Linda C. Kah
Kenneth G. Walker Associate Professor
Carbonate Sedimentology and Geochemistry
Department of Earth and Planetary Sciences
624 Strong Hall
1621 Cumberland Ave
Knoxville, TN 37996-1410
My students and I focus on integrating sedimentology, stratigraphy, geochemistry, and paleobiology in understanding the evolution of the Earth's biosphere. Research projects include reconstructing the ocean-atmospheric oxygenation and the redox structure of Mesoproterozoic shallow marine systems, exploring the effects of changing ocean circulation on the Great Ordovician Biodiversification Event (GOBE), and characterizing microbe-mineral interactions in the mineralization of Holocene lacustrine microbialites. In addition to Earth-based research projects, I am also investigating potential habitable environments as co-investigator on the Mars Science Laboratory mission.
- Post-Doctoral Fellow, 1999, University of Missouri (Dr. Timothy W. Lyons)
- Ph.D., 1997, Harvard University (Dr. Andrew H. Knoll)
- S.M., 1990, Massachusetts Institute of Technology (Dr. John P. Grotzinger)
- S.B., 1990, Massachusetts Institute of Technology
- Associate Professor, University of Tennessee (2006-present)
- Assistant Professor, University of Tennessee (2000-2006)
- Research Fellow, University of Missouri (1998-1999)
- Research Faculty, Tulane University (1997)
As a co-investigator on the Mars Science Laboratory mission, I am involved in both orbital mapping of Gale Crater, as well as in strategic planning, daily spacecraft operations, and the interpretation of geologic data. I work primarily with the Mast and MAHLI cameras, which were built by Malin Space Science Systems. After the Curiosity rover landed on 6 August 2012, we spent several months testing and calibrating analytical equipment. We then moved to a region of layered strata, called Yellowknife Bay, where we analyzed the depositional and diagenetic environments of ancient lacustrine deposits. At present, we are heading toward Mount Sharp, where we will begin to investigate the habitability potential of depositional environments recorded by a thick package of layered strata. I give many outreach presentations on the Curiosity mission, including a keynote at the 2012 Council for the Advancement of Science Writing (CASW) annual convention.
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Molar-tooth structure (MT) is an enigmatic Precambrian carbonate fabric characterized by variously shaped voids filled with a characteristically uniform, equant microspar. A combination of petrographic analysis (via transmitted light, SEM, and cathodoluminescence microscopy), mineralogical analysis (via raman spectroscopy), 3-dimensional structural analysis, geochemical analysis, and laboratory experiments has helped us better understand both the formation of this unusual microfabric, and its implications for the chemical evolution of the Proterozoic carbonate system. Other research focused on a related fabric, termed herringbone carbonate (HB), which consists of unusual carbonate cements whose c-axis shifts direction along the length of the crystal.
Cathodoluminescence image of MT microspar, showing discrete non-luminescent crystals with isopachous, luminescent rims
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Whereas stromatolite microfabrics reflect a combination of microbial community growth, decomposition and lithification, stromatolite morphology appears to reflect primarily physical depositional factors, such as water depth, wave energy, and sediment influx. As a result, stromatolitic laminae, which record both microscale and macroscale growth processes, are arguably the most fundamental aspect of stromatolite morphology. Each lamina represents the active growth surface of the mat at the time of deposition and the geometry of successive laminae produces a record of microbial mat growth over time. Detailed analysis of stromatolitic laminae can therefore help decipher the growth of enigmatic stromatolitic forms, such as conophyton and jacutophyton.
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Microbialites comprise the mineralized record of early life on Earth and preserve a spectrum of fabrics that reflect complex physical, chemical, and biological interactions. In ongoing research, we are investigating mineralized microbial structures in Laguna Negra, a high-altitude (>3500 m) Andean lake in Catamarca Province, Argentina. Extreme environmental conditions restrict multicellular life so that mineralization reflects a combination of local hydrologic conditions, lake geochemistry, and microbial activity. The resulting carbonate microtextures are strikingly similar to those observed in Proterozoic stromatolites, and thus provide critical insight into microbial activity and mineralization in ancient environments.
