scholarly journals Recycling of clastics in coastal areas inferred from quantitative analysis of reworked radiocarbon samples

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Susumu Tanabe ◽  
Toshimichi Nakanishi ◽  
Rei Nakashima

AbstractStudies of the evolution of coastal lowlands since the Last Glacial Maximum (LGM) typically ignore radiocarbon data from sediment samples that have undergone reworking. However, these samples contain information on their sediment sources and the timing of their redeposition. We analyzed 738 radiocarbon dates obtained from shell and plant material in samples of post-LGM coastal sediment from north of Tokyo Bay, Japan. Of these samples, 245 (33%) were reworked. Furthermore, the percentage of reworked samples and their average age offsets increased with the depth of the water environment (terrestrial, 15% and 360 ± 250 years, respectively; intertidal, 26% and 470 ± 620 years; subtidal, 39% and 550 ± 630 years). Taking these radiocarbon samples as a proxy for clastic material, our results imply that channel erosion accounted for relatively little clastic removal in the terrestrial and intertidal environments over short timescales, whereas ~ 40% of clastics were removed by storm winnowing and transported in stepwise fashion to deeper water over longer timescales and ~ 60% in the subtidal environment were transported by floods directly from river mouths. These findings imply that radiocarbon ages from reworked samples can be used to quantify clastic recycling processes and their history in coastal areas.

2021 ◽  
Author(s):  
Susumu Tanabe ◽  
Toshimichi Nakanishi ◽  
Rei Nakashima

Abstract Studies of the evolution of coastal lowlands since the Last Glacial Maximum (LGM) typically ignore radiocarbon data from sediment samples that have undergone reworking. However, these samples contain information on their sediment sources and their timing of redeposition. We analyzed 738 radiocarbon dates obtained from shell and plant material in samples of post-LGM coastal sediment from north of Tokyo Bay. Of these samples, 245 (33%) had reworked ages. Furthermore, the percentage of reworked samples and their average age offsets increased with the depth of the water environment (terrestrial, 15% and 360 ± 250 years, respectively; intertidal, 26% and 470 ± 620 years; subtidal, 39% and 550 ± 630 years). Taking these radiocarbon samples as a proxy for clastic material, our results imply that channel erosion accounted for relatively little clastic removal in the terrestrial and intertidal environments in short duration, whereas ~40% of clastics were removed by storm winnowing and transported in stepwise fashion to deeper water in long duration and ~60% were transported by floods directly from river mouths in the subtidal environments. These findings imply that radiocarbon ages from reworked samples can be used to quantify clastic recycling processes and their history in coastal areas.


1998 ◽  
Vol 49 (2) ◽  
pp. 233-237 ◽  
Author(s):  
Marie-Pierre Ledru ◽  
Jacques Bertaux ◽  
Abdelfettah Sifeddine ◽  
Kenitiro Suguio

Environmental conditions of the lowland tropical forests during the last glacial maximum (LGM) between ca 20,000 and 18,000 14C yr B.P., are reevaluated in terms of dating control and lithology analyzed in seven pollen records from South America. The reevaluation shows that probably in none of the published records are LGM sediments present or abundant. This conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates. These findings suggest that the LGM was represented probably by a hiatus of several thousand years, indicative of drier climates than before or after.


2018 ◽  
Vol 55 (3) ◽  
pp. 283-294
Author(s):  
Christopher N. Jass ◽  
Devyn Caldwell ◽  
Christina I. Barrón-Ortiz ◽  
Alwynne B. Beaudoin ◽  
Jack Brink ◽  
...  

Late Quaternary faunal remains from three underwater settings in Cold Lake, Alberta and Saskatchewan, Canada, include at least 13 vertebrate taxa consistent with assemblages that postdate the Last Glacial Maximum (LGM). Seven new radiocarbon dates range from 10 350 ± 40 to 161 ± 23 years BP and provide insight into the post-LGM biotic history of east-central Alberta and west-central Saskatchewan. The presence of an essentially modern large mammal biota is suggested for the mid-Holocene, and possibly earlier, if the absence of extinct or extirpated taxa in association with Late Pleistocene Bison at the Alberta–Saskatchewan site is meaningful. Taphonomically, some of the remains suggest deposition in open environments during the Holocene, possibly when lake levels were lower. The recovery of late Quaternary faunal remains from a present-day lacustrine setting is novel, and suggests that similar records may occur in other lakes in western Canada, including those in areas with scarce Quaternary vertebrate records.


