Contributors: M. Cremer, E. Gonthier, J. Duprat, J.-C. Faugères, T. Courp

Date: 2007-02-01

sediment cores across the Sao Tomé system (core location in Fig. 2). ...core) and temporal (average for glacial and interglacial sediments) variability...carbonate-rich sediment are lighter. «Sl» and «sl» stand for the silt ...sedimentation rates ...Quaternary...fraction) in the sediment cores. Data in Table 5. ...sediment records allow addressing the paleoceanographic changes that took...sediment...sedimentation rates. Cores location in Fig. 2. ...sediment cores across the Sao Tomé system (core location in Fig. 2). Lithologic...sediment dynamics that prevailed on this system during the late Quaternary...Carbonate record and sediment structures (X radiograph) in selected sequences...sediment dynamics that prevailed on this system during the late Quaternary...sedimentation. According to the location of the cores at the present day...sediment cores. Data in Table 5. ...sedimentation rate during glacials) the sediment records (chiefly the ...late glacial could be associated to Heinrich events, when NADW production...Spatial (average by core) and temporal (average for glacial and interglacial...Late Quaternary variability of the sedimentary record in the Sao Tome ...cores at the present day interface between NADW and AABW, we infer that...sediment cores located across a deep channel-levee system in the South ... Very few sediment records allow addressing the paleoceanographic changes that took place on orbital and/or sub-Milankovitch time scales in the South–West Atlantic. Here, a set of sediment cores located across a deep channel-levee system in the South Brazilian basin (3700–3900 m depth) is used to infer the sediment dynamics that prevailed on this system during the late Quaternary and to relate this pattern to climate changes. The spatial distribution of deposits (changes in mineralogy, texture, structure, and sedimentation rate according to the morphology) indicates bulk of sediment supplies is distributed on the Sao Tomé system by bottom advective processes. The silty–sandy layers, originate undoubtedly from turbidity currents whereas the fine-grained muds and oozes, that form the major part of the deposits, are controlled by deep geostrophic currents. In addition to variations forced by the orbital cycles, (more turbidites, less carbonates and higher sedimentation rate during glacials) the sediment records (chiefly the CaCO3 record) document outstanding higher frequency regional changes in sedimentation. According to the location of the cores at the present day interface between NADW and AABW, we infer that changes in sedimentation are related to pulses of AABW versus NADW production. These changes, commonly marked by asymmetric carbonate pattern of about 10 kyr, suggest that the relative influence of NADW versus AABW followed, throughout the last 190 kyr, a repetitive sequence of progressive increase and sharp decrease. The rather sharp shut down observed during the late glacial could be associated to Heinrich events, when NADW production stopped, but similar events are also well expressed during MIS 5, MIS 6 and at the end of MIS 7.

Contributors: Vasilios Lykousis, Aristomenis P. Karageorgis, George Th. Chronis

Date: 2005-11-15

sediment cores by open and solid circles. Radiocarbon analysis was performed...Late glacial progradational deposits (Unit C; Lowstand Systems Tract, ...representative sediment cores from the Thermaikos Gulf shelf and slope...Core TH-46 location is shown with the simplified sediment description ...late glacial prodeltaic deposits and slope to basin turbidites (Lowstand...sediment cores from the Thermaikos Gulf shelf and slope and the Sporades...Late Quaternary...Sedime...Late Quaternary...sediment fluxes...sediment core description and AMS 14C dates (yr BP) of Units A, B and ...only in X-ray radiographs. ...Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three...late glacial sea-level fall....Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three...core locations see Fig. 1. ...sediment fluxes since the last glacial in the Thermaikos Gulf and the ...location). Core TH-46 location is shown with the simplified sediment description...sediments deposited in a shallow, high-energy, estuarine environment during ... Late Quaternary sedimentary cover in the Thermaikos Gulf consists of three seismic Units: (i) the uppermost Unit A that represents delta progradation during the last 6000 yr when the sea surface almost reached the present level (Highstand Systems Tract, HST); (ii) Unit B that includes relatively coarse-grained sediments deposited in a shallow, high-energy, estuarine environment during the post-glacial transgression (Transgressive Systems Tract, TST); and (iii) the lowest Unit C which may represent late glacial prodeltaic deposits and slope to basin turbidites (Lowstand Systems Tract, LST). Seismic units A and B overlay a well-defined unconformity which resulted from sub-aerial erosion during the late glacial sea-level fall.

