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U.S. Department of the Interior
U.S. Geological Survey
Lithofacies, Depositional Environments, and
Regional Stratigraphy of the Lower Eocene
Ghazij Formation, Balochistan, Pakistan
U.S. Geological Survey Professional Paper 1599
Prepared in cooperation with the
Geological Survey of Pakistan
A
Cover. Exposures of the lower Eocene Ghazij Formation along the northeast flank of the Sor Range, Balochistan, Pakistan. Photograph by Stephen B. Roberts.
U.S. DEPARTMENT OF THE INTERIOR
BRUCE BABBITT, Secretary
U.S. GEOLOGICAL SURVEY
Charles G. Groat, Director
For sale by U.S. Geological Survey, Information Services Box 25286, Federal Center Denver, CO 80225
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government
Library of Congress Cataloging-in-Publication Data
Lithofacies, depositional environments, and regional stratigraphy of the lower Eocene Ghazij Formation, Balochistan, Pakistan / by Edward A. Johnson.. .[et al.]. p. cm.—(U.S. Geological Survey professional paper ; 1599) "Prepared in cooperation with the Geological Survey of Pakistan." Includes bibliographical references.
- Geology, Stratigraphic—Eocene. 2. Geology—Pakistan— Balochistan. 3. Coal—Geology—Pakistan—Balochistan. 4. Ghazij Formation (Pakistan). I. Johnson, Edward A. (Edward Allison), 1940-. II. Series. QE692.2.L58 1999 553.2'4'0954915—dc21 98- ISBN=0-607-89365-6 CIP
CONTENTS
CONTENTS V
About the Conglomerate Facies ............................................................................. 63
Correlation of the Ghazij Formation with Eocene Sedimentary Rocks in
Adjacent Regions............................................................................................ 63
Toward the North—North West Frontier Province................................................. 64
Thal-Kohat Area............................................................................................. 64
Surghar Range................................................................................................ 65
Toward the Southeast—Sindh Province................................................................. 66
Hyderabad....................................................................................................... 66
Post-Ghazij Geologic History......................................................................................... 66
Post-Ghazij Plate Tectonics.................................................................................... 66
Post-Ghazij Deposition........................................................................................... 67
Preorogenic Marine Deposits ......................................................................... 67
Preorogenic Nonmarine Deposits................................................................... 67
Synorogenic Deposits..................................................................................... 68
Selected References........................................................................................................ 68
Appendix. Coal Deposits of Northeastern Balochistan.................................................. 74
PLATES [Plates are in pocket]
1. Principal reference sections of the lower Eocene Ghazij Formation, Balochistan, Pakistan.
2. Stratigraphic sections showing coal beds and associated lithologies in the middle part of the lower Eocene
Ghazij Formation, Sor Range coal field, Balochistan, Pakistan.
FIGURES
1. Map showing Pakistan and provincial boundaries, and general location of study area......................................... 3
2. Map of north-central Pakistan showing most place names mentioned in text.......................................................
3. Simplified geologic map of northeastern Balochistan ...........................................................................................
4. Generalized Stratigraphic section of exposed Phanerozoic rocks in Quetta area...................................................
5. Schematic cross section of the post-rift, pre-collision passive margin of the Indian subcontinent .......................
6. Schematic cross section showing conditions just after initial collision and plan view of physiographic
elements of same area.......................................................................................................................................... 10
7. Isopachmap of total Eocene deposits in south-central Pakistan.......................................................................... 12
8. Generalized geologic map showing large exposures of the Ghazij Formation in north-central Pakistan............ 13
9. Generalized geologic map showing exposures of Ghazij Formation and sites of principal reference
sections...........................................................................................................^
10. Stratigraphic section and photographs showing lithologic character of lower, middle, and upper parts of the
Ghazij Formation................................................................................................................................................. 16
11. Photograph of typical sandstone sequence in lower part of the Ghazij Formation, Abraham Marri
mine section, Pir IsmailZiarat.............................................................................................................................l
12. Sketch section showing two consecutive, coarsening-upward sequences containing Type I sandstone bodies,
basal portion of middle part of the Ghazij Formation, Abraham Marri mine section .........................................
13-17. Photographs showing:
13. Horizontal and vertical burrows on surface of sandstone bed in Type II sandstone body, middle part
of the Ghazij Formation, Abraham Marri mine section................................................................................
14. Typical trough cross stratification in a Type III sandstone body, middle part of the Ghazij Formation,
Abraham Marri mine section........................................................................................................................
15. Interbedded fossiliferous limestone and coal, middle part of the Ghazij Formation, near Shahrig..............
16. Thin limestone bed typical of middle part of the Ghazij Formation in the Mach area.................................
17. Abundant fossil hash commonly found in limestones of middle part of the Ghazij Formation in the
VI CONTENTS
- Composite stratigraphic section showing characteristics typical of conglomerate facies of upper part of the Ghazij Formation in Sor Range.................................................................................................................................