2015 ◽  
Vol 84 (2) ◽  
pp. 262-271 ◽  
Author(s):  
Socorro Lozano-García ◽  
Beatriz Ortega ◽  
Priyadarsi D. Roy ◽  
Laura Beramendi-Orosco ◽  
Margarita Caballero

AbstractWe inferred millennial-scale climate variations and paleohydrological conditions in the northern sector of the American tropics for 30.3–5.5 cal ka BP using geochemical characteristics of sediments from Lake Chalco in central Mexico. The sediment sequence is chronologically constrainedwith three tephra and nine radiocarbon dates. Temporal variations in titanium, total inorganic carbon, total organic carbon/titanium ratio, carbon/nitrogen ratio, and silica/titanium ratio indicate changes in runoff, salinity, productivity, and sources. Higher concentrations of Ti indicate more runoff during latest Marine Isotope Stage (MIS) 3 (30.3–28.6 cal ka BP). Runoff was lower during the last glacial maximum (LGM; 23–19 cal ka BP) than during the Heinrich 2 event (26–24 cal ka BP). The interval of reduced runoff continued up to 17.5 cal ka BP but increased during the Bølling/Allerød. Trends of decreasing runoff and increasing salinity are observed throughout MIS 1. Lake Chalco received less runoff during the LGM compared to deglaciation, opposite the trend of other North American tropical records. Different amounts of rainfall at different sites are possibly due to shifts in the position of the Intertropical Convergence Zone, changes in the size of the Altlanticwarmpool, and varying sea-surface temperatures of the Atlantic and Pacific oceans


2021 ◽  
Author(s):  
Karen Søby Özdemir ◽  
Henrieka Detlef ◽  
Linda Lambertucci ◽  
Christof Pearce

<p>Little is known about climate and ocean conditions during the Last Glacial Maximum in Baffin Bay, Greenland. This is partly due to the dissolution of biogenic carbonates in the central Baffin Bay, preventing reliable <sup>14</sup>C-chronologies. We present the results from a transect of gravity cores retrieved during the 2019 BIOS cruise on the HDMS Lauge Koch in the northern Baffin Bay. Core LK19-ST8-14G has been analyzed for grain size variations, sea-ice biomarkers, XRF, and color spectrophotometry. A preliminary chronology based on radiocarbon dates from foraminifera show that the bottom of the core is approximately 35.000 cal. years BP while the top sediments are of Late Holocene age. The sediment archive thus covers the full extent of the LGM and the last deglaciation. High-resolution photography and CT scans allowed the identification of distinctly different lithofacies in the sediment archive. The lower sections of the core are characterized by laminated mud with no IRD and absence of microfossils indicating a sub ice-shelf environment during the glacial period. The laminated sequence is interrupted by several coarser, detrital-carbonate (DC) rich layers which are interpreted as episodes of glacial retreat or ice-shelf collapse. The youngest of these DC layers immediately precedes the Holocene, which is represented by approximately 40 cm of bioturbated sediments with some IRD. This interpretation is supported by the concentrations of HBIs and sterols throughout the core, which indicate near perennial ice cover in the glacial northern Baffin Bay and more open water conditions during the Holocene.</p>


The Holocene ◽  
2018 ◽  
Vol 28 (9) ◽  
pp. 1535-1544 ◽  
Author(s):  
Laurence M Dyke ◽  
Anna LC Hughes ◽  
Camilla S Andresen ◽  
Tavi Murray ◽  
John F Hiemstra ◽  
...  

Large marine-terminating glaciers around the margins of the Greenland Ice Sheet have retreated, accelerated and thinned over the last two decades. Relatively little is known about the longer term behaviour of the Greenland Ice Sheet, yet this information is valuable for assessing the significance of modern changes. We address this by reporting 11 new beryllium-10 (10Be) exposure ages from previously uninvestigated coastal areas across southeast Greenland. The new ages are combined with existing data from the region to assess the timing of glacier retreat after the Last Glacial Maximum. The results show that deglaciation occurred first in the north of the region (~68°N) and progressed southwards. This north–south progression is attributed to the influence of the warm Irminger Current on the ice margin. Areas in the south of the region were isolated from the warm waters by the shallow bathymetry of the continental shelf. This demonstrates that oceanographic forcing paced the deglaciation of southeast Greenland through the Younger Dryas and early Holocene. In most areas of southeast Greenland bedrock ages are systematically older than their counterpart boulder samples; this offset is likely the result of inherited 10Be content in bedrock surfaces. This suggests that subglacial erosion during the last glacial cycle was insufficient to completely remove pre-existing 10Be content. Alternatively, this pattern may be the signature of a substantial retreat and advance cycle prior to final Holocene deglaciation.