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Precambrian microbial mats can be exquisitely preserved in early diagenetic chert, yet many of our most fundamental geobiological questions regarding the diversity of organisms and metabolic processes in these ancient environments remain poorly constrained. This dichotomy in understanding stems from both the relatively simple morphologies represented by many microbial populations and the inability of traditional optical microscopy to provide information on the chemistry of preserved organic matter, which together severely limits taxonomic determination and resulting physiological inferences. Microbial mats within early diagenetic chert record of distinct benthic communities that are preserved across a full range of taponomic states, permitting detailed analysis of mat growth, decomposition, and preservation.
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Carbon isotope chemostratigraphy has become a principal tool for stratal correlation and the primary mechanism by which Proterozoic strata are placed in a chronostratigraphic framework. Chemostratigraphic correlation is particularly well established for the latter Neoproterozoic (<800 Ma), during which marine carbon isotopes record both elevated average values and high amplitude variation. Unfortunately, the resolution of our global chemostratigraphic record remains limited for much of the earlier Proterozoic. Research on Mesoproterozoic (1600-1000 Ma) successions has permitted definition of broad intervals of isotopic similarity, and has resulted in modeling efforts to link carbon isotopic variability to the PCO2 evolution of the Early Earth.
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A 4‰ positive shift in the carbon isotopic composition of the oceans is recorded globally in marine carbonate rocks at approximately 1.25 Ga, may be related to an increase in the oxygenation of the Earth's biosphere. This 'event' marks a threshold in the mid-Mesoproterozoic that may be recorded in the geologic record by the diversification of microbial and algal life, as well as by the appearance of the oldest laterally extensive, bedded marine sulfate evaporites. Ongoing research has used the petrographic analysis of gypsum and calcitized sulfate phases, isotopic (particularly S and Sr isotopes) and trace element chemistry of gypsum and carbonate-associated sulfate (CAS), and geochemical modeling to explore the sulfate content of ancient oceans as a proxy for Earth surface oxygenation.
Petrographic image showing silicified halite within gypsum, indicating that gypsum was more highly saturated in the oceans than halite by the late Mesoproterozoic
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Increased oxygenation of Earth surface environments in the Mesoproterozoic has been suggested to have greatly affected the distribution of bioessential, redox-sensitive elements (Anbar and Knoll, 2002). Investigation of sulfide minerals, patterns of iron speciation, and the relative abundance of redox-sensitive trace metals in epicratonic and pericratonic strata from the Mesoproterozoic of West Africa have provided critical insight into the redox structure of ancient epeiric seas. Data suggest that anoxic and persistently sulfidic environments existed in offshore environments immediately beneath wave base. Within intracratonic seas, where wave energy was likely dampened, anoxic, and variably sulfidic environments occurred at the sediment-water interface and within shallow pore waters (even when the overlying water column was oxic). Modeling efforts suggest that the redox structure of epeiric seas may have played a critical role in the distribution of bioessential nutrients.
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Despite evidence for increased oxygenation of the Earth's surface in the latest Proterozoic, oxygen-depleted environments appear to have characterized deeper-ocean environments well into the Ordovician. Sulfur isotopes from early and middle Ordovician strata from the Argentine Precordillera and Western Newfoundland suggest that deep-oceans remained persistently sulfidic until at least the late middle Ordovician. S-isotopic composition of coeval pyrite and carbonate-associated sulfate suggests that this deep-ocean reservoir acted as a distinct reactive sulfur reservoir, the behavior of which is best modeled via a 2-box model system (cf. Rothman et al., 2003).
Carbon and Sulfur isotopes (CAS) from Argentina, indicating the presence of a persistent reactive pool of hydrogen sulfide in deep-waters
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We are witness to extraordinary times. At latest count, the Earth has experienced the extinction of nearly 20% of known animal species, and at the same time, the debate rages as to the possibility of finding life on Mars or elsewhere in the universe. We have also witnessed incredible instances of nature's power and its affect on life on Earth — tornados, hurricanes, volcanoes, earthquakes, tsunamis, the threat of global climate change, and the deterioration of our natural resources. This course explores the structure of the Earth system and is history of dynamic change.
