AMS 14C Ages Research Articles

Response of the Irish Ice Sheet to abrupt climate change during the last deglaciation

We summarize 121 14C and in-situ cosmogenic (10Be and 36Cl) ages that constrain fluctuations of the Irish Ice Sheet (IIS) since the Last Glacial Maximum (LGM) that can be linked to abrupt climate changes in the North Atlantic region. These data provide a robust means to date ice-sheet fluctuations because similar-age events can be identified from widely spaced sites, they are constrained by stratigraphy, and they can be related to large changes in the configuration of a dynamic ice sheet. The following events are recognized. (1) AMS 14C ages and 10Be and 36Cl ages as well as offshore data suggest that the last maximum advance of the IIS occurred between ∼27 and 23 cal ka. (2) Deglaciation began on the western continental shelf and in the Irish Sea Basin at ∼23 cal ka. Dated sites from around Ireland constrain subsequent widespread retreat of ice-sheet margins from the shelf onto Irish coastlines during the Cooley Point Interstadial ≥20 cal ka. AMS 14C ages suggest that the Cooley Point Interstadial continued until ≤18.2 cal ka B.P. During this interstadial, retreat of the ice-sheet margin into the northern Irish Sea Basin indicates that the IIS may have lost up to two-thirds of its mass. (3) Dated sites from northwestern and eastern Ireland indicate that the Cooley Point Interstadial was terminated by ice readvance during the Clogher Head Stadial at ∼18.2 cal ka. (4) The Linns Interstadial was a brief interval (≥17.0–≥16.5 cal ka) of ice recession following the Clogher Head Stadial that is identified from raised marine sediments in eastern and northern Ireland and cosmogenic ages elsewhere in Ireland. (5) The IIS subsequently readvanced during the Killard Point Stadial, reaching its maximum extent ∼16.5 cal ka, indicating that the readvance began sometime earlier. (6) Widespread retreat of the IIS began by ∼15.5 cal ka during the Rough Island Interstadial. (6) Readvance of cirque glaciers in western Ireland occurred during the Younger-Dryas equivalent Nahanagan Stadial.

Co-seismic and cumulative offsets of the recent earthquakes along the Karakax left-lateral strike-slip fault in western Tibet

The 400 km-long Karakax left-lateral strike-slip fault is the westernmost segment of the Altyn Tagh fault. It separates northwestern Tibet to the south from the Tarim basin to the north. The western section of the Karakax fault exhibits clear co-seismic surface ruptures of past large earthquakes. Geomorphic offset measurements from the field and high-resolution Ikonos images along 1.5 km across the Sanshiliyingfang fan and along 55 km of the fault, range from 3 to 28 m, with distinct clusters at 6 ± 2(3), 14 ± 2, 19 ± 2 and 24 ± 3 m. The cluster of the smallest offsets around 6 m (full range from 3 to 10 m) distributed over a minimum length of 55 km, is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude Mw 7.4–7.6 earthquake along the Karakax fault. We interpret the other offset clusters as the possible repetition of similarly sized events thus favoring a characteristic slip model for the Karakax fault. In a 3 m-deep trench dug across the active trace of the fault we can identify the main rupture strands of the last and penultimate events. The penultimate event horizon, a silty-sand layer, has been radiocarbon dated at 975–1020 AD (AMS 14C age). It is proposed that large Mw 7.4–7.6 events with co-seismic slip of about 6 m rupture the Karakax fault with a return time of about 900 years implying an average slip-rate of about 6–7 mm/years during the late Holocene. These results suggest that the Karakax fault is the largest left-lateral strike-slip fault at the rim of northwestern Tibet accommodating eastward movement of Tibet due to the India–Eurasia collision.