Contributors: A. Anil Kumar, V. Purnachandra Rao, S.K. Patil, Pratima M. Kessarkar, M. Thamban

Date: 2005-10-15

...sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed...cores on the western margin of India. Geology after Rao and Wagle (1997...late Quaternary...late Quaternary...Do...1997). ...sediments of the eastern Arabian Sea: Evidence for late Quaternary climatic...sediments in GC1. (B) Down-core variations of sedimentological parameters...sediment sections of the cores ...Down-core variations of MS in GC11. ...Down-core variations of MS in core GC14 and GC15. ...sediments were determined for 15 gravity cores recovered from the western...sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin....GC13. ...the sediments in GC1. (B) Down-core variations of sedimentological parameters...sediments...sediments reflect the land-derived input and, in general, are the highest...Down-core variations of MS in GC11. ... Rock-magnetic measurements along with grain size, acid-insoluble residue (AIR), organic carbon (OC), CaCO3 and δ18O of the planktonic foraminifers of the sediments were determined for 15 gravity cores recovered from the western continental margin of India. Magnetic susceptibility (MS) values in the surficial sediments reflect the land-derived input and, in general, are the highest in terrigenous sediment-dominated sections of the cores off Saurashtra–Ratnagiri, followed by the sediments off Indus–Gulf of Kachchh and then Mangalore–Cape Comorin.

Contributors: Pierre Giresse, Henri Pauc, Jacques Déverchère

Date: 2009-05-01

sediment cores indicate that turbidite sequences are both thicker and ...sediment cores. ...Sediment cores...cores retrieved from the Algerian margin from Oran to 80km east of Algiers...Late Quaternary... profiles of sediment cores from the Algiers area: KMDJ01 (a), KMDJ02 ...sediment core implying various origin of the gravity flow (eustatic change...sediment cores indicate a decreasing frequency of turbidite sequences ...sediment gravity-flow deposits on the western Algerian margin during late...sediment rates of seven studied sediment cores. Thickness of debris flow...profiles of sediment cores from the Chenoua–Tenes area: KMDJ06 (a), KMDJ07...Late Quaternary...position of analysed sediment cores. ...sediment cores from the Chenoua–Tenes area: KMDJ06 (a), KMDJ07 (b), KMDJ08...position of analysed sediment cores. (B). Detailed maps of the Chenoua–Tenes...accumulation sediment rates of seven studied sediment cores. Thickness...sediment cores from the Algiers area: KMDJ01 (a), KMDJ02 (b), KMDJ03 (...sediment gravity-flow deposits and their sources. At the foot of the slope...sediment cores. (B). Detailed maps of the Chenoua–Tenes area locating ... Seven piston cores retrieved from the Algerian margin from Oran to 80km east of Algiers were studied to identify sediment gravity-flow deposits and their sources. At the foot of the slope, five sediment cores indicate a decreasing frequency of turbidite sequences from the transgressive systems tract to the highstand systems tract resulting in lower off-shelf sediment fluxes during the last highstand episode. There is an approximately log-normal frequency distribution of bed thickness that increases for larger grain-size class, but this relationship is frequently altered by truncation of the top of the turbidite sequence. In the deep basin off Algeria, two sediment cores indicate that turbidite sequences are both thicker and more preserved than at the foot of the slope and are observed through the entire sediment core implying various origin of the gravity flow (eustatic change, seismicity).

