共查询到20条相似文献,搜索用时 31 毫秒
1.
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. 相似文献
2.
Francine M. G. McCarthy John H. McAndrews Steve M. Blasco Sarah H. Tiffin 《Journal of Paleolimnology》2007,37(3):453-470
High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian
Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing
and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments
deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net
erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for
the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers
flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and
Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline
only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments
are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic
contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication
over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are
probably exported from the Bay. 相似文献
3.
Exposures along the lower Kaministiquia River (near Thunder Bay, Ontario, Canada) provide insight into early Holocene lake
level fluctuations and paleoenvironmental conditions in the northwestern Lake Superior basin. These exposures show at least
two large paleochannels which were downcut into offshore sediments, and were later filled with >2 m of sand, ~3 m of rhythmically
laminated silt and clay, and ~6 m of interbedded silt and sand. Buried by the rhythmically laminated silty clay unit is a
well-preserved organic deposit with abundant plant macrofossils from terrestrial and emergent taxa, including several upright
tree trunks. Three AMS radiocarbon ages were obtained on wood and conifer cones from this deposit: 8,135 ± 25 (9,130–9,010
cal), 8,010 ± 25 (9,010–8,780 cal), and 7,990 ± 20 (8,990–8,770 cal) BP. This sequence records an early postglacial high-water
phase, followed by the Houghton lowstand, and reflooding of the lower Kaministiquia River Valley. The drop in lake level associated
with the Houghton phase forced the ancestral Kaministiquia River to downcut. By ~9,100 cal (~8,100) BP, older channels eroded
into subaqueous underflow fan deposits in the Thunder Bay area near Fort William Historical Park (FWHP) were abandoned and
colonized by a Picea-Abies-Larix forest. Based on stratigraphic data corrected for differential isostatic rebound, the lake was below the Sault Ste. Marie
bedrock sill between at least 9,100 cal (8,100) and 8,900 cal (8,000) BP. Shortly after 8,900 cal BP, the lake quickly rose
and buried in situ lowland vegetation at FWHP with varved sediments. We argue that this transgression was due to overflow
from glacial Lakes Agassiz or Ojibway associated with the retreat of the Laurentide Ice Sheet from the Nakina moraine and/or
the Cochrane surge margins in the Hudson Bay Lowlands. A continued rise in lake level after 6,420 ± 20 (7,400 cal) BP at FWHP
may record uplift of the North Bay outlet above the Sault Ste. Marie bedrock sill and the onset of the Nipissing transgression
in the Lake Superior basin. 相似文献
4.
A late Pleistocene and Holocene mineral magnetic record from sediments of Lake Aibi,Dzungarian Basin,NW China 总被引:1,自引:0,他引:1
Alina Tudryn Piotr Tucholka Elisabeth Gibert Francoise Gasse Keiquin Wei 《Journal of Paleolimnology》2010,44(1):109-121
We studied mineral magnetic properties of a 6-m-long, late Pleistocene through Holocene sediment sequence from Lake Aibi in
Dzungaria (Zunggary, Junggar), northern Xinjiang, China. Results were used to infer environmental changes and are compared
with previously studied cores from Lake Manas. Both water bodies occupy the deepest parts of the Dzungarian Basin and are
remnants of large Holocene lakes. During the Late Pleistocene, the magnetic mineralogy in both lakes was dominated by detrital,
iron oxide minerals. Oxic conditions, which dominated during sedimentation and early diagenesis, persisted over the Pleistocene–Holocene
transition. Later, during the middle Holocene, lake bottom conditions enabled authigenic formation of iron sulphide minerals
such as pyrite (FeS2) in Lake Aibi, and pyrite and greigite (Fe3S4) in Lake Manas. This iron sulphide mineralogy suggests increased biological activity in stagnant, anoxic bottom waters. Anoxic
bottom conditions started about 9.8 cal kyr BP in Lake Manas and at about 7.2 cal kyr BP in Lake Aibi. A short dry event recorded
in Lake Manas between 6.8 and 5.2 cal kyr BP is not clearly observed in Lake Aibi. In the late Holocene, i.e. the last 2.8 cal
kyr, sediments of both lakes are again characterised by iron oxides, suggesting well-mixed, shallow water bodies. For this
recent period, it seems that the detrital material in the two lakes had a common origin. Magnetic properties of sediments
in Lakes Aibi and Manas show broadly similar environmental evolution during the late Pleistocene and Holocene. Nevertheless,
despite the close proximity of the two lakes (~200 km) in the same basin, they display some different magnetic properties
and record environmental changes at different times. 相似文献
5.
