extinÇÕes em massa do devÓnico superior · silúrico pridoli 419 3 segunda-feira, 17 de março...

EXTINÇÕES EM MASSA DO DEVÓNICO SUPERIOR

VIII ENCONTRO DE PROFESSORES DE GEOCIÊNCIAS DO ALENTEJO E ALGARVE

SILVESTEATRO GREGÓRIO MASCARENHAS

15 DE MARÇO, 2014

Paulo Fernandes - UALG e CIMA ([email protected])Zélia Pereira - LNEG ([email protected])

segunda-feira, 17 de Março de 2014

mailto:[email protected]




Devónico - Estratigrafia

Período Época Idade Começo (Ma.) Duração (Ma.)

Carbonífero Tournaisiano 359 14

Devónico

Devónico Superior

Fameniano 375 16

Devónico

Devónico Superior Frasniano 385 10

DevónicoDevónico

MédioGivetiano 392 7

DevónicoDevónico

Médio Eifeliano 398 6Devónico

Devónico Inferior

Emsiano 407 9

Devónico

Devónico Inferior

Pragiano 411 4

Devónico

Devónico Inferior

Lochkoviano 416 5

Silúrico Pridoli 419 3


Devónico Superior (370 Ma)

Eura

mér

ica

Sibéria

GondwanaA. do Sul

África Antárctica

Austrália

Oceano Rheic

China

E. do Sul

Oceano Pantalassa


A vida no Devónico“Idade dos Peixes”

http://www.devoniantimes.org/index.html




Peixes sem mandíbula (Agnatha)


Placodermes (Extintos)

Dunkleosteus


Acanthodii (Extintos)

Escamas úteis para datar

Acanthodes

Diplacanthus

Climatius

http://www.devoniantimes.org


http://www.devoniantimes.org/opportunity/soils.html


Actinopterygii

Maior grupo de peixes actuaisLimnomis delaneyi


Sarcopterygii


Holoptychius sp.

Único representante actual celacanto (Latimera chalumnae) e alguns peixes pulmonados.






Celacanto - Moçambique

Tiktaalik roseae

http://www-news.uchicago.edu/releases/06/images/060406.tiktaalik-3.jpg




Tetrapódes primitivos

Acanthostega

Ichthyostega





Invertebrados Marinhos

• Estromatoporídeos, formadores de recifes calcários

• Corais (Rugosa, Tabulata), formadores de recifes

• Braquiópodes

• Trilobites

Coral - Rugosa

Coral - Tabulata Trilobite - Phacops



Evolução das plantas

Esporos de briófitas (plantas não vasculares) - Ordovícico Médio

Esporos triletes de pré-traqueófitas e Rhynofitas - Silúrico inferior

A partir do Devónico Médio 2 grupos de traqueófitas: Licófitas e Eufilófitas




Milhões de anos

Núm

ero

de F

amíli

as c

onhe

cida

s

DevónicoSuperior

Sepkoski, 1992

Magnitude e grau da extinção do Devónico Superior



Extinção Perda de géneros observada (%)

Perda de espécies estimada (%)

Final do Ordovícico 60 85

Devónico Superior

57 83

Final do Pérmico 82 95

Final do Triásico 53 80

Final do Cretácico 47 76

Jablonski, 1991



Núm

ero

de F

amíli

as e

xtin

tas

por A

ndar

Milhões de anos

DevónicoSuperior

A extinção do Devónico Sup. não foi um evento instantâneo (ao nível de uma camada).

Consistiu numa série de pulsos de extinção que ocorreram ao longo de ca. 10 Ma.


As extinções em massa do Devónico Superior ocorreram durante regressões rápidas

(descida do nível médio do mar), após períodos de máxima transgressão.

O Devónico Superior é caracterizado por duas grandes crises e dois eventos na biosfera.

As crises foram períodos de tempo relativamente longos nas quais ocorreu a perda de biodiversidade e os eventos perturbações geológicas de curta duração (comparadas com as crises).

Crises: Frasniano final e Fameniano final.

Eventos: (1) Kellwasser (perto do limite Frasniano/Fameniano) e (2) Hangenberg (perto do limite Devónico/Carbonífero)

Racki, 2005


O exemplo do Evento Kellwasser

Corresponde a camada(s) de argilitos negros depositados em ambientes anóxicos durante períodos transgressivos

Racki, 2005


O exemplo do Evento Hangenberg

Caplan & Bustin, 1999




Perturbações geológicas relacionadas com as Extinções do Devónico Superior:

★ Deposição de “xistos negros”;

★ Evolução das plantas terrestres;

★ Perturbações geoquímicas;

★ Mudanças do nível do mar

★ Províncias ígneas de grandes dimensões (LIP’S);

★ Impactos de corpos extra-terrestres.


GSA TODAY, March 1995 65

important than increases in abundanceand biomass, which are harder to quan-tify but significantly more important interms of geochemical consequences.

DEVELOPMENT OF THERHIZOSPHERE AND SOILS

Soils are the geochemical interfacebetween the lithosphere and the atmo-sphere-hydrosphere, and their impor-tance in global geochemical cycleshas been largely underappreciated.Although thick Precambrian soil pro-files are known, generally high ratesof physical weathering in the pre-Devonian probably yielded widespreadbarren rock surfaces and thin microbialprotosoils similar to modern desertcrusts (Campbell, 1979). Increases inthe size and geographic distributionof large vascular plants and in rootbiomass probably resulted in substan-tial increases in the depth and volumeof soils during the Late Devonian(Retallack, 1986).

Development of the rhizospherehad important short- and long-termeffects on sedimentologic and geo-chemical processes associated withweathering (Fig. 5). In the short term,global weathering rates increased as rel-atively fresh substrates were physicallyand chemically attacked by rapidlyspreading root systems. Enhancedphysical weathering may have accom-panied the transition from largelyunvegetated to vegetated uplands,during which increases in root densitywould have accelerated mechanicalbreakup of rock but exerted only aweak stabilizing influence against ero-sion by episodic droughts, landslides,and wildfires (Stallard, 1985), yieldingtransient increases in regional or globalparticulate fluxes (Fig. 2G). Elevatedchemical weathering rates resultedfrom “pumping” of atmospheric CO2into the soil during rhizosphere expan-sion. Rapid drawdown of atmosphericCO2 led to a negative feedback onweathering rates, reestablishing a long-term balance in the rate of CO2 utiliza-tion through weathering and the rateof CO2 supply through volcanic out-gassing (Berner, 1992, 1994). The tran-sient increase in chemical weatheringrates associated with rhizosphereexpansion is likely to have caused apulse in nutrient flux to the oceans,resulting in eutrophication of semire-stricted epicontinental seas and stimu-

lating marine algal blooms (Fig. 5).Such blooms may have been the sourceof high concentrations of marine algalmatter in Upper Devonian black shales(Maynard, 1981) and of enigmatic fos-sils of wide geographic but restrictedstratigraphic occurrence such as Proto-salvinia (Foerstia; Schopf and Schwieter-ing, 1970). Analogous relations havebeen documented from the modernBlack and Baltic Seas, in which anthro-pogenic and natural increases in nutri-

ent fluxes have caused eutrophicationand transient expansion of oxygen-depleted bottom waters (Kuparinenand Heinänen, 1993; Lyons et al.,1993).

