Observations on depositional environments and benthos of the continental slope and rise, east of Newfoundland

1979 ◽  
Vol 16 (4) ◽  
pp. 831-846 ◽  
Author(s):  
Lionel Carter ◽  
Charles T. Schafer ◽  
M. A. Rashid
Keyword(s):  
Continental Slope ◽  
High Speed ◽  
Planktonic Foraminifera ◽  
Depositional Environments ◽  
Depth Interval ◽  
Western Boundary ◽  
Muddy Sand ◽  
Foraminiferal Assemblage ◽  
Labrador Current ◽  
Upper Slope

Sedimentologic, biologic, and morphologic criteria permit recognition of four depositional environments on the continental slope and rise, east of Newfoundland. The 'upper slope' (300–700 m) has a hummocky substrate with a mantle of terrigenous, gravelly muddy sand which is a mixture of ice-rafted detritus and sediment reworked from underlying glacial drift deposits. Reworking presumably took place during the last major lowering of sea level and it is continuing today under the influence of the Labrador Current and other oceanographic and biologically-related forces. The featureless bottom of the 'middle slope' (700–2000 m) is the principal depositional site of Recent mud. Fines, reworked from shelf and upper slope sediments, settle out together with fines transported to the area by the southeast-flowing Western Boundary Under-current (WBU). Compared to the upper slope this deeper environment receives less ice-rafted clasts, supports a richer macrofauna, and has a higher total species diversity of foraminifera. The 'lower slope' (2000–2500 m) is characterized by higher amounts of gravel and sand mixed with the mud, increasing numbers of current bedforms, and a more diverse foraminiferal assemblage, all of which correlate with the increasing power of the WBU with depth. The gravel was ice rafted probably at the end of the late Wisconsin to early Holocene and its presence on the seabed reflects the power of the WBU to inhibit deposition of Recent mud. The 'rise' (2500 to > 3000 m) is heralded by a subtle break in slope at about 2500 m. A high speed core of the undercurrent is situated in this area as indicated by the coarseness of the sediments (gravelly muddy sand) and the observed current bedforms. A marked increase in the numbers of benthonic and planktonic foraminifera is related primarily to the winnowing capacity of WBU. Numerous arenaceous deep sea forms first occur between 2500 and 3000 m and appear to reflect the reduced salinity, low temperature, high dissolved oxygen characteristics of the watermass that is associated with this depth interval.

Significance of some geotechnical properties of continental slope and rise sediments off northeast Newfoundland

1982 ◽  
Vol 19 (1) ◽  
pp. 153-161 ◽  
Author(s):  
Charles T. Schafer ◽  
Kenneth W. Asprey
Keyword(s):  
Shear Strength ◽  
Continental Slope ◽  
Bottom Current ◽  
Western Boundary ◽  
Sediment Texture ◽  
Surficial Sediments ◽  
Mean Values ◽  
Sediment Reworking ◽  
Middle Slope ◽  
Upper Slope

Shear strength measurements carried out on the 0–20 cm interval of continental slope and continental rise surficial sediments yielded mean values per station that ranged from 3.7 to 8.9 kPa. The factors controlling the bathymetric variation of sediment shear strength appear to be sediment texture (which is controlled locally by sediment spillover) on the upper slope, increased deposition of fines (silt- and clay-sized particles) from suspension and greater bioturbation activity on the middle slope, and bottom current sediment reworking on the base-of-slope and upper rise.Sediments deposited on the downslope side of the present presumed location of the Western Boundary Undercurrent (WBU) axis have comparatively high shear strength gradients that appear to denote the increased proportion of fine sediment deposition during early to middle Holocene time when the WBU axis may have been located further upslope than at present.

