Visualising the buried succession
Palynological and lithological correlation has shown how similar the Carboniferous-Permian glaciogenic and post-glaciogenic rocks of Oman and the Arabian Peninsula are to those of Pakistan. Perhaps this is not surprising given their proximity in plate reconstructions for the time. However the excellent exposure of rocks in the Salt and Khisor ranges allow these succession to be ‘eyeballed’ in a way not possible in Oman and the Arabian Peninsula, allowing largescale 2D and 3D appreciation of the complexities of Middle Eastern Carboniferous-Permian glaciogenic and post-glaciogenic rocks.
Comparison
Carboniferous-Permian glaciogenic and post-glaciogenic rocks are superbly exposed in the Salt and Khisor ranges in Pakistan. It is well known that the carbonate Amb, Wargal and Chhidru formations (Fig. 1) are equivalent to part of the Khuff Formation in Oman and central Arabia (e.g. Archbold 1999). However the well exposed Tobra, Warchha and Sardhai formations of the trans-Indus ranges, which underlie the carbonates, are also startlingly similar to hydrocarbon-bearing formations from the subsurface of Oman, the Emirates and Saudi Arabia.
Fig. 1 The superbly exposed Upper Permian Amb, Wargal and Chhidru formations of the Salt Range in Zaluch Nala, partly equivalent to the Khuff Formation in the Arabian Peninsula
In Zaluch Nala, western Salt Range and Saiyiduwali in the Khisor Range, the Tobra Formation (Fig. 2), a glacigenic deposit of greenish grey diamictite, sandstone and mudstones is unconformably overlain by the Warchha Formation, a medium- to coarse-grained, purple, arkosic sandstone interpreted as an arid climate fluvial deposit (Ghazi and Mountney 2009). In the eastern Salt Range, the Tobra Formation is conformably overlain by the Dandot Formation (Stephenson et al. 2012). The Dandot Formation consists of pale-grey to olive-green sandstone with scattered pebbles of up to 10 cm in diameter or pebbly beds with subordinate dark-grey and greenish splintery shales, as well as Eurydesma and Conularia (Stephenson et al. 2012).
Fig. 2. Location of the Salt and Khisor ranges, Pakistan; and Pennsylvanian reconstruction of continents after Torsvik & Cocks 2004.
Lithologically the Tobra Formation is closely similar to the Al Khlata Formation, while the marine sandstone of the Dandot Formation is closely similar to the Lower Gharif Member in subsurface Oman.
Palynological assemblages bear out this similarity. Sections in Pakistan are similar enough to allow the application of biozones based on the Pennsylvanian and Early Permian glacigene sediments of interior Oman. Samples from the Tobra Formation at Zaluch Nala, western Salt Range, and from the Khisor Range Pakistan (Fig. 3) yield palynomorph taxa indicating the late Pennsylvanian Oman 2165B Biozone (upper P5 PDO production zone). Assemblages from the Tobra Formation at the Choa Road section near Khewra in the eastern Salt Range, Pakistan are assignable to the earliest Permian 2141B Biozone (P1 PDO production zone), indicating a possible correlation between the ‘Tobra shale’ and the Rahab Shale Member of Oman (Stephenson et al. 2012; Jan and Stephenson 2011; Jan et al. 2016). The latter is considered to mark the final deglaciation sequence in Oman.
Fig. 3. Grey/green diamictites and mudstones of the Tobra Formation overlain by the red Warchha Formation at Saiyiduwali in the Khisor Range. The Tobra Formation is the biostratigraphic equivalent of the Al Khlata Formation in Oman; the Warchha Formation is closely similar to parts of the Middle and Upper Gharif members
The pre-carbonate Tobra, Warchha and Sarhai formations are superbly exposed in the southeast facing mountain front of the Khisor Range (Fig. 4).
Fig. 4. The Permian succession from the Tobra Formation to the Amb, Wargal and Chhidru formations in the southeast facing wall of the Khisor Range, near Saiyiduwali. Escarpment around 600m high
In the Salt Range, the Tobra is succeeded by the Dandot Formation (Fig. 5), and then by the Warchha and Sardhai formations, which are in turn again succeeded by the carbonates of the Amb Formation.
