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1.
Seventy-five surface and subsurface sediment samples collected on the Amazon continental shelf were analyzed by X-ray diffraction
(XRD) in the grain-size fractions smaller than 2 μm. The groups of clay minerals thus identified were smectite, kaolinite,
illite, and mixed-layer illite/smectite. Calculation of relative abundance shows a predominance of smectite (37%) in the whole
area, followed by kaolinite (27%), illite (23%), and a small percentage of mixed-layer illite/smectite (12%). The distal,
northwest region of the continental shelf is characterized by a high abundance of smectite (41%), high salinity values, and
high sediment accumulation rates (10 cm year−1), whereas the proximal region is characterized by a comparatively low abundance of smectite (30%), low salinity values, and
low sediment accumulation rates (<1 cm year−1). This trend of increasing abundance northwestwards documents a preferential settling of smectite in the distal and more
saline regions of this estuarine system.
Received: 17 September 1999 / Revision accepted: 17 January 2000 相似文献
2.
Within the Russian–German research project on “Siberian River Run-off (SIRRO)” dealing with freshwater discharge and its influence
on biological, geochemical, and geological processes in the Kara Sea, sedimentological and organic-geochemical investigations
were carried out on two well-dated sediment cores from the Yenisei Estuary area. The main goal of this study was to quantify
terrigenous organic carbon accumulation based on biomarker and bulk accumulation rate data, and its relationship to Yenisei
river discharge and climate change through Holocene times. The biomarker data in both cores clearly indicate the predominance
of terrigenous organic matter, reaching 70–100 and 50–80% of total organic carbon within and directly north of the estuary,
respectively. During the last ca. 9 cal ka b.p. represented in the studied sediment section, siliciclastic sediment and (terrigenous) organic carbon input was strongly
influenced by postglacial sea-level rise and climate-related changes in river discharge. The mid-Holocene Climatic Optimum
is documented by maximum river discharge between 8.2 and 7.3 cal ka b.p. During the last 2,000 years, river discharge probably decreased, and accumulation of both terrigenous and marine organic
carbon increased due to enhanced coagulation of fine-grained material. 相似文献
3.
Based on new and existing data on oxygen isotopes, alkenone-surface seawater temperature trends, planktonic foraminifers,
lithology, and clay mineral composition of piston cores, a distinct cooling event has been identified around 8,200 cal a b.p. in the middle Okinawa Trough, northwest Pacific. This corresponds to the 8,200 a b.p. cooling event recorded in many places of the Northern Hemisphere. During this event, the local temperature decreased by
1°C, and the δ18O value increased by 0.6‰. A strengthened Asian winter monsoon is the most probable cause for this event, which thus adds
further credibility to the contention that we are dealing here with a global phenomenon. 相似文献
4.
南海北部陆坡50 ka 以来黏土矿物来源与输运机制分析 总被引：2，自引：2，他引：0
在 AMS14C 定年的基础上,对南海北部 KNG5站和 KNG7站柱状沉积物中的粒度和黏土矿物进行了研究.KNG5孔黏土矿物组合的基本特点是以伊利石、绿泥石和高岭石为主,蒙脱石含量次之.而 KNG7孔黏土矿物组合的基本特点是以伊利石、绿泥石和蒙脱石为主,高岭石含量次之.物源分析进一步表明, KNG5和 KNG7孔高岭石主要来自于珠江,蒙脱石主要由吕宋岛提供,伊利石和绿泥石分别由珠江和台湾提供.相对于 KNG5孔而言, KNG7孔沉积物受珠江影响较小,而受台西南影响较大.由物源分析推测,珠江对南海北部的物源供应存在一个明显的界线,而这一界线可能位于 KNG5孔和KNG7孔之间,越过这一界线随着离岸距离的增加,南海北部陆坡陆源沉积物受珠江影响明显减弱,而主要由台湾贡献. 相似文献
5.
Detailed 14C AMS data and isotope based stratigraphies from high-resolution paleoceanographic records for the last 22 ka of cores from
the upper continental slope off NE Brazil reveal sedimentation rates of up to 100 cm per 1000 yr. Variations in the sediment
composition relate to changes in the input of terrigenous material. The sedimentation is controlled by sea level and by the
climatic regime of the hinterland. Short-term changes in the tropical wind field may act as a climatic trigger. The zonality
of the SE trades was probably increased and the monsoonal activity over Africa reduced during the Younger Dryas period. 相似文献
6.