Chronological framework for the deglaciation of the Lake Michigan lobe of the Laurentide Ice Sheet from ice‐walled lake deposits

AbstractA revised chronological framework for the deglaciation of the Lake Michigan lobe of the south‐central Laurentide Ice Sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low‐relief ice‐walled lakes. We analyze the precision and accuracy of 15 AMS 14C ages of plant macrofossils obtained from a single ice‐walled lake deposit. The semi‐circular basin is about 0.72 km wide and formed of a 4‐ to 16‐m‐thick succession of loess and lacustrine sediment inset into till. The assayed material was leaves, buds and stems of Salix herbacea (snowbed willow). The pooled mean of three ages from the basal lag facies was 18 270 ± 50 14C a BP (21 810 cal. a BP), an age that approximates the switch from active ice to stagnating conditions. The pooled mean of four ages for the youngest fossil‐bearing horizon was 17 770 ± 40 14C a BP (21 180 cal. a BP). Material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform. Based on the estimated settling times of overlying barren, rhythmically bedded sand and silt, the lacustrine environment persisted for about 50 more years. At a 67% confidence level, the dated part of the ice‐walled lake succession persisted for between 210 and 860 cal. a (modal value: 610 cal. a). The deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the Lake Michigan lobe have been assessed using this method. There is no overlap of time intervals documenting when ice‐walled lakes persisted on these landforms. The rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice‐walled lake sedimentation. Copyright © 2011 John Wiley & Sons, Ltd.

Properties and formation of Black Soils on the Island of Poel (NE Germany)

Recent soil mapping on the Island of Poel, situated in the southern Baltic Sea, shows an abundance of Black Soils developed in stratified parent material, whereby the upper layers are of periglacial origin covering calcareous till. The Black Soils have been formed in the upper layer overlying Luvisols, developed in decalcified till, with different degrees of stagnic influence. The Luvisols are not the result of a degradation of the Black Soil, as no humic clay coatings were detected in their Bt horizons. With a simplified Ap, Ah, (Eb/Ah), (2)E, 2Bt(g)b, C horizon sequence, these soils differ from the better known degraded Phaeozems on Fehmarn and the Uckermark region. The properties of three pedons are presented and their pedogenesis is discussed. AMS 14C ages from soil organic carbon of the Ah horizons from the Black Soils suggest that the development of the Luvisols stopped within the first half of the Subatlantic period.

Late Quaternary paleolimnology of Onepoto maar, Auckland, New Zealand: Implications for the drivers of regional paleoclimate

A high-resolution record of lacustrine environments spanning ca. 30–9calkaBP was obtained from Onepoto maar, northern North Island, New Zealand. The multi-proxy record of environmental change is constrained by tephrochronology and AMS 14C ages and provides evidence for episodes of rapid environmental change during the Last Glacial Coldest Period (LGCP: 28.5–18calkaBP) and Late Glacial–Interglacial Transition (LGIT) from northern New Zealand. The Onepoto pollen record indicates that the LGCP was cold, dry and windy in the Auckland region with vegetation dominated by herbs and grasses in a beech forest mosaic. At the same time the diatom record indicates oligotrophic conditions with low lakes levels and turbulence whilst cladocerans indicate low water temperatures. The inference of cold, dry and windy conditions during the LGCP is supported by geochemical evidence for increased sediment influx, charcoal and CO2 limiting conditions for terrestrial macrophytes. Rapid climate amelioration and forest expansion after ca. 18calkaBP corresponds with reduced sediment influx, diatom and cladoceran-inferred higher lake levels indicating increasing moisture availability and temperature. Diatom flora indicates that an oligotrophic, circumneutral lake was becoming established during the LGIT but conditions were still variable. Between ca. 13.8 and 12.5calkaBP two brief drier and possibly cooler episodes are apparent (ca. 13.8–13.2 and 13–12.5calkaBP) followed by a warm phase combined with generally stable high lake levels between ca. 12.5 and 10.5calkaBP. Subsequently the lake water chemistry became more alkaline and eutrophic, possibly because sea level had risen high enough by this time to influence ground water chemistry.