Contributors: S.H. Lee, J.J. Bahk, S.K. Chough, G.G. Back, H.S. Yoo

Date: 2004-05-31

sedimentation caused by an interaction between bottom currents and mass...Location, water depth and length of sediment cores ...core sediments ...late Quaternary. Cross sections cut through the South Korea Plateau and...Late Quaternary sedimentation in the Ulleung Interplain Gap, East Sea ...core sections. For symbols on the right side, see Table 3. Core locations...adjacent areas during the late Quaternary. Cross sections cut through ...sedimentary facies in core sediments ...sediments. Based on vertical distribution of sedimentary facies together...core sediments can be divided into Units I (∼15 ka)....sediment cores (8.6–11.4 m long) together with age data of tephra layers...sediment cores ...cores. For location of cores, see Figs. 1B, 7B, 9D and 10. Solid triangles...Core sediments consist of various deposits of turbidites, muddy contourites... core sections. For symbols on the right side, see Table 3. Core locations... correlation of cores. For location of cores, see Figs. 1B, 7B, 9D and ... The Ulleung Interplain Gap (UIG) is a deep (2300–2700 m) passage which has served as a conduit for deep-water circulation between the Ulleung and Japan basins. A detailed analysis of Chirp (2–7 kHz) subbottom profiles (ca. 6270 line-km) and nine sediment cores (8.6–11.4 m long) together with age data of tephra layers and four AMS 14C from the UIG and the adjacent areas reveals complex sedimentation caused by an interaction between bottom currents and mass flows during the last- and post-glacial periods. From high-resolution subbottom data, rock basement, slide/slump/rock-fall deposits, mass-flow chutes/channels, mass-flow deposits, bottom-current deposits, and a large-scale bottom-current channel system are recognized. Core sediments consist of various deposits of turbidites, muddy contourites, manganiferous contourites, and pelagic/hemipelagic sediments. Based on vertical distribution of sedimentary facies together with a chronostratigraphic framework, core sediments can be divided into Units I (∼15 ka).

Contributors: L. Ceccaroni, M. Frank, M. Frignani, L. Langone, M. Ravaioli, A. Mangini

Date: 1998-11-01

sediment core...sediment (6.25 dpm m−2 kyr−1). ...sediment, biogenic silica, organic carbon and biogenic Ba, and export ...sediment redistribution in the Ross Sea margin were enlightened from a...sediment core, collected from the western part of the continental slope...Glacial–interglacial setting of core Anta91-8 ... relative to core Anta91-8 ...Late Quaternary fluctuations of biogenic component fluxes on the continental...bulk sediment, biogenic silica, organic carbon and biogenic Ba, and export...Sediment accumulation rates ranged between 1.2 cm kyr−1 in the isotope...core ANTA91-8. ...Quaternary Research, 27: 1–29]. Sediment accumulation rates ranged between...core Anta91-8 ...the sediment (6.25 dpm m−2 kyr−1). ...sediment column. ... A sediment core, collected from the western part of the continental slope of the Ross Sea at 2380 m water depth, records events of the last two climatic cycles (250 kyr). A 230Thex-based chronology was obtained and boundaries of the isotope stages were set assuming that biological productivity was enhanced during periods of less ice cover. Then, 230Thex0, organic carbon, biogenic silica and biogenic Ba distributions were compared to the glacial–interglacial stage boundaries and corresponding ages of the δ18O record of Martinson et al. [Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Jr., Shackleton, N.J, 1987. Age dating and the orbital theory of the ice ages: development of a high-resolution 0 to 300,000-year chronostratigraphy. Quaternary Research, 27: 1–29]. Sediment accumulation rates ranged between 1.2 cm kyr−1 in the isotope stage 6 and 3.8 cm kyr−1 during the Holocene. Variations in the concentrations and fluxes of organic carbon, biogenic Ba, biogenic silica and Mn gave information on palaeoclimate changes. Processes of sediment redistribution in the Ross Sea margin were enlightened from a comparison of the measured and expected fluxes of 230Thex. Calculation of the focusing-corrected accumulation rates of biogenic Ba enabled us to evaluate the export palaeoproductivity. Corrected accumulation rates of biogenic components and calculated palaeoproductivities were low, compared to the Antarctic Polar Front in the Atlantic sector, throughout the last two climatic cycles. Glacial–interglacial changes of sea ice cover and ventilation of the Ross Sea were probably major causes of variations in biogenic particle flux and distribution of redox-sensitive elements within the sediment column.

