Pre-Quaternary microfossils—A guide to errors in radiocarbon dating

Nambudiri, E.M.V.; Teller, James T.

doi:10.1130/0091-7613(1980)8<123:pmgtei>2.0.co;2

Cited by 67 publications

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“…Le premier mécanisme est la contamination des niveaux datés par du matériel remanié et est illustré par la courbe des spores trilètes préquaternaires (Nambudiri et al, 1980).…”

Section: Mécanismes De Contamination Et Indicateurs Paléoenvironnemenunclassified

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

Jetté¹,

Mott²

2007

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Une carotte en provenance du lac Chance Harbour livre l'histoire postglaciaire de la végétation environnante. De l'argile rose, probablement glaciolacustre, est présente à la base de la séquence. L'argile est recouverte de 18 cm de silt noir et de marne qui représente une première période d'accumulation de matière organique. L'analyse sédimentaire révèle la succession suivante: herbes, arbustes, Populus-Juniperus, puis Picea. Cette succession représente la réponse de la végétation au réchauffement postglaciaire initial du climat. Entre 815 et 755 cm de profondeur, l'accumulation organique est interrompue par une argile rose déposée au cours d'une période d'instabilité des rives. Le pollen de Picea est alors remplacé par celui de Betula, de Salix et d'Alnus et la représentation des Gramineae et des Cyperaceae augmente, témoignant ainsi d'un climat plus rigoureux. Au-dessus de cet intervalle, 755 cm de gyttja représente une seconde période d'accumulation de matière organique dont l'analyse révèle la même succession pollinique déjà observée à la base, indicatrice d'un adoucissement du climat. On observe par la suite la succession pollinique typique de la région: pin, pruche, bouleau, hêtre, épinette et herbes. Sept dates au 14C précisent la chronologie. Les quatre dates inférieures, jugées trop vieilles, sont remplacées par une chronologie alternative. Le cycle climatique observé (réchauffement tardiglaciaire, suivi d'un intervalle plus froid et nouveau réchauffement au début de l'Holocène) est associé au cycle Allerod-Dryas III européen.A core from Chance Harbour Lake contains a record of the postglacial vegetational history of the area. Pink clay, possibly representing glaciolacustrine sedimentation is overlain by 18 cm of black silt with marl layers that represents a first period of organic accumulation. Analysis of the sediment reveals the following pollen succession : herb taxa, shrub taxa, Populus/ Juniperus and finally Picea. This succession is interpreted as the vegetational response to the initial postglacial warming. Between 815 and 755 cm depth, organic sedimentation is interrupted by pink clay deposition related to a period of slope instability. During this period Picea pollen is replaced by Betula, Salix and AInus while Gramineae and Cyperaceae representation increases, indicating cooler climate. Above this interval, 755 cm of gyttja represents a second period of organic accumulation. Analysis of this sediment reveals the same pollen succession observed in the basal organic silt, indicating warmer climate. The palynological succession typical of the Atlantic Region follows : pine, hemlock, birch, beech and finally spruce and herbs. Seven 14C dates define the chronology. The four lower dates are deemed anomalous, and an alternative chronology for this part is proposed. The climatic cycle of late-glacial warming followed by a cooler interval and finally a return to the initial warming trend at the beginning of the Holocene is associated with the European Allerod/Younger Dryas climatic cycle.Ein Bohrkern v...

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“…Le premier mécanisme est la contamination des niveaux datés par du matériel remanié et est illustré par la courbe des spores trilètes préquaternaires (Nambudiri et al, 1980).…”

Section: Mécanismes De Contamination Et Indicateurs Paléoenvironnemenunclassified

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

Jetté¹,

Mott²

2007

gpq

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“…If the slope (14C yr/cm) at either of the extreme data points appeared questionable the regression line was extrapolated as a straight line of slope compatible with the interior section (Fig 1), and the curvature (%/cm) in the questionable region(s) was presumed to be zero. (Fig 1, eg) If contamination by older carbon (Nambudiri et al, 1980) is to be an adequate explanation, the degree of contamination must progressively decrease with time. While allowance should be made for this possibility at some locations over some periods of time, it does not appear to be a universally adequate explanation.…”

Section: Methodsmentioning

confidence: 99%

“…A tendency for 14C age profiles of sedimentary features to be concave toward the 14C age axis has been noted in the literature and interpreted variously as an indication of compaction (Stuiver, 1967), contamination by older carbon (Nambudiri et al, 1980), and change in the biosphere 14C/12C ratio (La! & Revelle,1984).…”

