Evolution of the western Black Sea: Kinematic and sedimentological inferences from geological observations and analogue modelling

Abstract

The architecture of sedimentary basin is the result of the interplay between deep-seated tectonic processes at lithospheric or crustal scale creating or reducing the accommodation space, and the near-surface processes taking place in the source and depositional areas. Understanding the evolution of the sedimentary basin requires, therefore, an integrated study of the coupling between sediment routing and lithospheric processes that are responsible for basin formation, evolution and, ultimately, for its closure by complete stages of regressive basin fill, or inversion and exhumation. This thesis is focused on understanding the mechanism controlling the tectonic and sedimentary evolution of back-arc basins, from their opening to subsequent inversion. During the quest of understanding the particular type of basin formation and subsequent inversion in the Black Sea Basin, two main objectives were pursued. The first objective is related to understanding the role played by inherited extensional rheology in far-field transmission and localization of compressional deformation driven by an active orogenic area into a pre-existing back-arc domain. Back-arc contractional geometries are not necessarily controlled by major internal asymmetries, such as active subduction zones. Therefore, the presence of inherited rheologically weak zones controls the vergence of thrusting systems during back-arc inversion. The lateral variability of such weakness zones may create a contractional polarity change, which is a change in the thrusting vergence along the strike of the back-arc basin where its opposite margins act as indenters. This type of change, critical for understanding a number of worldwide basins, such as the Black Sea or the Huon-Finisterre arc, has received little attention so far in phenomenological studies. The second objective of the thesis is to understand the effects of large sea level variations in the depositional architecture and sedimentary exchange between basins connected through a shallow marine barrier. The objective is studied in the context of the Late Miocene-Quaternary sediment fluxes between the Carpatho-Balkans source area, the Dacian marginal basin and the Black Sea main sink by the means of seismic sequence stratigraphic analysis calibrated by wells in both basins. The thesis is organized in two main sections. Following a brief introduction in Chapter 1, two observational studies in Chapters 2 and 3 analyze the geometries and effects of Black Sea Basin back-arc opening and inversion, and the effects of the large scale sea-level drop recorded during the Messinian Salinity Crisis of the Paratethys. These observational studies form the base of the phenomenological process-oriented studies in Chapters 4 and 5 that analyze the mechanisms of backarc basin inversion by the means of analogue modeling. The thesis ends with the conclusions of Chapter 6.