Long-term effects of rhizospheredevelopment on weathering processesincluded increased landscape stabili-zation and a shift from weathering-limited to transport-limited weatheringregimes (Fig. 5; Stallard, 1985; Johns-son, 1993). Weathering of rocks to a

finer grained, compositionally moremature product was promoted by(1) production of organic and carbonicacids by roots, (2) trapping of moisturein soils, and (3) increased water-rockcontact time as a result of soil stabiliza-tion and enhanced evapotranspira-tional recirculation (Berner, 1992).These developments are consistentwith an Early Carboniferous shift from

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).

Figure 3. Correlation

of Devonian events:

(A) extinction events;

black shales from

(B) eastern North

America, (C) central to

western North America,

and (D) Europe; and

(E) paleobotanic events

(data sources available

upon request). For

columns B–D, note that

illustrated units repre-

sent anoxic maxima as

determined by total

organic carbon content;

black shales were

deposited through

much of the late Middle

and Late Devonian in

some areas. In column

E, FAD = first appear-

ance datum; the range

and peak abundance of

Archaeopteris are shown

by dashed and solid

lines, respectively;

and the age of South

American glaciation is

restricted by occurrence

of Foerstia (F; dashed;

Caputo, 1985) and

miospores (solid; Streel,

1986). Conodont zona-

tion from Ziegler and

Sandberg (1990), and

time scale from Harland

et al. (1990).

Plants continued from p. 64

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.

Correlação entre os eventos de extinção do Devónico e a deposição de “xistos negros” na América do Norte e Europa.

Eventos paleobotânicos em especial a distribuição e abundância da Archaeopteris.

Distribuição das glaciações observadas na América do Sul.

Nota: Abundância de “xistos negros” a partir do Devónico Médio. Explorados como rochas geradores de hidrocarbonetos, especialmente gás (shale-gas) na América do Norte.

Algeo et al., 1995segunda-feira, 17 de Março de 2014

Max. tree height (m)Algeo et al., 1995


Geminospora lemurata

Archaeopteris


Streel et al., 2000

Reconstituição paleofitogeográfica da distribuição dos miosporos Geminospora lemurata e Archaeoperisaccus

durante o Devónico Médio

Geminospora lemurata

Archaeoperisaccus


Ambientes Marinhos vs. Continentais

VASCULAR LAND PLANT

EVOLUTION

Although land plants appeared inthe Late Ordovician or Early Silurianand vascular plants diversified in theLate Silurian and Early Devonian(Edwards and Berry, 1991), full colo-nization of land surfaces is likely tohave been a protracted process thatcontinued throughout the Devonianand later. Initially, the impact of landplants on their physical environmentwas negligible owing to small size,limited biomass, shallow rooting, andrestriction to moist lowland habitats.As land plants increased in size andbecame more abundant and geographi-cally widespread, they exerted a pro-gressively stronger influence on theirphysical substrate. Two evolutionaryinnovations are of major significancein this regard: (1) arborescence, or tree-sized stature, and (2) the seed habit.With the advent of supporting tissues(2° xylem, 2° cortex) in the MiddleDevonian (Fig. 3E), several groupsof vascular plants (lycopods, cladoxy-laleans, progymnosperms) exhibitedincreases in stature (Fig. 4; Chalonerand Sheerin, 1979; Mosbrugger, 1990).However, Middle Devonian treesmostly occupied riparian habitats, andflood-plain forests probably developedin the Frasnian with the appearanceof the progymnosperm Archaeopteris.This genus, which grew ~30 m high,became the dominant element of ter-restrial floras between the mid-Frasnianand mid-Famennian, but declined

rapidly with the appearance of seedplants (Fig. 3E; Beck, 1981; Gensel andAndrews, 1984; Scheckler, 1986). Seedplants spread rapidly during the latestFamennian owing to the advantagesconferred by seeds, including ability toadapt to diverse ecological conditionsand to occupy drier upland habitats(Fig. 3E; Gillespie et al., 1981; Rothwellet al., 1989).

Close temporal relations existbetween Late Devonian anoxic andextinction events and these paleo-botanic developments. First, the onsetof a protracted late Middle–Late Devo-nian interval of widespread oceanicanoxia (Fig. 3, B–D) followed closelythe advent of secondary vascular sup-porting tissues (Fig. 3E) and coincidedbroadly with rapid increases in themaximum size of vascular land plantsin the Middle Devonian (Fig. 4). Sec-ond, the F-F boundary Kellwasser eventoccurred within the mid-Frasnian tomid-Famennian interval of archaeop-terid dominance and might representthe rapid spread of this genus (Fig. 3E).Third, the D-C boundary Hangenbergevent is preceded by the appearance ofthe earliest known seeds by one con-odont zone, or about 0.5 m.y. (Fig. 3E;Gillespie et al., 1981; Rothwell et al.,1989). In each case, an important pale-obotanic development that probablyled to a large increase in root biomasspreceded major paleontologic, sedi-mentologic, and geochemical eventsby no more than a few million years.In this regard, first appearances are less

64 GSA TODAY, March 1995

Figure 2. Phanerozoicrecords exhibiting Late

Devonian anomalies:(A) dominant Phanero-

zoic reef-buildinggroups (James, 1983);(B) marine carbonate!13C (Berner, 1989);

(C) atmospheric CO2(RCO2 is the ratio of

CO2 at a given time inthe past to that at

present; Berner, 1994);(D) North American

dolomite abundance(as volume percent of

total carbonate; thispaper); (E) marine sul-fate !34S (Holser et al.,

1989); (F) abioticmarine carbonate !18O(Lohmann, 1988); (G)North American sedi-

ment survival rates (thispaper); and (H) miner-

alogy of clay mineralassemblages (Weaver,1967). PDB is Peedee

belemnite



information about the key themes andkey points presented at the forum.

In the 1970s and 1980s, the extrac-tive-industries (petroleum and miner-als)–oriented companies hired moregraduating earth science students thanany other category of employer, for-merly providing employment to abouttwo-thirds of all graduates. Employ-ment and employment opportunitiesin these industries have declinedsharply over the past decade. Domesticgrowth is expected to be flat. Con-tributing to the continuing low levelof employment is the fact that extrac-tive companies are increasingly movingtheir operations overseas, where theyare hiring foreign nationals.