- Photograph showing typical outcrop of conglomerate facies at base of upper part of the Ghazij Formation, Sor Range ..................................................................................................................................................................
- Generalized geologic map of Khost-Shahrig-Harnai segment..................................................................................
- Stratigraphic section of a portion of the Ghazij Formation at PMDC mine, southeast of Shahrig........................... 29
- Generalized geologic map of Sor Range area ...........................................................................................................
- Generalized geologic map of Pir Ismail Ziarat-Sherki Kach-Ghate segment...........................................................
- Generalized geologic map of greater Mach area....................................................................................................... 33
- Stratigraphic section showing an interval of the upper Paleocene to lower Eocene(?) Rodangi Formation containing units of coaly carbonaceous shale ........................................................................................................... 34
- Generalized geologic map of greater Johan area....................................................................................................... 35
- Diagram comparing the three-part division of the Ghazij Formation, Quetta region, with lower Eocene nomenclatures in Sulaiman Range ............................................................................................................................
- Stratigraphic columns for lower Eocene deposits at Rakhi Nala and Zinda Pir........................................................ 37
- Stratigraphic section in Moghal Kot-Drazinda area ................................................................................................. 38
- Stratigraphic section of the Marap Conglomerate Member of the Ghazij Formation, Harboi Hills......................... 40
31. Photograph showing typical exposure of the Marap Conglomerate Member of the Ghazij Formation,
Harboi Hills .............................................................................................................................................^
- Stratigraphic section of lower Eocene rocks encountered in drill hole SuiNo. 1 .....................................................
- Map showing areal distribution of some drill holes and possible distribution of Sui Main Limestone, greater Jacobabad region....................................................................................................................................................... 43
- Cross section showing isolated character of the Sui Main Limestone ...................................................................... 44
- Photomicrograph of thin section cut from sandstone sample A-12-90 collected at Abraham Marri mine stratigraphic section................................................................................................................................................... 46
- Photomicrograph of thin section cut from sandstone sample A-26-90 collected at Abraham Marri mine stratigraphic section...................................................................................................................................................
- LQR diagram with points representing all sandstone thin sections studied.............................................................. 47
- Limestone-type diagram with points representing all sandstone thin sections studied............................................. 47
- Limestone-type diagram showing groupings of data points by area......................................................................... 49
- Map showing ophiolite complexes in central Pakistan.............................................................................................. 51
- Trigonal diagrams showing distribution of clast types in conglomerate facies of the Ghazij Formation, Sor Range and Harboi Hills....................................................................................................................................... 51
42. Generalized cross section of middle part of the Ghazij Formation and its relation to the conglomerate unit,
Sor Range ............................................................................................................................................................^
- Map showing present-day distribution of Eocene sedimentary rocks in north-central Pakistan and location of conglomerate facies of the Ghazij Formation or its equivalent................................................................................. 59
- Stratigraphic columns showing conglomerate intervals in top 500 m of the Ghazij Formation, Harboi Hills and Sor Range............................................................................................................................................................ 60
- Sketch depositional model showing possible distributary stream systems on the late Ghazij coastal plain............. 60
- Interpretive sketch of northwest edge of the early Eocene Indus Foreland Basin, showing deltas positioned along a southeast-prograding shoreline.....................................................................................................................
- Diagram correlating depositional environment with base-level fluctuations ............................................................ 64
- Diagram correlating lower Eocene strata in the Quetta region with lower Eocene strata in selected areas of North West Frontier Province and Sindh Province.................................................................................................... 65
- Map showing lithostratigraphic units in northern Sulaiman Range and to north that possibly correlate with the Ghazij Formation in Quetta region............................................................................................................................ 66
- Map showing lithostratigraphic units in Sindh Province that possibly correlate with the Ghazij Formation in Quetta region .............................................................................................................................................................
TABLES
- Rock-Eval pyrolysis data............................................................................................................................................ 18
LOWER EOCENE GHAZIJ FORMATION, BALOCHISTAN, PAKISTAN
interest to geologists is the formation's enigmatic depositional setting, which seems to change with every area of exposure.
LOCATION OF THE STUDY
The Ghazij Formation is exposed within a sigmoidally shaped mountain belt that covers much of northeastern Balochistan. As shown in figure 1, Balochistan is the larg- est province in Pakistan; it contains only 5 percent of the country's population, however. Most of the region is arid with an average annual rainfall of less than 250 mm. Eleva- tions in the province range from sea level to over 3,500 m. We used the provincial capital of Quetta as a base from which to conduct our study because of its proximity to good exposures of the Ghazij and for logistical reasons. In addi- tion, Quetta is the national headquarters of the Geological Survey of Pakistan. In the late 1980's Quetta had a population of about 100,000, but this number has increased dramatically by an influx of refugees. Figure 2 is a detailed map of north-central Pakistan showing the locations of most of the place names used in our report.
