Change of channel pattern and construction of fluvial terraces driven by SAMS since the LGM in southeastern South America: records from Tietê River, Brazil

2021 ◽  
Author(s):  
Caio Breda ◽  
Fabiano Nascimento Pupim
Keyword(s):  
Environmental Conditions ◽  
Environmental Changes ◽  
Late Quaternary ◽  
River System ◽  
Luminescence Dating ◽  
Southeastern Brazil ◽  
Stream Power ◽  
Climatic Fluctuations ◽  
Tropical Regions ◽  
Fluvial Terraces

<p>The last 30 ka is a period marked by well-documented abrupt environmental changes on Earth. Despite the growing efforts to investigate the effects of past environmental changes in the fluvial dynamics, there is a lack of studies in intraplate tropical regions. Here, we applied geomorphological, sedimentological, and optically stimulated luminescence dating (OSL) technics to investigate the effects of environmental factors on the evolution of the Upper and Middle Tietê River during the Late Quaternary. Tietê River is one of the most important rivers of the southeast of Brazil, flowing from steepest to low-relief intraplate terrains, and under tropical climate. In order to understand the responses of the Tietê River system to environmental changes during the Late Quaternary, two main questions were tentatively answered: (i) what are the most important allogeneic factors for the evolution of this system?; (ii) how did climatic fluctuations affect river dynamics over time? We recognized a sequence of seven terraces, from 2 to 105 m above the channel, in the Middle Tietê valley. These terraces are formed by thin deposits (< 10 m), composed of sandy and conglomeratic sediments. The high and intermediate terrace levels of the Middle Tietê River are strath, while the low terraces of the middle reach are cut-and-fill. The formation of seven terrace levels in the Middle Tietê River was controlled by the combination of low erosion resistance of the lithological substrate and high stream power and coarse bedload that increase the erosion efficiency of the channels. OSL dating of sedimentary deposits in different terrace levels indicate 5 periods of aggradation in the Middle Tietê valley since the Last Glacial Maximum: 18.5 ± 2.0 ka; 9.8 ± 1.0 to 8.6 ± 0.8 ka; 7.1 ± 0.7 to 5.8 ± 0.5 ka; 4.2 ± 0.4 to 3.1 ± 0.3 ka; and 0.6 ± 0.06 ka. The results indicate that the activity of the South American Monsoon System induced the occurrence of climatic fluctuations and changes in vegetation cover in the river valleys of southeastern Brazil over the past 20 ka. The aggradation periods are correlated with more arid environmental conditions and sparser vegetation, while the incision events in the valley developed under transitions to humid environmental conditions and stimulated by vegetation recovery.</p><p><strong>Key-words: </strong>Tietê River, fluvial evolution, fluvial terraces, Quaternary geochronology.</p>

Late Quaternary aggradation and incision in the headwaters of the Yangtze River, eastern Tibetan Plateau, China

2021 ◽  
Author(s):  
Yang Yu ◽  
Xianyan Wang ◽  
Shuangwen Yi ◽  
Xiaodong Miao ◽  
Jef Vandenberghe ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Yangtze River ◽  
Late Quaternary ◽  
Cold Climate ◽  
Luminescence Dating ◽  
Tectonic Activity ◽  
The Yangtze River ◽  
Eastern Tibetan Plateau ◽  
Sedimentary Process ◽  
Fluvial Terraces

River aggradation or incision at different spatial-temporal scales are governed by tectonics, climate change, and surface processes which all adjust the ratio of sediment load to transport capacity of a channel. But how the river responds to differential tectonic and extreme climate events in a catchment is still poorly understood. Here, we address this issue by reconstructing the distribution, ages, and sedimentary process of fluvial terraces in a tectonically active area and monsoonal environment in the headwaters of the Yangtze River in the eastern Tibetan Plateau, China. Field observations, topographic analyses, and optically stimulated luminescence dating reveal a remarkable fluvial aggradation, followed by terrace formations at elevations of 55−62 m (T7), 42−46 m (T6), 38 m (T5), 22−36 m (T4), 18 m (T3), 12−16 m (T2), and 2−6 m (T1) above the present floodplain. Gravelly fluvial accumulation more than 62 m thick has been dated prior to 24−19 ka. It is regarded as a response to cold climate during the last glacial maximum. Subsequently, the strong monsoon precipitation contributed to cycles of rapid incision and lateral erosion, expressed as cut-in-fill terraces. The correlation of terraces suggests that specific tectonic activity controls the spatial scale and geomorphic characteristics of the terraces, while climate fluctuations determine the valley filling, river incision and terrace formation. Debris and colluvial sediments are frequently interbedded in fluvial sediment sequences, illustrating the episodic, short-timescale blocking of the channel ca. 20 ka. This indicates the potential impact of extreme events on geomorphic evolution in rugged terrain.

