全新世气候适宜期黄土高原及黄土／沙漠过渡区年降水量的初步恢复

通过黄土高原及其临区１０４个地点地表土壤磁化率值与当地的现代多年平均降水量的回归分析，建立了磁化率与降水量的转换函数。在遍布黄土高原不同地区典型的全新世黄土－古土壤剖面磁化率测量的基础上，利用所建立的转换函数，初步恢复了全新世气候适宜期，黄土高原及黄土／沙漠过渡区年降水量的分布状况。     

云南寻甸地区全新世中期气候变化模式研究

通过对云南寻甸白石岩仙人洞1号石笋(XR1)进行TIMS-U系测年和氧碳同位素分析,揭示了该区全新世中期氧碳同位素气候演化的模式。依据石笋不同时段有机碳含量的变化,重建了基于石笋有机碳指标的气候变化模式。通过对比,发现这两种指标所记录的寻甸地区古气候变化过程几乎完全一致。云南寻甸地区全新世中期的气候演化可分为3个气候期:1)8 000—5 600 aBP为温暖湿润期,气温较高,降水丰沛,石笋的氧碳同位素偏负,有机碳含量偏高;2)5600—4500 aBP为气候突变期,气候由温湿变为冷干,石笋氧碳同位素持续偏正,有机碳含量持续降低;3)4500—2100 aBP为冷干气候期,该期气候稳定,氧同位素和有机碳含量变化不大,均维持在较低水平。     

青藏高原兹格塘错沉积物介形虫壳体同位素

兹格塘错是位于藏北高原腹地的封闭型湖泊,其变化过程可直接反映区域气候变化。对一支深727 cm沉积岩芯中介形虫进行了壳体同位素分析,发现介形虫壳体氧同位素变化主要取决于壳体形成时的湖水氧同位素组成和湖水温度的变化;封闭湖泊湖水的氧同位素组成主要取决于降水和蒸发比值的变化。兹格塘错介形虫壳体碳、氧同位素变化特征表明两者可能受控于不同的环境因子。介形虫壳体同位素记录反映了全新世气候环境变化的整体特征,同时对晚第四纪特征气候事件都有明确记录,包括8.2 ka冷事件、Roman暖期、中世纪暖期以及小冰期等,在响应全球气候变化的过程中又记录了区域间的差异响应。     

东疆北部全新世气候不稳定性的湖泊沉积记录

对新疆东疆北部巴里坤湖2.5 m深的沉积剖面进行了年代学、沉积物粒度、TOC、磁化率和CaCO₃含量分析,对比研究确定了巴里坤湖的碳库年龄约为750 a,据此建立了研究剖面的年代序列。研究表明,各气候代用指标序列揭示了巴里坤湖地区全新世期间存在多次干湿气候波动,并伴随着一系列突发气候事件,其中有6次事件可以与全新世北大西洋浮冰碎屑事件及GISP2冰芯氧同位素记录进行良好对比,且呈现出显著约1.6 ka的变化周期,表明高纬度北大西洋地区的气候变化可能通过对西风环流的影响与中国西北干旱区的气候变化密切相关。谱分析揭示出研究区气候变化还具有显著的200 a,133 a,108 a和77 a周期,可能与太阳活动周期有关。6300—5200 cal a BP和4300—3500 cal a BP期间巴里坤湖地区气候较为干旱,结合广泛的区域对比认为,中全新世干旱事件具有普遍性。     

白令海北部陆坡晚第四纪的古海洋与古气候学记录

白令海北部陆坡B2 9柱状样中放射虫Cycladophoradavisiana含量曲线和深海SPECMAP氧同位素记录的对比 ,为该柱状样建立了晚第四纪约 1 0万年以来的地层年代框架。该柱状样中微体化石、碳屑颗粒、筏冰碎屑 (石英和岩屑颗粒 )的定量分析结果表明 ,作为表层生产力指标的粗组份自氧同位素 5 .3期以来呈阶梯状增加 ,反映表层生产力阶段式的增长 ;碳屑颗粒丰度自氧同位素 5 .3期至末次冰消期的增加说明白令海末次冰消期以前气候较全新世干冷 ,天然火灾发生的概率较全新世大大增加 ;冰期和早、中全新世较高的筏冰碎屑反映了冰期和早、中全新世白令海陆架海冰的扩大以及气候转暖所导致的海冰消融的过程 ,揭示了白令海对过去全球气候变化的响应。     

