Contact Us

For Marketing, Sales and Subscriptions Inquiries
2637 E Atlantic Blvd #43110
Pompano Beach, FL 33062

Conference List

International Journal of Geography and Geology

October 2013, Volume 2, 10, pp 116-133

Retracted: Pierced Salt Domes in the Persian Gulf and in the Zagros Mountain Ranges in Southern Iran and their Relationship to Hydrocarbon and Basement Tectonics

Hamid Reza Samadi

Hamid Reza Samadi 1

  1. Member of Young Researchers Club, Ardestan Branch, Islamic Azad University, Ardestan, Iran 1

on Google Scholar
on PubMed

Pages: 116-133

DOI: 10.18488/journal.10/2013.2.10/

Share :


The most enigmatic problems with the nearly 200 salt domes pierced in the Persian Gulf and in the Zagros Mountain Ranges (ZMR) in southern Iran, a unique morphology in the world, have been the matter of this study, which is based on a combination of field work, enhancement of satellite and aerial photographs etc. In the ZMR, structural anomalies are frequently associated with similar facies distribution patterns. In the eastern portion of the region, emergent salt plugs of Infra-Cambrian age exhibit the same alignment patterns. Such trends bear no apparent genetic relationship to the Tertiary folding responsible for the present Zagros fold belt, but rather indicate their affinity with linear basement features which are readily observable on Land sat imagery and aerial photographs. Bending  of anticlines in the competent cover rock, combined with minor strike-slip faults and horizontal displacements of parts of folded structures, strongly point to the presence of these basement faults. The salt plugs, which have pierced cover rocks of up to 10000 m thick, are distributed on the Arabian Platform along regional basement faults. The area of diapir outcrops is bounded by the Oman Line to the east and by the Kazerun fault to the west. Pieces of the basement have been brought up to the surface on some of the salt domes. The fragments were transported by rotational ascent of the Hormuz Salt Formation to the present and former land surfaces. The recognition of features related to basement tectonics and realization of their implication in the control and modification of geological processes are important adjuncts to the search for hydrocarbon accumulations in this region. To our best knowledge, data of basement faults in the study area are scarce. Therefore, this study was carried out to determine basement faults and their relation to salt dome distribution. Considering the fold axes bending, the trend of the salt plugs and also the distribution of epicenters of the last century, n umerous new basement faults are introduced in this paper.

Contribution/ Originality


Pierced, Salt plugs, Zagros Fold Belt, Southeastern Iran, Kazerun fault.