Employment opportunities inenvironmentally oriented companiesare the brightest of those in any geoin-dustry. However, the evolution andmaturation of the industry and itstechnologies has reduced employmentopportunities when compared to therecent past. Competitive pressures haveprompted personnel restructuring,including layoffs in some areas and the

replacement of higher paid managerswith lower paid, entry-level staff. Slowto moderate growth in employment isanticipated and should provide thegreatest opportunities to students withB.S. and M.S. degrees. Continuation ofthe federal government’s dominationof environmental regulations will prob-ably favor large, multidisciplinaryfirms.

Shrinking budgets have beenand will continue to be responsible fordecreasing employment of earth scien-tists by state and federal governmentagencies. The number of state-fundedpositions for professional staff in stategeological surveys has declined about8% in the past four years, while thenumber of contract employees hasincreased. Positions in the USGS havealso declined over the past decade.These trends are likely to continue.Even larger reductions have occurredin the U.S. Bureau of Mines.

In academia, the number of facultypositions is expected to remain con-stant over the next 5–10 years. Facultypositions supported by external fundsprobably will decrease, because manyof these positions do not provide rev-

enue to the universities. Some universi-ties are using postdoctoral fellows inplace of teaching assistants. This cre-ates more temporary slots for scientistsseeking permanent positions.

Earth science job opportunitiesin the coming decade likely will be inpositions that address important soci-etal problems, such as natural hazards,health, infrastructure, energy andresource needs, and environmentalprotection and remediation. Employerswill be seeking geoscientists who haveknowledge of aqueous geochemistry,earth surface processes, and theyoungest part of the geological timescale. Particularly attractive will begraduates with a solid foundation infundamental science (biology, chem-istry, engineering, geology, physics),mathematics, and computer scienceand with skills in foreign languageand oral and written communication.Forum participants expressed the sensethat the generally prevailing collegeand university earth science curricu-lum, which has changed little over thepast 50 years, must be redesigned toprovide a multidisciplinary base thatintegrates scientific knowledge andbasic scientific skills that would allowstudents to adapt to changing societalpriorities. Although the forum did notprovide a specific plan for revision,participants agreed that earth sciencesocieties and colleges and universitiesshould encourage reform in severalways, including:

• Bringing together the academiccommunity, professional societies,government, and industry to coor-dinate curricular reform.

• Developing benchmarks for thecontent of courses.

• Providing recognition and awardsfor innovative courses, curricula,and teaching excellence.There was a consensus that earth

science societies need to become moreproactive in promoting the earth sci-

ences to policy makers and the publicat large in order to ensure the contin-ued viability of the profession. Thesocieties could promote earth sciencesin several ways:

• Encouraging colleges and uni-versities to provide integrativeearth science courses and experi-ences for nonmajors, particularlyfor preservice and in-service K–12teachers.

• Working with colleges and uni-versities to inject earth scienceperspectives into allied professions,such as engineering, and to pre-pare earth science students fornontraditional careers in areassuch as law, business, and politics.

• Working with academia and indus-try to provide access to lifelong,high-quality learning for practicingearth scientists.

• Encouraging and, where appropri-ate, coordinating the participationof earth scientists in local, state,and federal policy debates anddecisions.The key word at the forum was

change. Employment opportunities forearth scientists have decreased signifi-cantly over the past decade, and thispace is likely to continue into thefuture. In the face of this rapid change,colleges and universities need to beconstantly assessing their curricula.Geoscientists must work together toensure a well-educated and skilledearth science workforce that will beable to meet the future needs of society,such as preserving the environmentand providing an adequate supply ofnatural resources for a growing popula-tion. Perhaps the most important rolefor earth science societies in managingthis change is the collection and dis-semination of human resource datathat can serve as the basis for wisedecision making on employment andeducation issues. !

Trends continued from p. 47

Southeastern Section Meeting to Include Symposium on Energy and the Environment

A symposium, “Energy and the Environment in the Next Century,” at the GSASoutheastern Section meeting in April will feature speakers from both the privateand public sectors. The objective of the symposium, sponsored by GSA’s Institutefor Environmental Education, is to look at the many facets of the issue of energyuse and its effects on the environment, according to organizer Otto Kopp (Univer-sity of Tennessee).

Some of the subjects will be: acceptable levels of toxicity, fossil fuels and CO2,the economics of nuclear power, and techniques for monitoring the environmentalimpact of energy production. The symposium will be open to all attendees at theGSA Southeastern Section meeting in Knoxville, Tennessee, April 6–7, 1995.

For further information, contact Otto C. Kopp, Dept. of Geological Sciences,University of Tennessee, Knoxville, TN 37996-1410, (615) 974-2366, fax 615-974-2368, E-mail: [email protected].

VASCULAR LAND PLANT

EVOLUTION

Although land plants appeared inthe Late Ordovician or Early Silurianand vascular plants diversified in theLate Silurian and Early Devonian(Edwards and Berry, 1991), full colo-nization of land surfaces is likely tohave been a protracted process thatcontinued throughout the Devonianand later. Initially, the impact of landplants on their physical environmentwas negligible owing to small size,limited biomass, shallow rooting, andrestriction to moist lowland habitats.As land plants increased in size andbecame more abundant and geographi-cally widespread, they exerted a pro-gressively stronger influence on theirphysical substrate. Two evolutionaryinnovations are of major significancein this regard: (1) arborescence, or tree-sized stature, and (2) the seed habit.With the advent of supporting tissues(2° xylem, 2° cortex) in the MiddleDevonian (Fig. 3E), several groupsof vascular plants (lycopods, cladoxy-laleans, progymnosperms) exhibitedincreases in stature (Fig. 4; Chalonerand Sheerin, 1979; Mosbrugger, 1990).However, Middle Devonian treesmostly occupied riparian habitats, andflood-plain forests probably developedin the Frasnian with the appearanceof the progymnosperm Archaeopteris.This genus, which grew ~30 m high,became the dominant element of ter-restrial floras between the mid-Frasnianand mid-Famennian, but declined

rapidly with the appearance of seedplants (Fig. 3E; Beck, 1981; Gensel andAndrews, 1984; Scheckler, 1986). Seedplants spread rapidly during the latestFamennian owing to the advantagesconferred by seeds, including ability toadapt to diverse ecological conditionsand to occupy drier upland habitats(Fig. 3E; Gillespie et al., 1981; Rothwellet al., 1989).