广东湛江湖光岩玛珥湖全新世磁化率变化特征及其环境意义

对湖光岩玛珥湖沉积物进行了低频磁化率(下称磁化率)、粒度组合特征、烧失量以及磁化率随温度变化(κ-T)的分析.磁化率随温度变化的特征显示湖光岩沉积物中最主要的磁性矿物是磁铁矿;磁化率与黏土矿物含量呈正相关,反映了湖光岩沉积物中的磁性矿物主要赋存于黏粒组分中;全新世以来湖光岩地区的磁化率的低值指示湿润的气候条件,高值则反...     

冬夏季温度和降水变化对青海湖全新世环境变化的影响初探

青海湖是国内最大的内陆湖泊,位于青藏高原东北缘,因其处在东亚夏季风、印度季风和西风带的交替控制区域,对气候变化十分敏感,成为古环境变化研究的热点地区。有关青海湖的形成演化、环境变化和水文变化的研究也存在多种观点。本研究再分析了青海湖已报道的古环境指标和气候模式模拟的夏季、冬季温度和降水变化,力图更加全面地理解青海湖全新世以来的古环境变化。研究发现早全新世11~8 ka夏季降水量和表面蒸发量较大,冬季降水稀少,湖泊水位只有十余米深,使得青海湖周边风沙活动频繁。并且,早全新世的气候不稳定,经历了频繁和较大幅度的波动。全新世气候适宜期出现在8~6 ka,古环境指标指示这一时期为温暖湿润的气候环境,湖盆内植被以森林草原为主,湖泊水位不断上升。青海湖地区的夏季降水自6 ka开始减少,然而冬季降水增加,同时夏季温度和蒸发量减少,使得湖区植被组成由森林草原向高山草甸转变,湖区大范围形成古土壤。湖区古环境条件在晚全新世距今1.5 ka开始恶化,冬季和夏季降水同时减少,湖泊水位下降,风沙活动再次加强。     

云南中甸纳帕海湖泊沉积物的磁化率及环境意义

研究区母岩特性，搬运距离和搬运营力决定了磁性矿物主要赋存在砂砾级颗粒中，纳帕海潮泊沉积物的磁化率与颗粒粒径，沉积相和有机质含量存在密切的相关关系，滨浅湖环境中砂砾级颗粒含量增加以及波浪淘洗对磁性矿物的富集作用，磁化率较高；浅湖环境中粉砂增多，砂减少，磁化率较之滨浅湖有所降低，在低能的半深湖／深湖环境中，由于缺乏磁性矿物的输入，磁化率再次降低，有机质含量很高的湖岸湖环境由于有机质的稀释作用磁化率值最低，磁化率等环境替代指标以及和北半球气候变化阶段，深海氧同位素阶段的对比，将纳帕海近6ka年来划分成6个主要的环境演化阶段，32kaB.P.(14.99m)和15kaB.P.(6.06m)分别是环境和气候变化的重要转折点，32－15ka B.P.期间出现的高湖面表明，虽然大气温度下降但有效湿度增加，全新世湖泊的急剧萎缩预示在大气温度增加的同时有效湿度降低，暖偏于构成了研究区全新世气候演化的特色。     

