Thrust-belt structure—

My research on thrust-belt structure began and continues primarily in the Appalachians. Since retirement I have worked on styles of structures in the context of stratigraphy of the detachment, leading to publications of geologic quadrangle maps, field-trip guidebooks, and journal articles and a geological survey report.

Journal articles and a geological survey report.

Cook, B. S., and Thomas, W. A., 2010, Ductile duplexes as potential natural gas plays: An example from the Appalachian thrust belt in Georgia, USA:  Geological Society [London] Special Publication 348, p. 57-70.

Thomas, W. A., 2011, Cambrian-Devonian stratigraphy along the Southwest Montana transverse zone and tectonic history of the Willow Creek fault system:  Montana Bureau of Mines and Geology, Geologic Map 55, 39 p., 1 plate.

Pashin, J. C., Kopaska-Merkel, D. C., Arnold, A. C., McIntyre, M. R., and Thomas, W. A., 2012, Gigantic, gaseous mushwads in Cambrian shale: Conasauga Formation, southern Appalachians, USA:  International Journal of Coal Geology, v. 103, p. 70-91.

Sinha, A. K., Thomas, W. A., Hatcher, R. D., Jr., and Harrison, T. M., 2012, Geodynamic evolution of the central Appalachian orogen: Geochronology and compositional diversity of magmatism from Ordovician through Devonian: American Journal of Science, v. 312, p. 907-966.

Thomas, W. A., 2019, Evolution of the concept and structure of a MUSHWAD: Journal of Structural Geology, v. 125, p. 311-318. doi.org/10.1016/j.jsg.2018.05.001.

Cook, B. S., and Thomas, W. A., 2020, Three-dimensional model of a mushwad and its implications for the evolution of an Appalachian subrecess in northwestern Georgia, in Avary, K. L., Hasson, K. O., and Diecchio, R. J., eds., The Appalachian Geology of John M. Dennison: Geological Society of America Special Paper 545, https://doi.org/10.1130/2019.2545(12).

Thomas, W. A., and Hatcher, R. D., Jr., 2020 in press, Southern-central Appalachians–Ouachitas orogen: Encyclopedia of Geology, 2^nd Edition, Elsevier.

Geologic quadrangle maps.

Thomas, W. A., and Osborne, W. E., 2011, Geology of the Francis Mill 7.5-minute quadrangle, St. Clair, Calhoun, and Talladega Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 56, 24 p., 1 plate.

Thomas, W. A., and Drahovzal, J. A., 2012, Bedrock geology of the Harpersville 7.5-minute quadrangle, Shelby and Talladega Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 57, 34 p., 2 plates.

Thomas, W. A., and Ward, W. E., 2013, Geology of the Pell City 7.5-minute quadrangle, St. Clair and Talladega Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 60, 31 p., 1 plate.

Osborne, W. E., and Thomas, W. A., 2013, Geology of the Ohatchee 7.5-minute quadrangle, Etowah, Calhoun, and St. Clair Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 61, 51 p., 1 plate.

Thomas, W. A., and Irvin, G. D., 2013, Geology of the Eulaton 7.5-minute quadrangle, Calhoun County, Alabama:  Geological Survey of Alabama Quadrangle Series Map 62, 41 p., 1 plate.

Thomas, W. A., and Irvin, G. D., 2016, Geology of the Wellington 7.5-minute quadrangle, Calhoun and Etowah Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 65, 55 p., 2 plates.

Irvin, G. D., and Thomas, W. A., 2017, Geology of the Hyatt Gap 7.5-minute quadrangle, St. Clair, Blount, and Etowah Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 66, 55 p., 1 plate.

Thomas, W. A., and Irvin, G. D., 2017, Geology of the Westover 7.5-minute quadrangle, Shelby County, Alabama:  Geological Survey of Alabama Quadrangle Series Map 67, 37 p., 2 plates.

Irvin, G. D., and Thomas, W. A., 2018, Geology of the Cox Gap 7.5-minute quadrangle, St. Clair County, Alabama:  Geological Survey of Alabama Quadrangle Series Map 68, 70 p., 1 plate.

Osborne, W. E., and Thomas, W. A., 2018, Geology of the Steele 7.5-minute quadrangle, St. Clair and Etowah Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 69, 44 p., 1 plate.

Osborne, W. E., Garry, W. B., and Thomas, W. A., 2019, Geology of the Ashville 7.5-minute quadrangle, St. Clair and Blount Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map 70, 66 p., 1 plate.

Osborne, W. E., and Thomas, W. A., 2020 in press, Geology of the Glencoe 7.5-minute quadrangle, Etowah and Calhoun Counties, Alabama:  Geological Survey of Alabama Quadrangle Series Map.

Field-trip guidebooks.

Thomas, W. A., and Pashin, J. C., eds., 2011, Of mushwads and mayhem: Disharmonically deformed shale in the southern Appalachian thrust belt:  Alabama Geological Society, Forty-Eighth Annual Field Trip Guidebook, 126 p.

Thomas, W. A., ed., 2013, From the Gulf Coastal Plain to the Appalachian Plateau:  Alabama Geological Society, Fiftieth Annual Field Trip Guidebook, 136 p.

Thomas, W. A., Irvin, G.D., and Osborne, W. E., eds., 2017, The Anniston transverse zone in the Appalachian thrust belt: Alabama Geological Society, Fifty-Fourth Annual Field Trip Guidebook, 78 p.

