Offshore Pakistan Research Articles

Geomorphologic and infilling characteristics of the shelf-incising submarine canyon in the eastern Makran accretionary prism, offshore Pakistan

Seven shelf-incising submarine canyon systems are developed in the Makran accretionary prism, offshore Pakistan. This paper uses multibeam bathymetric data and multichannel seismic profiles to study the geomorphologic and infilling characteristics of E Canyon in the east of accretionary prism. The E Canyon extends nearly north–south from the upper slope to lower slope, the bottom of the canyon is located in 1000 to 3000 m water depth, the main axis extends about 55 km, and the width varies from 5 to 9 km. The E Canyon shows U-shaped concave features in the northern cross-section view and V-shaped concave features in the southern cross-section view. Two continuous erosion pools are developed at the fifth and third ridges of the southern segment, respectively. The steepest sidewall (with slopes of 25.75° and 40.47°) of E Canyon was found near the third ridge. The filling sequence of coarse channel lags, slump debris flows, stacked channel sands and mass transported deposits and turbidite deposits from bottom to top is developed in the northern segment of the canyon. Strong erosion is developed in the southern part of the canyon and there is no sedimentation inside. On the abyssal plain, the continuation of the E Canyon is clearly erosive. Our preliminary analysis shows that the factors controlling the evolution of E Canyon may include sediment gravity flow, tectonic activity, sea-level change, climate and onshore rivers activity. The correlation between evolution of E Canyon and gas hydrates was explored, and it is believed that the erosion of E Canyon plays a destructive role in hydrate accumulation. At the same time, the destruction of hydrate-bearing layer induces the escape and leakage of hydrocarbon-bearing fluid, leading to the development of pockmark on the sidewalls of E Canyon. And the evolution model of gas hydrate accumulation in the development area of E Canyon was established.

Internet of Things Based Transducer Application to Harness Tidal Energy from coastal and offshore Pakistan

This paper aims to transform tidal energy into rotation energy for electricity generation and in the course evaluating sea parameters. This is accomplished by integrating the Internet of Things with tidal energy off the coast (and in a home environment), which further enhances the capabilities of this prototype project to remotely monitor sea-like parameters to enable energy production using tidal energy. As South Korea is transducing tidal energy with a total installed tidal power capacity of above 500MW, Pakistan and Middle Eastern countries can benefit from its vast coastal line. This paper proposes a sustainable design that makes the turbine rotate at high speed. A vertical design is chosen, which is bi-directional. The design of the turbine consists of 3 blades, each occupying a 2 square feet area supported by an iron-rod frame. During the experimentation, an average voltage of 5V was generated, whereas the speed of the turbine generated was 75 RPM. It is the first known attempt of its kind supported by indigenous resources. It is proposed that this type of prototype can be scaled, to the coast to produce electrical energy to meet the energy production needs of the region.

Distribution and development of submarine mud volcanoes on the Makran Continental Margin, offshore Pakistan

Abstract In 2018, China Geological Survey and National Institute of Oceanography of Pakistan conducted a comprehensive geological survey on the Makran Continental Margin offshore Pakistan using the R/V Haiyangdizhi10. Seismic profiles, multibeam bathymetric and water column data, and seafloor observations were obtained during the expedition. Twelve mud volcanoes and three pockmarks were discovered in the surveyed area on the Makran Continental Margin. The heights of the mud volcanoes and the depths of the pockmarks are 12–121 m and −108 to −26 m, respectively, with diameter of 500–1400 m. The mud volcanoes are distributed on top of the W-E trending ridges at 1200–2800 m water depth. Six mud volcanoes and one pockmark were active during the investigation as indicated by the gas flares mapped in the multibeam water column data. Acoustic blanking zones, faults and gas chimneys are distributed ubiquitously beneath the mud volcanoes on the seismic profiles. Their spatial correlation with mud volcanoes indicates that the faults and gas chimneys provide pathways for fluid migration. In addition, the Bottom Simulating Reflectors (BSR), interface of gas hydrate and free gas, were also discovered in multiple seismic profiles. Based on the BSR discontinuity and piercing of the gas chimneys, it is inferred that mud volcano activities might cause gas hydrate dissociation, leading to the upward movement of the BSR. Tectonic uplifting, seismic-induced shock and fluid overpressure induced by rapid sedimentation are the major driving forces for the mud volcano formation and development. Gases from deep strata and gas hydrate decomposition are suspected to provide additional forces for fluid migration. Pressure decrease in the deep subsurface and gas hydrate sealing of the faults and fracture are speculated to be important in controlling the intermittent mud volcano activities and potential pockmark formation. The new model of mud volcano activities depicted in this study might be applicable to other mud volcanoes elsewhere.

