Irfan U. Jan

Palynology and correlation of the Upper Pennsylvanian Tobra Formation from Zaluch Nala, Salt Range, Pakistan

Samples from the upper 84 m of a 125 m thick section of the Tobra Formation at Zaluch Nala, western Salt Range, Pakistan yielded palynomorph taxa including the spores Horriditriletes sp. and Microbaculispora tentula, abundant monosaccate pollen including Barakarites cf. rotatus, Cannanoropollis janakii and Plicatipollenites malabarensis, and rare taeniate and non-taeniate bisaccate pollen. Converrucosisporites grandegranulatus, Cycadopites cymbatus, Horriditriletes ramosus, Horriditriletes tereteangulatus and Microbaculispora tentula indicate the South Oman 2165B Biozone (Late Pennsylvanian), suggesting that the Tobra Formation in Zaluch Nala is equivalent to the middle part of the Al Khlata Formation of South Oman (Petroleum Development Oman (PDO) Al Khlata production unit AK P5). Brevitriletes leptoacaina, Brevitriletes parmatus, Horriditriletes ramosus and Microbaculispora tentula indicate the lower part of the Oman and Saudi Arabia Palynological Zone 2 (OSPZ2). The Tobra Formation assemblages are also correlated with those from Stage 2 and the eastern Australian Microbaculispora tentula Oppel-zone, based on the occurrence of Brevitriletes cornutus, Brevitriletes parmatus, Cycadopites cymbatus, Horriditriletes ramosus, Horriditriletes tereteangulatus and Microbaculispora tentula. The Tobra Formation in Zaluch Nala lacks the deglaciation sequence that is present in several other palaeogeographically nearby basins such as those of south Arabia and Western Australia. This is an indication of either non-deposition during the deglaciation period or erosion associated with the unconformity between the Tobra Formation and the overlying Warchha Formation.

Progress in the Gondwanan Carboniferous-Permian palynology and correlation of the Nilawahan Group of the Salt Range, Pakistan: A brief review

This paper comprises of two sections. The first section describes challenges in the Carboniferous–Permian Gondwanan stratigraphic palynology, and progress in techniques such as presence of the ‘rare-marine intervals’, and ‘radiometric dating’ in some Gondwanan successions, e.g., South Africa, Australia and South America, as tools to confidently calibrate these palynozones. The second section describes developments in the palynological work on the Carboniferous–Permian Nilawahan Group of the Salt Range, Pakistan, and summarises their correlation with the coeval succession of the Gondwana continents and with the Russian/International stages.

The sedimentology of the Lower Permian Dandot Formation: a component of the Gondwana deglaciation sequence of the Salt Range, Pakistan

The Dandot Formation is a part of the Lower Permian, dominantly continental, Gondwanan Nilawahan Group in the Salt Range, Pakistan. The formation conformably overlies the glacio-fluvial Tobra Formation and has a sharp conformable contact with the overlying fluvio-continental Warchha Sandstone. Sedimentary analyses show that the Dandot Formation consists of 1: bioturbated sandstone lithofacies (L1), 2: dark green mudstone/shale lithofacies (L2), 3: flaser bedded sandstone lithofacies (L3), 4: rippled sandstone lithofacies (L4), 5: cross-bedded sandstone lithofacies (L5), and 6: planar sandstone lithofacies (L6). These can be grouped into shoreface, inner shelf, and tidal flat and estuarine facies associations, deposited in shallow marine to intertidal environments. The upper part of the Tobra Formation at the Choa-Khewra road section, where it conformably underlies the Dandot Formation, contains palynomorphs assignable to the earliest Permian 2141B Biozone. In south Oman, the 2141B Biozone is closely associated with the Rahab Shale Member, a widespread shale unit which is considered to represent part of a Permian deglaciation sequence which culminates in the marine beds of the Lower Gharif Member, interpreted as due to post glacial marine transgression. Thus, the Tobra Formation and the overlying marine Dandot Formation may form part of a similar deglaciation sequence.

