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TriassicJurassic boundary events: Problems, progress, possibilities
1. Problems
As for most geological period boundaries, the
TriassicJurassic (TJ) transition, 200 million years
ago, was a critical juncture in Earth history during which
profound biotic and environmental changes took place.
Early comparisons with the end-Cretaceous extinction
and the involvement of extraterrestrial impact have now
largely, although not entirely, given way to more Earth-
bound explanations of events. At the TJ boundary the
supercontinent Pangaea, which had dominated the
palaeogeographic face of the Earth for the previous
100 million years, began a fragmentation that has
lasted through to the present day. The most obvious
manifestation of this process was the production of an
estimated two and a half million cubic kilometres of
magma with a focus at the centre of Pangaea, and now
known as the Central Atlantic Magmatic Province, or
CAMP. At more-or-less the same time profound
changes took place in the key elements of the biosphere,
most notably and obviously in the marine carbonate
producing organisms, including those upon which we
rely for precise stratigraphic correlation such as
ammonites. The case for a dominant volcanic deus ex
machina now looks incontestable, even if the origin of
the volcanism and the precise mechanisms by which
environmental changes were driven require much
further explanation.
Details of timing are crucial for understanding cause
and effect relationships in Earth history, and the lack of a
reliable and widely applicable biostratigraphic frame-
work has greatly hampered our understanding of TJ
events. It is also plainly the case that in order to
reconstruct past events, a physical record of their
passing is essential. Here again the TriassicJurassic
boundary has proved problematic because complete
marine sedimentary successions are both few and not
very far apart, an observation that has strongly
suggested unusually low global sea levels. The relative
lack of good marine successions has also delayed the
definition of the boundary and the selection of a global
stratotype section and point (GSSP); at the time of
compilation of this collection of papers decisions had
not been made.
In order to facilitate advances in these major issues,
IGCP Project 458 was set up in 2001 under the
leadership of the editors of this special issue. The
project was conceived as multi-disciplinary with the aim
of integrating palaeontological, stratigraphical, sedi-
mentological, geochemical, geochronological, palaeo-
magnetic and mineralogical data from TJ boundary
sections globally. Amongst the principal activities we
anticipated were: field studies directed towards previ-
ously known localities as well as recently or newly
discovered ones; compilation of global databases with
improved and revised taxonomy, biochronology and
palaeobiogeography of major fossil groups, and analysis
of patterns of the end-Triassic extinction and Early
Jurassic recovery; new radiometric ages and high reso-
lution biostratigraphic correlation to establish a reliable
temporal framework; assessment of environmental
perturbations and their role in different extinction
scenarios using geochemical proxy methods; further
studies of the Central Atlantic Magmatic Province and
the search for a hypothetical end-Triassic impact to
provide clues to the trigger of global environmental
change. The overarching view was that reconstruction
of the end-Triassic events would use an Earth systems
approach to integrate all new findings into the most
plausible models.
The papers collected in the present volume individ-
ually touch upon many of the areas of study anticipated
for IGCP project 458. For convenience we have grouped
the papers into four main thematic sections, whilst
recognizing that many of them span several of these
topics. Some of the most important results in terms of
relative timing of events around at boundary are
summarized in Fig. 1.
Palaeogeography, Palaeoclimatology, Palaeoecology 244 (2007) 110
0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved.
Fig. 1. Relative timing of major events around the TJ boundary, as observed in key sections discussed in this volume. Successions are correlated on the basis of: 1) carbon isotope stratigraphy; 2)
ammonite biostratigraphy; 3) radiolarian biostratigraphy, and; 4) magnetostratigraphy. QCI= Queen Charlotte Islands; OM = Orange Mountain; LU = Lower Unit. Comments on P. tilmanni from von
Hillebrandt (pers comm.).
2. Progress
2.1. The stratigraphic record
The first set of six papers present syntheses of the
record of TJ boundary events, most in broadly Tethyan
locations. Relatively deep-water settings provide the best
opportunities for determination of the sequence of
stratigraphic events across the TJ boundary. The
carbonate succession at Csővár, Hungary, was deposited
in an intra-platform basin that exhibits relatively constant
sedimentation through the boundary interval. The
section has previously yielded evidence of a negative
carbon-isotope anomaly in both bulk carbonate and
organic matter co-incident with the palaeontologically
defined boundary as far as this could be identified on
the basis of scarce ammonites. In a new study, Pálfy et al.
present a truly integrated stratigraphic dataset. The new
data lead to important negative and positive findings.
Included amongst the most important observations is the
rare occurrence of the conodont Neohindeodelladetrei
3 m above the first definitively Jurassic psiloceratid
ammonite. Although it is difficult to categorically rule
out reworking (redeposited beds definitely occur in the
succession), the evidence supports the idea that the last
conodonts finally went extinct in the earliest Jurassic.
Other sedimentary and palaeontological parameters
show little change for example the late Rhaetian
clay mineral and foraminiferal assemblages are very
similar to those in the early Hettangian. New stable
isotope data, carefully screened for diagenetic effects,
are also used to suggest that the principal isotope
excursion recognized in the succession contains hitherto
unrecognized high frequency structure and also pre-
serves a record of significant water mass warming.
Sedimentary archives of three basins from the
northern, central and southern Apennines, the La Spezia,
the Mt. Camicia, and Lagonegro basins, provide a rich
source of information for reconstructing Late Triassic
palaeoenvironments and the palaeogeographic evolution
of western Tethyan areas. Ciarapica argues that these
continuous successions of basinal facies are of particular
value, as they also reflect coeval evolution of adjacent
platforms through occurrence of platform-derived com-
ponents. Evidence is inferred for a Late Norian platform
drowning, climate change from arid to humid conditions,
a spread of dysaerobic facies and increasing eutrophiza-
tion. The establishment of oligotypic benthic communi-
ties, for example suggested by foraminiferan
associations dominated by Triasina hantkeni, is inter-
preted as a biotic response and a first step in the end-
Triassic extinction. Somewhat at odds with observations
from elsewhere, the TJ boundary appears to mark only
a second, lesser step of the end-Triassic events. At the T
J boundary the disappearance of the stress-tolerant asso-
ciations, return of hot and arid climate, and a final, short
anoxic episode, followed by rapid resumption of carbon-
ate platform building are observed in the Apennines.
By way of contrast, the Southern Alps of Lombardy,
Italy, preserve a TJ transition recorded in a predom-
inantly carbonate shelf and ramp setting. Galli et al.
analyze the sedimentary history, faunal and microfloral
assemblages, and stable isotope evolution of the
boundary interval. The focus of their attention is the
newly proposed Malanotte Formation, a conspicuous,
thin-bedded, micritic limestone unit that occurs between
the fossilifererous, more shallow-water carbonates of
the Rhaetian Zu Limestone, and the Hettangian Con-
chodon Dolomite (cf. Galli et al., 2005). The TJ
boundary is drawn near the base of the transgressive
Malanotte Formation, on the basis of a gradual change
in the pollen assemblages. More pronounced is the
slightly earlier abrupt extinction of diverse micro- and
macrofaunal associations at the top of the Zu Limestone,
a level that is also inferred to represent platform
drowning. The TJ boundary is closely correlated
with lithological change, accentuated by a gap inferred
from an Fe-crusted hardground or a thin layer rich in
siliciclastic components. The Malanotte Formation is
largely devoid of micro- or macrofauna and lacks the
recognizable lithological cycles that characterize the
underlying Zu Formation, but it does reveal a three-
stage evolution of the carbon isotope ratio in sea water.
