scholarly journals Preliminary paleomagnetic studies of lake sediments in Eastern Canada

2011 ◽  
Vol 31 (3-4) ◽  
pp. 379-387 ◽  
Author(s):  
R. J. Mott ◽  
J. H. Foster
Keyword(s):  
Sediment Cores ◽  
Organic Content ◽  
Small Lakes ◽  
Eastern Canada ◽  
Secular Variations ◽  
Holocene Sediments ◽  
Lake Bottom ◽  
Organic Sediments ◽  
Lake Bottom Sediment ◽  
Spurious Results

Nine lake bottom sediment cores from small lakes in Eastern Canada, three of which were oriented to an azimuth, have been analyzed magnetically in an attempt to delineate the paleomagnetic character of the late-Pleistocene and Holocene sediments as an aid to stratigraphy and chronology. Secular variations are discernable in mineral sediments and in overlying organic sediments when intensities are strong enough to produce reliable results. Where organic content was high and intensities low, erratic results were obtained. Short segments of some cores, involving at most several centimetres, showed negative values for inclination, but whether or not these can be related to magnetic reversals or excursions or are spurious results, cannot be determined at this time.

Post-Pollution: Characterizing Ecological Recovery in a Historically Nutrient Enriched Lake.

2018 ◽  
Author(s):  
Iain MacKenzie
Keyword(s):  
Washington State ◽  
Septic System ◽  
Algal Communities ◽  
System A ◽  
Chemical Measurements ◽  
Healthy State ◽  
Lake Bottom ◽  
Lake Washington ◽  
Lake Bottom Sediment ◽  
Reconstructive Techniques

An iconic story of recovery from nutrient pollution is the restoration of the heavily enriched Lake Washington in Seattle, Washington State. Originally an integral part of the municipal septic system, a diversion of wastewater in 1968 has allowed Lake Washington to return to what has been recently described as a natural and healthy state. Yet is it accurate to characterize a lake as “recovered” based purely on chemical measurements? Does a legacy of pollution linger on in the ecology of a lake system long after the lake has been given a clean bill of health?Using paleolimological reconstructive techniques it is possible to compare pre-pollution and post-pollution communities of algae by looking at microfossils stored chronologically in the lake-bottom sediment. Use of this technique has afforded a test of the assumption that once pollution stress in a lake is alleviated, the algal communities quickly return to the pre-pollution state. Work on Lake Washington indicates that this does not always hold true. Instead, it suggests that a legacy of pollution persists in the algae and ecological community of the lake long after the nutrient levels have returned to normal.

scholarly journals Estimation of long-term Ph changes in lakes of the Caucasus using a bioindication method based on diatomaceous analysis

2019 ◽  
Vol 46 (1) ◽  
pp. 51-57 ◽  
Author(s):  
L. V. Razumovskii ◽  
V. L. Razumovskii
Keyword(s):  
Sediment Cores ◽  
Western Caucasus ◽  
Small Lakes ◽  
The Caucasus ◽  
Ph Values ◽  
Long Term Changes ◽  
The Western Caucasus ◽  
Central Caucasus ◽  
Hydrological Parameter

To analyze processes that may lead to long-term changes in pH, lake sediments from five small lakes in the Western and Central Caucasus were studied according to diatomaceous complexes from sediment cores. A proprietary principle of hydrological parameter unification was used to reconstruct numerical pH values. In isotopic dating experiments, a series of numerical pH values for 2000–130 years were generated for the lakes. These data indicate an absence of noticeable changes in pH in the lakes of the Western Caucasus and alkalization processes in the lakes of the Central Caucasus.

Late Quaternary sedimentation on the southwestern Scotian Slope, eastern Canada: relationship to glaciationGeological Survey of Canada Contribution 20070176.