Contributors: Holger Cremer, Damian Gore, Martin Melles, Donna Roberts

Date: 2003-06-15

late Quaternary palaeoenvironmental history of the southern Windmill Islands...sediments. The diatom assemblage in the upper sediments of both cores ...late Quaternary...late Quaternary...core PG1430 from Peterson Inlet. ...cores PG1433 and PG1430 ...core PG1433 from Browning Bay. ...late Pleistocene. During the following glacial, the Windmill Islands were...stratigraphy in core PG1433 from Browning Bay. ...sediment cores taken in two marine bays. The diatom assemblage of the ...sediments from the southern Windmill Islands ...late Quaternary palaeoenvironmental history of the southern Windmill Islands...late Quaternary diatom assemblages from southern Windmill Islands, East...Late Quaternary palaeoclimatic, oceanographic and palaeotopographic trends...Significant species in sediments from the southern Windmill Islands ...ages in core PG1430 from Peterson Inlet. ...sediments...sediment layers suggests a warm climate with mostly open water conditions...ages in core PG1433 from Browning Bay. ... The late Quaternary palaeoenvironmental history of the southern Windmill Islands, East Antarctica, has been reconstructed using diatom assemblages from two long, well-dated sediment cores taken in two marine bays. The diatom assemblage of the lowest sediment layers suggests a warm climate with mostly open water conditions during the late Pleistocene. During the following glacial, the Windmill Islands were covered by grounded ice preventing any in situ bioproductivity. Following deglaciation, a sapropel with a well-preserved diatom assemblage was deposited from ∼10 500 cal yr BP. Between ∼10 500 and ∼4000 cal yr BP, total organic carbon (Corg) and total diatom valve concentrations as well as the diatom species composition suggest relatively cool summer temperatures. Hydrological conditions in coastal bays were characterised by combined winter sea-ice and open water conditions. This extensive period of glacial retreat was followed by the Holocene optimum (∼4000 to ∼1000 cal yr BP), which occurred later in the southern Windmill Islands than in most other Antarctic coastal regions. Diatom assemblages in this period suggest ice-free conditions and meltwater-stratified waters in the marine bays during summer, which is also reflected in high proportions of freshwater diatoms in the sediments. The diatom assemblage in the upper sediments of both cores indicates Neoglacial cooling from ∼1000 cal yr BP, which again led to seasonally persistent sea-ice on the bays. The Holocene optimum and cooling trends in the Windmill Islands did not occur contemporaneously with other Antarctic coastal regions, showing that the here presented record reflects partly local environmental conditions rather than global climatic trends.