In the base, i.e. at the TJ boundary, a moderate
negative excursion is recorded in bulk organic carbon,
followed by a rebound to positive values, which is in
turn followed by a more modest negative shift.
Another area with previously less well-known
Tethyan TJ boundary sections is the High Tatra Mts in
the Western Carpathians, at the SlovakPolish border.
There, the intra-shelf Zliechov Basin, broadly similar to
the more familiar Alpine Kössen basins, preservea record
of TJ transition studied in several sections. Michalík et
al. present new data from four key sections that were
subject to multidisciplinary investigation. Carbonate
deposition of the Fatra Formation, consisting of numer-
ous shallowing-upward cycles, was abruptly terminated
at the erosional TJ boundary. The conspicuous
boundary shale' of the overlying Kopienec Formation
is suggested to reflect both a carbonate production crisis
and a sudden increase of riverine influx of terrigenous
fine siliciclastic sediment, conceivably related to global
changes in climate and ocean chemistry. The moderately
diverse Rhaetian biota of the Fatra Formation, largely
inferred from skeletal components in the microfacies,
disappears at the boundary. A turnoveris observed among
the foraminifera, which here provide the primary
biostratigraphic framework. The earliest Hettangian
associations in the Kopienec Formation are dominated
by stress tolerant ostracods, which also suggest eutrophic
conditions. Immediately below the boundary, a negative
carbon isotope anomaly is recorded from bulk carbonate,
although it is definitely modest in comparison to some
other reported TJ boundary anomalies. Even more
ambiguous is the presence of microspheres in limestone
beds not far below the boundary. Although they
approximately correlate with the level of extinction and
isotope anomaly, their origin has not been convincingly
demonstrated. However tempting it is to infer impact-
related spherules, a more mundane explanation is that
they are diagenetic or hydrothermal alteration products of
spherical primary sedimentary particles, e.g. ooids.
Depositional environments in the northeastern part of
the Iberian Peninsula were quite different from those in
the fully Tethyan areas around the TJ boundary. Gómez
et al. summarize a wealth of stratigraphic, sedimentolog-
ical, and palynological information and report new
geochemical data. Eustatic sea-level changes variably
covered the low-relief area with extensive, extremely
shallow carbonate platforms and coastal playa and sabkha
flats, leaving a stratigraphic record of mixed carbonates
and evaporites arranged in sedimentary cycles. Contrary
to earlier opinions, Gómez et al. find no evidence for any
major sea-level change or unconformity near or at the TJ
boundary, and emphasize the remarkable lateral continu-
ity of the latest Triassic and earliest Jurassic strata.
Asturias is the only area of Iberia with a slightly different
record: the TJ boundary is placed in a carbonate
sequence there, whereas elsewhere it falls within an
evaporitic unit. The carbonates in Asturias yield an
organic carbon isotope record and add a new entry to the
growing list of locations where the TJ boundary negative
C anomaly is recognized. The boundary is drawn with
varying precision on the basis of palynology, and the
distribution of palynomorphs is also used to infer a
climate and vegetation history. A moderate latest Rhaetian
plant extinction is followed by considerable diversifica-
tion in the earliest Hettangian, which appears related to a
shift from arid to warmer and more humid climate
conditions, as reflected by a change in dominance of
xerophytic to hygrophytic pollen producers.
The continental record of the TJ events is no less
important than the marine record. Tanner and Lucas
provide a significant re-interpretation of the facies and
stratigraphic relationships among the upper part of the
Chinle Group and the lower part of the Glen Canyon
Group of Utah and Arizona, which were situated near
the western margin of Pangaea at the time. Their
discussion centres on the development of erg deposits
within the Wingate Formation, which initiated in the
latest Triassic, and which were perhaps fuelled by
exposed shoreline sands during a Rhaetian lowstand in
sea-level. Their main conclusion is that the mosaic of
continental facies is best deciphered in the context of a
northsouth palaeogeographic transition from domi-
nantly fluviallacustrine environments in the north, to
dominantly aeolian palaeoenvironments in the south.
Reinterpretation of formation boundaries results in the
recognition of more than one regional unconformity
between demonstrable Triassic strata of the Chinle
Group and the Jurassic Glen Canyon Group. This has
significant implications regarding a precise placement of
aTJ boundary in these often poorly fossiliferous rocks.
2.2. Biotic change
There are many examples of major environmental
change events in the Phanerozoic that are characterized
by the flood abundances of opportunistic, or disaster
taxa, but their presence has not hitherto been highlighted
for the TJ boundary event. Van de Schootbrugge et al.
examine the stratigraphic micropalaeontology of the
candidate GSSP section at St Audrie's Bay, England, and
quantify changes in both organic walled and calcareous
microfossils at the start of the mainnegative isotope
excursion (i.e. the long duration shift to light carbon
isotope values that occurs at St Audrie's Bay about 2 m
below the lowest examples of the Jurassic ammonite
Psiloceras). In the St Audrie's Bay section it is shown
that members of the green algae prasinophytes and
acritarchs become particularly abundant at the onset of
the mainnegative excursion; at the same time, red algae
and calcareous nannoplankton are minor constituents of
the microflora. The observations are interpreted by Van
de Schootbrugge et al. to represent an ecosystem
response to raised atmospheric CO
. Isotope and
elemental data from the oyster Liostrea hisingeri,
collected through the same interval, provide valuable
indications of parallel changes in major environmental
variables. These data incidentally provide the first
convincing evidence that the mainTJ carbon isotopic
curve based on bulk organic matter is present in marine
carbonate as well, albeit with half the amplitude (in
common with other Mesozoic excursions). Oxygen
isotopes and Mg/Ca ratios from the oysters are used to
argue for a 4 °C sea-floor temperature increase, and a
parallel decrease in salinity by at least 3 PSU at the start
of the mainnegative isotope excursion.
The Queen Charlotte Islands of northwestern Canada
continue to provide rich palaeontological data, central
to our understanding of the TJ extinction. Longridge
et al. add new data on the ammonoid and radiolarian
diversity trends and biochronology of two important
TJ boundary sections in the Queen Charlotte Islands.
Of these sections, the one on Kunga Island, has pre-
viously provided the sole radiometric age estimate for
the TJ boundary in marine rocks, and the other, at
Kennecott Point, has yielded one of the best carbon
isotope records spanning the extinction interval. Long-
ridge et al. document a moderately diverse ammonoid
succession across the boundary, including new discov-
eries that significantly reduce the ammonoid gapof
the boundary interval and now permit correlation to
early Hettangian ammonoid zones recognized at New
York Canyon, Nevada. Not to be overlooked is the
excellent radiolarian record from this interval in which
Longridge et al. describe a profound decrease in not only
radiolarian diversity, but also morphologic complexity
amongst earliest Jurassic spumellarian and entactiniid
To measure a mass extinction only by the proportion
of lost taxa and change in diversity is an oversimplifi-
cation. The ecologic impact may be equally significant
and can be estimated by assessing the reorganization of
communities. The compositional change of brachiopod
communities across the TJ boundary in the Northern
Calcareous Alps is investigated by Tomašových and
Siblík. Using an array of multivariate analytical
techniques, they demonstrate the profound effects
among brachiopods during the TJ boundary extinction.
The turnover at the boundary is an order of magnitude
higher than within the Rhaetian and the Hettangian.
Contrary to some earlier suggestions, the TJ brachio-
pod extinction is abrupt, with no indication of any
protracted decline during the Rhaetian. Removal of the
incumbents, i.e. extinction of superfamilies with dom-
inant members in latest Triassic communities, led to a
fundamental reorganization of community structure.