Rifted margins—

My research on rifted continental margins has been ongoing since 1969, and recent work has been on large-scale reconstructions.

Thomas, W. A., 2010, Interactions between the southern Appalachian–Ouachita orogenic belt and basement faults in the orogenic footwall and foreland: Geological Society of America Memoir 206, p. 897-916.

Allen, J. S., Thomas, W. A., and Lavoie, D., 2010, The Laurentian margin of northeastern North America: Geological Society of America Memoir 206, p. 71-90.

Thomas, W. A., 2011, The Iapetan rifted margin of southern Laurentia: Geosphere, v. 7, p. 97-120.

Thomas, W. A., Tucker, R. D., Astini, R. A., and Denison, R. E., 2012, Ages of pre-rift basement and synrift rocks along the conjugate rift and transform margins of the Argentine Precordillera and Laurentia: Geosphere, v. 8, p. 1366-1383.

Mueller, P. A., Heatherington, A. L., Foster, D. A., Thomas, W. A., and Wooden, J. L., 2014, The Suwannee suture: Significance for Gondwana-Laurentia terrane transfer and formation of Pangaea: Gondwana Research, v. 26, p. 365-373.

Thomas, W. A., 2014, The Southern Oklahoma transform-parallel fault system, in Suneson, N. H., ed., Igneous and Tectonic History of the Southern Oklahoma Aulacogen: Oklahoma Geological Survey Guidebook 38, p. 375-387.

Thomas, W. A., 2014, A mechanism for tectonic inheritance at transform faults of the Iapetan margin of Laurentia: Geoscience Canada, v. 41, p. 321-344. [also in Hibbard, J. P., Pollock, J. C., van Staal, C. R., and Greenough, J. D., eds., Reeltime Geological Synthesis: Remembering Harold ‘Hank’ Williams: Geoscience Canada Reprint Series 10, p. 143- 166.]

Thomas, W. A., 2019, Tectonic inheritance at multiple scales during more than two complete Wilson cycles recorded in eastern North America: Geological Society of London Special Publications 470, p. 337-352. doi.org/10.1144/SP470.4.

Detrital zircons, sedimentary provenance, and dispersal pathways—

My research on detrital zircons and sedimentary provenance began around 2002, and it greatly accelerated in 2013 when George Gehrels (University of Arizona) and I received an NSF grant to use detrital zircons to trace late Paleozoic potential dispersal pathways westward from the Appalachians to the region of the Grand Canyon. I collected strategically located samples between West Virginia and Arizona, and these were analyzed at the Arizona LaserChron Center. We are still writing papers on this collection of data.

Thomas, W. A., 2011, Detrital-zircon geochronology and sedimentary provenance: Lithosphere, v. 3, p.304-308.

Thomas, W. A., Astini, R. A., Mueller, P. A., and McClelland, W. C., 2015, Detrital-zircon geochronology and provenance of the Ocloyic synorogenic clastic wedge, and Ordovician accretion of the Argentine Precordillera terrane: Geosphere, v. 11, p. 1749-1769.

Thomas, W. A., Gehrels, G. E., and Romero, M. C., 2016, Detrital zircons from crystalline rocks along the Southern Oklahoma fault system, Wichita and Arbuckle Mountains, USA: Geosphere, v. 12, p. 1224-1234.

Thomas, W. A., Gehrels, G. E., Greb, S. F., Nadon, G. C., Satkoski, A. M., and Romero, M. C., 2017, Detrital zircons and sediment dispersal in the Appalachian foreland: Geosphere, v. 13, p. 2206-2230.

Thomas, W. A., Gehrels, G. E., Lawton, T. F, Satterfield, J. I., Romero, M. C., and Sundell, K. E., 2019, Detrital zircons and sediment dispersal from the Coahuila terrane of northern Mexico into the Marathon foreland of the southern Midcontinent: Geosphere, v. 15, p. 1102-1127. https://doi.org/10.1130/GES02033.1.

Thomas, W. A., Gehrels, G. E., Sundell, K. E., Greb, S. F, Finzel, E. S., Clark, R. J., Malone, D. H., Hampton, B. A., and Romero, M. C., 2020, Detrital zircons and sediment dispersal in the eastern Midcontinent of North America: Geosphere, v. 16, https://doi.org/10.1130/GES02152.1.

Thomas, W. A., Gehrels, G. E., Sundell, K. E., and Romero, M. C., in review, Detrital-zircon analyses, provenance, and late Paleozoic sediment dispersal in the context of tectonic evolution of the Ouachita orogen: Geosphere, v. 16,

Intraplate earthquakes—

This research began with a grant from NSF to the University of Memphis (Chuck Langston and Chris Powell) in 2011 to explore the region around the New Madrid seismic zone; my role was to examine the distribution of seismicity in the context of mapable basement fault systems.

Powell, C. A., and Thomas, W. A., 2016, Grenville basement structure associated with the Eastern Tennessee seismic zone: Geology, v. 44, p. 39-42.

Thomas, W. A., and Powell, C. A., 2017, Necessary conditions for intraplate seismic zones in North America: Tectonics, v. 36, p. 2903-2917, doi.org/10.1002/2017TC004502

Powell, C. A., Thomas, W. A., and Hatcher, R. D., Jr., 2020 in press, The western limit of Iapetan rifting in the eastern United States: A new assessment: Seismological Research Letters.