华北平原中部晚上新世以来沉积物碳氧同位素特征及其古环境意义

利用华北平原中部衡水水文地质科研深孔的岩芯,对平原区古土壤钙结核层碳氧同位素组分的古气候环境意义及相关气候指标的定量转换进行探讨,发现碳氧同位素对古气候变化具有较好的响应关系:3.5MaB.P.以来华北平原古气候逐渐由湿润转向干旱,早更新世由多个干湿冷暖旋回组成,晚期气候由暖迅速转凉;中更新世气候略温和,由3个冷干-暖湿旋回组成;晚更新世气候变化趋势为湿润-干燥-湿润,总体上呈现增温趋势。进入全新世后,δ13C平均值(-5)较低,属于相对湿润期;δ18 O平均值(-9.5)较低,属于相对寒冷期。应用相关公式可以定量恢复古温度变化,但平原区古土壤层受后期地下水作用的影响较大,如何消除这一影响还需更多数据支持。     

中国内陆区湖泊沉积所反映的全新世干湿变化

湖泊沉积记录的环境演变是全球变化的重要研究领域之一,通过对中国内陆区中30 个湖泊研究成果的总结和梳理,探讨了全新世以来该地区干湿变化的规律和区域分异。通过降水量结合传统分区方法将中国内陆区分为西北干旱区、东亚季风边缘区和青藏高原区。对每个湖泊样点以500 年为时间间隔,以孢粉为主要干湿指标,综合氧同位素、有机质及碳酸盐等,将湖泊干湿状况划分3 个干湿等级（干旱,半湿润,湿润）,建立区域干湿指数。结果表明,中国内陆不同区域全新世可能经历了不同的干湿变化过程：①西北干旱区基本上是早中全新世干旱,中晚全新世相对湿润,但区域差异明显;②东亚季风边缘区早全新世早期干旱,早全新世晚期和中全新世相对湿润,晚全新世干旱;③青藏高原区的湿润时期主要发生在早中全新世,但是不同地区有所不同。对比分析显示：西北干旱区的干湿变化可能受西风环流控制,但在时间和强度上区域内部差异较明显;东亚季风边缘区可能主要受东亚季风控制;青藏高原地区早中全新世的湿润可能与印度季风的增强相关。     

Holocene environmental changes on the east coast of Korea

We present a record of Holocene environmental change on the east coast of Korea, inferred using pollen, carbon-isotopic composition (??¹³C), total organic carbon, total sulfur, carbon/nitrogen ratios, particle size analysis and major element geochemistry in a sediment core from Soonpogae Lagoon. A multi-proxy paleoenvironmental approach had not previously been applied in Korea and allowed us to reconstruct climate and vegetation change, sea-level rise, lagoon development, and human impact on the east coast of Korea over the last 8,000?years. Evidence from Soonpogae Lagoon supports the following three conclusions: (1) As a drying trend prevailed on the east coast of Korea after ~5,900?cal?yr BP, chemical weathering weakened and herbaceous plants became more important than during the previous humid phase (Holocene Climate Optimum), (2) Sea-level rise on the east coast slowed dramatically about 6,800?cal?yr BP, resulting in low rates of sedimentation in Soonpogae Lagoon, and (3) Soonpogae Lagoon was almost completely isolated from the sea by sand barriers when human impact intensified ~2,100 BP.     

Early Holocene drought in the Laurentian Great Lakes basin caused hydrologic closure of Georgian Bay