Palaeoclimatic information from stable water isotopes of Holocene ice wedges on the Dmitrii Laptev Strait, northeast Siberia, Russia

AbstractThe stable isotopic composition (δ18O, δD, d) of three Holocene‐age ice wedges at the Dmitrii Laptev Strait, Russia (Oyogos Yar coast, 72.7°N, 143.5°E) was studied at high resolution (100 to 200 samples each) in order to develop palaeoclimatic records. AMS 14C ages of organic matter in the ice prove the Late Holocene age of the studied horizontal ice‐wedge profiles and indicate syngenetic growth associated with sediment accumulation. Co‐isotopic relationships of wedge ice close to the Global Meteoric Water Line point to a good suitability for palaeoclimate studies and all three profiles show similar isotopic features. A general Late Holocene winter warming trend is inferred from δ18O data changing from about −26‰ to values of −23‰ to −21‰, with periods of marked variability superimposed on the trend. This trend is accompanied by a shift in the d excess from 8‰–11‰ to 5‰–8‰, probably caused by varying proportions of differing moisture sources for precipitation. The highest winter temperatures and an increased influence of regional moisture in recent decades may reflect ongoing Arctic climate change. Copyright © 2010 John Wiley & Sons, Ltd.

Holocene mass-wasting events in Lago Fagnano, Tierra del Fuego (54°S): implications for paleoseismicity of the Magallanes-Fagnano transform fault

High-resolution seismic imaging and coring in Lago Fagnano, located along a plate boundary in Tierra del Fuego, have revealed a dated sequence of Holocene mass-wasting events. These structures are interpreted as sediment mobilizations resulting from loading of the slope-adjacent lake floor during mass-flow deposition. More than 19 mass-flow deposits have been identified, combining results from 800 km of gridded seismic profiles used to site sediment cores. Successions of up to 6-m thick mass-flow deposits, pond atop the basin floor and spread eastward and westward following the main axis of the eastern sub-basin of Lago Fagnano. We developed an age model, on the basis of information from previous studies and from new AMS-14C ages on cored sediments, which allows us to establish a well-constrained chronologic mass-wasting event-catalogue covering the last ∼12 000 years. Simultaneously triggered, basin-wide lateral slope failure and the formation of multiple debris flow and postulated megaturbidite deposits are interpreted as the fingerprint of paleo-seismic activity along the Magallanes-Fagnano transform fault that runs along the entire lake basin. The slope failures and megaturbidites are interpreted as recording large earthquakes occurring along the transform fault since the early Holocene. The results from this study provide new data about the frequency and possible magnitude of Holocene earthquakes in Tierra del Fuego, which can be applied in the context of seismic hazard assessment in southernmost Patagonia.

Sedimentary record of environmental evolution off the Yangtze River estuary, East China Sea, during the last ∼13,000 years, with special reference to the influence of the Yellow River on the Yangtze River delta during the last 600 years

A 35.60-m-long core (ECS-0702) recovered from a water depth of 22 m in the muddy area off the Yangtze River estuary was analyzed for sedimentary characteristics, clay and detrital mineral components, and element geochemistry as well as by AMS 14C dating to document sediment provenance changes and environmental evolution during the postglacial period in the study area. On the basis of the lithology, the benthic foraminiferal and ostracod assemblages, and the AMS 14C ages, we divided the core into four depositional units (DU1–DU4 in descending order) representing the postglacial sedimentary sequence during the last ∼13,000 years. DU 4 was deposited in a littoral to tidal-flat environment during ∼13,000–11,500 cal yr BP; DU 3 in a nearshore, subtidal environment upwards to the nearshore shelf with tidal influence in response to the postglacial sea-level rise during ∼11 500–7400 cal yr BP; DU 2 in a tide-affected, nearshore shallow-sea environment during ∼7400–540 cal yr BP, on the delta-front of the Yangtze River when the delta was actively prograding; and DU 1 in a nearshore shallow-sea environment during the last ∼540 years, on the delta-front under modern marine conditions. In DU 1, the depositional rate was much higher than in the underlying units, and the sediment composition reflects more influence from the Yellow River; this unit can therefore be logically linked to the period when the Yellow River last discharged into the South Yellow Sea, from AD 1128 to 1855. According to historical records, this period can be divided into an early stage (AD 1128–1494), when the shoreline near the Yellow River mouth was advancing slowly eastward, and a late stage (1495–1855), when the shoreline was advancing rapidly. The initiation of DU 1 deposition corresponds to the latter part of the early stage, suggesting that since that time, a relatively large amount of sediment from the Old Yellow River mouth area has been transported to the offshore area of the Yangtze River mouth. Our study has identified a high-resolution sedimentary signature associated with the last course shift of the Yellow River in the Yangtze River delta-front, thus highlighting the intricate relationship between sediment sources and sinks in coastal areas. A significant contribution of the Old Yellow River sediments to the Yangtze subaqueous delta during the last ∼600 years must be considered when the evolutional history of the Yangtze delta is examined and especially when the influence of the Three Gorge Dam construction on the future changes of the Yangtze Estuary and ecological environments in the East China Sea is estimated.

