The sea-level history around the last glaciation is in the focus of recent, controversial debates. A profound understanding of sea-level changes during this time interval is, however, essential since ...sea level is a central parameter in the climate system as well as a major force on continental margin sedimentation. Here, we present a seismic record together with augmented data from the Sunda Shelf Hanebuth, T.J.J., Stattegger, K., Saito, Y., 2002. The architecture of the central Sunda Shelf (SE Asia) recorded by shallow-seismic surveying. Geo-Marine Letters 22, 86–94. and compare our results in a careful evaluation with the sparse existing data sets of global validity, i.e. the Bonaparte Gulf record Yokoyama, Y., Lambeck, K., DeDeckker, P., Johnston, P., Fifield, L.K., 2000. Timing of the Last Glacial Maximum from observed sea-level minima. Nature 406, 713–716.; Yokoyama, Y., De Deckker, P., Lambeck, K., Johnston, P., Fifield, L.K., 2001. Sea-level at the Last Glacial Maximum: evidence from nortwestern Australia to constrain ice volumes for oxygen isotope stage 2. Paleogeography Paleoclimatology Paleoecology 165, 281–297., the Barbados coral record Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea level record: influence of glacial melting dates on the Younger Dryas event and deep ocean circulation. Nature 342, 637–642.; Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23–24), 3322–3337. and the latest numerical model of continental deglaciation Peltier, W.R., Fairbanks, R.G., 2006. Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record. Quaternary Science Reviews 25 (23–24), 3322–3337..
Sea level seems to have been lower shortly prior to the conventional Last Glacial Maximum (LGM; 21–19 cal kyr BP). The time interval around this glacial lowstand is not covered by ages from the Sunda Shelf, but documented by an ancient barrier — tidal-flat system. These palaeo-coastal relict forms indicate such an early lowstand some 5 m deeper than sea level was during LGM times. The LGM sea level on the Sunda shelf is recalculated to −
123
±
2 m modern water depth. This depth fits nicely with the lowstand data derived from Barbados and the Bonaparte Gulf. The recently assumed 19-kyr sea-level rise is supported by the Sunda and Bonaparte data sets combined, although it might have started already as early as at 19.6 cal kyr BP lasting for some 800 kyr with an amplitude of at least 10 m. This early pulse-like rise might have played a crucial role in the physical preservation of the high-glacial to early deglacial deposits on the Sunda Shelf.
The modelled sea-level history is, thus, supported with respect to an initial high-glacial lowstand prior to the LGM, which might be in apparent contrast to observations from Bonaparte. Nevertheless, field data suggest a glacial sea-level evolution about 10 m deeper than the model. Also, the gradual rising trend from 26 to 16 cal kyr BP, as deduced from the model, can definitively not be approved by any field data. However, our knowledge is still unsatisfactory and an expansion of field data from suited areas is urgently needed.
Tsunami, storm and flash-flood event layers, which have been deposited over the last century on the shelf offshore Khao Lak (Thailand, Andaman Sea), are identified in sediment cores based on ...sedimentary structures, grain size compositions, Ti / Ca ratios and 210Pb activity. Individual offshore tsunami deposits are 12 to 30 cm in thickness and originate from the 2004 Indian Ocean Tsunami. They are characterized by (1) the appearance of sand layers enriched in shells and shell debris and (2) the appearance of mud and sand clasts. Storm deposits found in core depths between 5 and 82 cm could be attributed to recent storm events by using 210Pb profiles in conjunction with historical data of typhoons and tropical storms. Massive sand layers enriched in shells and shell debris characterize storm deposits. The last classified type of event layer represents reworked flash-flood deposits, which are characterized by a fining-upward sequence of muddy sediment. The most distinct difference between storm and tsunami deposits is the lack of mud and sand clasts, mud content and terrigenous material within storm deposits. Terrigenous material transported offshore during the tsunami backwash is therefore an important indicator to distinguish between storm and tsunami deposits in offshore environments.
On the Vietnam Shelf more than 1000 miles of shallow high-resolution seismics were analyzed to unravel post-glacial evolution in a tropical, siliciclastic environment together with 25 sediment cores ...from water depths between 21 and 169 m to determine stratigraphy, distribution and style of sedimentation. Fourty-seven samples were dated with the AMS-
14C technique.