Diapir structure and its constraint on gas hydrate accumulation in the Makran accretionary prism, offshore Pakistan

ABSTRACT The Makran accretionary prism is located at the junction of the Eurasian Plate, Arabian Plate and Indian Plate and is rich in natural gas hydrate (NGH) resources. It consists of a narrow continental shelf, a broad continental slope, and a deformation front. The continental slope can be further divided into the upper slope, middle slope, and lower slope. There are three types of diapir structure in the accretionary prism, namely mud diapir, mud volcano, and gas chimney. (1) The mud diapirs can be grouped into two types, namely the ones with low arching amplitude and weak-medium activity energy and the ones with high arching amplitude and medium-strong activity energy. The mud diapirs increase from offshore areas towards onshore areas in general, while the ones favorable for the formation of NGH are mainly distributed on the middle slope in the central and western parts of the accretionary prism. (2) The mud volcanoes are mainly concentrated along the anticline ridges in the southern part of the lower slope and the deformation front. (3) The gas chimneys can be grouped into three types, which are located in piggyback basins, active anticline ridges, and inactive anticline ridges, respectively. They are mainly distributed on the middle slope in the central and western parts of the accretionary prism and most of them are accompanied with thrust faults. The gas chimneys located at different tectonic locations started to be active at different time and pierced different horizons. The mud diapirs, mud volcanoes, and gas chimneys and thrust faults serve as the main pathways of gas migration, and thus are the important factors that control the formation, accumulation, and distribution of NGH in the Makran accretionary prism. Mud diapir/gas chimney type hydrate develop in the middle slope, mud volcano type hydrate develop in the southern lower slope and the deformation front, and stepped accretionary prism type hydrate develop on the central and northern lower slope. The middle slope, lower slope and deformation front in the central and western parts of the Makran accretionary prism jointly constitute the NGH prospect area.

Holocene monsoon and sea level-related changes of sedimentation in the northeastern Arabian Sea

The Indian Monsoon and the westerlies strongly influence the sedimentation in the northeastern Arabian Sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean. To disentangle the terrestrial and oceanic processes, we analysed mineralogical and bulk geochemical components of a Holocene sediment core offshore Pakistan. Endmember modelling of grain sizes and principal component analyses (PCA) of major and trace elements identify the origin of sediments and their dominant mode of transport. Sedimentation processes during the early Holocene (10.8–8.2 ka BP) were influenced by the post-glacial sea level rise and orbitally forced strengthening of the Indian summer monsoon (ISM) and westerlies. This led to a shift from rather terrestrial-dominated towards a marine-dominated sedimentation, whereas the fluvial source shifted from the Makran rivers to the Hab River near Karachi. During the mid-Holocene (8.2–4.2 ka BP) a combination of weakening ISM and southward displacement of the ITCZ enhanced the influence of the westerlies, together decreasing river discharges and enhancing aeolian input (probably from the Sistan Basin region). This trend continued during the last ca. 4 ka when the increasing aridification of the Hab River catchment further increased the aeolian inputs. Solar and lunar driven short-term variations as well as Bond events known from the North Atlantic Ocean superpose these trends. They lead to a pronounced increase of fluvial inputs between 8.6–8.4 ka BP and at ca. 3 ka BP as well as to dry events around 4.2 ka and 1.2–1 ka BP. Our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern Arabian Sea towards the late Holocene.