To date, only a few coral proxy studies have investigated coral growth as an indicator of climate variability. This study
presents the first extension-rate record (Porites lutea) from the Maldives (NW Indian Ocean), inferred from skeletal δ18O chronology for the lagoon of Rasdhoo Atoll (4°N/73°W) in the central area of the Maldives, influenced by the Indian monsoon.
The record spans 90 years over the period 1917–2007. The mean annual extension over this period was 9.9 mm/year, and an increase
of annual extension rates until 1990 by 3 mm/year can be explained by a rise of 0.7°C in sea surface temperature (SST) in
this region. After 1990, the extension rates do no continue increasing, possibly due to ecological stress caused by progressive
ocean warming and acidification. The correlation between annual extension rates and SSTs is thus significant and strong in
the lower part of the record until 1955 (r = +0.69, p < 0.0001), but weaker thereafter (r = +0.44, p < 0.001). The extension rates yield a distinct interannual variability of 3–4 years, caused by interannual SST fluctuations
driven by the El Ni?o-Southern Oscillation. A variability of 8–9 years is likely driven by SST variations endemic to the Indian
Ocean. Spectral peaks between 18–19 years and 6–7 years cannot be explained by SST fluctuations, but by variations in the
strength of the SW monsoon currents. It is suggested that during phases of stronger monsoon activity, the coral sacrificed
coral extension in favor of a denser, more robust skeleton. The geomorphology of the atoll may strengthen the potential of
this new coral archive to track climate variability. 相似文献
7.
Turbidites and their association with past earthquakes in the deep Çınarcık Basin of the Marmara Sea
Two gravity cores (CAG-3 and C-15) from the tectonically active, 1,276-m deep Çınarcık Basin of the Marmara Sea each include three sandy turbiditic mud units (1 mm–2 cm thick) with sharp basal contacts. The high benthic foraminifer content of these units suggests that the sediments were transported by turbidity currents from the upper slope region. These units represent the thin edges of turbidites thickening towards the subsiding north-eastern part of the basin, and contain quartz, detrital calcite, intact shells and shell fragments, smectite, pyrite framboids, muscovite, biotite, epidote and garnet. Their clay fractions are more enriched in smectite than those of adjacent layers. AMS 14C ages (957±43 a.d. and 578±31 a.d.) of two upper and middle turbiditic units in core C15 overlap with the historical İstanbul-Thrace (intensity=10) and İstanbul-Kocaeli (intensity=9) earthquakes of 26 October 986 and 15 August 553, respectively. This overlap, together with sedimentological characteristics, strongly suggests that the turbiditic units are related to the tectono-seismic activity of the North Anatolian Fault. The age of the lowest turbiditic unit in core C-3 was found to be 6,573±87 a b.p. (calendar) by AMS 14 C. In terms of chronostratigraphic relationships and lithological composition, the turbiditic units in core CAG-3 cannot be correlated with those in C15. This can be explained by gravity-controlled sedimentation causing wedging out of turbidites towards the edge of the basin. 相似文献
8.
Glacial and deglacial seafloor methane emissions from pockmarks on the northern flank of the Storegga Slide complex 总被引：2，自引：2，他引：0
The Storegga Slide complex is a multi-stage slope failure on the Norwegian continental margin where the most recent major
event occurred 8.1 ka b.p. (calendar years before present). Its northern flank contains pockmark features that are commonly inferred to be related
to the historical and modern venting of methane-bearing fluids. Three jumbo piston cores (JPC), one from a pockmark and two
background cores at variable distances from this site (proximal, 5 km, and distal, 15 km) on the northern flank of the slide
(806–1,524 m water depths), were sampled at 10 cm resolution to assess the geologic record of methane venting in the Nyegga
pockmark field. Six down-core radiocarbon measurements on mixed planktonic foraminifer species reveal ages of 9.4–16.4 ka
b.p. Bathymodiolus mussel shell horizons, indicators of methane-rich environments, have been dated at 15.8–17.6 and ~22 ka b.p. in the pockmark core. Stable isotope analyses on planktonic (Neogloboquadrina pachyderma sinistral) and benthic (Islandiella norcrossi, Melonis barleeanum) Foraminifera reveal δ18O values indicative of a clear glacial/deglacial transition (−1.5‰ shift in planktonic species). Both planktonic and benthic
δ13C signatures record multiple excursions, interpreted to reflect the influence of methane in the environment; these δ13C excursions occur in the pockmark core and also in the distal background core. While authigenic calcite formation on the
seafloor may play an important role in producing such excursions, these data together suggest the influence of methane seepage
within the pockmark field over the past 25 ka, whereby seepage was particularly active between 13 and 15 ka. This is consistent
with previously inferred regional increases in porewater pressure associated with glacial loading and higher sedimentation
rates, which can cause gas hydrate and slope instability. 相似文献
9.