The shelf was grouped into three regions: a southern part, a central part, and a northern part. On the broad
Southern Shelf, sedimentation is influenced by the Mekong River, which drains into the SCS in this area. Here, incised valley fills are abundant that were cut into the late Pleistocene land surface by the Paleo-Mekong River during times of sea level lowstand. Those valleys are filled with transgressive deposits. The Holocene sedimentation rate in this low gradient accommodation-dominated depositional system is in the range of 5–10 and 25–40 cm/ky at locations sheltered from currents. The
Central Shelf is narrow and the sedimentary strata are conformable. Here, numerous small mountainous rivers reach the SCS and transport large amounts of detrital sediment onto the shelf. Therefore, the Holocene sedimentation rate is high with values of 50–100 cm/ky in this supply-dominated depositional system. The broad
Northern Shelf in the vicinity of the Red River Delta shows, as on the
Southern Shelf, incised valleys cut into the Pleistocene land surface by paleo river channels. In this accommodation-dominated shelf area, the sedimentation rate is low with values of 5–10 cm/ky. Where applicable, we assigned the sampled deposits to different paleo-facies. The latter are related to certain intervals of water depths at their time of deposition. Comparison with the sea-level curve of Hanebuth, T.J.J., Stattegger, K., Grootes, P., 2000. Rapid flooding of the Sunda Shelf; a lateglacial sea-level record. Science, 288: 1033–1035. indicates subsidence on the
Central Shelf, which is in agreement with the high sedimentation rates in this area. In contrast, data from the
Northern Shelf suggest tectonic uplift that might be related to recent tectonic movements along the Ailao Shan–Red River Fault zone. Data from the
Southern Shelf are generally in agreement with the sea-level curve mentioned above.
The tropical ocean plays a major role in global climate. It is therefore crucial to establish the precise phase between tropical and high-latitude climate variability during past abrupt climate ...events in order to gain insight into the mechanisms of global climate change. Here we present alkenone sea surface temperature (SST) records from the tropical South China Sea that show an abrupt temperature increase of at least 1°C at the end of the last glacial period. Within the recognized dating uncertainties, this SST increase is synchronous with the Bølling warming observed at 14.6 thousand years ago in the Greenland Ice Sheet Project 2 ice core.
•The term cryptic event layers is introduced and defined.•The statistical approach to identification of cryptic event layers based on grain size data is outlined.•The advantage of identification of ...cryptic storm deposits based on unbiased statistical analyses is presented.•The role of cryptic event layers in environmental reconstructions is emphasized.
Identifying storm-induced coastal flooding deposits involves multiple laboratory techniques, with one of the fundamental methods being grain size and shape analysis. This study presents a new statistical approach for analysing grain size and shape data, enabling granulometric characterisation of storm deposits. The set of statistical methods used to objectively identify storm-related deposits includes multivariate techniques such as principal component analysis (PCA), factor analysis (FA), cluster analysis (CLA), linear discriminant analysis (LDA), and end-member modelling analysis (EMMA). The selected statistical analyses have proven valuable in identifying the storm origins of deposits. Moreover, they have enabled the depiction of cryptic event layers, referring to those not associated with discrete, macroscopically detectable sand layers. The statistical approach to granulometric data proved to be particularly useful in cases where the other lines of evidence, such as i.e. geochemical or micropalaeontological evidence are weak. Identifying cryptic event layers, the term defined in the article for the first time, improves paleoclimatic interpretations by revealing previously unexplored past storms and periods of storminess.
This study describes, and reviews, the stratigraphic architecture of the world's largest but least known tropical siliciclastic shelf using the sequence-stratigraphic concept. The Sunda Shelf ...provides conditions particularly suited for reconstructing its depositional history due to a low gradient and extreme width, the presence of huge paleo-valley systems and abundant filled channels, tectonic stability during the Quaternary, and high sediment input due to a large catchment area. We investigated the subsurface along the most prominent paleo-valley by shallow-seismic surveying and 36 gravity cores controlled by 80 radiocarbon dates.
The deposits during sea-level fall prior to the last glacial maximum lowstand and the subsequent deglacial rise correspond to four systems tracts: (a) wide, partly detached prograding deltaic clinoforms indicate forced regression related to a regressive systems tract; (b) sparse shoreline deposits and widespread soil formation refer to a lowstand systems tract; (c) rapidly backstepping coastline-related deposits form a confined transgressive systems tract without stacking patterns and are mainly restricted to the paleo-valley system; (d) a thin marine mud cover extends as a condensed section over the whole shelf area (the base of a highstand systems tract).
The stratigraphic architecture on the central Sunda Shelf strata over the past 50,000 years is the result of the interplay of three major factors: (1) rapid sea-level changes, (2) locally pronounced physiography and (3) changes in sediment supply that determined the distribution and accumulation pattern.
The South China Sea offers an excellent case for studying source-to-sink transport processes of fluvial sediments among the global marginal seas. This study synthesizes existing clay mineralogical ...and geochemical data from ~1500 samples from the seafloor and surrounding rivers, deepwater mooring observation results, and high-resolution glacial–cyclic clay mineralogy records from six high-quality sediment cores. Source-to-sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales: modern process and Late Quaternary glacial cycles. The results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the South China Sea, e.g., dominant illite and chlorite in Taiwan, overwhelming majority of smectite in Luzon, dominant kaolinite in South China, and similar amounts of the four clay mineral species in Red and Mekong river systems. The formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the East Asian monsoon climate with warm temperature and high precipitation, and subordinately by tectonic activity and specific lithological character. The basin-wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects. The differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the South China Sea. Through combining clay mineralogical distributions on the seafloor with observed oceanic current systems, the modern transport pathways can be well established, e.g., in the northern South China Sea, illite and chlorite from Taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies.
