Reconstruction of the long-term fire history of an old-growth deciduous forest in Southern Québec, Canada, from charred wood in mineral soils

Charcoal particles are widespread in terrestrial and lake environments of the northern temperate and boreal biomes where they are used to reconstruct past fire events and regimes. In this study, we used botanically identified and radiocarbon-dated charcoal macrofossils in mineral soils as a paleoecological tool to reconstruct past fire activity at the stand scale. Charcoal macrofossils buried in podzolic soils by tree uprooting were analyzed to reconstruct the long-term fire history of an old-growth deciduous forest in southern Québec. Charcoal fragments were sampled from the uppermost mineral soil horizons and identified based on anatomical characters. Spruce (Picea spp.) fragments dominated the charcoal assemblage, along with relatively abundant wood fragments of sugar maple (Acer saccharum) and birch (Betula spp.), and rare fragments of pine (Pinus cf. strobus) and white cedar (Thuja canadensis). AMS radiocarbon dates from 16 charcoal fragments indicated that forest fires were widespread during the early Holocene, whereas no fires were recorded from the mid-Holocene to present. The paucity of charcoal data during this period, however, does not preclude that a fire event of lower severity may have occurred. At least eight forest fires occurred at the study site between 10,400 and 6300 cal yr B.P., with a dominance of burned conifer trees between 10,400 and 9000 cal yr B.P. and burned conifer and deciduous trees between 9000 and 6300 cal yr B.P. Based on the charcoal record, the climate at the study site was relatively dry during the early Holocene, and more humid from 6300 cal yr B.P. to present. However, it is also possible that the predominance of conifer trees in the charcoal record between 10,400 and 6300 cal yr B.P. created propitious conditions for fire spreading. The charcoal record supports inferences based on pollen influx data (Labelle, C., Richard, P.J.H. 1981. Végétation tardiglaciaire et postglaciaire au sud-est du Parc des Laurentides, Québec. Géographie Physique et Quaternaire 35, 345-359) of the early arrival of spruce and sugar maple in the study area shortly after deglaciation. We conclude that macroscopic charcoal analysis of mineral soils subjected to disturbance by tree uprooting may be a useful paleoecological tool to reconstruct long-term forest fire history at the stand scale.     

Ancient charcoal as a natural archive for paleofire regime and vegetation change in the Mayumbe,Democratic Republic of the Congo

Charcoal was sampled in four soil profiles at the Mayumbe forest boundary (DRC). Five fire events were recorded and 44 charcoal types were identified. One stratified profile yielded charcoal assemblages around 530 cal yr BP and > 43.5 cal ka BP in age. The oldest assemblage precedes the period of recorded anthropogenic burning, illustrating occasional long-term absence of fire but also natural wildfire occurrences within tropical rainforest. No other charcoal assemblages older than 2500 cal yr BP were recorded, perhaps due to bioturbation and colluvial reworking. The recorded paleofires were possibly associated with short-lived climate anomalies. Progressively dry climatic conditions since ca. 4000 cal yr BP onward did not promote paleofire occurrence until increasing seasonality affected vegetation at the end of the third millennium BP, as illustrated by a fire occurring in mature rainforest that persisted until around 2050 cal yr BP. During a drought episode coinciding with the ‘Medieval Climate Anomaly’, mature rainforest was locally replaced by woodland savanna. Charcoal remains from pioneer forest indicate that fire hampered forest regeneration after climatic drought episodes. The presence of pottery shards and oil-palm endocarps associated with two relatively recent paleofires suggests that the effects of climate variability were amplified by human activities.     

Middle Holocene dry period in the northern Midwestern United States: Lake levels and pollen stratigraphy

Four cores from Lake Mendota in the Yahara River valley of south-central Wisconsin provide pollen, charcoal, and sediment-stratigraphic evidence of a middle Holocene dry period in the northern Midwest. The lake level was lower between about 6500 and 3500 yr B.P. indicating that runoff from the upper Yahara River basin may have ceased during the drier seasons of the year. Derived estimates of precipitation between 6500 and 3500 yr B.P. indicate a decrease of about 10% (down to about 700 mm) from the present precipitation value of 800 mm. A warming between 6500 and 3500 yr B.P. is also interpreted based on a change of vegetation from rich mesophytic forest before 6500 yr B.P. to Quercus savanna, with increased charcoal abundances after that time. After 3500 yr B.P., a closed Quercus forest and decreased charcoal suggest a cooler and wetter climate. The qualitative paleoecological interpretations, quantitative precipitation reconstructions based on pollen from the region (including the Lake Mendota data), and estimates of hydrologic budget based on lake-level changes, all show indications of a dry and warm middle Holocene. Evidence from a large regional array of sites also supports these interpretations.     

