The alternate assembly and breakup of supercontinents leave a record of tectonic inheritance at continental margins.  The rocks and structures of eastern North America record the assembly of supercontinent Rodinia (the Grenville orogen), breakup of Rodinia and opening of the Iapetus Ocean, assembly of supercontinent Pangaea (the Appalachian-Ouachita orogen), and breakup of Pangaea and opening of the modern Atlantic Ocean.  Documentation of these lithospheric global events requires detailed studies of geologic structures and stratigraphy. 

Professor Thomas and students working under his direction integrate stratigraphy, structural geology, and tectonics to conduct such studies, using outcrop geology and geologic mapping, samples and geophysical logs from deep wells, and geophysical data including seismic reflection profiles and potential field maps.  Currently, we are addressing two primary hypotheses:

1) The Argentine Precordillera, now in the eastern foothills of the Andes, is an exotic terrane that was rifted from the Ouachita embayment of Laurentia (now southern North America) during Cambrian time and collided with Gondwana (now western South America) during Ordovician time.

2) Pre-orogenic structure and stratigraphy, specifically rift-related basement faults and distribution of structurally weak sedimentary rocks, strongly influence the structural geometry of a thin-skinned thrust belt, as well as the subsidence history of the orogenic foreland

Map from Thomas, 2006 (GSA Today)

Please click on map for larger image

Currently active dissertation and thesis research:

•intersection of Appalachian and Ouachita thrust belts (Pangaean compressional structures) at the Alabama promontory (Iapetan rift margin) beneath the Gulf Coastal Plain (Atlantic passive margin) [Matt Surles, Ph.D. dissertation]

•magnitude of Appalachian thrust shortening between thrust sheets with contrasting middle Paleozoic stratigraphy in Alabama [Mike Solis, M.S. thesis]

•relation of Mississippi Valley, Rough Creek, and Rome intracratonic basement fault systems to the Iapetan rifted continental margin [John  Hickman, Ph.D. dissertation]

•overcoming the problems of three-dimensional balancing of palinspastic reconstruction at an abrupt bend in a recess of the Appalachian thrust belt in Georgia [Brian Cook, Ph.D. dissertation]

•palinspastic reconstruction of the Iapetan rift in Newfoundland and Quebec, and identity of the conjugate cratons to Laurentia in the Rodinian supercontinent [John Allen, Ph.D. dissertation]

•kinematic relationships of a transverse fault system to Appalachian thrust-belt structures in Pennsylvania [Liz Dodson, M.S. thesis]

•sequence stratigraphy of the Floyd black shale and underlying sandstone units at the toe of a carbonate ramp in the Black Warrior basin in the Ouachita foreland in Mississippi [Carrie Kidd, M.S. thesis]

Recently completed dissertation and thesis research:

•tectonic history and evolution of the Taconic foreland on the Alabama promontory [Germán Bayona, Ph.D. completed 2003]

• tectonic history and evolution of the Ouachita thrust-belt salient in the Ouachita embayment [Steve Jusczuk, Ph.D. completed 2002]

•three-dimensional palinspastic restoration of thrust-belt structures, particularly lateral ramps and transverse zones in the Appalachian thrust belt [Greg Graham, M.S. completed 1998; Brian Cook, M.S. completed 2001; Brent Garry, M.S. completed 2001; Maggie Brewer, Ph.D. completed 2004]

•provenance of Alleghanian synorogenic clastic wedges as indicators of tectonic composition of the orogen [Tom Becker, Ph.D. completed 2005)

•late synrift and early post-rift sedimentation along the Blue Ridge rift [Maggie Brewer, M.S. completed 1997]

•evolution of the Kentucky River drainage system [Drew Andrews, Ph.D. completed 2004]

In addition to dissertation and thesis research, Professor Thomas has active research in:

•palinspastic reconstruction of the Iapetan rift in North America

•conjugate rift margins of Laurentia and the Argentine Precordillera

•accretion of the Argentine Precordillera to Gondwana

•vestiges of an Ordovician thrust belt in the Argentine Precordillera

•reactivation history of basement faults in the Ancestral Rocky Mountains

•structural geometry, kinematics, and palinspastic reconstruction of the Appalachian thrust belt

•geologic mapping in the Appalachian thrust belt

•lithospheric structure of continental rifting

Thomas, W. A., 2006, Tectonic inheritance at a continental margin [2005 Geological Society of America Presidential Address]: GSA Today, v. 16, no. 2, p. 4-11.

Bayona, G., and Thomas, W. A., 2006, Influence of pre-existing plate-margin structures on foredeep filling: insights from the Taconian (Blountian) clastic wedge, southeastern USA: Sedimentary Geology, v. 191, p. 115-133.

