By Haleem Zaman Magsi Baloch Nazir Z. Magsi
Abstract:
The Fuel and Energy Complex is an artery of the socio-economic sector of one and another country. Pakistan, a traditional importer of oil, is now importing Natural Liquid Gas to meet Fuel and Energy complex for industry complex and urban development. Therefore, Pakistan is hunting for indigenous hydrocarbon deposits and the utilization of sustainable energy resources. The present study attempts to evaluate the hydrocarbon potential of Sost aulacogen, a tectonic element of Northern Sedimentary Terrain, Karakoram. The paleotectonic conditions of sedimentation of a Mesozoic sequence of Alpides of Pakistan, NW Himalayas, and the Karakoram indicates resemblance. Therefore, the authors postulate the probability of huge hydrocarbon fuel deposits in Sost aulacogen. However, still, detailed petroleum system studies and modeling of aulacogen are required for commercial activity.
Keywords: #Hydrocarbons, #Mesozoic Sequence, #Sost Aulacogen, #Paleotectonic Conditions, #Sources #Reservoirs.
Introduction:
If one follows the socio-economic sector development since stone stage, he will find that it was required to develop invention energy resources considering system of economic relations. The evolutionary and revolutionary dynamics of socio-economic sector development frames target of the Fuel and Energy Complex (FEC). Therefore, viable Fuel and Energy Complex (FEC) is important for one or another country. While viability of FEC depends on availability of hug indigenous hydrocarbon fuels and energy resources.
Pakistan is blessed with an enormous amount of renewable and natural energy resources. It has an excellent solar insolation; an extremely good wind energy potential; massive hydroelectric resource, substantial reserves of natural gas, 1054 KM long coastal line with a resource of tidal energy; large livestock population and agricultural waste to generate bioenergy. In addition, Pakistan has one of the largest coal resources in the world amounting to 185 billion tons of lignite located in Sindh province.
Despite massive renewable energy potential in the country, today only 70% of population has access to grid electricity in Pakistan. In terms of access to natural gas network, about 25% of population has access to natural gas network. This indicates that about two-third of population must rely on inefficient and unhealthy recourses such as fuels wood, dung, and other biomass to meet their basic energy needs for cooking, space heating and water heating etc. Certainly, the demand would continue to grow further as the population increases. According to Arkhipov et al., (2014) gas demand of fuel and energy complex will reach peak in 2040 in Pakistan. Moreover, emerging global megaproject China – Pakistan Economic Corridor (CPEC), a locomotive of socio-economic sector of region will also make relevant correction in targets of Fuel and Energy Complex of Pakistan. The above-mentioned future scenario of FEC target will eventually enhance hefty import bills of Pakistan, a traditional importer of oil and now is importing liquid natural gas (Brohi 2018)
The critical choice for affordable and reliable supply of hydrocarbon fuels and energy depend on exploration of indigenous hydrocarbon fuels deposits and the effective utilization of energy resources. Therefore, Pakistan is hunting for indigenous hydrocarbon fuels deposits and planning to enhance utilization of renewable energy sources to make sustainable FEC in accordance with future targets.
The Oil and Gas Companies are targeting Palaeozoic, Mesozoic, and Cenozoic sedimentary sequences in Pakistan because clastic and carbonate rocks of the above-mentioned Eras are hydrocarbon sources and reservoirs rocks in onshore and offshore basins of Pakistan (Bender and Raza 1995, Craig et al., 2018, Carmichael et al., 2009, Oakley 2016, Qadri 1995, Voskresenskiy et al., 1971 and Wandrey et al., 2004).
