Depositional Turbidity Currents in Diapiric Minibasins on the Continental Slope: Formulation and Theory

Abstract. Two ~20 m-long sedimentary cores collected in two neighbouring mid-slope basins of the Paritu Turbidite System in Poverty Bay, east of New Zealand, show a high concentration of turbidites (5 to 6 turbidites per meter), interlaid with hemipelagites, tephras and a few debrites. Turbidites occur as both stacked and single, and exhibit a range of facies from muddy to sandy turbidites. The age of each turbidite is estimated using the statistical approach developed in the OxCal software from an exceptionally dense set of tephrochronology and radiocarbon ages (~1 age per meter). The age, together with the facies and the petrophysical properties of the sediment (density, magnetic susceptibility and P-wave velocity), allows the correlation of turbidites across the continental slope (1400–2300 m water depth). We identify 73 synchronous turbidites, named basin events, across the two cores between 819 ± 191 and 17 729 ± 701 yr BP. Compositional, foraminiferal and geochemical signatures of the turbidites are used to characterise the source area of the sediment, the origin of the turbidity currents, and their triggering mechanism. Sixty-seven basin events are interpreted as originated from slope failures on the upper continental slope in water depth ranging from 150 to 1200 m. Their earthquake trigger is inferred from the heavily gullied morphology of the source area and the water depth at which slope failures originated. We derive an earthquake mean return time of ~230 yr, with a 90% probability range from 10 to 570 yr. The earthquake chronology indicates cycles of progressive decrease of earthquake return times from ~400 yr to ~150 yr at 0–7 kyr, 8.2–13.5 kyr, 14.7–18 kyr. The two 1.2 kyr-long intervals in between (7–8.2 kyr and 13.5–14.7 kyr) correspond to basin-wide reorganisations with anomalous turbidite deposition (finer deposits and/or non deposition) reflecting the emplacement of two large mass transport deposits much more voluminous than the "classical" earthquake-triggered turbidites. Our results show that the progressive characterisation of a turbidite record from a single sedimentary system can provide a continuous paleo-earthquake history in regions of short historical record and incomplete onland paleo-earthquake evidences. The systematic description of each turbidite enables us to infer the triggering mechanism.

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Quartz arenites of the Cambro-Ordovician Kamouraska Formation, Quebec Appalachians, Canada: I. Deep-water depositional processes in a continental-slope environment

Canadian Journal of Earth Sciences ◽

10.1139/e11-005 ◽

2011 ◽

Vol 48 (8) ◽

pp. 1209-1231 ◽

Cited By ~ 3

Author(s):

Pierre Malhame ◽

Reinhard Hesse

Keyword(s):

Continental Slope ◽

Deep Water ◽

Submarine Canyon ◽

Turbidity Currents ◽

Lawrence Estuary ◽

Depositional Processes ◽

Iapetus Ocean ◽

Quartz Arenite ◽

Exposed Part ◽

Polymictic Conglomerate

The Kamouraska Formation is an uppermost Cambrian – lowermost Ordovician quartz-arenite-dominated unit of controversial origin deposited on the southeastern slope of Laurentia bordering the Iapetus Ocean. It is exposed in the Quebec Appalachians on the south shore of the St. Lawrence Estuary. The formation consists of basal polymictic conglomerate and overlying massive sheet-like quartz arenite. The conglomerate beds are reversely and reversely to normally graded. The quartz arenite beds are generally massive, although they may show coarse-tail grading. Beds containing full or partial Bouma sequences are rare. Paleoflow directions from ripple-cross lamination, ripple marks on bed surfaces, and sole marks point towards southeast, south, and southwest. The clastic sediments of the Kamouraska were transported into the deep sea by sediment gravity flows that evolved from hyperconcentrated to concentrated density flows, and then to turbidity currents. The depositional environment is interpreted to have been a southwest-trending meandering submarine canyon. The exposed part of the canyon deposits is slightly oblique to the strike of slope. If correct, our interpretation establishes the preservation of continental-slope deposits in more distal deep-water siliciclastic sedimentary rocks of the Taconian orogen in Quebec, which traditionally have been interpreted as submarine-fan and (or) basin-plain deposits. The orientation of a canyon near parallel-to strike of the slope may have been controlled by syn-depositional growth faults. The coarsest hyperconcentrated flows, which deposited the conglomerate, were restricted to the deepest parts of the canyon during its early stages of development, whereas the concentrated density flows that deposited the massive quartz-arenite beds covered a wider area.