Indications of uplift from seismic stratigraphy and backstripping of the well data in western Indus offshore Pakistan

Two‐dimensional regional seismic reflection, oil well data, and biostratigraphic data have been used in integration to study the general structure, stratigraphic architecture, and subsidence history of the part of River Indus offshore Pakistan. The seismic data have been calibrated with the well data by generating the synthetic seismograms to identify the key reflectors indicative of major lithologic horizons. The sedimentary successions on the seismic sections are divided into passive and transpressive margin sediments on the basis of regional tectonics of the area. The western Indian margin is in oblique collision and transpression with Eurasian and Arabian plates creating Kirthar Range onshore and Murray Ridge offshore, respectively. Four mappable seismic sequences are identified within the passive margin sediments and two within the transpressive margin sediments. Due to the complex depositional setting of the basin, certain seismic sequences are not clear on the seismic records. In addition to depositional complexity, the seismic sequences are disturbed by the presence of normal faults generated probably under the action of gravity. It is interpreted from the seismic records that the normal faults were probably reactivated due to the movement of the basement blocks which have generated the push‐up structures within the offshore depression area. The subsidence curves show a gentle convex upward trend, which suggest an uplift around 40 Ma probably resulting from the reactivation of the basement blocks. The study could be helpful in understanding the tectonics of the worldwide passive margins dominated by rifting and transpression stages.

Formation of seep carbonates along the Makran convergent margin, northern Arabian Sea and a molecular and isotopic approach to constrain the carbon isotopic composition of parent methane

Authigenic carbonate deposits have been sampled with the remotely operated vehicle ‘MARUM-QUEST 4000m’ from five methane seeps between 731 and 1823m water depth along the convergent Makran continental margin, offshore Pakistan (northern Arabian Sea). Two seeps on the upper slope are located within the oxygen minimum zone (OMZ; ca. 100 to 1100m water depth), the other sites are situated in oxygenated water below the OMZ (below 1100m water depth). The carbonate deposits vary with regard to their spatial extent, sedimentary fabrics, and associated seep fauna: Within the OMZ, carbonates are spatially restricted and associated with microbial mats, whereas in the oxygenated zone below the OMZ extensive carbonate crusts are exposed on the seafloor with abundant metazoans (bathymodiolin mussels, tube worms, galatheid crabs). Aragonite and Mg-calcite are the dominant carbonate minerals, forming common early diagenetic microcrystalline cement and clotted to radial-fibrous cement. The δ18Ocarbonate values range from 1.3 to 4.2‰ V-PDB, indicating carbonate precipitation at ambient bottom-water temperature in shallow sediment depth. Extremely low δ13Ccarbonate values (as low −54.6‰ V-PDB) point to anaerobic oxidation of methane (AOM) as trigger for carbonate precipitation, with biogenic methane as dominant carbon source. Prevalence of biogenic methane in the seepage gas is corroborated by δ13Cmethane values ranging from −70.3 to −66.7‰ V-PDB, and also by back-calculations considering δ13Cmethane values of carbonate and incorporated lipid biomarkers. These calculations (Δδ13Cmethane–carbonate, Δδ13CANME–methane, Δδ13CMOX–methane) prove to be useful to assess the carbon stable isotope composition of seeping methane if this has not been determined in the first place; such an approach represents a useful tool to reconstruct fluid composition of ancient seeps. AOM is also revealed by lipid biomarkers of anaerobic methane oxidizing archaea such as crocetane, pentamethylicosane (PMI), and sn2-hydroxyarchaeol strongly depleted in 13C (δ13C values as low as −127‰ V-PDB). Biomarkers of sulphate-reducing bacteria are also abundant, showing slightly less negative δ13C values, but still significantly 13C-depleted (average values as low as −101‰). Other bacterial biomarkers, such as bacteriohopanepolyols (BHPs), hopanols, and hopanoic acids are detected in most carbonates, but are particularly common in seep carbonates from the non-OMZ sites. The BHP patterns of these carbonates and their low δ13C values resemble patterns of aerobic methanotrophic bacteria. In the shallower OMZ sites, BHPs revealed much lower contents and varying compositions, most likely reflecting other sources than aerobic methanotrophic bacteria. 230Th/U carbonate ages indicate that AOM-induced carbonate precipitation at the deeper non-OMZ seeps occurred mainly during the late Pleistocene–Holocene transition, i.e. between 19 and 15ka before present, when the global sea level was lower than today.