Serpent River Bog lies north of North Channel, 10 m above Lake Huron and 15 m below the Nipissing Great Lake level. A 2.3 m
Holocene sequence contains distinct alternating beds of inorganic clastic clay and organic peat that are interpreted as evidence
of successive inundation and isolation by highstands and lowstands of the large Huron-Basin lake. Lowstand phases are confirmed
by the presence of shallow-water pollen and plant macrofossil remains in peat units. Twelve 14C dates on peat, wood and plant macrofossils combined with previously published 14C ages of lake-level indicators confirm much of the known early Holocene lake-level history with one notable exception. A
new Late Mattawa highstand (8,390 [9,400 cal]–8,220 [9,200 cal] BP) evidenced by a sticky blue-grey clay bed is tied to outburst
floods of glacial Lake Minong during erosion of the Nadoway drift barrier in the eastern Lake Superior basin. A subsequent
Late Mattawa highstand (8,110 [9,040 cal]–8,060 [8,970 cal] BP) is attributed to enhanced meltwater inflows that first had
deposited thick varves throughout Superior Basin. Inundation by the Nadoway floods and possibly the last Mattawa flood were
likely responsible for termination of the Olson Forest (southern Lake Michigan). A pollen diagram supports the recognized
progression of Holocene vegetation, and defines a subzone implying a very dry, cool climate about 7.8–7.5 (8.6–8.3 cal) ka
BP based on the Alnus crispa profile during the Late Stanley lowstand. A new date of 9,470 ± 25 (10,680–10,750 cal) BP on basal peat over lacustrine clay
at Espanola West Bog supports the previous interpretation of the Early Mattawa highstand at ca. 9,500 (10,740 cal) BP. The
organic and clastic sediment units at these two bogs are correlated with other records showing coherent evidence of Holocene
repeated inundation and isolation around northern Lake Huron. Taken together the previous and new lake-level data suggest
that the Huron and Georgian basin lakes were mainly closed lowstands throughout early Holocene time except for short-lived
highstands. Three of the lowstands were exceptionally low, and likely caused three episodes of offshore sediment erosion which
had been previously identified as seismo-stratigraphic sequence boundaries. 相似文献
6.