Although we examined the Ghazij over a broad area of Balochistan, we concentrated our efforts in four specific areas: Pir Ismail Ziarat, the Sor Range, Mach, and Johan. Each of these areas is within a day's travel of Quetta, and each exhibits good exposures of the Ghazij; most are the site of an existing coal-mining effort.
SPONSORSHIP AND PURPOSE OF THE REPORT
This report resulted from a joint effort between the U.S. Geological Survey and the Geological Survey of Pakistan. The study was sponsored by the Government of Pakistan and the U.S. Agency for International Development (USAID). Funding was provided by US AID through Project 391-0478: Energy Planning and Development Project, Coal Resource Assessment Component 2a; Participating Agency Service Agreement (PASA) No. 1PK-0478-P-IC-5068-00.
By mutual decision of the two geologic organizations, the Ghazij Formation in Balochistan was selected for study because it is known to contain a considerable amount of coal, and because a comprehensive investigation of its regional geologic character had not previously been undertaken. As a result of out study, a better understanding of the depositional setting, regional stratigraphic framework, and coal potential of the formation can be presented. Moreover, both geologic organizations benefited greatly from the interactions between participating geologists.
PREVIOUS STUDIES
Short reports discussing the presence of coal-bearing strata in Balochistan appeared in the literature as early as the 1880's. More detailed reports on the Ghazij Formation were published by the pre-partition Geological Survey of India during the first half of the 20th century; references to this early work appear throughout our report. During the 1950's geologists working for Hunting Survey Corporation, Limited, conducted an extensive geologic reconnaissance of a large part of West Pakistan. This work was financed by the Government of Canada under a Colombo Plan Co-oper- ative Project. As part of this effort, the Ghazij was exam- ined regionally for the first time, and this accounting of the formation remains a major source of information on the unit (Hunting Survey Corporation, 1960). During the 1960's John Reinemund of the U.S. Geological Survey and geolo- gists from the Geological Survey of Pakistan conducted a detailed study of the Ghazij in the Sor Range coal field cen- tered about 17 km southeast of Quetta (fig. 2), and this effort resulted in a geologic map of the area (Reinemund and others, no date). In addition to the work just listed, the Geological Survey of Pakistan has published several impor- tant reports on the Ghazij, and these are referenced in our report.
METHODS OF INVESTIGATION
Because of time and logistical constraints, the task of investigating the Ghazij Formation was divided among the authors. Johnson, Khan, and Warwick measured and described in detail the Ghazij at five widely spaced locations in order to better interpret regional changes in the deposi- tional facies. Warwick took the lead in examining the forma- tion in reconnaissance over a broad area of Balochistan. Roberts studied the detailed lateral variations of the forma- tion in the Sor Range by measuring a set of closely spaced stratigraphic sections. Stratigraphic sections were measured using a Jacob's staff or tape and compass. Standard lithofacies descriptions such as color, grain size, and lithology were recorded, and special attention was directed toward describing bedding characteristics and sedimentary structures. Lateral changes defining the geometry of sandstone bodies were also noted. Where available, measurements of paleocurrent indicators were taken, and pebble counts were conducted on conglom- erates. Rock samples were collected from critical units along the line of section for petrographic and paleontologic studies. Petrographic studies involved the microscopic examination of thin sections, X-ray diffraction analyses, and work with the scanning electron microscope (SEM). Some mudrock samples were submitted for Rock-Eval analysis, and some limestone samples were submitted for insoluble residue
Introduction
Afghanistan X People's ~S"\y-f-—/^-X Republic f jij ^of China ( _/
(^0) I (^) i 100 I______I______| 200 300 KILOMETERS
Figure 1. Map of Pakistan showing provincial boundaries. Also shown is a general outline of the study area. N.A., Northern Area; N.W.F.P., North West Frontier Province; I, Islamabad; Q, Quetta; K, Karachi. j
determinations. Samples collected for paleontologic analyses were submitted to paleontologists at the U.S. Geological Survey.
ACKNOWLEDGMENTS
The authors of this report benefited greatly from vari- ous contributions from members of the U.S. Geological
Survey and the Geological Survey of Pakistan. This help ranged from informative discussions on the geology to actual assistance in conducting the field work. Of special mention in the U.S. Geological Survey are Elisabeth M. Brouwers, Thomas G. Gibson, Edwin R. Landis, Florian Maldonado, Joseph T. O'Connor, Leslie F. Ruppert, Jean M. Self-Trail, and Bruce R. Wardlaw. Those in the Geological Survey of Pakistan who deserve special mention are Mohsin A. Kazim and Asif N. Rana. In addition, the authors wish 19 thank
GEOLOGIC FRAMEWORK OF NORTHEASTERN BALOCHISTAN
those officials in the Balochistan provincial government who made our field activities possible, and the U.S. Agency for International Development staff at Quetta, now disbanded, for their logistical support.
