scholarly journals Impact of sea-level fluctuations on the sedimentation patterns of the SE African margin: implications for slope instability

2019 ◽  
Vol 500 (1) ◽  
pp. 267-276 ◽  
Author(s):  
Aaron Micallef ◽  
Aggeliki Georgiopoulou ◽  
Andrew Green ◽  
Vittorio Maselli
Keyword(s):  
South Africa ◽  
Sea Level ◽  
Coastal Region ◽  
Passive Margin ◽  
Slope Instability ◽  
Bottom Current ◽  
The South ◽  
Sea Level Fluctuations ◽  
International Ocean Discovery Program ◽  
Seismic Reflection Profiles

AbstractThe sheared-passive margin offshore Durban (South Africa) is characterized by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. International Ocean Discovery Program Expedition 361 provides a unique opportunity to investigate the role of sea-level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity and bulk density from site U1474, as well as regional seismic reflection profiles to: (1) document an increase in sand input since the Mid-Pliocene; (2) associate this change to a drop in sea-level and extension of subaerial drainage systems towards the shelf-edge; (3) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom-current scour and instability of fan complexes. This information is important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities.

Continental slope sedimentation in the Sheepbed Formation (Neoproterozoic, Windermere Supergroup), Mackenzie Mountains, N.W.T.

1996 ◽  
Vol 33 (6) ◽  
pp. 848-862 ◽  
Author(s):  
R. W. Dalrymple ◽  
G. M. Narbonne
Keyword(s):  
Sea Level ◽  
Continental Slope ◽  
Cold Water ◽  
Passive Margin ◽  
Slope Instability ◽  
Fine Grained ◽  
Windermere Supergroup ◽  
Mackenzie Mountains ◽  
Water Depths

The Sheepbed Formation (Ediacaran) is a 1 km thick, siliciclastic unit that overlies glacial deposits of the Ice Brook Formation and is overlain by carbonates of the Gametrail Formation. Observations in the Mackenzie Mountains indicate that the Sheepbed Formation accumulated in water depths of 1–1.5 km on a passive-margin, continental slope. The lower part of the formation consists predominately of dark mudstone. Fine-grained, turbiditic sandstone becomes more abundant upward, as does the scale and abundance of slope-instability indicators. Mesoscale facies successions (i.e., evidence of channels, lobes, and (or) compensation cycles) are developed in the upper half of the formation. The larger-scale changes are interpreted as reflecting a postglacial sea-level rise, followed by a relative fall and an increase in the rate of deposition. Contourites that may have been formed in response to the circulation of deep, cold water occur in the lowstand deposits. Their presence confirms previous speculation that the proto-Pacific Ocean was initiated at the beginning of Windermere deposition (ca. 780 Ma), not at the start of the Cambrian. The paleoflow direction toward the present-day northwest suggests that this part of Laurentia lay in the northern hemisphere. In situ Ediacaran megafossils are preserved on the soles of sandy turbidites; the deep-water setting indicates that these organisms were not photoautotrophs.

scholarly journals Notes on some animal parasites in British Guiana

1916 ◽  
Vol 7 (2) ◽  
pp. 179-190 ◽  
Author(s):  
G. E. Bodkin ◽  
L. D. Cleare
Keyword(s):  
Sea Level ◽  
Sand Dunes ◽  
Coastal Region ◽  
The South ◽  
British Guiana ◽  
North East ◽  
The North ◽  
South West ◽  
Western Side ◽  
River Valleys

British Guiana lies between the latitudes 0·41′ N. (source of the Essequebo River) and 8° 33′ 22″ N. (Punta Playa), has a depth from north to south of about 500 miles, a seaboard of about 270 miles trending in a south-easterly direction, and occupies in the north-east of South America an area approximately equal in extent to Great Britain. It is bounded on the north by the Atlantic Ocean, on the east by Surinam or Dutch Guiana, on the south and south-west by Brazil, and on the west by Venezuela.The Colony may be divided broadly into three belts. The northern one consists of a low-lying flat and swampy belt of marine alluvium—the coastal region. This rises gradually from the seaboard and extends inland for a distance varying from 5 to 49 miles. It is succeeded by a broader and slightly elevated tract of country of sandy and clayey soils. This belt is generally undulating, and is traversed in places by sand-dunes rising from 50 to 180 ft. above sea-level. The more elevated portion of the Colony lies to the southward of the above-mentioned regions. It rises gradually to the south-west, between the river valleys, which are in many parts swampy, and contains three principal mountain ranges, several irregularly distributed smaller ranges, and in the southern and eastern parts numerous isolated hills and mountains. The eastern portion is almost entirely forest-clad, but on the south-western side there is an extensive area of flat grass-clad savannah land elevated about 300 feet above sea-level.

