scholarly journals A New Framework for the Pleistocene Stratigraphy of the Central St. Lawrence Lowland, Southern Québec

2007 ◽  
Vol 43 (2) ◽  
pp. 119-129 ◽  
Author(s):  
Michel Lamothe
Keyword(s):  
Environmental Changes ◽  
Borehole Data ◽  
Depositional Sequence ◽  
Stratigraphic Framework ◽  
Stage 4 ◽  
Lithostratigraphic Units ◽  
New Framework ◽  
St Lawrence River ◽  
Glacial Advance ◽  
The Last Glacial

ABSTRACT For three decades, a stratigraphic framework involving one glaciation with two major ice advances (represented by the Bécancour Till and Gentilly Till), separated by one brief interstade (represented by the St. Pierre Sediments), has been invoked to explain the lithostratigraphic succession of Pleistocene sediments exposed in the St. Lawrence Lowland of southern Québec. New exposures found along the bluffs of the St. Lawrence River and recent borehole data provide evidence that the Pleistocene depositional sequence is the result of three glacial advances and two nonglacial events, each represented by organic-bearing units. Two lithostratigraphic units (Lotbinière Sand and Lévrard Till) and three climatostratigraphic units (St. Lawrence Stade, Grondines Interstade and Les Becquets Interstade) are introduced in the stratigraphie nomenclature. No definite age can be assigned to the lowermost till (Bécancour?) but it is now believed to be pre-Sangamonian. Field observations and geochronological data suggest the lower and upper interstadial sediments, and an intervening glacial unit represent brief but severe environmental changes that occurred at the beginning of the Wisconsin Glaciation, ca. 90-70 ka BP. This sequence may correlate with marine isotope stage 5a, stage 4, and the earliest part of stage 3. The age of the onset of the last glacial advance (Gentilly Till) is problematic, possibly ranging from 60 to 30 ka BP.

scholarly journals Identifying Changes in Sediment Texture along an Ephemeral Gravel-Bed Stream Using Electrical Resistivity Tomography 2D and 3D

2021 ◽  
Vol 11 (7) ◽  
pp. 3030
Author(s):  
Marcos A. Martínez-Segura ◽  
Carmelo Conesa-García ◽  
Pedro Pérez-Cutillas ◽  
Pedro Martínez-Pagán ◽  
Marco D. Vásconez-Maza
Keyword(s):  
Electrical Resistivity ◽  
Cross Sections ◽  
Electrical Resistivity Tomography ◽  
Environmental Changes ◽  
Subsurface Layer ◽  
Sediment Texture ◽  
Borehole Data ◽  
Resistivity Tomography ◽  
Gravel Bed ◽  
Basin Scale

Differences in deposit geometry and texture with depth along ephemeral gravel-bed streams strongly reflect fluctuations in bedload which are due to environmental changes at the basin scale and to morphological channel adjustments. This study combines electrical resistivity tomography (ERT) with datasets from borehole logs to analyse the internal geometry of channel cross-sections in a gravel-bed ephemeral stream (southeast Spain). The survey was performed through longitudinal and transverse profiles in the upper channel stretch, of 14 to 30 m in length and 3 to 6 m in depth, approximately. ERT values were correlated with data on sediment texture as grain size distribution, effective grain sizes, sorting, and particle shape (Zingg’s classification). The alluvial channel-fills showed the superposition of four layers with uneven thickness and arrangement: (1) the softer rocky substrate (<1000 Ω.m); (2) a thicker intermediate layer (1000 to 2000 Ω.m); and (3) an upper set composed of coarse gravel and supported matrix, ranging above 2000 Ω.m, and a narrow subsurface layer, which is the most resistive (>5000 Ω.m), corresponding to the most recent armoured deposits (gravel and pebbles). The ERT results coupled with borehole data allowed for determining the horizontal and vertical behaviour of the materials in a 3D model, facilitating the layer identification.

Mapping faults in an urban environment from borehole data (Oviedo, NW Spain)

2021 ◽  
Author(s):  
Luis Pando ◽  
Carlos López-Fernández ◽  
Germán Flor-Blanco ◽  
Sergio Llana-Fúnez
Keyword(s):  
Site Investigation ◽  
Geological Mapping ◽  
City Centre ◽  
Nw Spain ◽  
Regional Literature ◽  
Borehole Data ◽  
Urban Core ◽  
Structural Relationships ◽  
Geotechnical Database ◽  
Lithostratigraphic Units

&lt;p&gt;The detailed geological mapping in built-up areas presents challenges that arise mainly from the covering of outcrops, and the erase of natural geomorphological features during earthmoving works related to urban development. However, it also benefits from the existence of closely spaced site investigation data, including boreholes, not commonly available outside the cities.&lt;/p&gt;&lt;p&gt;This contribution explains the procedure carried out to improve the interpretation of faults below the city centre of an urban core located in NW Spain. Oviedo is placed on a basin formed by an alternation of sub-horizontal carbonate and siliciclastic formations of Cretaceous age, over which lies an unconformable cover of Paleogene fluvial-lacustrine deposits mostly composed by clays and marls. The paleorelief over which the Paleogene was deposited results in great lateral changes in the thickness of these sediments. Moreover, the basin was deformed during the Alpine convergence in northern Iberia developing an open syncline oriented East-West. During the shortening, a number of minor faults cutting across the gently dipping Cretaceous and Paleogene deposits affect moderately the cartographic pattern of lithostratigraphic units.&lt;/p&gt;&lt;p&gt;Therefore, this research was focused on the preferential use of information on the ground provided by hundreds of rotary boreholes managed through a GIS-type geotechnical database. The procedure of semiautomatic identification consisted essentially of investigating the spatial variations of the boundary between two Cretaceous formations, in order to find anomalies attributable to fault displacements. In using this boundary as a strain marker for post-depositional deformation, two scales were approached, one aimed at the identification of large faults, and another with greater detail based on trend-surface analysis for fractures of smaller size and local incidence (vertical offset less than 10 m).&lt;/p&gt;&lt;p&gt;The research has allowed to discuss faults deduced in previous geological maps, helping to interpret thickenings related to the paleorelief, and also to recognize the existence of structures not described in the regional literature. This study provides also better constrains to the analysis of the structural relationships between the faults affecting the Mesozoic-Palaeogene basin, and the Alpine reactivation of the underlying Palaeozoic basement.&lt;/p&gt;

Using precise CA-TIMS ages of volcanic air-fall tuff beds in correlating the Walloon Coal Measures of the Surat Basin, Australia

2017 ◽  
Vol 57 (2) ◽  
pp. 810 ◽  
Author(s):  
Carmine Wainman ◽  
Peter McCabe
Keyword(s):  
High Precision ◽  
Sedimentary Facies ◽  
Time Frame ◽  
Upper Jurassic ◽  
Marine Strata ◽  
Stratigraphic Framework ◽  
Lithostratigraphic Units ◽  
Spectrometry Technique ◽  
Discontinuous Nature ◽  
Coal Measures

The Upper Jurassic Walloon Coal Measures of the Surat Basin is one of Australia’s largest and most productive gas provinces. Despite the drilling of over 8500 wells and numerous publications, the stratigraphic framework is poorly defined. The laterally discontinuous nature of the sedimentary facies, including coals and fluvial channel sandstones, makes correlation difficult. The abundance of volcanic air-fall tuff beds within strata across the basin provides a unique opportunity to independently verify existing stratigraphic frameworks. Using the high-precision chemical abrasion thermal ionisation mass spectrometry technique, zircon grains from 28 tuff beds have been successfully dated within an error margin of less than 100 kyr. These dates substantially revise biostratigraphic and lithostratigraphic frameworks. Lithostratigraphic units are diachronous across the basin. In addition, the sparsity of key spore–pollen taxa limits the application of biostratigraphy. The complex interplay of climate and subsidence on facies distributions can now be documented over a time frame of ~4 Ma. Syntectonism played an important role in variable palaeodrainage patterns across the basin, the frequency of fluvial avulsions and preferential sites of peat accumulation through time. The new stratigraphic framework should aid in future exploration for coal seam gas in the area. Dating tuff beds using high-precision dating techniques should also assist in correlation of non-marine strata elsewhere in the world.

Labrador Sea bio-, tephro-, oxygen isotopic stratigraphy and Late Quaternary paleoceanographic trends

1980 ◽  
Vol 17 (7) ◽  
pp. 831-854 ◽  
Author(s):  
R. H. Fillon ◽  
J. C. Duplessy
Keyword(s):  
Deep Water ◽  
Late Quaternary ◽  
Planktonic Foraminifera ◽  
Open Water ◽  
Labrador Sea ◽  
Surface Cooling ◽  
Stratigraphic Framework ◽  
Stage 4 ◽  
Oxygen Isotopic ◽  
Stage 1

A stratigraphic framework for eastern Labrador Sea cores has been developed for the interval 0–90 000 years BP through analysis of oxygen isotopes, volcanic ash, benthonic foraminifera, and the radiolarian Diplocyclas davisiana. Benthonic and planktonic foraminiferal isotope stratigraphy and the time scale of Shackleton and Opdyke provide a basis for the approximate dating of a series of marker events which include ash zones at ca. 59 000 and ≤ 21 000 years BP; benthonic foraminiferal abundance maxima at ca. 83 000, 75 000, 60 000, 19 000, and 3000 years BP; and D. davisiana percentage maxima at ca. 90 000, 73 000, 64 000, 54 000, 45 000 – 32 000, and 10 000 years BP. Incursions of subpolar planktonic foraminifera into the area during parts of isotopic stage 2 (between about 13 000 and 25 000 years BP but probably excluding the 15 000–18 000 years BP glacial maximum interval) and during the isotopic stage 4/5a transition (around 75 000 years BP) suggest that the eastern Labrador Sea was free of sea ice, at least in summer during periods of rapid continental ice sheet growth which lead to the isotopic stage 4 and stage 2 glacial maxima. A larger than normal stage 1/stage 2 difference in the isotopic composition of benthonic foraminifera (1.8‰) implies that this open water and attendant surface cooling was a potential source for colder than modern deep water. In contrast the Norwegian Sea was a reservoir of warmer than modern deep water during the last glacial.

Millennial‐scale environmental changes in the northwestern Japan Sea during the last glacial cycle

Boreas ◽  
2020 ◽  
Author(s):  
Tatiana A. Evstigneeva ◽  
Marina V. Cherepanova ◽  
Sergey A. Gorbarenko ◽  
Xuefa Shi ◽  
Alexander A. Bosin ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Japan Sea ◽  
Glacial Cycle ◽  
Last Glacial ◽  
The Last Glacial ◽  
Millennial Scale

scholarly journals A new terrestrial palaeoenvironmental record from the Bering Land Bridge and context for human dispersal

2018 ◽  
Vol 5 (6) ◽  
pp. 180145 ◽  
Author(s):  
Matthew J. Wooller ◽  
Émilie Saulnier-Talbot ◽  
Ben A. Potter ◽  
Soumaya Belmecheri ◽  
Nancy Bigelow ◽  
...  
Keyword(s):  
Climate Models ◽  
Environmental Changes ◽  
Land Bridge ◽  
Human Dispersal ◽  
South Central ◽  
Bering Land Bridge ◽  
Last Glaciation ◽  
Close Proximity ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Palaeoenvironmental records from the now-submerged Bering Land Bridge (BLB) covering the Last Glacial Maximum (LGM) to the present are needed to document changing environments and connections with the dispersal of humans into North America. Moreover, terrestrially based records of environmental changes are needed in close proximity to the re-establishment of circulation between Pacific and Atlantic Oceans following the end of the last glaciation to test palaeo-climate models for the high latitudes. We present the first terrestrial temperature and hydrologic reconstructions from the LGM to the present from the BLB's south-central margin. We find that the timing of the earliest unequivocal human dispersals into Alaska, based on archaeological evidence, corresponds with a shift to warmer/wetter conditions on the BLB between 14 700 and 13 500 years ago associated with the early Bølling/Allerød interstadial (BA). These environmental changes could have provided the impetus for eastward human dispersal at that time, from Western or central Beringia after a protracted human population standstill. Our data indicate substantial climate-induced environmental changes on the BLB since the LGM, which would potentially have had significant influences on megafaunal and human biogeography in the region.

Tephra anchored floating varve chronology covering ca. 19.0-11.0 ka BP in new core from Lake Lago Grande di Monticchio: preliminary results

2020 ◽  
Author(s):  
Xueru Zhao ◽  
Sabine Wulf ◽  
Markus J. Schwab ◽  
Rik Tjallingii ◽  
Achim Brauer
Keyword(s):  
High Resolution ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Methodological Approach ◽  
Radiocarbon Dates ◽  
Thin Sections ◽  
Last Glacial ◽  
Varve Chronology ◽  
Varve Counting ◽  
The Last Glacial

&lt;p&gt;The high-resolution Monticchio (MON) sediment record has been demonstrated to be a key archive for reconstructing climate and environmental changes in the central Mediterranean for the last glacial-interglacial cycle. New sediment cores have been retrieved in April 2016 to investigate particularly the transition from the Last Glacial Maximum into the Holocene with a new high-resolution methodological approach. A floating varve chronology spanning ca. 8,000 years has been established by varve counting on thin sections using a petrographic microscope and layer thickness based sedimentation rate estimates for non- or poorly varved intervals. Varve counting is based on detailed seasonal deposition models of five different varve types. The resulting floating chronology consist of 66.6% individually counted varves and 33.4% interpolated years. The uncertainty estimate of the floating chronology has been determined by double counting and amounts to &amp;#177;5.8%.&lt;/p&gt;&lt;p&gt;The floating chronology is anchored to an absolute chronology using the Agnano Pomici Principali tephra, dated at 11,999&amp;#177;52 cal yrs BP from paleosols overlying proximal tephra (Bronk Ramsey et al. 2015), is a suitable anchoring point to cross correlation. The resulting varve-based chronology has been compared with several other marker tephras dated elsewhere including the Soccavo 4 tephra (11,700&amp;#177;150 cal yrs BP), the Neapolitan Yellow Tuff (NYT; 14,194&amp;#177;172 cal yrs BP) and the Greenish tephra (19226&amp;#177;104 cal yrs BP). Further comparison with published (Hajdas et al. 1997) and new radiocarbon dates from different terrestrial macro remains are discussed in this paper. This study presents an independent chronology for the last glacial/interglacial transition for a comparison of MON data with high-resolution lake records western and central Europe.&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Bronk Ramsey, C., P. G. Albert, S. P. E. Blockley, M. Hardiman, R. A. Housley, C. S. Lane, S. Lee, I. P. Matthews, V. C. Smith &amp; J. J. Lowe (2015) Improved age estimates for key Late Quaternary European tephra horizons in the RESET lattice. Quaternary Science Reviews, 118&lt;strong&gt;,&lt;/strong&gt; 18-32.&lt;/p&gt;&lt;p&gt;Hajdas, I., G. Bonani, B. Zolitschka, A. Brauer &amp; J. Negendank (1997) 14C Ages of Terrestrial Macrofossils from Lago Grande Di Monticchio (Italy). Radiocarbon, 40&lt;strong&gt;,&lt;/strong&gt; 803-807.&lt;/p&gt;

Problems in the Stone Age of South-East Asia

1993 ◽  
Vol 59 ◽  
pp. 1-15 ◽  
Author(s):  
T. E. G. Reynolds
Keyword(s):  
East Asia ◽  
Late Pleistocene ◽  
Environmental Changes ◽  
Middle Pleistocene ◽  
South East Asia ◽  
Site Location ◽  
Land Area ◽  
Dominant Characteristic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Whilst research has shown many faults with the Movius scheme of a Middle Pleistocene group of Chopper/Chopping tool industries in South-East Asia, it remains a fact that pebble tool industries are still the dominant characteristic of the South-East Asian record. Exploration has now revealed hundreds of Late Pleistocene and Holocene sites in Mainland South-East Asia and these are archaeologically very different from cave sites in Europe. Further problems exist with the current nomenclature of later industries, such as the Hoabinhian and the Neolithic, for there is a large amount of overlap between such assemblages. Should such factors as economy, site location, etc. be used to assist clarification of such problems?This paper outlines some of these issues and reveals that the pebble tool tradition as it is widely known in South-East Asia is a relatively recent phenomenon dating back to the Last Glacial Maximum (LGM). A possible reason for the change from flake to pebble tool industrial types and in the visibility of sites is the environmental changes and rise in sea level which submerged over half the available land area in the region during the Late Pleistocene. An existing broad spectrum system of exploitation was likely to have been intensified as a result of this.

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