Testing for two competing hypotheses, Tomašových
and Siblík find more support for true compositional
change across the TJ boundary than they do for a
previous proposal of changing habitat preference within
major brachiopod groups. Brachiopods are rare, but not
absent, in the earliest Hettangian survival phase. Their
recovery was underway by late early Hettangian to mid
Hettangian times, as indicated by newly established
communities with an increasing degree of between-
habitat differentiation.
An alternative way to analyze extinction character-
istics is to interrogate a global database. This approach
has the advantage of providing an overview, with the
disadvantage of reduced stratigraphic resolution. Kies-
sling et al. use the Paleobiology Database to analyze
abundance and diversity patterns of marine benthic
organisms (sponges, corals, bivalves, gastropods and
brachiopods) from the Middle Triassic (240 Ma ago)
to the Middle Jurassic (160 Ma ago), paying particular
attention to possible biases in the dataset. Their analysis
confirms the reality of the TJ mass extinction, but it
also throws up some evidence for selectivity for certain
groups. Taxa that were reef-dwelling, with an inshore
habitat preference, preferring carbonate substrates, and
confined to low latitudes, exhibit higher extinction risk
than other groups. Intriguingly, the same characteristics
seem also to apply to background extinctions, lending
weight to the idea that the TJ extinction represents an
intensification of background processes with, perhaps,
an emphasis on extinctions in reefs and inshore
environments during (or at the end of) the Rhaetian.
Where body fossils are absent, trace fossils might
provide crucial additional information about extinction
patterns. An analysis of the TJ boundary trace fossil
record is provided by Barras and Twitchett for three sites
in southern England, including the candidate GSSP at St
Audrie's Bay. This contribution provides a detailed
account of changing ichnofauna of an interval from the
upper Langport Member of the Lilstock Formation
through five Jurassic ammonoid zones of the Blue Lias
Formation (culminating in the semicostatum Zone).
Their data reveal how eight ichnogenera show signifi-
cant patterns of infaunal changes through the interval.
Above a moderately diverse ichnofossil assemblage in
the Langport Member is a notable gap in trace fossils in
the Pre-Planorbis Beds. The authors do not relate this
absence of ichnotaxa directly to CAMP effects, because
of perceived differences in timing, but instead point up a
role for marine anoxia. The focus of their study is the
Early Jurassic recovery interval, rather than the lead up to
the extinction. The recovery amongst ichnotaxa above
the Pre-Planorbis Beds documents a significant increase
in ichnotaxic diversity and an increase in the depth of
Complementary to the well-known continental
sequences in eastern North America are those of the
western United States: the vast outcrops of fluvial,
aeolian, and lacustrine sedimentary rocks of the Chinle
and Glen Canyon groups. In a companion paper to their
stratigraphic account, Lucas and Tanner document what
is perhaps the best known terrestrial vertebrate record
spanning the TJ boundary, including reptilian skeletal
remains as well as their traces. They provide a revised
biochronology for the interval and subdivide the Late
Triassic and Early Jurassic strata into five biochrons
based upon the first appearance of reptile taxa. A
significant finding is an increase in both the abundance
and size of dinosaurian ichnotaxa leading up to the TJ
boundary. This event corresponds to the loss of
cruotarsan and phytosaur reptiles and the footprint
ichnogenus Brachychirotherium.
2.3. Carbon-isotope stratigraphy
The precise stratigraphic relationship between bios-
tratigraphically important fossil groups and carboniso-
tope compositions of carbonate and organic sedimentary
matter has become critical to understanding TJ events,
as emphasized in Fig. 1. In an integrated palynological
and isotopic study of the classic boundary sections of the
Salzkammergut, Austria, Kürschner et al. provide an-
swers to several outstanding questions of correlation. By
constructing a composite carbon isotope curve of bulk
organic matter from two nearby sections, they find the
now increasingly replicated pattern of an abrupt initial
negative isotope excursion, closely followed by an
extended mainisotope excursion (Hesselbo et al.,
2002, 2004). The initial isotope excursion occurs
immediately above the top of the hemipelagic carbonate
Kössen Formation, in the lowest few centimetres of the
Grenzmergel(or boundary marl), and it had been
missed in a previous isotopic study of an adjacent section
due to relatively wide sample spacing. The negative
excursion is coincident with the highest occurrence of
conodonts, and the succeeding 12 m sees the highest
occurrences of typically Triassic palynomorphs. The
start of the mainisotope excursion occurs at the same
level as the lowest occurrence of Cerebropollenites
thiergartii, a pollen grain that has previously been
suggested as a base-Jurassic marker. Whatever taxon is
adopted as a definitive guide for the TJ boundary, it
becomes clear that the principal period of environmental
change takes place within the Grenzmergel and is
bracketed by the two negative isotope excursions.
Interestingly, like Van de Schootbrugge et al., Kuersch-
ner et al. also recognize the occurrence of a green-algal
bloom, but in this case at the same time as the initial
negative excursion.
The candidate GSSP at Muller Canyon, Nevada,
USA, is another crucial section that reveals the
relationship between the organic carbonisotope curve
and biostratigraphically important taxa in this case
ammonites and bivalves. In a re-sampling and re-
measuring exercise, Ward et al. reproduce the broad
characteristics of a previously published carbonisotope
curve based on bulk marine organic matter (Guex et al.,
2004). However, they also find important contrasts with
the previous work. Most notably, Ward et al. recognize
that the lowest occurrence of the typically Jurassic
pectinacean bivalve Agerchlamys boellingi, and the
lowest find of the ammonite Psiloceras sp., occur
immediately above an initialnegative isotope excur-
sion as defined by multiple data points. If the carbon
isotope curve can be relied upon for correlation, which
looks increasingly likely, then the implication is that
base of the Jurassic as defined in North American
sections on any faunal criterion correlates to horizons
many believe to be Triassic in European sections.
In addition to yielding an important record of biotic
change across the TJ interval boundary the Queen
Charlotte Islands' succession in Canada was one of the
first to show evidence for an abrupt negative carbon
isotope excursion coincident with biotic change, in this
case radiolarians. Williford et al. here present an extended
record of carbon isotope data from bulk organic matter
from the Hettangian succession at Kennecott Point in the
Queen Charlotte Islands (cf. Ward et al., 2004). A really
striking feature of their new data is the magnitude of a
positive excursion lying between an initial negative
excursion (corresponding closely to the level of radiolar-
ian turnover) and what they interpret as the main
(Hettangian) negative excursion. Explanations of the T
J boundary record now have to include both a potential
source of isotopically light carbon to produce the negative
excursion and an explanation for where all the light
carbon subsequently goes. Williford et al. prefer a
scenario that involves principally a switch of carbon
burial flux from carbonate to organic matter.
2.4. Causes and consequences
Plate motions incessantly operate in the background
of all other Earth phenomena. The changing palaeogeo-
graphy around the TJ boundary is analyzed by
Golonka, on the basis of two global palaeogeographic
maps constructed for the Late Triassic and Early Jurassic,
respectively. More detailed lithofacies maps for the two
intervals are provided for crucial areas where the TJ
transition proved eventful, including the western Tethys,
eastern Tethys, Palaeotethys and eastern Asia, north-
western Laurasia, and western Gondwana. The closure
of Palaeotethys was expressed in the main convergent
event, the Indosinian orogeny, which completed the
assembly of eastern Pangaea. In the same time, rifting in
the future Central Atlantic area heralded the break-up of
the supercontinent. The changing palaeogeography is an
important backdrop to the TJ boundary events but most
tectonic phenomena operate at longer time scales. A
notable exception is the magmatism of the Central
Atlantic Magmatic Province (CAMP).