Craig et al., (2018) and Oakley (2016) have studied the petroleum system and hydrocarbon potential of NW Himalaya of Pakistan and India and indicated Palaeozoic and Mesozoic sequences as sources and reservoir rocks in NW Himalayas. Wadia (1931) has categorized NW Himalayas as NW Himalaya Syntaxis. While Burtman (2013) and Khain (1979) have linked Trans Indus Range and the Salt Range with NW Himalayas Syntaxis and termed as Pamir- Punjab Syntaxis. Whereas Balasundaram and Ray have connected Karakoram Mesozoic geosyncline with Mesozoic Himalaya geosyncline south of Tibet. Despite Karakoram Meganticlinorium (Khain 1979), an internal tectonic element of Pamir-Punjab Syntaxis (Burtman 2013 Khain 2000) and comprises Palaeozoic and Mesozoic clastic and carbonate rocks (Desio 1974, Gaetani 1997, Schneider 1957, 1960, Zanchi and Gaetani 1994, 201) is excluded from petroleum system and hydrocarbon potentials studies of NW Himalayas Syntaxis (Craig et al., 2018, Oakley 2016). However, Magsi (2018, 2019) has overviewed abiotic and biotic hydrocarbons potential of Northern Sedimentary Terrain, Karakoram.
The object of the present study is to examine the petroleum system and hydrocarbon potentials of Mesozoic sequence (Donnelly 2004 and Zanchi and Gaetani 1994, 2011) of Sost aulacogen, Northern Sedimentary, Northern Karakoram Terrain (Fig.1) in accordance with the correlation of paleotectonic conditions of sedimentation of the Mesozoic sequence of sources and reservoir rocks of NW HimalayasFigure 1 Tectonostratigraphic units of Sost Aulacogen (after Zanchi and Gaetani 1994 with Changes). KAB - Karakoram Axial Batholithic
Figure 1. Tectonostratigraphic units of Sost Aulacogen (after Zanchi and Gaetani 1994 with Changes). KAB - Karakoram Axial Batholithic
Tectonic and Stratigraphic Context of Sost Aulacogen:
Schneider (1957,1960) delineated 5 zones of Karakoram meganticlinorium (Khain 1979, Belyayevskiy 1966) from north Northern Sedimentary Zone) to south (Gilgit zone). Gattinger (1961) assumed 7 zones of Karakoram meganticlinorium. While Desio (1974) split Karakoram segment into 6 zones: Northern Sedimentary Zone also term as Northern Sedimentary Terrain (Zanchi and Gaetani 2011); Axial Granite (Batholithic) Zone; Central Metamorphic Zone or Southern Sedimentary Zone (Zanchi and Gaetani 2011); Chalt Green Schist Zone; Basic Intrusion Zone and Gilgit Zone. However, Gaetani (1997), Gansser (1964), and Zanchi and Gaetani (2011) suggested three zones from north (Northern Sedimentary Zones to south Southern metamorphic Zone) and defined Chalt Green Schist zone as Karakoram - Kohistan suture, Basic Intrusion Zone and Gilgit Zone as part of Kohistan Arc. According proponent of plate tectonic (Gaetani 1997, Gansser 1964, Tahirkheli et al., 1990, and Zanchi and Gaetani 2011) Karakoram – Kohistan Suture Zone serves as collision boundary between Kohistan Arc with Karakoram segment. Whereas Balasundaram and Ray (1973) considered Karakoram- Kohistan Suture Zone as eugeosyncline that linked with Mesozoic geosyncline south of Tibit. Belousov et al., (1979), Belyayevskiy (1966), Bolt and Choi (2005), Gattinger (1961), Schneider (1957, 1960), Smoot (2007, 2018) also decline collision of Kohistan Arc and Karakoram Arc. The fold and block model of Garhwal Himalaya dis not support traditional plate tectonic concepts (Rogozhin et al., 2020).