Late Cenozoic evolution of Sackville Spur: a sediment drift on the Newfoundland continental slope

1990 ◽  
Vol 27 (6) ◽  
pp. 863-878 ◽  
Author(s):  
L. Kennard ◽  
C. Schafer ◽  
L. Carter
Keyword(s):  
Continental Slope ◽  
Large Scale ◽  
Lower Percentage ◽  
Western Boundary ◽  
Sediment Reworking ◽  
Grand Banks ◽  
The North ◽  
Sediment Drift ◽  
Labrador Current ◽  
Erosional Event

The Sackville Spur is a sediment drift feature that forms a northeastward extension of the Grand Banks continental slope between the 900 and 2500 m isobaths near latitude 48°N. At present, the Labrador Current (LC) and the Western Boundary Undercurrent (WBUC) appear to be the two major hydrodynamic forces controlling sedimentation patterns on the flanks of the spur. Near the upper part of the spur's north flank, a deep offshore component of the LC appears to be selectively winnowing silt and clay-size particles, leaving a lag deposit composed of about 43% sand-size material. The base of the north flank (≈2500 m) is in a zone in which sediments can be reworked by the fast-flowing core of the WUBC. Here surficial sediments are characterized by a relatively high percentage of fine (2–3[Formula: see text]) sand and by a lower percentage of silt compared with sediments observed near the spur crest.Reflection seismic data suggest that current-influenced deposition, associated predominantly with bottom-sediment reworking by the deeper offshore component of the LC, has been active over the uppermost part of the spur since Late Miocene to Early Pliocene time. The initiation of deep LC flow at this time is marked by a distinctive angular unconformity near the base of the spur drift deposit. Following this erosional event, deposition caused rapid progradation of the spur to the northeast. The latest phase of the spur's evolution is characterized by (i) intermittent erosion with concomitant large-scale submarine sliding; (ii) smaller scale mass-flow deposition; and (iii) a distinctive southeastward shift of its depocentre toward the Flemish Pass.

The Upper Cretaceous foraminiferal record of IODP Site U1512 (Great Australian Bight, Indian Ocean)

2021 ◽  
Author(s):  
Erik Wolfgring ◽  
Michael A. Kaminski ◽  
Anna Waśkowska ◽  
Maria Rose Petrizzo ◽  
Eun Young Lee ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Ocean Circulation ◽  
Planktonic Foraminifera ◽  
Late Eocene ◽  
Foraminiferal Assemblage ◽  
Benthic Foraminiferal Assemblage ◽  
International Ocean Discovery Program ◽  
Foraminiferal Record ◽  
Great Australian Bight ◽  
Microfossil Assemblage

<p>Site U1512 was drilled during Expedition 369 of the International Ocean Discovery Program (IODP), which is located in the Great Australian Bight, southern Indian Ocean. It provides exceptional insights into the benthic foraminiferal biostratigraphy and paleoecology of a high southern latitude restricted marginal marine basin during the Late Cretaceous hot greenhouse climate and the rifting between Australia and Antarctica. The sedimentary sequence recovered at Site U1512 presents a rare record of a deep water agglutinated foraminifera (DWAF) community from the Southern High Latitudes. The Cretaceous record at Site U1512 covers the lower Turonian through Santonian (nannofossil zones UC8b to UC12/CC10b to CC16, <em>H. helvetica</em> to <em>Marginotruncana</em> spp. - <em>Planoheterohelix papula</em> - <em>Globotruncana linneana</em> planktonic foraminifera zones). Diverse benthic foraminiferal assemblages yield many new taxa that are yet to be described.</p><p>Agglutinated forms dominate the assemblage in most intervals. In lower to mid Turonian and Santonian strata, calcareous benthic as well as planktonic foraminifera are frequent. Abundant radiolaria are recovered from the mid Turonian, and they increase up-section and exceed 50% of the microfossil assemblage. We documented a diverse benthic foraminiferal assemblage consisting of 162 taxa (110 agglutinated and 52 calcareous). The most common taxa of the DWAF assemblage are tubular (i.e., <em>Kalamopsis grzybowskii,</em> <em>Bathysiphon</em> spp.) and planispiral forms (i.e., <em>Ammodiscus</em> spp., <em>Haplophragmoides</em> spp., <em>Buzasina</em> sp., <em>Labrospira</em> spp.).</p><p>The Turonian strata yield highly abundant <em>Bulbobaculites problematicus</em> and <em>Spiroplectammina navarroana</em>. The presence of the agglutinated foraminiferal marker taxa <em>Uvigerinammina jankoi</em> and <em>Bulbobaculites problematicus</em> provides a tie-point to the Tethyan DWAF biozonation of Geroch and Nowak (1984). The composition of foraminiferal assemblages and the increase in radiolaria abundance suggest unstable environmental conditions at Site U1512 during the early Turonian through Santonian. These characteristics refer to changes in bathymetry associated with changing ocean chemistry. Results of quantitative analyses of the benthic foraminiferal assemblages indicate a restricted paleoenvironmental regime, dictated by changes in paleobathymetry, unstable patterns in ocean circulation, and the discharge of a nearby river delta system.</p><p>References: Geroch, S., Nowak, K., 1984. Proposal of zonation for the Late Tithonian – late Eocene. based upon arenaceous Foraminifera from the Outer Carpathians, Poland, 225-239, In: Oertli, H.J. (Ed.), Benthos ´83; 2nd international 915 Symposium on Benthic Foraminifera, Pau (France) April 11-15, 1983, Elf Aquitaine, ESO REP and TOTAL CFP, Pau and Bordeaux.</p><p> </p>