High-resolution sediment dynamic analysis for the Late Quaternary reveals different sediment transport patterns in the northern, western, and southern South China Sea when the land–sea configuration dramatically changed during glacial conditions. In the north, the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport. In the west, the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds. In the south, the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods. The transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern South China Sea. The relative contributions from three provenances (South China, Luzon, and Taiwan) highlight their distinct variability over the last 28ka, implying that the southward shift of the inter-tropical convergence zone (ITCZ) at 16ka BP caused an increased sediment contribution from South China, the intensified influence of the Kuroshio Current intrusion controls more efficient westward transport of Luzon sediments, and the stronger deepwater current transports Taiwan-sourced sediments further westward from the last glaciation to the Holocene.
The mid-Pleistocene climate transition is a complex global change leading to Late Pleistocene ice ages with increased mean ice volume and dominant 100-ka cycle. A thorough understanding of this ...transition demands quantitative investigations in the time and frequency domains, and in the "stochastic domain". Three methods of time-series analysis are presented which have been adapted for this purpose. They are tested by means of predefined, artificial time series and applied to benthic oxygen isotope (δ^sup 18^O) records which serve as ice volume indicator. Results are as follows: (a) The time-dependent mean shows an increase of 0.35per thousand vs PDB from 942 to 892ka. (b) Evolutionary spectral analysis reveals an abrupt increase of 100-ka cycle amplitude at approximately 650ka. (c) Probability density function exhibits a bifurcation behavior at approximately 725ka. These findings point to a multiple transition from a more linear climate system to a strong nonlinear system. The significant lead of the transition in mean, in relation to the 100-ka amplitude change and bifurcation is left open for explanation.PUBLICATION ABSTRACT
We present a compilation and analysis of 1099 Holocene relative shore-level (RSL) indicators located around the Baltic Sea including 867 relative sea-level data points and 232 data points from the ...Ancylus Lake and the following transitional phase. The spatial distribution covers the Baltic Sea and near-coastal areas fairly well, but some gaps remain mainly in Sweden. RSL data follow the standardized HOLSEA format and, thus, are ready for spatially comprehensive applications in, e.g., glacial isostatic adjustment (GIA) modelling. We apply a SQL database system to store the nationally provided data sets in their individual form and to map the different input into the HOLSEA format as the information content of the individual data sets from the Baltic Sea area differs. About 80% of the RSL data is related to the last marine stage in Baltic Sea history after 8.5 ka BP (thousand years before present). These samples are grouped according to their dominant RSL tendencies into three clusters: regions with negative, positive and complex (transitional) RSL tendencies. Overall, regions with isostatic uplift driven negative tendencies dominate and show regression in the Baltic Sea basin during the last marine stage. Shifts from positive to negative tendencies in RSL data from transitional regions show a mid-Holocene highstand around 7.5–6.5 ka BP which is consistent with the end of the final melting of the Laurentide Ice Sheet. Comparisons of RSL data with GIA predictions including global ICE-5G and ICE-6G_C ice histories show good fit with RSL data from the regions with negative tendencies, whereas in the transitional areas in the eastern Baltic, predictions for the mid-Holocene clearly overestimate the RSL and fail to recover the mid-Holocene RSL highstand derived from the proxy reconstructions. These results motivate improvements of ice-sheet and Earth-structure models and show the potential and benefits of the new compilation for future studies.
•A first standardized and publicly available Holocene relative sea-level database for the Baltic Sea is presented.•The database holds 1099 revised data points with an estimation of vertical and chronological uncertainties.•Negative RSL tendencies prevail over the positive and complex tendencies in the Baltic Sea Basin.•Mid-Holocene RSL highstand occurred around 7.5–6.5 ka BP being consistent with the end of the final melting of the LIS.•The contribution of ice loading in the eastern Baltic Sea Basin is likely overestimated in the ICE-5G and ICE-6G_C models.
High-resolution clay mineralogical investigations and their comparison with other sedimentological data from ODP Sites 908 and 909 (central Fram Strait) were used to reconstruct the paleoclimate and ...paleoceanography in the high northern latitudes since the Middle Miocene. Ice rafting has probably occurred since 15 Ma. The comparison of sand-sized components and clay mineral distribution demonstrate that both were not delivered by the same transport process. The input of the clay fraction is related to transport through sea ice and/or oceanic currents. A provenance change at 11.2 Ma is indicated by variations within clay mineral distribution and increased accumulation rates. This is interpreted as a result of an increase in water mass exchange through the Fram Strait. Decreases of the smectite to illite and chlorite ratio at Site 909 suggest a Middle Miocene cooling phase between 14.8 and 14.6 Ma, and a further cooling phase between 10 and 9 Ma. The intensification of glaciation in the Northern Hemisphere is documented by an increase of illite and chlorite from 3.4 to 3.3 Ma, which is synchronous to the onset of major Northern Hemisphere glaciation as indicated by oxygen isotope data.PUBLICATION ABSTRACT
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