Multiple proxies record aridity in the northern Great Lakes basin ~8,800–8,000 cal (8,000–7,200) BP when water levels fell below outlets in the Michigan, Huron and Georgian Bay basins. Pollen-climate transfer function calculations on radiocarbon-dated pollen profiles from small lakes from Minnesota to eastern Ontario show that a drier climate was sufficient to lower the Great Lakes, in particular Georgian Bay, to closed basins. The best modern climate analog for the early Holocene late Lake Hough stage in the Georgian Bay basin is Black Bass Lake near Brainerd MN. Modern annual precipitation at Brainerd is ~35% lower than at Huntsville ON, in the Georgian Bay catchment; warmer summers and colder, less snowy winters make Brainerd drier than the Georgian Bay snow belt. These values parallel transfer function reconstructions for the early Holocene from pollen records at five small lakes in the Georgian Bay drainage basin. Higher evaporation and evapotranspiration due to greater seasonality during the early Holocene produced a deficit in effective moisture in Georgian Bay that is recorded by the jack/red pine pollen zone that spanned ~8,800–8,200 cal (8,000–7,500) BP. This deficit drove late Lake Hough ~5 m below Lake Stanley in the Huron basin, following diversion of Laurentide Ice sheet meltwater from the Great Lakes basin. The level of Georgian Bay largely depends not on fluvial input from its own drainage basin, but rather from Lake Superior, where the early Holocene moisture deficit was greater. Reconstruction of paleoclimates in Minnesota, northwestern Ontario and Wisconsin produced a closed lake in the Superior basin, which removed the main water input to Georgian Bay. Once the inflow through the St. Marys River was reduced and inflow from other tributary streams was adjusted for isostatic and climatic differences, input was <5% of modern values. Consequent high evaporation rates produced a significant fall in lake level in the Georgian Bay basin and a negative water budget. This reduction in basin supply, together with the high conductivity of stagnant water in late Lake Hough inferred from microfossils in lowstand sediments, peaked at the end of the jack/red pine zone, ~8,300–8,200 (7,450 ± 90) BP. These major hydrologic changes resulting from climate change in the recent geologic past draw attention to possible declines of the Great Lakes under future climates.     

全新世中国东部亚热带地区气候变迁的古生物学证据

中国东部亚热带地区全新世期间的气候波动频繁,引起哺乳动物群的多次迁徙。该时期哺乳动物群的常见种属多见于亚热带地区,仅少数种属如貘、犀、长臂猿和亚洲象等在自然状态下主要分布于热带―中亚热带南部地区,指示了具热带气候性质的中亚热带南部的森林环境。文章在确定中国东部全新世不同阶段此类动物群的种属构成与分布特征的基础上,主要根据热带种的迁徙和分布特征,初步推断各阶段亚热带地区的气候变迁状况如下：盛冰期之后的冰消期,温度逐渐回升,14 000―12 000 a BP时,热带种分布北界大致南移2°,指示1月平均气温较今低3~5℃;12 000―8 500 a BP为升温期,气候转暖,热带种分布北界达中亚热带南部,逐渐类似于现今气候;8 500―5 000 a BP为大暖期,热带种分布北界抵秦岭―淮河一线,北移约6°,指示1月气温较今高约7~9℃;5 000―3 000 a BP为降温期,热带种分布北界位于秦岭―淮河以南的长江流域,北移约4°,指示1月气温较今高约5~6℃;3 000 a BP以来,气候逐渐变冷。这些变化体现了中国东部亚热带地区在全新世时期发生了多次较大的气候和生物气候带变迁事件。     

Runoff Scaling in Large Rivers of the World

Runoff and precipitation scaling with respect to drainage area is analyzed for large river basins of the world, those with mean annual runoff in excess of 10 k³/yr. The usefulness of the specific runoff (runoff per unit drainage area, m/yr) to categorize runoff scaling laws across the complete spectrum of climatic and hydrologic conditions is evaluated. It is found that (1) runoff scales with drainage are in those river basins with specific runoff in excess of 0.15 m/yr (r² = 0.88); (2) runoff scaling with drainage area shows remarkably high statistical correlation (r²= 0.97) in river basins with specific runoff equal to or larger than 1.0 m/yr; (3) runoff does not Inc.rease with Inc.reasing drainage area in river basins with specific runoff below 0.15 m/yr, where no discernible statistical association was found between runoff and drainage area; and (4) precipitation depth (m/yr) is inversely proportional to drainage area raised to a fractional exponent in river basins with specific runoff in excess of 0.15 m/yr.     

