How is a turbidite actually deposited?

The deposition of a classic turbidite by a surge-type turbidity current, as envisaged by conceptual models, is widely considered a discrete event of continuous sediment accumulation at a falling rate by the gradually waning density flow. Here, we demonstrate, on the basis of a high-resolution advanced numerical CFD (computational fluid dynamics) simulation and rock-record examples, that the depositional event in reality involves many brief episodes of nondeposition. The reason is inherent hydraulic fluctuations of turbidity current energy driven by interfacial Kelvin-Helmholtz waves. The experimental turbidity current, with realistic grain-size composition of a natural turbidite, used only 26 to 33% of its in-place flow time for deposition, while the remaining time went to the numerous episodes of sediment bypass and transient erosion. The general stratigraphic notion of a gross incompleteness of sedimentary record may then extend down to the deposition time scale of a single turbidite.publishedVersio

Supradetachment basins in necking domains of rifted margins: Insights from the Norwegian Sea

Supradetachment basins at passive rifted margins are a key witness of major-continental extension, and they may preserve a record from which the amount and rates of extension and metamorphic core complex exhumation may be reconstructed. These basins have mainly been recognised in back-arc and orogenic collapse settings, with few examples from rifted margins. Using 2D and 3D seismic reflection, wellbore, and gravity anomaly data, we here characterise the three-dimensional structural and tectonosedimentary evolution of a spoon-shaped supradetachment basin that was formed in the necking domain of a rifted margin, at the southern limit of the Møre and Vøring segments of the Norwegian rifted margin. The basin, with an areal extent of ca. 2400 km2, and a landward-rotated syn-tectonic succession up to ca. 30 km thick (true stratigraphic thickness), is separated from footwall continental margin core complex basement culminations by major large-offset (>30 km) normal fault complexes characterised by a cross-sectional geometry whereby an upper, steeper part of the fault gives way to a low-angle detachment fault at depth. These fault complexes are associated with a tectonic thinning of the continental crust to ca. 11 km, compared with a crustal thickness of ca. 27 km in the proximal domain. The basin is filled by a succession of pre-, syn- and post-tectonic deposits, that accumulated over time as the basin evolved over a series of rift- and detachment faulting events. The 30 km thick syn-tectonic succession reflects deposition during two separate rifting events, which are disconnected by deposits reflecting a relative short period of tectonic quiescence. The results are discussed in light of examples of supradetachment basins on other rifted margins globally, as well as in the context of the evolution of the Norwegian margin overall.publishedVersio

The interactions of volcanism and clastic sedimentation in rift basins: Insights from the Palaeogene-Neogene Shaleitian uplift and surrounding sub-basins, Bohai Bay Basin, China

Although volcanism is an important process in the evolution of rift basins, current tectono-sedimentary models largely neglect its impact on sediment supply, transport pathways, and depositional systems. In this paper, we integrate core, well logs, and 3D seismic data from the Palaeogene-Neogene Shaleitian (SLT) uplift and surrounding sub-basins, Bohai Bay Basin, China, to investigate the sedimentology and geomorphology of a volcanic rift basin. Results of this study show that the spatial distribution of extrusive centres was strongly controlled by basement-involved intra-basin normal faults. During the early part of the syn-rift stage, the SLT uplift supplied sediments to transverse fan deltas and braided-river deltas that fringed the adjacent syn-rift depocentres. Volcanic deposits mainly occurred as relatively thin lava flow and pyroclastic facies that partially filled fault-controlled topographic lows, reducing topographic rugosity, and enhanced breaching of basement highs between syn-rift depocentres. Integration of drainage to the syn-rift depocentres and development of through-flowing axial depositional systems was enhanced. During the later part of syn-rift and in early post-rift stages, the SLT uplift was progressively inundated, reducing sediment supply to the fringing transverse depositional systems. In contrast, axial braided-river deltas became the main depositional systems, sourced by large hinterland drainage from the Yanshan fold-belt to the northwest. Volcanism in the late syn-rift and early post-rift occurs as thick lava flow and pyroclastic facies that infill rift topographic lows and locally blocked axial fluvial systems creating isolated lakes. Within hanging wall depocentres, volcanic topographic highs split and diverted axial fluvial and deltaic systems. Furthermore, volcanism supplied large volumes of volcanic sediment to the rift resulting in increased sedimentation rates, and the development of unstable subaerial and subaqueous slopes and deposits, increasing the occurrence of landslides. Based on the observations of this study we update tectono-sedimentary models for rift basins to include volcanism.publishedVersio

How is a turbidite actually deposited?

