Responses of a shallow-water ecosystem to the early Paleogene greenhouse environmental conditions [Elektronische Ressource] : evolution of larger foraminifera and coral communities from the northern Tethys / Jessica Zamagni

Jessica Zamagni

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• Publié par: universitat_potsdam
• Publié le: 01 janvier 2009
• Nombre de lectures: 22
• Langue: English
• Poids de l'ouvrage: 18 Mo

Extrait

Institut für Geowissenschaften
Mathematisch-Naturwissenschaftliche Fakultät
Universität Potsdam
Responses of a shallow-water ecosystem to the
early Paleogene greenhouse environmental conditions
Evolution of Larger Foraminifera and coral communities
from the Northern Tethys
Jessica Zamagni
Dissertation
zur Erlangung des akademischen Grades
Doktor der Naturwissenschaften (Dr. rer. nat.)
in der Wissenschaftsdisziplin Geologie
eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam
Potsdam, im Februar 2009




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Published online at the
Institutional Repository of the University of Potsdam:
http://opus.kobv.de/ubp/volltexte/2009/3185/
urn:nbn:de:kobv:517-opus-31853
[http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-31853]
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Si fermò; e, guardandomi come per esser sicuro che capivo e che magari condividevo, si mise a
elencare quelle idee:
“Questo non è il solo mondo”, disse, indicando con un ampio gesto del braccio l´intero
orizzonte.
“Questo non è il solo tempo”, e puntò il dito contro il mio orologio.
ta non è la sola vita”, e indicò se stesso, Angela, me, il cane e tutto quel che c´era
attorno.
Si fermò come per farci riflettere.
“E questa non è la sola coscienza.” Toccandomi il petto concluse: “Ciò che è fuori è anche
dentro; e ciò che non è dentro non è da nessuna parte”.
Poi, come volesse allergerire l´atmosfera, scoppiò in una bella risata e, rivolto a me,
aggiunse: “Per questo viaggiare non serve. Se uno non ha niente dentro, non troverà mai niente
fuori. È inutile andare a cercare nel mondo quel che non si riesce a trovare dentro di sé”.
Mi sentii colpito. Aveva ragione.


Tiziano Terzani, “Un altro giro di giostra”










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- iv - ABSTRACT

Modern anthropogenic forcing of atmospheric chemistry poses the question of how the
Earth System will respond as thousands of gigatons of greenhouse gas are rapidly
added to the atmosphere. A similar, albeit nonanthropogenic,
situation occurred during the early Paleogene, when catastrophic release of carbon to
the atmosphere triggered abrupt increase in global temperatures. The best
documented of these events is the Paleocene-Eocene Thermal Maximum (PETM, ~55
Ma) when the magnitude of carbon addition to the oceans and atmosphere was similar
to those expected for the future. This event initiated global warming, changes in
hydrological cycles, biotic extinction and migrations. A recently proposed hypothesis
concerning changes in marine ecosystems suggests that this global warming strongly
influenced the shallow-water biosphere, triggering extinctions and turnover in the
Larger Foraminifera (LF) community and the demise of corals.
The successions from the Adriatic Carbonate Platform (SW Slovenia) represent an
ideal location to test the hypothesis of a possible causal link between the PETM and
evolution of shallow-water organisms because they record continuous sedimentation
from the Late Paleocene to the Early Eocene and are characterized by a rich biota,
especially LF, fundamental for detailed biostratigraphic studies. In order to reconstruct
paleoenvironmental conditions during deposition, I focused on sedimentological
analysis and paleoecological study of benthic assemblages. During the Late
Paleocene-earliest Eocene, sedimentation occurred on a shallow-water carbonate
ramp system characterized by enhanced nutrient levels. LF represent the common
constituent of the benthic assemblages that thrived in this setting throughout the Late
Paleocene to the Early Eocene. With detailed biostratigraphic and chemostratigraphic
analyses documenting the most complete record to date available for the PETM event
in a shallow-water marine environment, I correlated chemostratigraphically for the first
13time the evolution of LF with the δ C curves. This correlation demonstrated that no
major turnover in the LF communities occurred synchronous with the PETM; thus the
evolution of LF was mainly controlled by endogenous biotic forces.
The study of Late Thanetian metric-sized microbialite-coral mounds which
developed in the middle part of the ramp, documented the first Cenozoic occurrence of
microbially-cemented mounds. The development of these mounds, with temporary
dominance of microbial communities over corals, suggest environmentally-triggered
“phase shifts” related to frequent fluctuations of nutrient/turbidity levels during recurrent
wet phases which preceding the extreme greenhouse conditions of the PETM. The
paleoecological study of the coral community in the microbialites-coral mounds, the
study of corals from Early Eocene platform from SW France, and a critical, extensive
literature research of Late Paleocene – Early Eocene coral occurrences from the
Tethys, the Atlantic, the Caribbean realms suggested that these corals types, even if
not forming extensive reefs, are common in the biofacies as small isolated colonies,
piles of rubble or small patch-reefs. These corals might have developed ‘alternative’ life
strategies to cope with harsh conditions (high/fluctuating nutrients/turbidity, extreme
temperatures, perturbation of aragonite saturation state) during the greenhouse times
of the early Paleogene, representing a good fossil analogue to modern corals thriving
close to their thresholds for survival.
These results demonstrate the complexity of the biological responses to extreme
conditions, not only in terms of temperature but also nutrient supply, physical
disturbance and their temporal variability and oscillating character.