Sub-bottom profiling and coring were undertaken at eight sub-basins along the lower French River and at five small lakes near
North Bay, Ontario, to collect stratigraphical and chronological evidence to investigate whether lakes occupying the Huron–Georgian
basins during the early- to mid-Holocene became hydrologically closed. All of the coring sites are located within the route
of the North Bay outlet that carried outflow from the upper Great Lakes during this period. Sand beds containing organic detritus
are present within five cores from Muskrat, Crombie and Deep bays that otherwise are composed of glaciolacustrine rhythmites
or fine-grained lacustrine deposits. These sand beds are interpreted to represent intervals when water levels within the sub-basins
were lower than present, based on chronology, sediment texture, and macrofossil assemblages. It is inferred that the water
surface in the Huron–Georgian basins fell below the level of the Dalles Rapids sill isolating the lower French River sub-basins
from the large lake. A core from Depensier Lake, North Bay, contains an organic-rich sand interval within a thicker sand unit
barren of organic materials. Macrofossils within this organic-rich interval are interpreted to be evidence of substantially
diminished flow through the North Bay outlet channel. Radiocarbon dates of terrestrial macrofossils provide correlation of
the sand beds between the French River cores as well as with the organic-rich sand in the Depensier Lake core. The possibility
that the sand beds in the French River cores represent flood deposits rather than evidence of hydrologically closed conditions
is considered, but rejected, based on the occurrence of multiple peaty layers and the record of shallow water conditions inferred
from macrofossils within the upper sand bed of core MUS1, Muskrat Bay, in combination with the evidence of quiescent depositional
conditions from similarly aged macrofossils in the core from Depensier Lake. Eight radiocarbon dates from the French River
cores are incorporated into an elevation-age plot of paleo-indicators of water levels in the Huron–Georgian basins, using
additional data from the literature. This plot and stratigraphic evidence from the Muskrat Bay cores indicates that separate
closed-basin intervals occurred between 9.0 and 8.4, and 9.5 and 9.3 ka cal BP (~ 8.1 and 7.6, and ~ 8.5 and 8.3 ka BP).
The occurrence of these two closed-basin intervals between 9.6 and 8.4 ka cal BP (~ 8.7 and 7.6 ka BP) implies that run-off
derived exclusively from precipitation within the non-glaciated portions of the upper Great Lakes drainage basins was likely
insufficient at this time to support an open-basin lake hydrology during the contemporary climate, which was colder and drier
than present, without being supplemented from glacial Lake Agassiz overflow and/or Laurentide Ice Sheet meltwater. 相似文献
7.
Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and
silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative
of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation,
mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin
using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels
to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the
western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with
the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection
with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley
via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide
lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no
outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small
isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral
habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario
above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels
continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern
Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived
from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario. 相似文献
8.
Beatriz Ortega Gabriel Vázquez Margarita Caballero Isabel Israde Socorro Lozano-García Peter Schaaf Esperanza Torres 《Journal of Paleolimnology》2010,44(3):745-760
Geochemical data obtained from X-ray fluorescence, physical properties, total organic and inorganic carbon content (TOC/TIC),
and diatom analysis from a 6.61-m-long sedimentary sequence near the modern northern shore of Lake Zirahuen (101° 44′ W, 19°
26′ N, 2000 m asl) provide a reconstruction of lacustrine sedimentation during the last approximately 17 cal kyr BP. A time
scale is based on ten AMS 14C dates and by tephra layers from Jorullo (AD 1759-1764) and Paricutin (AD 1943-1952) volcanoes. The multiproxy analyses presented
in this study reveal abrupt changes in environmental and climatic conditions. The results are compared to the paleo-record
from nearby Lake Patzcuaro. Dry conditions and low lake level are inferred in the late Pleistocene until ca. 15 cal kyr BP,
followed by a slight but sustained increase in lake level, as well as a higher productivity, peaking at ca. 12.1 cal kyr BP.
This interpretation is consistent with several regional climatic reconstructions in central Mexico, but it is in opposition
to record from Lake Patzcuaro. A sediment hiatus bracketed between 12.1 and 7.2 cal kyr BP suggests a drop in lake level in
response to a dry early Holocene. A deeper, more eutrophic and turbid lake is recorded after 7.2 cal kyr BP. Lake level at
the coring site during the mid Holocene is considered the highest for the past 17 cal kyr BP. The emplacement of the La Magueyera
lava flows (LMLF), dated by thermoluminiscence at 6560 ± 950 year, may have reduced basin volume and contributed to the relative
deepening of the lake after 7.2 cal kyr BP. The late Holocene (after 3.9 cal kyr BP) climate is characterized by high instability.
