sedimentology of the early middle cambrian jutana formation of

Sci.Int.(Lahore),25(3),551-558,2013
ISSN 1013-5316; CODEN: SINTE 8
551
SEDIMENTOLOGY OF THE EARLY MIDDLE CAMBRIAN JUTANA
FORMATION OF KHEWRA AREA, EASTERN SALT RANGE,
DISTRICT CHAKWAL, PAKISTAN
Nazir Ahmad, Naveed Ahsan, Shahid Jameel Sameeni, Muhammad Armaghan Faisal Mirag,
and Babar Khan,
Institute of Geology, University of the Punjab, Quaid-e-Azam Campus, Lahore - 54590, Pakistan
E-mail: [email protected]
Abstract: The sedimentology of the early middle Cambrian, Jutana Formation was investigated from
Khewra area, above PMDC Tourist Resort, Eastern Salt Range, District Chakwal, Pakistan to elaborate its
microfacies and diagenetic settings. The Jutana Formation is composed of thick bedded to massive sandy
dolomite and dolomitic sandstone with interbedded shales and sandstone. The dolomites are dirty white,
light green, hard, micaceous, sandy and glauconitic towards the base. The sandstones are whitish grey,
fine grained, well sorted, dolomitic, silty and glauconitic. The shales are greenish grey, glauconitic and
highly micaceous. A detailed study was conducted after collecting systematically more than 30 rock
samples in vertical thickness of aprox.31.45m and studying selecting more than 30 thin sections. To
investigate its sedimentology, microfacies package and diagenetic settings, the petrographic study of
unstained and stained thin sections has been executed. Detailed field observations and laboratory
investigations revealed that it contains microfacies mainly of five types; lower sandy dolomite facies, silty
dolomitic sandstone facies, sandy dolomite facies, silty sandy dolomite facies and highly porous dolomite
facies. Research work demonstrates presence of cement and diagenetic process. The Jutana Formation was
deposited in the tidal environments.
Key words: Jutana Formation, Cross Bedding, Microfacies, Dolomite, Stylolites
INTRODUCTION
Fleming [1] named this unit “Magnesian sandstone”. The
Stratigraphic Committee of Pakistan named the unit as
“Jutana Formation”. The type locality lies near Jutana
Village in the eastern Salt Range [2 & 3]. Thickness at the
type locality is about 75 meters which is the maximum
recorded thickness. It thins towards west about 60 m near
Khewra Gorge and about 45 meters in the Khisor Range, at
Saidwali. Thinning towards south in Punjab Plain is
observed, where the Jutana formation is very thin [4].
In the Eastern Salt Range, it is well developed and is
exposed at Karangal, Diljabba, Chambal and the Jogi Tilla
ridges as well as in Mount Chello area. It is also exposed in
the eastern side of Nilawahan while in the south-eastern part
of the Khisor Range (Saiyiduwali) [5]. But it is absent in the
Western Salt Range. It is present in subsurface in the Potwar
area (Adhi, Kallar Kahar and Dhariala), but is absent in the
Mahesian and Joya Mair wells [4].
Jutana Formation shows siliciclastics assemblage and
represents the upper middle unit of Jhelum Group. It is very
well exposed in the southern part of East Central and Eastern
Salt Range and has its subcrop extension in the Potwar also.
However, it was measured above the PMDC Tourist resort,
Khewra Gorge (Lat. 32°38'44.6”; Long. 73°00’16.6”), where
it is measured approximately 31.45 meter thick.
The dolomite of the formation form cliffs and it is very
difficult to measure a stratigraphic section due to over
steeping of the slopes. The lower and upper contact with
Kussak and the overlying Baghanwala Formation is
conformable. In areas where the Tobra Formation
unconformably overlies the Jutana the contact is strictly
marked with a change from sandy dolomite to conglomerate.