  1. Ala, M.A., 1974. Salt diapirism in Southern Iran, American Association Petroleum Geologists Bulletin, 58(9): 1758-1770.
  2. Belderson, R.H., N.H. Kenyon and A.H. Stride, 1978. Local submarine salt-karst  formation on the hellenic outer ridge, Eastern mediterranean. Geology, 8(6): 716 – 720.
  3. Bjørlykke, K.O., 1989. Sedimentology and petroleum geology, translated of lærebok in sedimentologi og petroleums geologi, by beverly wahl. New York: Springer-Verlag Berlin Heidelberg.
  4. Bloom, A.L., 2002. Geomorphology, a systematic analysis of late cenozoic landforms. 3rd Edn., New Delhi: Prentice-Hall of India, Private Limited.
  5. Böckh, H.d., G.M. Lees and F.D.S. Richardson, 1929. Contribution to the stratigraphy and tectonics of the Iranian ranges, in J. W. Gregory, editor, The structure of Asia, London, Methuen.
  6. Bosak, P., J. Jaros, J. Spudil, P. Sulovsky and V. Vaclavek, 1998. Salt plugs in the Eastern Zagros, Iran: Results of Regional Geological Reconnaissance, GeoLines (Praha).
  7. Bostrom, R.C., 1985. Zonal wrenching in the tethys orogeny, geodynamics research symposium. Texas: A & M Univ.
  8. Brink, H.J., 1986. Salzwirbelim untergrund norddeutschlands. Geowiss. in Unserer Zeit, 4(3): 81-86.
  9. Busk, H.G. and H.T. Mayu, 1918. Some  notes  on  the geology of the Persian oil fields, Geological Institute of Petroleum Technology, 5(3): 3-33.
  10. Derakhshani, R. and G. Farhoudi, 2005. Existence  of  the oman line in the empty quarter of Saudi Arabia and its continuation in the red sea, Journal of Applied Sciences, 5(4): 745-752.
  11. Falcon, N.L., 1967; 1969. The geology of the northeast margin of the Arabian basement shield, British Association Advanced Society, 24(5): 31-42.
  12. Falcon, N.L., 1969. Problems of the relationship between surface structure and deep displacements illustrated by the zagros  range,  In:  P.  Kent,  G.  Satterthwaite  and  A. Spencer (Eds.), Time and Place orogeny, Geological Society of London.
  13. Falcon, N.L., 1974. Southern Iran: Zagros mountains, in Mesozoic-Cenozoic orogenic belts: Data for orogenic studies: Alpine-Himalayan Orogens, Geological Society London, Special Publication.
  14. Farhoudi, G., 1978. A comparison of zagros geology to Island Arcs, Journal of Geology, 86(4): 325-334.
  15. Farhoudi, G., 1984. Some morphotectonic aspect about the frequent earthquakes in the southern part of the Zagros mountains Iran, 27th International Geological Congress Moscow.
  16. Farhoudi, G., A. Faghih, H. Mosleh, T. Keshavarz, M.R. Heyhat and J. Rahnama-Rad, 2008. Using GIS/RS techniques to interpret different aspects of salt domes in Southern Iran, Geophysical Research Abstracts : EGU-A-06522, 10.
  17. Farhoudi, G. and M. Ghazizadeh, 1993. Stages of karst geomorphology cycle in  the Zagros mountain  ranges, Iran, Proceeding of International Symposium of Water Resources  in  karst  with  special  emphasis  on  arid  and semi-arid  zones,  jointly organized  by UNESCO  and Iranian authorities, Shiraz, Iran.
  18. Fredrich, J.T., A.F. Fossum and R.J. Hickman, 2007. Mineralogy of deepwater Gulf of Mexico salt, formations and implications for constitutive behavior, Journal of Petroleum Science and Engineering, 57(3–4): 354-374.
  19. Friedrichs, C.T. and J.E. Perry, 2001. Tidal salt marsh morphodynamics: A synthesis. Journal of Coastal Research, 27(1): 7-37.
  20. Fürst, M., 1990. Strike-slip faults and diapirism of the southeastern Zagros ranges. Proceeding symposium on diapirism with special reference to Iran, Geol. Survey Iran. Tehran, pp: 149-182.
  21. Gansser, A., 1960. Über schlammvulkane und salzdome, Vierteljahrss chrift Naturforschenden Geselschaft Zurich, 105(3): 1-46.
  22. Goudie, A.S., 1989. Salt  tectonics  and  geomorphology, Progress in Physical Geography, SAGE Publications, 13(4): 597-605.