Contributors: Zhongyuan Chen, Baoping Song, Zhanghua Wang, Yongli Cai

Date: 2000-01-15

sediment cores, vibrocores, surficial samples and seismic track line. ...sediment distribution. Belt A, delta front fine sand and silt, with trough...the core Cj4. Zone c, the warmest temperature period starting at ca. 7000...sediment sequences reveal a general trend of climate warming from early...late Pleistocene sediments in front of the estuarine depocenter. Gravity...core Cj4. Indicated 14C dates are based from Chen and Wang (1994). ...showing the location of sediment cores, vibrocores, surficial samples ...late Quaternary stratigraphy...Late Quaternary evolution of the sub-aqueous Yangtze Delta, China: sedimentation...sediment belts (A–D) of the Yangtze sub-aqueous delta are defined from...text. ...Sediment distribution of the sub-aqueous Yangtze Delta. Four sediment ...late Quaternary sub-aqueous Yangtze Delta. N, number; S, species; R, rare...S...late Pleistocene period (Ren and Zhen, 1980). ...late Quaternary stratigraphy of the delta consists from bottom upward ...late Quaternary stratigraphy...sediment loading within the depocenter is the major factor in causing ...sediment distribution...lithostratigraphic log of the late Quaternary sub-aqueous Yangtze Delta ... Four sediment belts (A–D) of the Yangtze sub-aqueous delta are defined from the sea-bottom sediment distribution. Belt A, delta front fine sand and silt, with trough cross stratification; Belt B, prodelta silty clay and clayey silt, with abundant burrowing and rich in organic matter; Belt C, prodelta to continental shelf sand–silt–clay, with thin layers of sand and clay interbedded; and Belt D, late Pleistocene relict sands (medium to fine grained), mixed with shell fragments. The late Quaternary stratigraphy of the delta consists from bottom upward of: late Pleistocene terrigenous (fluvial and lacustrine) sand and mud; Holocene transgressive silt, prodelta clay and delta front fine sand and silt. In addition, four pollen-spore zones (a–d) derived from these sediment sequences reveal a general trend of climate warming from early to late Holocene. The Zone c, distributed primarily within the prodelta muds, provides evidence for a temperature maximum starting at ca. 7000 years B.P. (Atlantic period). This indicates that the delta initiation was essentially coeval with the climate optimum in early Holocene. Sub-bottom seismic surveys reveal three (I–III) acoustic facies. Facies I and II are characterized by seaward remobilization of water-saturated Holocene prodelta muds; facies III is composed of highly-contorted late Pleistocene strata and mud diapirs that erupted from deep-seated late Pleistocene sediments in front of the estuarine depocenter. Gravity subsidence due to Holocene sediment loading within the depocenter is the major factor in causing the deformation of underlying unconsolidated strata. Furthermore, the sub-aqueous Yangtze Delta proper is now obviously diverting to southeast owing to the long-term, tectonically induced southward shift of the river mouth, and to the marine currents associated with the Coriolis effect. We thus predict that the large Chongming island in river mouth area will have been coalesced with the northern Yangtze coast in the recent future.

Contributors: N. Fagel, L.Y. Alleman, L. Granina, F. Hatert, E. Thamo-Bozso, R. Cloots, L. André

Date: 2005-01-01

sediment cores. Analyses by ICP-AES (Mn content, data from Table 3a) or...Sediment...sediments from cores CON01-604 (Posolsky Bank), CON01-603 (Continent Ridge...Late Quaternary... investigated sediment cores (plotted from South to North). Modified from...diatom-samples in any of the core sediment samples. ...Late Quaternary...sediment core: the concretions are concentrated at specific depths along...sediments. While reflecting an early diagenetic signal, the source of ...sediment cores spanning two to four interglacial stages in the northern...sedimentation rates (e.g., Academician and Continent ridges). At the site...sedimentation rates, and porewater chemistry. We conclude that vivianite...geochemical signature of sediments from cores CON01-604 (Posolsky Bank...sediment cores (plotted from South to North). Modified from Hauregard,...sediments...core sediment samples. ...sedimentation rates, and it is not a proxy for lacustrine paleoproductivity...concretions in sediment core: the concretions are concentrated at specific... sediment cores. Analyses by ICP-AES (Mn content, data from Table 3a) ... In an effort to better understand vivianite formation processes, four Lake Baikal sediment cores spanning two to four interglacial stages in the northern, central and southern basins and under various biogeochemical environments are scrutinized. The vivianite-rich layers were detected by anomalous P-enrichments in bulk geochemistry and visually by observations on X-radiographs. The millimetric concretions of vivianite were isolated by sieving and analysed by X-ray diffraction, scanning electron microscope (SEM), microprobe, infrared spectroscopy, inductively coupled plasma atomic emission spectrometry and mass spectrometry (ICP-AES, ICP-MS). All the vivianites display similar morphological, mineralogical and geochemical signature, suggesting a common diagenetic origin. Their geochemical signature is sensitive to secondary alteration where vivianite concretions are gradually transformed from the rim to the center into an amorphous santabarbaraite phase with a decreasing Mn content. We analysed the spatial and temporal distribution of the concretions in order to determine the primary parameters controlling the vivianite formation, e.g., lithology, sedimentation rates, and porewater chemistry. We conclude that vivianite formation in Lake Baikal is mainly controlled by porewater chemistry and sedimentation rates, and it is not a proxy for lacustrine paleoproductivity. Vivianite accumulation is not restricted to areas of slow sedimentation rates (e.g., Academician and Continent ridges). At the site of relatively fast sedimentation rate, i.e., the Posolsky Bank near the Selenga Delta, vivianite production may be more or less related to the Selenga River inputs. It could be also indirectly related to the past intensive methane escapes from the sediments. While reflecting an early diagenetic signal, the source of P and Fe porewater for vivianites genesis is still unclear.