STUDY OF POLLEN CONCENTRATES FOR AMS <SUP>14</SUP>C DATING IN BARKOL LAKE

14C测年是湖泊沉积物定年的主要方法之一,随着对过去气候环境变化的深入研究,对于湖泊样品中的年代要求更高,而不同的测年物质的14C定年结果,会有不同的误差。通过对巴里坤湖部分样品,分别进行块状样有机质、陆生高等植物残体以及孢粉浓缩物定年比较,以探讨干旱区湖泊中14C定年的方法。测试结果表明:孢粉浓缩物与陆生高等植物残体的测年值极为接近,在西北干旱区湖泊测年过程中,孢粉浓缩物有望成为一种可靠的测年材料。在探讨湖泊沉积物年代的碳库效应时,孢粉浓缩物定年可能会成为一种有效的方法。

Late‐glacial and Holocene vegetation, climate and fire dynamics in the Serra dos Órgãos, Rio de Janeiro State, southeastern Brazil

AbstractWe present a high‐resolution pollen and charcoal record of a 218 cm long sediment core from the Serra dos Órgãos, a subrange of the coastal Serra do Mar, located at 2130 m altitude in campos de altitude (high elevation grass‐ and shrubland) vegetation near Rio de Janeiro in southeastern Brazil to reconstruct past vegetation, climate and fire dynamics. Based on seven AMS 14C ages, the record represents at least the last 10 450 14C yr bp (12 380 cal years bp), The uppermost region was naturally covered by campos de altitude throughout the recorded period. Diverse montane Atlantic rain forest (ARF) occurred close to the studied peat bog at the end of the Late‐glacial period. There is evidence of small Araucaria angustifolia populations in the study area as late as the early Holocene, after which point the species apparently became locally extinct. Between 10 380 and 10 170 14C yr bp (12 310–11 810 cal yr bp), the extent of campos de altitude was markedly reduced as montane ARF shifted rapidly upward to higher elevations, reflecting a very wet and warm period (temperatures similar to or warmer than present day) at the end of the Younger Dryas (YD) chronozone. This is in opposition to the broadly documented YD cooling in the northern Hemisphere. Reduced cross‐equatorial heat transport and movement of the Intertropical Convergence Zone over northeastern Brazil may explain the YD warming. Markedly extended campos de altitude vegetation indicates dry climatic conditions until about 4910 14C yr bp (5640 cal yr bp). Later, wetter conditions are indicated by reduced high elevation grassland and the extension of ARF into higher elevation. Fire frequency was high during the early Holocene but decreased markedly after about 7020 14C yr bp (7850 cal yr bp).

Lithological and palynological evidence of late Quaternary depositional environments in the subaqueous Yangtze delta, China

AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an estuarine depositional system from 13 to 8.4 cal ka BP and a deltaic system from 5.9 cal ka BP to the present. The estuarine system consists of intertidal to subtidal flat, estuarine, and estuarine-front facies, characterized by sand–mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2–8.4 cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2–5.9 cal ka BP, the transition from estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9 cal ka BP.