晚冰期月亮湖炭屑记录反映的古气候演化

位于大兴安岭中段的月亮湖地处季风/非季风影响过渡地带,其沉积岩心下部886～546 cm的炭屑记录揭示了末次冰期晚期到全新世早期(20.9～10.8 cal.ka B.P.)的古气候演化历史,反映了东亚季风对研究区气候的影响。研究区炭屑浓度的变化主要由可供燃烧的生物量决定,生长在气候温暖时期的森林草原能够提供更多可供燃烧的生物量。在同一植被类型的条件下,气候寒冷湿润时炭屑浓度低,气候温暖干旱时炭屑浓度高。20.9～18.0 cal.ka B.P.炭屑浓度较低, 气候寒冷偏干,18.0～15.3 cal.ka B.P.炭屑浓度最低,气候寒冷湿润,15.3～14.4 cal.ka B.P.炭屑浓度增高,气候开始向温暖的方向发展,14.4～11.8 cal.ka B.P.炭屑浓度快速变化,气候也经历了一系列的快速变化,11.8～10.8 cal.ka B.P.炭屑浓度总体较高,气候温暖湿润。<50 μm的炭屑浓度指示了区域火演化的历史, >50 μm的炭屑则反映了当地野火发生的状况。     

Paleoindian environmental change and landscape response in Barger Gulch,Middle Park,Colorado

Middle Park, a high‐altitude basin in the Southern Rocky Mountains of north‐central Colorado, contains at least 59 known Paleoindian localities. At Barger Gulch Locality B, an extensive Folsom assemblage (˜10,500 ¹⁴C yr B.P.) occurs within a buried soil. Radiocarbon ages of charcoal and soil organic matter, as well as stratigraphic positions of artifacts, indicate the soil is a composite of a truncated, latest‐Pleistocene soil and a younger mollic epipedon formed between ˜6000 and 5200 ¹⁴C yr B.P. and partially welded onto the older soil following erosion and truncation. Radiocarbon ages from an alluvial terrace adjacent to the excavation area indicate that erosion followed by aggradation occurred between ˜10,200 and 9700 ¹⁴C yr B.P., and that the erosion is likely related to truncation of the latest‐Pleistocene soil. Erosion along the main axis of Barger Gulch occurring between ˜10,000 and 9700 ¹⁴C yr B.P. was followed by rapid aggradation between ˜9700 and 9550 ¹⁴C yr B.P., which, along with the erosion at Locality B, coincides with the abrupt onset of monsoonal precipitation following cooling in the region ˜11,000–10,000 ¹⁴C yr B.P. during the Younger Dryas oscillation. Buried soils dated between ˜9500 and 8000 ¹⁴C yr B.P. indicate relative landscape stability and soil formation throughout Middle Park. Morphological characteristics displayed by early Holocene soils suggest pedogenesis under parkland vegetation in areas currently characterized by sagebrush steppe. The expansion of forest cover into lower elevations during the early Holocene may have resulted in lower productivity in regards to mammalian fauna, and may partly explain the abundance of early Paleoindian sites (˜11,000–10,000 ¹⁴C yr B.P., 76%) relative to late Paleoindian sites (˜10,000–8000 ¹⁴C yr B.P., 24%) documented in Middle Park. © 2005 Wiley Periodicals, Inc.     

