Leaders of the project
Dr. Peter Königshof (*), Dr. Jurga Lazauskiene (**), Dr. Eberhard Schindler (*), PD Dr. Volker Wilde (*) and Prof. Dr. M. Namik Yalçin(***)
* Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany, Peter.Koenigshof@senckenberg.de (Phone: +49-69-970751686, Fax: +49-69-970751120), Eberhard.Schindler@senckenberg.de (Phone: +49-69-970751132, Fax: +49-69-970751137), Volker.Wilde@senckenberg.de (Phone: +49-69-970751160, Fax: +49-69-970751137)
The Devonian was a critical period with respect to the diversification of early terrestrial ecosystems. The geotectonic setting was characterized by the switch from the post-Caledonian to the pre-Variscan situation. Plant life on land evolved from tiny tracheophytes to trees of considerable size in combination with a global increase in terrestrial biomass, and vertebrates started to conquer the land. Extensive shallow marine areas and continental lowlands with a wide range of different habitats existed which are preserved in a large number of basins all around the world. Climate change finally led from greenhouse to icehouse conditions towards the end of the Devonian. Both, rapid evolution of terrestrial ecosystems and climate change had a pronounced influence on sedimentation and biodiversity not only in the terrestrial but also in the marine realm ("Devonian Change"). A major goal of the proposed project will be to focus on controls and interactions of the respective facies parameters in different paleogeographic settings in order to refine the global picture by international co-operation in a number of case studies. Geoscientific co-operation will include a variety of disciplines, such as sedimentology, paleontology, stratigraphy, paleoclimatology, paleogeography, geochemistry, paleooceanography, and structural geology.
The rapid evolution of early life on land and its interaction with sedimentary processes, climate, and paleogeography, both on land and in marine settings, will be covered by studies in different terrestrial and marine facies. Increasing colonization of the land by plants in combination with soil-forming processes and changing runoff led to major changes of sediment input into the marine system. On the other hand, sediment input and climate are major controls for carbonate production and reef development. The study of responses and interactions thus needs detailed characterization of facies and high-resolution correlation which can only be provided by a refined stratigraphy including biostratigraphy, lithostratigraphy, chronostratigraphy, etc. Characterization of facies and correlation of stratigraphic units is especially difficult in marine-terrestrial transitions and will be an important focus of the project. Resolution of sea-level changes will be enhanced by recognition and exact correlation of their effects which may be hidden just in these transitions. On the background of the global geotectonic situation (paleogeography s.l.), this will be an important prerequisite for a better discrimination of eustatic, climatic, and biotic controls, both on regional and global scale.
The focus of the project concerns the interrelated evolution of terrestrial and marine paleoecosystems with respect to biotic and abiotic factors in space and time. Studies will include individual paleoecosystems and their components as well as their paleobiogeographic distribution. Biotic and abiotic factors of paleoecosystems are controlled by both, earthbound and extraterrestrial triggers causing either cyclicity and/or distinct events. Thus in turn, such studies may give a clue to underlying causes of global changes. The project will include sedimentologic and climatic controls of reef development and distribution as well as diversity, and paleoecology of reef building organisms throughout the Devonian, because the Middle to Late Devonian was a peak in reef development with reefs spreading into latitudes as high as 45-60 degrees. On the other hand, accomodation space for Early Devonian reefs was greatly reduced due to major input of sediment from the continents in combination with sea-level lowstand(s). A marked decline in reef development towards the end of the Devonian was probably caused by climatic deterioration.
The integrative kind of research which is needed for the success of the project can only be carried out by a worldwide network of research groups representing different disciplines. Such a network can now be based on core groups successfully participating in the forerunner IGCP 421. Furthermore, the project will extend the results of the former IGCP 328. It will actively interlink with IGCP 491 which is mainly centered around vertebrate research. But, the IGCP 499 will concentrate on the correlation and interaction of different ecosystems in a more general way. Special attention will be paid to coupling effects between the terrestrial and marine realm. Co-operation is also intended with IGCP 497 "The Rheic Ocean: its origin, evolution and correlatives". Furthermore, an active network is represented by the members of the "Subcommission on Devonian Stratigraphy" (SDS). These existing networks will be integrated and thus providing the necessary base for an improved understanding of the Devonian period.