  23. Harding, T.P. and J.D. Lowell, 1979. Structural styles, their plate- tectonic habitats and hydrocarbon traps in petroleum provinces. American Association Petroleum Geologists Bulletin, 63(5): 1016-1058.
  24. Haynes, S.J. and H. McQuillan, 1974. Evolution of the Zagros suture zone, Southern Iran, Geological Society American Bulletin, 85(5): 739-744.
  25. Humphrey, W.E., 1958. Diapirs and diapirism in Persia and North Africa, American Association petroleum Geologists Bulletin, 42(7): 1736-1744.
  26. Jackson, M.P.A. and C.J. Talbot, 1986. External shapes, strain rates, and dynamics of salt structures. Geological Society American Bulletin, 97(3): 305-323.
  27. Jacob, H. and K. Quittmeyer, 1979. The Makran region of Pakistan  and  Iran,  Trench-arc  system with  active  plate subduction. In FARAH, A., de JONGH, K.A. (editors.): Geodynamics of Pakistan. Geological Survey Pakistan. pp: 305-317.
  28. James, G.A. and J.G. Wynd, 1965. Stratigraphic nomenclature of Iranian oil consortium agreement area, American Association Petroleum Geologists Bulletin, 49(6): 2182-2245.
  29. Kashfi, M.S., 1976. . Plate tectonics and structural evolution of the Zagros geosyncline, southwestern Iran, Geological Society  American  Bulletin, 87(10): 1486-1490.
  30. Kent, P.E., 1958. Recent studies of south Persian salt plugs, American Association Petroleum Geologists Bulletin, 42(12): 2951-2972.
  31. Kent, P.E., 1979. The  mergent  Hormuz  salt  plugs  of Southern Iran, Jour. Petroleum Geology, 2(2): 117-144.
  32. Kent, P.E., 1979; 1986. Island salt plugs in the middle east and their tectonic implications, In dynamic geology of salt and  related  structures,  Ed:  Leiche  I.  &  O'Brien  J.  J., Academic Press, NY. pp: 3-37.
  33. Lawrence, D.S.L., J.R.L. Allen and G.M. Havelock, 2004. Salt  marsh  morphodynamics: An investigation of tidal flows and marsh channel equilibrium. Journal of Coastal Research, 20(1): 301- 316.
  34. Lees, G.M., 1927. Salzgletscher in Persien, Wien Mitteitung Geologische Gesellschaft, 20(1): 29-34.
  35. Letouzey, J. and S. Sherkati, 2004. Salt movement, tectonic events, and structural style in the central zagros fold and thrust belt (Iran), In Salt sediments interactions and hydrocarbon prospectively, 24th Annual Gulf Coast Section SEP Foundation, Bob.
  36. Martinod, J., A. Ashtiani, R. Bayer, F. Tavakoli and J. Chery, 2004. Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements' in Iran and Northern Oman, Geophysical Journal Institute, 157(3): 381- 398.
  37. McQuillan, H., 1991. The role of basement tectonics in the control of sedimentary facies, structural patterns and salt plug emplacements in the Zagros fold belt of Southwest Iran,  Journal of Southeast Asian Earth Sciences, 5(4): 453-463.
  38. Motiei, H., 1990. The role of diapirism from the stand point of hydrocarbon reserves in South-West Iran, proceeding symposium on diapirism with special reference to Iran, 1, 138. Geol. Survey Iran. Tehran.
  39. North, F.K., 1985. Petroleum geology. Boston: Unwin Hyman,4(2):112-116
  40. Nowroozi, A.A., 1971. Seismo-tectonics of the Persian plateau Eastern Turkey, Caucasus, and Hindu-Kush regions, Bulletin Seismological Society America, 61(2): 317-341.
  41. Nowroozi, A.A., 1972. Focal mechanism of earthquakes in Persia, Turkey, West Pakistan, and Afghanistan and plate tectonics  of  the  middle  east,  Bulletin  Seismological Society America. N.I.O.C.  (National  Iranian  Oil  Company),  1977,  Tectonic map of Iran, National Iranian Oil Company, 62(7): 823-850.
  42. Pilgrim, G.E., 1908. The geology of the Persian Gulf and the adjoining portions of Persia and Arabia, Mem. Geol. Survey India, 34(4): 1-177.
  43. Pilgrim, G.E., 1922. The  Sculpture  deposits  of southern Persia, India Geol. Survey Research, 53(3): 343-358.