Section: Introductionmentioning

confidence: 99%

¹⁴C Depth Profiles as Indicators of Trends of Climate and ¹⁴C/¹²C Ratio

Brown

1986

Radiocarbon

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“…The mollusk shell collected from the modern lake in 1897 yielded a 14 C date of 170 ± 60 BP, indicating that the hard water effect on carbonate radiocarbon dates in the modern lake is about 120 years. Because of the paucity of identifiable woody or vegetal matter in the Lake Manitoba cores (needed to minimize the problem of dating "old" detrital organic material; Nambudiri et al, 1980), we chose to date ostracode shells, acknowledging the potential for contamination by the hard water effect. A 14 C date of 7450 ± 680 on charcoal, however, is similar to a date of 7520 ± 90 on ostracode calcite in the same interval, suggesting a minimal hard water effect at this time.…”

Section: Radiocarbon Datesmentioning

confidence: 99%

“…These previous stratigraphic studies, while based on conventional radiocarbon dating of bulk lake sediment samples, which may have produced an unreliable chronology (Nambudiri et al, 1980), all indicate that the late Pleistocene and Holocene history of the lake is exceedingly complex due to the interplay of differential isostatic crustal rebound, fluctuating climate, and variable river inflow. As well, the early history of the Lake Manitoba basin was controlled by variations in glacial Lake Agassiz because it was part of this extensive proglacial FIGURE 1.…”

Section: Introduction and Previous Workmentioning

confidence: 99%

Paleolimnology of Lake Manitoba: the Lithostratigraphic Evidence

Teller

2004

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Lake Manitoba, the largest lake in the prairie region of North America, is one of the most intensively studied lacustrine basins in western Canada. New AMS 14C dating, together with mineralogical, geochemical, and lithostratigraphic analyses of the 14-m-thick, offshore sediment sequence, document a complex Holocene history in which water levels and limnological conditions were controlled by the interplay of changing climate, variable river and groundwater inflow, and differential isostatic rebound. Varves, ice-rafted debris, and clast-rich laminated sediment record deposition in the lake when the basin was part of proglacial Lake Agassiz. As Agassiz retreated northward, Lake Manitoba became isolated by about 8500 14C yrs BP, and for the next 800 years was characterized by mainly shallow water to dry conditions. Deeper and more stable water conditions returned to the Lake Manitoba basin by 7700 14C yrs BP probably due to the damming effect of differential isostatic rebound and decreasing aridity. For the next 3000 years, relatively stable lake levels and water compositions were maintained, reflecting a delicate balance between differential isostatic rebound, climate, inflow of the Assiniboine River, and groundwater contribution. At ~4500 14C yrs BP the Assiniboine River was rerouted to its present easterly path, by-passing Lake Manitoba, and resulting in loss of a significant component of the lake’s hydrologic budget. Water levels dropped and the offshore sediments were once again subaerially exposed. By 3700 14C yrs BP, a cooler and wetter climate, together with continued southward transgression of water, compensated for the loss of fluvial input, resulting in reflooding of the basin. By about 2000 years ago the lake had evolved from a shallow, saline, and alkaline pool to its present depth and extent.Le lac Manitoba, le plus grand lac des Grandes Plaines de l’Amérique du Nord, est l’un des bassins lacustres le plus intensément étudiés de l’Ouest du Canada. De nouvelles dates 14C SMA, ainsi que des analyses minéralogiques, géochimiques et lithostratigraphiques de la séquence sédimentaire de 24 m d’épaisseur au large du rivage témoignent d’une évolution complexe du lac, à l’Holocène. Au cours de cette période, les niveaux lacustres et les conditions limnologiques ont été influencés par les effets combinés des changements climatiques, de la variation des apports d’eaux lacustre et souterraine et d’un relèvement isostatique différentiel. Les varves, les débris glaciels et les sédiments en lamines riches en éléments détritiques ont constitué l’apport sédimentaire au lac lorsque le bassin faisait partie du Lac glaciaire Agassiz. Après la vidange du lac glaciaire vers le nord, le lac Manitoba a été isolé vers 8500 BP ; pendant les 800 années suivantes, le lac était caractérisé par des eaux peu profondes et un climat sec. Des eaux plus profondes et plus stables ont caractérisé le lac vers 7700 BP, probablement en raison de l’endiguement qu’a entraîné le relèvement isostatique différentiel et une moins grande aridité. Pe...

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Pre-Quaternary microfossils—A guide to errors in radiocarbon dating

Cited by 67 publications

References 0 publications

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

¹⁴C Depth Profiles as Indicators of Trends of Climate and ¹⁴C/¹²C Ratio

Paleolimnology of Lake Manitoba: the Lithostratigraphic Evidence

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Pre-Quaternary microfossils—A guide to errors in radiocarbon dating

Cited by 67 publications

References 0 publications

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

Palynostratigraphie du Tardiglaciaire et de l’Holocène de la région du lac Chance Harbour, Nouvelle-Écosse

14C Depth Profiles as Indicators of Trends of Climate and 14C/12C Ratio

Paleolimnology of Lake Manitoba: the Lithostratigraphic Evidence

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¹⁴C Depth Profiles as Indicators of Trends of Climate and ¹⁴C/¹²C Ratio