Fluid generation and distribution in the highest sediment input accretionary margin, the Makran

Fluids in subduction zones can influence seismogenic behaviour and prism morphology. The Eastern Makran subduction zone, offshore Pakistan, has a very thick incoming sediment section of up to 7.5 km, providing a large potential fluid source to the accretionary prism. A hydrate-related bottom simulating reflector (BSR), zones of high amplitude reflectivity, seafloor seep sites and reflective thrust faults are present across the accretionary prism, indicating the presence of fluids and suggesting active fluid migration. High amplitude free gas zones and seep sites are primarily associated with anticlinal hinge traps, and fluids here appear to be sourced from shallow biogenic sources and migrate to the seafloor along minor normal faults. There are no observed seep sites associated with the surface expression of the wedge thrust faults, potentially due to burial of the surface trace by failure of the steep thrust ridge slopes. Thrust fault reflectivity is restricted to the upper 3 km of sediment and the deeper décollement is non-reflective. We interpret that fluids and overpressure are not common in the deeper stratigraphic section. Thermal modelling of sediments at the deformation front suggests that the deeper sediment section is relatively dewatered and not currently contributing to fluid expulsion in the Makran accretionary prism.

Quantification of gas bubble emissions from submarine hydrocarbon seeps at the Makran continental margin (offshore Pakistan)

Evidence for twelve sites with gas bubble emissions causing hydroacoustic anomalies in 18 kHz echosounder records (‘flares’) was obtained at the convergent Makran continental margin. The hydroacoustic anomalies originating from hydrocarbon seeps at water depths between 575 and 2870 m disappeared after rising up to 2000 m in the water column. Dives with the remotely operated vehicle ‘Quest 4000 m’ revealed that several individual bubble vents contributed to one hydroacoustic anomaly. Analyzed gas samples suggest that bubbles were mainly composed of methane of microbial origin. Bubble size distributions and rise velocities were determined and the volume flux was estimated by counting the emitted bubbles and using their average volume. We found that a low volume flux (Flare 1 at 575 mbsl: 90 ml/min) caused a weak hydroacoustic signal in echograms whereas high volume fluxes (Flare 2 at 1027 mbsl: 1590 ml/min; Flare 5 C at 2870 mbsl: 760 ml/min) caused strong anomalies. The total methane bubble flux in the study area was estimated by multiplying the average methane flux causing a strong hydroacoustic anomaly in the echosounder record with the total number of equivalent anomalies. An order‐of‐magnitude estimate further considers the temporal variability of some of the flares, assuming a constant flux over time, and allows a large range of uncertainty inherent to the method. Our results on the fate of bubbles and the order‐of‐magnitude estimate suggest that all of the ∼40 ± 32 × 106 mol methane emitted per year within the gas hydrate stability zone remain in the deep ocean.

The structure and fault activity of the Makran accretionary prism

The Makran Subduction Zone has the highest incoming sediment thickness (up to 7.5 km) of any subduction zone. These sediments have formed a wide accretionary prism (∼400 km). Seismicity in the Makran is generally low; however the margin experienced an Mw 8.1 earthquake in 1945 which generated a significant regional tsunami. Seismic reflection data and swath bathymetry data from offshore Pakistan are used to analyze the structure and fault activity of the outer accretionary prism. The outer prism has a simple structure of seaward verging imbricate thrust faults, many continuous for over 100 km along strike. Fault activity is analyzed using basin stratigraphy and fault geometry, revealing a frontal continuously active zone, a central intermittently active zone, and a landward inactive zone. Over 75% of the faults in the seaward ∼70 km of the prism show evidence for recent activity. The décollement occurs within the lower sediment section, but steps onto the top‐basement surface in regions of elevated basement topography. Fault spacing (6 km) and taper (4.5°) are comparable to other margins such as S. Hikurangi, Cascadia and Nankai, suggesting that high sediment input is not leading to an unusual prism structure. The décollement is unreflective, which is unexpected considering other prism characteristics predicting a weak surface, and may suggest a potentially stronger décollement than previously predicted. This study provides a significant advance in our understanding of the structure of an end‐member convergent margin and demonstrates that systematic analyses of accretionary prism structure can help to elucidate subduction zone dynamics with ultimate relevance to seismogenic potential.