Geological importance of luminescence dates in Oman and the Emirates: An overview

2011 ◽  
Vol 38 (3) ◽  
pp. 259-271 ◽  
Author(s):  
Kenneth Glennie ◽  
Steven Fryberger ◽  
Caroline Hern ◽  
Nicholas Lancaster ◽  
James Teller ◽  
...  
Keyword(s):  
Late Quaternary ◽  
Arabian Gulf ◽  
River System ◽  
Luminescence Dating ◽  
Glacial Cycle ◽  
Sea Levels ◽  
Gulf Of Oman ◽  
Climatic Variations ◽  
Wind Activity ◽  
The Last Glacial

AbstractIn the Wahiba Sands of eastern Oman, luminescence dating of sands enables us to relate wind activity to climatic variations and the monsoon cycle. These changes resulted from Polar glacial/interglacial cyclicity and changes in global sea levels and wind strengths. Luminescence dates show that development of the Sands began over 230 ka ago when the sand-driving winds were the locally arid, northward-blowing SW Monsoon.During late Quaternary low sea levels, the Tigris-Euphrates river system flowed across the floor of the Persian/Arabian Gulf to the Gulf of Oman SE of the Strait of Hormuz. OSL-dated sands containing calcareous bioclastic fragments deflated from the exposed Gulf floor during glacial low-water periods indicate that during the last glacial cycle, and at least one earlier cycle (∼120–200 ka and possibly as far back as 291 ka), the floor of the Arabian Gulf was exposed. This is deduced from the presence of aeolian dune sands containing bioclastic detritus on the coastal plain of the Emirates and south into Al Liwa (Abu Dhabi), which were built by northern “Shamal” winds. Those calcareous sands now locally overlie sabkhas formed during interglacial high sea levels. Within the present interglacial, marine flooding of the Gulf occurred between about 12 and 6 ka.

Late Quaternary Vegetational Changes in a Marsh Forest in Southeastern Brazil with Comments on Prehistoric Human Occupation

Radiocarbon ◽  
2015 ◽  
Vol 57 (5) ◽  
pp. 737-753 ◽  
Author(s):  
Walter Mareschi Bissa ◽  
Mauro B de Toledo
Keyword(s):  
Sediment Core ◽  
Environmental Changes ◽  
Human Impacts ◽  
Late Quaternary ◽  
Southeastern Brazil ◽  
Pollen Record ◽  
Important Indicator ◽  
Climate Conditions ◽  
Ams Radiocarbon Dating ◽  
Se Brazil

This article presents a palynological study carried out on a sediment core from a peat deposit in Serra de Botucatu, in SÃo Paulo State, southeastern Brazilian Plateau. This region has been covered by grassland vegetation and forest patches throughout the recorded period. AMS radiocarbon dating plus palynological analysis of 27 samples from the sediment core allowed the recognition of several environmental changes that took place during the last 33,000 yr recorded in the core. The relationship between sedimentation rates and changes in the abundance of plants recognized through their pollen record, particularly a few important indicator species, provided the paleoenvironmental history for the Serra de Botucatu region, allowing the identification of changes in climate conditions and comparison with other regions in Brazil. One of the most remarkable features of this record is the cold and humid conditions during the Last Glacial Maximum, which diverges from previous interpretations for southeastern and southern Brazil but is in good agreement with paleoclimatic data from trace elements from cave stalagmites in SE Brazil. No indications of human impacts on the vegetation were found in this record.