2008 ◽  
Vol 45 (3) ◽  
pp. 267-285 ◽  
Author(s):  
Thian Hundert ◽  
David J.W. Piper
Keyword(s):  
Late Quaternary ◽  
Sediment Cores ◽  
Sediment Supply ◽  
Scotian Shelf ◽  
Eastern Canada ◽  
Glacial Retreat ◽  
Air Gun ◽  
Continental Slopes ◽  
History Of ◽  
Seismic Reflection Profiles

The sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf. The glacial history of the southwestern part of the Scotian Shelf is poorly known. Air-gun and high-resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern Scotian Slope since the last glacial maximum (LGM). Seismic-reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope, and correlation to dated piston cores farther downslope show that this till dates from the LGM. Slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites. Progressively increasing importance of red-brown sediment derived from glacial supply to Laurentian Channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid-Scotian Shelf. With the termination of distal proglacial sediment supply, the sedimentation rate diminished rapidly and hemipelagic sedimentation prevailed through the Holocene.

Reconstructing the palaeoenvironment at the early Mesolithic site of Lake Duvensee: Ground-penetrating radar and geoarchaeology for 3D facies mapping

The Holocene ◽  
2020 ◽  
Vol 30 (6) ◽  
pp. 820-833 ◽  
Author(s):  
Erica Corradini ◽  
Dennis Wilken ◽  
Marco Zanon ◽  
Daniel Groß ◽  
Harald Lübke ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Three Dimensional ◽  
Sedimentary Facies ◽  
Landscape Development ◽  
Fine Grained ◽  
Stratigraphic Model ◽  
Lake Bottom ◽  
Organic Sediments ◽  
Spatio Temporal ◽  
Ground Penetrating

We investigate the landscape development of the early Mesolithic hunter-gatherer sites of Duvensee (10000–6500 cal. BCE). Based on ground-penetrating radar (GPR) and geoarchaeological drillings, we present for the first time a three-dimensional (3D) reconstruction of the palaeoenvironment of 63 ha covering subarea of the former lake during the Mesolithic. The archaeological aims were (1) to detect the location of former islands possibly hosting hunter-gatherer settlements and (2) to reconstruct the ancient landscape development for understanding prehistoric land use. The research in Duvensee lasts almost 100 years, providing vivid illustrations of early Mesolithic life. Clusters of Mesolithic camps have been found located on small sand hills that formed islands in the prehistoric lake. For this environment, we present depth maps of the three most important sedimentary facies interfaces of the ancient Lake Duvensee. Interface1 represents the transition between coarse organic sediments (peat and coarse detritus gyttja) and fine-grained organic sediments (fine detritus gyttja, calcareous gyttja), Interface2 represents the transition to the underlying clayish-loamy sediments, and Interface3 marks the top of the basal sand deposits at the lake bottom. From Interface3, we identified the location and extent of five former islands with Mesolithic camps. Stratigraphic information from the corings enabled us to create a 3D model of the spatio-temporal development of the Duvensee bog. The locations of the islands and their estimated dive-up times agree with the spatio-temporal pattern of the previous archaeological finds. The model shows where hunter-gatherers could settle and move from one island to another following the shorelines of the overgrowing lake. The 3D stratigraphic model provides growth and shrinking rates of the island and lake areas in the Mesolithic, and volumes of organic and non-organic deposited lake sediments. Besides, it provides a basis for a sustainable groundwater management needed for heritage preservation.

Late Quaternary Water-Level Variations and Vegetation History at Crooked Pond, Southeastern Massachusetts

2001 ◽  
Vol 56 (3) ◽  
pp. 401-410 ◽  
Author(s):  
Bryan Shuman ◽  
Jennifer Bravo ◽  
Jonathan Kaye ◽  
Jason A. Lynch ◽  
Paige Newby ◽  
...  
Keyword(s):  
New England ◽  
Water Level ◽  
Vegetation History ◽  
Late Quaternary ◽  
Sediment Cores ◽  
Climatic Conditions ◽  
Water Levels ◽  
Eastern Canada ◽  
Southern New England ◽  
Dramatic Rise

AbstractSediment cores collected along a transect in Crooked Pond, southeastern Massachusetts, provide evidence of water-level changes between 15,000 cal yr B.P. and present. The extent of fine-grained, detrital, organic accumulation in the basin, inferred from sediment and pollen stratigraphies, varied over time and indicates low water levels between 11,200 and 8000 cal yr B.P. and from ca. 5300 to 3200 cal yr B.P. This history is consistent with the paleohydrology records from nearby Makepeace Cedar Swamp and other sites from New England and eastern Canada and with temporal patterns of regional changes in effective soil moisture inferred from pollen data. The similarities among these records indicate that (1) regional conditions were drier than today when white pine (Pinus strobus) grew abundantly in southern New England (11,200 to 9500 cal yr B.P.); (2) higher moisture levels existed between 8000 and 5500 cal yr B.P., possibly caused by increased meridonal circulation as the influence of the Laurentide ice sheet waned; and (3) drier conditions possibly contributed to the regional decline in hemlock (Tsuga) abundances at 5300 cal yr B.P. Although sea-level rise may have been an influence, moist climatic conditions during the late Holocene were the primary reason for a dramatic rise in water-table elevations.

