International Symposium on Paleogene Biota and Stratigraphy of Eastern Asia Beijing, June 13-15, 2009
The Paleocene/Eocene boundary and biostratigraphy of the Ranikot Group in the Karachi Arch (Sindh, Pakistan) Grégoire Métais (1), Pierre-Olivier Antoine (2), Parveen A. Usmani (3), Sarfraz Hussain Solangi (3), Imdad Ali Brohi (3), Laurent Marivaux (4) & Jean-Loup Welcomme (5)
Manchar Formation
Several days were spent in Ranikot, and Bara Nai prospecting on both the east and west limbs of the northward plunging Bara Dome anticline (=Lakhra Anticline) exposed there (Fig. 2).
Eocene
Unconformity
The lower Bara Formation includes several repeated cycles of sandstone, each with a concretion or "clay pebble" conglomerate bed developed at the top, which is in turn overlain by shale. The sandstone with concretions is varicolored red, yellow, purple, and white. The concretion or conglomerate beds themselves include coprolites, burrows, some Turritella, snails, and oysters. Fossil wood is also abundant, as is a distinctive oval fossil fruit or seed pod. One isolatedand non-identified long bone, crocodilian teeth and fragments of turtle shell were found in these levels. This preliminary analysis indicates that the lower part of the Bara Formation represent an intertidal mud flat environment.
Laki Formation (Laki Village, 26°14’23”N ; 67°56’03”E)
?
Sohnari Formation (equivalent of the basal Laki laterite Member of Shah, 1999)
Lower Indus Valley
Unconformity
(1) What is the origin of the red series exposed in the Karachi Arc ? (2) Are they the result of the Indian Shield erosion ? (3) Are the coal layers equivalent in age to those of western India ? (4) Do these coal layers have potential of yielding Paleocene/Eocene faunas/floras ?
Photograph showing the lithology of the lower Bara Fm. The sandstone with concretions is varicolored red, yellow, purple, and white. The concretion or conglomerate beds themselves include coprolites, burrows, some Turritella, snails, and oysters. Fossil wood, seeds, and unidentified fruits are also abundant in the lower Bara Formation. (Photograph by G. Métais).
Lakhra Formation (Lakhra Village, 25°40’18”N ; 68°15’20”E)
RANIKOT Group
In a recent synthesis (Najman, 2006) on the detrical record of Himalaya, the Ranikot Group is even not cited while co-eval Gazij and Kithar Groups are mentioned as a sedimentary record of distal and remnant ocean basins. Also, beyound the paleontological survey of the Paleocene Bara Formation in the Lakhra Anticline, southern Pakistan; our work was directed toward four principal objectives:
Sulaiman Lobe
Kir th ar Ra nge
Paleocene mammals are not yet known from the Indo-Pakistan subcontinent. The Paleocene -Eocene outcrop of the Karachi Arc, southern Pakistan, provide information about the depositional environments, source areas, and paleogeographic and tectonic settings along the northwestern margin of the Indian Subcontinent during the closing of the Tethys Ocean. In the frame of a joint Franco-Pakistani research program, a survey of the Ranikot Group, and Laki Formation was carried out in November 2008 (Fig. 1).
Paleontology, Stratigraphy, and paleoenvironments of the Bara Formation
(Ypresian)
Introduction
MioPliocene
(1) Centre de Recherches sur la Paléobiodiversité et les Paléoenvironnements (CR2P), UMR 7207 du CNRS, Département Histoire de la Terre, Muséum national d'Histoire naturelle, CP 38, 57 rue Cuvier, F-75231 Paris cedex 05, France (Email:
[email protected]) (2) Laboratoire des Mécanismes et Transferts en Géologie, Institut des Sciences de la Terre, 14 Avenue Édouard Belin, F-31400 Toulouse, France (3) Centre for Pure and Applied Geology, University of Sindh, Jamshoro, Allama I.I.Kazi Campus, Jamshoro 76080, Pakistan (4) Laboratoire de Paléontologie, Institut des Sciences de l'Évolution, CNRS-UMR 5554, Université Montpellier II, c.c. 064, Place Eugène Bataillon, F-34095 Montpellier Cedex 5, France (5) 123 rue du Château d'eau, 34270 Le Triadou, France
Lakki Fm.
Reddish patches of Sohnari Fm.
Paleocene
Fig. 1. Location of the studied area
Upper
Bara Formation Middle
(Bara Nai, 26°03’08”N ; 67°53’09”E)
The upper part of the formation has yielded fragmentary mollusk shells, suggesting a a more coastal environment, similar to the shallow water intertidal mud flat environment of the lower Bara.
upper Ranikot Gp. Lower
We also spent some time checking the excavations of the numerous and spotty coalfield exploted in the core of the Lakhra Anticline. Coal is mined from the upper Bara Formation in the subsurface, and the coal detritus have yielded plant inprints. Those belong to at least three taxa.
Khadro Formation
Photograph showing the view eastward with the upper Lakhra marls and shales in the fore ground, reddish patchy outgrops of the Sohnari, and the marine shales and limestones of the Laki Formation in the back ground. (Photograph by G. Métais).