Close temporal relations existbetween Late Devonian anoxic andextinction events and these paleo-botanic developments. First, the onsetof a protracted late Middle–Late Devo-nian interval of widespread oceanicanoxia (Fig. 3, B–D) followed closelythe advent of secondary vascular sup-porting tissues (Fig. 3E) and coincidedbroadly with rapid increases in themaximum size of vascular land plantsin the Middle Devonian (Fig. 4). Sec-ond, the F-F boundary Kellwasser eventoccurred within the mid-Frasnian tomid-Famennian interval of archaeop-terid dominance and might representthe rapid spread of this genus (Fig. 3E).Third, the D-C boundary Hangenbergevent is preceded by the appearance ofthe earliest known seeds by one con-odont zone, or about 0.5 m.y. (Fig. 3E;Gillespie et al., 1981; Rothwell et al.,1989). In each case, an important pale-obotanic development that probablyled to a large increase in root biomasspreceded major paleontologic, sedi-mentologic, and geochemical eventsby no more than a few million years.In this regard, first appearances are less

64 GSA TODAY, March 1995

Figure 2. Phanerozoicrecords exhibiting Late

Devonian anomalies:(A) dominant Phanero-

zoic reef-buildinggroups (James, 1983);(B) marine carbonate!13C (Berner, 1989);

(C) atmospheric CO2(RCO2 is the ratio of

CO2 at a given time inthe past to that at

present; Berner, 1994);(D) North American

dolomite abundance(as volume percent of

total carbonate; thispaper); (E) marine sul-fate !34S (Holser et al.,

1989); (F) abioticmarine carbonate !18O(Lohmann, 1988); (G)North American sedi-

ment survival rates (thispaper); and (H) miner-

alogy of clay mineralassemblages (Weaver,1967). PDB is Peedee

belemnite



information about the key themes andkey points presented at the forum.

In the 1970s and 1980s, the extrac-tive-industries (petroleum and miner-als)–oriented companies hired moregraduating earth science students thanany other category of employer, for-merly providing employment to abouttwo-thirds of all graduates. Employ-ment and employment opportunitiesin these industries have declinedsharply over the past decade. Domesticgrowth is expected to be flat. Con-tributing to the continuing low levelof employment is the fact that extrac-tive companies are increasingly movingtheir operations overseas, where theyare hiring foreign nationals.

Employment opportunities inenvironmentally oriented companiesare the brightest of those in any geoin-dustry. However, the evolution andmaturation of the industry and itstechnologies has reduced employmentopportunities when compared to therecent past. Competitive pressures haveprompted personnel restructuring,including layoffs in some areas and the

replacement of higher paid managerswith lower paid, entry-level staff. Slowto moderate growth in employment isanticipated and should provide thegreatest opportunities to students withB.S. and M.S. degrees. Continuation ofthe federal government’s dominationof environmental regulations will prob-ably favor large, multidisciplinaryfirms.

Shrinking budgets have beenand will continue to be responsible fordecreasing employment of earth scien-tists by state and federal governmentagencies. The number of state-fundedpositions for professional staff in stategeological surveys has declined about8% in the past four years, while thenumber of contract employees hasincreased. Positions in the USGS havealso declined over the past decade.These trends are likely to continue.Even larger reductions have occurredin the U.S. Bureau of Mines.

In academia, the number of facultypositions is expected to remain con-stant over the next 5–10 years. Facultypositions supported by external fundsprobably will decrease, because manyof these positions do not provide rev-

enue to the universities. Some universi-ties are using postdoctoral fellows inplace of teaching assistants. This cre-ates more temporary slots for scientistsseeking permanent positions.

Earth science job opportunitiesin the coming decade likely will be inpositions that address important soci-etal problems, such as natural hazards,health, infrastructure, energy andresource needs, and environmentalprotection and remediation. Employerswill be seeking geoscientists who haveknowledge of aqueous geochemistry,earth surface processes, and theyoungest part of the geological timescale. Particularly attractive will begraduates with a solid foundation infundamental science (biology, chem-istry, engineering, geology, physics),mathematics, and computer scienceand with skills in foreign languageand oral and written communication.Forum participants expressed the sensethat the generally prevailing collegeand university earth science curricu-lum, which has changed little over thepast 50 years, must be redesigned toprovide a multidisciplinary base thatintegrates scientific knowledge andbasic scientific skills that would allowstudents to adapt to changing societalpriorities. Although the forum did notprovide a specific plan for revision,participants agreed that earth sciencesocieties and colleges and universitiesshould encourage reform in severalways, including:

• Bringing together the academiccommunity, professional societies,government, and industry to coor-dinate curricular reform.

• Developing benchmarks for thecontent of courses.

• Providing recognition and awardsfor innovative courses, curricula,and teaching excellence.There was a consensus that earth

science societies need to become moreproactive in promoting the earth sci-

ences to policy makers and the publicat large in order to ensure the contin-ued viability of the profession. Thesocieties could promote earth sciencesin several ways:

• Encouraging colleges and uni-versities to provide integrativeearth science courses and experi-ences for nonmajors, particularlyfor preservice and in-service K–12teachers.

• Working with colleges and uni-versities to inject earth scienceperspectives into allied professions,such as engineering, and to pre-pare earth science students fornontraditional careers in areassuch as law, business, and politics.

• Working with academia and indus-try to provide access to lifelong,high-quality learning for practicingearth scientists.

• Encouraging and, where appropri-ate, coordinating the participationof earth scientists in local, state,and federal policy debates anddecisions.The key word at the forum was

change. Employment opportunities forearth scientists have decreased signifi-cantly over the past decade, and thispace is likely to continue into thefuture. In the face of this rapid change,colleges and universities need to beconstantly assessing their curricula.Geoscientists must work together toensure a well-educated and skilledearth science workforce that will beable to meet the future needs of society,such as preserving the environmentand providing an adequate supply ofnatural resources for a growing popula-tion. Perhaps the most important rolefor earth science societies in managingthis change is the collection and dis-semination of human resource datathat can serve as the basis for wisedecision making on employment andeducation issues. !

Trends continued from p. 47

Southeastern Section Meeting to Include Symposium on Energy and the Environment

A symposium, “Energy and the Environment in the Next Century,” at the GSASoutheastern Section meeting in April will feature speakers from both the privateand public sectors. The objective of the symposium, sponsored by GSA’s Institutefor Environmental Education, is to look at the many facets of the issue of energyuse and its effects on the environment, according to organizer Otto Kopp (Univer-sity of Tennessee).

Some of the subjects will be: acceptable levels of toxicity, fossil fuels and CO2,the economics of nuclear power, and techniques for monitoring the environmentalimpact of energy production. The symposium will be open to all attendees at theGSA Southeastern Section meeting in Knoxville, Tennessee, April 6–7, 1995.

For further information, contact Otto C. Kopp, Dept. of Geological Sciences,University of Tennessee, Knoxville, TN 37996-1410, (615) 974-2366, fax 615-974-2368, E-mail: [email protected].