  44. Pilgrim, G.E., 1924. The geology of parts of the Persian provinces of fars, Kerman and Laristan, Mem. Geol. Survey India, 48(1): 1-118.
  45. Player, R.A., 1967. A note on the Fars salt plugs, N.I. O. C., Private Report.
  46. Player, R.A., 1969. Salt plug study, N. I. O. C., Report, 1146.
  47. Rabinowitz, P.D., M.F. Coffin and D. Falvey, 1982. Salt diapirs bordering the continental margin of northern Kenya and southern Somalia, Science, 21(5): 663 – 665.
  48. Rahnama-Rad, J., R. Derakhshani, G. Farhoudi and M. Ghorbani, 2008. Basement faults und salt plug emplacement in the Arabian platform in southern Iran, Journal of Applied Science, 8(18): 3235-3241.
  49. Richardson, R.K., 1926. Die geologie und die salzdome imsudwestlichen teil des persischen golfes, verhandlung naturhistorische medizin verein heidelberg (NF), Nummer 15, 51 Seite.
  50. Richardson, R.K., 1928. Weitere bemerkungen  zu  der geologie und den salzaufbruchen am persischen golf, centralblat mineralogie, Geologie u. Paläontologie Abteitung B: 45-49.
  51. Ross, D.A., R.B. Whitmarsh, S.A. Ali, J.E. Boudreaux, R. Coleman, R.L. Fleisher, R. Girdler, F. Manheim, A. Matter, C. Nigrini, P. Stoffers and P.R. Supko, 1973. Red sea drillings. Science, 17(3): 377-380.
  52. Schoenherr, J.U., L.K. Janos, A. Peter, R. Littke, Z. Schléder, J.-M. Larroque, M.J. Newall, N. Al-Abry, H.A. Al-Siyabi and Z. Rawahi, 2007. Limits to the sealing capacity of rock salt: A case study of the infra-Cambrian Ara Salt from the South Oman salt basin, American Association Petroleum Geologists Bulletin, 91(11): 1541-1557.
  53. Seni, S.J. and M.P.A. Jackson, 1983a. Evolution of salt structures, east texas diapir province; Part 1, Sedimentary Record of Halokinesis, 67(4): 1219-1244.
  54. Seni, S.J. and M.P.A. Jackson, 1983b. Evolution of salt structures, east texas diapir province; part 2, patterns and rates of halokinesis. American Association Petroleum Geologists Bulletin, 67(5): 1245 – 1274.
  55. Standridge, D., C. Bishop and L. Serpa, 2005. A high- resolution seismic survey to image the top of salt at Avery Island, Louisiana, SEG( Society of Exploration Geophysicists)  Technical  Program  Expanded  Abstracts: 1160-1163.
  56. Stöcklin, J. and M.H. Nabavi, 1975. Tectonic map of Iran, 1: 2500000, Geological Society Iran.
  57. Talbot, C.J. and M. Alavi, 1996. The post of a future syntaxis across  the  Zagross,  in  Alsop,  G.  I.,  Blunell,  D.J.  & Davison,  J.  (eds),  salt  tectonics:  Geological  Society London, Special Publication, 100(1): 89–109.
  58. Talbot, C.J. and M.P.A. Jackson, 1987. Internal kinematics of salt diapirs. American  Association Petroleum Geologists Bulletin, 71(5): 1068–1093.
  59. Talbot, C.J. and E.A. Rogers, 1980. Seasonal movements in a salt glacier in Iran, Science, 20(4): 395–397.
  60. Tchalenko, J.S. and J. Braud, 1974. Seismicity and structure of the Zagros (Iran), the main recent fault between 33o and 35o N, London Philos. Trans., Serie A., 27(7): 1-25.
  61. Trusheim, F., 1960. Mechanism of salt migration in northern Germany, American Association Petroleum Geologists Bulletin, 44(5): 1519–1540.
  62. Vernant, P., F. Nilforoushan, D. Hatzfeld, M.R. Abbassi, C. Vigny, F. Masson, H. Nankali, J. Martinod, A. Ashtiani, R. Bayer, F. Tavakoli and J. Chéry, 2004. Present- day  crustal  deformation  and  plate  kinematics  in  the middle east constrained by GPS measurements in Iran and northern Oman, Geophysical Journal International, 15(3): 381- 398.
  63. Woodbury, H.O., I.B. Murray and R.E. Osborne, 1980. Diapirs and their relation to hydrocarbon accumulation, in: A. D. Miall, (ed)., Fact and principles of world petroleum occurrence: Calgary, Canadian Society of Petroleum Geologists.