GEOLOGIC FRAMEWORK OF
NORTHEASTERN BALOCHISTAN
Northeastern Balochistan is a land of arid plains, dry river beds, and abruptly uplifted mountain ranges. The lack of vegetation affords the observer a clear, unobstructed view of the structural and sedimentologic complexities of the geo- logic record contained in the rocks. We can scarcely over- state the high degree of tectonism the region has been subjected to. For example, overturned unconformities and folded thrust faults are not uncommon, and Zarghun Peak at 3,580 m, the highest elevation in Balochistan, contains folded Pleistocene conglomerate at its summit.
STRUCTURAL FEATURES
As shown in figure 2, a significant mountain belt occu- pies the central part of northeastern Balochistan. The north- ern segment of this belt is the Sulaiman Range, which seems to swing westward in the Sulaiman lobe, and continue south as the Kirthar Range. This mountain belt is part of a classic foreland fold-and-thrust belt caused by the ongoing collision of the Indian subcontinent with the Asian mainland (hereaf- ter often referred to as simply the collision). That portion of the belt present in northeastern Balochistan thus represents a part of the southern extension of the Himalayan orogen. Hunting Survey Corporation (1960) referred to this feature in Balochistan as the Axial Belt, literally, a belt of axes. For simplicity of discussion, we will continue this usage. Powell (1979) reported that during the early Eocene, just after the initial collision, India apparently rotated about 9° counter- clockwise, and this action might have set the stage for the north-northeast orientation of the belt in north-central Paki- stan. The bend in the belt represented by the Sulaiman lobe represents a type of orocline, and this particular one is named the Quetta syntaxis. Powell (1979) also stated that since the early Eocene, India has rotated a total of about 29° counter- clockwise. This continuing counterclockwise rotation is probably responsible for creating a complicated belt of regional, left-lateral shear in the area of north-central Paki- stan, and the Quetta syntaxis might then be an expression of this transpression (see Abel-Gawad, 1971; Klootwijk and others, 1981; Farah and others, 1984). Figure 3 is a simplified geologic map of the same area shown in figure 2. Fold axes (not shown on map) and the trends of fault traces generally follow the sigmoidal trend of the Axial Belt. The axial planes of folds are usually east ver- gent in the Sulaiman and Kirthar Ranges, and south vergent
in the Sulaiman lobe. Many individual mountains within the belt are anticlinal in structure, and the fold axis in many of these cases is doubly plunging. It is common to observe steeply dipping strata adjacent to relatively undersized allu- vial fans at the mountain-valley break in slope, indicating that the mountain had been domed in rapid fashion. Most of the faults in the Sulaiman and Kirthar Ranges are low-angle thrusts with fault planes dipping less than 45°. Some faults in the Sulaiman lobe are high-angle reverse types. Fault planes are vergent in the same directions as the folds. From the geometry of these compressional structures, it is apparent that tectonic transport is in directions away from the orogen (see Banks and Warburton, 1986). High-angle normal faults are rare and strike-slip faults are uncommon throughout the Axial Belt. For more details on the structural geology of northeastern Balochistan, consult maps by Bannert (1992) and Maldonado and others (1998). The western swing of the Axial Belt in the Sulaiman lobe is only apparent. Actually, the feature is caused by that part of the belt being detached at depth, and gliding south- ward in response to the present oblique convergence of the Indian subcontinent and the Asian mainland. The lobe is composed of a series of arcuate compressional structures that represent a maximum of 378 km of crustal shortening since the beginning of the Miocene (Jadoon and others, 1990; Humayon and others, 1991; and Jadoon and others, 1994). A prominent left-lateral strike-slip fault on the east side of the lobe (fig. 3) trending north-northwest supports this model, but no corresponding fault has been mapped on the western margin of the lobe. However, Shahid H. Khan and Jan M. Mengel of the Geological Survey of Pakistan (oral commun.,
- reported that subtle changes in structural trends on the western margin indicate tectonic movement that fits the model (see also Kazmi, 1979). The mechanism involved is thought to involve either (1) a single decollement at depth, perhaps moving within a layer of ductile Eocambrian salt separating higher rocks in the lobe from the crystalline base- ment, or (2) several relatively smaller thrusts moving within thick shale sequences of the Cretaceous Sembar Formation or the Ghazij Formation (fig. 4). The front of the lobe is tec- tonically active, as indicated by seismicity (Quittmeyer and others, 1979), but no frontal thrust has broken the surface. This same tectonic situation is apparently operating in the Salt Range in Punjab Province where the frontal thrust has come to the surface (Gee, 1989). However, in the Salt Range the cover rocks are known to be gliding across a thin layer of Eocambrian salt, and there is no hard evidence of this lithol- ogy in the Sulaiman lobe. For more detailed discussions of the mechanisms involved in the evolution of the lobe, con- sult Sarwar and DeJong (1979), Jadoon and others (1990), and Humayon and others (1991). In closing this short dis- cussion of the compressional tectonics of the belt, we stress that, in general, the folding, faulting, and formation of the Quetta syntaxis have, since the Miocene, all occurred simultaneously.