Algeo et al., 1995


190 M.L. Caplan, R.M. Bustin / Palaeogeography, Palaeoclimatology, Palaeoecology 148 (1999) 187–207

Fig. 2. Variation in palaeontological abundance associated with the Hangenberg Event, and characteristic lithology of the D–C interval: 1D Korn (1986); 2 D Korn (1992); 3 D Brauckmann and Brauckmann (1986); 4 D Poty (1986); 5 D Vanguestaine (1986); 6 D Johnsonet al. (1985), Sandberg et al. (1988). Note Hangenberg Bio-Event occurs prior to D–C boundary. * Bio-events (Walliser, 1996a), 1 Dannulata Event, 2 D Hangenberg Event, 3 D crenulata Event; miospore zones (Bless et al., 1992).

of anoxic environments in Europe, North Americaand China and deposition of the Lower Alum Shale(Becker, 1993; Fig. 2).A wide diversity of marine phyla was affected by

the global Hangenberg Event, particularly at the baseof the Hangenberg Shale (Walliser, 1984a). Ammo-noids (the clymeniids and goniatites), trilobites andconodonts were most severely affected, and to alesser degree the agnathan fishes, acritarchs, placo-derms, homalozoans, cystoids, foraminifera, brachio-pods, corals, blastoids, stromatoporoids and ostra-cods (Walliser, 1984a,b; Bless et al., 1986; Vangues-taine, 1986; Walters, 1990; Simakov, 1993). Extinc-tion occurred in either an abrupt, stepwise or grad-ual manner. Abrupt declines were experienced bythe conodonts, trilobites and ammonoids (Walliser,1984a,b; Brauckmann and Brauckmann, 1986; Korn,1986; Simakov, 1993; Walliser, 1996a,b; McGhee,

1996), whereas declines to the foraminifers, brachio-pods, corals, cystoids, stromatoporoids, blastoids andostracods were more gradual and=or stepwise in na-ture (e.g., Kalvoda, 1986; Poty, 1986; Walters, 1990;Simakov, 1993; Wang et al., 1993a).Severity of ammonoid extinction almost matched

that of the F–F mass extinction event (Walliser,1984a; House, 1985; Becker, 1993). Lineages ofmost surviving groups of the F–F mass extinctionevent were terminated at the D–C mass extinctionevent (Fig. 2; Walliser, 1984b; Becker, 1992, 1993).Ammonoid diversity was highest in the upper sub-armata zone followed by a gradual decline towardthe upper paradoxa zone of the Wocklumeria Stufe(Fig. 2; Korn, 1992). The total number of ammonoidfamilies lost at the Hangenberg bio-event was tenincluding the Tornoceratidae, Posttornoceridae, Spo-radoceratidae and Clymeniidae (House, 1989). Only


Perturbações em organismos marinhos

Caplan & Bustin, 1999




( )M. Streel et al.rEarth-Science ReÕiews 52 2000 121–173 129

ing about a half million years in duration. We areaware of course that evolutionary events cannot bedemonstrated to occur at the same rate in any strati-

!graphic interval see also Fordham, 1992 for discus-.sion . But in order to subdivide the Late Devonian

Epochs, the conodont-based scale is the most oftenused and, moreover, its subdivision in time units

! .makes the calibration of events easier Fig. 6 .Originally, Late Devonian conodont zonal bound-

aries were dated backwards from a starting point of 0Ma at the DCB. Ties to the radiometric time scalewere avoided because of the often controversial dat-

! .ings McGhee, 1996, p. 7 proposed for the DCB! .Sandberg et al., 1997 . The finding, by Claoue-Long´

! .et al. 1992, 1993 , of a new, biostratigraphicallycontrolled zircon fission-track date of 353.2 Ma froma bentonite layer deposited just above the base of theEarliest Carboniferous sulcata Zone led Sandberg

! .and Ziegler 1996 to redate the DCB to 354 Ma.! .Recently, Tucker et al. 1998 claimed to have

obtained new U–Pb zircon dates from a series of!volcanic ashes closely tied supposed better than

. ! .before to biostratigraphic zones. 1 The Late Fa-mennian new data, which are assumed by Tucker et

! .al. 1998 to date the Fa2d part of the Belgian scale,i.e., the Late expansa conodont Zone, are not con-firmed by facts. They are based on a palynologicalanalysis of the Carrow Formation of the PiskaheganGroup in southern New Brunswick made by McGre-

! .gor and McCutcheon 1988 . However, these authorscould not really distinguish between their

! .pusillites–lepidophyta Zone Fa2d and flexuosa–! .cornuta Zone Fa2c . Indeed, one single specimen of

!one species only Retispora lepidophyta?, pl. 2, figs..15, 16 has been found which might indicate the

pusillites–lepidophyta Zone. But, with our present!experience of the R. lepidophyta Morphon Stee-

.mans et al., 1996 , we believe that this specimen!most probably belongs to R. cassicula now R.

.macroreticulata which first occurs in the Latest!marginifera conodont Zone in Belgium Streel and

.Loboziak, 1996, text-fig. 3 . In the absence of R.!lepidophyta, the single specimen of V. pusillites V.

.pusillites sensu lato, pl. 3, fig. 7 might belong to thepusillites–fructicosa Zone of Richardson and Ahmed! .1988 , the base of which is in the uppermost part ofthe Ellicott Formation or in the lowermost part of the

! .Cattaraugus Formation in New York State USA ,

Fig. 7. Diversity of miospore species in the Devonian. Data from! .Richardson and McGregor 1986 . Modified from Boulter et al.

! . !1988 , after McGhee 1996, fig. 4.24 redrawn. Used with the.permission of the author . The diversity of miospore species

shows a maximum during the Givetian and the Frasnian and arather dramatic drop between the Frasnian and the Famennian.

i.e., within the Latest marginifera Zone, thus 4 to 5! .millions years older than the DCB. 2 The new

Early Frasnian data are claimed by Tucker et al.! .1998 to characterize the punctata to Late hassiconodont Zones. It is based on an unpublished deter-mination by them of P. punctata from the Chat-tanooga Shale at Little War Gap, east Tennessee! .USA , formerly attributed by Dennison and Boucot! .1974 to the Eifelian on the basis of brachiopoddata. However, the presence of the brachiopodLeiorhynchus limitare in the Tioga tuffaceous bedsat the base of the Chattanooga Shale still supports an

!Eifelian age a late Eifelian age according to P..Sartenaer, personal communication, December 1999 .

Consequently, we believe that the Late Famennian! . !363.6"1.6 Ma and Early Frasnian 381.1"1.3

. ! .Ma dates given by Tucker et al. 1998 are poorlyconstrained biostratigraphically and, thus, for thetime being, we prefer to adopt Sandberg and Ziegler’s

( )M. Streel et al.rEarth-Science ReÕiews 52 2000 121–173132

! .Gregor 1986 . Eighteen species gradually disappearand 25 gradually appear in the interval spanning

from Zone AIVB to the beginning of Zone AVB. Two!species Diducites poljessicus and Grandispora gra-

.cilis marking the base of the torquata-gracilis As-! .semblage Zone of Richardson and McGregor 1986

occur within Zone AIVB. Therefore, the sharp! .turnover Fig. 11 illustrated by Richardson and Mc-! .Gregor 1986, fig. 3 cannot be observed in the

Boulonnais area. The Latest Frasnian is characterized!by a miospore assemblage the C. deliquescens–V.