Google Scholor ideas Microsoft Academic Search bing Google Scholor


This study received no specific financial support.

Competing Interests:

The author declares that there are no conflicts of interests regarding the publication of this paper.


Related Article

( 1 ) Retracted: Pierced Salt Domes in the Persian Gulf and in the Zagros Mountain Ranges in Southern Iran and their Relationship to Hydrocarbon and Basement Tectonics
( 2 ) Retracted: Study Hydrogeochemistry Exploration of Thermal Spring in Ramsar Area, (North of Iran)
( 4 ) A Study of Stream Sediments from Soltan Meydan Basaltic Formation Area, Northern Iran
( 6 ) Analysis of Dioxins Concentration in Domestic Waste and Burnt Tyre Residue at Gosa Dumpsite in Abuja, Nigeria
( 9 ) The Role of Stratigraphy in Growth Strata Studies: A Case Study from the Middle-Late Cretaceous Deposits in Persian Gulf, SW Iran
( 12 ) Exsolution Lamellae in Orthopyroxene of Lherzolite from the Pauza Ultramafic Rocks, Ne Iraq: Evidence of Deep Mantle Signature in the Zagros Suture Zone
( 13 ) Micro Biostratigraphy and Lithostratigraphy of the Upper Permian Dalan Formation (Zagros Basin, Southwest Iran)
( 14 ) Microbiostratigraphy and Lithostratigraphy of the Upper Permian Dalan Formation in Kuh-E-Surmeh (Zagros Basin, Southwest Iran)
( 15 ) Calcareous Nannofossils Events of Nephrolithus Frequens Zone to Markalius Inversus Zone in Section of Kazerun, Zagros (Iran)
( 19 ) Contribution of Glacier, Snow and Rain Components in Flow Regime Projected with HBV Under AR5 Based Climate Change Scenarios Over Chitral River Basin (Hindukush Ranges, Pakistan)
( 20 ) Comparison and Review of the Advantages of the Fractal Method (Variogram) With Respect To the Nettelton in Determining the Density of the Bouguer Plane in the Southern Hormozgan: Iran
( 22 ) Perceived Environmental and Health Impacts of Gas Flaring on Residents in Kwale Communities, Southern Nigeria
( 23 ) Evaluation of Environmental Awareness Level among Stakeholders in Rural and Urban Communities, Southern Nigeria
( 24 ) Qanat and Its Challenges in Ferdows County-Iran
( 26 ) Investigation into the Realization of Naturalism in Hashtgerd New Town Based On the Iranian Islamic Model
( 27 ) Optimal Density Determination of Bouguer Anomaly Using Fractal Analysis (Case of Study: Charak Area, Iran)
( 29 ) Tectomagmatic Origin of the Zahedan Batholiths – South East Iran (Reling on Intergrated Outcrop Study of the Petrology of High Mass in Loochan, Southwest Zahedan)
( 31 ) Inversion of Electrical Resistivity Data by VES Method for Water Exploring Case Study: South West of Iran
( 32 ) Investigating the Density Ratios of Geological Structure through Fractal Geometry Case Stady: (Dehno Region in Farss of Iran)
( 33 ) Expanded of Informal Jobs in Iranian Border Cities, Case: Zabol-Iran
( 35 ) Presentation of Empirical Equations for Estimating Internal Friction Angle of SP and SC Soils in Mashhad, Iran Using Standard Penetration and Direct Shear Tests and Comparison with Previous Equations
( 36 ) Urban Park Use, Quality Evaluation, and Resident Satisfaction Indicators in the City of Zahedan, Iran
( 37 ) Active Tectonics of Hamedan Area, West Iran
( 39 ) Characterization of Sand Dunes to Detect the Sand Source and their Stabilization, Abardej, Iran
( 40 ) Predicting Changes in the Land Use in Midsize Cities (Case Study: Urmia City of Iran in 2025)
( 41 ) Runoff Prediction by Support Vector Machine for Chalous River Basin of Iran
( 42 ) Indicators of Sustainability in Vernacular Settlements Hot Dry Region of Iran, [Case Study: Kerman-Meymand]
( 43 ) Microbiostratigraphy, Microfacies and Depositional Environment of the Sarvak Formation in Bi Bi Hakimeh Oil Field (Well No. 29), Southwest Iran
( 44 ) Landfill Site Selection Using Simple Additive Weighting (SAW) Method and Artificial Neural Network Method; A Case Study from Lorestan Province, Iran
( 48 ) Paleoecology of Permo-Triassic Boundary According to Palynoflora in Shourjestan, Iran
( 49 ) Analysis of the Factors Affecting Changes in Land Cover Patterns in Rural Districts in East of Guilan Province (Iran) for Foresight
( 50 ) Landslide Hazard Evaluation and Zonation of Karaj-Chalus Road (North of Iran)
( 51 ) Biostratigraphy and Paleoecology of Maastrichtian and Paleocene Sediments in the Northern Alborz, Iran, Using Foraminifera
