Geo-Biosphere, geodynamics and climates of the past
The history of our planet is unique because Life interacts with its physicochemical environment. Understanding the relationships and feedbacks between the Geosphere and the Biosphere on a planetary scale and on a time scale specific to the Earth's natural cycles (the geological time scale) is a fertile research theme that is gaining momentum. within the framework of IRePSE. It has been supported in the past through emerging multidisciplinary projects.
Given that researchers and teachers - researchers in this scientific field often have study sites located abroad, this theme can be based on numerous existing international collaborations (Russia, Mexico, China, Maghreb, Caucasus, Iran , Japan, Australia). These contacts could be used in the framework of coordinating IRePSE activities in support of UL's IR policy.
This area will be structured in 3 axes:
- Axis 1 “Primitive Life and Earth” will be able to rely on researchers with skills in geochemistry (organic and isotopic), mineralogy and paleontology, as well as on analytical devices available in mass spectrometry, to constrain co-evolution of Life and environments on Earth during the Proterozoic, before the emergence of complex marine ecosystems at the base of the Cambrian (Phanerozoic). The particularity of this theme, under development, in particular within the framework of the ANR M6fossils, consists in the determination of micro- and macro-fossils using new microanalyses and innovative techniques (ToF-SIMS, μL2MS) which allow molecular and anatomical information to be extracted from isolated cells; this information makes it possible to better constrain the determination of these fossils, which are difficult to recognize among the branches known today. It is also based on a Franco-Russian collaboration for the study of ediacarian fossils (late Proterozoic; around 550 Ma = million years), difficult to identify but exceptionally well preserved in Russia; their comparison with analogous morpho-structures that can be observed today on microbial mats formed in extreme hypersaline environments helps us to better interpret their biological origin and understand their formation. In addition, the Ediacaran - Cambrian transition, very probably also represented a major turning point in the greening of terrestrial landscapes (continental ecosystems), during which microbial communities gave way to an emerging algal community (charophytes) which constituted the ecological basis for the evolution of continental plants and the subsequent arrival of land animals. One of the inter-laboratory projects supported in 2018 by IRePSE makes it possible to integrate the environmental and geomicrobiological characterizations of different ecosystems by complementary approaches, from sedimentology to (bio) geochemistry. Another collaborative project is the study of the evolution of the Devonian - Carboniferous tracheophytes and protracheophytes, notably with the flora of Rhynie Chert in Scotland and the Paleontology collections of ULille.
- Axis 2 will focus on "the couplings between geodynamics, climate and paleobiodiversity". Following the problems associated with the use of fossil organic materials from geological reservoirs and the release of large quantities of greenhouse gases into the atmosphere, much reflection has been carried out within the scientific community on the natural processes which lead, on the geological time scale, to a modification of the distribution of the different carbon stocks on our planet. Thus, numerous studies suggest that in the long term, the internal dynamics of the Earth (degassing of CO2 due to volcanic eruptions) and the formation of mountain chains must have had a profound influence on the climate of the past. Indeed, the imposing reliefs resulting from the formation of mountain chains significantly increase the chemical alteration of rocks, the flow of nutrients to the oceans and the storage of organic carbon in ocean sediments (biological pump of CO2). Thus, the gradual climatic cooling observed since about 40 Ma and the entry into the current type of climate "Icehouse", are partly attributed to the uplift of the Alpine mountain range, from the Alps to the Himalayas.
However, the Upper Paleozoic (420-250 Ma) also corresponds to a major orogenic period, comparable in terms of reliefs created the last 40 Ma; indeed, many mountain systems were formed between the upper Devonian and the late Carboniferous and our planet experienced ice caps on the poles (at least the south pole) at that time; therefore, this geological interval can be considered as an analogue of recent times, at least as regards the paleotopographic and paleoclimatic dimension. Insofar as the evolution of these mountain systems has been much more advanced than the Alps-Himalayan system, which is still in a relatively early stage of its evolution, the understanding of the global terrestrial system in the Upper Paleozoic can provide us with valuable perspectives. on the natural evolution of the climate for the millennia to come. The first effects of this great orogenic period were recorded as early as the Frasnian / Famennian passage (Upper Devonian, ca 375 Ma) with the uplift of peri-equatorial mountain ranges, from Central Asia to North America. This period was also marked by a significant drop in marine biodiversity (this is one of the 5 major Phanerozoic crises, that of the Frasnian-Famennian limit, called the “Kellwasser event”) and by drastic contemporary environmental changes a global cooling of the climate leading to the establishment of ice caps at high latitudes in the Upper Famennian.
"The Hangenberg event", recorded at the Devonian / Carboniferous border, also constitutes a major crisis event. The harmful causes of these two events of biological crisis are to be found ultimately in global climate change. This thematic requires a multidisciplinary approach between paleontologists, sedimentologists, geochemists and tectonics, in order to highlight and understand the paleobiodiversity dynamics of the Upper Devonian / Lower Carboniferous, follow the evolution of oceanic paleoenvironments, take an interest in geometry and kinematics of mountain ranges, paleogeography and the dynamics of erosion on continents during this same time interval. The geochemical signal of alteration and oxygenation / anoxia of marine series measured in an integrated stratigraphy framework, can inform us about the forcing of orogenic pulses on the climate.
- Axis 3 will focus on "Quaternary climates, environments and people interactions". The development of this axis is based on the interactions of paleontological, sedimentological and geochemical expertise from the IRePSE laboratories. The data acquired so far shows that changes in climate may have conditioned human response to changes in their environment. Likewise, the fossil and sedimentary record also reveals the different ways in which Man himself has influenced his environment, in a deep and lasting way. One of the objectives is to monitor in parallel the adaptive capacities of human groups present in the region, from the nomadic hunter-gatherers of Prehistory to historic settled societies. The responses to these climatic and environmental changes in terms of management of the territories and natural resources of these different human groups are also easily developable in the form of Geographic Information Systems. One of the goals sought is in particular the understanding and monitoring of the modalities of the establishment of modern ecosystems present in the region, as well as the interactions between humans and these changes in environments.
Particular attention will be paid to the inventory of species present in the region during temperate phases or naturally adapted to current ecological conditions. Beyond these aspects, an identification of "true non-anthropized ecosystems" will make it possible to provide leads for land developers in the perspective, for example, of the reintroduction of certain species of animals. Furthermore, understanding the responses of coastal ecosystems to climatic and anthropogenic pressures is of academic interest, but also applied. More particularly, the transition zone between estuaries and coastal zones evolves very dynamically over time, driven by changes in sea level, sediment flows which change in close relation to climate and anthropogenic activity. It is therefore interesting to be able to follow over time the ecological and sedimentary evolution of estuaries and the transition zone between them and coastal areas in order to trace (and predict?) The influence of anthropo-climatic factors on the feature. next to. The Picardy and Flemish coastal plains and their numerous estuaries are particularly suitable for this study, especially since the estuaries contain a high-quality record of the Holocene history of the region. Finally, within this axis, are also envisaged all the studies resulting from the drilling of deep marine domains which allow, through the mineralogical and geochemical study of sedimentary particles to reveal and understand the earth-sea transfers and paleoclimatic changes that occurred in the Quaternary.