Extensive erosion, lower lake levels, dry conditions and pulses of high sediment influx due to high rainfall are inferred
for this time. Further decrease in lake level and increased erosion are recorded after ca. AD 1050, at the peak of Purepechas
occupation (AD 1300–1521), and until the eighteenth century. Few lacustrine records extend back to the late Pleistocene—early
Holocene in central Mexico; this paper contributes to the understanding of late Pleistocene-Holocene paleoclimates in this
region. 相似文献
9.
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. 相似文献
10.
Holocene Lake Evolution in the Elmali Basin,Southwest Turkey 总被引:1,自引:1,他引:0
《自然地理学》2013,34(3):234-253
The spatial coverage of paleoecological research from southwestern Turkey is expanded by reporting on a ca. 12,690 14C yr BP (14,935 cal yr BP) proxy record recovered from the Elmali basin. Four AMS radiocarbon age determinations, the litho-stratigraphic analysis of a lake bed core, and the analysis of subsurface sediment samples from 15 shallow auger holes across the basin document sedimentation patterns during the Holocene. Based on the widespread occurrence of Chara gyrogonite, and several species of ostracoda and gastropoda, the Elmali basin was dominated by lacustrine and palustrine environments but was continually influenced by alluvial fan sedimentation. Contrasting stratigraphy in the Kara Göl and Avlan Gölü sub-basins is a result of basin morphology, and possibly hydrologic control by karst features, and sub-basin isolation due to alluvial fan development. The cyclical deposition of marl/lime mud, gyttja, and peat in the Kara Göl core is indicative of periodic fluctuations in water level across a broad shallow basin, whereas the continuous clay record observed at Avlan Gölü implies deep-water sedimentation within a plugged former karst collapse feature. Calcareous clay deposited between 14,935 and 11,180 cal yr BP signals the growth and expansion of paleo Lake Elmali, which at its peak during the late Pleistocene, may have inundated over half of the of the 180 km2 Elmali basin. 相似文献
11.
Diatom-based inferences of post-glacial hydrological change from a sedimentary record from Felker Lake, British Columbia,
show millennial-scale pacing of climate over the past approximately 11670 calendar years with change at ca. 8140 cal. year BP,
ca. 6840 cal. year BP, ca. 5700 cal. year BP, and ca. 2230 cal. year BP. Early postglacial diatom assemblages are dominated
by fragilaroid taxa, suggesting that cool and moist climate conditions and relatively high lake levels prevailed at this time.
Early Holocene warming near ca. 8140 cal. year BP promoted Cyclotella bodanica var. lemanica, a fall bloomer competitive in limnological conditions associated with warmer water and stratified conditions. Short-lived
peaks of Stephanodiscus parvus/minutulus between ca. 6340 cal. year BP and ca. 5860 cal. year BP indicate periodic increases in nutrient availability and prolonged
mixing likely associated with long cool and moist spring seasons. The diatom-inferred depth of Felker Lake increased during
the mid-Holocene to reach a record high-stand at ca. 5860 cal. year BP. Large changes in hydrological variability and terrestrial
vegetation at Felker Lake occurred after ca. 2230 cal. year BP when high-amplitude centennial-scale fluctuations in diatom-inferred
lake depth and salinity are observed. Change is first documented in terrestrial vegetation at this time by a shift from open
Pinus parklands to a landscape that periodically supported populations of Cupressaceae. Three record low-stand high-salinity events
are reconstructed between ca. 1910 cal. year BP and ca. 1800 cal. year BP, ca. 1030 cal. year BP and ca. 690 cal. year BP,
and ca. 250 cal. year BP and ca. 140 cal. year BP. The low lake-level episode of ca. 1030 cal. year BP–ca. 690 cal. year BP
is coeval with the Medieval Warm Period (ca. 1000 cal. year BP–ca. 600 cal. year BP), a period of intense drought in western
North America. Post-glacial hydrological change at Felker Lake is coherent with regional, hemispherical, and global paleoclimate
events, suggesting that millennial-and centennial-scale shifts in water availability are a persistent feature of the climate
of western North America. 相似文献
12.