Cenozoic mud volcano activity along the Indus Fan: offshore Pakistan

ABSTRACTThis study documents the tectono‐stratigraphic setting and expulsion history of a major, previously undescribed mud volcano (MV) province in the Indus Submarine Fan, offshore Pakistan. A buried MV field of nine composite MVs has been recognized using two‐dimensional (2D) and 3D seismic reflection data in a confined area of 50 × 65 km2. Conduits are recognized on each of these MVs connecting the pre‐Eocene parent beds to the stacked mud cones. The buried MVs are up to 8.4 km wide (4.5 km average) with a central conduit of 1.23 km average diameter and an average mud cone thickness of 0.33 km. Three major phases of fluid and mud remobilization occurred in the Early to Middle Miocene, intra‐Middle Miocene and in the Late Miocene to Plio‐Pleistocene transition. Most of the mud source (parent beds) seems to be of pre‐Eocene origin. Geometrical information from 21 mud cones allows an estimate of the volume required to build these fluid escape features. The calculated volume of remobilized sediments is 71.5±9 km3. The location of the MV field is limited to the pre‐Eocene main depocentre, with major tectonic deformation occurring along the wrench system of the Indo–Arabian plate boundary, i.e. the southern edge of the Murray Ridge. The Indus MV field is, to our knowledge, the longest lived (∼22 Myr) remobilized, Cenozoic sedimentary system observed worldwide. No evidence of present‐day mud flow activity is seen on the seabed seismic reflection in the study area.

Automated gas bubble imaging at sea floor – a new method of in situ gas flux quantification

Abstract. Photo-optical systems are common in marine sciences and have been extensively used in coastal and deep-sea research. However, due to technical limitations in the past photo images had to be processed manually or semi-automatically. Recent advances in technology have rapidly improved image recording, storage and processing capabilities which are used in a new concept of automated in situ gas quantification by photo-optical detection. The design for an in situ high-speed image acquisition and automated data processing system is reported ("Bubblemeter"). New strategies have been followed with regards to back-light illumination, bubble extraction, automated image processing and data management. This paper presents the design of the novel method, its validation procedures and calibration experiments. The system will be positioned and recovered from the sea floor using a remotely operated vehicle (ROV). It is able to measure bubble flux rates up to 10 L/min with a maximum error of 33% for worst case conditions. The Bubblemeter has been successfully deployed at a water depth of 1023 m at the Makran accretionary prism offshore Pakistan during a research expedition with R/V Meteor in November 2007.

Thermal regime of the northwest Indian rifted margin – Comparison with predictions

We use a simple approach to estimate the present-day thermal regime along the northwestern part of the Western Indian Passive Margin, offshore Pakistan. A compilation of bottom borehole temperatures and geothermal gradients derived from new observations of bottom-simulating reflections (BSRs) allows us to constrain the relationship between the thermal regime and the known tectonic and sedimentary framework along this margin. Effects of basin and crustal structure on the estimation of thermal gradients and heat flow are discussed. A hydrate system is located within the sedimentary deep marine setting and compared to other provinces on other continental margins. We calculate the potential radiogenic contribution to the surface heat flow along a profile across the margin. Measurements across the continental shelf show intermediate thermal gradients of 38–44 °C/km. The onshore Indus Basin shows a lower range of values spanning 18–31 °C/km. The Indus Fan slope and continental rise show an increasing gradient from 37 to 55 °C/km, with higher values associated with the thick depocenter. The gradient drops to 33 °C/km along the Somnath Ridge, which is a syn-rift volcanic construct located in a landward position relative to the latest spreading center around the Cretaceous–Paleogene transition.

Effective medium modeling to assess gas hydrate and free-gas evident from the velocity structure in the Makran accretionary prism, offshore Pakistan

Seismic properties of sediments are strongly influenced by pore fluids. Stiffness of unconsolidated marine sediment increases with the presence of gas hydrate and decreases with the presence of gas. A strong bottom-simulating reflector (BSR) observed on a seismic profile in the Makran accretionary prism, offshore Pakistan, indicates the presence of gas hydrate and free-gas across the BSR. Elastic properties of gas depend largely on pressure and temperature. We, therefore, first determine the elastic modulus of gas at pressure and temperature calculated at the BSR depth in the study region. The interval velocities derived from the seismic data are interpreted by the effective medium theory, which is a combination of self-consistent approximation and differential effective medium theories, together with a smoothing approximation, for assessment of gas hydrate and free-gas. The results show the saturations of gas hydrate and free-gas as 22 and 2.4% of pore space, respectively, across the BSR.

Abstract: Gravity Imaging Deformation and Tectonics of the Indus Basins Onshore and Offshore Pakistan 

Abstract: Gravity Imaging Deformation and Tectonics of the Indus Basins Onshore and Offshore Pakistan