Holocene Environmental Changes from the Rio Curuá Record in the Caxiuanã Region, Eastern Amazon Basin

Holocene environments have been reconstructed by multiproxy studies of an 850-cm-long core from Rio Curuá dating to >8000 ¹⁴C yr B.P. The low-energy river lies in the eastern Amazon rain forest in the Caxiuanã National Forest Reserve, 350 km west of Belém in northern Brazil. Sedimentological, mineralogical, and geochemical dates demonstrate that the deposits correspond to two different environments, sediments of an active river before 8000 ¹⁴C yr B.P. and later a passive river system. The pollen analytical results indicate four different local and regional Holocene paleoenvironmental periods: (1) a transition to a passive fluvial system and a well-drained terra firme (unflooded upland) Amazon rain forest with very limited development of inundated forests (várzea and igapó) (>7990–7030 ¹⁴C yr B.P.); (2) a sluggish river with a local Mauritia palm-swamp and similar regional vegetation, as before (7030–5970 ¹⁴C yr B.P.); (3) a passive river, forming shallow lake conditions and with still-abundant terra firme forest in the study region (5970–2470 ¹⁴C yr B.P.); and (4) a blocked river with high water levels and marked increase of inundated forests during the last 2470 ¹⁴C yr B.P. Increased charcoal during this last period suggests the first strong presence of humans in this region. The Atlantic sea level rise was probably the major factor in paleoenvironmental changes, but high water stands might also be due to greater annual rainfall during the late Holocene.     

A 23,000-yr pollen record from Lake Euramoo, Wet Tropics of NE Queensland, Australia

A new extended pollen and charcoal record is presented from Lake Euramoo, Wet Tropics World Heritage rainforest of northeast Queensland, Australia. The 8.4-m sediment core taken from the center of Lake Euramoo incorporates a complete record of vegetation change and fire history spanning the period from 23,000 cal yr B.P. to present. The pollen record is divided into five significant zones; 23,000–16,800 cal yr B.P., dry sclerophyll woodland; 16,800–8600 cal yr B.P., wet sclerophyll woodland with marginal rainforest in protected pockets; 8600–5000 cal yr B.P., warm temperate rainforest; 5000–70 cal yr B.P., dry subtropical rainforest; 70 cal yr B.P.–AD 1999, degraded dry subtropical rainforest with increasing influence of invasive species and fire.The process of rainforest development appears to be at least partly controlled by orbital forcing (precession), though more local environmental variables and human activity are also significant factors. This new record provides the opportunity to explore the relationship between fire, drought and rainforest dynamics in a significant World Heritage rainforest region.     

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

In 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.     

23,000 yr of vegetation history of the Upper Lerma, a tropical high-altitude basin in Central Mexico

Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 ¹⁴C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 ¹⁴C yr B.P. and the Tres Cruces Tephra of 8500 ¹⁴C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 ¹⁴C yr B.P. to ca. 11,600 ¹⁴C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 ¹⁴C yr B.P., and at ca. 12,600 ¹⁴C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 ¹⁴C yr B.P. After 10,000 ¹⁴C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 ¹⁴C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 ¹⁴C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles.     

Vegetation dynamics during the late Pleistocene in the Barreirinhas region, Maranhão State, northeastern Brazil, based on carbon isotopes in soil organic matter

The study place is in the Barreirinhas region, Maranhão State, northeastern Brazil. A vegetation transect of 78 km was studied among four vegetation types: Restinga (coastal vegetation), Cerrado (woody savanna), Cerradão (dense woody savanna), and Forest, as well as three forested sites around Lagoa do Caçó, located approximately 10 km of the transect. Soil profiles in this transect were sampled for δ¹³C analysis, as well as buried charcoal fragments were used for ¹⁴C dating. The data interpretation indicated that approximately between 15,000 and ∼9000 ¹⁴C yr B.P., arboreal vegetation prevailed in the whole transect, probably due to the presence of a humid climate. Approximately between ∼9000 and 4000-3000 ¹⁴C yr B.P., there was the expansion of the savanna, probably related to the presence of drier climate. From ∼4000-3000 ¹⁴C yr B.P. to the present, the results indicated an increase in the arboreal density in the area, due to the return to a more humid and probably similar climate to the present. The presence of buried charcoal fragments in several soil depths suggested the occurrence of palaeofires during the Holocene. The vegetation dynamic inferred in this study for northeastern Brazil is in agreement with the results obtained in areas of Amazon region, based on pollen analysis of lake sediments and carbon isotope analysis of soil organic matter (SOM), implying than similar climatic conditions have affected these areas during the late Pleistocene until the present.     

