Changes

The phenomenon of rocks moving under their own means has always fascinated both scientists and the nonscientists. Salt is known to extrude and flow as a result of differences in density of the material and surrounding sediments. However, movement of fine-grained clastics as intrusive injectites or diapirs or as extrusive eruptive sand blows or mud volcanoes has captured the public's imagination and given scientists the impetus to reconsider the physics of how sediments behave in the subsurface.

The phenomenon of rocks moving under their own means has always fascinated both scientists and the nonscientists. Salt is known to extrude and flow as a result of differences in density of the material and surrounding sediments. However, movement of fine-grained clastics as intrusive injectites or diapirs or as extrusive eruptive sand blows or mud volcanoes has captured the public's imagination and given scientists the impetus to reconsider the physics of how sediments behave in the subsurface.

Because of the burgeoning of shale gas and shale oil research, geoscientists are gaining a better understanding of the petrographic framework of shales, as well as their behavior under various pressure and temperature regimes and the manner in how fluids move thorough these strata (for a review, see Day-Stirrat et al.<ref name=Daystirratetal_2010>Day-Stirrat, R. J., A. McDonnell, and L. J. Wood, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER02/CHAPTER02.HTM Diagenetic and seismic concerns associated with interpretation of deeply buried "mobile shales,"] ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 5–27.</ref>). Advances in seismic imaging and processing technologies illuminate stratal geometries associated with shale tectonics that have led to a new understanding of the processes responsible for the geometries we observe in shale strata (see Day-Stirrat et al.<ref name=Daystirratetal_2010 />; Elsley and Tieman<ref name=Elsleyandtieman_2010>Elsley, G. R., and H. Tieman, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER05/CHAPTER05.HTM A comparison of prestack depth and prestack time imaging of the Paktoa complex, Canadian Beaufort MacKenzie Basin], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 79–90.</ref>). In addition, advances in modeling and understanding of how both muds and shales behave after burial have led to new geodynamic models for interpreting process from response reflected in stratal packages.<ref name=Albertzetal_2010>Albertz, M., C. Beaumont, and S. J. Ings, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER03/CHAPTER03.HTM Geodynamic modeling of sedimentation-induced overpressure, gravitational spreading, and deformation of passive margin mobile shale basins], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 29–62.</ref> Field geoscientists have added to our understanding of the geochemistry and physical character of extrusive mud features and their relationship to the overall basin hydrocarbon system.<ref name=Battanietal_2010>Battani, A., A. Prinzhofer, E. Deville, and C. J. Ballentine, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER13/CHAPTER13.HTM Trinidad mud volcanoes: The origin of the gas], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 223–236.</ref><ref name=Delisleetal_2010>Delisle, G., M. Teschner, E. Faber, B. Panahi, I. Guliev, and C. Aliev, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER12/CHAPTER12.HTM First approach in quantifying fluctuating gas emissions of methane and radon from mud volcanoes in Azerbaijan], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 209–222.</ref><ref name=Mcneiletal_2010>McNeil, D. H., J. R. Dietrich, D. R. Issler, S. E. Grasby, J. Dixon, and L. D. Stasiuk, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER11/CHAPTER11.HTM A new method for recognizing subsurface hydrocarbon seepage and migration using altered foraminifera from a gas chimney in the Beaufort-Mackenzie basin], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], 195–208.</ref><ref name=Warrenetal_2010>Warren, J. K., A. Cheung, and I. Cartwright, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER10/CHAPTER10.HTM Organic geochemical, isotopic, and seismic indicators of fluid flow in pressurized growth anticlines and mud volcanoes in modern deep-water slope and rise sediments of offshore Brunei Darussalam: Implications for hydrocarbon exploration in other mud- and salt-diapir provinces,] ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 161–194.</ref> As with mobile salt, shale-cored structures are commonly closely associated with hydrocarbons in many basins around the world. In Henry et al.<ref name=Henryetal_2010>Henry, M., M. Pentilla, and D. Hoyer, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER04/CHAPTER04.HTM Observations from exploration drilling in an active mud volcano in the southern basin of Trinidad, West Indies], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 63–78.</ref>, information on the character of these strata can be found as well as documentation on drilling into mobile mud-cored anticlinal features (diapirs) in southern Trinidad.