Indeed, flood basalt volcanism of the CAMP is
implicated in the currently most favoured scenario
explaining environmental changes and biotic extinctions
at the TJ boundary. Clearly, relative timing of the
boundary events and the eruptions, and the duration of
the latter, is of paramount importance in refining or
refuting the purported causal link. Two sister papers in
this volume contribute new radio-isotopic ages for
CAMP basalts and interpret their significance.
Vérati et al. present a suite of 12 new
Ar ages
from Moroccan CAMP basalts complemented by
another two ages from correlative lava flows from
Portugal. In Morocco, the CAMP flows are grouped into
four units on the basis of their stratigraphy and
geochemical characteristics. The first three flow units
account for 90% of the total lava volume. Significantly,
their ages overlap within error, suggesting that the bulk
of volcanic activity occurred within a short time span, in
less (perhaps much less) than the 2 Ma resolution
afforded by the analytical uncertainty of the dating
method. The Moroccan ages are centered around a mean
of 199.1 ± 1 Ma ago. Only the fourth and volumetrically
minor flow unit has a resolvably youngest mean age of
196.6 Ma ago. The flow ages and chemical composi-
tions suggest that this unit is a product of late-stage
asthenospheric upwelling, representing a milestone in
the magmatic evolution of the Atlantic rifting process.
The Portuguese lava flows are demonstrably coeval with
their Moroccan counterparts and unquestionably can be
assigned to the CAMP. Significantly, the new suite of
ages presented here confirm the earlier suggestion that
CAMP volcanism is synchronous with the TJ
boundary. The caveat is a recognition of problems
associated with both the
Ar method applied here
and the UPb method used to date the boundary from an
ash bed in a marine section.
Nomade et al. set out to address the same problems:
what is the chronology (i.e. age and duration) of CAMP
volcanism and, on the basis of the temporal relation-
ships, how is it related to the TJ boundary events? The
team also reports a set of new
Ar ages from their
17 samples, split among three of the four continents
where CAMP occurs. This brings the total number of
published dates to over 100, making CAMP the
temporally best constrained large igneous province.
Despite chronologic reviews published as recently as in
2003 and 2004, a new effort is justified as some 50
Ar dates were obtained in the last 3 years
alone. The quality controlapplied by Nomade et al. is
also more stringent than in previous studies. After
filtering out less reliable dates and those exhibiting
disturbed isotopic systems, only the most robust
plateau ages are considered further and 58 dates are
accepted as valid. It is reassuring that this much larger
dataset principally confirms and refines the conclusions
of earlier studies. The new synoptic chronology of
CAMP reveals that intrusive magmatism commenced
201 Ma ago, extrusions occurring about 1 Ma later in
the African margin, and followed soon after in North
America, before spreading to South America. Peak
activity, represented by 80% of the dates, is restricted
to a short period between 199 and 197.5 Ma ago. Small-
volume eruptions form a protracted tail-end of activity
to as late as 190 Ma ago. A pattern of north-to-south
migration of volcanism emerges, although geographic
distribution of the data is uneven with the strongest
representation of African (mostly Moroccan) samples.
The difference in timing of CAMP volcanism in
North America and in North Africa is a matter of some
considerable debate (e.g. Knight et al., 2004; Marzoli et
al., 2004). Whiteside et al. frame the questions in terms
of synchronism between Moroccan and North America
activity, and the age relationship to the major pulse of
extinction in continental settings, and they attempt to
answer these questions using a variety of stratigraphic
arguments. Additionally, they provide new cyclostrati-
graphic, lithostratigraphic, and biostratigraphic data
from several continental basins in eastern North
America and Morocco. Significant are the new data
from Partridge Island (Fundy Basin, Nova Scotia) and
the Argana Basin (Morocco), and revised sections
elsewhere in North America (e.g. Newark and Hartford
basins). On both continents, the authors define an end-
Triassic extinction event based primarily on palynology
and, to a lesser extent, on tetrapod footprint data. The
loss of pollen species and tetrapod ichnotaxa coincides
more or less with the onset of Corollina (i.e. Classo-
pollis) dominated pollen assemblages.
As previously reported, based on astrochronology,
the extinction event is proposed to predate the earliest
CAMP flow by 20 ka (e.g. Olsen et al., 2002).
Existing basalt geochemical data are used to support this
correlation, and Whiteside et al. note that the strati-
graphically lowest flows from North America are
geochemically High Titanium Quartz normative
(HTQ) basalts that are most similar to the HTQ-type
flows from the Argana Basalt in Morocco. However,
correlation of the North American basalts to the Central
High Atlas Basin in Morocco is problematic as these are
High Iron High Titanium Quartz normative (HFTQ)
basalts for which there are no real correlatives in North
America. Whiteside et al. propose that the HFTQ flows
of the central High Atlas Basin are part of a magmatic
sequence in which the HFTQ evolved from earlier HTQ
magmas. Additionally, they specifically dispute a
previous correlation of the short reverse magnetochron
recognized in Morocco which had implied that North
American flood basalts are younger than those found in
Morocco. Instead, they suggest that a short reverse
magnetochron may yet be found in poorly sampled
North America basalts above the palynologically
defined TJ boundary, and propose that an independent
test of their hypothesis would be recognition of the
initialcarbonisotope negative excursion in strata
below the oldest basalts in these continental settings.
Ocean acidification, through the build up of dissolved
carbon dioxide in the oceans, has been an important
putative mechanism behind degradation of marine car-
bonate ecosystems for several past events (as well as at the
present day). This is particularly relevant for times when
carbonate platform drowning appears to have accelerated,
when extinctions take place preferentially within shallow
marine carbonate communities, and when carbonate
skeletal mineralogy seems to undergo significant change.
Berner and Beerling apply a numerical carbon cycle model
to investigate whether volcanic gases of direct magmatic
origin were sufficient in quantity to account for these
phenomena via oceanic carbonate undersaturation. In
addition to the role of carbon dioxide, they also examine
the part played by sulphur dioxide, and the possible relative
amounts of these two gases during basaltic volcanism,
together with feedback mechanisms that potentially
include release of methane from gas hydrates. Their
conclusions are simple; gasses directly produced from
CAMP volcanism can explain oceanic carbonate under-
saturation phenomena, but only just. It is necessary to have
starting conditions close to undersaturation (i.e. very high
atmospheric carbon dioxide) and release of amounts
volcanic gas at the very upper limits of plausibility.
CAMP is implicated not only in the generation of
excess atmospheric and oceanic carbon dioxide, but also
in its drawdown via carbonation reactions during
weathering. The seawater record of signatureisotopes
such as strontium and osmium, which are biased towards
unradiogenic values in juvenile basalts, may give a clue
as to how CAMP affected weathering processes. Cohen
and Coe compile parallel Sr and Os isotope datasets from
across the TJ boundary and carry out a semi-
quantitative analysis of the results. They find that close
similarities exist between the Sr and Os isotope records
of the TJ boundary and those of the Toarcian Oceanic
Anoxic Event, some 17 million years later, which also
coincided with eruption of a continental flood basalt
Large Igneous Province (LIP), the KarooFerrar.
Perturbations to the seawater Sr-isotope record coinci-
dent with LIP emplacement take the form of sudden
increases in the proportion of radiogenic strontium,
interpreted as increases in continental weathering rates
superimposed on an overall trend brought about by long-
term decreasing in
Sr ratios, presumably reflect-
ing long-term decreasing continental weathering rates.