.eÕlanensis Zone from eastern Europe which, excep-tionally during the Frasnian, is rather similar both inequatorial and tropical regions suggesting that theequatorial climatic belts had reached a maximumwidth in the Latest Frasnian.

4.2. Land plants

! .According to Boulter et al. 1988 and Raymond! .and Metz 1995, figs. 2 and 3 , the diversity of land

plant genera at substage boundaries also shows aclear Late Frasnian–Middle Famennian minimum! .Fig. 8 . The number of genera and number ofinvestigated localities are rather low for this intervalbut statistical tests suggest that poor sampling does

!not cause the observed diversity minimum Raymond.and Metz, 1995, table 6 . It is not possible, however,

to discriminate between the Late Frasnian and theEarly–Middle Famennian data so that no conclusioncan be drawn for the time being.

4.3. Acritarchs

! .Although Tappan 1971, fig. 1 clearly shows thatacritarch diversity collapses at the DCB, and not at

! .the FFB, McGhee 1996 used the diversity evalua-!tion of acritarchs including Prasinophycean green

. !algae at a poor resolution level, i.e., the Epoch see

Fig. 9. Composite stratigraphic ranges of miospores across theFFB, conodont and miospore Zonation, from western Canada,

! .after Braman and Hills 1992, text-fig. 5 modified . The loss inmiospore diversity obviously starts in the Late Frasnian. Eighty-

! .five taxa have last occurrences LO taxa and only 14 first! .occurrences FO taxa in the Late Frasnian to Middle Famennian

!interval 46 LO against 5 FO in the Late Frasnian which has lessthan 2 Ma in duration, and 39 LO against 9 FO in the Early and

.Middle Famennian which have altogether 5 Ma in duration .


Perturbações nas plantas terrestres

Streel et al., 2000


( )M. Streel et al.rEarth-Science ReÕiews 52 2000 121–173140

! .Fig. 18. Palynomorph stratigraphic distribution near the FFB at Hony, after Streel and Vanguestaine 1989, fig. 2 modified . Lithology and! . ! . ! .conodont Zones and Biofacies after Sandberg et al. 1988, fig. 9 redrawn . Oxygen Minimum Zone OMZ after Claeys et al. 1996, fig. 7 .

! .Sedimentological analysis based on microfacies study X. Devleeschouwer, personal communication, June 1999 indicates the existence of! .two relatively different shallow marine domains: 1 in the lower part of the lower unit, a zone where the sea floor was affected by storm

! .waves but not by fair-weather waves and where sediments show evidence of frequent storm reworking; 2 in the remaining part of thelower unit and the major part of the upper unit, a zone where sediments were deposited below the storm wave base. Allochthonous faunaland floral elements were transported from nearshore environments to deeper environments. In the uppermost dark-grey shale, microfacies

! .indicate a brief return to shallower conditions where sparse and distal tempestite deposition may occur. Acritarchs spiny acritarchs show a! .continuous decrease from 10,000 sp.rgr.sed. at the base of the lower unit to nothing at its top and in the upper unit this figure . They

increase again up to 6,000 sp.rgr.sed. in the olive-green shale above the top of the Famennian limestone. Miospores oscillate between 600and 2800 sp.rgr.sed. along the lower unit. They almost disappear in most of the upper unit except for the last 10 cm where they increaseagain and become more abundant in the olive-green shale on the top of the first Famennian limestone.

hesitated to conclude that similarity implies contem-poraneity, although noting that the dark-grey shalespresent at Hony might be missing at Sinsin. Subse-

! .quently, Casier and Devleeschouwer 1995 discov-ered a very rich and well preserved ostracod fauna inthe upper 5 cm of the dark-grey shales. This assem-blage is indicative of a brackish-water environmentwith strong marine influence and clearly correspondsto a regression in that part of the shales which Streel

! .and Vanguestaine 1989 had attributed to a trans-gression.We propose therefore that, at Sinsin, paly-

nomorphs originated from that part of the shelf basin

where the abundance of acritarchs is progressively! .reduced seaward hypothesis B of Fig. 19 . We

propose also that the similarity in the concentrationcurves of miospores and acritarchs in both Hony andSinsin sections is indicative of their contemporane-ity, also with the significant difference that a majorpart of the dark-grey shale at Hony is missing at

! .Sinsin Fig. 20 .In both sections, we observe successively a re-

gression in the last Frasnian limestones or shales! .containing limy lenses Sandberg et al., 1988 , a

transgression in most of the shaly interval culminat-ing at Hony in the development of oxygen-poor

Streel et al., 2000


(Bélgica)


Problemas de datação

(Streel et al., 2000). In any case, the D–C extinction event could be more profound than

previously thought (see summary in Walliser, 1996 and Caplan and Bustin, 1999).

3. Timing of the key boundaries

The second prominent uncertainty in Late Devonian event stratigraphy is tied to doubtful

timing of the key boundaries. Almost all the Devonian ages are in flux, and appropriate

time calibration is urgently needed. This is a principal goal of the Subcommission on

Devonian Stratigraphy, but the progress is very slow. As shown in Figure 4, the numerical

age of the F–F boundary remains highly controversial and has ranged from 376.5 Ma

(Tucker et al., 1998) to 364 Ma (Compston, 2000) to 374.5 Ma (Gradstein et al., 2004; see

also Gehmlich et al., 2000). However, a date around 376 Ma appears more probable after

new U-Pb zircon analysis from a bentonite layer, intercalated between the two KW horizons

at Steinbruch Schmidt, provided a date of 376.1 � 1.6 Ma (Kauffmann et al., 2004).

A lack of consistent numerical dates hampers any estimation of true rates of biodiversity

changes across the key intervals, as e.g. estimated ages for the Famennian Stage still range

from 5.3 to 14.7 Ma (Fig. 4). This hindrance also precludes a definitive acceptance or rejec-

tion of the impact vs. volcanism models for extinction. For example, the central point in

the impact discussion remains the timing of the Siljan crater, determined as 368 � 1 Ma

(see McGhee, 1996, Table 8.3). As stressed by Racki (1999b, p. 620): “although this crater

is real, we cannot say exactly whether the documented impact occurred near the F–F

Toward understanding Late Devonian global events 11

350

360

370

380

Ma

CARBON.

FRASNIAN

GIVETIAN

EIFELIAN

CARBON- IFEROUS

GIVETIAN

FRASNIAN

Tucker et al.

(1998)Compston

(2000)

CARBON- IFEROUS

EIFELIAN

GIVETIAN

FRASNIAN

FAMEN-NIAN FAMEN

-NIAN

BIOSTRATI- GRAPHICCALIBRATION

RADIOMETRIC AGES

FAMEN-NIAN

Silj

an c

rate

r

Liza

rd o

phio

lite

Gradsteinet al.

(2004)

CARBON- IFEROUS

FRASNIAN

FAMEN-NIANFAMEN

-NIAN

375.

0

1.7

Ma

Kau

fman

n et

al.