K��r?ad Kadir Eri? M. N. ?a?atay Sena Ak?er Luca Gasperini Yosi Mart 《Geo-Marine Letters》2011,31(1):1-18
The late glacial to Holocene sedimentary record of the northern shelf of the Sea of Marmara (SoM) has been documented by detailed
seismo-, chrono-, and biostratigraphic analyses using sub-bottom (Chirp) profiles and sediment cores. During MIS 3 and the
main part of MIS 2 (60–15 14C ka b.p.), disconnection from the Mediterranean and Black seas together with a dry climate resulted in a regression in the SoM, when
the Sea was transformed into a brackish lake. The river incisions below 105 m water depth along the northern shelf took place
during the last glacial maximum, when the lake level was modulated by stillstands at −98 and −93 m. The post-glacial freshwater
transgressive stage of the Marmara ‘Lake’ occurred between 15 and 13.5 14C ka b.p., leading to a rise in water level to −85 m by 13.0 14C ka b.p., as evidenced by broad wave-cut terraces along the northern shelf. Since 12 14C ka b.p., high-frequency sea-level fluctuations have been identified at the SoM entrance to the Strait of İstanbul (SoI). Thus, wave-cut
terraces have been recorded at water depths of −76 and −71 m that, according to an age model for core MD04-2750, have ages
of 11.5 and 10.5 14C ka b.p., respectively. Ancient shoreline at −65 m along the northern shelf presumably formed soon after the Younger Dryas (YD) at
ca. 10.1 14C ka b.p. Moreover, there is compelling evidence of Holocene outflow from the Sea of Marmara to the Black Sea. At the SoM entrance
to the SoI, the existence of bioherms on the reflector surface together with abundant Brizalina spathulata and Protoglobulimina pupoides in a core suggests a return to higher salinities due to strong Mediterranean water incursion into the SoM at ∼8.8 14C ka b.p. This finding is consistent with earlier suggestions that, after the YD, the Black Sea was flooded by outflow from the SoM
as a result of global sea-level rise. 相似文献
10.
The vertical distribution patterns of grain-size parameters, carbonate and organic carbon contents, and clay mineral abundances were examined in ten sediment cores from basins of the northern Aegean Sea. Sedimentation rates for Holocene deposition were determined on the basis of 11 14C datings and indirectly from the age of the lower sapropel S1; they were estimated at 14.9, 18.9–21.8 and 34.7 cm 103 year–1 for the North Skyros, Athos, and North Limnos basins respectively. The sedimentation rates decrease gradually towards the southern basins, as a consequence of the greater distance from sediment supply sources. Also, sedimentation rates appear to decrease from the last glacial to Holocene units. The clay minerals illite, smectite, kaolinite and chlorite were identified in the cores. Generally, illite is the predominant mineral, showing a north–south-decreasing trend, followed by smectite; both minerals have a terrigenous origin, and smectite occurrence is higher in basins located near Limnos Island where volcanic formations prevail. Terrigenous illite is abundant in the sapropel S1, exhibiting the highest content of all sedimentological units. High illite content is unusual in eastern Mediterranean sapropels. This pattern is attributed to the proximity of the N. Aegean Sea basins to Balkan and Turkish land sources. In general, sediment mass gravity flow processes coupled with seasonal deposition from nepheloid layers are the predominant sedimentation mechanisms in the N. Aegean basins. The relative sea-level stand, the proximity to terrigenous sources (rivers), the morphology of the N. Aegean basins (small dimensions, isolated, steep slopes), as well as seismic activity and strong bottom currents are probably the major factors controlling sedimentation in the region. 相似文献
11.
To date, coral proxy studies have proved largely unsuccessful in reconstructing temporal variability of the Indian monsoon
system in the NW Indian Ocean. In a recent publication in this journal, Storz and Gischler demonstrated that extension rates
in corals can be used to fill this gap. Those authors found a link between decadal and interannual variations of the SW monsoon
current velocities and Porites lutea extension rates in the lagoon of Rasdhoo Atoll (4°N/73°W) in the central Maldives for the period 1917–2007. This sister paper
shows that this extension-rate record can be used to reconstruct decadal variations of summer monsoon rainfall over peninsular
India and adjacent areas. The amount of monsoon rainfall and current velocities during summer are both affected by the strength
of the Indian monsoon system. Assessments of coral extension rates and the mean May–September All India Monsoon Rainfall index,
a measure of monsoon strength over the Indian subcontinent, revealed a significant spectral coherence within periods of 18–19
and 6–7 years. Almost 92% of variance is shared between both time series in the former band, and 85% in the latter. A correlation
between the 5-year running mean extension rate and rainfall records from the Western Ghats (grid of 73–76°E/13–15°N) is significant
especially for 1958–2006 (r = −0.82, p < 0.05). These findings imply that coral growth characteristics can serve as a new marine archive to reconstruct past variations
of the Indian monsoon system on interannual to decadal timescales. 相似文献
12.