We retrieved a lake sediment record from an oligosaline, meromictic lake in southwest Greenland. The record spans the last
8,200 cal. years and was radiocarbon dated and analysed for macroscopic remains of plants and animals. The record extends
the known history of several invertebrate species back in time, and provides minimum ages for their immigration to Greenland
after the last deglaciation. Shells of the ostracod Ilyocypris bradyi were found in sediments dated to the time interval c. 7,000–6,500 cal. years BP. Shells of this species were found previously in a nearby oligosaline lake, where its occurrence
was dated to about the same short time interval. The species is a thermophilous, non-arctic taxon that is absent from the
present day Greenland fauna, and we suggest that its former occurrence in west Greenland marks the peak of the Holocene thermal
maximum. This is in agreement with other records from Greenland. 相似文献
13.
Lake Algonquin, the largest glacial lake of the Great Lakes area, ended prior to 10,000 years BP by drainage to the Ottawa
Valley as the North Bay outlet was deglaciated. At that time, the outlet area was isostatically downwarped more than 100 m;
resulting low water, river-linked lakes Chippewa, Stanley, and Hough, lowstands in the basins of lakes Michigan, Huron, and
Georgian Bay respectively, were much below present lake level. While water levels were low, about half of the present lake
area was dry land. The land above the lowstands was dissected by streams and became forested. Uplift of the North Bay outlet
between 10,000 and 5,000 years BP raised lake level to above the present (the Nipissing transgression), submerging the forest
and valley system. Submerged stumps from those forests have often been encountered on the present lake floor; some stumps
have been dated.
Four sites in Ontario (Parkhill, Owen Sound, St. Joseph Island, Meaford) provide on-land evidence of pre-Nipissing drainage
and valley formation. Radiocarbon ages of valley fill organic materials range from 7,310 to 5,410 years BP. At three sites,
present drainage is known to be displaced from the pre-Nipissing drainage. Geophysical methods (EM, GPR, resistivity) have
been used to refine valley location and morphology at Parkhill and Meaford. There is the potential of tracing the valleys
down slope to the low-water shorelines with shipboard geophysics, with implications for archaeology, hydrology and hydrogeology,
paleogeography, and Great Lakes history.
This is the eighth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were
presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University
of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue. 相似文献
14.
C. F. M. Lewis G. D. M. Cameron T. W. Anderson C. W. HeilJr. P. L. Gareau 《Journal of Paleolimnology》2012,47(3):493-511
Water levels in the Lake Erie basin are inferred from glacial lake times to present. An era of early to middle Holocene lowstands
is defined below outlets by a submerged paleo-beach, and truncated reflectors in glaciolacustrine sediment beneath a mud-covered
wave-cut terrace. Also, the glacial clay surface above the paleo-shore level has elevated shear strength because of porewater
drainage during subaerial exposure. Below the paleo-shore where exposure did not occur, clay strength remained normal. Sedimentation
rates were reduced during the lowstands. The distortion of once-level shore zone indicators by differential glacial rebound
was removed by computing original elevations of the indicators using an empirical model of rebound based on observations of
upwarped former lake shorelines. Erie water-level history was inferred from a plot of the original elevations of lake-level
constraints and outlets versus age. The lake history was validated by reference to ~83 water-level indicators, not used as
constraints. During the deglaciation, lake-crossing moraines were likely eroded by fluvial drainage into low-level Lake Ypsilanti
and a subsequent unnamed low lake to produce the Lorain Valley and Pennsylvania Channel. Once inflow from the upper Great
Lakes basins was directed to Ottawa Valley about 10,400 (12,270 cal BP), Erie water levels descended in a dry, evaporative
climate to a closed lowstand during which ostracode δ18O increased ~2‰ above present values. Lake level began to rise 6,000 to 7,000 (6,830 to 7,860 cal) BP in response to increased
atmospheric moisture and later, to northern inflow as the Nipissing Transgression returned upper Great Lakes drainage to Lake
Erie by about 5,200 (6,000 cal) BP. At that time, the lake overflowed the uplifted Lyell–Johnson Sill north (downstream) of
the present Niagara Falls at higher-than-present levels. After recession of the Falls breached this sill about ~3,500 (~3,770 cal)
BP, Lake Erie fell 3–4 m to its present Fort Erie–Buffalo Sill. The extended low-water phase with its isolated sub-basins
could have restricted migration of aquatic fauna. The early to middle Holocene closed-basin response highlights the sensitivity
of Lake Erie to climatic reductions in its water budget. 相似文献
15.