Velocity and Structural Modeling of Mesozoic Chiltan Limestone and Goru Formation for Hydrocarbon Evaluation in the Bitrisim Area, Lower Indus Basin, Pakistan

The present study focuses on building a workflow for structural interpretation and velocity modeling and implementing to Jurassic-Cretaceous succession (Chiltan Limestone and Massive sand of the Lower Goru Formation). 2D-Migrated seismic sections of the area are used as data set and in order to confirm the presence of hydrocarbons in the study area, P and S-wave seismic velocities are estimated from single-component seismic data. Some specific issues in the use of seismic data for modeling and hydrocarbon evaluation need to deal with including distinguishing the reservoir and cap rocks, and the effects of faults, folds and presence of hydrocarbons on these rocks. This study has carried out the structural interpretation and modeling of the seismic data for the identification of traps. The results demonstrate existence of appropriate structural traps in the form of horst and grabens in the area. 2D and 3D velocity modeling of the horizons indicates the presence of high velocity zones in the eastern half of the study while relatively low velocity zones are encountered in the western half of the area. Two wells were drilled in the study area (i.e. Fateh-01 and Ichhri-01) and both are dry. Immature hydrocarbons migration is considered as a failure reason for Fateh-01 and Ichhri-01 well.

Microfacies and diagenetic studies of the early Eocene Sakesar Limestone, Potwar Plateau, Pakistan: approach of reservoir evaluation using outcrop analogue

The early Eocene Sakesar Limestone of the Salt Range has been investigated in detail for microfacies analysis, depositional modeling, diagenesis and reservoir characterization. This research work was comprised of two outcrop sections, i.e., Nilawahan Gorge Section (NGS) and Katas Temple Sections (KTS) of the Sakesar Limestone, central and eastern Salt Range, Potwar Plateau. This work is mainly concentrated on investigating and evaluating the reservoir quality through depositional and diagenetic fabrics. The depositional, diagenetic and deformational processes are controlling factors of porosity and permeability distribution. On the basis of relative estimated ratio of allochemical constituents and micrite, five microfacies have been recognized. These microfacies are: Benthonic Foraminiferal wackestone, Foraminiferal-Algal wackestone–packstone, Miliolidal-Algal wackestone–packstone, Nummulitic-Assilina Packstone and Alveolina-Algal packstone. On the basis of relative abundance of biota, their associations and the presence of micritic matrix in various microfacies, the Sakesar Limestone is interpreted to be deposited in the proximal inner ramp to middle ramp settings. The Sakesar Limestone is largely affected and modified by various diagenetic events which have destroyed primary nature of reservoir and developed it as prolific secondary reservoir. The paragenetic sequence includes micritization, cementation, dissolution, neomorphism, nodularity, silicification, mechanical compaction, stylolitization, fractures and veins formation. The identified porosity types include intraparticle, intercrystalline, moldic, cavernous and fracture. The visually estimated average micro porosities of the Sakesar Limestone vary between 0.5 and 2.1% in the NGS and KTS. The core plug porosity and permeability of outcrop samples vary between 0.9 and 2.9%. The relation of core plug porosity and permeability has moderate positive correlation coefficient. The fractures and dissolution on microscopic and macroscopic level are the dominant factors that enhance the reservoir potentiality of the Sakesar Limestone.

Relating petrophysical parameters to petrographic interpretations in carbonates of the Chorgali Formation, Potwar Plateau, Pakistan

An integrated approach was deployed to relate the petrographical and petrophysical parameters of the Chorgali Formation to assess its reservoir potential. The petrographical study of the Chorgali Formation, exposed in Khair-e-Murat Range, disclosed that the original texture and composition are affected by diagenetic events (i.e. micritization, dolomitization, microfractures, stylolitization, compaction, dissolution, neomorphism and cementation). Of these, dissolution, dolomitization and microfractures enhanced reservoir quality, while micritization, compaction, neomorphism and cementation reduced reservoir suitability. Micritization occurred in marine phreatic conditions; dolomitization existed in the marine-meteoric mixing environment; dissolution, neomorphism and cementation took place in meteoric conditions. The mechanical and chemical compaction occurred in a burial diagenetic environment. In addition, the relationship among formation resistivity factor (F), compressional wave velocity (Vp) and porosity (ɸ) was also validated for the Eocene Chorgali Formation of Meyal Oil Field, Potwar Plateau, Pakistan. There is an inverse relationship between ɸ and F, Vp, however, the relation between F and Vp is directly proportional. Such inter-relationships assist in determining and interpreting the geological processes based on petrophysical parameters (ɸ, F and Vp). F and Vp may be high due to cementation, compaction, sealed fractures and lack of deformation in carbonates. On the other hand, F and Vp may be low due to dissolution, dolomitization, vacant fractures, lack of compaction and cementation. Similarly, ɸ is enhanced by processes lowering F and Vp and reduced by processes increasing F and Vp. Hence the diagenetic processes enhancing and reducing the porosity influence the electric and elastic properties of the carbonate rocks.

