamorphic parentage (Voll, 1996; Pettijohn et aI., 1982). The grains composed of individual silt sized internal crystals showing preferred oreintation are indicative of a fine grained schistose provenance (Blatt, 1980; Espezo and Lopez Gamundi, 1994).
The framwork composition and petrofacies analysis conclusively suggcst that the Lariakantaha Quartzites were derived from a complex assemblage of sedimentary. low grade metamorphic and plutonic terrain. The QFL, Qm FLt ternary plots largely fall in a recycled orogenic field (Dickinson and Suczck, 1979). Further. the abundance of quartz and sedimentary metasedimentary lithic fragments in these quartzites point to a recycled orogenc provenance (cf. Miall, 1990).
The feldspar population of the rocks also point their derivation from a plutonic to metamorphic terrain (Pettijohn et al., 1982). The low representation offelspar in a few sections may be
The palaeocurrent analaysis of the Lariakantha succession (Goswami. 1995) and the underlying Nagthat Formation indicate derivation of the sediments from south and southwest of the
..
PROVENANCE
INTERPRET ATION OF THE LARIAKANTHA
Himalayan expanse (Valdiya, 1980; Singh, 1985; Ghosh, 1991; Shukla and Pant, 1996).Therefore, it is likely that the sediments were derived from the Aravali-Delhiorogenic belt perhaps extending into the Sub Himalayan Zone.
Acknowledgement
45
MEMBER
Dickinson, W.R., and Suczek, C.A, 1979. Plate tectonics and sandstone compositions. Amer Assoc. Petrol. Geol. Bull. 64:
2164-2182. Folk, R.L., 1980. Petrology of Sedimentary
Rock. Hemphill
Press, Austin Texas, 2nd Ed. Funchs. G. and Sinha, AK., 1974. On the geology of Naintal
We are grateful to the Head, Department of Geology, Kumaun University, Nainital for providing facilities. V. N. Ghosal prepared the diagrams and O. P. Sagta typed the manuscript.
(Kumaun Himalaya).Him.
Geol. 4: 563-580.
Gansser, A., 1964. The Geology of Himalayas. Wiley Interscience, New York. Ghosh, S.K., 1991. Source rock characteristic
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. ,