Because of the burgeoning of shale gas and shale oil research, geoscientists are gaining a better understanding of the petrographic framework of shales, as well as their behavior under various pressure and temperature regimes and the manner in how fluids move thorough these strata (for a review, see Day-Stirrat et al.<ref name=Daystirratetal_2010>Day-Stirrat, R. J., A. McDonnell, and L. J. Wood, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER02/CHAPTER02.HTM Diagenetic and seismic concerns associated with interpretation of deeply buried "mobile shales,"] ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 5–27.</ref>). Advances in seismic imaging and processing technologies illuminate stratal geometries associated with shale tectonics that have led to a new understanding of the processes responsible for the geometries we observe in shale strata (see Day-Stirrat et al.<ref name=Daystirratetal_2010 />; Elsley and Tieman<ref name=Elsleyandtieman_2010>Elsley, G. R., and H. Tieman, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER05/CHAPTER05.HTM A comparison of prestack depth and prestack time imaging of the Paktoa complex, Canadian Beaufort MacKenzie Basin], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 79–90.</ref>). In addition, advances in modeling and understanding of how both muds and shales behave after burial have led to new geodynamic models for interpreting process from response reflected in stratal packages.<ref name=Albertzetal_2010>Albertz, M., C. Beaumont, and S. J. Ings, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER03/CHAPTER03.HTM Geodynamic modeling of sedimentation-induced overpressure, gravitational spreading, and [[deformation]] of passive margin mobile shale basins], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 29–62.</ref> Field geoscientists have added to our understanding of the geochemistry and physical character of extrusive mud features and their relationship to the overall basin hydrocarbon system.<ref name=Battanietal_2010>Battani, A., A. Prinzhofer, E. Deville, and C. J. Ballentine, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER13/CHAPTER13.HTM Trinidad mud volcanoes: The origin of the gas], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 223–236.</ref><ref name=Delisleetal_2010>Delisle, G., M. Teschner, E. Faber, B. Panahi, I. Guliev, and C. Aliev, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER12/CHAPTER12.HTM First approach in quantifying fluctuating gas emissions of methane and radon from mud volcanoes in Azerbaijan], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 209–222.</ref><ref name=Mcneiletal_2010>McNeil, D. H., J. R. Dietrich, D. R. Issler, S. E. Grasby, J. Dixon, and L. D. Stasiuk, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER11/CHAPTER11.HTM A new method for recognizing subsurface hydrocarbon seepage and migration using altered foraminifera from a gas chimney in the Beaufort-Mackenzie basin], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], 195–208.</ref><ref name=Warrenetal_2010>Warren, J. K., A. Cheung, and I. Cartwright, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER10/CHAPTER10.HTM Organic geochemical, isotopic, and seismic indicators of fluid flow in pressurized growth anticlines and mud volcanoes in modern deep-water slope and rise sediments of offshore Brunei Darussalam: Implications for hydrocarbon exploration in other mud- and salt-diapir provinces,] ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 161–194.</ref> As with mobile salt, shale-cored structures are commonly closely associated with hydrocarbons in many basins around the world. In Henry et al.<ref name=Henryetal_2010>Henry, M., M. Pentilla, and D. Hoyer, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER04/CHAPTER04.HTM Observations from exploration drilling in an active mud volcano in the southern basin of Trinidad, West Indies], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 63–78.</ref>, information on the character of these strata can be found as well as documentation on drilling into mobile mud-cored anticlinal features (diapirs) in southern Trinidad.

==Terminology==

==Terminology==

To develop a working classification of shale tectonics, recognition that two primary classes of features occur is critical: (1) those associated with extrusion of fluids and material that does not involve grain-to-grain contact,<ref name=Battanietal_2010 /><ref name=Delisleetal_2010 /> and (2) those associated with larger scale deformation of apparent highly overpressured mud or shale substrates involving grain-to-grain plastic flow.<ref name=Elsleyandtieman_2010 /><ref name=Wieneretal_2010>Wiener, R. W., M. G. Mann, M. T. Angelich, and J. B. Molyneux, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER09/CHAPTER09.HTM Mobile shale in the Niger Delta: Characteristics, structure, and evolution], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 145–160.</ref> In addition, several varieties of highly fractured seep features exist.<ref name=Warrenetal_2010 /> These features allow fluid leakage from overpressured beds, but they do not always involve plastic or fluid-mud extrusion. Shales form a variety of nonextrusive structures, many of which resemble features generated through mobile salt movement, such as domes, welds, and walls. In contrast, muds form a variety of extrusive features, such as volcanoes, ponds, and flows and can erupt explosively.