LOWER EOCENE GHAZIJ FORMATION, BALOCHISTAN, PAKISTAN
67° E. 69° E
EXPLANATION
Tertiary rocks of the Khojak Basin Tertiary rocks of the Axial Belt f Pre-Tertiary rocks of the Axial Belt Ophiolite complexes Generalized contact— Dashed where concealed or approximately located Major faults —Barbs show direction of relative movement where known ^ s: -.^- ^i;"> /•• ••••••.•^ A /• :•• •:. • : .• : \ ^'_ v. '
29° ^
Figure 3. Simplified geologic map of northeastern Balochistan. Q, Quetta. Modified from Bakr and Jackson (1964) and Kazmi and Rana (1982). Fold axes are not shown.
LOWER EOCENE GHAZIJ FORMATION, BALOCHISTAN, PAKISTAN
VERTICAL DISTRIBUTION OF SEDIMENTARY ROCKS
Despite the significant tectonism, rocks older than Per-
mian are not exposed in northeastern Balochistan. More-
over, Permian and Triassic rocks are themselves
volumetrically insignificant, making Jurassic rocks the
essential base of the exposed sedimentary pile. Sedimentary
rocks exposed in this region amount to more than 11,000 m
(fig. 4), and this sequence can be divided into three parts
based on general lithology. The lower part consists of 5,
m of marine carbonate that was deposited prior to the colli-
sion. Except for the Paleocene strata at the top of this inter-
val, these rocks are generally exposed along the west side of
the Axial Belt (fig. 3). The middle part comprises 3,000 m
of mostly mudrock and lesser amounts of sandstone and car-
bonate that were deposited during or just after the initial col-
lision. The Ghazij Formation occupies the lower half of this
interval. The upper part of the sequence consists of 3,000 m
of conglomerate deposited in response to radical uplift asso-
ciated with the Himalayan orogeny. Rocks of both the mid-
dle and upper parts of the sequence are generally exposed
along the east side of the Axial Belt, and within the Sibi
trough (fig. 3). Significant unconformities in the exposed
section are present between Jurassic and Cretaceous strata,
Cretaceous and Paleocene strata, Eocene and Oligocene
strata, and separating Pleistocene conglomerate of the Siwa-
lik Group from younger conglomerates (fig. 4).
PRE-GHAZIJ GEOLOGIC HISTORY
Nowhere is the history of the Ghazij Formation ade-
quately described in a single publication. Rather, it is scat-
tered about as small bits and pieces in numerous
publications, either stated or implied, and in the heads of
many geologists. Because of the incredible amount of tec-
tonism this region has been subjected to, one never knows
how much structural rotation and (or) transport has affected
the rocks studied. This is especially true of rocks in the
Sulaiman lobe. Because of this fact, assigning compass
directions for source areas and paleoslopes is an educated
guess, at best.
PRE-GHAZIJ PLATE TECTONICS
The geologic history of this region cannot be told with-
out first describing the significant role that plate tectonics has
played. At about 130 Ma, during the Early Cretaceous, the
Indian subcontinent separated from Gondwana (Scotese and
others, 1988), and proceeded northward toward the Asian
mainland. Oceanic crust at the leading edge of the Indian
plate was probably subducted either (1) beneath oceanic
crust positioned in front of the Asian mainland with an
associated island arc, or (2) directly under the continental
crust of the Asian mainland. From about 130 to 80 Ma (Early
Cretaceous to Late Cretaceous) the Indian subcontinent con-
tinued to move northward at a rate of 3-5 cm/yr (Powell,
1979) as the southern Tethys Sea began to close. From 80 to
53 Ma (Late Cretaceous to early Eocene) the Indian subcon-
tinent's progress accelerated to perhaps 20 cm/yr (Powell,
1979). Sometime during Late Cretaceous to Paleocene time,
the leading edge of the marine shelf that was positioned off
the Indian subcontinent approached the subduction zone, and
sea-floor material in the form of submarine volcanic rocks
and deep-water sediments were obducted onto carbonate-
platform deposits (McCormick, 1989). Many workers (Pow-
ell, 1979; Besse and others, 1984; Patriat and Achache, 1984;
Searle and others, 1987; Scotese and others, 1988; Ricou,
1994) have placed the initial collision between 55 and 50 Ma
(early Eocene). Klootwijk and Peirce (1979) placed the
event generally within this range based on polar wandering
paths, and Powell (1979) reported that the rate of northward
movement of the Indian subcontinent decreased to 4-6 cm/yr
at about 53 Ma, which fits this timing. Evidence from the
Ghazij Formation contained in our report favors 55 Ma for
the initial collision. The initial collision was probably
between the Indian subcontinent and a terrestrial fragment,
such as a microcontinent or island arc, positioned just off the
Asian mainland (see Powell, 1979; Klootwijk and others,
1981; Waheed and Wells, 1990; Bannert and others, 1992;
Kemal and others, 1992). A variation of this scenario was
proposed by Garanti and others (1996). These workers pro-
posed that the initial collision was with the leading edge of
the Asian mainland. In either case, it was probably during
this time that the northward subduction of oceanic crust
ceased, and what remained of the southern Tethys Sea
closed. An important question is, "What became of the ter-
restrial fragment?" Perhaps the eastern part of this mysteri-
ous terrain lies under the Eocene to Miocene flysch deposits
of the Khojak Basin, and the west side of the terrain was
transported out of the region by the Chaman fault. (See
Wells, 1984; Waheed and Wells, 1990.)