D. Enters E. Kirilova A. F. Lotter A. Lücke J. Parplies S. Jahns G. Kuhn B. Zolitschka 《Journal of Paleolimnology》2010,43(4):719-737
Lacustrine sediments in north-eastern Germany have rarely been used as archives to address the effects of climate change and
human impact on both lake ecosystem and landscape evolution for this region. Sacrower See, a hardwater lake located in Brandenburg,
provides a unique sediment record covering the past 13,000 years which was used to reconstruct climatic and anthropogenic
forcing on lacustrine sedimentation. Time control is provided by 12 AMS 14C dates of terrestrial plant remains, the Laacher See Tephra, and the onset of varve formation in AD 1870 (80 cal. BP). Geochemical
(including XRF logging of major elements, CNS analyses as well as δ13Corg and δ15N measurements) and pollen analyses allowed detecting detailed environmental changes in the sediment record. During the Younger
Dryas cold phase increased soil erosion and hypolimnetic oxygen depletion enhanced the nutrient supply to the lake water causing
eutrophic conditions. The beginning of the Holocene is characterized by large changes in C/N ratios, total sulphur, δ13C of bulk organic matter as well as in K, Si, and Ti, reflecting the response of the lake’s catchment to climatic warming.
Reforestation reduced the influx of detrital particles and terrestrial organic matter. The first, rather weak evidence of
human impact is documented only in the pollen record at 5,500 cal. BP. However, until 3,200 cal. BP sedimentological and geochemical
parameters indicate relatively stable environmental conditions. During periods of intense human impact at around 3,200, 2,800,
and 900 cal. BP peaks in Ti and K represent phases of increased soil erosion due to forest clearing during the Bronze Age,
Iron Age, and Medieval Times, respectively. In general, greater variation is observed in most variables during these perturbations,
indicating less stable environmental conditions. The steady rise of biogenic silica accumulation rates during the Holocene
reflects an increasing productivity of Sacrower See until diatoms were outcompeted by other algae during the last centuries.
The applied multi-proxy approach fosters the interpretation of the sediment record to reveal a consistent picture of environmental
change including environmental factors controlling lake ontogeny and the effects of human impact. 相似文献
16.
Ricarda Voigt Eberhard Grüger Janina Baier Dieter Meischner 《Journal of Paleolimnology》2008,40(4):1021-1052
Studies combining sedimentological and biological evidence to reconstruct Holocene climate beyond the major changes, and especially
seasonality, are rare in Europe, and are nearly completely absent in Germany. The present study tries to reconstruct changes
of seasonality from evidence of annual algal successions within the framework of well-established pollen zonation and 14C-AMS dates from terrestrial plants. Laminated Holocene sediments in Lake Jues (10°20.7′ E, 51°39.3′ N, 241 m a.s.l.), located
at the SW margin of the Harz Mountains, central Germany, were studied for sediment characteristics, pollen, diatoms and coccal
green algae. An age model is based on 21 calibrated AMS radiocarbon dates from terrestrial plants. The sedimentary record
covers the entire Holocene period. Trophic status and circulation/stagnation patterns of the lake were inferred from algal
assemblages, the subannual structure of varves and the physico-chemical properties of the sediment. During the Holocene, mixing
conditions alternated between di-, oligo- and meromictic depending on length and variability of spring and fall periods, and
the stability of winter and summer weather. The trophic state was controlled by nutrient input, circulation patterns and the
temperature-dependent rates of organic production and mineralization. Climate shifts, mainly in phase with those recorded
from other European regions, are inferred from changing limnological conditions and terrestrial vegetation. Significant changes
occurred at 11,600 cal. yr. BP (Preboreal warming), between 10,600 and 10,100 cal. yr. BP (Boreal cooling), and between 8,400
and 4,550 cal. yr. BP (warm and dry interval of the Atlantic). Since 4,550 cal. yr. BP the climate became gradually cooler,
wetter and more oceanic. This trend was interrupted by warmer and dryer phases between 3,440 and 2,850 cal. yr. BP and, likely,
between 2,500 and 2,250 cal. yr. BP. 相似文献
17.