Fig. 5. The greenish grey sandstone of the Dandot Formation overlying the Tobra Formation and grey Tobra Shale in the Eastern Salt Range, Choa Road section. The Tobra shale is the biostratigraphic equivalent of the Rahab Shale member of the subsurface of Oman. The Dandot Formation is similar to the Lower Gharif Member of the subsurface of Oman
The Warchha Formation consists of conglomerate, sandstone and claystone in fining-upward cycles, including planar and trough cross-bedding, planar lamination, and soft sediment-deformed bedding (Fig. 6). Structures in the finer-grained facies include desiccation cracks, raindrop imprints, caliche nodules and bioturbation. The unit is interpreted as containing channels, gravel bars, sandy bedforms, downstream and laterally accreting barforms, sand sheets, crevasse splays, levees, floodplain units and shallow lakes), all suggesting a fluvial depositional environment in a relatively arid climate (Ghazi and Mountney 2009).
Fig. 6 The Warchha Formation in Zaluch Nala
The Sardhai Formation consists of bluish to greenish-grey claystone with subordinate sandstone and siltstone interbeds, and minor carbonaceous clays (Stephenson et al. 2013). The formation contains occasional plant remains in the exposures in the Salt Range.
Although there has been no palynological recovered thus far from the Warchha Formation, the Sardhai Formation yielded rich palynological assemblages (Jan et al. 2009; Fig. 7), with abundant bisaccate pollen grains and a few spores. In particular, well-preserved specimens of Florinites? balmei, a bilaterally symmetrical monosaccate pollen grain, are common. The presence of this pollen and the stratigraphic context suggest that the Sardhai Formation correlates with the Khuff transition beds of Oman and the basal Khuff clastics of central Saudi Arabia (OSPZ6 biozone).
Fig. 7. Steeply dipping beds of the Sarhai Formation in the Saiyiduwali, Khisor Range, the biostratigraphic and lithological equivalent of the basal Khuff transition beds in Oman
Useful analogues for subsurface formations
This brief article has shown how similar the Carboniferous-Permian glaciogenic and post-glaciogenic rocks of Oman and the Arabian Peninsula are to those of Pakistan. The excellent exposure of rocks in the Salt and Khisor ranges allow these succession to be ‘eyeballed’ in a way not possible in Oman and the Arabian Peninsula, allowing largescale 2D and 3D appreciation of the complexities of Middle Eastern Carboniferous-Permian glaciogenic and post-glaciogenic rocks.
Field visits to these Pakistan localities can be arranged
For details contact:
Dr Irfan Jan, Associate Professor: NCEG, University of Peshawar, Pakistan (irfanjan6@gmail.com)
Prof Mike Stephenson, Director Stephenson Geoscience Consulting Ltd (mikepalyno@me.com)
References
Archbold, N.W., 1999, Permian Gondwana correlations: The significance of the western Australian marine Permian: Journal of African Earth Sciences, v. 29, p. 63–75, doi: 10.1016/S0899-5362(99)00080-9.
Ghazi, S., Mountney, N.P., 2009. Facies and architectural elements of a meandering fluvial succession: the Permian Warchha Sandstone, Salt Range, Pakistan. Sedimentary Geology 221, 99–126.
Jan, I U, Iqbal, S, Davies, S J, Zalasiewicz, J A, Stephenson, M H, Wagreich, M, Haneef, M, Hanif M, and Ahmad, S. 2017. Periglacial Palaeoenvionment in the Upper Carboniferous–Lower Permian Tobra Formation of the Salt Range, Pakistan. Acta Geologica Sinica, 91, 801–84.
Jan, I U, Shah, A, Stephenson, M H, Iqbal, S, Hanif, M, Wagreich, M, and Hussain, H S. 2016. The sedimentology of the Lower Permian Dandot Formation: a component of the Gondwana deglaciation sequence of the Salt Range, Pakistan. Rivista Italiana di Paleontologia e Stratigrafia, 122, 75-90.
Jan, I, and Stephenson, M H. 2011. Palynology and correlation of the Upper Pennsylvanian Tobra Formation, Zaluch Nala, Salt Range, Pakistan. Palynology, 35, 212-225.
Jan, I. U. Stephenson, M. H., Khan, F. R. 2009. Palynostratigraphic correlation of the Sardhai Formation (Permian) of Pakistan. Review of Palaeobotany and Palynology, 156, 402-442.
Stephenson, M H, Jan, I U, and Al-Mashaikie, S Z A K. 2012. Palynology and correlation of Carboniferous – Permian glacigene rocks in Oman, Yemen and Pakistan. Gondwana Research, 24, 203-211.
Torsvik T. H. & Cocks L. R. M. — Earth geography from 400 to 250 Ma: a palaeomagnetic, faunal and facies review, Journal of the Geological Society, London. Journal of the Geological Society 161(4):555-572