Relationships between Trophic State, Paleosalinity and Climatic Changes during the First Holocene Marine Transgression in Rocha Lagoon, Southern Uruguay

Paleolimnological data are presented on trophic development, climatic change and sea level variations in Rocha Lagoon, a 72 km² coastal lagoon in southern Uruguay. Using a sediment core that extended from 7000 to about 3700 yr BP, analyses of organic matter, carbonate, diatoms and chrysophyte cysts were used to track the early Holocene paleolimnological conditions of Rocha Lagoon. Opal phytoliths were also counted and identified, both temperature and humidity indices were calculated, and Opal Phytolith Association Zones (OPAZ) were identified by performing Principal Coordinates Analysis (PCO). Diatom Association Zones (DAZ) corresponding to marine/brackish and brackish/freshwater episodes were closely related to changes in trophic state. Those DAZ representing marine/brackish stages exhibited a lower trophic state than those DAZ dominated by brackish and freshwater diatoms. This highlights that during the first Holocene marine transgression, Rocha Lagoon did not continuously exhibit marine/brackish conditions as reported in previous papers. Instead, three brackish/freshwater episodes related to sea level variation and changes in humidity were identified. The first episode, by ~6000 yr BP, was related to sea level change as no significant changes in either temperature or humidity indices were observed. The second episode, between 5000 and 4400 yr BP, was related to both a sea level decrease and an increase in humidity, as a transition from humid to very humid climate was inferred. Concomitant decreases in salinity and increases in trophic state were also observed. The third episode, after ~4000 yr BP, was related to the end of the first Holocene regressive phase when sea level was slightly below present levels. Further decreases in salinity and increases in trophic state were detected. The paleoclimatic trends inferred in this study were in close agreement with other regional studies on climatic change, as cool temperatures were inferred. However, major changes in humidity were also detected. A humid to very humid climate was inferred for ~7000–4500 yr BP, but the occurrence of a semiarid/arid climate was inferred for ~4500–3700 yr BP. Our data suggest that during transgressive and regressive events there might be higher frequency and lower amplitude sea level oscillations that might lead to changes in salinity and trophic state of coastal aquatic systems. Such oscillations could only be tracked by high resolution analyses of sedimentary records and could be best interpreted with complementary data on paleoclimate. In addition, microfossils such as diatoms and opal phytoliths were shown to be very sensitive to such paleoenvironmental changes.     

Paleolimnological evidence of Holocene climatic changes in Lake Blanca, southern Uruguay

Paleolimnological data are presented on Holocene climatic changes in Lake Blanca, a small (0.6 km²), coastal fresh waterbody in southern Uruguay. Using a sediment core that extended to 7,300 year BP, analyses of pooid, panicoid and chloridoid phytoliths (Poaceae) allowed us to identify 16 Opal Phytoliths Association Zones (OPAZ). Both temperature and humidity indices were calculated from relative percentages of opal phytoliths and the climatic trends were inferred. During the early Holocene, prior to the first Holocene marine transgression (∼ ∼8,000–7,000 yr BP), cool-arid climatic conditions were inferred. After the first Holocene transgression, predominance of cool-humid conditions was registered until about 4,000 yr BP. A transition from cool-semiarid/arid to alternate warm-temperate and humid-very-humid conditions was detected for ∼∼4,000–1,000 yr BP. Increases in trophic state were observed because of such a climatic amelioration. After ∼ ∼1,000 yr BP, a shift from warm to temperate and cool temperatures was inferred. Such a cooling episode was assigned to a “LIA” which took place by the end of the 18th century and the beginning of the 19th century. A decrease in trophic state was observed during this climatic deterioration. After such a little ice age, present temperate humid conditions were established. The humidity indices calculated from relative percentages of opal phytoliths for the last ∼ ∼70 years were compared to annual rainfall data. Such a comparison showed that opal phytoliths are reliable indicators of humidity.     

A sedimentary and geochemical record of water-level changes from Rantin Lake, Yukon, Canada