(200

4)

SELECTED EVENTS

Woo

dlei

gh c

rate

r

Kol

a in

trus

ion

Sib

eria

n-tr

aps

Ziegler & Sandberg

(1996)

Figure 4. Comparison of four most recent Devonian time scales, and the selected Earth-bound and extraterres-

trial event signatures to show their ambiguous absolute timing within established dating errors of the F–F bound-

ary. Ages compiled from Kramm et al. (1993), Beard et al. (1996), Kravchinsky et al. (2002), Courtillot and

Renne (2003), Vaughan and Scarrow (2003), Pervov et al. (2005), Reimold et al. (2005) and Uysal et al. (2005).

Fronteira F/F 374,5 Ma (Ogg et al., 2008)

Racki, 2005


Fig. 7. Comparison of running mean (time window of 0.3 Ma), locfit curve (with 90% confidence interval), sea-level changes (Johnson et al., 1985,1996) and occurrence of black shale deposits (black shales in black, dark grey shales in grey) in Europe/North Africa (A) and Laurentia (B). Eventsaccording to House (2002).

81W. Buggisch, M.M. Joachimski / Palaeogeography, Palaeoclimatology, Palaeoecology 240 (2006) 68–88

Fig. 1. A: European Variscan terranes according to reconstruction of Franke (2002) with sample localities of Buggisch and Mann (2004) and thisstudy. B: Lithologic columns and stratigraphic range of studied sections. 1—Cantabrian Mountains, 2—Pyrenees, 3—Montagne Noire (3a—Puechde la Suque, 3b—Pic de Bissous, 3c—La Serre C), 4—Carnic Alps Timau, 5—Prague Syncline, 6—Saxothuringian (6a—Köstenhof, 6b—Kahlleite, 6c—Vogelsberg), 7—Harz Mountains (Hühnertal), 8 to 14—Rheinisches Schiefergebirge (8—Blauer Bruch, 9—Hengstebeck, 10—Beringhausen, 11—Benner, 12—Drever, 13—Anseremme, 14—Geron-Celles).

70 W. Buggisch, M.M. Joachimski / Palaeogeography, Palaeoclimatology, Palaeoecology 240 (2006) 68–88

Perturbações geoquímicas

Excursões positivas δ13Ccarb relacionadas com soterramento de matéria orgânica (xistos negros).

Excursões positivas de δ18O relacionadas com períodos glaciares.

Buggisch & Joachimski, 2006


northern Canada (e.g. Patchett et al., 1999; Levman and Von Bitter, 2002; Klapper et al.,

2004).

Thanks to broad international cooperation, the most comprehensively studied F–F section

from event-stratigraphical, palaeobiological and geochemical perspectives is located in

Poland, at the active Kowala quarry near Kielce, Holy Cross Mountains (see the array of arti-

cles in Racki and House, 2002, and Balinski et al., 2002; also Joachimski et al., 2001; Bond

and Zaton , 2003, and Bond et al., 2004; Fig. 9). The Kowala deep shelf-basin succession is

distinguished by uniquely immature character of the organic matter (burial temperatures did

not exceed 75°C; Belka, 1990), a key to modern geochemistry. Important results include:

● Discovery of isorenieratane and related organic compounds, diagnostic for green sulfur

bacteria (Chlorobiaceae), an evidence for photic-zone anoxia (Joachimski et al., 2001; see

also Bond et al., 2004).

18 G. Racki

P/Al x10Ni/Alx1000Al/Al+Fe+MnAl (%)

V/Alx250

Zn/Alx100Ti/Alx100

FF

terrigen

ousinput

terrigen

ousinput

hydrothe

rmal

inpu

t

basalts gypsumterrigenous rocks(mostly sandstones)

limestonesand marls

0 84 0.4 0.6 0 450 900 0 15 30

FAM

EN

NIA

NFRASNIA

Nlingu

iform

isLo

wer

triang

ularis

Middletriang

ularis

?

Figure 8. Simplified stratigraphic column of the F–F transition at the Bachu section in the Tarim basin, north-

ern China, and trends of selected event-geochemical proxies (see discussion in Racki et al., 2002), based on

Fig. 2 and analytical data from Table 1 in Hao et al. (2003). The position of the F–F boundary is approximated

by a combined biostratigraphical–chemostratigraphical approach. Note an interruption of the mafic extrusive

activity in the crucial interval, but also two white gypsum layers and a differentiated geochemical signature of

two other events, interpreted by Hao et al. (2003) as a manifestation of large-scale rifting-hydrothermal processes

in the Tarim (see also Han and Zhao, 2003), Kazakhstan and even South China basins (e.g. Ma and Bai, 2002).

The weak Ni-anomaly near the F–F boundary, however, is obviously overwhelmed by continental input possibly

paired with eutrophication and spread of anoxia (the very high V/Al ratio, but in one sample only), similar to

Iranian and S-Chinese successions (Mahmudy Gharaie et al., 2004; Chen et al., 2005).

Perturbações geoquímicas

Racki, 2005


mechanism during highstand as the cause of the F–F extinction.Orchard (1988) notes that the basin was later !lled with siliciclastics,beginning in the triangularis Zone. This may re"ect shallowing abovethe F–F boundary, and the top of T–R cycle IId, but regression andkarsti!cation in the region has generally been dated to the stageboundary (Copper, 2002), although detailed conodont biostrati-graphic constraint is lacking.

Excellent conodont biostratigraphic control is available from theMoose River Basin of northern Ontario where the F–F boundaryinterval is recorded in a mudrock succession (Levman and von Bitter,2002). At the Abitibi River section the rhenana Zone sediments consistof greenmudstones with two thin dolostone layers. The upper of thesedolostones is capped by a hardground and thin lag layer, and overlainby 4 m of black shale. Conodonts of the linguiformis Zone occur in thebasal 2–3 cm of the black shale and basal triangularis conodonts occurabove this (Levman and von Bitter, 2002). Once again, a basal lingui-formis regressionwas succeeded by a rapid rise of sea-level, associatedwith the spread of anoxic facies, that continued into the triangularisZone.

5. Conodont biofacies analysis

Many studies of sea-level change during the F–F mass extinctionhave used changes in conodont assemblages to infer a eustatic history.The results are often in con"ict with the interpretations derived fromfacies and sequence stratigraphic analysis. Early work by Sandberg(1976) identi!ed 11 biofacies along a nearshore-basinal transect. Inparticular, the genera Palmatolepis and Polygnathus were used toindicate deep and/or open waters, whilst Icriodus indicated shallow-water. Thus, Sandberg et al. (1988) demonstrated a progressiveincrease in the proportion of Icriodus elements from the linguiformisto the triangularis zones in two European sections (Hony, Belgium, andSteinbruch Schmidt, Germany) and inferred “an abrupt eustatic fallimmediately preceded the late Frasnian mass extinction and that thefall continued unabated into the early Famennian” (Sandberg et al.,1988, p. 267). This conclusion is in stark contrast to the transgression-

related anoxia and mass extinction inference of Johnson et al. (1985),published only three years before.