A periglacial palaeoenvionment in the Upper Carboniferous-Lower Permian Tobra Formation of the Salt Range, Pakistan

The Upper Carboniferous–Lower Permian (Upper Pennsylvanian–Asselian) Tobra Formation is exposed in the Salt and Trans Indus ranges of Pakistan. The formation exhibits an alluvial plain (alluvial fan–piedmont alluvial plain) fades association in the Salt Range and Khisor Range. In addition, a stream flow facies association is restricted to the eastern Salt Range. The alluvial plain facies association is comprised of clast-supported massive conglomerate (Gmc), diamictite (Dm) facies, and massive sandstone (Sm) lithofacies whereas the stream flow-dominated alluvial plain facies association includes fine-grained sandstone and siltstone (Fss), fining upwards pebbly sandstone (Sf), and massive mudstone (Fm) lithofacies. The lack of glacial signatures (particularly glacial grooves and striations) in the deposits in the Tobra Formation, which are, in contrast, present in their time-equivalent and palaeogeographically nearby strata of the Arabian peninsula, e.g. the Al Khlata Formation of Oman and Unayzah B member of the Saudi Arabia, suggests a pro- to periglacial, i.e. glaciofluvial depositional setting for the Tobra Formation. The sedimentology of the Tobra Formation attests that the Salt Range, Pakistan, occupied a palaeogeographic position just beyond the maximum glacial extent during Upper Pennsylvanian–Asselian time.

Palaeoenvironmental and sequence stratigraphic analyses of the Jurassic Datta Formation, Salt Range, Pakistan

The Lower Jurassic Datta Formation, western Salt Range, Pakistan, comprises three facies associations: (1) channel belt facies association (CBFA), (2) channel margin, and overbank facies association (CMOFA), and (3) lagoonal facies association (LFA). A cyclic fining-upward trend in the succession is represented by basal quartzose conglomerate/pebbly sandstone, through coarse to fine quartzose sandstone to siltstone and shales/claystone, which contains some carbonate accumulation. Two prominent depositional sequences are recognized in the Datta Formation with the lower high and upper low magnitude cycles. The Datta Formation thus represents a thick sedimentary succession and in the study area, i.e., western Salt Range, mainly channel belt, flood plain and/or delta top facies are exposed. The palaeocurrent analysis shows that the source area with acidic plutonic rocks laid to S–SE in the Indian shield, aravalies or older sedimentary rocks of the Indus Basin (i.e., Khewra, Tobra and Warchha formations). A tentative stratigraphic correlation of the Datta Formation with the lower Jurassic Lathi Formation, India invites further work in parts of India, which will elaborate the extent of the Datta Formation in the Greater Indian peninsula and develop palaeogeographic setting for this Lower Jurassic deltaic rock unit.

Using larger benthic foraminifera for the paleogeographic reconstruction of Neo-Tethys during Paleogene

The biostratigraphic range distribution of larger benthic foraminifera (LBF) from the eastern part of Neo-Tethys in the Kohat Basin of Pakistan is compared with the Western and Central Neo-Tethys. The results are used to establish the migration pathways of LBF for the paleogeographic reconstruction of the Neo-Tethys that existed in the Paleogene. This comparison across the Neo-Tethys revealed that LBF species are mostly confined to the Gondwanan (Iran, Iraq, Pakistan, India, Indonesia) and Laurasian-derived blocks (Italy, France, and Spain), with only a few on the margin of the Gondwanan continents (Oman).