The seawater osmium isotope records for both events
also show abrupt changes to more radiogenic values,
albeit much more transient than for strontium. Thus, it
appears from the TJ boundary record that CAMP
eruptions initially promoted a large increase in conti-
nental weathering, without the lavas themselves being
strongly weathered and contributing a significant
unradiogenic flux (the same is also true for Karoo
Ferrar). In the case of CAMP, the subsequent Os-isotope
record suggests that this situation was short lived: a rapid
return to unradiogenic Os values in the earliest
Hettangian indicates input of Os directly from the
intense weathering of CAMP lavas that lasted for the
next 3 Ma. By the end of the Hettangian it was all over,
with both Sr and Os isotope values returning to their
long-term trajectories.
Some of the best clues to the end-Triassic events may
have been buried deep in Panthalassa. Hori et al. made an
attempt to read the palaeontological and geochemical
archives preserved in a slowly accumulated deep-sea
chert sequence in Japan. The radiolarian extinction is one
of the most promising palaeontological markers of the
TJ boundary. In the Kurusu section of the Inuyama
area, the rapid radiolarian turnover is subdivided into
three events (E1 to E3). First go some of the taxa of a
diverse Triassic assemblage (E1). No more than 0.5 Ma
later there is a wholesale extinction of the remaining
species and the origination of a few new Jurassic forms.
This E2 event is recorded in a single bed that is estimated
to have accumulated in less than 10 ka and is taken as the
TJ boundary. Significantly, the E2 event also corre-
sponds to the last occurrence of conodonts (Misikella
posthersteini). Then E3 is a post-extinction interval
characterized by a low diversity fauna of small, spherical
spumellarians. The level of E1 coincides with tantalizing
geochemical signals. Among the Rare Earth Elements, a
distinct Ce anomaly is interpreted to signal a brief
acidification of sea water. The next higher chert bed
records an anomalously high abundance of Platinum
Group Elements (PGEs). The Ce anomaly is compatible
with CO
and SO
emissions from either a volcanic or an
impact source. However, the PGE peak can be best
accounted for by a calculated 2.5% admixing of impact
melt-derived material. If this is correct, the putative
impact may have played a role in the plankton extinction
at E1, but it cannot be directly implicated in the TJ
boundary extinction, half a million years after. Signif-
icantly, in between lies another chert layer that contains
basaltic glass and lithic fragments. If derived from a
CAMP source, this may be the first direct evidence that
some CAMP eruptions were violent enough to spread
airborne volcanic particles around the globe. The Kurusu
section clearly yields important pieces of the TJ puzzle,
yet fitting them together is not straightforward.
Similarly puzzling is a uniquely extensive metre-
scale horizon of soft sediment deformation which occurs
immediately below the initial carbon isotope excursion
in eight discrete sedimentary basins in the UK region,
and covering an area of N250,000 km
. Simms reviews
published evidence for this seismiteand concludes that
it represents only a single shock event, and is at least
locally overlain by sedimentary facies of plausible
tsunami origin. The facies successions are closely
comparable to those described from shallow marine
strata in proximity to the end-Cretaceous Chicxulub
impact crater. In view of the great distance from the TJ
boundary seismiteto the nearest CAMP volcanic
rocks, Simms rejects the idea that these beds originated
in relation to violent CAMP eruptions. Instead he
suggests that the observed phenomena are compatible
with an impactor of relatively modest dimensions,
possibly some 23 km across, forming a so far
undiscovered crater of 4050 km diameter, too small
to have had a significant effect on biotic change.
3. Possibilities
Despite much progress, a sufficiently high-resolution
geochronological framework is still lacking to firmly
establish the temporal link of CAMP's first and/or
largest eruptions, the environmental events, and the
extinction. The main unresolved issue is the comparison
Ar and UPb dates. The first method is used
extensively in dating CAMP basalts but suffers from
uncertainty in the decay constant of
K. A current
revision of the constant (Villa and Renne, 2005) may
require recalculation of all
Ar ages and their
upward adjustment by 1% (i.e. a published age of
200 Ma would be in fact be close to 202 Ma). Curiously,
the UPb method may also have produced ages that
systematically err on the young side. The going estimate
of the TJ boundary age hinges on a multi-grain zircon
UPb age (199.6 ± 0.4 Ma, Pálfy et al., 2000). Multi-
grain analyses are prone to leave slight Pb loss
undetected, hence producing marginally younger ages.
The remedy is now available, analysis of individual
crystals of zircon, also using improved methods to
eliminate the effects of Pb loss (e.g. Mundil et al.,
2004). Significantly, a single-crystal
U age of
201.27 ± 0.27 Ma has been obtained for the North
Mountain basalt, a CAMP flow in Nova Scotia, Canada
(Schoene et al., 2006). Only the application of these
recent advances will help compare the timing of CAMP
and TJ boundary events with greater confidence.
There has been some attempt to use cyclostratigraphy
to calibrate the duration of events at the TJ boundary,
notably with respect to the CAMP volcanism in eastern
North America, but so far cyclostratigraphy has not been
used effectively to help understand the marine sections.
This is partly because most of the marine sections
investigated so far show major facies changes across the
boundary, and yet early attempts to use this method have
not been entirely unsuccessful (cf. Weedon et al., 1999).
With the development of high resolution lithological
and chemostratigraphic datasets much future progress
should be possible.
The proxy record for atmospheric carbon dioxide
change (e.g. McElwain et al., 1999; Tanner et al., 2001)
remains relatively weak, and there is much scope for
further work in this area, based on analyses of the well-
preserved plant fossils and soil carbonates that abound
in several basins around the world (e.g. Harris, 1937).
An improved terrestrialmarine correlation is essential.
One potentially powerful approach that has not yet been
harnessed for the TJ boundary, is the use of compound
specific carbonisotopes as an alternative to analysis of
bulk organic matter, to provide a carbonisotope
stratigraphy where the effects of mixing of different
organic components can be better controlled.
Whatever the quality of the present proxy record,
there does now seem to be widespread agreement that
carbon dioxide produced directly from CAMP, even with
a gas hydrate supplement brought about by greenhouse
warming, may not have been enough to cause all of the
evident environmental impacts. However, it has been
pointed out for other LIPs that baking of organic rich
rocks may generate massive additional amounts of
atmospheric and oceanic carbon (Svensen et al., 2004;
McElwain et al., 2005) and this mechanism remains an
unexplored possibility in the case of CAMP. Certainly
the huge extensional basins into which CAMP magmas
were intruded were at times enriched in organic matter
and might have provided a ready substrate for production
of thermogenic methane.
The debate about extraterrestrial versus volcanic
drivers for environmental change has not yet been
concluded, and it is noteworthy that all of the candidate
indicators of extraterrestrial impact reports of PGE's
and soft sediment deformation occur shortly prior to
CAMP volcanic activity. Pure coincidence aside, this
observation keeps alive the idea that there is an impact
signal’–LIP connection, even if the mechanisms remain
highly controversial; for example, impact decompres-
sion melting, as recently articulated by Elkins-Tanton
and Hager (2005), or lithospheric gas explosion (Phipps
Morgan et al., 2005).
We wish to thank all the participants of IGCP 458,
and in particular all the referees whose hard work in
helping to produce this special issue is much appreci-
ated. Axel von Hillebrandt provided welcome critical
comment on this introduction.
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Stephen P. Hesselbo
Department of Earth Sciences, University of Oxford,
Parks Road, Oxford, OX13P3, UK
E-mail address:
Corresponding author.