2020 ◽  
Author(s):  
Sarahmae Buen ◽  
Fernando Siringan ◽  
Ronald Lloren

<p>Deep marine sediments may provide insights of past climate and oceanographic events. Knowledge of the past events can aid in scenario setting of future climate and their oceanographic consequences. A deep sea sediment core from the western side of Bohol Sea, a marginal sea located south of the Philippines, was used to reconstruct precipitation and identify the impacts of sea level rise on the circulation of Bohol Sea.  Five radiocarbon dates from bulk organic matter provide age control spanning back to the Last Glacial Maximum. Sedimentological (lithics and carbonate fractions; bulk density; sedimentation rate and mass accumulation rate) and geochemical (Ti, Al, Zr, Ti/Al and Y/Ni) data were used to reconstruct the sediment input for the area. Sediment input was decreasing from 20-15ka, followed by a relatively stable trend until ~9ka. After ~9ka sediment input increased up until the most recent years. Sedimentation trend follows the average winter (DJF) insolation curve at 10<sup>o</sup>N. This signifies that the sediment input reflects the general changes in precipitation in the area. Lithics and carbonate contents reflect a shift in sediment source that could be attributed to the change in circulation in the basin as the sea level rose to overtop the Surigao Strait located at the northeastern side of the basin. Greater westward transport of suspended material from large rivers to the east would contribute to the sedimentation in the western part of Bohol Sea.</p>


2013 ◽  
Vol 50 (12) ◽  
pp. 1178-1194 ◽  
Author(s):  
Jonathan Roger ◽  
Francky Saint-Ange ◽  
Patrick Lajeunesse ◽  
Mathieu J. Duchesne ◽  
Guillaume St-Onge

The geomorphology of the Eastern Canadian margin has been shaped by glacial processes during the Quaternary. Many studies have focused on the ice-sediment pathway through Hudson Strait to reconstruct the dynamics of the Laurentide Ice Sheet, and as a consequence, little is known on its marginal ice domes. Here we reconstruct the dynamics of two trough mouth fans (TMFs) offshore NE Newfoundland using sediment cores and radiocarbon ages supported by very high resolution seismic reflection profiles. These two TMFs, namely Notre Dame and Hawke, are fed by two glacial troughs incised in the bedrock. The TMFs show a complete sedimentary sequence from 30 ka BP to the beginning of the Holocene. The sampled sedimentary record on the upper slope extends back to a thick Heinrich event 3 (H3) deposit that corresponds to the end of the maximum extent of the Newfoundland ice dome. Above H3, a thick succession of turbidite deposits (>10 m) observed in both TMFs is correlated with periods of major meltwater supply from 28–29 to 17 ka BP. Our results show that the Last Glacial Maximum (LGM) period was characterized by major input of meltwater events stemming from the Newfoundland dome. The presence of H1 (∼17 ka BP) coincide with the end of the turbidite activity which is replaced by an open-water environment characterized by hemipelagic sediments rich in ice-rafted debris. The proglacial muddy sediment older than 13.3 ka BP on the shelf shows that ice was not grounded after H1, suggesting a very rapid retreat of the ice on the Newfoundland shelf after 17 ka BP.


1992 ◽  
Vol 38 (1) ◽  
pp. 1-31 ◽  
Author(s):  
Jan Mangerud ◽  
Magne Bolstad ◽  
Anne Elgersma ◽  
Dag Helliksen ◽  
Jon Y. Landvik ◽  
...  

AbstractMost scientists have concluded previously that the west coast of Spitsbergen, Svalbard, remained ice-free during the late Weichselian, between 25,000 and 10,000 yr B.P. We conclude that the glaciation was more extensive. Terraces that were postulated to have been ice-free are covered by a thin, late Weichselian till. Sudden drop in the marine limit and basal radiocarbon dates of raised glaciomarine sediments demonstrates that the glaciers in the main fjords, Isfjorden and Van Mijenfjorden, terminated west (outside) of the fjord mouths. Basal radiocarbon dates from glaciomarine clay above till in cores from the continental shelf west of Spitsbergen yielded ages of about 12,500 yr B.P., from which we conclude that the ice extended to the shelf edge. Based on the extent of amino acid diagenesis in radiocarbon-dated molluscs, the duration of the maximum extension of the late Weichselian glaciation was short, certainly less than 10,000 years. During the ice-free period preceding that glaciation, at least back to 40,000 yr B.P., the glaciers on Svalbard were not significantly larger than at present, as shown by marine deposits close to the glacier snouts. Many radiocarbon dates place deglaciation of the outer coast at about 12,500 yr B.P. At about 10,000 yr B.P., the rest of the archipelago rapidly became ice-free.


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