Speaker: Thomas E. Ewing, Frontera Exploration Consultants

Topic: Late Paleozoic Tectonic Setting of the Eastern Shelf: From Faulted Ouachita Foredeep to Intracratonic Basin Flank within the Ancestral Rocky Mountains


Although the Eastern Shelf of the West Texas (Permian) Basin has only a few recognized structural elements, it lies within the broad Late Paleozoic framework of the Ancestral Rocky Mountains (ARM), as well as on the fringe of Ouachita orogenic foredeep basins. Both Ouachita and ARM uplifts have shed sediment into the area.

            In Early Pennsylvanian time, the area was located on the forebulge of the Fort Worth Basin, a foredeep basin that developed beneath and west of the advancing Ouachita thrust sheets. Early Pennsylvanian strike-slip fault systems also occur in the area, notably the Fort Chadbourne and Matador/Red River systems. Foredeep-related subsidence continued into Late Pennsylvanian time, advancing or broadening westward. Uplift of the Wichita ARM axis to the north probably occurred throughout the Pennsylvanian, as seen on its better-dated northern flank.

            Beginning in mid-Pennsylvanian time, the West Texas Basin began to subside as an intracratonic basin with its center near Pecos, Texas; this subsidence continued throughout the Permian, overlapping but outlasting ARM deformation. The Eastern Shelf was tilted westward (forming the Bend Arch as mapped today), and a high-relief carbonate/clastic shelf margin developed that bounded the deep-water Midland Basin from Missourian through Leonardian time. A small amount of additional westward tilting took place in the Mesozoic (probably as rift-flank uplift to Gulf-forming extension), forming the regional sub-Albian truncation evident in surface map patterns.

            Hydrocarbon generation and migration were controlled by the successive tectonic regimes. Most Pennsylvanian hydrocarbon reservoirs were probably sourced by updip migration from the Midland Basin either in the late Permian or the early Mesozoic. However, Mississippian source rocks were locally important, with lateral migration from the Fort Worth depocenter and vertical migration along the Red River axis possibly charging significant accumulations.


Dr. Thomas Ewing is a geoscientist with over 40 years of experience in hydrocarbon exploration and research. He is a Registered Professional Geoscientist in the State of Texas (#1320) and the State of Louisiana (#468) and an AAPG/DPA Certified Petroleum Geologist (#4538), and holds certification #1610 from SIPES.

 He received a B.A. in Geology from the Colorado College (1975), an M.S. in Geochemistry from New Mexico Institute of Mining and Technology (1977), and a Ph.D. in Geological Sciences from the University of British Columbia (1981).

Dr. Ewing was a research geologist for four years at the Texas Bureau of Economic Geology in Austin, where he served as a co-author of the “Atlas of Texas Oil Reservoirs”, and compiled the Tectonic Map of Texas.  Since 1985 he has been an owner of Frontera Exploration Consultants, Inc., a San Antonio-based geoscience consulting company. He worked with Venus Oil and Venus Exploration from 1985 to 2005 as staff consultant and Senior Explorationist, playing a main role in its successful exploration in the Yegua Trend of the Gulf Coast Basin and elsewhere in Texas.

Dr. Ewing has served in many offices in AAPG and its Divisions, He served as Vice-President for Sections of AAPG (2012-14). He received Honorary Membership in the South Texas Geological Society in 2009, Honorary Membership in the GCAGS in 2010, AAPG Distinguished Service Award, and BEG Alumnus of the Year in 2011. Most recently he has completed service as President of the GCAGS (2016-2017). In 2018 he was awarded the “Don Boyd Medal for Excellence in Gulf Coast Geology” from the GCAGS (Gulf Coast Association of Geological Societies), their highest award, and this year has been selected for Honorary Membership in AAPG.

Tom has spoken extensively at local, regional, and national geological meetings and published nearly 100 papers and abstracts. Among other awards, he has received the AAPG Levorsen Award three times, twice in Gulf Coast Section and once in Southwest Section. He has written articles on Gulf Coast geology and hydrocarbons, the geology and tectonics of Texas, and history and urban geology of the San Antonio area. He wrote the popular guidebook “Landscapes, Water and Man: Geology and Man in the San Antonio Area” published by the South Texas Geological Society in 2008. In 2016, Dr. Ewing completed “Texas Through Time”, an illustrated book and website on the geologic history and earth resources of Texas published by the Bureau of Economic Geology. Subsequently, he has authored chapters on the tectonic evolution of the Permian Basin (Ruppel volume) and on the geological development of the Gulf of Mexico Basin (with W.E. Galloway).

 In his spare time, he directs a 50-voice German men’s chorus, the San Antonio Liederkranz.