Holocene Variations of Radiocarbon Reservoir Ages in a Mediterranean Lagoonal System

To obtain a precise radiocarbon Holocene chronology in coastal areas, it is necessary to estimate the modern14C reservoir age R(t) and its possible variations with time in relation to paleoenvironmental changes. The modern reservoir14C age was estimated by comparing AMS14C ages of 2 recent mollusk shells found in sediment cores sampled in the Palavasian lagoonal system (south of France) with ages derived from210Pb and137Cs data and historical accounts of identifiable storm events. The calculated modern R(t) value of 943 ± 2514C yr is about 600 yr higher than the global mean sea surface reservoir age. This high value, probably due to the relative isolation of the lagoon from marine inputs, is in good agreement with other R(t) estimates in Mediterranean lagoonal systems (Zoppi et al. 2001; Sabatier et al. 2008).14C ages were also obtained on a series of Holocene mollusk shells sampled at different depths of the ∼8-m-long core PB06. Careful examination of the14C ages versus depth relationships suggests that R(t) in the past was lower and similar to the value presently measured in the Gulf of Lion (618 ± 3014C yr, Siani et al. 2000). The change in R(t) from 618 to 943 yr is thought to result from final closure of the coastal lagoon by the sandy barrier, due to the along-shore sediment transfer.

Detailed architecture of a compound incised valley system and correlation with forced regressive wedges: Example of Late Quaternary Têt and Agly rivers, western Gulf of Lions, Mediterranean Sea, France

Abstract Quaternary incised valley systems are usually characterized by the preservation of a single valley-fill attributed to the last post-glacial period. Moreover, there are very few cases of correlation between incised valley system developed on inner shelf and sedimentary units observed on the mid to outer shelf, mainly forced regressive wedges. The Roussillon shelf, in the western part of the Gulf of Lion, is a particular example of preserved Quaternary compound incised valley system also characterized by a direct correlation with the forced regressive lowstand wedges on the mid-outer shelf. High-resolution seismic data and a borehole, 60 m deep, located on the beach barrier permit an accurate study of the geometry and lithology of the system. Six imbricated and more or less preserved incised valleys and valley-fills are observed up to the inner to mid-shelf. The key surfaces associated to the incised valleys are correlated to the boundaries of the forced regressive wedges. They are assumed to be reworked surfaces. At the borehole location, only few thin layers, less than 1 m thick, of coarse grain and/or floating pebbles, are observed and should correspond to preserved fluvial lowstand deposits reworked under marine influence. The valley fills are mainly composed of estuarine muddy silts. From AMS 14C age dating it is inferred that the uppermost incised valley system is younger than 45 ky cal BP. Based on those observations, the six preserved incised valley systems are assumed to be controlled by the last six 4th order sea-level cycles — 100 ky — of the middle to late Quaternary. The paleo-topography of the underlying Plio-Quaternary deposits controls the compound incised valley system location. The deep topography of the Messinian Erosionnal Surface is a controlling factor at a lower degree. The partial preservation of the successive valley fill is attributed not only to the differential subsidence but also to the lateral migration of each incision and to the hydrodynamic regime.

High‐Resolution Records of the Holocene Paleoenvironmental Variation Reflected by Carbonate and Its Isotopic Compositions in Bosten Lake and Response to Glacial Activities

Abstract:The Early Holocene paleoclimate in Bosten Lake on the northern margin of the Tarim Basin, southern Xinjiang, is reconstructed through an analysis of a 953 cm long core (BSTC2000) taken from Bosten Lake. Multiple proxies of this core, including the mineral components of carbonate, carbonate content, stable isotopic compositions of carbonate, Ca/Sr, TOC and C/N and C/S of organic matter, are used to reconstruct the climatic change since 8500 a B.P. The chronology model is made by nine AMS 14C ages of leaves, seeds and organic matter contained in two parallel cores. The climate was cold and wet during 8500 to 8100 a B.P. Temperature increased from 8100 to 6400 a B.P., the climate was warm and humid, and the lake expanded. The lake level was highest during this stage. Then from 6400 to 5100 a B.P., the climate became cold and the lake level decreased slightly. During the late mid‐Holocene, the climate was hot and dry from 5100 to 3100 a B.P., but there was a short cold period during 4400 to 3800 a B.P. At this temporal interval, a mass of ice and snow melting water supplied the lake at the early time and made the lake level rise. The second highest lake level stage occurred during 5200 to 3800 a B.P. The climate was cool and wet during 3100 to 2200 a B.P., when the lake expanded with decreasing evaporation. The lake had the last short‐term high level during 3100 to 2800 a B.P. After this short high lake level period, the lake shrank because of the long‐term lower temperature and reduced water supply. From 2200 to 1200 a B.P., the climate was hot and dry, and the lake shrank greatly. Although the temperature decreased somewhat from 1200 a B.P. to the present, the climate was warm and dry. The lake level began to rise a little again, but it did not reach the river bed altitude of the Konqi River, an outflow river of the Bosten Lake.