Insights into Holocene megafauna survival and extinction in southeastern Brazil from new AMS 14C dates

2011 ◽  
Vol 79 (2) ◽  
pp. 152-157 ◽  
Author(s):  
Alex Hubbe ◽  
Mark Hubbe ◽  
Ivo Karmann ◽  
Francisco W. Cruz ◽  
Walter A. Neves
Keyword(s):  
South America ◽  
Human Activities ◽  
Environmental Changes ◽  
Late Quaternary ◽  
Southeastern Brazil ◽  
Radiocarbon Dates ◽  
Archaeological Data ◽  
Extinction Event ◽  
Ground Sloth ◽  
Ground Sloths

AbstractThe extinction of late Quaternary megafauna in South America has been extensively debated in past decades. The majority of the hypotheses explaining this phenomenon argue that the extinction was the result of human activities, environmental changes, or even synergism between the two. Although still limited, a good chronological framework is imperative to discuss the plausibility of the available hypotheses. Here we present six new direct AMS 14C radiocarbon dates from the state of São Paulo (Brazil) to further characterize the chronological distribution of extinct fauna in this part of South America. The new dates make evident that ground sloths, toxodonts, and saber-toothed cats lived in the region around the Pleistocene/Holocene transition, and in agreement with previous studies, also suggest an early Holocene survival for the ground sloth Catonyx cuvieri. Taken together with local paleoclimatic and archaeological data, the new dates do not support hunting or indirect human activities as a major cause for megafauna extinction. Although more data are required, parsimony suggests that climatic changes played a major role in this extinction event.

scholarly journals Late Quaternary climatic fluctuations and the depositional history of the Bengal basin

1996 ◽  
Vol 14 ◽  
Author(s):  
M. H. Monsur ◽  
M. M. M. Chowdhury
Keyword(s):  
Sea Level ◽  
Salt Marshes ◽  
Late Quaternary ◽  
River System ◽  
Unconsolidated Sediments ◽  
Hydrodynamic Condition ◽  
Bengal Basin ◽  
Maximum Height ◽  
Climatic Fluctuations ◽  
Last Glaciation

The peak of the last glaciation (18,000 years BP) was evidenced by dry climatic condition and a narrow palaeoriver system in the Bengal basin. At the end of the last glaciation (about 10,000 years BP), amplified monsoon water plus deglaciated melt water from the Himalayas enormously flowed through these palaeoriver systems. The rivers were overloaded and overflowed, deposited a series of gravel beds in north Bengal, and also caused the erosion of Madhupur, Barind and Chalanbil, leaving a north-south elongated landmass. Sea-level started rising, attained its maximum height at about 5,500 years BP. The lines drawn from Ganakghata to North Nalbila in the Maiskhali Island and also from Cox's Bazar to Teknaf (eastern extremities of salt marshes) represent such an elevated palaeobeach line. Holocene sea­ level rise changed the hydrodynamic condition of river system and the deeply incised valleys were filled up with unconsolidated sediments. Holocene sea-level drop resulted the aerial exposition of the Hatia, Kutubdia, Sandip and other near shore islands of the Bay of Bengal.

Late Quaternary vegetation and coastal environmental changes at Ilha do Cardoso mangrove, southeastern Brazil

2012 ◽  
Vol 363-364 ◽  
pp. 57-68 ◽  
Author(s):  
Luiz Carlos Ruiz Pessenda ◽  
Elaine Vidotto ◽  
Paulo Eduardo De Oliveira ◽  
Antonio Alvaro Buso ◽  
Marcelo Cancela Lisboa Cohen ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Late Quaternary ◽  
Southeastern Brazil

scholarly journals Metapopulation dynamics of the migratory fish Prochilodus lineatus (Characiformes: Prochilodontidae) in a lotic remnant of the Grande River, Southeastern Brazil

2021 ◽  
Vol 19 (4) ◽  
Author(s):  
Violeta R. Perini ◽  
Alessandro L. Paschoalini ◽  
Nilo Bazzoli ◽  
Elizete Rizzo ◽  
Daniel C. Carvalho
Keyword(s):  
Population Dynamics ◽  
Genetic Structure ◽  
Environmental Changes ◽  
River System ◽  
Southeastern Brazil ◽  
Metapopulation Dynamics ◽  
Migratory Fish ◽  
Prochilodus Lineatus ◽  
Allele Number ◽  
Significant Genetic Structure