The geological record is by no means complete, yet with careful observation it allows us to observe the interactions between life and nature throughout Earth's long history…and we find that the history of life and the physical and chemical evolution of the Earth's environment are inextricably linked. In this course we consider the complexity of these interactions in the modern world (i.e., what controls the nature and distribution of life on Earth today, and what are the limits to life on Earth?). We then see how these observations provide the basis for speculation (i.e., the building of testable hypotheses) regarding the nature of similar interactions throughout the geologic past. Finally, we will examine the geologic record to determine the causes and consequences of these changing interactions through Earth history.
The investigation of sedimentary rocks differs significantly from that of either igneous or metamorphic rocks, and is, in many respects, unmatched in terms of the information that can be amassed regarding the history of the Earth's surface. The composition, texture, structure, packaging, and chemistry of sedimentary rocks provide unique insights into everything from the evolution of the biosphere to plate tectonic configuration. This course aims to provide you with the tools necessary to: understand the origin and behavior sedimentary grains, describe and classify the major types of sedimentary rocks, decipher environments of deposition and diagenesis, use information from sedimentary rocks to understand biospheric evolution, appreciate the role of the sedimentary record in "telling time," and interpret sedimentation patterns in terms of tectonic processes
This course introduces students to various aspects of physical, chemical, and biological oceanography, and will help them integrate these varied disciplines in an exploration of the Earth's past, present, and future oceans. The course design sallow active participation of students from a variety of scientific disciplines, and this interdisciplinary interaction will help us all view the oceans in a different light. Through the course, students will focus on understanding the basic oceanographic principles and processes; integrating physical, chemical, and geological processes to gain an understanding of complex oceanographic processes, and completing in-depth research on a topic of their choice
Carbonate sediments are extraordinarily complex in that they reflect not only the physical conditions of deposition, but chemical and biological parameters as well. One of the most exciting consequences of this complexity is that the geologic record of carbonate rocks – their distribution in time and space, textural detail, biological makeup, and chemistry – provides a wealth of data about the evolution of Earth surface environments. This course provides a general introduction to the inherently complex nature of carbonate sediments, practical experience in identifying and interpreting carbonate sediments, and an understanding of how to interpret aspects of their depositional and diagenetic record in the interpretation of long- and short-term changes in Earth surface environments.
This course is an interactive seminar for graduate students. Weekly readings and discussion provide an opportunity to experience a wide range of scientific viewpoints. Topics of the seminar change (and often reflect the interest of the student participants). Past topics include: Evolution of Planetary Biospheres (co-taught with Hap McSween); Five-Hundred Million Years that Changed the World; Evolution of Proterozoic Life and Environments; Carbon and Sulfur through Earth's History; and the use and Abuse of Sequence Stratigraphy.
- Gilleaudeau, G.J., and Kah, L.C., Oceanic molybdenum drawdown by epeiric sea expansion in the Mesoproterozoic. Chemical Geology (in press).
Chakrabarti, G., Shome, D., Kumar, S., Stephens III, G.M., and Kah, L.C., Carbonate platform development in a Palaeoproterozoic extensional basin, Vempalle Formation, Cuddapah Basin, India. Journal of Asian Earth Sciences (in press).
- Knoll, A.H., Wörndle, S., and Kah, L.C., Covariance of microfossils assemplages and microbialite textures across a late Mesoproterozoic carbonate platform. Palaios (in press).