Towards radiocarbon calibration beyond 28 ka using speleothems from the Bahamas

We present a new speleothem record of atmospheric Δ 14C between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period. The record is based on a comprehensive suite of AMS 14C ages, using new low-blank protocols, and U–Th ages using high precision MC-ICPMS procedures. Atmospheric Δ 14C was calculated by correcting 14C ages with a constant dead carbon fraction (DCF) of 22.7 ± 5.9%, based on a comparison of stalagmite 14C ages with the IntCal04 ( Reimer et al., 2004) calibration curve between 15 and 11 ka. The new Δ 14C speleothem record shows similar structure and amplitude to that derived from Cariaco Basin foraminifera (Hughen et al., 2004, 2006), and the match is further improved if the latter is tied to the most recent Greenland ice core chronology ( Svensson et al., 2008). These data are however in conflict with a previously published 14C data set for a stalagmite record from the Bahamas — GB-89-24-1 ( Beck et al., 2001), which likely suffered from 14C analytical blank subtraction issues in the older part of the record. The new Bahamas speleothem ∆ 14C data do not show the extreme shifts between 44 and 40 ka reported in the previous study ( Beck et al., 2001). Causes for the observed structure in derived atmospheric Δ 14C variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity. Data-model comparison indicates that major fluctuations in atmospheric ∆ 14C during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity, although ocean–atmosphere system reorganisation also played a supporting role.

The timing of ostrich existence in Central Asia: AMS 14C age of eggshells from Mongolia and southern Siberia (a pilot study)

The presence of Asiatic ostrich in Central Asia in the later Cenozoic time is well-documented; nevertheless, a few direct age determinations existed until recently. We performed AMS 14C dating of ostrich eggshells found in Mongolia, Transbaikal, and Tuva. It shows that ostriches existed throughout the second part of Late Pleistocene, until the Late Glacial time (ca. 13,000–10,100 BP). It seems that Asiatic ostrich went extinct in Central Asia just before or even in the Holocene.

The oldest directly-dated human remains in Siberia: AMS 14C age of talus bone from the Baigara locality, West Siberian Plain

Paleoanthropological data suggest that the Late Pleistocene was a time of population contact and possibly dispersal in Central Asia. Geographic and paleoclimatic data suggest that a natural corridor through Kazakhstan linked areas to the north and east (Siberia, China) to those further to the west and south (Uzbekistan), much like a Paleolithic Silk Road. We review the known Pleistocene archaeology and paleoclimatic setting of this region and provide a geoarchaeological framework for contextualizing preliminary survey results of the PALAEOSILKROAD project's first three seasons of fieldwork. We discuss some systematic biases in three geomorphic and sedimentary archives: karst, loess, and spring deposits, specifying ways in which these biases might determine the kinds of data that are extractable by systematic survey. In particular, we caution about the possibility of future systematic biases in chronology that could come about as a result of the type of geomorphic context in which the sites are recovered. We conclude with recommendations for future work in the area.

Geoarchaeological investigations at the upper Paleolithic site of Kamihoronai‐Moi, Hokkaido, Japan

AbstractIn order to better understand modern human behavioral variability in Hokkaido, Japan, we consider the geoarchaeology of the Kamihoronai‐Moi site in terms of its geochronology, stratigraphy, depositional environments, and post‐depositional disturbances. A Paleolithic component is stratigraphically situated between the Eniwa‐a (15,000–17,000 14C yr B.P.) and the Tarumae‐d (8000–9000 14C yr B.P.) tephras. Moreover, six AMS 14C ages on charcoal from a Pleistocene‐aged hearth feature are between 14,400 and 14,800 14C yr B.P. Quantitative examinations of patterns in artifact distributions show a low degree of vertical and horizontal displacement of chipped‐stone artifacts, suggesting that post‐depositional movement of the cultural material was insufficient to disrupt the original pattern of artifact distribution. © 2009 Wiley Periodicals, Inc.