Origin of pockmarks and chimney structures on the flanks of the Storegga Slide,offshore Norway 总被引：2，自引：1，他引：2
Seafloor pockmarks and subsurface chimney structures are common on the Norwegian continental margin north of the Storegga
Slide scar. Such features are generally inferred to be associated with fluid expulsion, and imply overpressures in the subsurface.
Six long gravity and piston cores taken from the interior of three pockmarks were compared with four other cores taken from
the same area but outside the pockmarks, in order to elucidate the origins and stratigraphy of these features and their possible
association with the Storegga Slide event. Sulfate gradients in cores from within pockmarks are less steep than those in cores
from outside the pockmarks, which indicates that the flux of methane to the seafloor is presently smaller within the pockmarks
than in the adjacent undisturbed sediments. This suggests that these subsurface chimneys are not fluid flow conduits lined
with gas hydrate. Methane-derived authigenic carbonates and Bathymodiolus shells obtained from a pockmark at >6.3 m below the seafloor indicate that methane was previously available to support a
chemosynthetic community within the pockmark. AMS 14C measurements of planktonic Foraminifera overlying and interlayered with the shell-bearing sediment indicate that methane
was present on the seafloor within the pockmark prior to 14 ka 14C years b.p., i.e., well before the last major Storegga Slide event (7.2 ka 14C years b.p., or 8.2 ka calendar years b.p.). These observations provide evidence that overpressured fluids existed within the continental margin sediments off Norway
during the last major advance of Pleistocene glaciation. 相似文献
13.
Thomas Leipe Franz Tauber Henry Vallius Joonas Virtasalo Szymon U?cinowicz Nicole Kowalski Sven Hille Susanna Lindgren Tero Myllyvirta 《Geo-Marine Letters》2011,31(3):175-188
In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic
Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep
muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry
bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum
POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm–3) and moderate POC concentrations (4–7 mg cm–3). Furthermore, sediment mass accumulation rates (MAR), based on 210Pb and 137Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial
rates. Overall, these vary between 14 and 35 g m–2 year–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC
contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented
data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition
can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor
(morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon
cycle in this large brackish-water marginal sea. 相似文献
14.
于１９８８年对云南星云湖盆地区进行调查，运用Ｘ射线衍射，差热分析，红外光谱分析和扫描电镜方法，对该盆地的第四系泥岩和现代沉积环境的泥质沉积物的４９个样品进行研究。发现，现代环境中粘土矿物分布规律明显，且与第四系沉积物有对比性，从而推断盆地沉积环境分布和演化与泥质沉积物的微量元素聚类分析结果相吻合。 相似文献
15.
Late Holocene chronology,origin, and evolution of the St. Bernard Shoals,Northern Gulf of Mexico,USA
Several shore-parallel marine sand bodies lie on the Louisiana continental shelf. They are Trinity Shoal, Ship Shoal, Outer
Shoal, and the St. Bernard Shoals. These shoals mark the submerged positions of ancient shorelines associated with abandoned
deltas. Three of these shoals are single elongate deposits. The fourth shoal, the St. Bernard Shoals, consists of a group
of discrete sand bodies ranging in size from 44 to 0.05 km2, 25 km southeast of the Chandeleur Islands in 15–18 m of water. The St. Bernard Shoals are stratigraphically above the St.
Bernard delta complex, which was active 2,500–1,800 years b.p. Understanding the evolution of the St. Bernard Shoals is necessary to reconstruct the Holocene chronology of the St. Bernard
delta complex and the eastern Louisiana continental shelf. For this study, 47 vibracores and 400 km of shallow seismic reflection
data collected in 1987 across the Louisiana shelf were analyzed. In June 2008, 384 km of higher-resolution seismic reflection
data were acquired across the study area and appended to the preexisting datasets. Vibracores were integrated with seismic
profiles to identify facies and their regional distribution. Our results demonstrate that the deltaic package stratigraphically
below the St. Bernard Shoals is chronologically younger than the northern distributaries, but derived from the same trunk
distributary channel (Bayou la Loutre). The river eventually bypassed the northern distributaries, and began to deposit sediment
further onto the continental shelf. After abandonment, the overextended delta lobe was rapidly transgressed, creating a transgressive
shoreline that eventually coalesced with earlier shorelines in the region to form the Chandeleur Islands. The St. Bernard
Shoals formed by the reworking of the relict distributary deposits exposed on the inner to mid shelf during and subsequent
to shoreface ravinement. 相似文献
16.