Christopher A. McRoberts
Department of Geology, State University of New York at
Cortland, P.O. Box 2000, Cortland, NY 13045, USA
József Pálfy
Research Group for Paleontology, Hungarian Academy
of Sciences-Hungarian Natural History Museum,
P.O. Box 137, Budapest, H-1431, Hungary
10 Editorial
... These probable traces of subaerial exposure lead us to consider it as a sequence boundary. For this Norian part of Milaha Formation, our local sea-level curve seems to reflect the super-regional interpretation of Haq and Al-Qahtani (2005; stable sealevel followed by a sea-level-drop) and is not in contradiction with the global curve of Hesselbo et al. (2007;slowly rising trend). ...
... Above, alternations of marlstones and limestones without quartz input and multiple occurrences of Retiophyllia and thamnasteriid coral rudstones/floatstones at the very top suggest the gradual shift from a restricted subtidal zone to more open subtidal zone again (Senowbari- Daryan and Maurer, 2008). This could correspond either to a gradual but constant sea-level rise (Hesselbo et al., 2007) or a more pronounced rise followed by a stable sea-level at the top of the member (Hallam and Wignall, 1999) but not to a stable phase as hypothesized by Haq and Al-Qahtani (2005). The top of the Sumra Member is developed with two erosional surfaces, extensively described in the Triassic-Jurassic boundary subchapter of this discussion. ...
... The depositional environment is interpreted as restricted and most probably lagoonal. The sea level tends to gradually fall, as proposed by Hesselbo et al. (2007) and opposed to the assumptions of Hallam and Wignall (1999). ...
Full-text available
The end-Triassic Mass Extinction (ETME) is generally regarded as a consequence of the environmental changes associated with the emplacement of the Central Atlantic Magmatic Province (CAMP) and ranks among the 'big five' mass extinctions in Earth history. A notable feature of the ETME is a halt in marine carbonate deposition followed by the formation of unusual facies such as carbonate cement fans and oolites in the early aftermath of the event. The ETME time interval has been well studied over the last few decades, in contrast to a few minor extinction events that preceded it, among them the extinctions associated with the Norian-Rhaetian boundary (NRB). This study provides new insights into these extinction events with complete mid-Norian to Hettangian δ 18 O carb and δ 13 C carb record from a key section at Wadi Milaha (Ras Al Khaimah Emirate, United Arab Emirates). Ooids are important proxies for palaeoenvironmental reconstruction. The post ETME oolite horizon is documented providing morphological classification as well as a detailed modal analysis of rock components and different types of coated grains. Through a multi-technique approach, we argue for the stability of the carbon cycle across the NRB extinction event and the existence of a hiatus at the TJB (Triassic-Jurassic Boundary) in Wadi Milaha. Our new morphological classification of post-extinction ooids is compatible with a major role for seawater geochemistry with respect to sedimentological processes, by example in the peculiar way ooids diversify and alternate with other kinds of coated grains.
... Other nonammonoid possibilities that were considered for defining a precise base-Jurassic level that could be globally correlated included a major turnover of siliceous radiolarian microfossils or a negative excursion in carbon isotopes. After a major international effort to correlate environmental and biostratigraphic events associated with the end-triassic extinctions and the extensive eruption of the Central Atlantic Magmatic Province (CAMP) at B201 Ma (e.g., review by Hesselbo et al., 2007a), it was decided to place the base of the Jurassic at the initial stages of biological recovery from the end-Triassic extinction as marked by the earliest forms of Psiloceras ammonites. ...
... The TriassicÀJurassic transition is marked by a major carbon cycle perturbation, and associated excursion in δ 13 C records. The end-Triassic mass extinction coincides with a negative carbon isotope excursion that may be linked to the initiation of widespread CAMP flood basalt volcanism, oceanic productivity collapse, and/or the release of methane (e.g., Pálfy et al., 2001;Hesselbo et al., 2002Hesselbo et al., , 2007aRuhl et al., 2009Ruhl et al., , 2011Ogg and Chen, 2020). The brief latest Rhaetian "initial" negative carbon isotope excursion preceded the base of the Jurassic by 100À200 kyr and is separated from the following earliest Hettangian "main" negative carbon isotope excursion by a brief return to more positive δ 13 C values . ...
... Cycle strat duration fromHuang (2018). Dash base-exact position of zonal limits with respect to cycles is not precise.Onset of main OAE 5 base of H. serpentinum (seeHesselbo et al., 2007a about problems with interregional correlation); the preferred duration is from Huang (2018). In GTS2016 the age (and duration of underlying stage) was constrained to 183.2 6 0.3 Ma(Sell et al., 2014) for the uppermost D. tenuicostatum Zone.Full name 5 Dactylioceras (Orthodactylites) tenuicostatum. ...
Full-text available
Ammonites underwent an evolutionary diversification after the mass extinction of the end Triassic induced by the formation of a Large Igneous province (LIP), and this group provides the most useful marine biostratigraphy. Only two levels within the Jurassic are relatively well determined using U–Pb dating from single zircons in ash beds, at the base Hettangian and the Pliensbachian–Toarcian boundary. Otherwise the Lower Jurassic is scaled using astrochronology and the Middle and Upper Jurassic scaled from Pacific seafloor spreading rates correlated to magnetic reversals. LIP activity during the Early Jurassic (Triassic–Jurassic boundary and Toarcian) perturbed global environments to extents not evidenced since the end Permian, and age relationships allow for a strong causal connection between these LIP eruptions and mass extinctions caused by major paleoenvironmental change, including ocean anoxia. Breakup of the supercontinent Pangea dominated paleogeography and paleoceanography and created shallow seaways that form sources and traps for hydrocarbons. Calcareous planktonic algae diversified and migrated from shallow seaways to open oceans to set the stage for the beginning of modern oceanic biogeochemical cycling; calcareous nannofossils provide additional widely used correlation tools.
... The Triassic-Jurassic transition (Tr-J, 201.36 ± 0.17 Ma, Wotzlaw et al., 2014) is marked by the end-Triassic mass extinction, one of the "Big Five" extinction events of the Phanerozoic (Benton, 1995;Raup & Sepkoski, 1982;Sepkoski, 1981). The biotic turnover, ecological crisis, and environmental background across the Tr-J transition have drawn significant attention over the last decades (Barash, 2015;Hesselbo et al., 2007). The impact of the end-Triassic mass extinction on marine organisms has been extensively documented (e.g., radiolarians, Hallam, 2002;foraminifera, Michalík et al., 2007;ammonites and brachiopods, Tomašových & Siblík, 2007;corals and calcisponges, Stanley Jr. et al., 2018; bivalves, Atkinson et al., 2019). ...
The end‐Triassic mass extinction is considered one of the “Big Five” extinction events in the Phanerozoic. However, whether the terrestrial ecosystem began to deteriorate or even collapse prior to the Triassic–Jurassic (Tr‐J) transition remains controversial. Compared with the documented data from the western Tethyan region, evidence from the eastern Tethyan realm is limited. We undertake a fitting analysis of the sedimentary system, floral community successions and major geological events of the Xujiahe Formation as reflected by the Qilixia Section, Xuanhan area, northeast Sichuan Basin, China. Our results reveal an oscillating fluvial‐lacustrine depositional system during the Late Triassic, with the dominant sedimentary processes mainly controlled by the Indosinian Movement. Beside the sedimentary influence on the Xujiahe Flora, climate changes played a more important role. Fluctuating conditions to cooler and dryer climates at this time promoted diversification of gymnosperms under an overall warm and humid climate setting in the Late Triassic in the Xuanhan area. Superimposed on this oscillating long‐term climate state, ecosystem destabilization occurred over 1 million years prior to the Tr–J interval in the Xuanhan study area, possibly in response to the intensified storm and wildfire activity and the following environmental changes. Although the Xujiahe Flora always recovered from the interruption of the tectonic movement, it ultimately collapsed under extreme climatic events and ecological pressures induced by the Late Triassic Central Atlantic Magmatic Province event. An oscillating fluvial‐lacustrine system occurred prior to the end‐Triassic, and the sedimentary processes influenced the floral community successions of the Xujiahe flora in the northeastern Sichuan Basin, China. The Xujiahe flora ultimately collapsed under extreme climatic events and ecological pressures induced by the Late Triassic CAMP event.