Sandberg et al. (1989, 2002) further developed their techniques toproduce a series of palaeobiogeographic lithofacies maps and an eventhistory, largely based on the concept of conodont biofacies, but nowalso supported by a study of the sediments that contain theseconodonts. Their event history includes the major transgressionduring the Early rhenana Zone which saw the rapid evolution anddispersal of the deep-water conodont Palmatolepis semichatovae(hence the “semichatovae transgression” — see Section 3.1 above).This is followed by an abrupt eustatic fall which occurred still withinthe Early rhenana Zone. The fall had little effect on sedimentation inthe western United States, but resulted in the cessation of carbonateplatform sedimentation in other areas (e.g. the Jefferson Formation ofMontana, Sandberg et al., 1989). A major transgression then occurredduring the Late rhenana and linguiformis Zones, leading to thewidespread establishment of basinal anoxia (Events 5 and 6 ofSandberg et al., 2002, see Fig. 7). This transgression was succeeded byEvents 7 and 8 of Sandberg et al. (2002), two pulses of regression thatbegan in the linguiformis Zone and continued into the Early triangu-laris Zone (Fig. 7). This regression is again based upon changes inconodont percentages and is also supported by an increase in theclastic content in all four lithofacies described in map 4 of Sandberget al. (1989). However, this lithofacies map corresponds to the Earlytriangularis Zone and so it is unclear why the onset of regression isplaced within the Frasnian. The subsequent transgression begins inthe Middle triangularis Zone. Sandberg et al.'s (1988, 1989, 2002) sea-level history recognises two F–F transgressive–regressive cycles, asper the original Johnson et al. (1985) curve, but it differs from that ofJohnson et al. (1985) in the timing of these eustatic changes. Theassociation of themass extinctionwith regression at the F–F boundaryis the fundamental and key difference with the Johnson et al. (1985)curve which clearly linked the mass extinction to a phase of anoxiathat spread during a transgression in the late linguiformis Zone.

So why is there such a discrepancy in these sea-level interpreta-tions? Sandberg et al. (1988) rely heavily on the assumption that

Fig. 7. Detailed sea-level history across the F–F boundary, reproduced from Sandberg et al. (2002). Lithologic key as in Fig. 4. Note that shaded lithologies represent dark grey to blacklimestones.

115D.P.G. Bond, P.B. Wignall / Palaeogeography, Palaeoclimatology, Palaeoecology 263 (2008) 107–118

Variações eustáticas do nível do mar

Bond & Wignall, 2008


Grandes Províncias Ígneas (LIP’S)

http://www.geolsoc.org.uk/Geoscientist/Archive/November-2012/Volcanism-impacts-and-mass-extinctions-2




Impacto de meteorítos





Conjugação de vários dados geológicos para a fronteira Frasniano - Fameniano





A hipótese da evolução das plantas como causas das extinções do Devónico Superior

Ciclo hidrológico e meteorização pedogénica

Pré-Devónico

Elevada carga sedimentar

Meteorização física rápida Solos

Solos

Protosolo pouco espesso

Horizontes do solo de difícil reconhecimento

Sedimentos imaturos

Aumento da espessura dos solos e formação de horizontes definidos

Aumento do tempo de contacto minerais-água

Maior maturidade dos sedimentos

Devónico e pós-Devónico

Aumento do tempo de residência dos sedimetos

Aumento da descarga de águas subterrãneas

Aumento da evapo-transpiração

Estabilização dos canais

Estabilização das vertentes

Algeo et al., 2001


A evolução das plantas levou à formação de solos mais espessos e à formação dos primeiros jazigos de carvão e consequente “sequestro” de carbono,

Algeo et al., 2001


Plantas e Solos


Redução da erosão, maior tempo de residência dos minerais e meteorização química (ácidos orgânicos) e física mais extensa.Aumento da espessura dos solos e começaram a organizarem-se em horizontes distintos. Ocorre a formação e novos minerais de argila (caulinite, esmectites, laterites). Os novos solos ajudam a estabilizar vertentes e canais e a cobertura vegetal absorve grandes quantidades de água e fenómenos com as enchentes são menos destructivas. Grandes quantidades de nutrientes orgânicos e inorgânicos são levados pelos rios para o meio marinho.Aumento da meteorização química dos silicatos (Ca e Mg), por aumenta o tempo de residência dos minerais nos solos. Aqueles elementos dissolvidos na água dos rios podem chegar ao meio marinho e depositarem como carbonatos (calcários e dolomitos), diminuindo o CO2 atmosférico.O sequestro de grandes quantidades de Corgânico (carvão, mat. orgânica dos Black Shales) e carbono inorgânico (carbonatos), reduziu os níveis de CO2 atmosférico (arrefecimento global).

Raízes mais profundas




Efeitostransitórios

Efeitos longos no tempo

Intensa formação de solos

Primeiras florestas

Plantas com sementes

Aumento da carga sedimentar

Aumento do fluxo de

nutrientes

Meteorização dos silicatos remove CO2

Estabilização das paisagens

Aumento das taxas de

sedimentação Fenómenos de eutrofização

ANÓXIA

“Xistos Negros”

Extinções

Aumento do soterramento de

Corg

Carbonatos enriquecidos em

δ13C

Aumento do soterramento de sulfuretos (pirite)

Sulfatos enriquecidos em

δ34S GLACIAÇÃO

Diminuição do CO2 atmosférico

Arrefecimento global

Desenvolvimento de perfis de

solos “modernos”

Aumento da abundância da

caulinite e esmectite

Aumento da maturidade textural das

rochas clásticas

Carbonatos enriquecidos em

δ18O

Dolomitos pouco

abundantes

Água do mar saturada em

CaCO3



Pluma Mantélica

Astenosfera

Litosfera continentalLitosfera Oceânica

Erupção & levantamento

Pluma mantélica ascende até à base da litosfera oceânica e funde por descompressão formando uma grande intrusão submarina.

Deslocamento da água do mar

Transgressão

Àgua do mar ácida

Fluidos hidrotermais com elementos traço

Aumento de Fe nas

águas superficiais

CO2

CO2 removido da

atmosfera

Aumento da productividade

orgânica

Oxidação da matéria orgânica

Água do mar empobrecida em oxigénio

Oxidação dos elementos

traçoÁguas

superficiais quentes

Carbonatos dissolvidos

Aumento da meteorização

dos continentesEvaporação das

águas superficiais

Circulação oceânica induzida

Aumento da productividade

orgânica

Upwelling de nutrientes

Oxidação da matéria orgânica

Água do mar empobrecida em oxigénio

Perturbação nos padrões de

circulação oceânica

Eventos anóxicos nos oceanos

ExtinçõesDeposição de “xistos

negros”




Carbonífero

Devónico

Pedra Ruiva


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