Stratigraphic framework for the Cambrian–Ordovician rift and passive margin successions from southern Quebec to western Newfoundland

2003 ◽  
Vol 40 (2) ◽  
pp. 177-205 ◽  
Author(s):  
Denis Lavoie ◽  
Elliott Burden ◽  
Daniel Lebel
Keyword(s):  
Sea Level ◽  
Continental Margin ◽  
Passive Margin ◽  
Early Cambrian ◽  
Sea Level Fluctuations ◽  
Late Cambrian ◽  
Head Groups ◽  
Stratigraphic Framework ◽  
Lower Ordovician ◽  
First Time

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the rift–drift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in early–middle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (Tremadocian–Arenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession.

scholarly journals Depositional environment of the Branch Sandstone and correlative sequences: Late Cretaceous changes in relative sea level in the East Coast Basin of New Zealand

2021 ◽  
Author(s):  
◽  
Lisa McCarthy
Keyword(s):  
Sea Level ◽  
East Coast ◽  
Depositional Environments ◽  
Passive Margin ◽  
Sea Level Changes ◽  
Relative Sea Level ◽  
Sea Level Fluctuations ◽  
The North ◽  
Tasman Sea ◽  
History Of

<p>The Branch Sandstone is located within an overall transgressive, marine sedimentary succession in Marlborough, on the East Coast of New Zealand’s South Island. It has previously been interpreted as an anomalous sedimentary unit that was inferred to indicate abrupt and dramatic shallowing. The development of a presumed short-lived regressive deposit was thought to reflect a change in relative sea level, which had significant implications for the geological history of the Marlborough region, and regionally for the East Coast Basin.  The distribution and lithology of Branch Sandstone is described in detail from outcrop studies at Branch Stream, and through the compilation of existing regional data. Two approximately correlative sections from the East Coast of the North Island (Tangaruhe Stream and Angora Stream) are also examined to provide regional context. Depositional environments were interpreted using sedimentology and palynology, and age control was developed from dinoflagellate biostratigraphy. Data derived from these methods were combined with the work of previous authors to establish depositional models for each section which were then interpreted in the context of relative sea level fluctuations.  At Branch Stream, Branch Sandstone is interpreted as a shelfal marine sandstone, that disconformably overlies Herring Formation. The Branch Sandstone is interpreted as a more distal deposit than uppermost Herring Formation, whilst the disconformity is suggested to have developed during a fall in relative sea level. At Branch Stream, higher frequency tectonic or eustatic sea-level changes can therefore be distinguished within a passive margin sedimentary sequence, where sedimentation broadly reflects subsidence following rifting of the Tasman Sea. Development of a long-lived disconformity at Tangaruhe Stream and deposition of sediment gravity flow deposits at Angora Stream occurred at similar times to the fall in relative sea level documented at the top of the Herring Formation at Branch Stream. These features may reflect a basin-wide relative sea-level event, that coincides with global records of eustatic sea level fall.</p>

The Alberta foreland basin: relationship between stratigraphy and Cordilleran terrane-accretion events

1989 ◽  
Vol 26 (10) ◽  
pp. 1964-1975 ◽  
Author(s):  
Douglas J. Cant ◽  
Glen S. Stockmal
Keyword(s):  
Sea Level ◽  
Foreland Basin ◽  
Temporal Correlation ◽  
Sediment Supply ◽  
Passive Margin ◽  
Sea Level Fluctuations ◽  
Lithospheric Flexure ◽  
Half Wavelength ◽  
Bending Stresses ◽  
Clastic Wedges

A foreland-basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded, with a shallowing-upward pattern, like the classic Flysch to Molasse sequence of Alpine foreland basins. The basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts. The shallowing occurs because sediment supply at first is low – early stages of accretion near the continental slope generate little or no topography above sea level; later stages result in significant tectonic uplift, and much sediment is shed into the foreland, filling the basin. The upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting, and reduction of the flexural load on the lithosphere through erosion and (or) tectonic denudation of the overthrusts causes regional uplift or basin "rebound". Actual sequences show differences from this idealized version in that (i) basal unconformities may not develop under conditions of high eustatic sea level; and (ii) they may not shallow upward in all cases. These differences can occur because later terranes that accrete onto the seaward side of a previously accreted terrane may simply push it farther onboard, thus initiating sediment supply as rapidly as the load-induced subsidence. Also, in this way, a small terrane can influence the filling of a foreland basin that is more than one "lithospheric flexural half-wavelength" away from the site of accretion.The stratigraphy of the Alberta basin has been divided after comparison with the idealized sequence resulting from an individual accretion event. The six clastic wedges recognized (Fernie–Kootenay, Mannville, Dun vegan, Belly River, Edmonton, and Paskapoo) show a temporal correlation with the times of accretion of terranes (Intermontane superterrane, Bridge River, Cascadia, Insular superterrane, Pacific Rim – Chugach, and Olympic, respectively) in the Cordillera. Therefore, the stratigraphy of the foreland basin may be best interpreted in terms of Cordilleran tectonics rather than sea-level fluctuations. Eustatic sea-level variations are believed to affect the internal stratigraphy and sedimentology of some clastic wedges and are responsible for the deposition of some thin units, but they appear to operate on time scales that differ from those of the clastic wedges identified here.

Sign in / Sign up

Export Citation Format

Share Document