... The ETE is marked by a loss of up to 50% in marine biodiversity and a massive biotic turnover in both marine and terrestrial environments (Hallam and Wignall, 1997;Sepkoski, 1997). The event is characterised by a carbon isotope excursion which reflects a perturbation in the global carbon cycle (Palfy et al., 2001;Hesselbo et al., 2002;, with leaf stomata studies indicating a fourfold increase in atmospheric CO 2 concentrations (McElwain et al., 1999; linked to the development of the Central Atlantic Magmatic Province (CAMP) during the break-up of Pangaea (Beerling and Berner, 2002;Hesselbo et al., 2002;Hesselbo et al., 2007). Recent studies indicate that the initial carbon isotope excursion recorded a depletion of 8.5 per mil (‰) atmospheric carbon-13, suggesting a total injection of~12,000 to 38,000 Gt of carbon as methane over only 10-12 kyr from two sources: marine methane-hydrate reservoir, and volcanic sill intrusions and flood basalt associated with CAMP . ...
The End-Triassic mass extinction event [ETE] (201.5 Ma) marks a drastic turnover and loss of > 50% of marine biodiversity. Suggested environmental factors include extreme climate change and global carbon-cycle perturbations linked to Central Atlantic Magmatic Province (CAMP) volcanism. Considerable attention has been paid to disentangling the causes and selectivity of the ETE, whilst downplaying the patterns of change in the structure and functioning of marine paleofauna. Here we provide detailed quantitative information from across the Triassic-Jurassic boundary at Waterloo Bay, Larne, Northern Ireland, to describe patterns of changes in different palaeoecological parameters across the ETE. The analysis was based on abundance data of species sampled from approximately 1 m intervals through the sequence. Dominance and richness were estimated using rarefaction techniques and β-diversity index, and distinctness diversity indices were calculated. Changes in species composition were evaluated by multivariate analysis (nMDS, ANOMSIM and SIMPER). Rank abundance models were fitted, and functional diversity were estimated based on an ecospace model, applied to each sampled unit to detect changes in structure and ecological complexity. Across the ETE three distinctive states were identified: the pre-extinction state (Westbury Formation), characterised by an assemblage with high species richness and ecological redundancy, and with low taxonomic variation and functional diversity. The extinction state (Cotham and Langport members) represents a shift of the marine ecosystem, where > 70% marine species disappears decreasing the ecosystems functioning the marine ecosystem around 80%. The recovery state (Lias Group), commencing some ~ 150 ky after the extinction, with ecologically complex assemblages as new taxa colonised, increasing variation in taxonomic distinctness and new contributing ecological traits and functional richness through the Hettangian. The palaeoecological patterns described here are robust enough to discount possible facies effects, but more important, is consistent with other studies reported globally, and demonstrates that the ecological signals detected in this study are real.
Mass extinctions shape the history of life and can be used to inform understanding of the current biodiversity crisis. In this paper, a general introduction is provided to the methods used to investigate the ecosystem effects of mass extinctions (Part I) and to explore major patterns and outstanding research questions in the field (Part II). The five largest mass extinctions of the Phanerozoic had profoundly different effects on the structure and function of ecosystems, although the causes of these differences are currently unclear. Outstanding questions and knowledge gaps are identified that need to be addressed if the fossil record is to be used as a means of informing the dynamics of future biodiversity loss and ecosystem change.
Les changements globaux, du fait de l’empreinte humaine, sont associés à de nombreux déclins de populations et de disparitions d'espèces, et ce, notamment au sein des systèmes insulaires. L'importante biodiversité abritée par de tels écosystèmes est particulièrement vulnérable aux pressions anthropiques en raison de diverses caractéristiques (p. ex. syndrome d’insularité, faible redondance fonctionnelle, isolement géographique des îles). En dépit de cette vulnérabilité accrue, peu d’études se sont jusqu'à lors intéressées à ces systèmes comme modèle d’étude pour évaluer les patrons de menaces sur les différentes facettes de la diversité (taxonomique, fonctionnelle, et phylogénétique). Pourtant, un tel travail permettrait d’améliorer notre compréhension des menaces qui pèsent au sein des îles. Dans ce sens, l’objectif de cette thèse est de décrire les patrons de diversité endémique insulaire dans le contexte actuel des changements globaux et dans un contexte futur de changements climatiques, en explorant les différentes facettes de la diversité. Une finalité de ce travail est de mettre en évidence des priorités éventuelles de conservation pour ces écosystèmes particulièrement vulnérables. Nous avons abordé l'ensemble de ce travail de thèse à une grande échelle à l’aide de deux bases données recensant les îles mondiales et les espèces qui y sont endémiques. Dans une première partie, nous avons caractérisé les menaces pesant sur les écosystèmes insulaires à l'échelle globale, et prospecté également leurs distributions au sein de différents groupes taxonomiques et régions insulaires. Dans une deuxième partie, nous avons analysé l'incidence des menaces sur la biodiversité endémique insulaire et en particulier sur la composante fonctionnelle. Dans une troisième partie, nous avons identifié les régions insulaires à forte représentativité de la biodiversité endémique menacée au travers de différentes facettes et prospecté leurs niveaux de protection via les aires protégées et les menaces les affectant. Dans une dernière partie, nous avons étudié la vulnérabilité future des îles et de la biodiversité endémique face au changement climatique à l’échéance 2050. À la lumière de nos résultats (identification de menaces majeures dont l'importance varie suivant les groupes taxonomiques, les régions insulaires et également les dimensions de biodiversité considérées), nous avons discuté de l’implication des changements globaux pour la biodiversité endémique insulaire dans un contexte de conservation. Cette thèse révèle l’importance d’intégrer de multiples menaces (et leurs associations) et dimensions de diversité pour les approches de changements globaux et de conservation.