Late holocene human impact on lake basins in central mexico

Palaeolimnological investigations in the volcanic highlands of Central Mexico (19°N) have yielded clear evidence of environmental degradation associated with episodes of forest clearance and agricultural expansion during the last 3500 years. Preliminary results are presented from five lake basins situated at altitudes of 1700 to 2575 m a.s.l., along a gradient of decreasing aridity and temperature from north to south: Hoya San Nicolás de Parangueo (Guanajuato); La Piscina de Yuriria (Guanajuato); Pátzcuaro (Michoacán); Zacapu (Michoacán) and Upper Lerma (Estado de México). Samples from sediment cores and pits are being analyzed for loss-on-ignition, magnetic susceptibility (X and X_fd), major cations, total P, C/N, carbonate content, δ¹³C, δ¹⁸O, diatoms, pollen, and charcoal content. Evidence for disturbance is provided by increases in non-arboreal pollen types, especially maize (Zea mays), peaks of X, X_fd and charcoal; increased concentrations of elements associated with soil material such as Al, Fe, Ti, and P, and diatoms indicative of cultural eutrophication. Pátzcuaro, Hoya San Nicolás, Zacapu, and Upper Lerma show an initial phase of disturbance dating from ca. 3500 to 1400 yr B.P., reflecting the widespread adoption of maize cultivation during the Preclassic. A later, more intense phase is recorded in all the basins. In Hoya San Nicolás, La Piscina de Yuriria, Zacapu, and Pátzcuaro, which lay within, or on the margins of the Tarascan state, this episode dates from Postclassic to Hispanic times (<1100 yr B.P.). In contrast, disturbance in the Matlatzincan area (the Upper Lerma Basin) was apparently more continuous, culminating during the late Classic to early Postclassic (ca. 1400-700 yr B.P.).     

贵州石笋记录的中晚全新世东亚夏季风变化

研究全新世典型气候突变事件的内部结构及区域特征,有助于明晰季风气候突变事件的成因机制。通过对贵州七星洞石笋14个高精度²³⁰Th定年和779个氧同位素数据的分析,重建了过去6 380～2 700 yr B.P.时段平均分辨率达4.7年的东亚夏季风演化序列。该石笋δ¹⁸O值整体上呈逐渐偏正的特征,指示中晚全新世以来东亚夏季风持续变弱的趋势。叠加在此长期季风减弱变化趋势上,最为显著的百年尺度振荡主要发生在4 548～3 715 yr B.P.时段,对应于4.2 kyr B.P.事件。该记录与同区域董哥洞石笋δ¹⁸O记录一致,均显示在此事件内部并非持续干旱,而是具有两次显著的季风强降雨期。相似的季风强降雨期在我国北方气候记录中也有体现。在更大的空间尺度上,这种4.2 kyr B.P.事件的内部结构特征与澳洲—印度尼西亚(澳—印)季风区的石笋记录结构相对应,但呈显著的反相位耦合关系,证实了亚洲与澳—印季风间的动力学联系。此外,该事件结构与ENSO记录的耦合暗示了4.2 kyr B.P.事件的发生可能与热带太平洋密切相关。     

Petrographic aspects of a sequence of Quaternary volcanic ashes from the Laguna de Fuquene area, Colombia, and their stratigraphic significance

A core section from the Fuquene area (Cordillera Oriental, Colombia) with a total length of 60 m shows a predominantly peaty-clay zone in the upper 12 m containing 15 laminae and thin layers of fine-grained, pyroclastic material. These 15 layers consist of crystal-vitric ash derived from dacitic-andesitic magmas. Mineralogic data and refractive index (r.i.) values of the associated glass shards make it possible to distinguish a lower group of mica-rich and an upper group of pyroxene-bearing ash layers. The successive layers illustrate a progressive increase of hydration of the shards with time and with decreasing particle size. The frequency distribution curves of the r.i. values of 8–4- and 75–50-μm shards are in general rather similar. Provisional pollen data and some radiocarbon dates allow comparison of the petrographic properties of these ashes with those of some ash occurrences in a nearby palynologically investigated core section. This comparison indicates that the mica-rich ashes were produced between about 44,000 and 20,000 yr B.P. and that the production of the pyroxene-bearing ashes took place after about 20,000 yr B.P. The petrographic features of a number of ashes, collected from sections and cores at different sites of the Sabana de Bogotá, appear to be comparable with those established in the sequence of Fuquene ashes. This suggests that these petrographic characteristics may be of use in correlation studies in the Sabana de Bogotá and adjacent areas.     