- Williams, R.M.E., et al., including Kah, L.C., 2013, Martian fluvial conglomerates at Gale Crater. Science, v. 340, p. 1068-1072. Click here for PDF
- Hazen, R.M., Downs, R.T., Jones, A.P., Kah, L.C., 2013, Carbon mineralogy and crystal chemistry. In Hazen, R.M., Baross, J., Hemley, R.J., and Jones, A.P. (eds.), Reviews in Mineralogy and Geochemistry, v. 75, p. 7-46. Click here for PDF
- Hazen, R.M., Downs, R.T., Kah, L.C., and Sverjensky, D., 2013, Carbon mineral evolution. In Hazen, R.M., Baross, J., Hemley, R.J., and Jones, A.P. (eds.), Reviews in Mineralogy and Geochemistry, v. 75, p. 79-107. Click here for PDF
- Gilleaudeau, G.J. and Kah, L.C., 2013, Carbon isotope records in a Mesoproterozoic epicratonic sea: Carbon cycling in a low-oxygen world. Precambrian Research, v. 228, p. 85-101. Click here for PDF
- Guo, H., Du, Y., Kah, L.C., Huang, J., Hu, C., Huang, H., 2013, Isotopic compositions of organic and inorganic carbon from the Mesoproterozoic of North China: Implications for biological and oceanic evolution. Precambrian Research, v. 224, p. 169-183. Click here for PDF
- Edgett, K.S., Yingst, R.A., Ravine, M.A., Caplinger, M.A., Maki, J.N., Ghaemi, F.T., Schaffner, J.A., Bell III, J.F., Edwards, L.J., Herkenhoff, K.E., Heydari, E. Kah, L.C., Lemmon, M.T., Minitti, M.E., Olson, T.S., Parker, T.J., Rowland, S.K., Schieber, J., Sullivan, R.J., Sumner, D.Y., Thomas, P.C., Jensen, E.H., Simmonds, J.J., Sengstacken, A.J., Willson, R.G., Goetz, W., 2012, Curiosity's Mars Hand Lens Imager (MAHLI) Investigation. Space Science Reviews, v. 170, p. 259-317. Click here for PDF
- Thompson, C.K., Kah, L.C., Astini, R., Bowring, S.A., Buchwaldt, R., 2012, Bentonite geochronology, marine geochemistry, and the Great Ordovician Biodiversification Event (GOBE). Palaeogeography, Palaeoclimatology, Palaeoecology, v. 321-322, p. 88-101. Click here for PDF
- Kah, L.C., Bartley, J.K., and Teal, D.A., 2012, Chemostratigraphy of the late Mesoproterozoic Atar Group, Mauritania: Muted isotopic variability, facies correlation, and global isotopic trends. Precambrian Research, v. 200-203, p. 82-103. Click here for PDF
- Thompson, C.K., and Kah, L.C., 2012, Sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in Early to Middle Ordovician greenhouse oceans. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 313-314, p. 189-214. Click here for PDF
- Blumenberg, M., Theil, V., Riegel, W., Doering, S., Kah, L.C., and Reitner, J., 2012, Black shale formation by microbial mats lacking sterane-producing eukaryotes, Late Mesoproterozoic (1.1 Ga) Taoudeni basin, Mauritania. Precambrian Research, v. 196-197, p. 113-127. Click here for PDF
- Kah, L.C., and Bartley, J.K., 2011, The Precambrian record of evolving oxygen: International Geology Review, v. 53, p. 1424-1442. Click here for PDF
- Kah, L.C., Bartley, J.K., and Stagner, A.F., 2009, Reinterpreting a Proterozoic enigma: Conophyton-Jacutophyton stromatolites of the Mesoproterozoic Atar Group, Mauritania: International Association of Sedimentology Special Publication 41, p. 277-295. Click here for PDF
- Kah, L.C., and Riding, R., 2007, Mesoproterozoic carbon dioxide levels inferred from calcified cyanobacteria: Geology, v. 35, p. 799-802. Click here for PDF
- Bartley, J.K., Kah, L.C., McWilliams, J.L., Stagner, A.F. 2007 Carbon Isotope Chemostratigraphy of the Avzyan Formation (Southern Urals, Russia): Signal recovery in a fold-and-thrust belt: Chemical Geology, v. 237, p. 211-232. Click here for PDF
- Kah, L.C., Crawford, J.C., Bartley, J.K., Kozlov, V.I., Sergeeva, N.D., Puchkov, V.N., 2007, Carbon isotope chemostratigraphy as a tool for constraining the age of subsurface strata (Kama-Belaya Trough, East European Platform, Russia): Stratigraphy and Geological Correlation, v. 15, p. 12-29. Click here for PDF
- Lyons, T.W., Gellatly, A.M., McGoldrick, P.J., and Kah, L.C., 2006, Proterozoic sedimentary exhalative (SEDEX) deposits and their links to evolving ocean chemistry: in Ohmoto, H., and Kesler, S.E., eds., Evolution of the Early Atmosphere, Hydrosphere, and Biosphere: Constraints from Ore Deposits: GSA Special Paper, v. 198, p. 169-184. Click here for PDF
- Pollock, M.D., Kah, L.C., and Bartley, J.K., 2006, Morphology of molar-tooth structures in Precambrian carbonates: influence of substrate rheology and implications for genesis: Journal of Sedimentary Research, v. 76, p. 310-323. Click here for PDF
- Kah, L.C., Bartley, J.K., Frank, T.D., and Lyons, T.W., 2006, Reconstructing sea-level change from the internal architecture of stromatolite reefs: an example from the Mesoproterozoic Sulky Formation, Dismal Lakes Group, arctic Canada: Canadian Journal of Earth Sciences, v. 43, p. 653-669. Click here for PDF
- Johnston, D.T., Wong, B.A., Farquhar, J., Kaufman, A.J., Strauss, H., Lyons, T.W., Kah, L.C., Canfield, D.E., 2005, Active microbial sulfur disproportionation in the Mesoproterozoic: Science, v. 310, p. 1477-1479. Click here for PDF
- Kah, L.C., Lyons, T.W., and Frank, T.D., 2004, Low marine sulphate and protracted oxygenation of the Proterozoic biosphere: Nature, v. 431, p. 834-838. Click here for PDF
- Bartley, J.K., and Kah, L.C., 2004, Marine carbon reservoir, Corg-Ccarb coupling, and the evolution of the Proterozoic carbon cycle: Geology, v. 32, p. 129-132. Click here for PDF
- Lyons, T.W., Kah, L.C., and Gellatly, A.M., 2004, The Precambrian sulfur isotope record of evolving atmospheric oxygen: in Tempos and events in Precambrian time (P.G. Erikkson, ed.), Developments in Precambrian Geology, v. 12, p. 421-440. Click here for PDF
- Frank, T.D., Kah, L.C., and Lyons, T.W., 2003, Changes in organic matter production and accumulation as a mechanism for isotopic evolution in the Mesoproterozoic Ocean: Geological Magazine, v. 140, p. 397-420. Click here for PDF
- Kah, L.C. and Bartley, J.K., 2001, Preface: in J.K. Bartley and L.C. Kah, eds., Rodinia and the Mesoproterozoic Earth-Ocean System, Precambrian Research, v. 111, p. 1-4. Click here for PDF
- Kah, L.C., Lyons, T.W., and Chesley, J., 2001, Geochemistry of a 1.2 Ga carbonate-evaporite succession, northern Baffin and Bylot islands: Implications for Mesoproterozoic marine evolution: in J.K. Bartley and L.C. Kah, eds., Rodinia and the Mesoproterozoic Earth-Ocean System, Precambrian Research, v. 111, p. 203-234. Click here for PDF
- Kah, L.C., 2000, Preservation of depositional δ18O signatures in Proterozoic dolostones: Geochemical constraints on seawater chemistry and early diagenesis: in J.P. Grotzinger and N.P. James, eds., Deposition and Diagenesis in an Evolving Precambrian World, SEPM Special Publication, v. 67, p. 245-360. Click here for PDF
- Kah, L.C., Sherman, A.B., Narbonne, G.M., Kaufman, A.J., and Knoll, A.H., 1999, δ13C stratigraphy of the Proterozoic Bylot Supergroup, northern Baffin Island: Implications for regional lithostratigraphic correlations: Canadian Journal of Earth Sciences, v. 36, p. 313-332. Click here for PDF
- Kah, L.C. and Knoll, A.H., 1996, Microbenthic distribution of Proterozoic tidal flats: Environmental and taphonomic considerations: Geology, v. 24, p. 79-82. Click here for PDF
- Kah, L.C. and Grotzinger, J.P., 1992, Early Proterozoic (1.9 Ga) thrombolites of the Rocknest Formation, Northwest Territories, Canada: Palaios, v. 7, p. 305-315. Click here for PDF
- Awarded Roger and Beverly Bohanan Faculty Achievement Award (2013)
- Named Kenneth G. Walker professor (2008)
- Who's Who of Outstanding College and University Professors (2003, 2005)
- University Award for Outstanding Services to Arts and Sciences Advising Services (2003)
- George Martin Hall Departmental Service Award (2002, 2008)
Current Research Funding
- NASA Mars Science Laboratory (2005). Co-I on "MAHLI – MArs Hand Lens Imager for the Mars Science Laboratory"
Past Research Funding
- NSF Earth Sciences (2008). P-I on "Laterally extensive breccias in the Mesoproterozoic Atar Group, Mauritania: Tsunami deposition resulting from a marine extraterrestrial impact?"
- National Geographic Society (2008). P-I on "Unusual breccias of the 1.2 Ga Atar Group: tsunami deposits potentially related to an extraterrestrial impact event?"
- NSF Earth Sciences (2008). P-I on "Behavior of marine sulfate in the Early Paleozoic: Testing the trace sulfate proxy."
- American Chemical Society – Petroleum Research Fund (2008). P-I on "Ocean circulation, nutrient cycling and the S-isotope composition of Early Paleozoic marine systems."
- University of Tennessee SARIF Small Grant (2008). Carbon and sulfur isotopes, ocean circulation, and the Ordovician radiation in central China
- University of Tennessee Provost's Professional Development Award (2008). P-I on "Mineralizing microbial mats of the high Andes, Argentina: an astrobiological analogue to early Earth and Mars?"
- NSF GK-12 (2006). Co-I on "Track I, GK-12: Enriching earth science in rural Tennessee middle schools through research-based activities on climate and environmental history."
- National Geographic Society (2005). P-I on "Trace sulfate as a proxy for biospheric oxygenation: Implications for the ecologic expansion of animal life in the early Paleozoic."
- National Science Foundation SGER (2004). P-I on "Genesis and diagenesis of an enigmatic Precambrian carbonate cement: An investigation using microanalytical and experimental techniques."
- University of Tennessee SARIF Small Grant (2004). P-I on "Genesis and diagenesis of an enigmatic Precambrian carbonate cement: An investigation using microanalytical and experimental techniques."
- NSF Earth Sciences (2002). Co-I on "Distribution and genesis of unusual carbonate fabrics (Atar Group, Mauritania) – Understanding the evolution of the Proterozoic carbonate factory."
- NASA Exobiology (2001). P-I on "Recognizing biotic influences on planetary evolution: Investigating the biogeochemical record of microbial metabolism during Mesoproterozoic ocean-atmosphere oxidation."
- National Geographic Society (2001). P-I on "Carbonate precipitation and the development of Proterozoic stromatolitic reefs, Mauritania."
- National Geographic Society (2000). Co-I on "Mesoproterozoic biogeochemical change: field studies in the Southern Urals."
- University of Tennessee SARIF Small Grant (2001). P-I on "Stratigraphy and development of Proterozoic stromatolite reefs, Dismal Lakes Group, NWT, Canada"
- University of Tennessee Provost's Professional Development Award (2001). P-I on "Stratigraphy and development of Proterozoic stromatolite reefs, Dismal Lakes Group, NWT, Canada."
- University of Tennessee SARIF GRA Award (2001). P-I on "Distribution and genesis of "molar-tooth" fabric, Montana."
- University of Tennessee SARIF Research Award (2000). Co-I on "Investigation of geologic materials: analysis and acquisition of image data by optical and cathodoluminescence microscopy."
- University of Tennessee SARIF Award (2000). P-I on "Enhancement of sedimentary geochemistry preparatory facilities."
- NSF Earth Sciences (1998). Co-I on "Geochemical and isotopic constraints on Mesoproterozoic ocean chemistry – working toward a global perspective."
- National Geographic Society (1997). P-I on "Mesoproterozoic cycling of C, S, and Sr isotopes: do global tectonics influence biogeochemical cycling?"
- University of Missouri Research Board (1998). Co-I on "Sulfur isotopic records of Precambrian ocean chemistry via Carbonate Associated Sulfate (CAS)."
- NSF Earth Sciences (1997). P-I, originally awarded to the late R.J. Horodyski, on "Studies in Precambrian Paleontology."
- National Geographic Society (1994). P-I on "Physical, chemical and biological controls on Mesoproterozoic carbonate sedimentation."
- Member, Geological Society of America
- Member, Society for Economic Paleontologists and Mineralogists
- Member, American Geophysical Union
- Member, Association of Women Geoscientists
- Member, Sigma Xi
- Member, National Association of Geoscience teachers