Jutana Formation is mainly characterized by, trough-,
herring-bone-, hummocky- cross bedding at upper bedding
planes and bedding parallel stylolites. Above the shale
interval, there is dolomite which becomes fine grained and
then gradually changes to dolomitic sandstone. Dolomites
are dirty white, light green, hard, micaceous, sandy and
glauconitic towards the base. The sandstones are whitish
grey, fine grained, well sorted, dolomitic, silty and
glauconitic. The shales are greenish grey, glauconitic and
highly micaceous. Important features of the upper part
include fenestral porosity (bird eye about 2-7 cm).
Sedimentary Structures of Jutana Formation
Sedimentary structures are used to identify depositional
setting of sedimentary rocks in conjunction with:
Lithology
Bedding geometries
Subdividing surfaces
Fauna
552
ISSN 1013-5316; CODEN: SINTE 8
Sci.Int.(Lahore),25(3),551-558,2013
Fig.1: Location of Jutana Formation above PMDC Tourist Resort, Khewra
Depositional setting of sedimentary rocks used to assess and
predict the fabric of the rocks at that locality Extrapolate
their distribution along and perpendicular to the strike, or
vertically within that geologic section. Observed
sedimentary structures in the Jutana Formation is trough,
herringbone, hummocky cross bedding and fenestral
porosity [6].
Trough Cross Bedding
In the section boundaries are characterized as being either
planar or parallel. Trough cross bedding sets have strongly
curved concave-up lower set boundaries as seen in vertical
sections transverse to flow (Fig. 2).
Herringbone Cross Bedding
Periodic flow of current is observed in opposite direction.
Opposite dipping of cross beds resembles with herring ribs.
These bidirectional cosets are deposited by tidal currents,
nearly equal in duration and strength (Fig. 3).
Hummocky Cross Bedding
Hummocky cross bedding is the medium-scale to large-scale
cross bedding, generally produced by kind of oscillatory
flow. Laminae sets that are both concave upward and convex
upward, bounded by sharp bounding surfaces which
themselves may be either concave or convex upward.
Hummocky cross beds formed at water depth of 5 to 15m,
where a strong storm wave produces (Fig. 4).
Fenestral Porosity
These are small cavity structures in micritic dolomite-birds
eyes which is laminoid (lamina cracks parallel to bedding).
It is developed where a gap in the rock framework larger
than the normal grain-supported pore spaces are present. It is
most commonly associated with tidal flat deposits and other
peritidal sediments. This type of porosity is less frequently
encountered (Fig. 5, Plate 5a, 5b, 5c).
Classification of Dolomite
Four different dolomite types are identified within the Jutana
Formation [7].
1. Type-1 Dolomite
This type of dolomite is showing early replacive, dirty, nonferroan, unimodal and nonplanar-anhedral crystalline. It has
homogenous dully orange to orange luminescent pattern.
2. Type-2 Dolomite
It is mimetically and/or nonmimetically replaced packstone/
grainstone and its crystals are unimodal, nonplanar-anhedral.
They show orange, bright yellow and red luminescence.
3. Type-3 Dolomite
Unimodal, non-ferroan and nonplanar-anhedral postcompaction dolomite crystals associated with quartz grains.
It shows dull cores and orange luminescent rims.
4. Type-4 Dolomite
Early to intermediate replacive, non-ferroan polymodal and
planar-subhedral crystalline. Crystals of dolomite show
orange luminescent cloudy cores and dull or nonluminescent
rims.
Sci.Int.(Lahore),25(3),551-558,2013
ISSN 1013-5316; CODEN: SINTE 8
Fig. 2: Trough Cross Stratification, the middle part of Jutana
Formation (above PMDC Tourist resort, Eastern Salt Range),
camera facing SSW
Fig. 3: Herringbone cross bedding, upper part of Jutana Formation
(above PMDC Tourist resort, Eastern Salt Range), camera facing
SW.
Fig. 4: Hummocky Cross Stratification, upper part of Jutana
Formation (above PMDC Tourist resort, Eastern Salt Range),
camera facing SW.