C. F. M. Lewis C. W. HeilJr. J. B. Hubeny J. W. King T. C. MooreJr. D. K. Rea 《Journal of Paleolimnology》2007,37(3):435-452
J.L. Hough in 1962 recognized an erosional unconformity in the upper section of early postglacial lake sediments in northwestern
Lake Huron. Low-level Lake Stanley was defined at 70 m below present water surface on the basis of this observation, and was
inferred to follow the Main Algonquin highstand and Post-Algonquin lake phases about 10 14C ka, a seminal contribution to the understanding of Great Lakes history. Lake Stanley was thought to have overflowed from
the Huron basin through the Georgian Bay basin and the glacio-isostatically depressed North Bay outlet to Ottawa and St. Lawrence
rivers. For this overflow to have occurred, Hough assumed that post-Algonquin glacial rebound was delayed until after the
Lake Stanley phase.
A re-examination of sediment stratigraphy in northwestern Lake Huron using seismic reflection and new core data corroborates
the sedimentological evidence of Hough’s Stanley unconformity, but not its inferred chronology or the level of the associated
lowstand. Erosion of previously deposited sediment, causing the gap in the sediment sequence down to 70 m present depth, is
attributed to wave erosion in the shoreface of the Lake Stanley lowstand. Allowing for non-deposition of muddy sediment in
the upper 20 m approximately of water depth as occurs in the present Great Lakes, the inferred water level of the Stanley
lowstand is repositioned at 50 m below present in northwestern Lake Huron. The age of this lowstand is about 7.9 ± 0.314C ka, determined from the inferred 14C age of the unconformity by radiocarbon-dated geomagnetic secular variation in six new cores. This relatively young age shows
that the lowstand defined by Hough’s Stanley unconformity is the late Lake Stanley phase of the northern Huron basin, youngest
of three lowstands following the Algonquin lake phases. Reconstruction of uplift histories for lake level and outlets shows
that late Lake Stanley was about 25–30 m below the North Bay outlet, and about 10 m below the sill of the Huron basin. The
late Stanley lowstand was hydrologically closed, consistent with independent evidence for dry regional climate at this time.
A similar analysis of the Chippewa unconformity shows that the Lake Michigan basin also hosted a hydrologically closed lowstand,
late Lake Chippewa. This phase of closed lowstands is new to the geological history of the Great Lakes.
This is the ninth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004),
held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M Lewis were guest editors of this special
issue. 相似文献
18.