( 53 ) Satisfaction Assessment of the Quality of Life of Urban Families and their Roles in the Development of Zabol
( 54 ) Geographical Distribution of Egyptian Lot-Chosen and Civil Associations’ Pilgrims - Chronic Diseases and their Demographic Characteristics
( 56 ) The Relationship Between P-Wave Velocity and Slake Durability Index
( 58 ) Is the Sosiani River Healthy? Investigating the Relationship between Water Quality Indicators and Macroinvertebrate Assemblages in the Sosiani River
( 59 ) The Relationship Between Low-Carbon Finance and Sustainable Development: A Case Study of Industrial Bank of China
( 60 ) Supercapacitors Based on Activated Carbon and Polymer Electrolyte
( 61 ) The Remote Sensing Imagery, New Challenges for Geological and Mining Mapping in the West African Craton - The Example of Cote D’ivoire
( 63 ) Sea oil Spill: An Approach Difficult to Overcome by Insurance and International Regulation
( 64 ) Land Degradation Due To Mining: The Gunda Scenario
( 67 ) Energy Demand and Financial Sector Performance in Sub-Saharan African Region
( 68 ) Power Loss Reduction in PWM Inverters of Induction Motor Drives Based on Soft Switching Technique
( 69 ) Sustainable Sources of Energy and the Expected Benefits to Nigerian Economy
( 70 ) Numerical Modeling of Wires Incorporation Response Applied To a Concealed Cable
( 71 ) Energy Education as a Necessary Condition to Transition to a Robust Future Energy Security in Suriname
( 72 ) Identifying Potential Zones of Crime Commitment against Tourists in a Park: Conceptual and Logical Spatial Data Modeling
( 73 ) Environmental Conservation and Use of Economic Incentives to Conserve Biological Resources in Nigeria
( 74 ) Improved Analytical Approach of Vibration Behavior Destined To Ball Bearings in The Case of Angular Contact
( 75 ) Tourism Advertisement Management and Effective Tools in Tourism Industry
( 76 ) Application of Fractal Geometry to Study the Geological Structure of the Zarin Plain (Plain Razak)
( 77 ) UPFC Integrated With Battery Energy Storage Systems for Stability Improvement
( 78 ) Eutrophication State Monitoring for Unhealthy Aquatic Ecosystem via Free-Floating Macrophytes Pattern and Behavioral
( 79 ) Aquatic Plants as Ecological Indicator for Urban Lakes Eutrophication Status and Indices
( 80 ) Sequestration Rate of Heavy Metal Contaminants Using Riccia Fluitans as Potential Phytoremediation Agent in Polluted Aquatic Ecosystem
( 81 ) Well Log Sequence Stratigraphic and Palynological Analysis of Late Miocene to Pliocene Agbada Formation, Southwestern Niger Delta Basin, Nigeria
( 82 ) Strategies for Tourism Development in National Parks with the Use of Swot Model (Case: Golestan National Park)
( 83 ) Phytoremediation Model System for Aquaculture Wastewater Using Glossostigma Elatinoides and Hemianthus Callitrichoides
( 84 ) Comparative Assessment of Co2 Emission Factors Estimated Using Stack Flue Gas Measurement Data for Two Types of Brick Kiln: A Case Study in Phu Tho Province, Vietnam
( 85 ) An Exploratory Study of Effects of Prepaid Metering and Energy Related Behaviour among Ghanaian Household
( 86 ) Wind To Select the Recreation Flying Site
( 90 ) Analysis of Farmers’ Vulnerability, Perception and Adaptation to Climate Change in Kwara State, Nigeria
( 92 ) A Study on River Ecotourism Development: Case Study: Karaj River
( 93 ) An Analysis of Effective Factors on Spatial Distribution of Poverty in Rural Regions of Hamedan Province
( 94 ) Prioritization of Museums in Terms of Performance in Attracting Tourists (Case Study: Museum of North of Sistan and Baluchestan Province)
( 97 ) “Structural Post-Disaster Damage Classification with Consideration of Liquefaction Due To Flood: Manek Urai, Kelantan, Malaysia”
( 98 ) Attritional Structures the Major Factor in Increasing Endangerment by Earthquakes in Cities
( 99 ) Assessing the Catalytic Influence of Modern Information System and Socio-Economic Status on Communities’ Attitude and Awareness to Forest Resource Sustainability in Boki Local Government Area, Nigeria
( 101 ) Lease of Noxious Gases During Burning of Mosquito Coils: A Pilot Study
( 102 ) Strategic Management of Rural Tourism Towards Gender - Sensitive Planning
( 104 ) The Role of Handicrafts in the Sustainable Development of Rural Tourism with an Emphasis on Indigenous Knowledge