553
Fig. 5: Fenestral porosity, upper part of Jutana Formation (above
PMDC Tourist Resort, Eastern Salt Range), camera facing SSW.
Microfacies Analysis of Jutana Formation
Jutana formation is divided into five microfacies on the basis
of thin sections studies [8 & 9].which are;
1. Lower Sandy Dolomite Facies
2. Silty Dolomitic Sandstone Facies
3. Sandy Dolomite Facies
4. Silty Sandy dolomite Facies
5. Highly Porous Dolomite Facies
Lower Sandy Dolomite Facies (MF-1)
Field Interpretation
This facie is 4.7m thick .The formation mainly consists of
medium to thick bedded dolomite in the lower part .There is
cyclic deposition i.e. the alternating beds of sandy dolomite
and impure micaceous rich silty sandstone.
Microscopic Interpretation
Under the microscope, two types of grains are observed i.e.
dolomite in the form of rhombs which constitute 80% to 90
% and Quartz which are nearly 20%. Dolomite shows light
green color in X-Nicole and gives greenish tint in PPL.
Glauconite, muscovite and biotite are also present. Hematite
is present as cement (Plate 1a, 1b).
Silty dolomitic Sandstone Facies (MF-2)
Field Interpretation
Facie is 4.33m thick, shows characteristic tidal bedding. This
facies is mainly yellowish brown which shows cyclic
deposition of dolomitic sandstone and shale. The thickness
of individual cycle is increased and dolomitic sandstone
thickness increases upward. Weavy bedding is present in this
facies.
Microscopic Interpretation
Dominant grains in this facies are Quartz. Very fine grained
dolomite is present. Sorting is very poor. Quartz constitutes
approx.10%. Other minerals like dolomite, muscovite and
biotite are present.
Hematite is present as cement (Plate 2a, 2b, 2c, 2d).
Sandy dolomite Facies (MF-3)
Field Interpretation
Facie is 0.90m (90 cm) thick. This is very hard and contains
intraclasts, and is light yellow in color.
554
ISSN 1013-5316; CODEN: SINTE 8
Sci.Int.(Lahore),25(3),551-558,2013
Fig. 6: Litho- and Micro- Facies log of the Jutana Formation, Khewra area, District Chakwal, Pakistan
Sci.Int.(Lahore),25(3),551-558,2013
ISSN 1013-5316; CODEN: SINTE 8
Plate 1a: Dolomite of type-1 and type-3 under Plane Polarized
Light (ppl) containing glauconite (green color), quartz
(transparent), stained part, Magnification= 40x.
Plate 1b: Dolomite of type-1 and type-3 under cross nicol
containing minor gla uconite (green color), quartz (transparent),
stained part, Magnification= 40x.
Plate 2a: Dolomite of type-3 under cross nicol containing minor
glauconite (green color), quartz (transparent), mica flakes (minor),
stained part, Magnification= 40x.
555
Plate 2b: Dolomite of type-3 under Plane Polarized Light (ppl)
containing minor glauconite (green color), quartz (transparent), silty
mica flakes stained part, Magnification= 40x.
Plate 2c: Dolomite of type-3 under cross nicol containing minor
glauconite (green color), quartz (transparent), silty mica flakes
stained part, Magnification= 40x.
Plate 2d: Dolomite of type-4 under cross nicol containing quartz
(transparent), silty mica flakes, unstained part, Magnification= 40x.
556
ISSN 1013-5316; CODEN: SINTE 8
Sci.Int.(Lahore),25(3),551-558,2013
Plate 3a: Dolomite of type-1, type-2, type-3 under Plane Polarized
Light (ppl) containing quartz (transparent), Ghosts (fill by dolomite
crystals), cement is of hematite (brown color), stained part,
Magnification= 40x.
Plate 4b: Dolomite of type-3, type-1(minor) under cross nicol
containing minor glauconite (green color), quartz (transparent), silty
mica flakes, stained part, Magnification= 40x.