The deposition of a classic turbidite by a surge-type turbidity current, as envisaged by conceptual models, is widely considered a discrete event of continuous sediment accumulation at a falling rate by the gradually waning density flow. Here, we demonstrate, on the basis of a high-resolution advanced numerical CFD (computational fluid dynamics) simulation and rock-record examples, that the depositional event in reality involves many brief episodes of nondeposition. The reason is inherent hydraulic fluctuations of turbidity current energy driven by interfacial Kelvin-Helmholtz waves. The experimental turbidity current, with realistic grain-size composition of a natural turbidite, used only 26 to 33% of its in-place flow time for deposition, while the remaining time went to the numerous episodes of sediment bypass and transient erosion. The general stratigraphic notion of a gross incompleteness of sedimentary record may then extend down to the deposition time scale of a single turbidite

Supradetachment basins in necking domains of rifted margins: Insights from the Norwegian Sea

Supradetachment basins at passive rifted margins are a key witness of major-continental extension, and they may preserve a record from which the amount and rates of extension and metamorphic core complex exhumation may be reconstructed. These basins have mainly been recognised in back-arc and orogenic collapse settings, with few examples from rifted margins. Using 2D and 3D seismic reflection, wellbore, and gravity anomaly data, we here characterise the three-dimensional structural and tectonosedimentary evolution of a spoon-shaped supradetachment basin that was formed in the necking domain of a rifted margin, at the southern limit of the Møre and Vøring segments of the Norwegian rifted margin. The basin, with an areal extent of ca. 2400 km2, and a landward-rotated syn-tectonic succession up to ca. 30 km thick (true stratigraphic thickness), is separated from footwall continental margin core complex basement culminations by major large-offset (>30 km) normal fault complexes characterised by a cross-sectional geometry whereby an upper, steeper part of the fault gives way to a low-angle detachment fault at depth. These fault complexes are associated with a tectonic thinning of the continental crust to ca. 11 km, compared with a crustal thickness of ca. 27 km in the proximal domain. The basin is filled by a succession of pre-, syn- and post-tectonic deposits, that accumulated over time as the basin evolved over a series of rift- and detachment faulting events. The 30 km thick syn-tectonic succession reflects deposition during two separate rifting events, which are disconnected by deposits reflecting a relative short period of tectonic quiescence. The results are discussed in light of examples of supradetachment basins on other rifted margins globally, as well as in the context of the evolution of the Norwegian margin overall

Assessing first-order BQART estimates for ancient source-to- sink mass budget calculations

Constraining the timing and volume of sediment dispersal in an ancient sedimentary system is vital to understand a basin's infill history. One preferred method for a first-order approximation of ancient sediment load estimates, the BQART model, is based on empirical observations of modern river systems relating basin morphology, topography, climate, run-off and bedrock characteristics. Despite the popularity of such methods, a comprehensive assessment on the validity of using modern river observations to measure sediment load on geological timescales is lacking. Here, we investigate the uncertainties, sensitivities and practicalities surrounding the use of modern empirical observations in general and the BQART model in particular, to evaluate ancient sediment river loads. Although catchment area and relief are the least constrained parameters in an ancient sedimentary system, the temperature parameter may have an even more significant impact in the range of predicted sediment load estimates using a BQART approach. The applicability of BQART is most suitable for regional to continental scale source-to-sink systems that are based on robust paleogeographic and paleoclimatic models of cold (8°C) climates. One further needs to consider the high amplitude discharge events that can dominate the stratigraphic record which are not captured by historical observations of sediment load over a 30-year period. In addition, our limited understanding of bedload material transport and an unknown pristine environment in the Anthropocene reduce the reliability of modern sediment load estimates for the ancient. Mass budget estimates in deep time based on empirical relationships of modern river systems can thus provide first-order estimates within an order of magnitude but need to consider the limitations imposed by extrapolating the modern to the ancient. Here, we present a framework to consider the suitability of the BQART method for ancient source-to-sink mass budget analyses

The interactions of volcanism and clastic sedimentation in rift basins: Insights from the Palaeogene-Neogene Shaleitian uplift and surrounding sub-basins, Bohai Bay Basin, China

Although volcanism is an important process in the evolution of rift basins, current tectono-sedimentary models largely neglect its impact on sediment supply, transport pathways, and depositional systems. In this paper, we integrate core, well logs, and 3D seismic data from the Palaeogene-Neogene Shaleitian (SLT) uplift and surrounding sub-basins, Bohai Bay Basin, China, to investigate the sedimentology and geomorphology of a volcanic rift basin. Results of this study show that the spatial distribution of extrusive centres was strongly controlled by basement-involved intra-basin normal faults. During the early part of the syn-rift stage, the SLT uplift supplied sediments to transverse fan deltas and braided-river deltas that fringed the adjacent syn-rift depocentres. Volcanic deposits mainly occurred as relatively thin lava flow and pyroclastic facies that partially filled fault-controlled topographic lows, reducing topographic rugosity, and enhanced breaching of basement highs between syn-rift depocentres. Integration of drainage to the syn-rift depocentres and development of through-flowing axial depositional systems was enhanced. During the later part of syn-rift and in early post-rift stages, the SLT uplift was progressively inundated, reducing sediment supply to the fringing transverse depositional systems. In contrast, axial braided-river deltas became the main depositional systems, sourced by large hinterland drainage from the Yanshan fold-belt to the northwest. Volcanism in the late syn-rift and early post-rift occurs as thick lava flow and pyroclastic facies that infill rift topographic lows and locally blocked axial fluvial systems creating isolated lakes. Within hanging wall depocentres, volcanic topographic highs split and diverted axial fluvial and deltaic systems. Furthermore, volcanism supplied large volumes of volcanic sediment to the rift resulting in increased sedimentation rates, and the development of unstable subaerial and subaqueous slopes and deposits, increasing the occurrence of landslides. Based on the observations of this study we update tectono-sedimentary models for rift basins to include volcanism