scholarly journals Insights into the Cenozoic geology of North Beirut (harbour area): biostratigraphy, sedimentology and structural history

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Germaine Noujaim Clark ◽  
Marcelle Boudagher-Fadel
Keyword(s):  
Planktonic Foraminifera ◽  
Foraminiferal Assemblage ◽  
Early Pliocene ◽  
North East ◽  
The North ◽  
Rock Structure ◽  
Structural History ◽  
Orbulina Universa ◽  
Geological Complexity ◽  
Harbour Area

The biostratigraphy and sedimentology of the outcrops and bedrock recently exposed in archaeological excavations around the harbour area of Beirut (~5 km²) unlock the geological and structural history of that area, which in turn are key to understanding the hydrocarbon and hydrogeological potential of the region. A key location (Site 2) of a studied outcrop section and newly uncovered bedrock is on the northern foothill cliff of East Beirut (Achrafieh). The outcrop section of carbonates is of Eocene beds overlain by conformable Miocene beds. The excavation of the slope bordering the outcrop uncovered a bedrock section of an early Pliocene shoreline of carbonate/siliciclastic sands at its base and topped by a beach-rock structure. The early Pliocene age of the shoreline section is dated by an assemblage of planktonic foraminifera that includes Sphaeroidinellopsis subdehiscens , Sphaeroidinella dehiscens and Orbulina universa . The Eocene carbonates of Site 2 extend the coverage of the previously reported Eocene outcrops in the harbour area. They form a parasequence of thin-bedded, chalky white limestones that includes the youngest fossil fish deposits in Lebanon ( Bregmaceros filamentosus ). The deposits are dated as early Priabonian by their association with the planktonic foraminiferal assemblage of Porticulasphaera tropicalis , Globigerinatheka barri , Dentoglobigerina venezuelana , Globigerina praebulloides , Turborotalia centralis and Borelis sp. The Middle Miocene carbonates that conformably overlie the early Priabonian, parasequence include a planktonic foraminiferal assemblage of Globigerinoides trilobus , Orbulina universa and Borelis melo . Elsewhere, in the harbour area, the preserved Eocene limestones are also overlain by conformable Miocene carbonate parasequences of Langhian–Serravallian age. Younger argillaceous limestone beds of the Mio/Pliocene age occur in the eastern central part of the harbour area and enclose an assemblage of Truncorotalia crassaformis , Globorotalia inflata and Orbulina universa . The three markers of old and recently raised structural blocks in the harbour area are a Lutetian/Bartonian marine terrace in the south west corner, a lower Pliocene shoreline carbonate section in the north east side and a Holocene raised beach of marine conglomerates in the north east corner of the area. The locations of these paleo-shorelines, less than 2 km apart, indicate a progressive platform narrowing of North Beirut since the Paleogene. This study underpins the geological complexity of the region and contributes to understanding the underlying geology, which will be needed for future regional archaeological, hydrocarbon and hydrogeological exploration.

