Distribution of sediments and palaeosols in ancient distributive fluvial systems: proxies for palaeoenvironmental and stratigraphic interpretations

Abstract

Fluvial facies models are vastly based on models of tributary rivers under humid climates. However, state-of-art in fluvial sedimentology demonstrates that the majority of the stratigraphic record is composed of distributive fluvial systems (DFS). As a consequence, this approach, focused a priori over a restrict fluvial end-member, establishes a deficient ground to comprehend ancient distributive fluvial systems. In particular, dryland distributive fluvial systems because the current approach do not account for their incredibly complex spatio-temporal variability, resulting in depositional models of poor stratigraphic resolution. Current challenge in fluvial sedimentology relies on the investigation of palaeoclimatic factors that control the dynamics and stratigraphic organisation of ancient distributive fluvial systems. DFS models are focused primarily on palaeohydraulic reconstructions from sediments, with little or no attention to palaeosols. This method results in great disadvantage to the scientific community with loss of valuable palaeoenvironmental and stratigraphic information that palaeosols preserve. Due to the absence of models that include palaeosols, this research project deals with the sediment-palaeosol interaction in ancient distributive fluvial systems and involves two sedimentary successions: the Bauru Group (SE Brazil) and the Esplugafreda Formation (NE Spain). Both successions were developed during the Upper Cretaceous at the margins of their respective sedimentary basins under dryland conditions, allowing a comparative study on the interaction of sediments-palaeosols for ancient distributive fluvial systems. The main objective of this proposal is to apply information from palaeosols and clastic sediments as palaeoenvironmental and stratigraphic proxies. In particular, to verify how palaeoclimatic, palaeomorphologic, temporal, palaeobiologic, and sediment supply information (from palaeosols), as well as depositional processes and their controlling factors (from sediments), govern the sedimentary processes and depositional dynamics of ancient distributive fluvial systems. By applying this approach, this project proposes to construct a palaeopedosedimentary model that recognises palaeoenvironmental factors controlling the sedimentary and palaeopedogenetic processes considering the lateral and downstream dynamics of such intricate systems. As a consequence, this research project is justified by: (i) the highly scientific value of palaeosols as palaeoenvironmental and stratigraphic proxies, (ii) because studies on the interactions of palaeosols/sediments are scarce in literature and (iii) by the absence of models that consider the distribution of sediments and palaeosols in ancient distributive fluvial systems.