A multi-proxy analysis of two sediment cores from Rantin Lake are used to reconstruct past lake-level changes and to make inferences about millennial-scale variations in precipitation/evaporation (P/E) balance in the southern Yukon, Canada between 10,900 and 3,100?cal?yr BP. Analyses of calcium carbonate and organic matter concentration, magnetic susceptibility, titanium content, dry bulk density, and macrofossils are used to reconstruct water-level changes. The development of sand layers and deformed sediments at the deep-water core site (i.e. Core A-06) prior to ~10,900?cal?yr BP suggest that lake level was lower at this time. Fine-grained organic sediment deposited from 10,600 to 9,500?cal?yr BP indicates a rise in lake level. The formation of an unconformity at the shallow cores site (Core C-06) and the deposition of shallow-water calcium carbonate-rich facies at the Core A-06 site between ~9,500 and ~8,500?cal?yr BP suggest lower lake levels at this time. Shallow-water facies gradually transition into a sand layer that likely represents shoreline reworking during an extreme lowstand that occurred at ~8,400?cal?yr BP. Following this low water level, fine-grained organic-rich sediment formed by ~8,200?cal?yr BP, suggesting deeper water conditions at core site A-06. Calcium carbonate concentrations are relatively low in sediment deposited from ~6,300 to 3,100?cal?yr BP in Core A-06, indicating that lake level was comparatively higher during the middle and late Holocene. In general, results from this study suggest that the early Holocene was characterized by high P/E from ~10,500 to 9,500?cal?yr BP, low P/E from ~9,500 to 8,400?cal?yr BP, and return to higher P/E from ~8,200 to 3,100?cal?yr BP.     

长江三角洲城市群区域滨海湿地利用时空变化特征

应用遥感和地理信息系统技术,以研究区遥感影像为主要数据源,研究了1990～2000年和2000～2005年间长江三角洲城市群区域围海造地行为下滨海湿地利用的时空演变特征。围海造地在不同城市化发展时期分别为农业用地和建设用地扩张所需。以海岸线为基准,通过分别向陆地和向海洋方向进行滨海湿地分区,每个方向设立7个缓冲带,靠近海岸线的前6个缓冲带宽1km,第7个缓冲带宽10km。结果表明,1990～2000年期间,围海造地以农业用地扩张为主,其平均年扩张速率为48.9km2/a,明显大于建设用地的平均年扩张速率(28.2km2/a);而2000～2005年期间,建设用地成为围海造地的主要目的,建设用地平均年扩张速率大幅增大至91.8km2/a,而农业用地平均年扩张率仅为4.2km2/a。在空间分布上,1990～2000年期间,农业用地平均年扩张百分率最大值出现在距海岸线5km的陆地缓冲区;但在2000～2005年期间,各陆地缓冲区农业用地面积在减少,其平均年扩张百分率为-1.3%/a;而建设用地在各缓冲区的平均年扩张百分率由1990～2000年期间的0.62%/a增大为2000～2005年期间的2.66%/a。对长江三角洲滨海湿地土地流转驱动力的分析表明,城市化是建设用地扩张的重要驱动力;一些天然滨海湿地直接转变为建设用地,两个时期建设用地净扩张区域相同,即距海岸线1～3km和>6km陆地缓冲带;还有一些天然滨海湿地,如滩涂,被用于水产养殖,而转变为人工湿地,在1990～2000年期间,农业用地的扩张区域是距海岸线4～6km的陆地缓冲带,在2000～2005年期间,农业用地的扩张区域是1～3km的近海缓冲带。     

基于PCA和BP神经网络的径流预测

径流预测为流域水资源的合理开发利用与统筹配置提供依据。运用多元线性回归、主成分回归、BP神经网络及主成分分析和BP神经网络相结合的方法,对新疆呼图壁河流域石门水文站2009-2011年各月径流量进行预测,并采用相关系数、确定性系数及均方根误差对各模型预测精度进行比较。结果表明：（1）神经网络等智能算法具有高速寻优的能力,对短时间尺度的月径流量的预测结果较好;（2）主成分回归等常规算法能充分反映出某地区径流的年际的稳定性,对全年径流总量的模拟精度较高;（3）主成分分析和BP神经网络相结合的方法,提高了神经网络的收敛速度,同时降低了局部极值的影响,优于简单的BP神经网络,适用于呼图壁河月径流量预测。     

Sub-bottom profiling and coring of sub-basins along the lower French River, Ontario: insights into depositional environments within the North Bay outlet

Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000 and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression, Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP), the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved pre-9,500 cal BP (~8,500 BP) post-glacial deposits.