ABSTRACT River impoundments for electricity generation lead to environmental changes which severely affect fish migration and species richness. However, little is known about their effect on the genetic structure and population dynamics downstream from the reservoir. Here, we analyzed a set of ten microsatellite loci of Prochilodus lineatus, an important South American migratory fish. Specimens (n = 150) were sampled from five sites in a remnant lotic system that includes sections of the Grande, Pardo and Mogi Guaçu rivers, southeastern Brazil. The data showed that all microsatellites were polymorphic with the allele number per locus ranging from 5 to 32, and genetic diversity (H e ) varied from 0.74 to 0.80. Indices of genetic differentiation and Bayesian analysis showed a significant genetic structure and three genetic clusters inhabiting this river system. An asymmetric gene flow suggests source-sink metapopulation dynamics from tributaries (genetic source) to the main river (genetic sink). A genetic cluster that was not detected in the upper Mogi and Pardo rivers tributaries may indicate there is a “trapped gene pool” downstream from the Porto Colômbia dam. Thus, here we provide new insights into the genetic structure and population dynamics of a migratory fish species in a highly dammed river basin.

Diachronism as process-inherent part of Pleistocene river terrace formation: First results based on luminescence dating for testing a well-established theoretical concept and possible implications for practical field work

2021 ◽  
Author(s):  
Thomas Kolb ◽  
Markus Fuchs
Keyword(s):  
Environmental Changes ◽  
Luminescence Dating ◽  
Environmental Research ◽  
River Terrace ◽  
Local Conditions ◽  
Fluvial Systems ◽  
Fluvial Deposits ◽  
Fluvial Terraces ◽  
Fluvial Morphology ◽  
Single Location

<p>There are two main statements of a long-accepted paradigm of fluvial morphodynamics formalized inter alia by S.A. Schumm: (i) changes in fluvial systems strongly depend on exceeding external and / or internal thresholds ​​and (ii) they are always characterized by a nonlinear and asynchronous character. While the first aspect of this paradigm is part of numerous studies on fluvial morphology and river dynamics, the second aspect has so far tended to be sidelined in practical geomorphology.</p><p>With particular respect to the field of paleo-environmental research, this is evident from studies that aim at determining ages of Pleistocene river terraces in order to provide a time frame for the reconstruction of paleo-environmental conditions. Typically, numerical dating approaches are only applied to a single location that is supposed to be exemplary for the respective terrace level. Numerical ages determined for this specific location are then extrapolated and interpreted in a generalizing way to derive "THE age" of the river terrace as a whole.</p><p>With respect to the concept of asynchronism of fluvial reactions to environmental changes, such an approach seems problematic. In fact, asynchronism implies different sections of a river showing different and specific reactions to environmental changes at a given point in time. For fluvial terraces, this means that the processes controlling their formation may already have started in some sections of a valley, while in other sections they do not yet have any impact on landscape evolution.</p><p>In this contribution, we present luminescence ages of fluvial deposits originating from an Upper Pleistocene river terrace in a small valley located in the headwater of the Main River, Germany. Here, several samples from various locations throughout the river longitudinal course have been analysed. The luminescence ages determined for the lowermost part of the valley are significantly older than those from the middle section, which in turn are older than those from the valley’s upper reaches.</p><p>Our results suggest a diachronic alignment of sedimentation ages for fluvial deposits, starting with old ages close the mouth of a river and getting progressively younger for locations approaching the upper reaches. If these findings are confirmed in other fluvial systems and are not only the result of specific local conditions, they will be of great relevance for geomorphological research in fluvial landscapes. As a result, the widespread approach of deriving age estimates for fluvial terraces from numerical results merely determined for a single location appears to be inadequate and should be subjected to a critical review.</p>

scholarly journals Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA

2016 ◽  
Vol 12 (7) ◽  
pp. 1459-1472 ◽  
Author(s):  
Joanna Pawłowska ◽  
Marek Zajączkowski ◽  
Magdalena Łącka ◽  
Franck Lejzerowicz ◽  
Philippe Esling ◽  
...  
Keyword(s):  
Ancient Dna ◽  
Environmental Conditions ◽  
Little Ice Age ◽  
Environmental Changes ◽  
Water Masses ◽  
Ice Age ◽  
Last Millennium ◽  
Climatic Fluctuations ◽  
High Sedimentation ◽  
Calving Rate