scholarly journals Foraminiferal evidence for inner neritic deposition of Lower Cretaceous (Upper Aptian) radiolarian-rich black shales on the Western Australian margin

2005 ◽  
Vol 24 (1) ◽  
pp. 55-75 ◽  
Author(s):  
David W. Haig
Keyword(s):  
Planktonic Foraminifera ◽  
Black Shales ◽  
Continental Margins ◽  
Foraminiferal Assemblage ◽  
Dissolved Silica ◽  
High Nutrient ◽  
Minimum Zone ◽  
Western Australian ◽  
Oxygen Minimum ◽  
Carnarvon Basin

Abstract. Diverse foraminifera, Lingula-like brachiopods and the geological setting indicate that Aptian radiolarian-rich black shales forming the Windalia Radiolarite were deposited at water depths probably less than 40 m in the Southern Carnarvon Basin. Elsewhere in Australia, coeval radiolarian-rich deposits are widespread in other western-margin basins and in vast interior basins. The organic-rich mudstones containing the radiolaria include the foraminiferal Ammobaculites Association, a sparse benthic macrofauna and kerogens of mainly terrestrial plant origin. The deposits suggest that there was substantial high-nutrient freshwater input into the epeiric seas as well as high levels of dissolved silica resulting from marine flooding of a mature silicate-rich landscape bordered on the eastern and western continental margins by large volcanic provinces. The widespread presence of organic-rich muds through the broad, shallow Southern Carnarvon Basin and through the coeval interior basins suggests that regional geomorphology controlled the distribution of eutrophic facies in the Australian Aptian rather than any global expansion of the oceanic oxygen minimum zone. The foraminiferal assemblage from the Windalia Radiolarite consists of calcareous hyaline benthic types (diverse Lagenida as well as abundant Lingulogavelinella, Epistomina and Coryphostoma) and organic-cemented agglutinated species (including common Ammobaculites humei, Haplophragmoides–Recurvoides spp., and Verneuilinoides howchini). Planktonic foraminifera are very rare and present only in the northern, more open part of the basin.

Upper slope processes and seafloor ecosystems on the Sabrina continental slope, East Antarctica

2020 ◽  
Vol 422 ◽  
pp. 106091 ◽  
Author(s):  
A.L. Post ◽  
P.E. O'Brien ◽  
S. Edwards ◽  
A.G. Carroll ◽  
K. Malakoff ◽  
...  
Keyword(s):  
Continental Slope ◽  
East Antarctica ◽  
Upper Slope

Cenomanian to Coniacian sea-level changes in the Lower Benue Trough (Nkalagu Area, Nigeria) and the Eastern Dahomey Basin: palaeontological and sedimentological evidence for eustasy and tectonism

2019 ◽  
Vol 498 (1) ◽  
pp. 233-255 ◽  
Author(s):  
Holger Gebhardt ◽  
Samuel O. Akande ◽  
Olabisi A. Adekeye
Keyword(s):  
Sea Level ◽  
Deep Water ◽  
Close Relation ◽  
Depositional Environments ◽  
Sea Level Changes ◽  
Foraminiferal Assemblage ◽  
Benue Trough ◽  
Sea Level Fluctuations ◽  
Dahomey Basin ◽  
Lower Benue Trough