Chronology of glacial Lake Agassiz meltwater routed to the Gulf of Mexico

Sediment cores with new radiocarbon dates from the southern outlet of glacial Lake Agassiz indicate that meltwater delivery to the Mississippi valley was disrupted at 10,800 ¹⁴C yr B.P. and the outlet was abandoned by 9400 ¹⁴C yr B.P. These findings confirm the timing of generally accepted terminations of the Lockhart and Emerson Phases of Lake Agassiz. Additionally, the radiocarbon chronology indicates that the spillway was fully formed by 10,800 ¹⁴C yr B.P. and that the occupancy in late-Emerson time was likely short-lived with minimal spillway erosion.     

Ancient pine forest on inland dunes in the Spanish northern meseta

We present a new stratigraphic (pollen and nonpollen microfossils and charcoal particle) sequence with five AMS dates, covering about the last 9000 yr, of a core collected from the Spanish northern meseta, one of the territories of the Iberian Peninsula for which little paleobotanical information is available. The results support the hypothesis of the permanence of the pine forests, in more or less pure masses or large timber stands, during the Holocene in some Iberian continental zones. The typical substitution in postglacial dynamics of heliophyllous species, such as pines or Cupressaceae, by broadleaf trees did not occur in this inland region. Presumably, factors linked to the substrate, in this case very deep sand dunes covering vast areas, may have contributed to the scarce local competitiveness of the broadleaf trees, which would account for the hegemony of pines in this region. Based on the dynamics of aquatic plants and nonpollen microfossils, an initial phase previous to 7500 ¹⁴C yr B.P. of high levels in the lake can be identified by high percentages of hydrophytes. A progressive increase in helophytes and the gradual infilling of the lake over the last 5000 yr appear to indicate a phase of aridification similar to those established for the western Mediterranean. Study of charcoal particles, more abundant in the last 2500 yr, has given rise to certain hypotheses regarding the incidence of recurring fires of a local or regional nature.     

Late-Glacial Vegetation and Climate Change in Western Oregon

Pollen records from two sites in western Oregon provide information on late-glacial variations in vegetation and climate and on the extent and character of Younger Dryas cooling in the Pacific Northwest. A subalpine forest was present at Little Lake, central Coast Range, between 15,700 and 14,850 cal yr B.P. A warm period between 14,850 and 14,500 cal yr B.P. is suggested by an increase inPseudotsugapollen and charcoal. The recurrence of subalpine forest at 14,500 cal yr B.P. implies a return to cool conditions. Another warming trend is evidenced by the reestablishment ofPseudotsugaforest at 14,250 cal yr B.P. Increased haploxylonPinuspollen between 12,400 and 11,000 cal yr B.P. indicates cooler winters than before. After 11,000 cal yr B.P. warm dry conditions are implied by the expansion ofPseudotsuga.A subalpine parkland occupied Gordon Lake, western Cascade Range, until 14,500 cal yr B.P., when it was replaced during a warming trend by a montane forest. A rise inPinuspollen from 12,800 to 11,000 cal yr B.P. suggests increased summer aridity.Pseudotsugadominated the vegetation after 11,000 cal yr B.P. Other records from the Pacific Northwest show an expansion ofPinusfrom ca. 13,000 to 11,000 cal yr B.P. This expansion may be a response either to submillennial climate changes of Younger Dryas age or to millennial-scale climatic variations.     

Stratigraphy, Chronology, and Paleoenvironmental Reconstruction of the Quaternary Sedimentary Infilling of a Volcanic Tube in Fuerteventura, Canary Islands

La Cueva del Llano is a volcanic tube of Pleistocene age on Fuerteventura Island, in the Canary Islands. Part of it is infilled with sediments of external origin. These deposits are exceptional in stratigraphic complexity and thickness compared with other known tube infillings, and they comprise nine stratigraphic units deposited in five phases. In Phase I, which has not been dated, sedimentation of cinder from a nearby cone occurred. Phase II began ca. 16,830 ± 900 ¹⁴C yr B.P., whereas phase IV dates to 9280 ± 370 ¹⁴C yr B.P. The interpretation of sedimentary features shows that phases III and V correspond to a dry climate, similar to the present one, whereas the climate was much wetter during phases II and IV. This paleoclimatic sequence agrees with those suggested by the study of deposits formed in other sedimentary environments, not only in Fuerteventura but on other islands of the Canary group and the Sud-Maroc region.     