To develop a working classification of shale tectonics, recognition that two primary classes of features occur is critical: (1) those associated with extrusion of fluids and material that does not involve grain-to-grain contact,<ref name=Battanietal_2010 /><ref name=Delisleetal_2010 /> and (2) those associated with larger scale [[deformation]] of apparent highly overpressured mud or shale substrates involving grain-to-grain plastic flow.<ref name=Elsleyandtieman_2010 /><ref name=Wieneretal_2010>Wiener, R. W., M. G. Mann, M. T. Angelich, and J. B. Molyneux, 2010, [http://archives.datapages.com/data/specpubs/memoir93/CHAPTER09/CHAPTER09.HTM Mobile shale in the Niger Delta: Characteristics, structure, and evolution], ''in'' L. Wood, ed., Shale tectonics: [http://store.aapg.org/detail.aspx?id=1023 AAPG Memoir 93], p. 145–160.</ref> In addition, several varieties of highly fractured seep features exist.<ref name=Warrenetal_2010 /> These features allow fluid leakage from overpressured beds, but they do not always involve plastic or fluid-mud extrusion. Shales form a variety of nonextrusive structures, many of which resemble features generated through mobile salt movement, such as domes, welds, and walls. In contrast, muds form a variety of extrusive features, such as volcanoes, ponds, and flows and can erupt explosively.

Several terms are used to describe the processes and features of shale mobility. These include shale tectonics, mud diapirism, shale diapirism and diapirs, mobile shales, mud volcanoes, mud diatremes, mud flows, and finally, from the Greek, argillokinesis and pellitokinesis. Although many scientists continue to argue against the existence of mobile shale, the term is well entrenched in the lexicon and unlikely to go away. A [http://www.americangeosciences.org/georef/georef-information-services GeoRef] search on the topic of mobile shale resulted in 34 instances of the combined term present in the peer-reviewed literature. Mobile shale and mud are the primary subject of a 2003 publication from the Geological Society of London, Subsurface Sediment Mobilization.<ref name=Vanrensbergenetal_2003>Van Rensbergen, O., R. R. Hillis, A. J. Maltman, and C. K. Morley, 2003, Subsurface sediment mobilization: Introduction, ''in'' P. Van Rensbergen, R. R. Hillis, A. J. Maltman, and C. K. Morley, eds., [http://sp.lyellcollection.org/content/216/1 Subsurface sediment mobilization]: Geological Society (London) Special Publication 216, p. 1–8.</ref> This single publication accounts for 36 additional articles on the subject, quadrupling the previous literature offering.  

Several terms are used to describe the processes and features of shale mobility. These include shale tectonics, mud diapirism, shale diapirism and diapirs, mobile shales, mud volcanoes, mud diatremes, mud flows, and finally, from the Greek, argillokinesis and pellitokinesis. Although many scientists continue to argue against the existence of mobile shale, the term is well entrenched in the lexicon and unlikely to go away. A [http://www.americangeosciences.org/georef/georef-information-services GeoRef] search on the topic of mobile shale resulted in 34 instances of the combined term present in the peer-reviewed literature. Mobile shale and mud are the primary subject of a 2003 publication from the Geological Society of London, Subsurface Sediment Mobilization.<ref name=Vanrensbergenetal_2003>Van Rensbergen, O., R. R. Hillis, A. J. Maltman, and C. K. Morley, 2003, Subsurface sediment mobilization: Introduction, ''in'' P. Van Rensbergen, R. R. Hillis, A. J. Maltman, and C. K. Morley, eds., [http://sp.lyellcollection.org/content/216/1 Subsurface sediment mobilization]: Geological Society (London) Special Publication 216, p. 1–8.</ref> This single publication accounts for 36 additional articles on the subject, quadrupling the previous literature offering.  

* Rocks that have low mechanical strength, that are commonly undercompacted, and that have a low degree of consolidation.

* Rocks that have low mechanical strength, that are commonly undercompacted, and that have a low degree of consolidation.

* Compressive tectonic stress to provide ductile deformation and increased pore pressures.

* Compressive tectonic stress to provide ductile [[deformation]] and increased pore pressures.

* Structural culminations that focus decompacted water and hydrocarbons.

* Structural culminations that focus decompacted water and hydrocarbons.

* Carrier beds for migrating fluids and gases.

* Carrier beds for migrating fluids and gases.