Plate 3b: Dolomite of type-2 (mainly), type-3 (very minor) under
Plane Polarized Light (ppl) containing quartz (transparent), cement
is of hematite (brown color), stained part, Magnification= 40x.
Plate 4c: Dolomite of type-4, type-3 (minor), type-1(minor) under
cross nicol containing , quartz (transparent), unstained part,
Magnification= 40x.
Plate 4a: Dolomite of type-3 under cross nicol (x-nicol) containing
minor glauconite (green color), quartz (transparent), silty mica flakes,
stained part, Magnification= 40x.
Plate 4d: Dolomite of type-2, type-3 under cross nicol containing
quartz (colorless), stained part, Magnification= 40x.
Sci.Int.(Lahore),25(3),551-558,2013
ISSN 1013-5316; CODEN: SINTE 8
557
Plate 4e: Dolomite of type-2, type-3, type-4 under cross nicol
containing quartz (colorless), unstained part, Magnification= 40x.
Plate 5a: Dolomite of type-3 under cross nicol containing quartz
(colorless), Fenestral porosity partially filled by hematite cement,
stained part, Magnification= 40x.
Plate 4f: Dolomite of type-3 under Plane Polarized Light (ppl)
containing quartz (colorless), cement is of hematite (dark brown
color), unstained part, Magnification= 40x.
Plate 5b: Dolomite of type-3 under cross nicol containing quartz
(colorless), Fenestral porosity increasing partially filled by hematite
cement, stained part, Magnification= 40x.
Plate 4g: Dolomite of type-4, type-3 under cross nicol containing
quartz (colorless), cement is of hematite (dark brown color),
unstained part, Magnification= 40x.
Plate 5c: Dolomite of type-3 under cross nicol containing quartz
(colorless), Fenestral porosity increasing partially filled by hematite
cement, unstained part, Magnification= 40x.
558
ISSN 1013-5316; CODEN: SINTE 8
Microscopic Interpretation
Under microscope, it shows two types of Dolomite. One is
in the form of subhedral to euhedral crystals and second is in
the form of intraclasts of dolomite. The intraclasts contain
very fine grained dolomite. Quartz is also present in
intraclasts as well as in the form of grains and it constitutes
nearly 25% of the facies (Plate 3a, 3b).
Silty Sandy Dolomite Facies (MF-4)
Field Interpretation
This facie contains a 12.29m thick sequence which shows
cyclic repetition and some beds were very hard and some
were soft. Mainly color is changing from yellow to light
green and somewhat dark green (weathered color).
Microscopic Interpretation
Under microscope it shows mixing of silt and sand contents
as at different levels increasing vice versa. In the thin section
some dolomite rhomb show zoning, filling showing
dedolomitization in upper part. Dolomite and quartz are in
various proportions. Other minerals are muscovite and
biotite. Cement is mainly of hematite (Plate 4a, 4b, 4c, 4d,
4e, f4, 4g).
Highly Porous Dolomite Facies (MF-5)
Field Interpretation
This facie is composed of massive bedded yellow dolomite.
It is 9.23m thick. The lower upper part is thickly massive
bedded and the middle upper part 2-4m thick zone is highly
porous having fenestral pores. The macrostylolites are
present throughout this facies. Upper part is brecciated and
cataclasite is present. Absence of glauconite, bioturbation
and sand grains but the presence of herringbone cross
stratification in dolomite suggests intratidal to supratidal
environment of deposition.
Microscopic Interpretation
Dolomite is the most commonly occurring mineral in this
facies and their percentage ranges from 80 to 90. Other
minerals are quartz, muscovite, biotite and hematite. Thin
section shows stylolites in this facies. At the lower part
dolomite crystals are very fine grained while in the middle
part crystals size increases and planar subhedral crystals
with xenotopic texture are present. At the upper part, very
fine grained dolomite crystals are dominant. This part shows
laminations due to difference in grain size and color. The
percentage of hematite cement increases upwards (Plate 5- a,
b, c).
