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Sedimentation in the upstream reaches of incised valleys is predominantly of alluvial origin and, in most cases, independent from relative sea-level or lake-level oscillations. Preserved facies distributions record the depositional response to a combination of allogenic factors, including tectonics, climate and landscape evolution. Tectonics drive fluvial aggradation and degradation through local changes in gradient, both longitudinal and transverse to the valley slope. This article deals with a Pliocene-Pleistocene fluvial valley fill developed in the north-eastern shoulder of the Siena Basin (Northern Apennines, Italy). Evolution of the valley was not influenced by sea-level or lake-level changes and morphological and depositional evolution of valley resulted from extensional tectonics that gave rise to normal and oblique-slip faults orthogonal and parallel to the valley axis. Data from both field observations and geophysical study are interpreted to develop a comprehensive tectono-sedimentary model of coeval longitudinal and lateral tilting of the developing alluvial plain. Longitudinal tilting was generated by a transverse, upstream-dipping normal fault that controlled the aggradation of fining-upward strata sets. Upstream of the fault zone, valley back-filling generated an architecture similar to that of classic, sea-level-controlled, coastal incised valleys. Downstream of the fault zone, valley down-filling was related to an overwhelming sediment supply sourced and routed from the active fault zone itself. Lateral tilting was promoted by the activity of a fault oriented parallel to the valley axis, as well as by different offsets along near orthogonal faults. As a result, the valley trunk system experienced complex lateral shifts, which were governed by interacting fault-generated subsidence and by the topographic confinement of progradational, flank-sourced alluvial fans. [ABSTRACT FROM AUTHOR]

The mode of channel-bend transformation (i.e. expansion, translation, rotation or a combination thereof) has a direct bearing on the dimensions, shape, bedding architecture and connectivity of point-bar sandstone bodies within a fluvial meander belt, but is generally difficult to recognize in vertical outcrops. This study demonstrates how the bend transformation mode and relative rate of channel-floor aggradation can be deciphered from longitudinal outcrop sections aligned parallel to the meander-belt axis, as a crucial methodological aid to the reconstruction of ancient fluvial systems and the development of outcrop analogue models for fluvial petroleum reservoirs. The study focuses on single-storey and multi-storey fluvial meander-belt sandstone bodies in the Palaeogene piggyback Boyabat Basin of north-central Turkey. The sandstone bodies are several hundred metres wide, 5 to 40 m thick and encased in muddy floodplain deposits. The individual channel-belt storeys are 5 to 9 m thick and their transverse sections show lateral-accretion bed packages representing point bars. Point bars in longitudinal sections are recognizable as broad mounds whose parts with downstream-inclined, subhorizontal and upstream-inclined bedding represent, respectively, the bar downstream, central and upstream parts. The inter-bar channel thalweg is recognizable as the transition zone between adjacent point-bar bedsets with opposing dip directions into or out of the outcrop section. The diverging or converging adjacent thalweg trajectories, or a trajectory migrating in up-valley direction, indicate point-bar broadening and hence channel-bend expansion. A concurrent down-valley migration of adjacent trajectories indicates channel-bend translation. Bend rotation is recognizable from the replacement of a depositional riffle by an erosional pool zone or vice versa along the thalweg trajectory. The steepness of the thalweg trajectory reflects the relative rate of channel-floor aggradation. This study discusses further how the late-stage foreland tectonics, with its alternating pulses of uplift and subsidence and a progressive narrowing of the basin, has forced aggradation of fluvial channels and caused vertical stacking of meander belts. [ABSTRACT FROM AUTHOR]