AIMS AND BACKGROUND
The study of catastrophic events that affected the ecosystems in the past results of great interest, because it offers the possibility of establishing models for applying to environmental changes occurring currently and in the future. During the Toarcian Oceanic Anoxic Event (T-OAE), a change of the marine ecosystems related to massive extinction from several sections has been characterized around the world. From some regions, this event is recorded as a barren stratigraphic interval (without fossils) rich in organic matter.
The multidisciplinary integrated analysis of this event in stratigraphic successions from different regions over the world taking into account biotic (microfossils, macroinvertebrates and vertebrate assemblages) and abiotic data (sedimentology, cyclostratigraphy, mineralogy, elemental geochemistry, organic geochemistry and isotopic geochemistry) makes necessary the development of an international framework involving researchers from different disciplines and countries with the aim of collaborating and sharing advances and laboratory facilities.
Many marine ecosystems are under threat at the present day. The growing interest of the society for environmental changes occurring in the present and potentially in the future justifies the significance of the analysis of past climatic changes.
The Pliensbachian-Toarcian transition and the Toarcian Oceanic Anoxic Event (T-OAE) (Jenkyns, 1985, 1988; Jenkyns and Clayton, 1997) are two global episodes known by their palaeoenvironmental perturbations worldwide recorded. The end of the Pliensbachian regression (Brandt, 1986; Haq et al., 1987; Wignall and Maynard, 1993; de Graciansky et al., 1998) is followed by the transgression of the Early Toarcian (e.g. Haq et al., 1987; Hardenbol et al., 1998), together with the deposition of black shales (Jenkyns, 1988, 2010), a global warming (e.g. McArthur et al., 2000; Suan et al., 2011; García Joral et al. 2011; Korte and Hesselbo, 2011) and perturbations of the carbon cycle. These perturbations are evidenced by the negative carbon isotopic excursion (CIE) documented in both marine and terrestrial material recorded at the base of Levisoni Zone (Lower Toarcian) in several places around the world (e.g. Jenkyns and Clayton, 1986; Hesselbo et al., 2000, 2007; Schouten et al., 2000; Jenkyns et al., 2002; Emmanuel et al., 2006; Van Breugel et al., 2006; Al-Suwaidi et al., 2010; Caruthers et al., 2011; Izumi et al., 2012; Kafousia et al., 2014; Reolid, 2014; Xu et al., 2017).
An important second-order mass extinction is specially recorded during the Pliensbachian/Toarcian and Polymorphum (=Tenuicostatum)/ Levisoni zones (=Serpentinum) transitions (Lord, 1982, 1988; Little and Benton, 1995; Aberhan and Fürsich, 1997, 2000; Harries and Little, 1999; Wignall, 2001; Vörös, 2002; Cecca and Macchioni, 2004; Wignall et al., 2005; Bilotta et al., 2009; Mailliot et al., 2009; Gómez and Goy, 2011; García Joral et al., 2011; Danise et al., 2013; Caruthers et al., 2014; Ullman et al., 2014; Rita et al., 2016), mainly among the benthic organisms. Oxygen depleted conditions (from suboxic to euxinic) affected from platforms to oceanic deep environments (e.g. Röhl et al., 2001; Bucefalo Palliani et al., 2002; Wignall et al., 2005; Hermoso et al., 2009; Reolid et al., 2012; Rita et al., 2016). This interval has been recorded from many outcrops of Boreal Domain (Boreal and Subboreal provinces) and Tethys Domain (Submediterranean and Mediterranean provinces).
The project aims to deep in the climatic change evidenced by the related sea-level rise, carbon cycle perturbation, sea water acidification, global warming and second-order mass extinction occurred during the Pliensbachian/Toarcian boundary and the T-OAE through analyses of the rock and fossil records of Morocco, Algeria, Spain, Portugal, England, France, Italy, Switzerland, Germany, Poland, Greece, Iran, North Siberia, South China, Japan, Canada and Argentina. Through detailed studies of Upper Pliensbachian to Middle Toarcian biostratigraphy, ichnology, palaeoecology, ecostratigraphy, sedimentology, mineralogy, geochemistry, biogeochemistry and cyclostratigraphy in the above regions, this project will attempt to: (a) document marine global ecosystem’s collapse and the subsequent recovery, formulate the mechanism biotic response to climatic and environmental adverse conditions at fossil group level (calcareous nannoplankton, radiolarians, foraminifera, ostracods, bivalves, brachiopods, ammonites, and vertebrates) and trophic level; (b) to reconstruct the Lower Jurassic oceanic and climatic conditions and probe reciprocal effect mechanism between carbon cycle perturbation and global warming; and (c) to correlate all of these data in a global stratigraphic framework. To sum up, the main goals of this project are:
(1) To reveal the impact on marine ecosystems of carbon cycle perturbation and the global warming through productivity, water stagnation and oxygen depleted conditions.
(2) To elucidate the causes triggering this environmental change.
(3) To clarify the initial phases of the biotic crisis and the factors controlling biotic recovery in different trophic levels from various habitats and climate zones (Artic, Boreal, Sub-boreal, Tethyan and Austral), with special attention to adaptations of opportunists and specialists during the surviving and extinction stages (e.g. Lilliput effect, Lazarus effect, resilience…).
Finally, comparison with other oceanic anoxic events may be interesting for testing models, mainly with the OAE2 of the Cenomanian-Turonian boundary (Cretaceous). The Cretaceous oceanic anoxic events are one of the subjects of the project IGCP 609 Cretaceous sea-level changes, and collaborations will give a potential scientific feedback.
The support and active involvement in this project of most top scientists in the analysis of the T-OAE and other mass extinction events from around the world will lead to unique training opportunities for postgraduate students from a range of countries (Algeria, France, Germany, Iran, Italy, Portugal, Russia, Spain, Switzerland, and UK) as well as professionals from emerging countries alike. As a result, the IGCP project will supply a friendly platform for participants to communicate their own research results and also bring together global experts and research facilities to solve a truly global-scale problem.
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The analysis of ancient global environmental changes that affected the ecosystems always constitutes a relevant advance for scientific community as well as for society, because these studies allows establishing models for applying to environmental changes occurring currently and in the future. Many marine ecosystems are under threat at the present day because the activity of humans (contamination and emission of greenhouse gas). The growing interest of the society for environmental changes occurring in the present and potentially in the future justify the interest of the analysis of ancient climatic changes. Around one third of the greenhouse gas disappears from the atmosphere as it becomes dissolved in sea water and part of it is taken up by phytoplankton during photosynthesis. By this way the carbon is included in the trophic web and these organisms later die and then sink to the sea bottom and with them the carbon. High productivity may result on deposition of black shales (but collaterally produces high consume of oxygen and potential oxygen depleted conditions in deep waters). That makes the sea an ideal repository for greenhouse gas. The case of the Toarcian Oceanic Anoxic Event (T-OAE) shows a series of very interesting processes for establishing models: a perturbation of the carbon cycle, a global warming, oceanographic reorganization, changes in the productivity, enhanced deposition of organic matter, poorly oxygenated waters and the extinction of organisms (mainly affecting benthic forms). Therefore, the analysis of T-OAE is a good analogue for present and future changes in our oceans and constitutes a benefit to the society. However, most studies of the factors triggering this environmental change (thermogenic methane from vulcanism/ methane dissociation from marine platforms), the relation causes-effects, and the incidence in different areas (Arctic, Boreal, Sub-Boreal, Tethyan and Austral) are necessaries.