PRE-GHAZIJ DEPOSITION
A shallow-marine shelf supporting a carbonate platform
existed along a portion of coastal Gondwana from at least the
Permian, and when the Indian subcontinent separated from
the supercontinent in the Early Cretaceous, this environment
accompanied the subcontinent northward. As the Indian
plate proceeded north during the remainder of Cretaceous
and Paleocene time, this carbonate platform continued to
accumulate carbonate sediments on the passive continental
margin of the Indian subcontinent. Toward the north lay the
open ocean of the southern Tethys Sea and toward the south
lay the nonmarine environments of the subcontinent (fig. 5).
It was on this platform that the pre- and post-rift, Jurassic
Early Eocene Depositional Setting
through Paleocene carbonates that dominate the lower part of the stratigraphic column (fig. 4) were deposited. Of vol- umetric importance in the Quetta area are the Jurassic Shirinab Formation and Chilian Limestone, the Cretaceous Parh Limestone, and the Paleocene Dungan Formation. This sequence also contains some limited amounts of clastic rocks such as the mudrock in the Cretaceous Sembar Formation and the sandstone in the Cretaceous Pab Sandstone (a unit at the top of the Cretaceous strata that is present in some areas of the Sulaiman and Kirthar Ranges; not shown in fig. 4). According to Kemal and others (1992), the carbonate rocks were deposited during long periods of marine highstand, and the clastic rocks were deposited during periods of marine lowstand. Two significant periods of erosion, or nondeposi- tion, are evident in this sequence: one between Jurassic and Cretaceous strata, and another between Cretaceous and Pale- ocene strata (fig. 4). These two surfaces define a major transgressive-regressive event during the Cretaceous that culminated locally with the progradational Pab Sandstone. Another period of erosion is indicated by the local presence of an unconformity between Paleocene and Eocene strata. The presence of this surface indicates that another transgressive-regressive event probably occurred during the Paleocene. In the southern part of the Kirthar Range, volcanic material is present in association with post-rift carbonate rocks. This thick sequence, known as the Bela Volcanic Group, contains basaltic pillow lava, tuff, and agglomerate interbedded with mudrock, carbonate, conglomerate, and radiolarian chert (Hunting Survey Corporation, 1960). Auden (1974) reported the rocks to be Early to middle Cre- taceous in age, and therefore older than the latest Cretaceous to earliest Paleocene Deccan Basalt of India and southern Pakistan. The history of the Bela volcanics is poorly under- stood, but they might have been emplaced when the carbon- ate platform passed over a hot spot in the mantle as the Indian plate moved northward. McCormick (1989) sup- ported this idea, and referred to the rocks as within-plate alkali basalts associated with volcanic islands. Any clastic material entering the pre- and post-rift dep- ositional system probably did so from the south, southeast, or east. Waheed and Wells (1990) reported that paleocurrent data from the Pab Sandstone in the southern part of the Sulaiman Range indicate paleoflow toward the northwest, and in the northern part of the range, toward the southwest. Moreover, they reported that these same sandstones are quartz arenites, which might have been derived from exposed Precambrian shield rocks on the Indian subconti- nent. Meissner and Rahman (1973) studied Paleocene rocks from exposures in the Axial Belt and from information obtained from drill holes under the Indus Plain. They reported that Paleocene rocks contain more sandstone toward the east, suggesting a clastic source in that direction. Toward the southeast and east, the thick sequence of pre-Ghazij Formation carbonates apparently thins, and the
NORTHWEST SOUTHERN TETHYS SEA
SOUTHEAST
CARBONATE PLATFORM
INDIAN SUBCONTINENT INDIAN PLATE
Figure 5. Schematic cross section of post-rift, pre-collision pas- sive margin of the Indian subcontinent. No scale implied.