Abstract. This paper presents a reconstruction of climate-driven environmental changes over the last millennium in Hornsund Fjord (Svalbard), based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by an analysis of foraminiferal ancient DNA (aDNA), focusing on the non-fossilized monothalamous species. The main climatic fluctuations during the last millennium were the Medieval Warm Period (MWP, AD 1000–1600), the Little Ice Age (LIA, AD 1600–1900) and the modern warming (MW, AD 1900 to present). Our study indicates that the environmental conditions in Hornsund during the MWP and the early LIA (before ∼ AD 1800) were relatively stable. The beginning of the LIA (∼ AD 1600) was poorly evidenced by the micropalaeontological record but was well marked in the aDNA data by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (∼ 1600 to ∼ AD 1800) was marked by an increase in the abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus. In the late LIA (after ∼ AD 1800), the conditions in the fjord became glacier-proximal and were characterized by increased meltwater outflows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus. During the MW, the major glacier fronts retreated rapidly to the inner bays, which limited the iceberg discharge to the fjord's centre and caused a shift in the foraminiferal community that was reflected in both the fossil and aDNA records. The palaeoceanographic changes in the Hornsund fjord over the last millennium were driven mainly by the inflow of shelf-originated water masses and glacial activity. However, the environmental changes were poorly evidenced in the micropalaeontological record, but they were well documented in our aDNA data. We considerably increased the number of potential proxy species by including monothalamous foraminifera in the palaeoecological studies.

scholarly journals Palaeoceanographic changes in Hornsund Fjord (Spitsbergen, Svalbard) over the last millennium: new insights from ancient DNA

2015 ◽  
Vol 11 (4) ◽  
pp. 3665-3698 ◽  
Author(s):  
J. Pawłowska ◽  
M. Zajączkowski ◽  
M. Łącka ◽  
F. Lejzerowicz ◽  
P. Esling ◽  
...  
Keyword(s):  
Ancient Dna ◽  
Environmental Conditions ◽  
Little Ice Age ◽  
Environmental Changes ◽  
Water Masses ◽  
Ice Age ◽  
Last Millennium ◽  
Climatic Fluctuations ◽  
High Sedimentation ◽  
Calving Rate

Abstract. This paper presents the reconstruction of climate-driven environmental changes of the last millennium from Hornsund Fjord (Svalbard) based on sedimentological and micropalaeontological records. Our palaeo-investigation was supported by the analysis of foraminiferal ancient DNA (aDNA), focusing on non-fossilised monothalamous species. The main climatic fluctuations over the last millennium were the Medieval Warm Period (MWP, 1000–1600 AD), the Little Ice Age (LIA, 1600–1900 AD), and the Modern Warming (MW, 1900 AD–present). Our study indicated that environmental conditions in Hornsund during the MWP and the early LIA (before ~ 1800 AD) were relatively stable, resulting from the distant position of glaciers. The beginning of the LIA (~ 1600 AD) was poorly evidenced by the micropalaeontological record, but well marked in the aDNA data, by an increased proportion of monothalamous foraminifera, especially Bathysiphon sp. The early LIA (~ 1600– ~ 1800 AD) was marked by the increase in abundance of sequences of Hippocrepinella hirudinea and Cedhagenia saltatus. In the late LIA (after ~ 1800 AD), conditions in the fjord became glacier-proximal, characterised by increased meltwater outflows, high sedimentation and a high calving rate. This coincided with an increase in the percentages of sequences of Micrometula sp. and Vellaria pellucidus. During the MW, major glaciers fronts retreated rapidly to the inner bays, limiting the iceberg discharge to the fjord centre and causing the shift in the foraminiferal community reflected in both fossil and aDNA records. Palaeoceanographic changes in the Hornsund Fjord over the last millennium were driven mainly by the inflow of shelf-originated water masses and glaciers' activity. However, the environmental changes were poorly evidenced in the micropalaeontological record, but well documented in our aDNA data. We considerably increased the number of potential proxy species by including monothalamous foraminifera in the palaeoecological studies.

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