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Searching for the seafloor signature of the 21 May 2003 Boumerdès earthquake offshore central Algeria

Natural Hazards and Earth System Science ◽

10.5194/nhess-12-2159-2012 ◽

2012 ◽

Vol 12 (7) ◽

pp. 2159-2172 ◽

Cited By ~ 26

Author(s):

A. Cattaneo ◽

N. Babonneau ◽

G. Ratzov ◽

G. Dan-Unterseh ◽

K. Yelles ◽

...

Keyword(s):

Continental Slope ◽

Turbidity Currents ◽

Submarine Cable ◽

Active Deformation ◽

Sediment Dispersal ◽

The Past ◽

Algerian Coast ◽

Multiple Breaks ◽

Large Earthquakes ◽

Boumerdes Earthquake

Abstract. Shaking by moderate to large earthquakes in the Mediterranean Sea has proved in the past to potentially trigger catastrophic sediment collapse and flow. On 21 May 2003, a magnitude 6.8 earthquake located near Boumerdès (central Algerian coast) triggered large turbidity currents responsible for 29 submarine cable breaks at the foot of the continental slope over ~150 km from west to east. Seafloor bathymetry and backscatter imagery show the potential imprints of the 2003 event and of previous events. Large slope scarps resulting from active deformation may locally enhance sediment instabilities, although faults are not directly visible at the seafloor. Erosion is evident at the foot of the margin and along the paths of the numerous canyons and valleys. Cable breaks are located at the outlets of submarine valleys and in areas of turbiditic levee overspilling and demonstrate the multi-source and multi-path character of the 2003 turbiditic event. Rough estimates of turbidity flow velocity are not straightforward because of the multiple breaks along the same cable, but seem compatible with those measured in other submarine cable break studies elsewhere. While the signature of the turbidity currents is mostly erosional on the continental slope, turbidite beds alternating with hemipelagites accumulate in the distal reaches of sediment dispersal systems. In perspective, more chronological work on distal turbidite successions offshore Algeria offers promising perspectives for paleoseismology reconstructions based on turbidite dating, if synchronous turbidites along independent sedimentary dispersal systems are found to support triggering by major earthquakes. Preliminary results on sediment core PSM-KS23 off Boumerdès typically show a 800-yr interval between turbidites during the Holocene, in accordance with the estimated mean seismic cycle on land, even if at this stage it is not yet possible to prove the earthquake origin of all the turbidites.

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Sea floor—morphology

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1962.0027 ◽

1962 ◽

Vol 265 (1322) ◽

pp. 381-385

Keyword(s):

Environmental Factor ◽

Continental Slope ◽

Point Of View ◽

Turbidity Currents ◽

Fishing Industry ◽

Sedimentary Sequence ◽

Sea Floor ◽

Sea Bed ◽

Population Economics ◽

A Current

Just as the division of continents, from the point of view of climate, vegetation, population, economics and even politics is based on the natural topographic divisions, so the topography of the sea floor provides natural divisions for water masses, marine populations, sediment movement and even parishes for the work of sea-going geophysicists. The study of the shape and structure of these features of the sea bed has a bearing on most marine sciences and the topography must be considered as an important environmental factor in all fields. Thus regions of upwelling may be caused by a current impinging on the continental slope, giving rise therefore to an area rich in nutrients where a fishing industry may flourish. Or else turbidity currents may transport sediments from one side of a basin to another producing anomalous stratification in the sedimentary sequence. These are both controlled by the topography.

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