rocks in the sequence were probably deposited in shallower water settings in these directions. In discussing the more than 8,000 m of Mesozoic rocks in the Sulaiman Range, Humayon and others (1991) reported that the carbonates were deposited in relatively shallow water, and at least some of the mudrocks were deposited in deeper water. They went on to report that toward the east on the east side of the Indus Plain, information from a drill hole documents that these same Mesozoic rocks have thinned to 750 m, and evidence from this hole suggests that some of the sandstones and mudrocks contained in the sequence were deposited in a nearshore setting. The eastward thinning of the pre-Ghazij carbonates is also supported by Kemal and others (1992). Meissner and Rahman (1973) reported that carbonates in the Paleocene deposits increase toward the west, indicating deeper water conditions in that direction. In addition, toward the southeast in Sindh Province, Paleocene strata include flu- vial deposits and a considerable amount of coal. Sediments now contained in these units might well have prograded in a westerly direction, to be deposited on the northwest edge of the Indian subcontinent. (See also Sahni and Kumar, 1974.)
EARLY EOCENE DEPOSITIONAL
SETTING
Sometime just before or just after the beginning of the Eocene, the depositional setting in what is now northeastern Balochistan changed dramatically. As discussed previously, apparently the leading edge of the marine shelf that extended off the Indian subcontinent came in contact with some type of terrestrial fragment that was close to, but separated from, the Asian mainland. The compass direction of the long axes of these physiographic elements might never be known with any certainty, but we favor a simple northeast trend as a first approximation. As a result of tectonism associated with this event, a topographically positive area developed just north- west of the main part of the marine shelf. This uplifted area consisted of carbonate-platform deposits that had accumu- lated on the distal part of the platform. This feature was referred to by Hunting Survey Corporation (1960) as the Central and Las Bela geanticlines. Thus for the first time, a northwestern source area for clastic sediments was created, and the depositional slope changed from northwest facing to southeast facing (fig. 6 A). Evidence supporting this paleo- geography is presented herein.
Lower Eocene Sedimentary Rocks
The sudden presence of elevated topography northwest
of the main part of the marine shelf created a generally north-
east trending foreland basin with a tectonic highland to the
northwest and the exposed Indian craton to the southeast.
Thus, the embryonic Indus Foreland Basin was formed. The
relatively shallow intracratonic sea that occupied the basin
was undoubtedly somewhat connected with the open sea-
way, at least toward the south. During early Eocene, the
Ghazij Formation was deposited on the west side of the
basin. The lower part of the Ghazij was probably deposited
offshore, but the middle and upper parts of the formation
were apparently deposited higher on the depositional slope,
near the shoreline and on the coastal plain, respectively (fig.
Lower Eocene deposits in Sindh Province are mostly
marine carbonates suggesting that the pre-Eocene carbonate
platform persisted on the east side of the basin. Clastic mate-
rial interbedded with the carbonates in this area was proba-
bly derived from the east off the Indian shield.
The Indus Foreland Basin was divided by the north-
west-trending Sargodha high into a northern part and a
southern part. An isopach map (fig. 7) of Eocene deposits in
south-central Pakistan shows that basin-floor irregularities
existed. Of particular importance is the northwest-trending
Jacobabad high that separated the southern part of the basin
into two subbasins now known as the Kirthar and Sulaiman
provinces. The Ghazij was deposited in both of these prov-
inces. Small ephemeral irregularities north of the Jacobabad
high might have resulted in areas of restricted marine circu-
lation, which could explain the presence of rare evaporites in
the upper part of the Ghazij in the southern Sulaiman Range.
According to Powell (1979), India has migrated from
about lat 30° S. to about lat 30° N. since the Late Cretaceous.
Powell further calculated that during the formation of Paki-
stan's Paleocene and Eocene coal deposits, the region was
approximately at the equator. Klootwijk and others (1981)
placed this region slightly north of this position.
LOWER EOCENE SEDIMENTARY
ROCKS
Lower Eocene sedimentary rocks in north-central Paki-
stan are contained within the Ghazij Formation. The Ghazij
is intermittently exposed throughout the Axial Belt (fig. 8)
from the vicinity of Bannu 440 km northeast of Quetta in the
northern Sulaiman Range, to the vicinity of Karkh about 350
km south of Quetta in the central Kirthar Range. North of
Bannu, lower Eocene strata are included in other formations,
and south of Karkh the formation is no longer recognized,
probably because of a facies change. In the Quetta region,
exposures of the formation are limited on the west by a sig-
nificant north-trending fault, the Ghazaband fault (Bannert,
1992). East of the Axial Belt, the formation is recognized in
the subsurface of the Indus Plain as far east as Mirpur
Mathelo (fig. 2), 340 km southeast of Quetta.