(Bara Nai, 26°07’06”N ; 67°53’14”)
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co a
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m
e fin ry ve
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m m ss
vc
p cg
st nd
Plant remains
er at
es on
es
Conglomerates
Coal Major unconformity
Bones and teeth Shark teeth
m lo ng co
sa
es on st ud
Sands Sandstones
c vf md m
Limestones Clays-Marls Marls Sandy Clays-Marls
Fossils and Bioturbation
rs e
Lithology
20 m
Foraminifers Marine ostracods Oysters Gastropods
Sedimentary Structures Mudcracks Laminations Sigmoidal cross-bedding Planar cross-bedding Trough cross-bedding
Ichnofacies burrows
Fig. 2. Synthetic section of the southeast flank of the Bara Dome based on measured sections at Ranikot and Bara Nai for the Ranikot Group, and near the Laki Village for the upper part of the section. Khadro Formation (lower Paleocene) of the Ranikot Group.—The oldest unit of the Ranikot Group is exposed near the Ranikot Fort, and at the locality Bara Nai. It consists of sandstone, with soft weathered Deccantrap basaltic lava, mixted with sulphurous shales and gypsum. Bara Formation (middle Paleocene) of the Ranikot Group.—This unit is well exposed in the core of the Lakhra anticline. It consists of fluviatil sandstone, siltstne, shale, underclay, and coal and is the main source of coal in the anticline. Photograph showing the view eastward down the dip slope on the Laki Formation, Pakistan. The red outcrop in the middle ground is the underlying Sohnari Formation (Photograph by G. Métais).
General geological context of the area Throughout the last 50 Ma, what is now Pakistan witnessed massive changes that have strongly marked the topography of that region. In its drive northward, the Indian plate continues its subduction under Asia, and the resulting tectonic forces are continuously molding the geology of the Alpine-Himalayan chain margins. The collision of the Indian and Eurasian continents resulted in the upheaval of Himalayas, Karakoram, and Hindukush, and the gradual disappearance of the Palaeogene margins of the Tethys Sea. In the southern Kirthar Range, the Upper Cretaceous-Paleocene system comprised a major progradational clastic succession of linked fluvial, shoreline, shelf, slope and basin floor depositional systems. Depositional trends were affected by incipient growth of major structural features, reflecting the early collision of the Indian and Arabian plates. As the collision continued, basin (and ultimately coastline) morphology changed, resulting in a change to the deltaic/tide dominated systems of the Ranikot Formation.
The middle part of the Bara Formation is somewhat different, with a greater development of sandstone lenses, less shale, and less lateral continuity of bedding than in the lower part of the formation. These sandstone lenses are cross-bedded and appear to represent fluvial channel sands. We found fragments of chelonian bones, wood, and a crocodilian tooth. The middle Bara clearly appears more fluviatile than the lower part of the formation, and would thus deserve further investigations.
Lakhra Formation (upper Paleocene) of the Ranikot Group.—Conformably overlying the Bara Formation is the Lakhra Formation of late Paleocene age. It consists of evenly bedded limestone and calcareous shale and is richly fossiliferous. Sohnari Formation (upper Paleocene) of the Ranikot Group.—The Sohnari Formation was redefined by Outerbridge and others (1991). Formerly called the Basal Laki Laterite (largely because of its deep red color), the Sohnari Formation consists of sandstone, conglomerate, shale, coal, and underclay. It is fossiliferous, and we have observed clams in growth position deep in the coal. The Sohnari interfingers with the Lakhra Formation. Laki Formation (upper Paleocene?, Ypresian).—The basal Limestone Member overlies the Sohnari Formation along a sharp conformable contact. The formation consits of fossiliferous and nodular (at its top) white to creamy-white rubbly bedded limestone alternating with calcareous shales and marls. The Laki Limestone Member is a richly fossiliferous rubbly bedded limestone. The Oligocene limestones and calcareous sandstones of the Nari Formation are not exposed in the prospected. Likewise, the sandstones annd conglomerates of the early Miocene Gaj Formation have been observed in the Lakhra Anticline area. Manchar Formation (Mio-Pliocene).—The Manchhar Formation, as it is called in Sindh Province, or the Siwalik Group, as it is known in northern Pakistan (Shah, 1977), is probably of Pliocene to Pleistocene age (Jones, 1960). It unconformably overlies the Laki Formation around the Lakhra anticline. It consists of gravel, sand, and clay with large fossil bones and petrified wood.
A
B
C
Photograph showing fossils collected from the Bara Formation. A, coal layer of the upper Bara preserving plant remains. B, fragmentary long bone of turtle from the middle Bara. C, assemblage of mollusks from the uppermost Bara Formation (Photograph by G. Métais).
Conclusion and Perspectives In conclusion, some potential remains for discovering Paleocene mammals in the Bara Formation. We have confirmed all previous reports that this formation is fluvial in origin (at least in the middle part of the formation), and we have confirmed that it yields reptile bones, and plants remains. To date no mammals have been found, but a longer survey concentrating on the middle. Bara Formation in Rahman Dhoro, Ranikot Dhoro, and elsewhere in the Karachi Arc, might well yield positive results. The Bara Formation should be investigated further and, in view of the importance of discovering Paleocene mammals in Pakistan, we hope to spend a longer period of time working in southern Pakistan on this formation in the near future. ACKNOWLEDGMENTS We are very grateful to K. Majidhula for its constant support. Many thanks are addressed to the French consul Pierre Seillant , and the French Ambassador Daniel Jouanneau for their help, and support. The Mission Paléontologique Française au Balouchistan, the CNRS, and the Museum national d’Histoire naturelle have financially supported this project. This work is the initiation of current research project supported by the French ANR-PALASIAFRICA Program (ANR-08-JCJC-0011-01 - ANR-ERC).
References Najman, Y., 2006. The detrital record of orogenesis: A review of approaches and techniques used in the Himalayan sedimentary basins. Earth-Science Reviews, 74: 1-72 Outerbridge, W.F. et al., 1991, The Sohnari Formation in southern Pakistan, in Stratigraphic notes, 1989-90: U.S. Geological Survey Bulletin 1935, p. 2-40.
