Tectonic control on the dynamics of turbidite channels: evidence from fields and subsurface data

Turbidite channels are fundamental depositional/architectural elements in deep-water systems, serving as pathways for sediment dispersal into the basin. This depositional element is of particular interest: (i) from a scientific point of view, because it underlies the development of turbidite systems that form the framework of many orogenic belts with remarkable outcrop exposures, and (ii) from an economic point of view, because it hosts significant hydrocarbon accumulations. For practical mapping purposes, ancient channel deposits include all sedimentary strata formed within the channels. Mutti and Normark (1987, 1991) proposed a practical and straightforward characterization of the main types of channel fill observed in ancient systems, based on both outcrop and subsurface studies. However, this framework, as well as more recent models, does not fully account for variations in sedimentary processes, bed thickness, and stacking patterns across different channels. In light of this, the present work aims to investigate the factors that control the filling dynamics of turbidite channels throughout their evolutionary history. To elucidate these controls, geological processes were analyzed at multiple scales and in different basins, ranging from the depositional mechanisms of individual turbidite beds, studied in the field and in cores, to the generation of three-dimensional numerical models at exploration well and seismic scales. The analyzed outcrops are exceptionally well-exposed successions in the Northern Apennines (Italy) and in the south-central Pyrenees. In contrast, subsurface systems in divergent margins include hydrocarbon reservoirs of the Campos Basin, offshore Brazil. The results demonstrate that turbidite channels can be subdivided into two distinct phases: bypass and depositional channels. The results of the work provide evidence that the filling of each channel type occurs in phases that vary according to the interaction between turbidity currents and transverse barriers encountered along the channel pathway. In the bypass phase, sedimentation proceeds without obstacles to the turbidity currents. The initial phase is characterized by residual lag deposits (facies F3 and F4; sensu Mutti et al. 2003 and Tinterri 2025), with the main sedimentary structures including supercritical bedforms, amalgamation surfaces, mud-draped scours, and cross-bedded conglomerates. The actual channel fill occurs after system deactivation or during a marine transgression. Sedimentation in this phase is marked by low sandstone-to-mudstone ratios and by fining-upward, thin-bedded intervals of F8 and F9 facies, in which lateral accretions related to a meandering belt can be common. This phase is generally associated with periods of tectonic quiescence. Conversely, the depositional phase develops in the presence of a transverse obstacle to the paleocurrent direction. Its initial phase is characterized by a bypass phase, followed by marked depositional facies such as facies F5b, F5m, F5f, F6d, F6r, and F8b, F8m, F8f (sensu Tinterri, 2025). Other important diagnostic structures include flame and load casts, water escapes, amalgamation surfaces, mudstone clasts, and backstepping beds. Beds are thick to very thick and can reach thicknesses exceeding 10 meters, forming megabeds. Furthermore, the sandstone-to-mudstone ratio is high to very high. These features are clear evidence of abrupt decelerations of high-density turbidity currents induced by transverse morphologies. Such conditions commonly arise from tectonic activity, including faulting and folding, or from depositional controls such as diapirs, mass-transport deposits (MTDs), or thick lobes that impose physical barriers to flow. Accordingly, this study proposes an updated scheme for characterizing turbidite channel deposits that incorporates syntectonic control and sedimentation phases. It further details the facies types, internal structures, bed geometries, bed thicknesses, and net-to-gross ratios characteristic of each channel type. This model also explains the backstepping nature of the sedimentary successions, bed-thickness variations, and, most importantly, the processes governing grain-size and facies distribution. Identifying the channel types and control factors that dictate channel-fill dynamics is directly relevant to hydrocarbon exploration, as the depositional processes involved are both simulatable and predictive.