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Il Foglio 249 - Massa Carrara è stato realizzato nell’ambito del Progetto CARG (Legge 438/95), tramite convenzione del 3/12/1998 tra la Regione Toscana e la Presidenza del Consiglio dei Ministri - Servizio Geologico d’Italia (ora ISPRA). Direttore scientifico del Foglio: L. CARMIGNANI; Direttori del rilevamento: P. CONTI e M. MECCHERI. Per la stesura della carta geologica sono stati utilizzati: --- rilevamenti di campagna eseguiti tra il 1974 e il 1985 da: M.L. ANTOMPAOLI, L. BURBI, L. CARMIGNANI, G. FORNACE, M. GATTIGLIO, G. GOSSO, R. KLIGFIELD, V. LORENZONI, S. MATTEOLI, M. MECCHERI, P.F. MILANO, L. MONI, P. NOTINI, P. PALAGI, F. RICCERI, G. RUFFINI per la realizzazione della “Carta geologico - strutturale del Complesso Metamorfico delle Alpi Apuane - Foglio Nord” (CARMIGNANI, 1985); ---rilevamenti successivi eseguiti da M. MECCHERI, G. BIGONI, P. CONTI, M. PILI, N. VIETTI; --- a partire dall’anno 2000 rilevamenti nell'ambito del Progetto CARG eseguiti da: L. CARMIGNANI, M. MECCHERI, P. CONTI, G. MASSA, L. VASELLI, G. MOLLI, E. GUASTALDI, M. ROSSI, F. BONCIANI, I. CALLEGARI, M. ZAZZERI, G. MASETTI, S. MANCINI, D. PIERUCCIONI e F. MILAZZO. ------------------------------------------- E. PATACCA e P. SCANDONE hanno diretto e curato la stratigrafia delle successioni toscane
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The results of the biostratigraphic study based on the radiolarian analysis of the rhythmically layered terrigenous deposits from the Islands of the Rimsky-Korsakov Archipelago (Peter the Great Bay, Japan Sea) have been presented. These deposits are most similar to the medium-grained turbidites. For the first time the distribution and stratigraphic division of the boundary sediments of the upper Triassic and lower Jurassic separated by a marking layer were substantiated in the research area. On the basis of comparisons with isochronous zonal units of the Pacific and Tethyan areas in the upper Triassic sediments of the studied sections, layers with Globolaxtorum tozeri (upper Rhaetian) were established, and in the lower Jurassic zone Pantanellium tanuense Zone (Hettangian) was traced and layers with Parahsuum simplum (Sinemurian – Pliensbachian) were established.
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Analysis of tetrapod footprints and skeletal material from more than 70 lo- calities in eastern North America shows that large theropod dinosaurs appeared less than 10,000 years after the Triassic-Jurassic boundary and less than 30,000 years after the last Triassic taxa, synchronous with a terrestrial mass extinction. This extraordinary turnover is associated with an iridium anomaly (up to 285 parts per trillion, with an average maximum of 141 parts per trillion) and a fern spore spike, suggesting that a bolide impact was the cause. Eastern North American dinosaurian diversity reached a stable maximum less than 100,000 years after the boundary, marking the establishment of dinosaur-dominated communities that prevailed for the next 135 million years.
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Three British Jurassic mudrock formations have been investigated, via time–series analysis, for evidence of sedimentary cyclicit related to orbital–climatic (Milankovitch) cyclicity: the Blue Lias, the Belemnite Marls and the Kimmeridge Clay Formation. Magnetic–susceptibility measurements through the Blue Lias (uppermost Triassic to Sinemurian) were used to generate high–resolutio time–series. The data indicate the presence of a regular sedimentary cycle that gradually varies in wavelength according t sedimentation rate. Tuning of this cycle to the 38ka Jurassic obliquity cycle produces spectral evidence for two additiona regular cycles of small amplitude. These correspond to the 95 ka component of orbital eccentricity and the 20 ka orbital–precessio cycles. Cycle counting allowed the minimum duration of four ammonite zones to be estimated and the duration of the Hettangia stage is estimated to be at least 1.29 Ma. Calcium carbonate measurements through the Belemnite Marls (lower Pliensbachian are characterized by two scales of cyclicity that can be firmly linked to orbital–precession (20 ka) and the 123 ka componen of eccentricity. A time–scale has been developed from the precession–related sedimentary cycles, with cycle counts used t constrain the duration of two ammonite zones. In the Kimmeridge Clay Formation (Kimmeridgian–Tithonian), magnetic–susceptibilit measurements made on exposures, core material and down boreholes can be correlated at the decimetre scale. Only measurement of magnetic susceptibility made below the Yellow Ledge Stone Band (midway through the formation) are suitable for analysi of the bedding–scale cyclicity. A large–amplitude sedimentary cycle detected in the lower part of the formation is probabl related to the orbital–obliquity cycle (38 ka). In certain stratigraphic intervals, there is evidence for small–amplitud cycles related to orbital precession (20 ka). This study of the British Jurassic shows that, in the Rhaetian–Sinemurian, the dominant cyclicity was related to obliquity. In the Pliensbachian this had shifted to dominantly precession, and in the Kimmeridgian obliquity again dominated. These shift in cycle dominance presumably reflect changing local or global palaeoclimatic and/or palaeoceanographic conditions.
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The evolution of life on Earth is marked by catastrophic extinction events, one of which occurred ca. 200 Ma at the transition from the Triassic Period to the Jurassic Period (Tr-J boundary), apparently contemporaneous with the eruption of the world's largest known continental igneous province, the Central Atlantic magmatic province. The temporal relationship of the Tr-J boundary and the province's volcanism is clarified by new multidisciplinary (stratigraphic, palynologic, geochronologic, paleomagnetic, geochemical) data that demonstrate that development of the Central Atlantic magmatic province straddled the Tr-J boundary and thus may have had a causal relationship with the climatic crisis and biotic turnover demarcating the boundary.
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The Triassic – Jurassic boundary is generally considered as one of the major extinctions in the history of Phanerozoic. The high-resolution ammonite correlations and carbon isotope marine record in the New York Canyon area allow to distinguish two negative carbon excursions across this boundary with different paleoenvironmental meanings. The Late Rhaetian negative excursion is related to the extinction and regressive phase. The Early Hettangian d 13 C org negative excursion is associated with a major floristic turnover and major ammonite and radiolarian radiation. The end-Triassic extinction – Early Jurassic recovery is fully compatible with a volcanism-triggered crisis, probably related to the Central Atlantic Magmatic Province. The main environmental stress might have been generated by repeated release of SO 2 gas, heavy metals emissions, darkening, and subsequent cooling. This phase was followed by a major long-term CO 2 accumulation during the Early Hettangian with development of nutrient-rich marine waters favouring the recovery of productivity and deposition of black shales. D 2004 Elsevier B.V. All rights reserved.
We present a model to assess the viability of the creation of volcanic eruptions of up to flood-basalt size from a giant impactor striking a relatively thin lithosphere. A 300-km-radius crater in 75-km-thick lithosphere can create 10 6 km 3 of magma from instantaneous in situ decompression of mantle material with a potential temperature of 1300 °C. For a range of lithospheric thicknesses and potential temperatures, subsequent adiabatic melting caused by mantle convection beneath the lithosphere at the site of the impact can create additional magma. Though the evidence that a giant impactor has struck at the location of any terrestrial flood-basalt province is equivocal, there are possible age coincidences between evidence for impacts and occurrences of flood basalts. Our model demonstrates that a giant impactor could cause a flood basalt, and this process may have been significant early in Earth history when impactors were more frequent and mantle temperatures likely higher, though other processes are required for at least the majority of flood-basalt provinces today.
The mass extinction at the Triassic-Jurassic (Tr-J) boundary at 200 Ma ranks amongst the five most extreme in the Phanerozoic and occurred approximately at the same time as one of the largest volcanic episodes known from the geological record, that which characterized the Central Atlantic Magmatic Province (CAMP). Interpretations of climate change across the boundary are contradictory, whilst changes in the carbon cycle are poorly constrained. Here we present new organic carbon isotope data that demonstrate that changes in flora and fauna from both terrestrial and marine environments occurred synchronously with a transient light-carbon-isotope excursion and that this happened significantly earlier than the conventionally established marine Tr-J boundary. A second negative carbon-isotope excursion dominated the shallow-marine and atmospheric reservoirs for at least 600 k.y. These data suggest that a major perturbation occurred in the global carbon cycle at the Tr-J boundary which resulted in a significant increase in atmospheric pCO2 in less than a million years. Our results indicate synchroneity between the carbon-isotope excursion, the extinction event, the eruption of the first CAMP lavas, suggesting a causal link between loss of terrestrial and marine taxa and the very earliest eruptive phases.