Left: The Cretaceous-Tertiary boundary on the west bank  of the Brazos River, Texas, on 13 May 1996. This is the Brazos-1 section.The light-colored layer is calcareous siltsone overlying sands and debris flow deposits.

• Molluscan biotas: The biotas of the Carboniferous and Permian are special because they contain abundant molluscs, which were common in both shallow water and deeper water settings (Yancey, 1978). Frequent changes in sealevel, generated by repeated change in Gondwanan icesheets, produced major environmental shifts and environmental instability that allowed opportunistic species to flourish. This especially favored molluscs, among which are the earliest representatives of many groups considered characteristic of the Mesozoic. The study of these groups is revealing the origins of groups dominant after the great extinction event of the end Permian.
• Paleoceanography: A collaborative project (with Ethan Grossman and students) has been the documentation of stable isotope stratigraphy of the Carboniferous and Permian, primarily by utilizing brachiopod shell carbonate (Adlis et al., 1988; Grossman et al., 1991, 1993, 1996; Mii et al., 1997, 1999, 2000). The project focuses on the icehouse climatic interval, including the beginnings and emergence from icehouse conditions. This work has produced detailed stratigraphies for the midcontinent of North America and Russian platform, both located on the Laurussian supercontinent during the late Paleozoic. Ongoing work focuses on high paleolatitude sites, to provide data for north polar seas and Gondwana.
• Exceptional paleontology: Work is underway on the biotas of the Buckhorn Asphalt deposit of Oklahoma, an example of exceptional preservation in which shell materials have been protected from diagenetic alteration and degradation by being sealed in asphalt (Yancey & Heaney, 2000; Yancey et al., 2000). The shells were deposited in tar and asphalt or embedded in it soon after depostion, sealing them from degradation by acids and oxidation and preventing chemical changes. Fine details of shell microstructure and ornament are preserved, along with exquisite details of larval shell of many molluscan groups, early growth stages that provide evidence of the early ontogeny. Sedimentologic work has demonstrated that this famous deposit is a mixed assemblage of shallow and deeper water taxa, many of which were transported to the depositional site by mass flow sediment movement. The site contains transported bivalves and gastropods and open ocean cephalopods.
• Unusual bivalves: My favorite topic is the study of unusal bivalves, an interest that has led to work describing two great groups of giant, winged bivalves: alatoconchids of the mid Permian (Yancey & Boyd, 1983; Yancey & Ozaki, 1986) and the wallowaconchids of the late Triassic (Yancey & Stanley, 1999). Both groups are characterized by large size and broad flattened "wing" extensions of the shell - however, the two groups are homeomorphs and unrelated to each other. At the other end of the size range, recent work has described an equally unusual group of praecardioid bivalves (Yancey & Heaney, 2000). These bivalves undergo major transformations in shape during growth and the adults have a sharply truncated posterior margin, producing a shell form very similar to some conocardiid rostroconchs. Again, the similarity in form is a matter of homeomorphic convergence. The praecardioids appear to be fairly common in deeper water environments, but many remain to be described.

There are many silicic volcanic ash layers present in the section and dates for some of these ashes in the mid-late Eocene part of the section have been published (Guillemette & Yancey, 1996; Yancey & Guillemette, 1998). Several ash layers deposited on land or in fresh water have preserved hydrated but otherwise unaltered glass, providing opportunity to characterize the geochemistry of the magma, as preserved in the glass. This geochemical and radiometric dating program is providing an independent framework for correlating the section. The most abundant microfossils in the section are palynomorphs and ongoing work focuses on spore-pollen palynology and dinoflagellate palynology to better date the marginal marine and coastal plains sections. The common occurrence of lignites makes this effort especially rewarding.

The famous Stone City outcrop, exposing richly fossiliferous glauconitic sediments (Yancey & Davidoff, 1994; Yancey, 1995)is located a short distance from College Station. This is the best location in the region to obtain Tertiary marine shells and is a favorite field trip destination (provided river levels are low). There is public access and parking and it is just a short stroll to the collecting site. The strata contain a high diversity of marine species, most of which are small. The Crockett Formation contains a thick interval of richly fossiliferous marine strata, but only the Stone City site is adequately exposed or of easy access. We continue to collect from these sections.

Yancey, T. E., and Heaney, M. J., III, 2000, Carboniferous praecardioid bivalves from the exceptional Buckhorn Asphalt biota of south-central Oklahoma, USA, in Harper, E. M., Taylor, J. D., and Crame, J. A., eds., The evolutionary biology of the Bivalvia: Geological Society, London, Special Publications v. 177, p. 291-301.

Yang, Z. and Yancey, T. E., 2000, Fusulinid biostratigraphy and paleontology of the middle Permian (Guadalupian) strata of the Glass Mountains and Del Norte Mountains, west Texas; Smithsonian Contributions to the Earth Sciences, no. 32, p. 185-259.

Mii, H-S., Grossman, E. L., and Yancey, T. E., 1999. Carboniferous isotope stratigraphies of North America: Implications for Carboniferous paleoceanography and Mississippian glaciation: Geol. Soc. America Bull., v. 111, p. 960-973.

Yancey, T. E., and Stanley, G. D., Jr., 1999, Giant alatoform bivalves in the upper Triassic of western North America; Palaeontology, v. 42, p. 1-23.

Yancey, T. E. and Guillemette, R., 1998, Major volcanic ash units in the Late Eocene of east Texas; Gulf Coast Association of Geological Societies Transactions, v. 48, p. 511-516.

Heymann, D., Yancey, T.E., Wolbach, W.S., Thiemens, M.H., Johnson, E.A., Roach, D., & Moecker, S., 1998, Geochemical markers of the Cretaceous-Tertiary boundary event at Brazos River, Texas, USA; Geochimica et Cosmochimica Acta, v. 62, p. 173-181.

Mii, H.-S., Grossman, E.L. & Yancey, T.E., 1997, Stable carbon and oxygen isotope shifts in Permian seas of West Spitsbergen - Global change or diagenetic artifact?; Geology, v. 25, p. 227-230. 

Yancey, T.E., 1996, Stratigraphy and depositional environments of the Cretaceous-Tertiary boundary complex and basal Paleocene section, Brazos River, Texas; Gulf Coast Association of Geological Societies, Transactions, vol. 46, p. 433-442. 

Guillemette, R. & Yancey, T.E., 1996, Composition and provenance of volcanic glass in Late Eocene Manning Formation, east-central Texas; Gulf Coast Association of Geological Societies, Transactions, vol. 46, p. 159-166. 

Grossman, E.L., Mii, H.S., Zhang, C., & Yancey, T.E., 1996, Chemical variation in Pennsylvanian brachiopod shells - diagenetic, taxonomic, microstructurall, and seasonal effects; Journal of Sedimentary Research, vol. 66, p. 1011-1022. 

Yancey, T.E., 1995, Depositional trends in siliciclastic deposits of the Stone City transgressive systems tract, middle Eocene, Texas; Gulf Coast Association of Geological Societies, Transactions, vol. 45, p. 581-586.