Full description of the project:
Knowledge about behaviour and development of ecosystems and climate in the geologic past is one of the most interesting tasks for future research. It is essentially needed for the understanding of Earth's history. Deciphering the respective archives requires a highly diversified approach, including biotic and abiotic systems. Accordingly, some key topics have to be considered which are contributing to the general picture of past ecosystems. Therefore, any kind of stratigraphic tool must be applied in order to understand, compare, and interpret the different kinds of rock sequences in space and time. This includes radiometric dating and the analysis of all kinds of biotic and abiotic events. Most important are controlling factors, both earthbound (endogenic and exogenic) and extraterrestrial. Effects such as cyclicity and the evolution of climate are directly triggered by these processes and events, and they in turn trigger bioevolutionary mechanisms. Where possible, comparison with modern ecosystems may allow for a more profound interpretation of the past.
The major focus of the project concerns the Devonian land-sea interaction with special regard to the following aspects. The Devonian period was characterized by extensive shallow marine and continental lowland areas. Therefore, a wide range of different habitats is preserved in the sedimentary record. The geotectonic situation following the Caledonian orogeny, the decreasing influence of climatic differentiation, and the rapid evolution of terrestrial ecosystems led to a unique framework of abiotic and biotic factors which has been comparatively well studied in areas like western and central Europe and North America (Old Red Continent and adjacent regions). Thus, controls and interactions of these factors should now be studied in a multitude of different facies and paleogeographic settings from fully continental to fully marine in other less known areas such as Asia and South America. This needs the global-scale co-operation of different working groups in geosciences including a number of disciplines: stratigraphy, paleontology, paleoecology, sedimentology, paleogeography, and structural geology.
Within the project, the rapid evolution of early life on land (e.g., Scott 1984, Gordon & Olson 1995, Niklas 1997, Gensel & Edwards 2001), and its interaction with sedimentary processes, including soil formation (Retallack 2001), and the atmosphere as especially expressed by climate (e.g., Gordon & Olson 1995) will be the subject of case studies in different settings (e.g., lacustrine, fluviatile, deltaic, shallow marine) and areas (e.g., Europe, North and South America, Asia). Special attention will be paid to collecting data with respect to related coupling effects (e.g., Algeo et al. 1995, Algeo & Scheckler 1998) on a global scale. The most important radiation of landplants is leading from primitive homosporous tracheophytes at the beginning of the Devonian to complex forest ecosystems including early gymnosperms in the Upper Devonian (e.g., Edwards 1980, Scott 1984, Gensel & Edwards 2001). This is coupled to an increase in the production of plant biomass from negligible in the Lower Devonian to considerable quantities in the Upper Devonian. The rapid evolution of landplants is the base for the rise of complex terrestrial ecosystems including organisms like fungi and arthropods (e.g., the Rhynie Chert ecosystem; Kerp 2002), and later in the Upper Devonian even vertebrates. Another consequence is a rapidly increasing influence of soil-forming processes on weathering and sedimentation (Retallack 2001). Accordingly, the global carbon budget changed fundamentally with respect to upcoming terrestrial sinks. At the same time, sedimentary input from the continents decreased radically with increasing plant cover and soil formation (e.g., Algeo et al. 1995, Algeo & Scheckler 1998). Nutrient cycling may have changed correspondingly, especially including phosphorus and nitrogen. As a result, marginal and other shallow marine ecosystems, including reefs, were strongly influenced.
The Devonian is one of the most important reef building episodes of the Phanerozoic (e.g., Copper 1988, 2002). The reefs were mainly constructed by stromatoporoids and corals as dominant frame-builders. One of the aims of the project is the parameterization of the environmental sequence in which reefs grew and their relation to other facies. A key factor in understanding the onset of reef growth is the identification and biology of pioneer organisms as well their environmental capabilities with regard to limiting external and internal parameters. Studies of the reef bodies themselves must cover the nature and size of reef builders including presence and abundance of cryptic habitats. An important aspect of the project will be the study of cyclic reef growth which can provide a tool for regional and global correlation with respect to different facies in shallow marine settings. Therefore, criteria for extending correlation of series/stage boundaries within and beyond these important Paleozoic shallow water sequences need to be established.