AbstractThe Benue Trough formed in close relation to the opening of the South Atlantic and experienced sea-level fluctuations of different magnitudes during the Cenomanian to Coniacian interval. We identify depositional environments from outcrop sections and a drilling as control record. Lines of evidence for the interpretation include facies analyses, foraminiferal assemblage composition (P/B-ratio) and the presence of planktonic deep-water indicators. While the analysis of the well data from the Dahomey Basin indicates a continuous deep-water (bathyal) environment, the succession in the Nkalagu area of the Lower Benue Trough evolved in a different and more complex way. Beginning with latest Cenomanian shoreface to shelf deposits, a long period of subsidence lasted until the middle Turonian when pelagic shales and calcareous turbidites were deposited at upper to middle bathyal depths. These conditions continued during late Turonian and Coniacian times. The general deepening trend of the Lower Benue Trough was mainly controlled by tectonic subsidence and was superimposed by eustatic sea-level changes, resulting in periodically changing palaeowater depths. We were able to identify eight sea-level rises and falls that can be attributed to 405 kyr eccentricity cycles. The amplitudes of the sea-level changes were most likely in the range of several tens to a few hundred metres. The deposition of carbonate turbidites at Nkalagu was probably triggered by eustatic sea-level lowstands.

scholarly journals The Recent temperate foraminiferal biofacies of the Gippsland Shelf: an analogue for Neogene environmental analyses in southeastern Australia

2001 ◽  
Vol 20 (2) ◽  
pp. 127-142 ◽  
Author(s):  
Andrew J. Smith ◽  
Stephen J. Gallagher ◽  
Malcolm Wallace ◽  
Guy Holdgate ◽  
Jim Daniels ◽  
...  
Keyword(s):  
Planktonic Foraminifera ◽  
Environmental Studies ◽  
Fine Sand ◽  
Silty Sand ◽  
Outer Shelf ◽  
Ecological Niches ◽  
Inner Shelf ◽  
Foraminiferal Assemblage ◽  
Southeastern Australia ◽  
Marine Lakes

Abstract. This study describes the foraminiferal biofacies of a temperate stenohaline shelf and associated euryhaline marine lakes of Gippsland in southeast Australia. The study incorporates facies analyses and interpretations of three types of foraminiferal distributional data: forms alive at the time of collection, recently dead forms and relict forms. Four principal biofacies types occur: (1) the euryhaline marine Gippsland Lakes silts and sands; (2) inner shelf medium to coarse quartz-rich sands and bioclastic silty sands; (3) medium shelf bryozoan-rich bioclastic silt and silty sand; (4) outer shelf bryozoan- and plankton-rich silts and fine sands.The euryhaline marine Gippsland Lakes silts and sands contain abundant Ammonia beccarii and Eggerella, with minor Quinqueloculina, Elphidium and Discorbinella. The Gippsland inner shelf biofacies (0–50 m depths) consists of medium to coarse quartz-rich sands and bioclastic silty sand. Abundant living, relict and recently dead miliolids occur in the inner shelf with rare planktonic forms. Common planktonic foraminifera, with Cibicides, Parrellina, Elphidium and Lenticulina and relict forms occur in the bryozoan-rich bioclastic silt and silty sand of the Gippsland middle shelf (50–100 m depth). Bryozoan and plankton-rich silts and fine sand occur in the outer shelf to upper slope facies (100–300 m) below swell wave base on the Gippsland Shelf. A diverse fauna with common textulariids, Uvigerina, Bulimina, Anomalinoides and Astrononion and rare relict forms, occurs in this biofacies. Planktonic foraminifera and Uvigerina are most abundant at the shelf break due to local upwelling at the head of the Bass Canyon.Estimates of faunal production rates from live/dead ratios and full assemblage data suggest that the fauna of the Gippsland Shelf has not been significantly reworked by wave and/or bioturbation processes. Most relict foraminifera occur in the inner shelf, with minor relict forms in the middle to outer shelf. This pattern is similar to other shelf regions in Australia, where shelf areas were exposed during Pleistocene lowstand times, principally reworking pre-existing inner to middle shelf faunas. Correspondence analyses of the foraminiferal data yield a clear depth-related distribution of the faunal assemblage data. Most of the modern Gippsland Shelf fauna are cosmopolitan species and nearly a third are (semi-)endemic taxa suitable for regional palaeo-environmental studies. From biostratigraphic studies it is clear that the modern Gippsland foraminiferal assemblage evolved since Early Miocene times, with most elements present by the Late Miocene. Hence, the Recent Gippsland Shelf foraminiferal biofacies distribution is a good analogue for Neogene palaeo-environmental studies in the region. The longer ranging pre-Miocene mixture of epifaunal and infaunal taxa are deeper shelf cosmopolitan forms and are inferred to be more conservative since they evolved in relatively lower stress environments, typifying mesotrophic to eutrophic conditions compared to inner shelf epifaunal forms with ecological niches markedly affected by sea-level and temperature fluctuations in zones of constant wave action, in oligotrophic environments.The foraminiferal and facies analogues of this study on the Gippsland Shelf can be used for palaeo-environmental analyses of the Gippsland and Otway Neogene sedimentary successions. Such improvements will lead ultimately to a better understanding of the evolution of the neritic realm in southeastern Australia, an area facing the evolving Southern Ocean during the Cenozoic.