Thomas, W. A., and Bayona, G., 2005, The Appalachian thrust belt in Alabama and Georgia: thrust-belt structure, basement structure, and palinspastic reconstruction:  Geological Survey of Alabama Monograph 16, 48 p., 2 plates.

Becker, T. P., Thomas, W. A., Samson, S. D., and Gehrels, G. E., 2005, Detrital zircon evidence of Laurentian crustal dominance in the lower Pennsylvanian deposits of the Alleghanian clastic wedge in eastern North America: Sedimentary Geology, v. 182, p. 59-86.

Thomas, W. A., Astini, R. A., Mueller, P. A., Gehrels, G. E., and Wooden, J. L. 2004, Transfer of the Argentine Precordillera terrane from Laurentia: constraints from detrital-zircon geochronology:  Geology, v. 32, p. 965-968.

Thomas, W. A., with contributions by 29 others, 2004, Meeting challenges with geologic maps:  American Geological Institute, Environmental Awareness Series 7, 64 p.

Thomas, W. A., Becker, T. P., Samson, S. D., and Hamilton, M.A., 2004, Detrital zircon evidence of a recycled orogenic foreland provenance for Alleghanian clastic-wedge sandstones:  Journal of Geology, v. 112, p. 23-37.

Thomas, W. A., 2004, Genetic relationship of rift-stage crustal structure, terrane accretion, and foreland tectonics along the southern Appalachian-Ouachita orogen: Journal of Geodynamics, v. 37, p. 549-563.

Thomas, W. A., and Astini, R. A., 2003, Ordovician accretion of the Argentine Precordillera terrane to Gondwana: a review: Journal of South American Earth Sciences, v. 16, p. 67-79.

Bayona, G., Thomas, W. A., and Van der Voo, R., 2003, Kinematics of thrust sheets within transverse zones: a structural and paleomagnetic investigation in the Appalachian thrust belt of Georgia and Alabama: Journal of Structural Geology, v. 25, p. 1193-1212.

Bayona, G., and Thomas, W. A., 2003, Distinguishing fault reactivation from flexural deformation in the distal stratigraphy of the peripheral Blountian foreland basin, southern Appalachians, USA: Basin Research, v. 15, p. 503-526.

Thomas, W. A., and Bayona, G., 2002, Palinspastic restoration of the Anniston transverse zone in the Appalachian thrust belt, Alabama:  Journal of Structural Geology, v. 24, p. 797-826.

Thomas, W. A., 2001, Mushwad: Ductile duplex in the Appalachian thrust belt in Alabama:  American Association of Petroleum Geologists Bulletin, v. 85, p. 1847-1869.

Thomas, W. A., Astini, R. A., and Denison, R. E., 2001, Strontium isotopes, age, and tectonic setting of Cambrian salinas along the rift and transform margins of the Argentine Precordillera and southern Laurentia: Journal of Geology, v. 109, p. 231-246.

Brewer, M. C., and Thomas, W. A., 2000, Stratigraphic evidence for Neoproterozoic-Cambrian two-phase rifting of southern Laurentia: Southeastern Geology, v. 39, p. 91-106.

Thomas, W. A., and Astini, R. A., 1999, Simple-shear conjugate rift margins of the Argentine Precordillera and the Ouachita embayment of Laurentia: Geological Society of America Bulletin, v. 111, p. 1069-1079.

Mars, J. C., and Thomas, W. A., 1999, Sequential filling of a late Paleozoic foreland basin: Journal of Sedimentary Research, v. 69, p.1191-1208.

Thomas, W.A., and Astini, R.A., 1996, The Argentine Precordillera: a traveler from the Ouachita embayment of North American Laurentia: Science, v. 273, p. 752-757.

Thomas, W.A., and Baars, D.L., 1995, The Paradox transcontinental fault zone: Oklahoma Geological Survey Circular 97, p. 3-12.

Thomas, W.A., and Whiting, B.M., 1995, The Alabama promontory: Example of the evolution of an Appalachian-Ouachita thrust-belt recess at a promontory of the rifted continental margin: Geological Association of Canada Special Paper 41, p. 3-20.

Thomas, W.A., 1991, The Appalachian-Ouachita rifted margin of southeastern North America: Geological Society of America Bulletin v. 103, p. 415-431.

Thomas, W.A., 1990, Controls on locations of transverse zones in thrust belts: Ecologae Geologicae Helvetiae, v. 83, p. 727-744.

Thomas, W. A., 1977, Evolution of Appalachian-Ouachita salients and recesses from reentrants and promontories in the continental margin:  American Journal of Science, v. 277, p. 1233-1278.