Lucia Wick Jacqueline F.N. van Leeuwen Willem O. van der Knaap André F. Lotter 《Journal of Paleolimnology》2003,30(3):261-272
Pollen and plant macrofossils were analysed at Sägistalsee (1935 m asl), a small lake near timber-line in the Swiss Northern Alps. Open forests with Pinus cembra and Abies alba covered the catchment during the early Holocene (9000–6300 cal. BP), suggesting subcontinental climate conditions. After the expansion of Picea abies between 6300 and 6000 cal. BP the subalpine forest became denser and the tree-line reached its maximum elevation at around 2260 m asl. Charcoal fragments in the macrofossil record indicate the beginning of Late-Neolithic human impact at ca. 4400 cal. BP, followed by a extensive deforestation and lowering of the forest-limit in the catchment of Sägistalsee at 3700 cal. BP (Bronze Age). Continuous human activity, combined with a more oceanic climate during the later Holocene, led to the local extinction of Pinus cembra and Abies alba and favoured the mass expansion of Picea and Alnus viridis in the subalpine area of the Northern Alps. The periods before 6300 and after 3700 cal. BP are characterised by high erosion activity in the lake's catchment, whereas during the phase of dense Picea-Pinus cembra-Abies forests (6300–3700 cal. BP) soils were stable and sediment-accumulation rates in the lake were low. Due to decreasing land-use at higher altitudes during the Roman occupation and the Migration period, forests spread beween ca. 2000 and 1500 cal. BP, before human impact increased again in the early Middle Ages. Recent reforestation due to land-use changes in the 20th century is recorded in the top sediments. Pollen-inferred July temperature and annual precipitation suggest a trend to cooler and more oceanic climate starting at about 5500 cal. BP. 相似文献
19.
F. Boenzi M. Caldara D. Capolongo P. Dellino M. Piccarreta O. Simone 《Geomorphology》2008,102(3-4):297-306
Studies in the middle Basento river basin supported by reliable chronological data (tephra layers and a number of absolute datings) have allowed the reconstruction of Late Pleistocene–Holocene geomorphological evolution of the middle to low Fossa Bradanica area (Basilicata, southern Italy). The original Upper Pleistocene hillslope has been dissected by deep gullies leaving relict slope pediments. Holocene filling of the Basento river valley and gullies occurred as a succession of downcut and fill episodes. A first phase of accumulation occurred in the Late Neolithic, which was followed by a downcutting between 4500 and 3700 cal. yr BP. A second deposition phase took place in the Greek–Roman period between 2800 and 1620 cal. yr BP, which was interrupted at around 2500 cal. yr BP. Another downcutting phase took place between 1620 and 1500 cal. yr BP, followed by a deposition phase between 1440 and 1000 cal. yr BP. After 1000 cal. yr BP a deep downcutting took place. Evidence collected with this study, coupled with climate data recorded in other Italian and European locations, suggests that filling and downcutting episodes in Fossa Bradanica were predominantly climate-driven. Anthropogenic impact only intensified or weakened these processes. 相似文献
20.
Changes in the diatom assemblages preserved in a sediment core taken from a small lake located north of arctic treeline on the western Taimyr Peninsula, Russia, were examined in order to investigate late Holocene (i.e., ca 5000 cal yr BP to present) climatic and environmental changes within the region. Early diatom assemblages were dominated by benthic Fragilaria taxa and indicate a transitional phase in the lake history, most likely reflecting lake development and environmental change associated with treeline retreat to the south of the study site. Concurrent with pollen and macrofossil evidence of a vegetation shift to shrub tundra in the catchment basin at ca 4200 cal yr BP, an increase in cold-water taxa, followed by little change in diatom assemblages until ca 2800 cal yr BP, suggests that conditions were relatively cool and stable at this time. The last 2000 years of the Middendorf Lake record have been marked by fluctuating limnological conditions, characterized by striking successional shifts between Fragilaria pinnata and Aulacoseira distans var. humilis. Recent conditions in Middendorf Lake indicate an increase in diatom taxa previously rare in the record, possibly associated with twentieth-century climatic warming. The Middendorf Lake record indicates that significant limnological change may occur in the absence of catchment vegetation shifts, suggesting late-Holocene decoupling of aquatic and terrestrial responses to climatic and hydrological change. Our study results represent one of the few paleoecological records currently available from northern Russia, and highlight the need for further development of calibration data sets from this region. 相似文献