Correlation of TL layers for the synchronous paleoceanographic events in the East Sea (Sea of Japan) during the Late Quaternary

TL layers (i.e., dark mud layers), either thin or thick, as determined by the L* values with lithologic observation, are distinct paleoceanographic signatures in the East Sea (Sea of Japan), which were formed in response to the global eustatic sealevel fluctuations between interglacials and glacials during the Late Quaternary. These lithologic markers were consistently correlated among the three sediment cores (MD01-2407, 05GCRP21, and KR05-09PC1) collected from the Oki Ridge of the southern Yamato Basin, the South Korea Plateau of the northern Ulleung Basin, and the Matsumae Plateau of the northeastern Japan Basin, respectively. Reconstruction of age models for cores 05GCRP and KR05-09PC1 was aided in a good way by the AMS 14C ages of planktonic foraminifera and identification of the tephra layers, and mainly by lithostratigraphic correlation with TL layers of well-dated core MD01-2407, based on the L* values. The correlation of TL layers among the three sediment cores was remarkable, indicating that the East Sea (Sea of Japan) experienced the synchronous and basin-wide scale paleoceanographic events during the Late Quaternary. Our study exemplifies the significant usefulness of these lithologic markers for further Late Quaternary paleoceanographic investigation.

ボーリングコア解析と｀１４´Ｃ年代測定にもとづく木曽川デルタの形成プロセス

The depositional process of the Latest Pleistocene to Holocene shallow-marine and fluvial successions is investigated using five 14C-dated borehole cores from the Kiso River delta, central Japan. The delta succession provides high-quality records of the transgression and regression of an enclosed delta system and reveals the development of fluvial-dominated coastal lowlands. Based on a facies analysis, the cored sediments are classified into five sedimentary units: A) basal gravel, B) fluvial and intertidal sand and silt, C) transgressive lag deposit, prodelta mud, and sandy silt, D) delta-front-slope sandy silt and sand, and delta-front-platform sand, and, E) delta-plain and fluvial sand and silt. Detailed age-depth curves of these cores are reconstructed based on 108 AMS 14C ages including 83 new 14C ages. These curves show patterns similar to those of temporal variations in accumulation rates, and are divided into four sections (I to IV) from the base to the top: I mainly consists of unit B with rapid accumulation (7.3-21.4mm/yr); II mainly consists of unit C with moderate accumulation (2.4-2.8mm/yr); III mainly consists of unit D with rapid accumulation (6.7-17.8mm/yr); and, IV consists of unit D and E with moderate accumulation (1.3-3.9mm/yr). The section boundaries of I/II and II/III, which coincide with the unit boundaries of B/C and C/D, reflect the inundation of a flood plain by seawater, developing a bay environment, and the subsequent progradation of the delta–front slope, respectively. The ages of these boundaries constrain the estimation of the expanding rate of the bay and progradation rates of the delta. The expanding rate of the bay is estimated at 10m/yr during the period 10200-7900 cal yrs BP, and the progradation rates of the delta are 3-4m/yr (6500-4100 cal yrs BP), 5m/yr (4100-1300 cal yrs BP), and 10m/yr (1300 cal yrs BP to the present). These age data indicate that the transition from transgression to regression occurred between 7800 and 7300 cal yrs BP. The geological cross-section along the Kiso River along with the isochrones constructed by over a hundred 14C dates indicates the following depositional history of the Kiso River delta: (1) from 10000 to 7280 cal yrs BP (K-Ah horizon) —During the expansion of the bay, onlap of unit C on unit B is visible, and unit C overlapped all the core sites just before the K-Ah fall, and (2) from 7280 cal yrs BP to present—Isochrones younger than 6500 cal yrs BP are similar to each other and cross the unit boundaries of C/D and D/E. This demonstrates that units C–E are contemporaneous heterotopic facies formed in response to delta progradation after the K-Ah fall.