Inshore–Offshore Sedimentation Differences Resulting from Resuspension in the Eastern Basin of Lake Erie

1982 ◽  
Vol 39 (5) ◽  
pp. 748-759 ◽  
Author(s):  
J. Bloesch
Keyword(s):  
Lake Erie ◽  
Sediment Cores ◽  
Dry Weight ◽  
Sediment Traps ◽  
Particulate Phosphorus ◽  
Particulate Nitrogen ◽  
Eastern Basin ◽  
Fine Grained ◽  
Lake Bottom ◽  
Offshore Station

From June through October 1978 sediment traps were moored at three stations in an inshore–offshore transect in the Eastern Basin of Lake Erie. Settling fluxes measured with the traps exposed close to lake bottom were rather similar at all three stations during summer stratification, averaging 6.1 g∙m−2∙d−1 for dry weight, 293 mg∙m−2∙d−1 for particulate organic carbon (POC), 38 mg∙m−2∙d−1 for particulate nitrogen (PN), and 5.44 mg∙m−2∙d−1 for particulate phosphorus (PP). A comparison of the hypolimnetic traps with the epilimnetic traps at the offshore station indicated that considerable resuspension takes place even in summer. During fall, however, the nearshore sedimentation rates were markedly increased because of storm-induced bottom resuspension. By comparing the trap catches with sediment cores taken at all three stations, a resuspension model for dry weight, POC, and PN was developed. The calculations showed that newly formed organic material is resuspended and redeposited more frequently at nearshore locations than offshore. This repeated nearshore resuspension enhances decomposition of detritus, as shown by low relative phytoplankton activity in the hypolimnetic traps, and results in horizontal transport of fine-grained organic matter in the offshore direction. The significant POC and PN concentration differences found in the inshore–offshore transect of the bottom sediments can be explained by these two processes.Key words: sedimentation, sediment traps, sediment cores, resuspension, inshore–offshore differences

Effects of strong seismic shaking in lake sediments, and earthquake recurrence interval, Témiscaming, Quebec

1991 ◽  
Vol 28 (9) ◽  
pp. 1349-1352 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Relative Frequency ◽  
Sediment Cores ◽  
Recurrence Interval ◽  
Small Lakes ◽  
Earthquake Recurrence ◽  
Uppermost Layer ◽  
Earthquake Recurrence Interval ◽  
A Minor ◽  
Epicentral Region ◽  
Silt Layer

The magnitude 6.3 Timiskaming earthquake of 1935 resulted in discoloration in small lakes in the epicentral region. Sonar profiles for Lac Tee have shown that organic-rich gyttja has been removed from the sides and redeposited in the deep parts of the lake. Lake sediment cores from deep basins contain a 2–3 cm uppermost layer, which is interpreted as the normal accumulation of sediment since 1935. This is followed by a 20 cm chaotic zone of black gyttja mixed with partly tabular fragments of a previously formed silt layer, underlain by a dense 1–2 cm thick silt horizon. The latter is interpreted as having formed by rapid settling of the denser silicate portion of the resuspended sediment. This 20 cm zone is insufficient to account for the abnormal thickness of gyttja in the basins, so events of this kind would have had to have occurred repeatedly since deglaciation. The only major prehistoric event revealed by these ~100 cm cores is at a depth equivalent to about 1500 years ago, based on the amount of sediment deposited since 1935. A minor silting event occurred about 400 years ago. On this basis, the recurrence interval of magnitude 6 or greater earthquakes is longer at Témiscaming than at Charlevoix, Quebec (75 years historically), consistent with the present relative frequency of small earthquakes in these two regions.

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