The Northern Sedimentary Terrain, Karakoram stretches between Northern fault also term as Kilik Fault (Zanchi and Gaetani 2011) and Axial Batholithic Zone (Fig.1). Whereas Reshun – Upper Hunza Fault splits Northern Sedimentary Terrain into Northern and Southern Units (Zanchi and Gaetani 2011), where the Sost unit and Guhjal Unit are internal tectonostratigraphic elements of Northern Unit and Southern Units respectively (Fig.1). Zanchi and Gaetani (2011) have elucidated morphological reactivation of Reshun- Upper Hunza Fault where segments of fault change morphology as reverse, normal and strike slip faults. Belousov (1976) categorized morphological changing structure faults as overthrust slashes. Belyayevskiy (1966) and Khain (1991) termed overthrust slashes as abyssal faults which control geoblocks dynamics. The abyssal faults are present in Tien Shan and Caucasus mountains where serve as boundaries between neotectonic uplifts and subsidences (Belousov 1980, Belyayevskiy 1966). Therefore, Reshun – Upper Hunza Fault being abyssal fault influences on the Northern Sedimentary basin dynamics. The Upper Hunza Fault and Northern Fault (Fig.1) are major thrusts plane stacking Guhjal block and Misgar Block on the Sost Block respectively (Donnelly 2004, Zanchi and Gaetani 2011). Authors postulate that Upper Hunza Thrust Fault and Northern Thrust Fault form Sost Aulacogen tectonic element (Fig.2).
Figure 2. Sost Aulacogen, Northern Karakoram Terrain
The Sost graben structure comprises of a thick pile of folded and thrusted sheets forming antiformal stack, where strike slip faults with E-W strike disturb the structures (Donnelly 2004, Zanchi and Gaetani 2011). The Northern Sedimentary Terrain, Karakoram is comprised of Paleozoic and Mesozoic clastic and carbonate rocks (Gaetani 1997, Gaetani 1997, Zanchi and Gaetani 1994, 2011) where outcrop rocks ratio is: volcanic 0.5%, Plutonic 4-5%) Sedimentary 67% and Metamorphic 28% (Desio 1974). Whereas Sost graben consists of thick Permian and Mesozoic clastic and carbonate sediment sequences, Gricha formation (Permian) outcrops as core of Sost anticline (Zanchi and Gaetani 1994). The coals seams are present in Ashtigar and Yashkuk formations in Chapursan block of Sost graben (Donnelly 2004). Guhjal horst characterises with anticline and syncline structures controlled with faults (Fig.3). Gricha formation black slates and sandstone (Permian) overlain by massive carbonate (Permian – part of undefined Mesozoic) of Guhjal Formation and well bedded Buattar Limestone, marl, and shaly sandstone (Permian) interbedded with Gricha and Guhjal formations (Zanchi and Gaetani 2011). Whereas dark slates, arkose sandstone, quartzite, bioclastic limestone and strongly deformed Shaskar granitoid outcrops in Misgar horst.
Figure 3. Geological Cross Section Guhjal Unit and Sost Unit.
Discussion and Conclusion:
The sustainable and prolonged subsidence of the earth's crust refers as basin. The basin dynamics frames sedimentation trends and progressive lithogenesis that sedimentary rocks - the composition and the structure, whereas the lithogenesis processes make favourable environment for the formation, accumulation, and preservation of hydrocarbons (Galimov 1989).
Bender and Raza (1995), Carmichael et al., (2009), Craig et al., (2018) Oakley (2016), Qadri (1995), Voskresenskiy et al., (1971) and Wandrey et al., (2004) examined petroleum system and hydrocarbon potentials of Alpides, Pakistan, NW Himalayas and Offshore Indus Basin of Pakistan and delineated Alpides, NW Himalayas into Indus basin, Balochistan Basin, Kohat- Potwar Basin, Peshawar Basin, Lesser Himalaya basin, Trans Indus Range, Salt Ranges, Kashmir Basin, Indus Offshore Basin and Makran offshore Basin as prospective hydrocarbon producing basins. According to Bender and Raza (1995), Carmichael et al., (2009), Craig et al., (2018) Oakley (2016), Qadri (1995), Voskresenskiy et al., (1971) and Wandrey et al., (2004) Mesozoic clastic and carbonate rocks are hydrocarbon source and reservoir rocks in Lesser and Sub Himalayas, Trans Indus, Range, Salt Range and NW Himalayas of Pakistan. The Mianwali formation shale (Early Triassic) and Chichali formation shale (Jurassic – Early Cretaceous) are sources rocks and Kingriali formation dolomite (Upper Triassic) and Datta formation sandstone and Samansuk formation limestone are reservoir rocks in Lesser Himalaya, Sub-Himalaya, Trans Indus Range and Salt Range, respectively (Craig et al., 2018, Oakley 2016 and Wandrey et al., 2004).