Late Pleistocene and Holocene Paleoenvironments of Chalco Lake, Central Mexico

In order to establish paleoenvironmental conditions during the late Quaternary, four cores from the Basin of Mexico (central Mexico) were drilled in Chalco Lake, located in the southeastern part of the basin. The upper 8 m of two parallel cores were studied, using paleomagnetic, loss-on-ignition, pollen, and diatom analyses. Based on 11 ¹⁴C ages, the analyzed record spans the last 19,000 ¹⁴C yr B.P. Volcanic activity has affected microfossil abundances, both directly and indirectly, resulting in absence or reduction of pollen and diatom assemblages. Important volcanic activity took place between 19,000 and 15,000 yr B.P. when the lake was a shallow alkaline marsh and an increase of grassland pollen suggests a dry, cold climate. During this interval, abrupt environmental changes with increasing moisture occurred. From 15,000 until 12,500 yr B.P. the lake level increased and the pollen indicates wetter conditions. The highest lake level is registered from 12,500 to ca. 9000 yr B.P. The end of the Pleistocene is characterized by an increase in humidity. From 9000 until ca. 3000 yr B.P. Chalco Lake was a saline marsh and the pollen record indicates warmer conditions. After 3000 yr B.P. the lake level increased and human disturbance dominates the lacustrine record.     

Age of the five islands formation, Nova Scotia, and the deglaciation of the Bay of Fundy

Three atomic mass spectrometry (AMS) dates have been obtained for shell material from the bottomset beds of a glaciomarine delta at Spencers Island, Nova Scotia, near the head of the Bay of Fundy. The sediments in the delta are part of the previously undated Five Islands Formation, and are the first direct indictaion of the age of deglaciation in this region. The dates range from 14,300 to 12,600 yr B.P. and record the duration of deposition of a diamicton under the deltaic deposits and of the delta itself. The diamicton may have formed around 14,000 yr B.P. under ice-shelf or calving-bay conditions, or by a readvance of grounded ice. The Spencers Island delta is part of a prominent ice-marginal stand marked by numerous deltas along the Minas Basin. The time of formation of the deltas and the inferred ice margin is between 13,500 and 12,000 yr B.P. based on the Spencers Island dates and palynologically confirmed dates on the base of lake-sediment cores from the delta surface. Ice-marginal glaciomarine deposits near St. John, New Brunswick, record a range of radiocarbon dates similar to the Spencers Island dates. This implies that the Bay of Fundy became virtually ice free about 14,000 yr B.P.     

The geoarchaeological and paleoenvironmental context of Paleoindian sites in western Middle Park,Colorado, USA

Geoarchaeological investigations in western Middle Park provide important information for understanding the soil‐stratigraphic context of Paleoindian components, as well as the latest Quaternary environmental change and landscape evolution in a Southern Rocky Mountain intermontane basin. Paleoindian components are associated with the oldest two of four latest Quaternary stratigraphic units (1–4) recognized in co‐alluvial mantles (combined slopewash and colluvium) in uplands and in alluvial valley fills. Limited data suggest accumulation of unit 1 as early as ∼12,500 ¹⁴C yr B.P. in alluvial valleys and by at least ∼11,000 ¹⁴C yr B.P. in uplands was followed by brief stability and soil formation. A relatively widespread disconformity marks earliest Holocene erosion and substantial removal of latest Pleistocene deposits in upland and alluvial settings followed by unit 2 deposition ∼10,000–9000 ¹⁴C yr B.P., perhaps signaling the abrupt onset of an intensified summer monsoon. In situ Paleoindian components in uplands are found in a moderately developed buried soil (the Kremmling soil) formed in units 1 and 2 in thin (≤1m) hillslope co‐alluvial mantles. The Kremmling soil reflects geomorphic stability in upland and alluvial settings ∼9000–4500 ¹⁴C yr BP, and represents a buried landscape with the potential to contain additional Paleoindian components, although elsewhere in western Middle Park Early Archaic components are documented in morphologically similar soils. Kremmling soil morphology, the relative abundance of charcoal in unit 2 relative to younger units, and charcoal morphology indicate the expansion of forest cover, including Pinus, and grass cover during the early and middle Holocene, suggesting conditions moister than present. © 2010 Wiley Periodicals, Inc.