Contributors: J.S Laberg, T.O Vorren, J Mienert, D Evans, B Lindberg, D Ottesen, N.H Kenyon, S Henriksen

Date: 2002-08-15

sediment input of glacigenic sediments are prone to failure as illustrated...cores. Sedimentary provinces identified include a partly buried slide ...Late Quaternary palaeoenvironment and chronology in the Trænadjupet Slide...those in Fig. 6. The core comprises two units of glacimarine sediments...late Quaternary...sediments were deposited while the Fennoscandian ice sheet was at the ...late Quaternary...core comprises two units of glacimarine sediments (greyish brown sandy...s), sediment density (g/cm3) and magnetic susceptibility (cgs)) of core...sedimentation and a slide scar north-east of the Trænadjupet Slide. The...illustrating the late Quaternary sedimentary environment of the study ...sediment density (g/cm3) and magnetic susceptibility (cgs)) of core M23554...late Quaternary sedimentary environment of the study area including the...late Weichselian glacial maximum (prior to 13.2 14C kyr BP). Hemipelagic...diamicton) overlain by late glacial/Holocene hemipelagic sediments (yellow...sediments...late Weichselian glacial maximum (inner Vøring Plateau and north-east ...late glacial/Holocene hemipelagic sediments (yellow brown mud). See text...core comprises debris flow sediments (massive, grey diamicton) overlain ... The northern mid-Norwegian continental slope was studied based on high-resolution side-scan sonar data, multibeam bathymetry, high-resolution and multichannel seismics together with gravity cores. Sedimentary provinces identified include a partly buried slide on the eastern, inner Vøring Plateau, an area dominated by glacigenic debris flows south-west of the Trænadjupet Slide, the Trænadjupet Slide, and an area of glacimarine sedimentation and a slide scar north-east of the Trænadjupet Slide. The Trænadjupet Slide affected an area of about 14 100 km2 and mobilised about 900 km3 of sediments. Little is known about the areal extent and volume of the older events. The glacigenic debris flows and glacimarine sediments were deposited while the Fennoscandian ice sheet was at the shelf break during the late Weichselian glacial maximum (prior to 13.2 14C kyr BP). Hemipelagic and/or contouritic sedimentation prevailed during the Holocene period. Two large slide scars were probably formed sometime prior to or during the late Weichselian glacial maximum (inner Vøring Plateau and north-east of the Trænadjupet Slide) and another during the mid-Holocene interglacial period immediately prior to 4000 14C kyr BP (the Trænadjupet Slide). The two older scars may represent one event or two separate events. Deposition of poorly permeable glacigenic sediments over high-water-content fine-grained hemipelagic and/or contourites may have prevented water escape and increased failure potential. Thus continental slope areas of episodically high sediment input of glacigenic sediments are prone to failure as illustrated by this study, which has identified at least two large slope failures. Failures have occurred both during glacial maxima, periods of climate deterioration and low global eustatic sea level, and during interglacials as today with improved climatic conditions and a high global eustatic sea level.