scholarly journals Coherence of Western Boundary Pressure at the RAPID WAVE Array: Boundary Wave Adjustments or Deep Western Boundary Current Advection?

2013 ◽  
Vol 43 (4) ◽  
pp. 744-765 ◽  
Author(s):  
Shane Elipot ◽  
Chris Hughes ◽  
Sofia Olhede ◽  
John Toole
Keyword(s):  
Continental Slope ◽  
Time Scales ◽  
Propagation Speed ◽  
Large Error ◽  
Western Boundary ◽  
Ocean Bottom ◽  
Boundary Current ◽  
Coherent Signals ◽  
Woods Hole Oceanographic Institution ◽  
Meridional Transport

Abstract This study investigates the coherence between ocean bottom pressure signals at the Rapid Climate Change programme (RAPID) West Atlantic Variability Experiment (WAVE) array on the western North Atlantic continental slope, including the Woods Hole Oceanographic Institution Line W. Highly coherent pressure signals propagate southwestward along the slope, at speeds in excess of 128 m s−1, consistent with expectations of barotropic Kelvin-like waves. Coherent signals are also evidenced in the smaller pressure differences relative to 1000-m depth, which are expected to be associated with depth-dependent basinwide meridional transport variations or an overturning circulation. These signals are coherent and almost in phase for all time scales from 3.6 years down to 3 months. Coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagation speed of about 1 m s−1 over 990 km of continental slope but with large error bounds on the speed. This is roughly consistent with expectations for propagation of coastally trapped waves, though somewhat slower than expected. A comparison with both Eulerian currents and Lagrangian float measurements shows that the coherence is inconsistent with a propagation of signals by advection, except possibly on time scales longer than 6 months.

scholarly journals Convection above the Labrador Continental Slope

2005 ◽  
Vol 35 (4) ◽  
pp. 489-511 ◽  
Author(s):  
Jérôme Cuny ◽  
Peter B. Rhines ◽  
Friedrich Schott ◽  
John Lazier
Keyword(s):  
Water Column ◽  
Continental Slope ◽  
Potential Vorticity ◽  
Deep Convection ◽  
Baroclinic Instability ◽  
World Ocean ◽  
Labrador Sea ◽  
Labrador Current ◽  
The World ◽  
Slantwise Convection

Abstract The Labrador Sea is one of the few regions of the World Ocean where deep convection takes place. Several moorings across the Labrador continental slope just north of Hamilton Bank show that convection does take place within the Labrador Current. Mixing above the lower Labrador slope is facilitated by the onshore along-isopycnal intrusions of low-potential-vorticity eddies that weaken the stratification, combined with baroclinic instability that sustains slanted mixing while restratifying the water column through horizontal fluxes. Above the shelf break, the Irminger seawater core is displaced onshore while the stratification weakens with the increase in isopycnal slope. The change in stratification is partially due to the onshore shift of the “classical” Labrador Current, baroclinic instability, and possibly slantwise convection.

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