The Underwater Development of Holocene Fan Deltas

Prior, David B.; Bornhold, Brian D.

doi:10.1002/9781444303858.ch4

Cited by 81 publications

(85 citation statements)

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“…However, judging from the shape, the size and the position of the terrace, the ridges here are not common upslope-downslope ridges, like the other seep-marked ridges on the slope. The lobed morphology of the terrace with the central ridges is reminiscent of a lobed delta front with tributaries (Prior and Bornhold, 1990). We therefore propose that the terrace originated from an old delta front in which coarse sediments were deposited during a period of sea-level lowstand and that these coarser sediments currently act as highly permeable stratigraphic horizons that facilitate fluid migration and seepage at the sea floor.…”

Section: Terracementioning

confidence: 89%

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

et al. 2006

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The Dnepr paleo-delta area in the NW Black Sea is characterized by an abundant presence of methane seeps. During the expeditions of May-June 2003 and within the EU-funded CRIMEA project, detailed multibeam, seismic and hydro-acoustic water-column investigations were carried out to study the relation between the spatial distribution of methane seeps, sea-floor morphology and sub-surface structures.2778 new methane seeps were detected on echosounding records in an area of 1540 km 2 . All seeps are located in the transition zone between the continental shelf and slope, in water depths of 66 to 825 m. The integration of the different geophysical datasets clearly indicates that methane seeps are not randomly distributed in this area, but are concentrated in specific locations.The depth limit for the majority of the detected seeps is 725 m water depth, which corresponds more or less with the stability limit for pure methane hydrate at the ambient bottom temperature (8.9 8C) in this part of the Black Sea. This suggests that, where gas hydrates are stable, they play the role of buffer for the upward migration of methane gas and thus prevent seepage of methane bubbles into the water column.Higher up on the margin, gas seeps are widespread, but accurate mapping illustrates that seeps occur preferentially in association with particular morphological and sub-surface features. On the shelf, the highest concentration of seeps is found in elongated depressions (pockmarks) above the margins of filled channels. On the continental slope where no pockmarks have been observed, seepage occurs along crests of sedimentary ridges. There, seepage is focussed by a parallel-stratified sediment cover that thins out towards the ridge crests. On the slope, seepage also appears in the vicinity of canyons (bottom, flanks and margins) or near the scarps of submarine landslides where mass-wasting breaches the fine-grained sediment cover that acts as a stratigraphic seal. The seismic data show the presence of a distinct bgas front,Q which has been used to map the depth of the free gas within the sea-floor sediments. The depth of this gas front is variable and locally domes up to the sea floor. Where the gas front approaches the seafloor, gas bubbles were detected in the water column. A regional map of the sub-surface depth of the gas front emphasises this bgas front-versus-seepQ relationship. The integration of all data sets indicates that the spatial distribution of methane seeps in the Dnepr paleo-delta is mainly controlled by the gas-hydrate stability zone as well as by stratigraphic and sedimentary factors. D

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Section: Terracementioning

confidence: 89%

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

et al. 2006

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“…However, much of the distinction lies in the nature of the feeder system, as opposed to the stratigraphy which is the focus of this work [Postma, 1990]. Because of the presence of a standing body of water, the stratigraphy is more similar to deltas than purely subaerial alluvial fans [Prior and Bornhold, 1990;Dabrio, 1990]. Therefore fan deltas are considered to be within the broader category of deltas for the purposes of this analysis.…”

Section: Implications For Formationmentioning

confidence: 99%

Stratigraphic analysis of the distributary fan in Eberswalde crater using stereo imagery

Lewis

Aharonson

2006

J. Geophys. Res.

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[1] The eroded remains of a fluvial distributary network in Eberswalde crater are uniquely well preserved among similar structures on Mars. A quantitative analysis of the exposed stratigraphy has been performed to investigate the internal structure of the deposit. Using topographic information derived from stereo pairs of high-resolution Mars Orbiter Camera images, we have for the first time quantified the orientation of individual layers exposed along the distal end of the distributary network. In combination with topographic data from the Mars Orbiter Laser Altimeter, we have examined plausible scenarios for the formation of this structure. We find that the evidence is inconsistent with formation both as an alluvial fan and as a progradational delta. Instead, we find that an aggradational delta best fits the observed characteristics of the channel network and the Eberswalde basin as a whole. We conclude that the delta likely formed not in a stable long-lived lake but over the course of a small number of shorter lacustrine episodes, which were not sustained at equilibrium conditions.

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“…6, 10A, 13). Smooth delta slopes are common for steep fan deltas affected by repeated, unconfined flows and/or suspension sedimentation (Prior & Bornhold, 1990). Local channel features are interpreted as formed by undercurrents during hyperpycnal flood events (Mulder & Chapron, 2011).…”

Section: Figure 11mentioning

confidence: 99%

Morphological signatures of mass wasting and delta processes in a fjord-lake system: insights from Lovatnet, western Norway

Hansen¹,

Waldmann²,

Storms³

et al. 2016

NJG

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High-resolution bathymetrical data from the Lovatnet lake, western Norway, reveal a diverse morphology including traces from historic and prehistoric landslides. Onshore LiDAR and selected seismic profiles support the interpretation. Our data from the lake show significant debris lobes below Ramnefjellet that was the source of the well-known rock avalanche and tsunami disasters in 1905 and 1936 which caused a total of 134 casualties. The debris is divided into three main lobes reaching a total length of 1.8 km along the lake bottom from the impact site, and diffuse lobe features below the Bødalsdelta. Frontal deformations are minor. Lobes on the basin plain have a volume of more than 1.2 × 10 6 m 3 including debris entrained from the surrounding slopes and lake floor. The entire lake volume was set in motion during the catastrophic events. Returning bottom flows transported debris into the lake where lobes and minor, distinct mounds were deposited up to c. 1.5 km from the lake's outlet. The mounds could be anthropogenic, and possibly include a vessel that disappeared during the event. Erosion and smaller failures occurred elsewhere in the lake basin. Fan-delta morphologies are varied, with ridges and protuberances, reflecting deltaic sedimentation interrupted by major mass-wasting or other events in the deltas and/or their catchments. This is especially clear for the Raudi, Hellsete and Bødalen deltas, but minor protuberances are also found in other deltas. The data also reveal traces from large and previously undocumented landslide events. Gravitational deposits generally dominate the steep slopes and glacial landforms are scarce. The study demonstrates the importance of linking onshore and offshore morphological datasets in order to obtain an overview over process variability in fjord-type lakes of importance for further investigation and hazard assessment.

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The Underwater Development of Holocene Fan Deltas

Cited by 81 publications

References 0 publications

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

Stratigraphic analysis of the distributary fan in Eberswalde crater using stereo imagery

Morphological signatures of mass wasting and delta processes in a fjord-lake system: insights from Lovatnet, western Norway

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