Regionally, the Ghazij Formation is mainly an argilla-
ceous deposit that contains increasing amounts of sandstone
toward the west, and increasing amounts of carbonate
toward the east. Based on this generality, Hunting Survey
Corporation (1960) divided the Ghazij into two major litho-
logic groups: the complex assemblage on the west and the
simple assemblage on the east. These workers also subdi-
vided the complex assemblage into lower, middle, and upper
zones (parts).
The Ghazij Formation comprises a crudely shaped clas-
tic wedge that, in general, thins toward the east. Hunting
Survey Corporation (1960) reported the thickness of the
Ghazij to range from 305 to 3,353 m, and Shah (1977)
reported the range to be from 160 to 3,330 m. These differ-
ences in thickness range are difficult to interpret. They
might reflect differential subsidence in the depositional
basin, or they might simply be the measurements of incom-
plete stratigraphic sections. Complete sections of the forma-
tion are rarely exposed, and because of compressional
tectonics and the great amount of soft mudrock in the forma-
tion, thickness measurements of even so-called complete
sections are questionable. Williams (1959) reported the
Ghazij to be almost 600 m thick at its type locality near
Spintangi, about 110 km southeast of Quetta.
HISTORY OF STRATIGRAPHIC NOMENCLATURE
The first mention of the term Ghazij was by R.D. Old-
ham (Oldham, 1890a). In a short note, he first mentioned
that at least 600 m of shale overlies the "Dungan limestone"
just northwest of Spintangi (about 110 km southeast of
Quetta). Later in the same note, he described an anticlinal
structure in the Kipar Valley where "Ghazij shales" are
exposed. His accompanying sketch map shows this structure
on the north side of the northwest-trending Kipar Valley, 11
km southeast of Spintangi, and "Ghazij Group," as listed in
his index (explanation), is shown exposed in the core.
Ghazij N., a northwest-flowing tributary to Kipar Valley, is
shown on his sketch map just north of the anticline. Later in
that year, Oldham more closely defined his usage of the term
Ghazij in a slightly longer note (Oldham, 1890b). In this
note, Oldham described the "Ghazij group" as a great thick-
ness of gray and olive-green shale with subsidiary beds of
lime (sic), sandstone, and, locally, coal, all sandwiched
between the "Dungan limestone" and the "Spintangi group."
He stated that the unit is named after the valley that runs
down from near Dungan Mountain to Spintangi. Maps of
this area show this drainage as either Ghazij Nala or Ghazij
Rud.
In the Kirthar Range, Vredenburg (1909) described a
shaly sequence underlying the upper and middle "Kirthar
12 LOWER EOCENE GHAZIJ FORMATION, BALOCHISTAN, PAKISTAN
64° E. 70° E.
150 300 KILOMETERS
Figure 7. Isopach map of total Eocene deposits in south-central Pakistan. Axis of Sargodha high approximate. Contours in meters. Mod- ified from Ahmad (1982).
limestone," and he divided the sequence into "lower Kirthar shales" in the upper part and "Ghazij beds" in the lower part. Eames (1952a) and Nagappa (1959) presented detailed nomenclature for lower Eocene rocks in the Sulaiman Range that included and limited the term "Ghazij Shales." Will- iams (1959) was the first to use the word "formation" in asso- ciation with the Ghazij. Following Oldham's work, he
Vertical Subdivisions and Lithofacies of the Ghazij Formation
nated Spintangi as the type locality. Hunting Survey Corpo- ration (1960) preferred the term "Ghazij Shale," and included in the unit the "lower Kirthar shales" of Vredenburg (1909). Shah (1977) and Iqbal and Shah (1980) returned to the term Ghazij Formation and tightened the definition of the formation by accounting for the terms introduced by Eames (1952a), Nagappa (1959), and Hunting Survey Corporation (1960).
PRINCIPAL REFERENCE SECTIONS
During the course of our study, we measured and described in detail five stratigraphic sections of the Ghazij Formation in four widely spaced areas to serve as strati- graphic anchor points: one in the Sor Range, one near Pir Ismail Ziarat, two in the vicinity of Mach, and one near Johan (fig. 9). The first three of these four areas are the sites of ongoing coal mining activity, and the fourth area has the potential, although low, for such activity. Measuring sec- tions of the Ghazij can be quite difficult. Because of the high percentage of mudrock in the formation, the unit commonly forms valleys where the rocks are poorly exposed. More- over, faults and the axial planes of folds are often parallel to bedding, making their presence difficult to detect. There- fore, in each of these areas, we selected exposures where the