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- vi - ZUSAMMENFASSUNG

Die anthropogene Beeinflussung der Chemie der Atmosphäre in der modernen Zeit
wirft die Frage nach dem Schicksal des Systems Erde auf, wenn tausende von Tonnen
an Treibhausgasen in kurzer Zeit in die Atmosphäre einströmen. Im Känozoikum trat
bereits eine ähnliche Situation während des frühen Paläogens auf, als eine
katastrophale Freisetzung von Kohlenstoff in die Atmosphäre einen plötzlichen Anstieg
der globalen Temperatur hervorrief. Das am besten dokumentierte dieser Ereignisse
stellt das Paläozän-Eozäne Temperatur Maximum (PETM, ~55 Ma) dar, bei welchem
die Größenordnung der Kohlenstoffzufuhr in Ozeanen und Atmosphäre jener ähnelte,
die in der Zukunft zu erwarten ist. Das damalige Ereignis initiierte eine globale
Erwärmung, Veränderungen hydrologischer Kreisläufe, biotische Auslöschung und
Abwanderungen. Eine kürzlich veröffentlichte Hypothese zu Veränderungen in marinen
Ökosystemen postuliert, dass diese globale Erwärmung die Biosphäre der
Flachwässer stark beeinflusste, indem sie Aussterben und Fluktuation innerhalb der
Gemeinschaft der Großforaminiferen (GF) sowie den Niedergang einiger Korallen
bewirkte.
Die Abfolgen der Adriatischen Karbonatplattform (SW-Slovenien) stellen einen
idealen Ort dar, um die Hypothese des kausalen Zusammenhangs zwischen dem
PETM und der Evolution der Flachwasserorganismen zu überprüfen, da sie aufgrund
ihrer kontinuierlichen Sedimentation vom Spätpaläozän bis zum Früheozän und ihres
Reichtums an Biota, insbesondere an GF, fundamentale Voraussetzungen für eine
detaillierte biostratigraphische Studie erfüllen. Um die Paläoumweltbedingungen
während der Sedimentablagerung zu rekonstruieren, wurde der Schwerpunkt dieser
Arbeit auf eine sedimentologische Analyse und eine paäoökologische Studie
benthischer Vergesellschaftungen gesetzt. Während dem Spätpaläozan bis zum
frühesten Eozän fand die Sedimentation auf einem Flachwasse