Box cores were collected close to river mouths along the eastern Brazilian shelf at water depths of 10–30 m. One core was
taken from more than 1000 m depth at the shelf slope. 210Pb and 226Ra activities were measured to establish sediment accumulation rates. Seven of the 10 cores exhibited an exponential decrease
with depth of excess 210Pb activities. The sediments from the sheltered Sudeste Channel off Caravelas revealed the highest sediment accumulation rate
of 0.81 cm yr−1. The sediments at the shelf slope seaward of the Rio Doce revealed the lowest accumulation rate of 0.13 cm yr−1. Sediment accumulation rates increased towards the Caravelas Bank. Current patterns and the morphology of the seabed favor
sediment deposition in this area. 相似文献
17.
Seabed outcrops of glaciodeltaic sediments were identified in four places east of Cape Cod, Massachusetts, during seismic-reflection,
multibeam bathymetric and backscatter, bottom photographic, and sediment sampling surveys. These strata record coarser-grained
ice-proximal glaciofluvial topset to finer-grained distal glaciolacustrine bottomset deposition within deltaic systems that
prograded southwestward into glacial lakes from the South Channel lobe about 18 ka b.p. These beds are important because they (1) influence the outer Cape’s hydrogeologic framework, and (2) constitute relatively
stable, locally rough habitats within an area of seafloor dominated by mobile sand and gravelly sediment, and benefit the
benthic fauna by providing shelter and a substrate amenable to burrow construction. 相似文献
18.
G. H. Hong S. H. Kim C. S. Chung D.-J. Kang D.-H. Shin H. J. Lee S.-J. Han 《Geo-Marine Letters》1997,17(2):126-132
Recent sediment accumulation rates are 18–230 mg cm-2 yr-1 (0.02–0.2 cm yr-1) based on excess 210Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers,
210Pb-derived sediment accumulation rates are 18–32 mg cm-2 yr-1 in the northern part of the Yamato Ridge and the Ulleung Basin, 29–136 mg cm-2 yr-1 in the Korea Plateau, and 230 mg cm-2 yr-1 in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers.
Received: 6 October 1995 / Revision received: 31 May 1996 相似文献
19.
A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola
Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits
filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across
the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting
that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ∼6,400 and ∼2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of
the bay. An eastern deltaic lobe was active for a shorter time, between ∼5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time.
It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream
divide. Estuarine conditions were established very early in the post-glacial flooding of the bay. 相似文献
20.
Erdal Dolu Erkan Gökaşan Engin Meriç Mustafa Ergin Tolga Görüm Hüseyin Tur Berkan Ecevitoğlu Niyazi Avşar Muhittin Görmüş Fatmagül Batuk Buğser Tok Oktay Çetin 《Geo-Marine Letters》2007,27(6):355-381
The Quaternary evolution of the Gulf of İzmit, situated on the tectonically active North Anatolian Fault Zone (NAFZ), was
investigated using seismic reflection, paleontologic, and sediment textural data. On the basis of seismic stratigraphic and
sedimentologic-paleontologic interpretations, four depositional units were distinguished within the Plio-Quaternary sequence
of the Gulf of İzmit. According to these data, Plio-Quaternary deposits supplied from the northern terrestrial area started
to accumulate during a progradational phase, in a south-facing half-graben. A coarse-grained sedimentary unit prograding into
the gulf from the south since 200 ka b.p. indicates a dramatic variation in the evolution of the gulf, with the initiation of a new strike-slip fault of the NAFZ
and a corresponding uplift of the Armutlu Peninsula in the south of the gulf. During the evolution of this fault from a wide
shear zone consisting of right-stepped strike-slip faults and pull-apart basins to a localized principal fault zone, sediments
were deposited under the influence of northerly prograding terrestrial and shallow-marine conditions due to relative sea-level
fluctuations in the Marmara Sea. During this period, the Gulf of İzmit was invaded mainly by Mediterranean and partly by Black
Sea waters. In the latest glacial period, shallow areas in the gulf became subaerially exposed, whereas the central and western
sub-basins of the gulf turned into lakes. The present evolution of the Gulf of İzmit is controlled by the after effects of
the new rupture of the NAFZ and the estuarine nature of the gulf environment. 相似文献