Origins of the Caballos Novaculite Formation, Marathon Uplift, West Texas

Robert L. Folk and Earle F. McBride, UT Austin

Drs. Folk and McBride have a long-standing disagreement on the origin of novaculite units within the Silurian-Devonian-age Caballos Formation, which crops out in the Marathon region of Trans-Pecos Texas (Figure 1). The Marathon uplift is a topographic basin, but a structurally high remnant of southwest-northeast trending Ouachita mountain chain, which is otherwise buried by sediments throughout Texas. Novaculite is an uncommon rock type thought by some to be metamorphosed bedded chert. Folk and McBride (1976) describe the two Caballos novacultite members as “white, pelletal, spiculitic chert”. In the early 1970s Folk and McBride independently came up with contrasting descriptions for the origin of the novaculites. McBride and Thompson (1970) proposed deposition in a deep marine environment; Folk (1973) interpreted the depositional environment as “shallow marine with occasional subaerial exposure”. They chose to revisit field exposures of the rocks together in 1972, and subsequently published a collaborative article on their differing interpretations (Folk and McBride, 1976). In October they will continue their good spirited debate on the origins of the Caballos Novaculite for the Austin Geological Society.


Dr. Robert L. Folk was born 30 Sept. 1925 in Shaker Heights in Cleveland, Ohio. He obtained all three degrees from the Pennsylvania State College, Ph.D. 1952. From 1953-1988 he taught sedimentary geology at The University of Texas at Austin. He has won two medals for his work in sedimentary petrology, and two national teaching awards. In 1974, Dr. Folk published Petrology of Sedimentary Rocks, a reference guide used in teaching throughout the world. The book was reprinted in 1980, and in 2002 he donated it to the Walter Geology Library at UT Austin to be scanned and made available via the internet. Dr. Folk has had a life-long passion for all things Italian, and conducted much research in Viterbo and Acireale, Italy. In 1980 he first became interested in the role of bacteria in forming materials. After retiring from teaching in 1988, Dr. Folk became intrigued by the influence of nannobacteria on formation of minerals and weathering of rocks; in 1990 he discovered, along with Drs. Brenda Kirkland, F. Leo Lynch, and Amanda Lawrence the first mineralized nannobacteria. To read more about this passion of his, visit:

Dr. Earle F. McBride became an instructor at The University of Texas at Austin in 1959, and received a Ph.D. from Johns Hopkins University in 1960. Dr. McBride, also an author of numerous scientific articles, guidebooks, and references on deep water sedimentation (especially flysch deposits), continued teaching sedimentary geology at UT Austin Department of Geological Sciences until his retirement in 2005. In the 1970s and 1980s, he had visiting professorships at the University of Kansas (distinguished), the University of Perugia, Italy (sponsored by NATO), and consulted for a Mexican commission for coal exploration. Dr. McBride served as geology department chair at UT Austin from 1980-1984. His chief interests remain sandstone diagenesis, physical and chemical properties that alter sandstone, and the fate of sandstone pores, which he has applied in geological consulting work with over a dozen oil companies throughout his career. In 2011, Dr. McBride along with M. Dane Picard discovered relict evidence of the WWII D-Day battles on Omaha Beach in France in the form of small spherical beads of iron and glass, which are fused remnants of shrapnel and quartz sand. For more information on the Omaha Beach discoveries, see: