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Home , Archaeopteris, Devonian, Famennian, Givetian

Vol. 5, No. 3 March 1995

INSIDE GSA TODAY • Geopals Program, p. 46 • 1995 GeoVentures, p. 48 A Publication of the Geological Society of America • 1994 Medals and Awards, p. 51

Late Oceanic Anoxic Events and Biotic Crises: “Rooted” in the Evolution of Vascular Land ? Thomas J. Algeo, H. N. Fisk Laboratory of Sedimentology, Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 Robert A. Berner, Department of Geology and Geophysics, Yale University, New Haven, CT 06511 J. Barry Maynard, H. N. Fisk Laboratory of Sedimentology, Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013 Stephen E. Scheckler, Departments of Biology and Geological Sciences, Virginia Polytechnic Institute, Blacksburg, VA 24061

ABSTRACT Evolutionary developments among vascular land plants may Figure 1. Paleobotanic have been the ultimate cause for reconstructions of oceanic anoxic events, biotic crises, (A) an Early Devonian global change, and geochem- coastal delta, (B) an Early ical and sedimentologic anomalies of Devonian upland flood Late Devonian age. The influence of plain, (C) a Late Devonian vascular land plants on weathering coastal delta, and (D) a processes and global geochemical Late Devonian upland cycles is likely to have increased flood plain. Early Devonian substantially during the Late - plants: Pr = , Ps = , Sc = Sciado- ian owing to large increases in root phyton, and Sw = ; biomass associated with develop- Late Devonian plants: A = ment of (1) arborescence (-sized , B = Barino- stature), which increased root pene- phyton, L = tree lycopod, tration depths, and (2) the R= Rhacophyton, and habit, which allowed colonization S = seed . Data from of drier upland areas. We hypothe- Scheckler (1986), Gensel size that rapidly increasing root mass and Andrews (1984, 1987), led to transient intensification of the and P. G. Gensel (personal rate of formation and to perma- commun.). nent gains in the thickness and areal extent of deeply weathered soil pro- files. In the short term, greater pedo- genesis caused increased sediment yields owing to episodic disturbance of vascular land plants, in the biomass 1983), whereas high-latitude and cold- chemical records. Laminated black of developing and to increased and complexity of floral communities, water were less affected (Cop- shales indicate episodic development nutrient fluxes to the oceans as a and in the geographic distribution of per, 1986). The two maxima of widespread oceanic anoxia in many result of enhanced chemical weather- terrestrial vegetation (Fig. 1; Scheckler, of widest taxonomic impact occurred cratonic sequences during this interval ing. Long-term effects included 1986; Gensel and Andrews, 1987). In at or near the - (F-F) (Fig. 3, B–D). Deposition of organic-rich increased landscape stabilization, this paper, we propose that evolution- and Devonian- (D-C) shales and coals during the Devonian- drawdown of atmospheric CO 2 ary innovations among vascular land boundaries and are known as the Kell- Carboniferous transition sequestered through enhanced uptake in silicate plants were the ultimate cause of both wasser and Hangenberg events, respec- large quantities of isotopically light car- weathering and burial of organic car- the Late Devonian biotic crisis and a tively (Fig. 3A; Talent et al., 1993). bon in the sedimentary reservoir, caus- bon, and global cooling. Coeval ter- variety of coeval sedimentologic and The origin of the Late Devonian ing an enrichment of marine carbonate restrial paleobotanic developments geochemical anomalies. The main lines biotic crisis has been the subject of δ13C values of about 4‰ (Fig. 2B; and marine anoxic and extinction of evidence supporting this hypothesis considerable debate. Much recent Lohmann, 1988; Berner, 1989). A events are likely to have been linked are (1) close temporal relations between research has sought evidence of a combination of increased burial of causally through transient nutrient Late Devonian paleobotanic develop- bolide impact, an idea stimulated by organic carbon and enhanced silicate pulses that caused eutrophication of ments and major episodes of oceanic proposals for such a catastrophic mech- weathering by vascular plants drew semirestricted epicontinental sea- anoxia and mass extinction, and (2) a anism at the - (K-T) down atmospheric CO levels from ways, stimulating marine algal 2 model that successfully links these boundary (Alvarez et al., 1980). ~12–16 present atmospheric level (PAL) blooms. Correlativity of black shale paleobotanic developments to the Late Although minor iridium anomalies in the early–middle to ~1 PAL horizons and episodes of extinction Devonian biotic crisis and coeval sedi- (Geldsetzer et al., 1987; Wang et al., in the Carboniferous and (Fig. of tropical marine benthos impli- mentologic and geochemical anomalies 1993) and small concentrations of 2C; Berner, 1994). Evidence of lowered cates oceanic anoxia rather than through changes in pedogenic rates microspherules (Wang, 1992; Claeys atmospheric CO is provided by global cooling as the proximate 2 and processes. et al., 1992) have been identified close changes in soil carbonate δ13C (Mora et cause of the Late Devonian biotic to the F-F and D-C boundaries at sev- al., 1991) and by a marked decline crisis. LATE DEVONIAN BIOTIC eral locales, siderophile element ratios in dolomite abundance across the D-C INTRODUCTION CRISIS AND ANOMALIES are incompatible with those of mete- boundary (Fig. 2D). Marine evaporites orites, and these anomalies have been of this age exhibit a +8‰ to +10‰ During the Late Devonian biotic The origin of the Late Devonian interpreted as resulting from concen- δ34S excursion as a consequence of crisis (Frasnian-Famennian extinction), biotic crisis is a subject of continuing tration of metals by or large-scale bacterial reduction of dis- about 21% of families and 50% of gen- debate. Although various causes have changes in redox conditions (Playford solved sulfate in association with burial era among marine organisms disap- been proposed, including bolide et al., 1984; Wang et al., 1993). Other of organic carbon (Fig. 2E; Holser et al., peared (Sepkoski, 1986). This event was impacts, oceanic overturn, sea-level causes proposed for the Late Devonian 1989). Drawdown of atmospheric CO unusual in three respects (1) duration, 2 changes, and global climate change biotic crisis include climate change initiated global cooling, recorded as a ~20 m.y. (beginning in the , or (Copper, 1986; Geldsetzer et al., 1987; associated with global tectonics (Cop- about +3‰ enrichment of abiotic late Middle Devonian); (2) episodicity, McGhee, 1991; Claeys et al., 1992), per, 1986), oceanic overturn (Geldsetz- marine carbonate δ18O values across comprising at least eight separate none has gained general acceptance. er et al., 1987), and sea-level elevation the D-C boundary (Fig. 2F; Lohmann, episodes of extinction (House, 1985); Few, if any, of these theories have changes (McGhee, 1991), but none of 1988), and resulted in continental and (3) selectivity, disproportionately attempted to link Late Devonian ex- these fully accounts for the duration, glaciation by the late Famennian eliminating tropical marine benthos tinctions to coeval paleobotanic events; episodicity, and selectivity of the crisis. (Fig. 3E; Caputo, 1985). (Bambach, 1985; Sepkoski, 1986). however, the Givetian–Famennian The Late Devonian is also charac- were particularly severe epochs are characterized by important terized by an unusual combination of among the middle Paleozoic paleobotanic developments, including major excursions or permanent shifts community, dominated by stromato- large increases in the maximum size in a variety of sedimentologic and geo- poroids and (Fig. 2A; James, Plants continued on p. 64 Plants continued from p. 45 rapidly with the appearance of seed plants (Fig. 3E; Beck, 1981; Gensel and VASCULAR LAND PLANT Andrews, 1984; Scheckler, 1986). Seed EVOLUTION plants spread rapidly during the latest Famennian owing to the advantages Although land plants appeared in conferred by , including ability to the Late or Early adapt to diverse ecological conditions and vascular plants diversified in the and to occupy drier upland habitats Figure 2. Late Silurian and Early Devonian (Fig. 3E; Gillespie et al., 1981; Rothwell records exhibiting Late (Edwards and Berry, 1991), full colo- et al., 1989). Devonian anomalies: nization of land surfaces is likely to Close temporal relations exist (A) dominant Phanero- have been a protracted process that zoic reef-building between Late Devonian anoxic and continued throughout the Devonian groups (James, 1983); extinction events and these paleo- and later. Initially, the impact of land (B) marine carbonate botanic developments. First, the onset plants on their physical environment δ13C (Berner, 1989); of a protracted late Middle–Late Devo- was negligible owing to small size, (C) atmospheric CO2 nian interval of widespread oceanic limited biomass, shallow rooting, and (RCO2 is the ratio of anoxia (Fig. 3, B–D) followed closely CO at a given time in restriction to moist lowland habitats. 2 the advent of secondary vascular sup- the past to that at As land plants increased in size and porting tissues (Fig. 3E) and coincided present; Berner, 1994); became more abundant and geographi- broadly with rapid increases in the (D) North American cally widespread, they exerted a pro- maximum size of vascular land plants dolomite abundance gressively stronger influence on their (as volume percent of in the Middle Devonian (Fig. 4). Sec- physical substrate. Two evolutionary total carbonate; this ond, the F-F boundary Kellwasser event innovations are of major significance paper); (E) marine sul- occurred within the mid-Frasnian to in this regard: (1) arborescence, or tree- fate δ34S (Holser et al., mid-Famennian interval of archaeop- sized stature, and (2) the seed habit. 1989); (F) abiotic terid dominance and might represent δ18 With the advent of supporting tissues marine carbonate O the rapid spread of this (Fig. 3E). (Lohmann, 1988); (G) (2° xylem, 2° cortex) in the Middle Third, the D-C boundary Hangenberg North American sedi- Devonian (Fig. 3E), several groups event is preceded by the appearance of ment survival rates (this of vascular plants (lycopods, cladoxy- the earliest known seeds by one con- paper); and (H) miner- laleans, ) exhibited odont zone, or about 0.5 m.y. (Fig. 3E; alogy of clay increases in stature (Fig. 4; Chaloner assemblages (Weaver, Gillespie et al., 1981; Rothwell et al., and Sheerin, 1979; Mosbrugger, 1990). 1967). PDB is Peedee 1989). In each case, an important pale- However, Middle Devonian belemnite obotanic development that probably mostly occupied riparian habitats, and led to a large increase in root biomass flood-plain probably developed preceded major paleontologic, sedi- in the Frasnian with the appearance mentologic, and geochemical events of the Archaeopteris. by no more than a few million . This genus, which grew ~30 m high, In this regard, first appearances are less became the dominant element of ter- restrial floras between the mid-Frasnian and mid-Famennian, but declined Plants continued on p. 65

Trends continued from p. 47 replacement of higher paid managers enue to the universities. Some universi- ences to policy makers and the public with lower paid, entry-level staff. Slow ties are using postdoctoral fellows in at large in order to ensure the contin- information about the key themes and to moderate growth in employment is place of teaching assistants. This cre- ued viability of the profession. The key points presented at the forum. anticipated and should provide the ates more temporary slots for scientists societies could promote earth sciences In the 1970s and 1980s, the extrac- greatest opportunities to students with seeking permanent positions. in several ways: tive-industries (petroleum and miner- B.S. and M.S. degrees. Continuation of Earth science job opportunities • Encouraging colleges and uni- als)–oriented companies hired more the federal government’s domination in the coming decade likely will be in versities to provide integrative graduating earth science students than of environmental regulations will prob- positions that address important soci- earth science courses and experi- any other category of employer, for- ably favor large, multidisciplinary etal problems, such as natural hazards, ences for nonmajors, particularly merly providing employment to about firms. health, infrastructure, energy and for preservice and in-service K–12 two-thirds of all graduates. Employ- Shrinking budgets have been resource needs, and environmental teachers. ment and employment opportunities and will continue to be responsible for protection and remediation. Employers • Working with colleges and uni- in these industries have declined decreasing employment of earth scien- will be seeking geoscientists who have versities to inject earth science sharply over the past decade. Domestic tists by state and federal government knowledge of aqueous geochemistry, perspectives into allied professions, growth is expected to be flat. Con- agencies. The number of state-funded earth surface processes, and the such as engineering, and to pre- tributing to the continuing low level positions for professional staff in state youngest part of the geological time pare earth science students for of employment is the fact that extrac- geological surveys has declined about scale. Particularly attractive will be nontraditional careers in areas tive companies are increasingly moving 8% in the past four years, while the graduates with a solid foundation in such as law, business, and politics. their operations overseas, where they number of contract employees has fundamental science (biology, chem- • Working with academia and indus- are hiring foreign nationals. increased. Positions in the USGS have istry, engineering, geology, physics), try to provide access to lifelong, Employment opportunities in also declined over the past decade. mathematics, and computer science high-quality learning for practicing environmentally oriented companies These trends are likely to continue. and with skills in foreign language earth scientists. are the brightest of those in any geoin- Even larger reductions have occurred and oral and written communication. • Encouraging and, where appropri- dustry. However, the evolution and in the U.S. Bureau of Mines. Forum participants expressed the sense ate, coordinating the participation maturation of the industry and its In academia, the number of faculty that the generally prevailing college of earth scientists in local, state, technologies has reduced employment positions is expected to remain con- and university earth science curricu- and federal policy debates and opportunities when compared to the stant over the next 5–10 years. Faculty lum, which has changed little over the decisions. recent past. Competitive pressures have positions supported by external funds past 50 years, must be redesigned to The key word at the forum was prompted personnel restructuring, probably will decrease, because many provide a multidisciplinary base that change. Employment opportunities for including layoffs in some areas and the of these positions do not provide rev- integrates scientific knowledge and earth scientists have decreased signifi- basic scientific skills that would allow cantly over the past decade, and this students to adapt to changing societal pace is likely to continue into the priorities. Although the forum did not future. In the face of this rapid change, Southeastern Section Meeting to provide a specific plan for revision, colleges and universities need to be Include Symposium on Energy participants agreed that earth science constantly assessing their curricula. and the Environment societies and colleges and universities Geoscientists must work together to should encourage reform in several ensure a well-educated and skilled A symposium, “Energy and the Environment in the Next Century,” at the GSA ways, including: earth science workforce that will be Southeastern Section meeting in April will feature speakers from both the private • Bringing together the academic able to meet the future needs of society, and public sectors. The objective of the symposium, sponsored by GSA’s Institute community, professional societies, such as preserving the environment for Environmental Education, is to look at the many facets of the issue of energy government, and industry to coor- and providing an adequate supply of use and its effects on the environment, according to organizer Otto Kopp (Univer- dinate curricular reform. natural resources for a growing popula- sity of ). • Developing benchmarks for the tion. Perhaps the most important role Some of the subjects will be: acceptable levels of toxicity, fuels and CO , 2 content of courses. for earth science societies in managing the economics of nuclear power, and techniques for monitoring the environmental • Providing recognition and awards this change is the collection and dis- impact of energy production. The symposium will be open to all attendees at the for innovative courses, curricula, semination of resource data GSA Southeastern Section meeting in Knoxville, Tennessee, April 6–7, 1995. and teaching excellence. that can serve as the basis for wise For further information, contact Otto C. Kopp, Dept. of Geological Sciences, There was a consensus that earth decision making on employment and University of Tennessee, Knoxville, TN 37996-1410, (615) 974-2366, fax 615- science societies need to become more education issues. ■ 974-2368, E-mail: [email protected]. proactive in promoting the earth sci-

64 GSA TODAY, March 1995 Plants continued from p. 64 important than increases in abundance and biomass, which are harder to quan- tify but significantly more important in terms of geochemical consequences.

DEVELOPMENT OF THE RHIZOSPHERE AND SOILS Figure 3. Correlation of Devonian events: Soils are the geochemical interface (A) extinction events; between the lithosphere and the atmo- black shales from sphere-hydrosphere, and their impor- (B) eastern North tance in global geochemical cycles America, (C) central to has been largely underappreciated. western , Although thick soil pro- and (D) Europe; and files are known, generally high rates (E) paleobotanic events (data sources available of physical weathering in the pre- upon request). For Devonian probably yielded widespread columns B–D, note that barren rock surfaces and thin microbial illustrated units repre- protosoils similar to modern desert sent anoxic maxima as crusts (Campbell, 1979). Increases in determined by total the size and geographic distribution organic carbon content; of large vascular plants and in root black shales were biomass probably resulted in substan- deposited through tial increases in the depth and volume much of the late Middle of soils during the Late Devonian and Late Devonian in some areas. In column (Retallack, 1986). E, FAD = first appear- Development of the rhizosphere ance datum; the range had important short- and long-term and peak abundance of effects on sedimentologic and geo- Archaeopteris are shown chemical processes associated with by dashed and solid weathering (Fig. 5). In the short term, lines, respectively; global weathering rates increased as rel- and the age of South atively fresh substrates were physically American glaciation is and chemically attacked by rapidly restricted by occurrence spreading root systems. Enhanced of Foerstia (F; dashed; Caputo, 1985) and physical weathering may have accom- miospores (solid; Streel, panied the transition from largely 1986). zona- unvegetated to vegetated uplands, tion from Ziegler and during which increases in root density Sandberg (1990), and would have accelerated mechanical time scale from Harland breakup of rock but exerted only a et al. (1990). weak stabilizing influence against - sion by episodic droughts, , and (Stallard, 1985), yielding transient increases in regional or global particulate fluxes (Fig. 2G). Elevated chemical weathering rates resulted from “pumping” of atmospheric CO2 into the soil during rhizosphere expan- sion. Rapid drawdown of atmospheric CO led to a negative feedback on 2 lating marine algal blooms (Fig. 5). ent fluxes have caused eutrophication finer grained, compositionally more weathering rates, reestablishing a long- Such blooms may have been the source and transient expansion of oxygen- mature product was promoted by term balance in the rate of CO utiliza- 2 of high concentrations of marine algal depleted bottom waters (Kuparinen (1) production of organic and carbonic tion through weathering and the rate matter in Upper Devonian black shales and Heinänen, 1993; Lyons et al., acids by roots, (2) trapping of moisture of CO supply through volcanic out- 2 (Maynard, 1981) and of enigmatic fos- 1993). in soils, and (3) increased water-rock gassing (Berner, 1992, 1994). The tran- sils of wide geographic but restricted Long-term effects of rhizosphere contact time as a result of soil stabiliza- sient increase in chemical weathering stratigraphic occurrence such as Proto- development on weathering processes tion and enhanced evapotranspira- rates associated with rhizosphere salvinia (Foerstia; Schopf and Schwieter- included increased landscape stabili- tional recirculation (Berner, 1992). expansion is likely to have caused a ing, 1970). Analogous relations have zation and a shift from weathering- These developments are consistent pulse in nutrient flux to the oceans, been documented from the modern limited to transport-limited weathering with an Early Carboniferous shift from resulting in eutrophication of semire- Black and Baltic Seas, in which anthro- regimes (Fig. 5; Stallard, 1985; Johns- stricted epicontinental seas and stimu- pogenic and natural increases in nutri- son, 1993). Weathering of rocks to a Plants continued on p. 66

Figure 5. Model linking Late Devonian geochemi- cal, sedimentologic, and climatic anomalies to the development of arbores- cence and the seed habit among vascular land plants. Features are arrayed by relative dura- tion, transient effects on the left and long-term effects on the right. Solid outlines indicate docu- mented geologic records; dashed outlines indicate processes linking records. See text for discussion.

Figure 4. Maximum size of vascular land plants during the Devonian; note the rapid increase associated with appearance of trees in the Givetian. Maximum diameters of plant axes, esti- mated tree heights, and representative fossil genera from Chaloner and Sheerin (1979), Gensel and Andrews (1984), and Mosbrugger (1990).

GSA TODAY, March 1995 65 Plants continued from p. 65 Campbell, S. E., 1979, Soil stabilization by a prokaryotic desert crust: Implications for Precam- GSA ANNUAL MEETINGS brian land biota: Origins of Life, v. 9, p. 335–348. illite-chlorite– to smectite-kaolinite– dominated clay mineral assemblages Caputo, M. V., 1985, Late Devonian glaciation in : , Palaeoclimatol- 1995 (Fig. 2H; Weaver, 1967). At present, ogy, Palaeoecology, v. 51, p. 291–317. formation of smectite and kaolinite New Orleans, Louisiana Chaloner, W. G., and Sheerin, A., 1979, Devonian November 6–9 is closely associated with moderate to macrofloras, in House, M. R., et al., eds., The strong pedogenic weathering in tem- Devonian : London, Palaeontological Ernest N. Morial perate to semiarid and in humid tropi- Association, Special Papers in Palaeontology 23, Convention Center, p. 145–161. cal climate zones, respectively (Singer Hyatt Regency New Orleans and Munns, 1991). Claeys, P., Casier, J.-G., and Margolis, S. V., 1992, General Chair: William R. Craig, University of New Orleans Microtektites and mass extinctions: Evidence for a Late Devonian asteroid impact: Science, v. 257, Technical Program Chair: Laura Serpa, University of New Orleans CONCLUSIONS p. 1102–1104. Field Trip Chair: Whitney Autin, Louisiana State University See November 1994 GSA Today for a complete list of field trips. The influence of vascular land Cook, T. D., and Bally, A. W., editors, 1975, plants on weathering processes and Stratigraphic atlas of North and Central America: Princeton, New Jersey, Princeton University Press, CALL FOR PAPERS—APRIL GSA TODAY global geochemical cycles is likely to 272 p. Themes, Symposia, Field Trips, and Continuing Education Courses have increased substantially during the Copper, P., 1986, Frasnian/Famennian mass Late Devonian owing to development extinction and cold-water oceans: Geology, v. 14, of arborescence and the seed habit. p. 835–839. 1996 These paleobotanic innovations led to Edwards, D., and Berry, C., 1991, Silurian and Denver, Colorado • October 28–31 rapid expansion of the global rhizo- Devonian, in Cleal, C. J., ed., Plant in geo- Colorado Convention Center, Marriott City Center sphere, resulting in a transient intensi- logical investigation: New York, Ellis Horwood, General Chairs: Kenneth E. Kolm and Gregory S. Holden, Colorado School of Mines fication of the rate of soil formation p. 117–153. Technical Program Chair: John D. Humphrey, Colorado School of Mines Geldsetzer, H. H. J., Goodfellow, W. D., McLaren, and in a permanent increase in the Call for Field Trip Proposals: Please contact the Field Trip Chairs listed below. thickness and areal extent of deeply D. J., and Orchard, M. J., 1987, Sulfur-isotope anomaly associated with the Frasnian-Famennian Charles L. Pillmore, Ren A. Thompson weathered soils. Intensified chemical extinction, Medicine Lake, Alberta, Canada: Geol- U.S. Geological Survey, MS 913, P.O. Box 25046 weathering may have caused a tran- ogy, v. 15, p. 393-396. Denver Federal Center, Denver, CO 80225 sient increase in riverine nutrient Gensel, P. G., and Andrews, H. N., 1984, Plant life phones: Charles L. Pillmore, (303) 236-1240; Ren A. Thompson (303) 236-0929 fluxes, resulting in eutrophication of in the Devonian: New York, Praeger, 380 p. semirestricted epicontinental seaways For general information on any meeting call the GSA Meetings Department, Gensel, P. G., and Andrews, H. N., 1987, The evo- 1-800-472-1988 or (303) 447-2020, ext. 141; E-mail: [email protected] and stimulating marine algal blooms lution of early land plants: American Scientist, and widespread deposition of black v. 75, p. 478–489. shales. Correlativity of black shale hori- Gillespie, W. H., Rothwell, G. W., and Scheckler, zons with episodes of extinction of S. E., 1981, The earliest seeds: , v. 293, GSA SECTION MEETINGS tropical marine benthos implicates p. 462–464. oceanic anoxia rather than global cool- Harland, W. B., Armstrong, R. L., Cox, A. V., NORTHEASTERN SECTION ing as the proximate cause of the Late Craig, L. E., Smith, A. G., and Smith, D. G., 1990, Radisson Hotel and Conference Center in Cromwell, Hartford, Connecticut, A 1989: Cambridge, United Devonian biotic crisis. Drawdown of March 20–22, 1995. Information: Gregory McHone, Graduate Liberal Studies Program, Kingdom, Cambridge University Press, 263 p. Wesleyan University, 255 High St., Middletown, CT 06457, (203) 344-7930, fax 203- atmospheric CO2 and global cooling Holser, W. T., Maynard, J. B., and Cruikshank, 344-7957. were secondary effects of enhanced sili- K. M., 1989, Modelling the natural cycle of sul- SOUTHEASTERN SECTION cate weathering and rapid organic car- phur through Phanerozoic time, in Brimblecombe, Knoxville Hilton Hotel, Knoxville, Tennessee, April 6–7, 1995. Information: bon burial. Thus, evolutionary develop- P., and Lein, A. Y., eds., Evolution of the global biogeochemical sulphur cycle: Chichester, United Robert D. Hatcher, Jr., Dept. of Geological Sciences, University of Tennessee, Knoxville, ments among vascular land plants are Kingdom, Wiley, p. 21–56. TN 37996-1410, (615) 974-2368, fax 615-974-2368, E-mail: [email protected]. likely to have been the ultimate cause NORTH-CENTRAL and SOUTH-CENTRAL SECTIONS of oceanic anoxic events, biotic crises, House, M. R., 1985, Correlation of mid-Palaeozoic ammonoid evolutionary events with global sedi- University of Nebraska, Lincoln, Nebraska, April 27–28, 1995. Information: and global climate change during the mentary perturbations: Nature, v. 313, p. 17–22. Robert F. Diffendal, Jr., 113 Nebraska Hall, University of Nebraska–Lincoln, Lincoln, NE Late Devonian. 68588-0517, (402) 472-2410, fax 402-472-2410, E-mail: [email protected]. James, N. P., 1983, Reefs, in Scholle, P. A., et al., eds., Carbonate depositional environments: Amer- ROCKY MOUNTAIN SECTION ACKNOWLEDGMENTS ican Association of Petroleum Geologists Memoir Montana State University, Bozeman, Montana, May 18–19, 1995. Information: 33, p. 345–462. Stephan G. Custer, Department of Earth Sciences, Montana State University, Bozeman, MT North American sediment mass- 59717-0348, (406) 994-6906, fax 406-994-6923, E-mail: [email protected]. Johnsson, M. J., 1993, The system controlling age distributions were compiled from the composition of clastic sediments, in Johnsson, CORDILLERAN SECTION Cook and Bally (1975) with assistance M. J., and Basu, A., eds., Processes controlling the University of Alaska, Fairbanks, Alaska, May 24–26, 1995. Information: David B. from Bradley Opdyke, Steven Boss, and composition of clastic sediments: Geological Soci- Stone, Geophysical Institute, University of Alaska, Fairbanks, AK 99775-0800, (907) Bruce Wilkinson. The manuscript bene- ety of America Special Paper 284, p. 1–19. 474-7622, fax 907-474-7290, E-mail: [email protected]. fited greatly from our discussions with Kuparinen, J., and Heinänen, A., 1993, Inorganic Elso Barghoorn, John Hayes, Jacek nutrient and carbon controlled bacterioplankton growth in the Baltic Sea: Estuarine, Coastal and Student Travel Grants Jaminski, Lisa Pratt, Greg Retallack, Shelf Science, v. 37, p. 271–285. and Tom Robl, and from reviews by The GSA Foundation will award matching grants up to a total of $3500 each to the six GSA Lohmann, K. C, 1988, Geochemical patterns of Patricia Gensel, Eldridge Moores, and Sections. The money, when combined with equal funds from the Sections, will be used to meteoric diagenetic systems and their application assist GSA Student Associates traveling to the 1995 GSA Annual Meeting in New Orleans in an anonymous reviewer. Lisa Trump to studies of paleokarst, in James, N. P., and Cho- November and to the 1995 Section meetings. Contact your Section Secretary for application drafted Figure 1. Financial support was quette, P. W., eds., Paleokarst: New York, Springer, procedures. provided by the University of Cincin- p. 58–80. Cordilleran ...... Bruce A. Blackerby ...... (209) 278-2955 nati Research Council (Algeo); by Lyons, T. W., Berner, R. A., and Anderson, R. F., Rocky Mountain ...... Kenneth E. Kolm ...... (303) 273-3932 North-Central ...... George R. Hallberg ...... (319) 335-4500 National Science Foundation grant 1993, Evidence for large pre-industrial perturba- tions of the Black Sea chemocline: Nature, v. 365, South-Central ...... Rena M. Bonem ...... (817) 755-2361 EAR-9117099 (Berner); and by the p. 538–540. Northeastern ...... Kenneth N. Weaver ...... (410) 554-5532 U.S. Department of Energy (Maynard). Southeastern ...... Harold H. Stowell ...... (205) 348-5098 Maynard, J. B., 1981, Carbon isotopes as indica- We are grateful to the many researchers tors of dispersal patterns in Devonian-Mississip- whose contributions have been helpful pian shales of the Appalachian Basin: Geology, in formulating the hypothesis of this v. 9, p. 262–265. paper. McGhee, G. R., Jr., 1991, Extinction and diversifi- Schopf, J. M., and Schwietering, J. F., 1970, Talent, J. A., Mawson, R., Andrew, A. S., Hamilton, cation in the Devonian brachiopoda of New York The Foerstia zone of the Ohio and Chattanooga P. J., and Whitford, D. J., 1993, Middle Paleozoic State: No correlation with sea level?: Historical Shales: U.S. Geological Survey Professional Paper extinction events: Faunal and isotopic data: REFERENCES CITED Biology, v. 5, p. 215–227. 1294-H, 15 p. Palaeogeography, Palaeoclimatology, Palaeo- , v. 104, p. 139–152. Alvarez, L. W., Alvarez, W., Asaro, F., and Michel, Mora, C. I., Driese, S. G., and Seager, P. G., 1991, Sepkoski, J. J., 1986, Phanerozoic overview of mass H. 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H., 1989, Elkinsia gen. nov., a Late Devonian long-term carbon cycle: Geochimica et Cosmo- with cupulate ovules: Botanical chimica Acta, v. 56, p. 3225–3231. Gazette, v. 150, p. 170–189. Each month, GSA Today features a short science article on fast-breaking items or Berner, R. A., 1994, Geocarb II: A revised model of current topics of general interest to the 17,000 members of GSA. What do you think Scheckler, S. E., 1986, Geology, floristics and atmospheric CO over Phanerozoic time: Ameri- 2 paleoecology of Late Devonian coal swamps of these articles? Do you have an idea for an article that you would like to see pub- can Journal of Science, v. 294, p. 56–91. from Appalachian : Société Géologique lished in GSA Today? If so, please contact Eldridge Moores, Science Editor, GSA Today, de Belgique, Annales, v. 109, p. 209–222. (916) 752-0352, fax 916-752-0951.

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