Palaeosols as ancient critical zone for past and future predictions: the quarrel between sedimentary and pedogenic processes in ancient continental deposits

Abstract

In sedimentary basins, the soils form when the sedimentation stops or becomes slower. Accordingly, in sedimentary successions the palaeosols represent the antithesis of the sediments and the alternating presence of one and the other represents a "quarrel" between the two. Palaeosols (buried soils) are very common in continental successions from Archean to present, often forming the entire stratigraphic section. Palaeosols are geological bodies that make up a palaeo-Critical Zone, that is, a physical entity in which three palaeo-systems (palaeoatmosphere, palaeobiosphere e palaeolithosphere) operated. This is why palaeosols can record during their development (from hundreds to millions of years) all those phenomena that occurred within these three palaeo-systems. As a result, palaeosols are invaluable collector of past information such as palaeoclimate, palaeotopography, palaeobiology, palaeodeposition and time. The interactive study of deposits and palaeosols allows to understand the dynamics of the formation of continental sedimentary successions and the responsible processes. Therefore, this allows predicting the future behaviour of the terrestrial surface. According to these prerogatives, the palaeosols are useful for academic and applicative targets for: (i) determining palaeoclimate models, (ii) defining the architecture of the sedimentary bodies, (iii) on larger scale, constituting the boundaries of Sequence Stratigraphy units, (iv) discriminating the palaeoecosystem, palaeotopography and palaeolandscape and (v) detecting places of natural resources such as coal, water, clays, uranium, phosphates. Despite this, palaeosols are barely considered in both academia and industry. In this project a team of Brazilian and foreign researchers will develop three research themes associated with palaeosols and deposits: (i) climate changes recorded in palaeosols; (ii) cyclical alternations between sedimentary and pedogenic processes in continental successions and relationships with depositional dynamics; (iii) small- and large-scale control of the palaeotopography on the distribution of palaeosols. Field works are carried out in known areas by the research team: Serra do Pasmar (Diamantina, MG) and Eastern Pyrenees (Spain). The goal of the project is to demonstrate that the study of the interaction between deposits and palaeosol allows reveal the dynamics of continental sedimentary successions. The specific objectives are linked to the research themes: (i) palaeoclimate, (ii) small-scale stratigraphy and (iii) palaeotopography. Facies analysis and depositional architecture is the methodology applied to study deposits. Macrodescription, micromorphology and geochemistry are the basic methodologies of palaeosol analyses. Palaeontological studies, radiometric dating, remote sensing, data quantifications and statistical analyses contribute to these analytical methods. Finally, our perspective is to contribute to the academic and applicative diffusion of the palaeopedology. (AU)