The correlation between clastic and carbonate (Triassic – Cretaceous) outcrops of Sost aulacogen (Donnelly, Zanchi and Gaetani 2011) and Mesozoic sequences of NW Himalayas, Lesser and Sub Himalayas basin source and reservoir rocks indicates resemblance of palaeotectonic environments of sedimentation of Mesozoic sequences (Fig.4.). While Khain and Limonov (2004), Gaetani (2015), Gaetani (1997), Desio (1979), Voskresenskiy et al., (1971), and Zanchi and Gaetani (2011) are of opinion that new stage of tectonic development history of Alpides, Alpine-Karakoram (Desio 1979) started on the border of Palaeozoic Era and Mesozoic Era. Khain and Limonov (2004), Gaetani (2015), Gaetani (1997), Desio (1979), Voskresenskiy et al., (1971), and Zanchi and Gaetani (2011) categorized Permian- Triassic complex as Cimmerian Folding system. The gradual transition is sediment deposition is documented from Permian period to Triassic period in Kirthar -Sulaiman of Alpides (Voskresenskiy et al., 1971) and Sost aulacogen, Northern Sedimentary Terrain (Gaetani 1997, and Zanchi and Gaetani 2011). The Early Triassic shale deposition and limestone accumulation in second half of Triassic period occurred in all basin (Donnelly 2004, Voskresenskiy et al., 1971 and Zanchi and Gaetani 2011).
Figure 4. Correlation of Mesozoic sedimentary sequence of Lesser Himalayas and Northern Sedimentary Terrain (after Craig et al., 2018, Donnelly 2004, Zanchi and Gaetani 2011).
The paleotectonic environment of Triassic period indicates that Alpides of Pakistan, Karakoram, and Higher Himalayas were connected with each other (Fig. 5). Balasundaram and Ray (1973) also elucidate link between Mesozoic geosyncline south of Tibit with Karakoram Mesozoic geosyncline. While Khain (1979)) and Voskresensky et al., (1971) have indicated that deposition of shale and carbonate (Lower Triassic) occurred during start of new tectonic development stage base on weak Henrician Orogeny in Karakoram and NW Himalayas which covered Alpides of Pakistan. The present petroleum system and hydrocarbon potentials studies base on the evaluation of paleotectonic conditions sedimentation of Mesozoic sequence in Alpides of Pakistan, NW Himalayas, and Karakoram. It is observed that deposition conditions of Mesozoic sequence in all above-mentioned basins are approximately similar. Since Mesozoic sequence of Sost aulacogen, Norther Sedimentary Terrain, Karakoram and other tectonic elements of Alpine-Himalaya Belt of Pakistan is same, so authors postulate Sost aulacogen can be hydrocarbon rich structure. The Sukkur aulacogen structure of Indus basin is one of main gas producing structure in Pakistan Voskresenskiy et al., 1971, Wandrey et al., 2004).
In the author's opinion, Wirokhun formation black shale (Early Triassic) and Jurassic Ashtigar Formation shale and marl interbedded with coal seams and Yashkuk formation sandstone and siltstone along with coal seams (Donnelly 2004, Zanchi and Gaetani 2011) can be prospective hydrocarbon sources rocks. While limestone and dolomite of Aghil formation (Triassic), Guhjal Formation (Permian -? Mesozoic) and Jurassic – Cretaceous limestones can be reservoirs of hydrocarbon in Sost aulacogen. The Jurassic – Cretaceous limestones are maybe reservoir in Sost aulacogen. However, further studies of petroleum systems and modeling of Sost Aulacogen can clarify hydrocarbon potentials.
Figure 5. Triassic Palaeotectonic Map of Pak-Indian Platform (Khain 1979 with changes).
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