The Early Devonian was an episode of increasing coral, sponge and brachiopod diversity and provincialism (see e.g., Urals and South China). At the same time, erosion of the Caledonian orogens produced a large amount of clastic material reducing the accomodation space for reefs to continental margins, enhanced by sea-level lowstand(s). Therefore, these comparatively rare and poorly known reefs need to be studied in different paleogeographic settings. During the Middle Devonian there were several major reef belts extending over more than 2.000 km along western Laurentia, western Europe, southern Europe-North Africa, the Urals and the eastern side of the Baltic area, Siberia and Mongolia, and a smaller belt in South China with a length of more than 1.000 km (Copper 2002). Besides the well known reefs in Europe or North Africa, little is known about reefs in the western Sahara region, Russia (Pechora region, Siberia), or the Chinese reef complexes in Guangxi Province (Yu & Wu 1988, Bai et al.1994). Reef deterioration in the late Middle and Late Devonian was influenced by the Taghanic Event (middle-late Givetian) and the late Frasnian Kellwasser Crisis. This was finally leading to the disappearance of biohermal reef structures close to the Frasnian/Famennian boundary.
Evolution of terrestrial ecosystems in the Devonian as mainly mirrored by plants was obviously rapid and almost continuous. On the other hand it included major steps, such as the invention of extended rooting systems, secondary xylem, and elaborate mechanisms for reproduction (heterospory, gymnospermy) and dispersal (seeds) (e.g. Gensel & Edwards 2001, Kenrick & Crane 1997, Niklas 1997). In contrast, a number of global bioevents affected the marine realm throughout the Devonian, some of which are especially important for reef development. Causes as well as temporal and areal extent and effects of these bioevents affecting mainly groups of the marine fauna have been intensely studied, e.g., within the successful IGCP 216 and 335 and can be traced in different facies (summaries in Walliser 1996, Hart 1996). Even when the event-related phenomena are preferably recognizable in open marine settings, efforts are needed to trace them in near-shore environments and even into the terrestrial realm. It must be clarified to which extent there is a coupling between the marine bioevents, sea-level changes, major steps in landplant evolution, and/or climate changes, or even extraterrestrial catastrophes. An elaborate stratigraphical framework is one of the indispensable prerequisites for any correlation, and modern techniques and approaches (e.g., radiometric dating, palynology) have to be applied. Many specialists working on various elements of the Devonian fauna and flora which were affected by bioevents (e.g., corals, stromatoporoid sponges, brachiopods, conodonts, goniatites, trilobites, tentaculitids, ostracodes, bryozoans, and palynomorphs) have already contributed to event research and could get involved in the project (compare list of participants).
The project is partly succeeding IGCP 328 and 421. IGCP 328 focused on Paleozoic vertebrates and the results (see final report by Blieck and Turner 2000) have shown that many Paleozoic fish-bearing deposits can be correlated on a regional, paleocontinental or even a global scale. Microvertebrate remains have been found and analyzed mainly from deeper water facies, especially in order to correlate these data in the Devonian with the conodont standard zonation. The IGCP 499 will now focus on the interaction of shallow water and terrestrial ecosystems with respect to their evolution and climate change which was not the main focus of the IGCP 328 or 421. The latter one has terminated, but some research initiatives that emerged from it should continue with regard to the topics of the new project. Such a continuation was highly recommended by participants of the former IGCP 328 and 421. Additionally, there is a link to the existing IGCP 491 on middle Paleozoic vertebrate biogeography, paleogeography and climate which is succeeding IGCP 328. Interaction has also started with the new ICGP 497 on the "Rheic ocean: its origin, evolution and correlatives". These three projects should complement and benefit from each other.