Origin of Dolomite in Jutana Formation
Dolomites are mostly medium to fine grained and best
preserve the original features, form in semi-arid regions on
high intratidal to supratidal flats [10]. On the basis of very
fine to medium grain size of dolomite crystals and
syndepositional sedimentary structures like herringbone-,
trough-, and the hummocky cross beds, dolomite of the
Jutana Formation is considered to be primary in origin [11]
Stylolites
Stylolites formed by pressure solution, the study section also
depict presence of stylolites in between different grains of
dolomite and clearly identified by the minor traces of clay
along the contact between dolomite grains (Plate 2a, 3a, 5b),
[12].
Sci.Int.(Lahore),25(3),551-558,2013
CONCLUSION
On the basis of very fine grained size of dolomite crystals
and syndepositional sedimentary structures like herringbone
cross bedding, trough cross bedding, hummocky cross
stratification, we consider dolomite in the Jutana Formation
to be primary in origin.
The lithology of the formation in lower part suggests that the
area comes under both clastic and non-clastic influx
cyclically. The cyclicity in deposition is because of many
reasons: the presence of alternating beds of sandy dolomite,
dolomitic sandstone, pure dolomite, mica rich silty
sandstone shows a transition from sub-tidal to intra-tidal
environment.
In the middle part of the formation, percentage of glauconite
decreases and bioturbation is not observed, the thickness of
individual cycle is increased and dolomitic bed up to 2-3
meters thick in which trough and herring bone cross bedding
is clearly observed. Herring bone cross bedding shows
bidirectional flow of water which is typical feature of tidal
flat environment.
The upper part of formation is massive bedded yellow
dolomite. The lower upper part is thickly massive bedded
and the middle upper part 2-3 m thick zone is highly porous
having elongated fenestral pores. Absence of glauconite,
bioturbation and sand grains but the presence of herringbone
cross bedded dolomite in the upper part of formation
suggests intratidal to supratidal depositional environment.
REFERENCES
1. Fleming A., On the Salt Range in the Punjab,
Geological Society of London, Quarterly Journal, 9,
pt.1, 189-200, (1853).
2. Shah, S. M. I., Memoirs of the Geological Survey of
Pakistan, GSP, 12, 5-7, (1977).
3. Iqbal, M.W.A. and S.M.I. Shah, A Guide to the
Stratigraphy of Pakistan, Geol. Surv. Pak., Mem. 53, 133, (1980).
4. Kadri, I.B, Petroleum Geology of Pakistan, Graphic
Publishers, Karachi, Pakistan, 53-61, (1995).
5. Fatmi, A.N., Lithostratigraphic units of the KohatPotwar Province, Indus Basin, Pakistan, Geol. Surv.
Pak., Mem. 10, 1-80, (1973).
6. Selley, R. C., Applied Sedimentology, 2nd ed. London:
Academic Press, 420-424, (2000).
7. Warren, J., Dolomite: occurrence, evolution and
economically important associations, Earth-Science
Reviews 52, 1-81, (2000).
8. Tucker, M.F., and V.P. Wright, Carbonate
Sedimentology, Blackwell Scientific Publications,
Oxford, London, 365-396, (1990).
9. Adams, A., W.S. Mackenzie, and C. Guilford, Atlas of
Sedimentary Rocks under the Microscope, English
Language Book Society/Longman, UK, 1-102, (1988).
10. Lindholm, R. A Practical Approach to Sedimentology,
Allen & Unwin, Inc., London, UK, 1-276, (1987).
11. Boggs, S., Principles of Sedimentology and
Stratigraphy, New York, 382-400, (2009).
12. Nichols, G., Sedimentology and Stratigraphy, 2nd ed.,
John Wiley & Sons, Ltd., UK, 282-290, (2009).